Search query: Optical and photocatalytic properties of two-dimensional MoS2

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abstract: The electronic structure and optical spectrum of monolayer MoS2 are calculated using both the modified Becke Johnson (mBJ) approximation and Bethe Salpeter equation. Bulk MoS2 is an indirect band gap semiconductor, but thinned to a monolayer it converts to a direct band gap semiconductor with increased gap. The calculated mBJ band gaps of MoS2 amount to 1.15 eV for the bulk and 1.90 eV for the monolayer, in excellent agreement with experiment. The experimental excitonic peaks of monolayer MoS2 at 1.88 eV and 2.06 eV are reproduced by the calculations. The high photoluminescence yield can be attributed to a high binding energy of the excitons and is not due to a splitting of the valence bands, as is commonly assumed. We also show that monolayer MoS2 has the ability to oxidize H2O and produce O2 as well as to reduce H+ to H2.
author_names: N Singh

Ghassan E Jabbour

Udo Schwingenschlogl
title: Optical and photocatalytic properties of two dimensional MoS2
year: 2012

abstract: Very recently, the two dimensional (2D) form of MoSi2N4 has been successfully fabricated [Hong et al. Sci. 369, 670 (2020) Motivated by theses recent experimental results, herein we investigate the structural, mechanical, thermal, electronic, optical and photocatalytic properties using hybrid density functional theory (HSE06 DFT) Phonon band dispersion calculations reveal the dynamical stability of MoSi2N4 monolayer structure. Furthermore, the mechanical study confirms the stability of MoSi2N4 monolayer. As compared to the corresponding value of graphene, we find the Youngs modulus decreases by 30% while the Poissons ratio increases by 30% In addition, its work function is very similar to that of phosphorene and MoS2 monolayers. The electronic structure investigation shows the MoSi2N4 monolayer is an indirect bandgap semiconductor. We have determined the bandgap using the HSE06 (GGA) is 2.35 (1.79) eV, which is an overestimated (underestimated) value of the experimental bandgap (1.99 eV) The thermoelectric study shows a good thermoelectric performance of the MoSi2N4 monolayer with a figure of merit slightly larger than unity at high temperatures. The optical analysis using the RPA method constructed over HSE06 shows that the first absorption peak of the MoSi2N4 monolayer for in plane polarization is located in the visible range of spectrum, i.e. it is a promising candidate for advancing optoelectronic nanodevices. The photocatalytic study indicates the MoSi2N4 monloayer can be a promising photocatalyst for water splitting as well as and CO2 reduction. In summary, the fascinating MoSi2N4 monloayer is a promising 2D material in many applications due to its unique physical properties.
author_names: Asadollah Bafekry

M Faraji

D M Hoat

Mohamed M Fadlallah

Masoud Shahrokhi

Fazel Shojaei

Daniela Gogova

Mitra Ghergherehchi
title: MoSi2N4 single layer: a novel two dimensional material with outstanding mechanical, thermal, electronic, optical, and photocatalytic properties
year: 2020

abstract: Abstract Van der Waals (vdW) heterostructure can improve the performance of the 2D materials and provide more applications. Based on density functional theory (DFT) calculations, the properties of vertical heterostructures formed by transition metal dichalcogenides (TMDs) MX2 (M Mo, W; X S, Se) and boron nitride (BP) were addressed. In particular, the vdW interaction exist in all these heterostructures instead of covalent bonding. The MoSe2/BP and WSe2/BP vdW heterostructures possess direct bandgap characterized by type II band alignment and powerful built in electric field across the interface, which can effectively separate the photogenerated charge. Meanwhile, the MoS2/BP and WS2/BP vdW heterostructures also have the direct bandgap and intrinsic type I band alignment. Furthermore, all heterostructures exhibit excellent optical absorption in the visible and near infrared regions. Our investigation shows an effective method to design new vdW heterostructures based on TMDs and explores their applications for photocatalytic, photovoltaic, and optical devices.
author_names: Kai Ren

Minglei Sun

Yi-dong Luo

Sake Wang

Jin Yu

Wencheng Tang
title: First principle study of electronic and optical properties of two dimensional materials based heterostructures based on transition metal dichalcogenides and boron phosphide
venue: Applied Surface Science
year: 2019

abstract: Abstract Four vertical heterostructures based on two dimensional transition metal dichalcogenides (TMDs) MoS2/GeC, MoSe2/GeC, WS2/GeC, and WSe2/GeC, were studied by density functional theory calculations to investigate their structure, electronic characteristics, principle of photogenerated electron hole separation, and optical absorption capability. The optimized heterostructures were formed by van der Waals (vdW) forces and without covalent bonding. Their most stable geometric configurations and band structures display type II band alignment, which allows them to spontaneously separate photogenerated electrons and holes. The charge difference and built in electric field across the interface of these vdW heterostructures also contribute to preventing the photogenerated electron hole recombination. Finally, the high optical absorption of the four TMD based vdW heterostructures in the visible and near infrared regions indicates their suitability for photocatalytic, photovoltaic, and optical devices.
author_names: Kai Ren

Minglei Sun

Yi-dong Luo

Sake Wang

Yujin Xu

Jin Yu

Wencheng Tang
title: Electronic and optical properties of van der Waals vertical heterostructures based on two dimensional transition metal dichalcogenides: First principles calculations
venue: Physics Letters A
year: 2019

abstract: Two new two dimensional (2D) layered materials, namely, MgX2Se4 (X Al, Ga) monolayers, are predicted to possess novel electronic properties. Ab initio electronic structure calculations show that both MgAl2Se4 and MgGa2Se4 monolayers are direct gap semiconductors with bandgaps of 3.14 eV and 2.34 eV, respectively. The bandgap of both 2D materials is very sensitive to the in plane biaxial strain, while the strain induced bandgap changes allow the tuning of optical absorption from the violet to green light region. Also importantly, the in plane electron mobility of both 2D materials is predicted to be as high as ~0.7 1.0 x 103 cm2 V 1 s 1, notably higher than that of the MoS2 sheet ~200 cm2 V 1 s 1) while it is comparable to that of black phosphorene ~1000 cm2 V 1 s 1) suggesting their potential application in n type field effect transistors. Moreover, suitable bandgap and band edge alignment make the monolayer MgX2Se4 a potential photocatalyst for water splitting. Lastly, we show that MgX2Se4 possesses a lower monolayer cleavage energy than that of graphite, indicating easy exfoliation of MgX2Se4 layers from their bulk.
author_names: Pengfei Li

Weiping Zhang

Changhao Liang

Xiao Cheng Zeng
title: Two dimensional MgX2Se4 (X Al, Ga) monolayers with tunable electronic properties for optoelectronic and photocatalytic applications.
venue: Nanoscale
year: 2019

abstract: Abstract Photocatalytic water splitting is one of the methods to produce hydrogen fuel by reducing the water into the oxygen and hydrogen provided that the bandgap of one catalyst is larger than +1.23 eV. In this paper, based on density functional theory, we investigated the structural, electronic and optical properties of heterostructure MoS2 (WS2) paired with GaN and we found out that MoS2/GaN/MoS2, WS2/GaN and WS2/GaN/WS2 vdW heterostructures are potential photocatalysts for photocatalytic applications. From the band structure and electronic partial density of states (PDOS) we confirm that all simulated heterostructures are direct semiconductors of type II band alignment with valence band maximum and conduction band minimum localized at pz orbital N atom of GaN and dz2 orbital Mo (or W) atom of MoS2 and WS2 respectively. The band offset induced by efficient interlayer charge transfer form a staggered gap which aids in exciton disassociation and charge separation. Our studied models are expected to harvest UV to visible light with absorption coefficient up to 3.38 x 10 5 cm 1 at wavelength of 102 nm. On top of that, our proposed heterosystem are also believed to be a promising device for various optoelectronic application specifically in from UV to near infrared with high performance.
author_names: Nur 'Adnin Akmar Zulkifli

Suhana Binti Mohd Said

Mohamad Fariz Mohamad Taib

Khuzaimah Arifin

Shaima Mohamad Ali Mahmood

Kai Lin Woon

Shobhit K Patel

C L Tan

Rozalina Binti Zakaria
title: Photocatalytic Application of Two dimensional Materials based Heterostructure Based on Molybdenum and Tungsten Disulfides and Gallium Nitride: A Density Functional Theory Study
year: 2020

abstract: Abstract Uniform two dimensional MoS2 nanoflakes were vertically assembled on the surface of reduced graphene oxide (MoS2/rGO composite film) via a hydrothermal process. The structure, morphology and optical properties of MoS2/rGO composite were studied. It is demonstrated that photocatalytic activity of the composite films for the degradation of methylene blue in the visible light range is much higher than that of isolated MoS2 and rGO. This is associated with an efficient transfer and a rapid separation of photogenerated electrons and holes at the heterojunction between MoS2 nanoflakes and rGO film.
author_names: Minfang Chen

Carla Bittencourt

Rony Snyders
title: Photocatalytic properties of MoS2 nanoflakes vertically assembled on reduced graphene oxide
venue: Thin Solid Films
year: 2019

abstract: Transition metal sulfide semiconductors have achieved significant attention in the field of photocatalysis and degradation of pollutants. MoS2 with a two dimensional (2D) layered structure, a narrow bandgap and the ability of getting excited while being exposed to visible light, has demonstrated great potential in visible light driven photocatalysts. However, it possesses fast paced recombination of charges. In this study, the coupled MoS2 nanosheets were synthesized with ZnO nanorods to develop the heterojunctions photocatalyst in order to obtain superior photoactivity. The charge transfer in this composite is not adequate to achieve desirable activity. Therefore, heterojunction was modified by reduced graphene oxide (RGO) nanosheets and carbon nanotubes (CNTs) to develop the RGO/ZnO/MoS2 and CNTs/ZnO/MoS2 ternary nanocomposites. The structure, morphology, composition, optical and photocatalytic properties of the as fabricated samples were characterized through X ray diffraction (XRD) Fourier Transform Infrared (FTIR) Field Emission Scanning Electron Microscopy (FESEM) Transmission Electron Microscopy (TEM) Energy Dispersive X ray (EDX) elemental mapping, Photoluminescence (PL) Ultraviolet Visible spectroscopy (UV VIS) and Brunauer Emmett Teller (BET) techniques. The photo catalytic performance of all samples was evaluated through photodegradation of aniline in aqueous solution. The combination of RGO or CNTs into the ZnO/MoS2 greatly promoted the catalytic activity. However, the resulting RGO/ZnO/MoS2 ternary nanocomposites showed appreciably increased catalytic performance, faster than that of CNTs/ZnO/MoS2. Charge carrier transfer studies, the BET surface area analysis, and the optical studies confirmed this superiority. The role of operational variables namely, solution pH, catalyst dosage amount, and initial concentration of aniline was then investigated for obtaining maximum degradation. Complete degradation was observed, in the case of pH 4, catalyst dosage of 0.7 g/L and aniline concentration of 80 ppm, and light intensity of 100 W. According to the results of trapping experiments, hydroxyl radical was found to be the main active species in the photocatalytic reaction. Meanwhile, a plausible mechanism was proposed for describing the degradation of aniline upon ternary composite. Moreover, the catalyst showed excellent reusability and stability after five consecutive cycles due to the synergistic effect between its components. Total Organic Carbon concentration (TOC) results suggested that complete mineralization of aniline occurred after 210 min of irradiation. Finally, a real petrochemical wastewater sample was evaluated for testing the catalytic ability of the as fabricated composites in real case studies and it was observed that the process successfully quenched 100% and 93% of Chemical Oxygen Demand (COD) and TOC in the wastewater, respectively.
author_names: Parisa Ghasemipour

Moslem Fattahi

Behnam Rasekh

Fatemeh Yazdian
title: Developing the Ternary ZnO Doped MoS2 Nanostructures Grafted on CNT and Reduced Graphene Oxide (RGO) for Photocatalytic Degradation of Aniline
venue: Scientific Reports
year: 2020

abstract: Abstract Owing to their unique physicochemical, optical and electrical properties, two dimensional (2D) MoS2 cocatalysts have been widely applied in designing and developing highly efficient composite photocatalysts for hydrogen generation under suitable light irradiation. In this review, we first elaborated on the fundamental aspects of 2D MoS2 cocatalysts to include the structural design principles, synthesis strategies, strengths and challenges. Subsequently, we thoroughly highlighted and discussed the modification strategies of 2D MoS2 H2 evolution cocatalysts, including doping heteroatoms (e.g. metals, non metals, and co doping) designing interfacial coupling morphologies, controlling the physical properties (e.g. thickness, size, structural defects or pores) exposing the reactive facets or edge sites, constructing cocatalyst heterojunctions, engineering the interfacial bonds and confinement effects. In the future, the forefront challenges in understanding and in precise controlling of the active sites at molecular level or atomic level should be carefully studied, while various potential mechanisms of photogenerated electrons interactions should be proposed. The applications of MoS2 cocatalyst in the overall water splitting are also expected. This review may offer new inspiration for designing and constructing novel and efficient MoS2 based composite photocatalysts for highly efficient photocatalytic hydrogen evolution.
author_names: Zizhan Liang

Rongchen Shen

Yun Hau Ng

Peng Zhang

Quanjun Xiang

Xiao-ming Li
title: A review on 2D MoS2 cocatalysts in photocatalytic H2 production
year: 2020

abstract: While two dimensional layered MoS2 nanosheets have been extensively studied owing to their fascinating optoelectronic properties, less attention has been paid on the corresponding zero dimensional nano crystals. In this contribution, we report the efficacy of MoS2 nanocrystals for their size tunable properties for optical and photocatalytic applications. We have synthesized different sized (10 70 nm) crystalline, hexagonal 2H MoS2 nanoparticles (NPs) dispersed in DMF solvent using a simple exfoliation technique. Synthesized NPs are found to exhibit size dependent optical properties and excitation dependent fluorescence characteristics in the visible region, which are not observed in bulk or 2D MoS2 layers. Size tunable band gap and broad absorbance and emission spectrum covering the visible range could be exploited in the fabrication of various opto electronic devices. Charge carrier emission dynamics of different sized MoS2 NPs are investigated using time correlated single photon counting (TCSPC) spectroscopic technique. We found two time components, one in the order of several hundreds of ps, which arises due to the radiative recombination of charge carriers, while the other one is of the order of a few ns, which emanates from the defect states of MoS2 NPs. The average time constants are found to decrease with increase in particle size. A noticeable photocatalytic activity of the synthesized MoS2 NPs under visible light illumination for the degradation of Brilliant Green dye is also demonstrated for the first time and the effect of size variation of NPs in the dye degradation process is reported.
author_names: D Bhattacharya

Subhrajit Mukherjee

Samit Kumar Ray

Rajib Kumar Mitra
title: Size dependent optical properties of MoS2 nanoparticles and their photo catalytic applications.
venue: Nanotechnology
year: 2019