bluuebunny/crossref_metadata_2025_split huggingface dataset:
White-Light Emitting Carbon Dot Species from Carbonization in Zeolite Template
Authors: Ko Seung Hyeon , Park Hongjun , Lee Taekyoung , Ryoo Ryong 
Published: February 2020

Over the last few years, extensive research efforts have focused on development of solid-state white-light-emitting materials because of their potential for energy-efficient illumination. Common approaches to generate white light emission are either by properly mixing red, green, and blue-emitting semiconductor quantum dots or integrating them with traditional organic phosphors. However, semiconductor nanocrystals containing Cd or other heavy metals have serious toxicity as well as high costs, which considerably limits their practical applications. In recent years, compared to the quantum dots, carbon-based fluorescent nanodots including carbon dots and graphene quantum dots have emerged as promising substitutes for the present fluorescent nanomaterials because of their competitive optical performance - high photostability, non-blinking photoluminescence and versatile tunability of optical properties.
Herein we report on a facile synthesis of carbon dot species from acetylene using Ca2+ ion catalyst in zeolite template. The resulting product directly exhibits strong white-fluorescence in N-methyl-2-pyrrolidone (NMP) solution under a single wavelength excitation. The photoluminescence quantum yield of the white emission was determined to be 13.7 % under 340 nm excitation in NMP solution. The current synthesis method is a reliable low-cost synthetic technique, rendering potential various scientific and industrial applications.

Figure 1
Nonlinear Electrochemical Impedance Spectrosocpic Analysis of Ti Dissolution in HF
Authors: Srinivasan Ramanathan , Pachimatla Rajesh 
Published: February 2020

Electrochemical impedance spectroscopy (EIS) is a versatile technique that is commonly used to characterize electrochemical systems [1]. In EIS conducted in pseudo-potentiostatic mode, sinusoidal potential perturbations are applied and the magnitude and phase of the resulting current perturbations are used to calculate impedance as a function of frequency. Typically small amplitude perturbations are employed and the response is analyzed assuming that the system behavior is linear and that higher harmonics are not present in the response. Most of the commercial equipment can measure the response at fundamental frequency but higher harmonics are usually discarded. If large amplitude perturbations are employed, the resulting current will have higher harmonic components, which, if recorded, can provide more information about the system examined [2].
In this work, we report measurement of nonlinear electrochemical impedance spectroscopic (NLEIS) response of titanium dissolution in HF. A potentiostat (EC301), Lockin amplifier (SR830) and a FFT analyzer (SR780) from Stanford Research System were combined and a software was written to seamlessly acquire NLEIS data. The applied perturbation frequency was varied from 100 kHz to 125 mHz and the amplitude was varied from 20 mV to 100 mV. The response current (both magnitude and phase) at fundamental and higher harmonics (up to 3rdharmonic) was measured using Lockin amplifier and FFT anlayzer. In order to measure the phase and magnitude accurately, the frequencies and span were chosen such that the fundamental and harmonics fall exactly in the measurement bins. No windowing was performed during FFT signal processing. The results are presented in Fig. 1. Open symbols are the results from Lockin amplifier while the filled symbols are results from FFT analyzer. At 20 mV perturbation amplitude, second harmonic was low but measurable, but the third harmonic was below detection limit. At 100 mV perturbation, all three harmonics could be measured. The results of Lockin amplifier and FFT analyzer matched well.
Ti dissolution in HF has been studied earlier using potentiodynamic polarization and EIS [3,4]. A four step mechanism with two adsorbed intermediates was proposed to explain the observed results. NLEIS measurements were performed on Ti dissolving in HF and the experimental results are presented in Fig. 1 as magnitude and phase of current response as a function of frequency. The experimental results were compared with the reaction mechanism model predictions.

Figure 1
Effect of Silver Particles Electrodeposited on Reticulated Vitreous Carbon for Nitrate Reduction
Authors: Oishi Silvia Sizuka , Couto Andrea Boldarini , Botelho Edson Cocchieri , Ferreira Neidenei Gomes 
Published: February 2020

Nitrate is a serious contaminant of ground and surface water, which cause high concern in the field of health and environmental protection. Many processes have been used for nitrate removal and the electrochemical treatment is one of the most efficient due to its advantages regarding low cost effectiveness and ability to treat highly concentrated nitrate effluents. The cathode material is an important variable for the nitrate electroreduction process and the development of new electrodes to improve their catalytic activity is a challenge. Modification of electrodes by electrodeposition of metals has been frequently used for electrocatalysis of various reactions in solution and carbon materials are often used as supports for electrocatalysts. In this work, the reticulated vitreous carbon (RVC) was used as support for silver eletrodeposition and the effect of different parameters (applied potential, AgNO3 concentration and deposition time) on the morphology and electrocatalytic activity for nitrate reduction was studied. RVC was processed using poly(furfuryl alcohol) (PFA) resin synthesized according to the best condition established previously. Polyurethane foams with 70 ppi (pores per inch) were used as matrix for the PFA anchorage and after curing, they were heat treated at 1000 °C. All electrochemical experiments were performed in a conventional three electrode cell, using the RVC with electrodeposited Ag as working electrode, a Pt screen and Ag/AgCl as the counter and reference electrodes, respectively. The deposition potentials were chosen through cyclic voltammetry at 0.1, -0.3 and -0.7 V vs Ag/AgCl that can be related to the following regions, respectively: onset of Ag deposition, massive deposition and diffusion controlled deposition. The AgNO3 concentrations solutions used were 5, 10 and 20 mmol L-1, and the deposition times applied were 10, 60 and 180 s. The morphologies obtained by field emission scanning electron microscopy (FESEM) showed that Ag deposition is not uniform due to the RVC three-dimensional structure. Ag dendrites were formed on the highest RVC stems as shown in Figure 1. Ag aggregates of different sizes and shapes dispersed on the entire electrode surface could be observed depending on the experimental condition employed and sample depth. Difference in electrocatalytic activity of the Ag/RVC electrodes for nitrate reduction was confirmed by cyclic voltammetry in 0.1 mol L-1 K2SO4 solution containing 0.01 mol L-1 KNO3 and varied with the Ag amount on electrode surface in addition to its morphology.
Figure 1 - FESEM micrograph of Ag electrodeposited on RVC at -0.3 V (vs Ag/AgCl), with a duration time of 60 s and AgNO3 concentration solution of 10 mmol L-1.

Figure 1
Electrocatalytic Performance of Three Dimensional Electrode Cu/Reduced Oxide Graphene/ Carbon Fiber for Nitrate Reduction
Authors: Couto Andrea Boldarini , Oishi Silvia Sizuka , Sardinha Andre Ferreira , Ferreira Neidenei Gomes 
Published: February 2020

Nitrate ions are well-known water toxic inorganic pollutants and their high concentrations can cause a serious problem for both aquatic systems and human health. In this sense, it is of great importance to monitor nitrate ions in various kind of source [1]. Among several analytical technologies that been used for its detection, electrochemical technique offers a simple, rapid, selective, sensitive, inexpensive, safety method for this purpose, not to mention its considered green technology [2]. To improve the nitrate process performance and selectivity, novel electrode materials have been widely investigated. This work aims to develop a sensitive and reliable three dimensional electrode consisting of Cu particles/reduced oxide graphene (rGO)/carbon fiber (CF) for monitoring nitrate concentration. CF produced at heat treatment temperature of 1000 ºC was used in this study. The rGO electrodeposition on CF (1 cm2) was performed at a fixed potential of -1.25 V vs. Ag/AgCl/KCl(sat) for 15 min in a 20 mL of the graphene oxide (3mg mL-1) + 0.1 mol L-1 LiClO4 aqueous solution. The Cu electrodeposition on rGO/CF was carried out at a fixed potential of -0.7 V for 3, 6, 10, 20 min in a 10 mmol L-1 CuSO4 + 100 mmol L-1 H2SO4 aqueous solution. Cu/rGO/CF composites morphologies and structures were analyzed by field emission gun scanning electron microscopy (FEG-SEM), X-ray diffraction, and Raman spectroscopy. Nitrate electro-reduction was evaluated using cyclic voltammetry at 50 mV s-1 in 0.1 mol L-1 K2SO4 solution (pH = 3.0) with and without the presence of 10-2 mol L-1 KNO3. For rGO/CF binary composite, FEG-SEM images showed the characteristic aggregates with irregular and flakes-like shape with high particle density on CF substrate. The Cu deposits depicted small grain morphologies distributed throughout the rGO/CF surface. As expected, Cu deposit rate increased with increasing the deposition time. From X-ray diffraction analyses of the Cu particles, a mixture of phases containing cuprous oxide and metallic copper was identified. Under optimal experimental conditions, the Cu/rGO/CF electrode showed good catalytic activity for nitrate electro-reduction. This behavior can be associated to the presence of rGO and CF with high specific surface area in addition to Cu particle with high electron transfer capability. These results showed that Cu/rGO/CF composite has a great potential as new promising electrode for nitrate electroreduction application.
Acknowledgements: This work was supported by FAPESP, Process 2016/13393-9, CAPES, and CNPq Brazilian Agencies.
References
[1]R. Gürkan, N. Altunay, J. Food Composition Anal., 2016.
[2] J. Martínez, A. Ortiz, I. Ortiz, Applied Catalysis B: Environmental, 207, 2017.
Electrochemical Interaction Mechanisms of Metal Reducing Bacteria with Functionalized Gold Surfaces during Initial Attachment and in Artificial Biofilms
Authors: Kastania Eleni , Ozcan Ozlem 
Published: February 2020

Bacterial biofilms represent a ubiquitous form of microbial life on Earth. Due to an evolved armory of protean biological responses to external stimuli, bacteria are able to adhere to, colonize and thrive on virtually all surfaces, whether natural or synthetic, even in challenging environmental conditions. In addition to significant health risks, biofilms are among the salient contributors to the deterioration of metals and their alloys, thereby causing safety risks for technical equipment. Hence, understanding the interaction mechanisms of electroactive sessile bacteria with metal surfaces is vital for facilitating the development of efficient control strategies and novel anti-fouling surfaces in various industries and technologies.
The present study focuses on a combined spectroelectrochemical approach, melding methods of surface enhanced Raman spectroscopy (SERS) and electrochemical techniques, to investigate the chemical characteristics and redox activities of electroactive bacteria during the initial stages of biofilm formation. Gold has been selected as a model substrate due to its inert character, considerably high surface enhancement factor, as well as its capability to allow surface chemistry modifications and substrate polarization in order to precisely control the surface charge. Square wave voltammetry (SWV) and cyclic voltammetry (CV) studies have been performed for quantitative determination of flavin concentration and electrochemical impedance spectroscopy (EIS) has been utilized to study the changes in electrochemical processes within biofilms during different stages of growth. Shewanellasp. have been chosen as microorganisms within this work due to their versatile exoelectrogenic respiratory behavior and their distinct ability to reduce metals via extracellular electron transfer mechanisms involving self-secreted electron shuttle redox molecules such as flavins. To further explicate the process of diffusion of flavins within biofilms, a model system has been developed to simulate the structural features of the bacterial extracellular polymeric substances typically found in biofilms. This has been achieved by creating hydrogel films comprised of calcium-cross-linked alginate. The results demonstrate an interplay of factors contributing to the initial phases of bacterial settlement and biofilm formation as a function of environmental parameters. Furthermore, the results allow insight into the diffusion of flavins, much like they would in a natural biofilm, and how their redox behavior affects the biofilm development.
Analysis of Water-Assisted Crystallization Process in Anodically Grown Titania Nanotube Arrays
Authors: Ahiabu Ivy Berlinda , Paulose Maggie , Varghese Oomman K 
Published: February 2020

Titania nanotube arrays grown using anodic oxidation have exhibited enormous potential as a semiconductor nanoarchitecture beneficial for a wide range of applications including solar energy conversion and storage. High degree of crystallinity is a pre-requisite for several of these applications. While conventional furnace annealing has long been identified as an effective method to crystallize the amorphous as-prepared nanotubes, recent research efforts to reduce the thermal budget revealed that titania nanotube arrays could be crystallized using water at or near room temperature. Crystallization and phase transformation was, however, accompanied by morphological changes. Although several reports on the topic appeared after this finding, most of these papers presented conflicting information on the mechanism of crystallization at room temperature and performance of this material when used for applications such as photocatalysis that exploit semiconducting properties. While some groups believed water as responsible for the crystallization, some others attributed it to electrolyte species such as fluorine. We performed a comprehensive investigation on water-assisted crystallization of nanotubes prepared under different conditions and our study revealed the true process behind crystallization. The quantum efficiency measurements on solar photoelectrochemical fuel generation cells fabricated using the room-temperature water crystallized nanotubes showed almost no improvement in the photocatalytic properties despite having the phase transition from amorphous to anatase. We will discuss the details of our findings in this presentation.
(Invited) TiO2 Nanotubes in Photocatalysis
Authors: Schmuki Patrik 
Published: February 2020

TiO2 nanotubes in photocatalysis

Ning Liu, Anca Mazare, Patrik Schmuki

Department of Materials Science WW-4, LKO, University of Erlangen-Nuremberg, Martensstrasse 7, 91058 Erlangen, Germany

In the past decade, anodically formed self-organized TiO2 nanotube layers attracted considerable scientific interest (see e.g. reviews [1,2]). This is mainly due to the fact that these layers combine the defined nanotubular geometry with a broad range of functional features inherent to TiO2. Particularly in photoelectrochemical and photocatalytic applications nanotubular layers have shown remarkable results. The presentation will first give an overview of the most promising features of classic nanotube layers for photocatalysis and then focus on TiO2 nanotube (NT) arrays, converted by a high pressure H2 treatment to anatase-like "black titania"[3,4]. This modification shows a remarkable high open-circuit photocatalytic hydrogen production rate without the presence of any cocatalyst. We will discuss the main effects caused by the high H2pressure annealing and the origin of this outstanding activity of black titania.
REFERENCES

P. Roy, S. Berger, P. Schmuki, Angew. Chem. Int. Ed. (2011), 2904

K. Lee, A. Mazare, P. Schmuki, CHEMICAL REVIEWS, 114 (2014) 9385

N. Liu, P. Schmuki et.al. Nano Letters, 14 (2014) 3309

N. Liu, P. Schmuki et.al. 53 (2014) 14201
(Invited) Visible Light CO2 Reduction and Water Oxidation on Modified Semiconductor Photocatalysts
Authors: Maeda Kazuhiko 
Published: February 2020

CO2 reduction and water oxidation on semiconductor photocatalysts are of great importance from the viewpoint of solar-to-fuel energy conversion toward artificial photosynthesis. In this presentation, recent progress on the development of new photocatalysts will be given. In particular, surface modification techniques developed by our group to construct active sites and light-absorbing centers will be presented.
It is known that certain metal complexes based on rhenium or ruthenium catalyze CO2 reduction into CO or HCOOH photocatalytically with high selectivity and quantum yields. However, the oxidation ability of metal complex photocatalysts is generally low, requiring a strong electron donor for operation. On the other hand, semiconductors have high activity and stability for oxidation reactions, although the selectivity to CO2 reduction is low. Here we developed a new system for CO2 reduction using a visible-light-responsive semiconductor and a binuclear metal complex having a redox photosensitizer and a catalytic unit. In this reaction scheme, both the semiconductor and the photosensitizer unit of the metal complex undergo photoexcitation. The conduction band electrons in the semiconductor move to the excited state of the sensitizer unit, producing a one-electron reduced species. After subsequent intermolecular electron transfer from the one-electron-reduced species to the catalyst unit, CO2 is reduced into HCOOH (or CO), while holes left in the valence band of the semiconductor participate in the oxidation reactions. Because of the electron transfer pathway, this is called “Z-scheme” CO2 reduction system. We found that TaON, CaTaO2N, Y2Ta2O5N2, and C3N4 became active component for the Z-scheme system driven by visible light (> 400 nm) in combination with a suitable binuclear metal complex.
As the component of water oxidation half cycle, we developed a new powdered photocatalyst consisting of Co(OH)2 and TiO2. TiO2 is known to be an active photocatalyst, but only works under UV irradiation. By contrast, the Co(OH)2/TiO2 hybrid photocatalyst is capable of absorbing visible light with wavelengths of up to 850 nm and oxidizing water into oxygen gas, even though it consists of only earth-abundant elements only. To our knowledge, this system provides the first demonstration of a photocatalytic material capable of water oxidation upon excitation by visible light up to such a long wavelength.
On the Control of Electron Transfer Rates through the Morphology of Nanoparticles
Authors: Spitler Mark 
Published: February 2020

It will be shown how the morphology and dimension of inorganic nanostructures in a solution should affect the rates of outer sphere electron transfer for nearby redox ions much differently than is predicted for a macroscopic planar interface. Simple Marcus theory and electrostatic evaluations of the self-energy of the ions near these nanostructures are used to calculate this effect, which is controlled by the degree to which the environment about the ion is the high dielectric permittivity of the solid rather than solution. A higher degree results in a lower reorganization energy for the ion and a smaller activation energy for electron transfer. The extreme of interest to this discussion is that of a redox ion within a spherical or cylindrical nanocavity of an inorganic solid.
It has long been known how simple Marcus theory predicts electron transfer rates for donor and acceptor couples as a function of the difference in the free energy of the reaction and experimentation1 has confirmed the predicted parabolic form of transfer rates and the “inverted region,” where rates slow down. Variations in the outer sphere reorganization energies of donor-acceptor couples also result in changes of charge transfer rates predicted by this theory and also indicate this decrease in transfer rates.2 Recently, it has been demonstrated how the temperature dependence of electron transfer rates for a specific donor-acceptor couples also describes this parabolic behavior according to theory.3 This presentation on nanostructures and outer sphere electron transfer explores how the dielectric permittivity within Marcus theory may be an additional variable to control rates of electron transfer reactions.
Geometric configurations will be examined in this work in the limits where the radius of the nanocavity of the solid varies from large compared to that of the redox ion within it to where it approaches the size of the redox ion. The electron transfer will be calculated as a self-exchange rate for reduced and oxidized forms of a redox couple to avoid considerations of electron exchange with the solid. To illustrate the principles involved, the solution will be taken as acetonitrile and the solid as ZnO. Spherical nanoshells will also be considered to illustrate how the same redox ion can have an accelerated electron transfer rate within the cavity while its rate for ions outside the shell slows down.4

References:
1. Closs, G.L.; Miller, J.R. Science
1988, 240, 440-447.
2. Kuss-Petermann, M.; Wenger, O.S. J. Am.
Chem. Soc.
2016, 138, 1349-1358.
3. Waskasi, M. M. et al., J. Am. Chem. Soc.,
2016, 138, 9251-9257.
4. Spitler, M.T. Electrochim. Acta, 2007, 52, 2294-2301.
A Physics-Based Model to Investigate Degradation-Related Performance Loss in Photoelectrochemical Devices
Authors: Nandjou Fredy , Haussener Sophia 
Published: February 2020

Understanding and mitigating performance loss in photoelectrochemical devices are key factors for advancing their large-scale implementation and industrialization. Performance loss is caused not only by the degradation of single components (semiconductor, catalyst and electrolyte), but also by the interplay between the operating conditions and the various degradation phenomena. While the catalyst and electrolyte degradations are considerable challenges for long-term durability, the short-term durability mainly depends on the semiconductor material and its interface with the electrolyte [1]. Semiconductors with good photoabsorption behavior and interesting band alignments are inherently non-stable, and therefore degrade within hours due to photocorrosion.
Usually, photocorrosion is interpreted on the basis of energy schemes, comparing the quasi-Fermi levels of minority carriers to the corrosion potentials of the photoelectrode [2]. However, the competition between the pure redox process of water splitting and photoelectrode dissolution/passivation is mainly determined by kinetic parameters [3].
In this study, we use a physics-based model to quantify the effect of photocorrosion phenomenon on the global performance loss of the photoelectrochemical device. The studied device is composed of different catalyst covered semiconductors, immersed in a liquid electrolyte. The catalyst layer is considered a nanoporous media, the solid phase being composed of a supporting structure and catalyst particles.
The simulation results highlight the practical limitation of using thermodynamic calculations for the investigation of photoelectrochemical devices durability, and how irradiation, mass transport, and kinetic properties can impact the stability of the photoelectrode/electrolyte interface.
[1] F. Nandjou and S. Haussener. Degradation in photoelectrochemical devices: Review with an illustrative case study. J. Phys. D: Appl. Phys. 50 (2017) 124002.
[2] H. Gerischer et al. Report EUR 9531 EN (1984), Commission of the European Communities.
[2] R. Memming. The Role of Energy Levels in Semiconductor
‐
Electrolyte Solar Cells. J. Electrochem. Soc. 125 (1978) 117.