# Carcinogenic dioxane detection using pristine and metal-doped 2D VSe2: Insights from density functional theory simulations

Sreejith Pallikkara Chandrasekharan, Seetha Lakshmy, Saju Joseph, Nandakumar Kalarikkal

<figure><img src="image_1.png" /></figure>

► To cite this version:

Sreejith Pallikkara Chandrasekharan, Seetha Lakshmy, Saju Joseph, Nandakumar Kalarikkal. Carcinogenic dioxane detection using pristine and metal-doped 2D VSe2: Insights from density functional theory simulations. Aip Advances, 2023, 13 (6), pp.065024. 10.1063/5.0139779 . hal-04198629

HAL Id: hal-04198629

https://hal.science/hal-04198629

Submitted on 24 May 2024

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_2.png" /></figure>
# Carcinogenic dioxane detection using pristine and metal-doped 2D VSe2: Insights from density functional theory simulations

Sreejith Pallikkara Chandrasekharan, Seetha Lakshmy, Saju Joseph, Nandakumar Kalarikkal

► To cite this version:

Sreejith Pallikkara Chandrasekharan, Seetha Lakshmy, Saju Joseph, Nandakumar Kalarikkal. Carcinogenic dioxane detection using pristine and metal-doped 2D VSe2: Insights from density functional theory simulations. AIP Advances, 2023, 13 (6), pp.065024. 10.1063/5.0139779. hal-04198629

HAL Id: hal-04198629

https://hal.science/hal-04198629v1

Submitted on 24 May 2024

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# Carcinogenic dioxane detection using pristine and metal-doped 2D VSe₂: Insights from density functional theory simulations 🌐

Special Collection: **2022 Chemical Physics**

Sreejith Pallikkara Chandrasekharan 🐦 ; Seetha Lakshmy 🐦 ; Saju Joseph 📥 ; Nandakumar Kalarikkal 📥

<figure><img src="image_3.png" /></figure>

Check for updates

AIP Advances 13, 065024 (2023)

https://doi.org/10.1063/5.0139779

<figure><img src="image_4.png" /></figure>

View
Online

<figure><img src="image_5.png" /></figure>

Export
Citation

<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /></figure>
# Carcinogenic dioxane detection using pristine and metal-doped 2D VSe₂: Insights from density functional theory simulations 🌐

Special Collection: **2022 Chemical Physics**

Sreejith Pallikkara Chandrasekharan 🌐; Seetha Lakshmy 🌐; Saju Joseph 📥; Nandakumar Kalarikkal 📥

<figure><img src="image_2.png" /></figure>

Check for updates

AIP Advances 13, 065024 (2023)

https://doi.org/10.1063/5.0139779

<figure><img src="image_3.png" /></figure>

View
Online

<figure><img src="image_4.png" /></figure>

Export
Citation

<figure><img src="image_5.png" /></figure>

<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /></figure>
# Carcinogenic dioxane detection using pristine and metal-doped 2D VSe₂: Insights from density functional theory simulations F

Cite as: AIP Advances 13, 065024 (2023); doi: 10.1063/5.0139779

Submitted: 24 December 2022 • Accepted: 1 June 2023 •

Published Online: 16 June 2023

<figure><img src="image_8.png" /></figure>

View Online

<figure><img src="image_9.png" /></figure>

Export Citation

<figure><img src="image_10.png" /></figure>

CrossMark

Sreejith Pallikkara Chandrasekharan<fnref n="1" />,<fnref n="2" /> ID, Seetha Lakshmy,<fnref n="1" /> ID, Saju Joseph<fnref n="1" />,³a) ID
and Nandakumar Kalarikkal<fnref n="1" />,<fnref n="3" />,⁴a) ID

## AFFILIATIONS

## ABSTRACT

Dioxane (diethylene oxide) is a synthetic organic compound classified as heterocyclic ether, a potentially carcinogenic water toxicant. Prolonged exposure can cause eye irritation, carcinogenic liver reactions, and other severe issues. Therefore, efficient dioxane detectors are needed to be designed and developed. Inspired by the recent developments of 2D materials in biosensing, in this work, the dioxane detection potentiality of pristine and metal-doped (Al, Au, and Ag) 2D VSe₂ have been systematically examined using Density Functional Theory (DFT) based simulations. Among all the metallic dopants considered, Al binds energetically on the VSe₂ surface with an energy of -2.158 eV. The adsorption of dioxane was studied by considering the electronic properties, adsorption energy, orbital interactions, and charge transfer. Our DFT calculation suggests that dioxane adsorption in Al-doped VSe₂ is more promising than the pristine and other metal-doped VSe₂ systems, due to the reasonable adsorption energy of -0.80 eV, charge transfer of -0.567e, and strong orbital interaction between Al 3p and O 2p orbitals. Additionally, the room temperature structural solidity of the sensor has also been verified using the *ab initio* molecular dynamics simulations. The reported theoretical results inspire the fabrication and engineering of efficient dioxane sensors using Al-doped VSe₂.

© 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). https://doi.org/10.1063/5.0139779

## I. INTRODUCTION

Rapid industrialization and population growth resulted in the discharge of large quantities of organic pollutants, undeniably contributing to water resource pollution.<fnref n="1" />⁻<fnref n="3" /> Diethylene oxide (widely known as dioxane or 1,4-dioxane), classified as ether, with the chemical formula C₄H₈O₂, is a colorless liquid with a soft sweet smell like dimethyl ether. Dioxane is used on a large scale to produce paper, textiles, electronics, cosmetics, etc. They are often regarded as a powerful solvent and stabilizer for chlorinated solvents in laboratory applications. It is well known that dioxane is an environmental water toxicant with high water solubility, hydrophilicity, long-term

stability, and non-bio-degradability. Their excess presence can contaminate the ground, surface, and drinking water and are highly dangerous to living beings. Long term exposure can elicit severe eye irritation and carcinogenic reactions in the liver in various species. As per the studies, nearly one-fifth of the public drinking water sources in the United States (US) have measurable quantities of dioxane.<fnref n="4" /> The International Agency for Research on Cancer (IARC) and the US Environmental Protection Agency (USEPA) have categorized dioxane as a potential human carcinogen.⁵ Moreover, the Agency for Toxic Substances and Disease Registry (ATSDR) designated dioxane as a superfund precedence category due to the chemical harmful effects and proclivity to pollute drinking water.<fnref n="4" /> Because

<footnote n="1">¹ International and Inter University Centre for Nanoscience and Nanotechnology, Mahatma Gandhi University, Kottayam, Kerala 686 560, India</footnote>

<footnote n="2">² Univ. Rennes, INSA Rennes, CNRS, Institut FOTON – UMR 6082, F-35000 Rennes, France</footnote>

<footnote n="3">³School of Nanoscience and Nanotechnology, Mahatma Gandhi University, Kottayam, Kerala 686 560, India</footnote>

<footnote n="4">⁴School of Pure and Applied Physics, Mahatma Gandhi University, Kottayam, Kerala 686 560, India</footnote>

<footnote>a) Authors to whom correspondence should be addressed: nkkalarikkal@mgu.ac.in and psajujoseph@gmail.com</footnote>
# Carcinogenic dioxane detection using pristine and metal-doped 2D VSe₂: Insights from density functional theory simulations F

Cite as: AIP Advances 13, 065024 (2023); doi: 10.1063/5.0139779

Submitted: 24 December 2022 • Accepted: 1 June 2023 •

Published Online: 16 June 2023

<figure><img src="image_8.png" /></figure>

View Online

<figure><img src="image_9.png" /></figure>

Export Citation

<figure><img src="image_10.png" /></figure>

CrossMark

Sreejith Pallikkara Chandrasekharan<fnref n="1" />,<fnref n="2" /> ID, Seetha Lakshmy,<fnref n="1" /> ID, Saju Joseph<fnref n="1" />,³a) ID
and Nandakumar Kalarikkal<fnref n="1" />,<fnref n="3" />,⁴a) ID

## AFFILIATIONS

## ABSTRACT

Dioxane (diethylene oxide) is a synthetic organic compound classified as heterocyclic ether, a potentially carcinogenic water toxicant. Prolonged exposure can cause eye irritation, carcinogenic liver reactions, and other severe issues. Therefore, efficient dioxane detectors are needed to be designed and developed. Inspired by the recent developments of 2D materials in biosensing, in this work, the dioxane detection potentiality of pristine and metal-doped (Al, Au, and Ag) 2D VSe₂ have been systematically examined using Density Functional Theory (DFT) based simulations. Among all the metallic dopants considered, Al binds energetically on the VSe₂ surface with an energy of -2.158 eV. The adsorption of dioxane was studied by considering the electronic properties, adsorption energy, orbital interactions, and charge transfer. Our DFT calculation suggests that dioxane adsorption in Al-doped VSe₂ is more promising than the pristine and other metal-doped VSe₂ systems, due to the reasonable adsorption energy of -0.80 eV, charge transfer of -0.567e, and strong orbital interaction between Al 3p and O 2p orbitals. Additionally, the room temperature structural solidity of the sensor has also been verified using the *ab initio* molecular dynamics simulations. The reported theoretical results inspire the fabrication and engineering of efficient dioxane sensors using Al-doped VSe₂.

© 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). https://doi.org/10.1063/5.0139779

## I. INTRODUCTION

Rapid industrialization and population growth resulted in the discharge of large quantities of organic pollutants, undeniably contributing to water resource pollution.<fnref n="1" />⁻<fnref n="3" /> Diethylene oxide (widely known as dioxane or 1,4-dioxane), classified as ether, with the chemical formula C₄H₈O₂, is a colorless liquid with a soft sweet smell like dimethyl ether. Dioxane is used on a large scale to produce paper, textiles, electronics, cosmetics, etc. They are often regarded as a powerful solvent and stabilizer for chlorinated solvents in laboratory applications. It is well known that dioxane is an environmental water toxicant with high water solubility, hydrophilicity, long-term

stability, and non-bio-degradability. Their excess presence can contaminate the ground, surface, and drinking water and are highly dangerous to living beings. Long term exposure can elicit severe eye irritation and carcinogenic reactions in the liver in various species. As per the studies, nearly one-fifth of the public drinking water sources in the United States (US) have measurable quantities of dioxane.<fnref n="4" /> The International Agency for Research on Cancer (IARC) and the US Environmental Protection Agency (USEPA) have categorized dioxane as a potential human carcinogen.⁵ Moreover, the Agency for Toxic Substances and Disease Registry (ATSDR) designated dioxane as a superfund precedence category due to the chemical harmful effects and proclivity to pollute drinking water.<fnref n="4" /> Because

<footnote n="1">¹ International and Inter University Centre for Nanoscience and Nanotechnology, Mahatma Gandhi University, Kottayam, Kerala 686 560, India</footnote>

<footnote n="2">² Univ. Rennes, INSA Rennes, CNRS, Institut FOTON – UMR 6082, F-35000 Rennes, France</footnote>

<footnote n="3">³School of Nanoscience and Nanotechnology, Mahatma Gandhi University, Kottayam, Kerala 686 560, India</footnote>

<footnote n="4">⁴School of Pure and Applied Physics, Mahatma Gandhi University, Kottayam, Kerala 686 560, India</footnote>

<footnote>a) Authors to whom correspondence should be addressed: nkkalarikkal@mgu.ac.in and psajujoseph@gmail.com</footnote>
of these implications, it is urgent to develop sensors that selectively detect and remove the dioxane molecules from the environment.

In recent years, many sophisticated physicochemical and bio-
logical approaches have been used to successfully remove dioxane
from affected environments. The unique chemical features of diox-
ane, such as its low Henry's law constant, high water solubility,
and coexistence with the chlorinated solvents and other contami-
nants, make efficient removal difficult.⁶ Complex water treatment
procedures can be utilized to eradicate trace contaminants of diox-
ane.⁷ Some of these include the photoinduced oxidation method
(UV/H₂O₂) to substantially eliminate the structure of organic
chemical; and, the Fenton's reagent (Fe and H₂O₂), advanced
oxidation processes using systems, such as ozone (O₃)/H₂O₂), and
H₂O₂ - TiO₂ combined vacuum UV. The sonolytic decomposi-
tion chemistry of dioxane in an aqueous solution has also been
investigated,⁷ where dioxane is dissolved into smaller short-chain
organic by-products using ultrasound, which can subsequently
be destroyed more successfully by other methods like biologi-
cal processes. Although several other advanced dioxane removal
technologies, such as solid-phase microextraction (SPME), distil-
lation, gas chromatography (GC), thermal methods, air stripping
and membrane filtration techniques, etc., are incompetent due to
their high rate of cost and energy consumption.⁸⁻¹¹ Recent stud-
ies including electrochemical dioxane-detection by using nickel
oxide doped on neodymium oxide nanocomposites (NiO@Nd₂O₃
NCs) embedded on glassy carbon electrode¹² and reduced graphene
oxide-curcumin nanocomposite synthesized by a simple solution
approach¹³ promotes the need of developing this water pollutant.

However, properties, such as binding energy, adsorption geometry, adsorption configuration, charge transfer, etc., for detecting biomolecules cannot be directly determined by the time-consuming real experiment methods. Computational techniques are the best way to perform quantum mechanical calculations to analyze materials' various properties and phenomena and model them.

In this study, we have adopted the widely applicable quantum
mechanical theoretical simulation approach called Density Func-
tional Theory (DFT)¹⁴ to analyze the molecular interactions. In these
first-principle based calculations, the energy is represented as func-
tionals of density. Many theoretical investigations have recently been
conducted to search for novel materials for sensing applications.
Interestingly, some cutting-edge theoretical research on SiCNT was
conducted utilizing DFT simulations to examine the adsorption and
removal of dioxane.¹⁵ Furthermore, the DFT-D3/revPBE calcula-
tion is verified using the MP2 theoretical method. The study showed
that dioxane has significant adsorption toward this nanotube, but
the higher recovery time limits the practical usage. However, most
traditional sensing materials have several flaws due to their low
sensitivity and selectivity. The interaction of biomolecules with 2D
material is mainly via physisorption because of weak van der Waals
forces. By modifying the functional qualities of 2D materials, such
as defects engineering hybrid structure formation, the adsorption
performances of these materials may be enhanced. Usually, metal-
lic doping methods are adopted in the studies of 2D materials. Its
unique and robust coupling of electromagnetic properties gives a
charge transferring nature. They form covalent bonds with neigh-
boring atoms via charge transfer, improving the conductivity of the
pristine 2D material and hence the sensing properties.

Transition-metal dichalcogenides (TMDCs) are emerging 2D
materials with a stoichiometric formula of MX₂. M denotes a transi-
tion metal element, such as Sc, V, Mo, Ti, or W, while X stands for
a chalcogen element, such as Te, Se, or S. Here, a single layer of M
atoms is stacked between the bi-layer of X atoms in this tri-layered
structure, creating the layered structure X-M-X. Long-range van der
Waals (VdW) forces dominate between these layers, resulting in the
weak interaction. It exhibits unique photoelectronic, thermal, chem-
ical, and mechanical properties,¹⁶,¹⁷ making it promising for gas or
biosensing applications.¹⁸⁻²⁰ The uniqueness of TMDCs is due to the
presence of the *d* orbitals of the heavy metals, which causes a robust
spin-orbit interaction, leads to valley polarization. The TMDCs have
out-of-plane and broken in-plane mirror symmetry. The polymor-
phic nature of TMDC structures is a fascinating feature. TMDCs
can be mainly classified into two structural phases: 2H and 1T.²¹,²²
The 2H is semiconducting, and the coordination of metal atoms is
trigonal prismatic, while the 1T structure is metallic with octahedral
coordination. In view of the above, it is reasonable to conclude that
TMDCs offer enormous untapped potential as a future choice for
numerous biomolecule sensing applications with their wide range of
characteristics.

2D vanadium dichalcogenides (VX₂), such as VSe₂, VTe₂, and VS₂, have recently attracted much interest²³⁻²⁶ due to their exceptional optical, electrical, and chemical characteristics. Our research focused on the 1T VSe₂ monolayer, a paramagnetic material where the vanadium atoms are surrounded by a trigonally deformed cage of selenium atoms in an octahedral environment.²⁷ Zhang et al.²⁸ used a chemical vapor deposition (CVD) approach to establish a van der Waals epitaxial strategy for synthesizing stable 1T VSe₂ nanosheets on mica. Surprisingly, these 2D structures have exceptional metallic characteristics, including the electrical conductivity up to 10⁶ S m⁻¹, higher than the other conductive 2D materials. Synthesizing VSe₂ monolayer also have been reported by effective methods, such as liquid exfoliation,²⁹ from [(SnSe)₁.₁₅]ₘ(VSe₂)ₙ ferecrystals via physical vapor deposition,³⁰ low-pressure chemical vapor deposition (LPCVD),³¹ etc. In very recent work, the potential of 1T VSe₂ for nitrobenzene detection was explored.²⁶ The DFT study reveals that the transition metal doped VSe₂ is more sensitive to nitrobenzene molecules.

Although some significant observational facts exist for diox-
ane sensing studies, evidence of investigating TMDCs as a sensing
material, particularly monolayered VSe₂, as a potential dioxane
sensing material is unknown to the authors' available knowledge.
In this current work, the adsorption and electronic properties of
VSe₂ as a biosensor for dioxane have been examined using first
principle-based DFT calculations. To overcome the weak interaction
of VSe₂ monolayer toward dioxane, VSe₂ has been modified by dop-
ing with various metals (Al, Ag, Au, W, and Ti). Total Density of
States (TDOS) and Partial Density of States (PDOS) analyses have
been done to study the orbital interactions of states near the Fermi
level and the charge transfer analysis via Lowdin Charge Analysis
(LCA). Finally, because of its high adsorption energy toward diox-
ane, we suggest the Al-doped VSe₂ structure is among the most
potential dioxane sensing materials. Furthermore, the structural
durability of VSe₂ + Al was examined using ab initio MD simu-
lations at 300 K, which revealed that the combination is extremely
stable.
of these implications, it is urgent to develop sensors that selectively detect and remove the dioxane molecules from the environment.

In recent years, many sophisticated physicochemical and bio-
logical approaches have been used to successfully remove dioxane
from affected environments. The unique chemical features of diox-
ane, such as its low Henry's law constant, high water solubility,
and coexistence with the chlorinated solvents and other contami-
nants, make efficient removal difficult.⁶ Complex water treatment
procedures can be utilized to eradicate trace contaminants of diox-
ane.⁷ Some of these include the photoinduced oxidation method
(UV/H₂O₂) to substantially eliminate the structure of organic
chemical; and, the Fenton's reagent (Fe and H₂O₂), advanced
oxidation processes using systems, such as ozone (O₃)/H₂O₂), and
H₂O₂ - TiO₂ combined vacuum UV. The sonolytic decomposi-
tion chemistry of dioxane in an aqueous solution has also been
investigated,⁷ where dioxane is dissolved into smaller short-chain
organic by-products using ultrasound, which can subsequently
be destroyed more successfully by other methods like biologi-
cal processes. Although several other advanced dioxane removal
technologies, such as solid-phase microextraction (SPME), distil-
lation, gas chromatography (GC), thermal methods, air stripping
and membrane filtration techniques, etc., are incompetent due to
their high rate of cost and energy consumption.⁸⁻¹¹ Recent stud-
ies including electrochemical dioxane-detection by using nickel
oxide doped on neodymium oxide nanocomposites (NiO@Nd₂O₃
NCs) embedded on glassy carbon electrode¹² and reduced graphene
oxide-curcumin nanocomposite synthesized by a simple solution
approach¹³ promotes the need of developing this water pollutant.

However, properties, such as binding energy, adsorption
geometry, adsorption configuration, charge transfer, etc., for detect-
ing biomolecules cannot be directly determined by the time-
consuming real experiment methods. Computational techniques are
the best way to perform quantum mechanical calculations to analyze
materials' various properties and phenomena and model them.

In this study, we have adopted the widely applicable quantum
mechanical theoretical simulation approach called Density Func-
tional Theory (DFT)¹⁴ to analyze the molecular interactions. In these
first-principle based calculations, the energy is represented as func-
tionals of density. Many theoretical investigations have recently been
conducted to search for novel materials for sensing applications.
Interestingly, some cutting-edge theoretical research on SiCNT was
conducted utilizing DFT simulations to examine the adsorption and
removal of dioxane.¹⁵ Furthermore, the DFT-D3/revPBE calcula-
tion is verified using the MP2 theoretical method. The study showed
that dioxane has significant adsorption toward this nanotube, but
the higher recovery time limits the practical usage. However, most
traditional sensing materials have several flaws due to their low
sensitivity and selectivity. The interaction of biomolecules with 2D
material is mainly via physisorption because of weak van der Waals
forces. By modifying the functional qualities of 2D materials, such
as defects engineering hybrid structure formation, the adsorption
performances of these materials may be enhanced. Usually, metal-
lic doping methods are adopted in the studies of 2D materials. Its
unique and robust coupling of electromagnetic properties gives a
charge transferring nature. They form covalent bonds with neigh-
boring atoms via charge transfer, improving the conductivity of the
pristine 2D material and hence the sensing properties.

Transition-metal dichalcogenides (TMDCs) are emerging 2D
materials with a stoichiometric formula of MX₂. M denotes a transi-
tion metal element, such as Sc, V, Mo, Ti, or W, while X stands for
a chalcogen element, such as Te, Se, or S. Here, a single layer of M
atoms is stacked between the bi-layer of X atoms in this tri-layered
structure, creating the layered structure X-M-X. Long-range van der
Waals (VdW) forces dominate between these layers, resulting in the
weak interaction. It exhibits unique photoelectronic, thermal, chem-
ical, and mechanical properties,¹⁶,¹⁷ making it promising for gas or
biosensing applications.¹⁸⁻²⁰ The uniqueness of TMDCs is due to the
presence of the *d* orbitals of the heavy metals, which causes a robust
spin-orbit interaction, leads to valley polarization. The TMDCs have
out-of-plane and broken in-plane mirror symmetry. The polymor-
phic nature of TMDC structures is a fascinating feature. TMDCs
can be mainly classified into two structural phases: 2H and 1T.²¹,²²
The 2H is semiconducting, and the coordination of metal atoms is
trigonal prismatic, while the 1T structure is metallic with octahedral
coordination. In view of the above, it is reasonable to conclude that
TMDCs offer enormous untapped potential as a future choice for
numerous biomolecule sensing applications with their wide range of
characteristics.

2D vanadium dichalcogenides (VX₂), such as VSe₂, VTe₂, and VS₂, have recently attracted much interest²³⁻²⁶ due to their exceptional optical, electrical, and chemical characteristics. Our research focused on the 1T VSe₂ monolayer, a paramagnetic material where the vanadium atoms are surrounded by a trigonally deformed cage of selenium atoms in an octahedral environment.²⁷ Zhang et al.²⁸ used a chemical vapor deposition (CVD) approach to establish a van der Waals epitaxial strategy for synthesizing stable 1T VSe₂ nanosheets on mica. Surprisingly, these 2D structures have exceptional metallic characteristics, including the electrical conductivity up to 10⁶ S m⁻¹, higher than the other conductive 2D materials. Synthesizing VSe₂ monolayer also have been reported by effective methods, such as liquid exfoliation,²⁹ from [(SnSe)₁.₁₅]m(VSe₂)n ferecrystals via physical vapor deposition,³⁰ low-pressure chemical vapor deposition (LPCVD),³¹ etc. In very recent work, the potential of 1T VSe₂ for nitrobenzene detection was explored.²⁶ The DFT study reveals that the transition metal doped VSe₂ is more sensitive to nitrobenzene molecules.

Although some significant observational facts exist for diox-
ane sensing studies, evidence of investigating TMDCs as a sensing
material, particularly monolayered VSe₂, as a potential dioxane
sensing material is unknown to the authors' available knowledge.
In this current work, the adsorption and electronic properties of
VSe₂ as a biosensor for dioxane have been examined using first
principle-based DFT calculations. To overcome the weak interaction
of VSe₂ monolayer toward dioxane, VSe₂ has been modified by dop-
ing with various metals (Al, Ag, Au, W, and Ti). Total Density of
States (TDOS) and Partial Density of States (PDOS) analyses have
been done to study the orbital interactions of states near the Fermi
level and the charge transfer analysis via Lowdin Charge Analysis
(LCA). Finally, because of its high adsorption energy toward diox-
ane, we suggest the Al-doped VSe₂ structure is among the most
potential dioxane sensing materials. Furthermore, the structural
durability of VSe₂ + Al was examined using ab initio MD simu-
lations at 300 K, which revealed that the combination is extremely
stable.
## II. COMPUTATIONAL DETAILS

This study calculated all the structural, electronic, interfacial, and sensing properties of 2D VSe₂ and metal doped structures using DFT with the Quantum Espresso package.³² As an exchange-correlation energy functional approximation, Perdew-Burke-Ernzerhof (PBE) in the Generalized Gradient Approximation (GGA) function (PBE-GGA) were used.³³ As per the literature, GGA is appropriate for accurately predicting the electronic, magnetic, and optical properties of 2D TMDCs. To accommodate the long-range van der Waal's interactions, Grimme DFT-D2 were also introduced in the calculations. For the current work, we have modeled a 2 × 2 supercell of 2D 1T VSe₂ monolayer containing 12 atoms. To eliminate the interactions between the periodic images, a 20 Å vacuum spacing is introduced in the vertical direction of the VSe₂ monolayer, i.e., in the z-direction. The plane-wave-cutoff energy was set to 35 Ry. The geometrical structures were relaxed until each atom's total computed energy and force were less than 10⁻⁶ and 10⁻⁴ eV, respectively. The Brillium zone integration was achieved by 4 × 4 × 1 Monkhorst-Pack. For the most promising

system, molecular dynamic simulations at 300 K were also done to remark on the sensor material's integrity at ambient temperatures.

## III. RESULTS AND DISCUSSION

### A. Electronic and structural properties of VSe₂ monolayer

In this study, we have considered the 1T phase of pristine VSe₂, in which a layer of metal Vanadium is placed between two selenium sheets. The optimized 2 × 2 supercell structure of VSe₂ is displayed in Fig. 1(a). The obtained lattice constants are a = b = 3.334 Å, correlating neatly with published primitive cell experimental value, a = b = 3.356 Å³⁴ and a = b = 3.36 Å,³⁵ and indeed corresponds to the previously determined DFT calculated value of a = b = 3.328 Å.²³ The optimized V-Se bond length is 2.487 Å with the computed interlayer distance of 1.84 Å, matching the earlier available interlayer result of 1.56 Å.³⁵ The TDOS of VSe₂ have been calculated using the GGA + U approach (U value ≈ 3.5 eV for V³⁶) and are displayed in Fig. 2. The continuous and asymmetric spin states at

<figure><img src="image_11.png" /><figcaption>FIG. 1. The geometrically optimized structure of 1T VSe₂ monolayer in (a) armchair and (b) zigzag, (c) the relaxed structure of dioxane molecule, and (d) TDOS plot of 1T VSe₂.</figcaption></figure>
## II. COMPUTATIONAL DETAILS

This study calculated all the structural, electronic, interfacial, and sensing properties of 2D VSe₂ and metal doped structures using DFT with the Quantum Espresso package.³² As an exchange-correlation energy functional approximation, Perdew-Burke-Ernzerhof (PBE) in the Generalized Gradient Approximation (GGA) function (PBE-GGA) were used.³³ As per the literature, GGA is appropriate for accurately predicting the electronic, magnetic, and optical properties of 2D TMDCs. To accommodate the long-range van der Waal's interactions, Grimme DFT-D2 were also introduced in the calculations. For the current work, we have modeled a 2 × 2 supercell of 2D 1T VSe₂ monolayer containing 12 atoms. To eliminate the interactions between the periodic images, a 20 Å vacuum spacing is introduced in the vertical direction of the VSe₂ monolayer, i.e., in the z-direction. The plane-wave-cutoff energy was set to 35 Ry. The geometrical structures were relaxed until each atom's total computed energy and force were less than 10⁻⁶ and 10⁻⁴ eV, respectively. The Brillion zone integration was achieved by 4 × 4 × 1 Monkhorst-Pack. For the most promising

system, molecular dynamic simulations at 300 K were also done to remark on the sensor material's integrity at ambient temperatures.

## III. RESULTS AND DISCUSSION

### A. Electronic and structural properties of VSe₂ monolayer

In this study, we have considered the 1T phase of pristine VSe₂, in which a layer of metal Vanadium is placed between two selenium sheets. The optimized 2 × 2 supercell structure of VSe₂ is displayed in Fig. 1(a). The obtained lattice constants are a = b = 3.334 Å, correlating neatly with published primitive cell experimental value, a = b = 3.356 Å³⁴ and a = b = 3.36 Å,³⁵ and indeed corresponds to the previously determined DFT calculated value of a = b = 3.328 Å.²³ The optimized V-Se bond length is 2.487 Å with the computed interlayer distance of 1.84 Å, matching the earlier available interlayer result of 1.56 Å.³⁵ The TDOS of VSe₂ have been calculated using the GGA + U approach (U value ≈ 3.5 eV for V³⁶) and are displayed in Fig. 2. The continuous and asymmetric spin states at

<figure><img src="image_11.png" /><figcaption>FIG. 1. The geometrically optimized structure of 1T VSe₂ monolayer in (a) armchair and (b) zigzag, (c) the relaxed structure of dioxane molecule, and (d) TDOS plot of 1T VSe₂.</figcaption></figure>
<figure><img src="image_12.png" /><figcaption>FIG. 2. Optimized structures of (a) dioxane adsorbed pristine VSe₂ and metal-doped VSe₂ after geometrical relaxation, (b) Al, (c) Au, and (d) Ag.</figcaption></figure>

the Fermi level indicate that 1T VSe₂ is magnetic and metallic.³⁵ The reasonable match of pristine VSe₂ bond length and other electronic parameters with previously reported results gives us confidence in the simulation procedures and methods' accuracy. 1T MX₂ structure shows two major directions, armchair and zigzag. For the monolayer 1T VSe₂, the zigzag direction shows significantly stronger and more stretchy than armchair³⁷ [see Fig. 1(b)].

## B. Adsorption studies of dioxane on pristine VSe₂

Here, we have placed the dioxane molecule ~2 Å above the surface of the pristine VSe₂ at four different adsorption sites: hcp, fcc, top, and hollow sites.³⁷ Several combinations of the initial structures were explored; for example, the O atom of the dioxane molecule is close to the different sites of VSe₂ and is geometrically relaxed to minimum energy configuration. The most stable geometric

<table><caption>TABLE I. DFT calculated adsorption energy and bond length of metal-doped VSe₂ systems.</caption><thead><tr><th>System</th><th>Adsorption energy (eV)</th><th>Bond length (Å)</th></tr></thead><tbody><tr><td>VSe<sub>2</sub> + Ti</td><td>+3.623</td><td>2.340 (Se-Ti)</td></tr><tr><td>VSe<sub>2</sub> + W</td><td>+7.388</td><td>2.285 (Se-W)</td></tr><tr><td>VSe<sub>2</sub> + Al</td><td>-2.158</td><td>2.495 (Se-Al)</td></tr><tr><td>VSe<sub>2</sub> + Au</td><td>-1.412</td><td>2.437 (Se-Au)</td></tr><tr><td>VSe<sub>2</sub> + Ag</td><td>-1.124</td><td>2.534 (Se-Ag)</td></tr></tbody></table>

structure of VSe₂ + dioxane/dopant is attained by the adsorption energy ($E_{ad}$) calculation using the following expression:

$$E_{ad}(D) = E(VSe_2 + D) - E(VSe_2) - E(D), \quad (1)$$

where $E(VSe₂)$, $E(D)$, and $E(VSe₂ + D)$ are, respectively, the energies of pristine VSe₂, dioxane molecule or dopant, and VSe₂ + dioxane/dopant system. Figure 2(a) depicts the DFT optimized structure of dioxane adsorbed VSe₂. The top site of Se with adsorption energy of -0.15 eV at a bond distance of 3.71 Å is found to be the most favorable position for the dioxane adsorption. The adsorption energy is negative, indicating that the adsorption is spontaneous and energetically feasible. The Density of States (DOS) of the VSe₂ gets altered after the dioxane adsorption, and it is clearly visible in Fig. 3(b). The adsorption configuration of dioxane molecules on the VSe₂ monolayer results in the transfer of charges between them. The LCA is performed to quantify the charge transfer between the dioxane and the pristine VSe₂ monolayer. As per the LCA, only a minute charge of 0.041e transfers from the VSe₂ to the dioxane molecule. The negligible charge transfer, weak adsorption energy, and large interaction distance suggest that the dioxane adsorption on pristine VSe₂ monolayer is physisorption, which would be due to the long-range van der Waal's forces. The practical implementation of the sensor requires

<figure><img src="image_13.png" /><figcaption>FIG. 3. PDOS plots of (a) pristine and (b) dioxane adsorbed VSe₂.</figcaption></figure>
<figure><img src="image_12.png" /><figcaption>FIG. 2. Optimized structures of (a) dioxane adsorbed pristine VSe₂ and metal-doped VSe₂ after geometrical relaxation, (b) Al, (c) Au, and (d) Ag.</figcaption></figure>

the Fermi level indicate that 1T VSe₂ is magnetic and metallic.³⁵ The reasonable match of pristine VSe₂ bond length and other electronic parameters with previously reported results gives us confidence in the simulation procedures and methods' accuracy. 1T MX₂ structure shows two major directions, armchair and zigzag. For the monolayer 1T VSe₂, the zigzag direction shows significantly stronger and more stretchy than armchair³⁷ [see Fig. 1(b)].

## B. Adsorption studies of dioxane on pristine VSe₂

Here, we have placed the dioxane molecule ~2 Å above the surface of the pristine VSe₂ at four different adsorption sites: hcp, fcc, top, and hollow sites.³⁷ Several combinations of the initial structures were explored; for example, the O atom of the dioxane molecule is close to the different sites of VSe₂ and is geometrically relaxed to minimum energy configuration. The most stable geometric

<table><caption>TABLE I. DFT calculated adsorption energy and bond length of metal-doped VSe₂ systems.</caption><thead><tr><th>System</th><th>Adsorption energy (eV)</th><th>Bond length (Å)</th></tr></thead><tbody><tr><td>VSe<sub>2</sub> + Ti</td><td>+3.623</td><td>2.340 (Se-Ti)</td></tr><tr><td>VSe<sub>2</sub> + W</td><td>+7.388</td><td>2.285 (Se-W)</td></tr><tr><td>VSe<sub>2</sub> + Al</td><td>-2.158</td><td>2.495 (Se-Al)</td></tr><tr><td>VSe<sub>2</sub> + Au</td><td>-1.412</td><td>2.437 (Se-Au)</td></tr><tr><td>VSe<sub>2</sub> + Ag</td><td>-1.124</td><td>2.534 (Se-Ag)</td></tr></tbody></table>

structure of VSe₂ + dioxane/dopant is attained by the adsorption energy ($E_{ad}$) calculation using the following expression:

$$E_{ad}(D) = E(VSe_{2} + D) - E(VSe_{2}) - E(D), \quad (1)$$

where $E(VSe₂)$, $E(D)$, and $E(VSe₂ + D)$ are, respectively, the energies of pristine VSe₂, dioxane molecule or dopant, and VSe₂ + dioxane/dopant system. Figure 2(a) depicts the DFT optimized structure of dioxane adsorbed VSe₂. The top site of Se with adsorption energy of -0.15 eV at a bond distance of 3.71 Å is found to be the most favorable position for the dioxane adsorption. The adsorption energy is negative, indicating that the adsorption is spontaneous and energetically feasible. The Density of States (DOS) of the VSe₂ gets altered after the dioxane adsorption, and it is clearly visible in Fig. 3(b). The adsorption configuration of dioxane molecules on the VSe₂ monolayer results in the transfer of charges between them. The LCA is performed to quantify the charge transfer between the dioxane and the pristine VSe₂ monolayer. As per the LCA, only a minute charge of 0.041e transfers from the VSe₂ to the dioxane molecule. The negligible charge transfer, weak adsorption energy, and large interaction distance suggest that the dioxane adsorption on pristine VSe₂ monolayer is physisorption, which would be due to the long-range van der Waal's forces. The practical implementation of the sensor requires

<figure><img src="image_13.png" /><figcaption>FIG. 3. PDOS plots of (a) pristine and (b) dioxane adsorbed VSe₂.</figcaption></figure>
<figure><img src="image_14.png" /><figcaption>FIG. 4. TDOS plots for (a) pristine VSe₂, VSe₂ + Al, VSe₂ + Au, and VSe₂ + Ag systems (b) merged plots of pristine VSe₂ and VSe₂ + Al.</figcaption></figure>
<figure><img src="image_14.png" /><figcaption>FIG. 4. TDOS plots for (a) pristine VSe₂, VSe₂ + Al, VSe₂ + Au, and VSe₂ + Ag systems (b) merged plots of pristine VSe₂ and VSe₂ + Al.</figcaption></figure>
the dioxane molecules to be adsorbed strongly on the surface. In this
respect, a metallic doping strategy was adopted.

C. Modification of the VSe₂ monolayer by metallic doping

We have placed metals, such as Al, Ag, Au, W, and Ti ~2 Å,
above the VSe₂ surface at different adsorption sites and allowed
the systems to relax. The adsorption energies and bond lengths for
the best configuration of VSe₂ + metal are calculated using Eq. (1)
and are shown in Table I. From adsorption calculations at differ-
ent sites, it was found that the top site above the Se atom was the
best site for doped metals Al, Au, and Ag. The W and Ti showed
positive adsorption energies, implying that they do not bind on the
VSe₂ surface. The corresponding relaxed structures of the metal-
doped VSe₂ monolayer are illustrated in Figs. 2(b)-2(d). As per
the calculated adsorption energy values, Al binds strongly on the
VSe₂ monolayer with an energy of -2.158 eV. At the same time,
the Au and Ag have comparatively low adsorption energy of -1.412

and –1.124 eV, respectively. Hence, the adsorption energy analysis
confirms Al as the best dopant. Figure 4(a) denotes the TDOS of
pristine and metal-doped VSe₂ systems. The improvement of energy
states close to the Fermi level indicates the increase in conductivity
of metal-doped VSe₂. The asymmetric spin states in the TDOS of
VSe₂ + metal reminds the persistence of the magnetic nature. Addi-
tionally, Fig. 4(b) plots the TDOS plots of the pristine VSe₂ merged
with the Al-doped VSe₂. Unlike the original VSe₂ monolayer, the
DOS of the Al-doped system differs in several energy levels, with
some significant increase in the Fermi level, which may be due to the
electron exchange between the VSe₂ monolayer to the Al atom.

The PDOS analysis provides a clear idea of the orbital interac-
tions and the direction of transfer of charges between the dioxane
molecule and the substrate VSe₂. Figure 5 compares PDOS of the
valence orbitals of VSe₂ (V 3d orbital and Se 4p orbital), 3p orbitals
of isolated Al atom and Al atom in the VSe₂ + Al system. When the
Al atom binds to the VSe₂ surface, a reduction in the energy states
of the Al 3p orbital at the Fermi level occurs compared to that in the
isolated Al atom. Simultaneously, the V 3d and Se 4p near the Fermi

<figure><img src="image_15.png" /><figcaption>FIG. 5. The PDOS plots compare the valence orbitals of VSe₂ in the pristine and Al + VSe₂ system in the left panel, whereas in the right panel compare the 3p orbitals of isolated Al atom and the Al + VSe₂ system.</figcaption></figure>
the dioxane molecules to be adsorbed strongly on the surface. In this
respect, a metallic doping strategy was adopted.

C. Modification of the VSe₂ monolayer by metallic doping

We have placed metals, such as Al, Ag, Au, W, and Ti ~2 Å,
above the VSe₂ surface at different adsorption sites and allowed
the systems to relax. The adsorption energies and bond lengths for
the best configuration of VSe₂ + metal are calculated using Eq. (1)
and are shown in Table I. From adsorption calculations at differ-
ent sites, it was found that the top site above the Se atom was the
best site for doped metals Al, Au, and Ag. The W and Ti showed
positive adsorption energies, implying that they do not bind on the
VSe₂ surface. The corresponding relaxed structures of the metal-
doped VSe₂ monolayer are illustrated in Figs. 2(b)-2(d). As per
the calculated adsorption energy values, Al binds strongly on the
VSe₂ monolayer with an energy of -2.158 eV. At the same time,
the Au and Ag have comparatively low adsorption energy of -1.412

and –1.124 eV, respectively. Hence, the adsorption energy analysis
confirms Al as the best dopant. Figure 4(a) denotes the TDOS of
pristine and metal-doped VSe₂ systems. The improvement of energy
states close to the Fermi level indicates the increase in conductivity
of metal-doped VSe₂. The asymmetric spin states in the TDOS of
VSe₂ + metal reminds the persistence of the magnetic nature. Addi-
tionally, Fig. 4(b) plots the TDOS plots of the pristine VSe₂ merged
with the Al-doped VSe₂. Unlike the original VSe₂ monolayer, the
DOS of the Al-doped system differs in several energy levels, with
some significant increase in the Fermi level, which may be due to the
electron exchange between the VSe₂ monolayer to the Al atom.

The PDOS analysis provides a clear idea of the orbital interac-
tions and the direction of transfer of charges between the dioxane
molecule and the substrate VSe₂. Figure 5 compares PDOS of the
valence orbitals of VSe₂ (V 3d orbital and Se 4p orbital), 3p orbitals
of isolated Al atom and Al atom in the VSe₂ + Al system. When the
Al atom binds to the VSe₂ surface, a reduction in the energy states
of the Al 3p orbital at the Fermi level occurs compared to that in the
isolated Al atom. Simultaneously, the V 3d and Se 4p near the Fermi

<figure><img src="image_15.png" /><figcaption>FIG. 5. The PDOS plots compare the valence orbitals of VSe₂ in the pristine and Al + VSe₂ system in the left panel, whereas in the right panel compare the 3p orbitals of isolated Al atom and the Al + VSe₂ system.</figcaption></figure>
level get magnified, and the overall states are redistributed. This reduction in the Al and enhancement in VSe₂ energy states signifies a charge transfer from Al 3p orbital to 4p and 3d orbitals of Se and V in VSe₂ and is a result of the existence of an unpaired valence electron in the outermost p orbital. Hence, the Al atom tends to donate the electron and become an anion.

A similar redistribution of states can be observed from the PDOS plots of Au- and Ag-doped VSe₂ systems (supplementary material, Fig. S1). Since Au and Ag have an unpaired electron in

their valence s orbitals, they can either act as an electron donator or an acceptor. On interacting with the VSe₂ system, the energy states of both the metals got depleted around the Fermi level (right panel of Fig. S1). This indicates the charge donating behavior of the Au and Ag metals. At the same time, the increased energy states near the Fermi level of the valence orbitals of the V and Se in VSe₂ denote the charge accumulation (left panel of Fig. S1), i.e., the VSe₂ gains charge from Au and Ag's 6s and 5s orbitals, respectively. According to the LCA, the Al atom loses a charge of 0.299e to the VSe₂ system.

<figure><img src="image_16.png" /><figcaption>FIG. 6. The HOMO (a), LUMO (b), figures and MD snapshot at 300 K (c) of Al-doped VSe₂.</figcaption></figure>

<figure><img src="image_17.png" /><figcaption>FIG. 7. Optimized structures of dioxane adsorbed (a) VSe₂ + Al, (b) VSe₂ + Au, and (c) VSe₂ + Ag systems.</figcaption></figure>
level get magnified, and the overall states are redistributed. This reduction in the Al and enhancement in VSe₂ energy states signifies a charge transfer from Al 3p orbital to 4p and 3d orbitals of Se and V in VSe₂ and is a result of the existence of an unpaired valence electron in the outermost p orbital. Hence, the Al atom tends to donate the electron and become an anion.

A similar redistribution of states can be observed from the PDOS plots of Au- and Ag-doped VSe₂ systems (supplementary material, Fig. S1). Since Au and Ag have an unpaired electron in

their valence s orbitals, they can either act as an electron donator or an acceptor. On interacting with the VSe₂ system, the energy states of both the metals got depleted around the Fermi level (right panel of Fig. S1). This indicates the charge donating behavior of the Au and Ag metals. At the same time, the increased energy states near the Fermi level of the valence orbitals of the V and Se in VSe₂ denote the charge accumulation (left panel of Fig. S1), i.e., the VSe₂ gains charge from Au and Ag's 6s and 5s orbitals, respectively. According to the LCA, the Al atom loses a charge of 0.299e to the VSe₂ system.

<figure><img src="image_16.png" /><figcaption>FIG. 6. The HOMO (a), LUMO (b), figures and MD snapshot at 300 K (c) of Al-doped VSe₂.</figcaption></figure>

<figure><img src="image_17.png" /><figcaption>FIG. 7. Optimized structures of dioxane adsorbed (a) VSe₂ + Al, (b) VSe₂ + Au, and (c) VSe₂ + Ag systems.</figcaption></figure>
In contrast, Au and Ag lose about 0.173e and 0.145e, respectively, to VSe₂ systems. The results obtained from LCA are pretty consistent with the PDOS.

Figures 6(a) and 6(b), respectively, shows the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) distributions of the Al-doped VSe₂ system. It is noted that a significant portion of HOMO and LUMO, basically the electron receiving/donating part, is distributed near the Se atom to which the Al is bonded. This signifies that the addition of Al atom enriched the active region on the VSe₂ surface and hence the sensitivity of the material. All the DFT calculations were performed at 0 K; therefore, it is highly essential to see the structural stability at ambient temperatures. Desorption of the molecules from the sensor materials is usually achieved by heating the material to higher temperatures. This also requires the consistency of the system at a higher temperature. To establish the same, we performed the *ab initio* Molecular Dynamics (AIMD) simulations at 300 K for the best system, i.e., VSe₂ + Al system. Figure 6(c) depicts the MD snapshot of the VSe₂ + Al system for 3 ps. Although the structural plot of VSe₂ + Al shows minor bond length variations due to the

<table><caption>**TABLE II.** The adsorption energy and bond length of dioxane adsorbed pristine and metal-doped VSe₂ systems.</caption><thead><tr><th>System</th><th>Adsorption energy (eV)</th><th>Bond length (Å)</th></tr></thead><tbody><tr><td>Pristine VSe<sub>2</sub> + dioxane</td><td>-0.15</td><td>3.71 (Se–O)</td></tr><tr><td>VSe<sub>2</sub> + Al + dioxane</td><td>-0.80</td><td>3.38 (Al–O)</td></tr><tr><td>VSe<sub>2</sub> + Au + dioxane</td><td>-0.30</td><td>2.26 (Au–O)</td></tr><tr><td>VSe<sub>2</sub> + Ag + dioxane</td><td>-0.20</td><td>2.62 (Ag–O)</td></tr></tbody></table>

thermal agitations, the system remains stable without any distortion at 300 K. Therefore, the Al-doped VSe₂ system is quite feasible for practical sensor applications.

### D. Adsorption of dioxane on metal-doped VSe₂

To observe the dioxane adsorption on the metal-doped VSe₂ system, we have placed the dioxane molecule above the structurally

<figure><img src="image_18.png" /><figcaption>**FIG. 8.** TDOS plots of dioxane interaction on (a) pristine VSe₂, (b) VSe₂ + Al, (c) VSe₂ + Au, and (d) VSe₂ + Ag systems.</figcaption></figure>
In contrast, Au and Ag lose about 0.173e and 0.145e, respectively, to VSe₂ systems. The results obtained from LCA are pretty consistent with the PDOS.

Figures 6(a) and 6(b), respectively, shows the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) distributions of the Al-doped VSe₂ system. It is noted that a significant portion of HOMO and LUMO, basically the electron receiving/donating part, is distributed near the Se atom to which the Al is bonded. This signifies that the addition of Al atom enriched the active region on the VSe₂ surface and hence the sensitivity of the material. All the DFT calculations were performed at 0 K; therefore, it is highly essential to see the structural stability at ambient temperatures. Desorption of the molecules from the sensor materials is usually achieved by heating the material to higher temperatures. This also requires the consistency of the system at a higher temperature. To establish the same, we performed the *ab initio* Molecular Dynamics (AIMD) simulations at 300 K for the best system, i.e., VSe₂ + Al system. Figure 6(c) depicts the MD snapshot of the VSe₂ + Al system for 3 ps. Although the structural plot of VSe₂ + Al shows minor bond length variations due to the

<table><caption>**TABLE II.** The adsorption energy and bond length of dioxane adsorbed pristine and metal-doped VSe₂ systems.</caption><thead><tr><th>System</th><th>Adsorption energy (eV)</th><th>Bond length (Å)</th></tr></thead><tbody><tr><td>Pristine VSe<sub>2</sub> + dioxane</td><td>-0.15</td><td>3.71 (Se–O)</td></tr><tr><td>VSe<sub>2</sub> + Al + dioxane</td><td>-0.80</td><td>3.38 (Al–O)</td></tr><tr><td>VSe<sub>2</sub> + Au + dioxane</td><td>-0.30</td><td>2.26 (Au–O)</td></tr><tr><td>VSe<sub>2</sub> + Ag + dioxane</td><td>-0.20</td><td>2.62 (Ag–O)</td></tr></tbody></table>

thermal agitations, the system remains stable without any distortion at 300 K. Therefore, the Al-doped VSe₂ system is quite feasible for practical sensor applications.

### D. Adsorption of dioxane on metal-doped VSe₂

To observe the dioxane adsorption on the metal-doped VSe₂ system, we have placed the dioxane molecule above the structurally

<figure><img src="image_18.png" /><figcaption>**FIG. 8.** TDOS plots of dioxane interaction on (a) pristine VSe₂, (b) VSe₂ + Al, (c) VSe₂ + Au, and (d) VSe₂ + Ag systems.</figcaption></figure>
relaxed metal-doped VSe₂ system such that the distance between the metal and the molecule is ~2 Å. The resulting structural combinations are allowed to optimize geometrically. The corresponding structures in their minimum energy configurations are shown in Fig. 7.

The adsorption energy and bond length of dioxane on different VSe₂ systems are tabulated (Table II). The dioxane has a greater binding on the Al-doped system with an adsorption energy of -0.8 eV. This high energy value indicates that dioxane molecules chemisorb on the Al-doped system. While dioxane adsorption on the Ag- and Au-doped VSe₂ systems are mostly physisorption, the adsorption energies are -0.30 and -0.20 eV, respectively. It is also noted that the dioxane adsorption strength increases by the strategy of metal doping, which in turn signifies the improvement in the sensing activity of the pristine VSe₂ system. The shortest distance between the O atom of the dioxane molecule and the Al atom in the VSe₂ + Al system is 3.38 Å. While the O-Au and O-Ag distances are 2.26 and 2.62 Å, respectively. The adsorption energy calculations conclude that the Al-doped VSe₂ system is well suited as the sensor material for detecting dioxane molecules from the atmosphere.

### E. Mechanism of dioxane adsorption in metal-doped VSe₂ system

The DOS analysis explains how the electronic structure of the metal-doped VSe₂ system varies with the dioxane adsorption. Figure 8 compares the TDOS of the pristine and metal-doped VSe₂ system after the dioxane adsorption. The main reason for the origin of new energy states of the pristine and metal-doped VSe₂ system near the Fermi level is mainly because of the presence of dioxane molecules on its surface.

We have also analyzed the PDOS to clarify the orbital level interactions and charge transfer in the metal-doped VSe₂ systems. The PDOS of the Al 3p orbitals of VSe₂ + Al and VSe₂ + Al + dioxane systems are shown in the left top and bottom panel, respectively, in Fig. 9. At the same time, the right upper panel of the same figure represents the PDOS for the O 2p orbitals of the isolated dioxane, and the lower panel compares the PDOS for the O 2p orbitals of the VSe₂ + Al + dioxane system. It is worth noting that, after the interaction of the dioxane molecule with the VSe₂ + Al system, the energy states around the Fermi level of the Al 3p orbital diminished. At the same time, new states originated around the Fermi level of

<figure><img src="image_19.png" /><figcaption>FIG. 9. Orbital interaction analysis of VSe₂ + Al + dioxane using PDOS plots, compare the valence orbitals of Al in the VSe₂ + Al and VSe₂ + Al + dioxane system in the left panel. In contrast, the right panel compares the 2p orbitals of isolated dioxane atoms and the VSe₂ + Al + dioxane systems.</figcaption></figure>
relaxed metal-doped VSe₂ system such that the distance between the metal and the molecule is ~2 Å. The resulting structural combinations are allowed to optimize geometrically. The corresponding structures in their minimum energy configurations are shown in Fig. 7.

The adsorption energy and bond length of dioxane on different VSe₂ systems are tabulated (Table II). The dioxane has a greater binding on the Al-doped system with an adsorption energy of -0.8 eV. This high energy value indicates that dioxane molecules chemisorb on the Al-doped system. While dioxane adsorption on the Ag- and Au-doped VSe₂ systems are mostly physisorption, the adsorption energies are -0.30 and -0.20 eV, respectively. It is also noted that the dioxane adsorption strength increases by the strategy of metal doping, which in turn signifies the improvement in the sensing activity of the pristine VSe₂ system. The shortest distance between the O atom of the dioxane molecule and the Al atom in the VSe₂ + Al system is 3.38 Å. While the O-Au and O-Ag distances are 2.26 and 2.62 Å, respectively. The adsorption energy calculations conclude that the Al-doped VSe₂ system is well suited as the sensor material for detecting dioxane molecules from the atmosphere.

### E. Mechanism of dioxane adsorption in metal-doped VSe₂ system

The DOS analysis explains how the electronic structure of the metal-doped VSe₂ system varies with the dioxane adsorption. Figure 8 compares the TDOS of the pristine and metal-doped VSe₂ system after the dioxane adsorption. The main reason for the origin of new energy states of the pristine and metal-doped VSe₂ system near the Fermi level is mainly because of the presence of dioxane molecules on its surface.

We have also analyzed the PDOS to clarify the orbital level interactions and charge transfer in the metal-doped VSe₂ systems. The PDOS of the Al 3p orbitals of VSe₂ + Al and VSe₂ + Al + dioxane systems are shown in the left top and bottom panel, respectively, in Fig. 9. At the same time, the right upper panel of the same figure represents the PDOS for the O 2p orbitals of the isolated dioxane, and the lower panel compares the PDOS for the O 2p orbitals of the VSe₂ + Al + dioxane system. It is worth noting that, after the interaction of the dioxane molecule with the VSe₂ + Al system, the energy states around the Fermi level of the Al 3p orbital diminished. At the same time, new states originated around the Fermi level of

<figure><img src="image_19.png" /><figcaption>FIG. 9. Orbital interaction analysis of VSe₂ + Al + dioxane using PDOS plots, compare the valence orbitals of Al in the VSe₂ + Al and VSe₂ + Al + dioxane system in the left panel. In contrast, the right panel compares the 2p orbitals of isolated dioxane atoms and the VSe₂ + Al + dioxane systems.</figcaption></figure>
<table><caption>**TABLE III.** LCA information on charge transfer of VSe₂ + metal systems to the dioxane molecule.</caption><thead><tr><th>System</th><th>Charge transfer</th></tr></thead><tbody><tr><td>VSe<sub>2</sub> + Al + dioxane</td><td>-0.567e (Al 3p orbital – O 2p orbital)</td></tr><tr><td>VSe<sub>2</sub> + Au + dioxane</td><td>-0.101e (Au 6s orbital – O 2p orbital)</td></tr><tr><td>VSe<sub>2</sub> + Ag + dioxane</td><td>-0.132e (Ag 5s orbital – O 2p orbital)</td></tr></tbody></table>

the O 2p orbital. These states were absent in the same energy range of the PDOS of isolated dioxane. This formation of new states in the O 2p orbital and decrement in the intensity of available energy states in the Al 3p orbital implies that the electronic charges are transferred from the O 2p to Al 3p orbital. In addition, the strong dioxane adsorption is because of the p-p orbital overlap. The quantitative charge transfer study by LCA also justifies this charge transfer, i.e., ~0.567e charges are lost by the 3p orbitals of Al in the VSe₂ + Al system to the O 2p orbital of the dioxane molecule.

A comparable reallocation of the energy states is observed in the PDOS of VSe₂ + Au and VSe₂ + Ag systems after the dioxane adsorption (Fig. S2). Similar to the Al 3p orbitals, the energy states of Ag 5s and Au 6s orbitals near the Fermi level decrease. Meanwhile, there is an enhancement in the energy states in the vicinity of the Fermi level of O 2p orbital of dioxane in the adsorbed system. The charge transfer from Ag and Au's s orbitals to the O 2p orbitals causes this reduction and enhancement in states. According to LCA, Au 6s lose 0.101e, and Ag 5s lose 0.132e charges to the O 2p orbital of dioxane, shown in Table III.

A large amount of charge transfer between the Al-doped VSe₂ system and dioxane molecule is due to the strong chemical adsorption. The minor charge transfer from the Ag and Au to the dioxane molecule is due to the physisorption. Since adsorption energy and charge transfer are the important parameters in sensing, the Al-doped VSe₂ system will be beneficial for the fabrication of electrochemical dioxane sensors.

## IV. CONCLUSION

In conclusion, we used the first principle density functional theory technique to explore the dioxane sensing abilities of pristine and metal-doped (Al, Au, and Ag) 2D VSe₂ systems. We have investigated various adsorption sites of the dioxane molecules on the pristine VSe₂ surface. Our adsorption energy calculation suggests that the dioxane interaction is more with the metal-doped VSe₂ system, particularly the Al-doped VSe₂, than its pristine counterpart. The Al atom binds strongly on the VSe₂ surface than the other metals with higher energy and charge transfer. The metal doping improved the conductivity and hence the adsorption ability of the VSe₂ system. The strong adsorption of the dioxane molecules with the VSe₂ + Al system is mainly due to the extensive charge transport and orbital interaction between the O 2p of dioxane and the 3p orbitals of Al. The MD simulation at 300 K verified the room temperature stability of the VSe₂ + Al system; therefore, the Al-doped VSe₂ system could be a more promising dioxane sensor. This work aims to provide a theoretical foundation and an interpretation of the adsorption behaviors of VSe₂-based biosensors to facilitate future empirical creations.

## SUPPLEMENTARY MATERIALS

See the **supplementary material** for the PDOS analysis of Au and Ag doping in pristine VSe₂ and the dioxane interaction on Au and Ag doped VSe₂.

## ACKNOWLEDGMENTS

N.K. acknowledges SERB: CRG (Grant No. CRG/2021/001506), UGC: Special Assistance Program (SAP; Grant Nos. F.530/12/DRS/2009 and F.530/13/DRS II/2016), UGC: Scheme for Promotion of Academic and Research Collaboration (SPARC; Grant Nos. P930, P1400, P1429, and P1460), DST: Nano Mission [Grant No. SR/NM/NS-1420-2014(C)], DST: Fund for Improvement of S&T Infrastructure (FIST; Grant No. SR/FST/P SI-143/2009), DAE: UGC-Consortium for Scientific Research (CSR; Grant No. UGC-DAE-CSR-KC/CRS/19/RC08/0983/1018), DAE-Board of Research in Nuclear Sciences (BRNS; Grant No. 39/29/2015-BRNS/39009), and DST Promotion of University Research and Scientific Excellence [PURSE; Grant No. SR/S9/Z-23/2010/22(C, G)], Government of India programs for providing the facilities for research and development in IIUCNN, MGU. The authors would like to thank the High-Performance Computing facilities provided by MGU.

## AUTHOR DECLARATIONS

### Conflict of Interest

The authors have no conflicts to disclose.

### Author Contributions

**Sreejith Pallikkara Chandrasekharan:** Conceptualization (equal); Data curation (equal); Formal analysis (equal); Funding acquisition (equal); Investigation (equal); Methodology (equal); Software (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal). **Seetha Lakshmy:** Conceptualization (equal); Data curation (equal); Formal analysis (equal); Investigation (equal); Methodology (equal); Software (equal); Writing – original draft (equal); Writing – review & editing (equal). **Saju Joseph:** Conceptualization (equal); Data curation (equal); Formal analysis (equal); Investigation (equal); Methodology (equal); Project administration (equal); Software (equal); Supervision (equal); Writing – original draft (equal); Writing – review & editing (equal). **Nandakumar Kalarikkal:** Conceptualization (equal); Formal analysis (equal); Funding acquisition (equal); Project administration (equal); Resources (equal); Supervision (equal); Validation (equal); Writing – original draft (equal).

## DATA AVAILABILITY

The data that support the findings of this study are available from the corresponding authors upon reasonable request.
<table><caption>**TABLE III.** LCA information on charge transfer of VSe₂ + metal systems to the dioxane molecule.</caption><thead><tr><th>System</th><th>Charge transfer</th></tr></thead><tbody><tr><td>VSe<sub>2</sub> + Al + dioxane</td><td>-0.567e (Al 3p orbital – O 2p orbital)</td></tr><tr><td>VSe<sub>2</sub> + Au + dioxane</td><td>-0.101e (Au 6s orbital – O 2p orbital)</td></tr><tr><td>VSe<sub>2</sub> + Ag + dioxane</td><td>-0.132e (Ag 5s orbital – O 2p orbital)</td></tr></tbody></table>

the O 2p orbital. These states were absent in the same energy range of the PDOS of isolated dioxane. This formation of new states in the O 2p orbital and decrement in the intensity of available energy states in the Al 3p orbital implies that the electronic charges are transferred from the O 2p to Al 3p orbital. In addition, the strong dioxane adsorption is because of the p-p orbital overlap. The quantitative charge transfer study by LCA also justifies this charge transfer, i.e., ~0.567e charges are lost by the 3p orbitals of Al in the VSe₂ + Al system to the O 2p orbital of the dioxane molecule.

A comparable reallocation of the energy states is observed in the PDOS of VSe₂ + Au and VSe₂ + Ag systems after the dioxane adsorption (Fig. S2). Similar to the Al 3p orbitals, the energy states of Ag 5s and Au 6s orbitals near the Fermi level decrease. Meanwhile, there is an enhancement in the energy states in the vicinity of the Fermi level of O 2p orbital of dioxane in the adsorbed system. The charge transfer from Ag and Au's s orbitals to the O 2p orbitals causes this reduction and enhancement in states. According to LCA, Au 6s lose 0.101e, and Ag 5s lose 0.132e charges to the O 2p orbital of dioxane, shown in Table III.

A large amount of charge transfer between the Al-doped VSe₂ system and dioxane molecule is due to the strong chemical adsorption. The minor charge transfer from the Ag and Au to the dioxane molecule is due to the physisorption. Since adsorption energy and charge transfer are the important parameters in sensing, the Al-doped VSe₂ system will be beneficial for the fabrication of electrochemical dioxane sensors.

## IV. CONCLUSION

In conclusion, we used the first principle density functional theory technique to explore the dioxane sensing abilities of pristine and metal-doped (Al, Au, and Ag) 2D VSe₂ systems. We have investigated various adsorption sites of the dioxane molecules on the pristine VSe₂ surface. Our adsorption energy calculation suggests that the dioxane interaction is more with the metal-doped VSe₂ system, particularly the Al-doped VSe₂, than its pristine counterpart. The Al atom binds strongly on the VSe₂ surface than the other metals with higher energy and charge transfer. The metal doping improved the conductivity and hence the adsorption ability of the VSe₂ system. The strong adsorption of the dioxane molecules with the VSe₂ + Al system is mainly due to the extensive charge transport and orbital interaction between the O 2p of dioxane and the 3p orbitals of Al. The MD simulation at 300 K verified the room temperature stability of the VSe₂ + Al system; therefore, the Al-doped VSe₂ system could be a more promising dioxane sensor. This work aims to provide a theoretical foundation and an interpretation of the adsorption behaviors of VSe₂-based biosensors to facilitate future empirical creations.

## SUPPLEMENTARY MATERIALS

See the **supplementary material** for the PDOS analysis of Au and Ag doping in pristine VSe₂ and the dioxane interaction on Au and Ag doped VSe₂.

## ACKNOWLEDGMENTS

N.K. acknowledges SERB: CRG (Grant No. CRG/2021/001506), UGC: Special Assistance Program (SAP; Grant Nos. F.530/12/DRS/2009 and F.530/13/DRS II/2016), UGC: Scheme for Promotion of Academic and Research Collaboration (SPARC; Grant Nos. P930, P1400, P1429, and P1460), DST: Nano Mission [Grant No. SR/NM/NS-1420-2014(C)], DST: Fund for Improvement of S&T Infrastructure (FIST; Grant No. SR/FST/P SI-143/2009), DAE: UGC-Consortium for Scientific Research (CSR; Grant No. UGC-DAE-CSR-KC/CRS/19/RC08/0983/1018), DAE-Board of Research in Nuclear Sciences (BRNS; Grant No. 39/29/2015-BRNS/39009), and DST Promotion of University Research and Scientific Excellence [PURSE; Grant No. SR/S9/Z-23/2010/22(C, G)], Government of India programs for providing the facilities for research and development in IIUCNN, MGU. The authors would like to thank the High-Performance Computing facilities provided by MGU.

## AUTHOR DECLARATIONS

### Conflict of Interest

The authors have no conflicts to disclose.

### Author Contributions

**Sreejith Pallikkara Chandrasekharan:** Conceptualization (equal); Data curation (equal); Formal analysis (equal); Funding acquisition (equal); Investigation (equal); Methodology (equal); Software (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal). **Seetha Lakshmy:** Conceptualization (equal); Data curation (equal); Formal analysis (equal); Investigation (equal); Methodology (equal); Software (equal); Writing – original draft (equal); Writing – review & editing (equal). **Saju Joseph:** Conceptualization (equal); Data curation (equal); Formal analysis (equal); Investigation (equal); Methodology (equal); Project administration (equal); Software (equal); Supervision (equal); Writing – original draft (equal); Writing – review & editing (equal). **Nandakumar Kalarikkal:** Conceptualization (equal); Formal analysis (equal); Funding acquisition (equal); Project administration (equal); Resources (equal); Supervision (equal); Validation (equal); Writing – original draft (equal).

## DATA AVAILABILITY

The data that support the findings of this study are available from the corresponding authors upon reasonable request.
REFERENCES

<footnote n="1">¹A. Fullana, J. A. Conesa, R. Font, and S. Sidhu, "Formation and destruction of chlorinated pollutants during sewage sludge incineration," *Environ. Sci. Technol.* **38**(10), 2953-2958 (2004).</footnote>

<footnote n="2">²H.-S. Iñaki, "Exploring the dissemination of environmental certifications in high and low polluting industries," *J. Cleaner Prod.* **89**, 50–58 (2015).</footnote>

<footnote n="3">³R. Hu, S. Dai, D. Shao, A. Alsaedi, B. Ahmad, and X. Wang, "Efficient removal of phenol and aniline from aqueous solutions using graphene oxide/polypyrrole composites," *J. Mol. Liq.* **203**, 80–89 (2015).</footnote>

<footnote n="4">⁴K. J. Godri Pollitt, J.-H. Kim, J. Peccia, M. Elimelech, Y. Zhang, G. Charkoftaki, B. Hodges, I. Zucker, H. Huang, N. C. Deziel, K. Murphy, M. Ishii, C. H. Johnson, A. Boissevain, E. O'Keefe, P. T. Anastas, D. Orlicky, D. C. Thompson, and V. Vasiliou, "1,4-dioxane as an emerging water contaminant: State of the science and evaluation of research needs," *Sci. Total Environ.* **690**, 853–866 (2019).</footnote>

<footnote n="5">⁵D. K. Stepien, P. Diehl, J. Helm, A. Thoms, and W. Püttmann, "Fate of 1,4-dioxane in the aquatic environment: From sewage to drinking water," *Water Res.* **48**, 406–419 (2014).</footnote>

<footnote n="6">⁶S. Zhang, P. B. Gedalanga, and S. Mahendra, "Advances in bioremediation of 1,4-dioxane-contaminated waters," *J. Environ. Manage.* **204**, 765–774 (2017).</footnote>

<footnote n="7">⁷M. A. Beckett and I. Hua, "Elucidation of the 1,4-dioxane decomposition pathway at discrete ultrasonic frequencies," *EnvIRON. Sci. Technol.* **34**(18), 3944–3953 (2000).</footnote>

<footnote n="8">⁸U. Karges, D. Ott, S. De Boer, and W. Püttmann, "1,4-dioxane contamination of German drinking water obtained by managed aquifer recharge systems: Distribution and main influencing factors," *Sci. Total Environ.* **711**, 134783 (2020).</footnote>

<footnote n="9">⁹Y. Xiong, Q. Zhang, R. Wandell, S. Bresch, H. Wang, B. R. Locke, and Y. Tang, "Synergistic 1,4-dioxane removal by non-thermal plasma followed by biodegradation," *Chem. Eng. J.* **361**, 519–527 (2019).</footnote>

<footnote n="10">¹⁰C.-S. Lee, A. K. Venkatesan, H. W. Walker, and C. J. Gobler, "Impact of groundwater quality and associated byproduct formation during UV/hydrogen peroxide treatment of 1,4-dioxane," *Water Res.* **173**, 115534 (2020).</footnote>

<footnote n="11">¹¹M. J. Zenker, R. C. Borden, and M. A. Barlaz, "Occurrence and treatment of 1,4-dioxane in aqueous environments," *Environ. Eng. Sci.* **20**(5), 423–432 (2003).</footnote>

<footnote n="12">¹²M. M. Rahman, A. Wahid, and A. M. Asiri, "Development of highly sensitive 1,4-dioxane sensor with semiconductor NiO-doped Nd₂O₃ nanostructures by electrochemical approach," *New J. Chem.* **43**(44), 17395–17402 (2019).</footnote>

<footnote n="13">¹³T. K. Sana Fathima, A. Arshiya Banu, T. Devasena, and S. Ramaprabhu, "A novel, highly sensitive electrochemical 1,4-dioxane sensor based on reduced graphene oxide-curcumin nanocomposite," *RSC Adv.* **12**(30), 19375–19383 (2022).</footnote>

<footnote n="14">¹⁴R. G. Parr, "Density functional theory of atoms and molecules," in *Horizons of Quantum Chemistry* (Springer, 1980), pp. 5–15.</footnote>

<footnote n="15">¹⁵Z. Chen, Y. Liu, S. Liao, N. Yi, and Q. Hu, "Treatment of adsorption of dioxane by using SiCNT toward efficient remediation of refractory organic contaminants from wastewater: DFT and DFTB-MD simulations," *J. Mol. Liq.* **316**, 113869 (2020).</footnote>

<footnote n="16">¹⁶Q. H. Wang, K. Kalantar-Zadeh, A. Kis, J. N. Coleman, and M. S. Strano, "Electronics and optoelectronics of two-dimensional transition metal dichalcogenides," *Nat. Nanotechnol.* **7**(11), 699–712 (2012).</footnote>

<footnote n="17">¹⁷B. Radisavljevic, A. Radenovic, J. Brivio, V. Giacometti, and A. Kis, "Single-layer MoS₂ transistors," *Nat. Nanotechnol.* **6**(3), 147–150 (2011).</footnote>

<footnote n="18">¹⁸A. Vaidyanathan, S. Lakshmy, G. Sanyal, S. Joseph, N. Kalarikkal, and B. Chakraborty, "Nitrobenzene sensing in pristine and metal doped 2D dichalcogenide MoS₂: Insights from density functional theory investigations," *Appl. Surf. Sci.* **550**, 149395 (2021).</footnote>

<footnote n="19">¹⁹S. Xu, Y. Zhang, F. Xu, C. Chen, and Z. Shen, "Theoretical study of the adsorption behaviors of gas molecules on the Au-functionalized MoS₂ nanosheets: A search for highly efficient gas sensors," *Comput. Theor. Chem.* **1188**, 112935 (2020).</footnote>

<footnote n="20">²⁰S. Lakshmy, G. Sanyal, A. Vaidyanathan, S. Joseph, N. Kalarikkal, and B. Chakraborty, "Catechol detection in pure and transition metal decorated 2D MoS₂: Acumens from density functional theory approaches," *Appl. Surf. Sci.* **562**, 150216 (2021).</footnote>

<footnote n="21">²¹M. Chhowalla, D. Voiry, J. Yang, H. S. Shin, and K. P. Loh, "Phase-engineered transition-metal dichalcogenides for energy and electronics," *MRS Bull.* **40**(7), 585–591 (2015).</footnote>

<footnote n="22">²²M. Calandra, "Chemically exfoliated single-layer MoS₂: Stability, lattice dynamics, and catalytic adsorption from first principles," *Phys. Rev. B* **88**(24), 245428 (2013).</footnote>

<footnote n="23">²³M. Salavati and T. Rabczuk, "Application of highly stretchable and conductive two-dimensional 1T VS₂ and VSe₂ as anode materials for Li-, Na- and Ca-ion storage," *Comput. Mater. Sci.* **160**, 360–367 (2019).</footnote>

<footnote n="24">²⁴C. Ataca, H. Şahin, and S. Ciraci, "Stable, single-layer MX₂ transition-metal oxides and dichalcogenides in a honeycomb-like structure," *J. Phys. Chem. C* **116**(16), 8983–8999 (2012).</footnote>

<footnote n="25">²⁵Z. Zhang, J. Niu, P. Yang, Y. Gong, Q. Ji, J. Shi, Q. Fang, S. Jiang, H. Li, X. Zhou, L. Gu, X. Wu, and Y. Zhang, "Van der Waals epitaxial growth of 2D metallic vanadium diselenide single crystals and their extra-high electrical conductivity," *Adv. Mater.* **29**(37), 1702359 (2017).</footnote>

<footnote n="26">²⁶G. Sanyal, S. Lakshmy, A. Vaidyanathan, N. Kalarikkal, and B. Chakraborty, "Detection of nitrobenzene in pristine and metal decorated 2D dichalcogenide VSe₂: Perspectives from density functional theory," *Surf. Interfaces* **29**, 101816 (2022).</footnote>

<footnote n="27">²⁷G. V. Kamarchuk, A. V. Khotkevich, V. M. Bagatsky, V. G. Ivanov, P. Molinié, A. Leblanc, and E. Faulques, "Direct determination of Debye temperature and electron-phonon interaction in 1T VSe₂," *Phys. Rev. B* **63**(7), 073107 (2001).</footnote>

<footnote n="28">²⁸Z. Zhang, P. Yang, M. Hong, S. Jiang, G. Zhao, J. Shi, Q. Xie, and Y. Zhang, "Recent progress in the controlled synthesis of 2D metallic transition metal dichalcogenides," *Nanotechnology* **30**(18), 182002 (2019).</footnote>

<footnote n="29">²⁹K. Xu, P. Chen, X. Li, C. Wu, Y. Guo, J. Zhao, X. Wu, and Y. Xie, "Ultrathin nanosheets of vanadium diselenide: A metallic two-dimensional material with ferromagnetic charge-density-wave behavior," *Angew. Chem., Int. Ed.* **52**(40), 10477–10481 (2013).</footnote>

<footnote n="30">³⁰R. Atkins, M. Dolgos, A. Fiedler, C. Grosse, S. F. Fischer, S. P. Rudin, and D. C. Johnson, "Synthesis and systematic trends in structure and electrical properties of [(SnSe)₁.₁₅]m(VSe₂)₁, m = 1, 2, 3, and 4," *Chem. Mater.* **26**(9), 2862–2872 (2014).</footnote>

<footnote n="31">³¹A. L. Hector, M. Jura, W. Levason, S. D. Reid, and G. Reid, "Vanadium selection and selenolate complexes, potential single-source precursors for CVD of VSe₂ thin films," *New J. Chem.* **33**(3), 641–645 (2009).</footnote>

<footnote n="32">³²P. Giannozzi, S. Baroni, N. Bonini, M. Calandra, R. Car, C. Cavazzoni, D. Ceresoli, G. L. Chiarotti, M. Cococcioni, I. Dabo, A. Dal Corso, S. de Gironcoli, S. Fabris, G. Fratesi, R. Gebauer, U. Gerstmann, C. Gougoussis, A. Kokalj, M. Lazzeri, L. Martin-Samos, N. Marzari, F. Mauri, R. Mazzarello, S. Paolini, A. Pasquarello, L. Paulatto, C. Sbraccia, S. Scandolo, G. Sclauzero, A. P. Seitsonen, A. Smogunov, P. Umari, and R. M. Wentzcovitch, "QUANTUM ESPRESSO: A modular and open-source software project for quantum simulations of materials," *J. Phys.: Condens. Matter* **21**(39), 395502 (2009).</footnote>

<footnote n="33">³³J. P. Perdew, K. Burke, and M. Ernzerhof, "Generalized gradient approximation made simple," *Phys. Rev. Lett.* **77**(18), 3865–3868 (1996).</footnote>

<footnote n="34">³⁴J. Henke, F. Flicker, J. Laverock, and J. van Wezel, "Charge order from structured coupling in VSe₂," *SciPost Phys.* **9**(4), 056 (2020).</footnote>

<footnote n="35">³⁵A. Huang, C.-H. Chen, C.-H. Chang, and H.-T. Jeng, "Topological phase and quantum anomalous Hall effect in ferromagnetic transition-metal dichalcogenides monolayer 1T - VSe₂," *Nanomaterials* **11**(8), 1998 (2021).</footnote>

<footnote n="36">³⁶B. Stahl and T. Bredow, "Critical assessment of the DFT + U approach for the prediction of vanadium dioxide properties," *J. Comput. Chem.* **41**(3), 258–265 (2020).</footnote>

<footnote n="37">³⁷Y. Wang, J. Wan, W. Tian, Z. Hou, X. Gu, and Y. Wang, "Theoretical screening of VSe₂ as support for enhanced electrocatalytic performance of transition-metal single atoms," *J. Colloid Interface Sci.* **590**, 210–218 (2021).</footnote>
REFERENCES

<footnote n="1">¹A. Fullana, J. A. Conesa, R. Font, and S. Sidhu, "Formation and destruction of chlorinated pollutants during sewage sludge incineration," *Environ. Sci. Technol.* **38**(10), 2953-2958 (2004).</footnote>

<footnote n="2">²H.-S. Iñaki, "Exploring the dissemination of environmental certifications in high and low polluting industries," *J. Cleaner Prod.* **89**, 50–58 (2015).</footnote>

<footnote n="3">³R. Hu, S. Dai, D. Shao, A. Alsaedi, B. Ahmad, and X. Wang, "Efficient removal of phenol and aniline from aqueous solutions using graphene oxide/polypyrrole composites," *J. Mol. Liq.* **203**, 80–89 (2015).</footnote>

<footnote n="4">⁴K. J. Godri Pollitt, J.-H. Kim, J. Peccia, M. Elimelech, Y. Zhang, G. Charkoftaki, B. Hodges, I. Zucker, H. Huang, N. C. Deziel, K. Murphy, M. Ishii, C. H. Johnson, A. Boissevain, E. O'Keefe, P. T. Anastas, D. Orlicky, D. C. Thompson, and V. Vasiliou, "1,4-dioxane as an emerging water contaminant: State of the science and evaluation of research needs," *Sci. Total Environ.* **690**, 853–866 (2019).</footnote>

<footnote n="5">⁵D. K. Stepien, P. Diehl, J. Helm, A. Thoms, and W. Püttmann, "Fate of 1,4-dioxane in the aquatic environment: From sewage to drinking water," *Water Res.* **48**, 406–419 (2014).</footnote>

<footnote n="6">⁶S. Zhang, P. B. Gedalanga, and S. Mahendra, "Advances in bioremediation of 1,4-dioxane-contaminated waters," *J. Environ. Manage.* **204**, 765–774 (2017).</footnote>

<footnote n="7">⁷M. A. Beckett and I. Hua, "Elucidation of the 1,4-dioxane decomposition pathway at discrete ultrasonic frequencies," *EnvIRON. Sci. Technol.* **34**(18), 3944–3953 (2000).</footnote>

<footnote n="8">⁸U. Karges, D. Ott, S. De Boer, and W. Püttmann, "1,4-dioxane contamination of German drinking water obtained by managed aquifer recharge systems: Distribution and main influencing factors," *Sci. Total Environ.* **711**, 134783 (2020).</footnote>

<footnote n="9">⁹Y. Xiong, Q. Zhang, R. Wandell, S. Bresch, H. Wang, B. R. Locke, and Y. Tang, "Synergistic 1,4-dioxane removal by non-thermal plasma followed by biodegradation," *Chem. Eng. J.* **361**, 519–527 (2019).</footnote>

<footnote n="10">¹⁰C.-S. Lee, A. K. Venkatesan, H. W. Walker, and C. J. Gobler, "Impact of groundwater quality and associated byproduct formation during UV/hydrogen peroxide treatment of 1,4-dioxane," *Water Res.* **173**, 115534 (2020).</footnote>

<footnote n="11">¹¹M. J. Zenker, R. C. Borden, and M. A. Barlaz, "Occurrence and treatment of 1,4-dioxane in aqueous environments," *Environ. Eng. Sci.* **20**(5), 423–432 (2003).</footnote>

<footnote n="12">¹²M. M. Rahman, A. Wahid, and A. M. Asiri, "Development of highly sensitive 1,4-dioxane sensor with semiconductor NiO-doped Nd₂O₃ nanostructures by electrochemical approach," *New J. Chem.* **43**(44), 17395–17402 (2019).</footnote>

<footnote n="13">¹³T. K. Sana Fathima, A. Arshiya Banu, T. Devasena, and S. Ramaprabhu, "A novel, highly sensitive electrochemical 1,4-dioxane sensor based on reduced graphene oxide-curcumin nanocomposite," *RSC Adv.* **12**(30), 19375–19383 (2022).</footnote>

<footnote n="14">¹⁴R. G. Parr, "Density functional theory of atoms and molecules," in *Horizons of Quantum Chemistry* (Springer, 1980), pp. 5–15.</footnote>

<footnote n="15">¹⁵Z. Chen, Y. Liu, S. Liao, N. Yi, and Q. Hu, "Treatment of adsorption of dioxane by using SiCNT toward efficient remediation of refractory organic contaminants from wastewater: DFT and DFTB-MD simulations," *J. Mol. Liq.* **316**, 113869 (2020).</footnote>

<footnote n="16">¹⁶Q. H. Wang, K. Kalantar-Zadeh, A. Kis, J. N. Coleman, and M. S. Strano, "Electronics and optoelectronics of two-dimensional transition metal dichalcogenides," *Nat. Nanotechnol.* **7**(11), 699–712 (2012).</footnote>

<footnote n="17">¹⁷B. Radisavljevic, A. Radenovic, J. Brivio, V. Giacometti, and A. Kis, "Single-layer MoS₂ transistors," *Nat. Nanotechnol.* **6**(3), 147–150 (2011).</footnote>

<footnote n="18">¹⁸A. Vaidyanathan, S. Lakshmy, G. Sanyal, S. Joseph, N. Kalarikkal, and B. Chakraborty, "Nitrobenzene sensing in pristine and metal doped 2D dichalcogenide MoS₂: Insights from density functional theory investigations," *Appl. Surf. Sci.* **550**, 149395 (2021).</footnote>

<footnote n="19">¹⁹S. Xu, Y. Zhang, F. Xu, C. Chen, and Z. Shen, "Theoretical study of the adsorption behaviors of gas molecules on the Au-functionalized MoS₂ nanosheets: A search for highly efficient gas sensors," *Comput. Theor. Chem.* **1188**, 112935 (2020).</footnote>

<footnote n="20">²⁰S. Lakshmy, G. Sanyal, A. Vaidyanathan, S. Joseph, N. Kalarikkal, and B. Chakraborty, "Catechol detection in pure and transition metal decorated 2D MoS₂: Acumens from density functional theory approaches," *Appl. Surf. Sci.* **562**, 150216 (2021).</footnote>

<footnote n="21">²¹M. Chhowalla, D. Voiry, J. Yang, H. S. Shin, and K. P. Loh, "Phase-engineered transition-metal dichalcogenides for energy and electronics," *MRS Bull.* **40**(7), 585–591 (2015).</footnote>

<footnote n="22">²²M. Calandra, "Chemically exfoliated single-layer MoS₂: Stability, lattice dynamics, and catalytic adsorption from first principles," *Phys. Rev. B* **88**(24), 245428 (2013).</footnote>

<footnote n="23">²³M. Salavati and T. Rabczuk, "Application of highly stretchable and conductive two-dimensional 1T VS₂ and VSe₂ as anode materials for Li-, Na- and Ca-ion storage," *Comput. Mater. Sci.* **160**, 360–367 (2019).</footnote>

<footnote n="24">²⁴C. Ataca, H. Şahin, and S. Ciraci, "Stable, single-layer MX₂ transition-metal oxides and dichalcogenides in a honeycomb-like structure," *J. Phys. Chem. C* **116**(16), 8983–8999 (2012).</footnote>

<footnote n="25">²⁵Z. Zhang, J. Niu, P. Yang, Y. Gong, Q. Ji, J. Shi, Q. Fang, S. Jiang, H. Li, X. Zhou, L. Gu, X. Wu, and Y. Zhang, "Van der Waals epitaxial growth of 2D metallic vanadium diselenide single crystals and their extra-high electrical conductivity," *Adv. Mater.* **29**(37), 1702359 (2017).</footnote>

<footnote n="26">²⁶G. Sanyal, S. Lakshmy, A. Vaidyanathan, N. Kalarikkal, and B. Chakraborty, "Detection of nitrobenzene in pristine and metal decorated 2D dichalcogenide VSe₂: Perspectives from density functional theory," *Surf. Interfaces* **29**, 101816 (2022).</footnote>

<footnote n="27">²⁷G. V. Kamarchuk, A. V. Khotkevich, V. M. Bagatsky, V. G. Ivanov, P. Molinié, A. Leblanc, and E. Faulques, "Direct determination of Debye temperature and electron-phonon interaction in 1T VSe₂," *Phys. Rev. B* **63**(7), 073107 (2001).</footnote>

<footnote n="28">²⁸Z. Zhang, P. Yang, M. Hong, S. Jiang, G. Zhao, J. Shi, Q. Xie, and Y. Zhang, "Recent progress in the controlled synthesis of 2D metallic transition metal dichalcogenides," *Nanotechnology* **30**(18), 182002 (2019).</footnote>

<footnote n="29">²⁹K. Xu, P. Chen, X. Li, C. Wu, Y. Guo, J. Zhao, X. Wu, and Y. Xie, "Ultrathin nanosheets of vanadium diselenide: A metallic two-dimensional material with ferromagnetic charge-density-wave behavior," *Angew. Chem., Int. Ed.* **52**(40), 10477–10481 (2013).</footnote>

<footnote n="30">³⁰R. Atkins, M. Dolgos, A. Fiedler, C. Grosse, S. F. Fischer, S. P. Rudin, and D. C. Johnson, "Synthesis and systematic trends in structure and electrical properties of [(SnSe)₁.₁₅]m(VSe₂)₁, m = 1, 2, 3, and 4," *Chem. Mater.* **26**(9), 2862–2872 (2014).</footnote>

<footnote n="31">³¹A. L. Hector, M. Jura, W. Levason, S. D. Reid, and G. Reid, "Vanadium selection and selenolate complexes, potential single-source precursors for CVD of VSe₂ thin films," *New J. Chem.* **33**(3), 641–645 (2009).</footnote>

<footnote n="32">³²P. Giannozzi, S. Baroni, N. Bonini, M. Calandra, R. Car, C. Cavazzoni, D. Ceresoli, G. L. Chiarotti, M. Cococcioni, I. Dabo, A. Dal Corso, S. de Gironcoli, S. Fabris, G. Fratesi, R. Gebauer, U. Gerstmann, C. Gougoussis, A. Kokalj, M. Lazzeri, L. Martin-Samos, N. Marzari, F. Mauri, R. Mazzarello, S. Paolini, A. Pasquarello, L. Paulatto, C. Sbraccia, S. Scandolo, G. Sclauzero, A. P. Seitsonen, A. Smogunov, P. Umari, and R. M. Wentzcovitch, "QUANTUM ESPRESSO: A modular and open-source software project for quantum simulations of materials," *J. Phys.: Condens. Matter* **21**(39), 395502 (2009).</footnote>

<footnote n="33">³³J. P. Perdew, K. Burke, and M. Ernzerhof, "Generalized gradient approximation made simple," *Phys. Rev. Lett.* **77**(18), 3865–3868 (1996).</footnote>

<footnote n="34">³⁴J. Henke, F. Flicker, J. Laverock, and J. van Wezel, "Charge order from structured coupling in VSe₂," *SciPost Phys.* **9**(4), 056 (2020).</footnote>

<footnote n="35">³⁵A. Huang, C.-H. Chen, C.-H. Chang, and H.-T. Jeng, "Topological phase and quantum anomalous Hall effect in ferromagnetic transition-metal dichalcogenides monolayer 1T - VSe₂," *Nanomaterials* **11**(8), 1998 (2021).</footnote>

<footnote n="36">³⁶B. Stahl and T. Bredow, "Critical assessment of the DFT + U approach for the prediction of vanadium dioxide properties," *J. Comput. Chem.* **41**(3), 258–265 (2020).</footnote>

<footnote n="37">³⁷Y. Wang, J. Wan, W. Tian, Z. Hou, X. Gu, and Y. Wang, "Theoretical screening of VSe₂ as support for enhanced electrocatalytic performance of transition-metal single atoms," *J. Colloid Interface Sci.* **590**, 210–218 (2021).</footnote>