Minimizing electron-hole pair recombination through band-gap engineering in novel ZnO-CeO2-rGO ternary nanocomposite for photoelectrochemical and photocatalytic applications.

A novel ZnO-CeO2-rGO (ZCG) ternary nanocomposite with varying ZnO/CeO2 weight proportions was synthesized by a hydrothermal process for photoelectrochemical water splitting and photocatalytic application. XRD diffraction peaks of ZCG nanocomposites displayed the patterns of ZnO and CeO2 nanoparticles, and SEM revealed irregular flake-like particles, which were uniformly decorated on the rGO matrix. Increase in the intensity ratio of D and G bands from Raman spectra revealed changes in oxygen bonding in the ZnO-rGO (ZG) and ZCG nanocomposites. The shift in the band edge positions and the decrease in the band gap with increase in the cerium oxide content in ZCG composites were observed from UV-Vis and Mott-Schottky plots. XPS results showed that Ce3+ fraction increased with an increase in the cerium oxide content in ZCG nanocomposites. The ZCG3 (85:15) nanocomposite exhibited decreased electron-hole recombination rate as evidenced from the photoluminescence and electrochemical impedance spectroscopy Nyquist plots. The characteristic frequency in Bode's plot shifted to a lower frequency for the ZCG3 electrode demonstrating low interfacial charge transfer resistance, and ZCG3 photoelectrode displayed a higher photocurrent density of 0.69 mA/cm2 at 1.5 V compared with other photoelectrode. The optimized and highly efficient ZCG3 nanocomposite exhibited improved photocatalytic degradation of methylene blue (MB) with a reaction rate constant of 0.0201 min-1. Combination of defects in the form of Ce3+ ion and surface oxygen vacancies coupled with rGO as the electron acceptor improved the charge carrier density and carrier transport in addition to the formation Schottky-type junction and the presence of an internal electric field.

Synergistic effect of band convergence and carrier transport on enhancing the thermoelectric performance of Ga doped Cu2Te at medium temperatures.

Recent advances in high performance thermoelectric materials have garnered unprecedented attention owing to their capability of direct transformation of heat energy to useful electricity. Copper Telluride (Cu2Te), a member of the chalcogenide family has emerged as a state-of-the-art thermoelectric material with low thermal conductivity and high thermoelectric (TE) performance, however, this material exhibits exceptional transport properties only at very high temperatures. In this study, we have investigated the synergistic effects of Ga doping on the TE performance by first principles calculations along with experimental validations. The DFT (Density Functional Theory) calculations predicted that Ga doping, within considerable limits enhanced the electrical conductivity and Seebeck coefficients in Cu2Te. This proof of concept was validated by experimental synthesis of Ga doped Cu2Te by simple direct annealing for shorter durations of 48 hours at 1120 ºC  (~1/4th) than in previous work and subsequent thermoelectric characterization. The enhanced electrical conductivity, thermopower, and moderate thermal conductivities led to the optimized TE performance in 3 atomic % Ga doping (Cu1.97Ga0.03Te), exhibiting a ZT value of 0.46 at 600 K, almost three times that of pristine Cu2Te in this temperature range. This comprehensive study provides the platform for developing new low-cost and energy efficient TE materials with enhanced ZT performance in medium temperature applications.

Hybridized Tungsten Oxide Nanostructures for Food Quality Assessment: Fabrication and Performance Evaluation.

Tungsten oxide based micro and nanosized structures possess good capacitance as well as enhanced rate capability. Such properties are useful in various applications including electrochemical supercapacitors. Apart from supercapacitance, WO3 and their 2D integrated structures have been modified using different methods to widen their range of the utility. Modification using layer coating, functionalization with other nanomaterial or molecules are methods that can be used to improve the core structure of WO3. But such modifications often alter electrochemical performance. The effects and outcomes of such modifications incorporated in WO3 structures were studied using electrochemical methods, sensing behavior, and morphological examination. One goal for such modifications was to improve robustness of the WO3 structures apart from any change in supercapacitance performance. After detailed electrochemical analyses of WO3 structures, a preliminary study was performed regarding the feasibility of the WO3 based sensors for food safety applications based on electrochemical detection of hazardous dyes in food. Preliminary results obtained after various electrochemical tests including pulsed voltammetry, cyclic voltammetry, and electrochemical impedance spectroscopy suggest the viability of WO3 structures for food safety applications.

Fabrication and response of alpha-hydroxybutyrate sensors for rapid assessment of cardiometabolic disease risk.

Early diagnosis and treatment can prevent or delay progression of early-stage type 2 diabetes and prediabetes. Unfortunately, tests such as hemoglobin A1c (HbA1c)/fasting plasma glucose (FPG) alone fail to diagnose or miscategorize up to 40% of individuals with impaired glucose tolerance (IGT) or frank diabetes based on the rarely utilized oral glucose tolerance test (OGTT). The serum metabolite alpha-hydroxybutyrate (AHB) is increasingly recognized as a reliable IGT and diabetes predictor, and can be measured using liquid chromatography-tandem mass spectrometry. However, to address AHB adoption as a population screening tool, the reliable and low-cost measurement techniques are proposed. A periodate based oxidation was performed for an AHB-based buffer, and both nitroprusside and Raman tests confirmed the formation of a slow-oxidation product. Electrochemical tests of AHB-based buffers using electrodes such as Au-honeycomb, thiol self-assembled monolayers coated Au, 2D material (black-P) coated FTO, (3-aminophenyl) triethoxysilane modified TiO2, were performed. Many of these electrodes exhibited a systematic response when AHB concentration was varied from ~1.0-12.0µg/ml. A colorimetric assay containing a vicinal-diol recognition moiety, additives, and a photoinitiator, exhibited a different color for AHB based buffer. Benesi-Hildebrand analysis indicated the association behavior of boronic acid and AHB. These methods have a potential to be used for rapid point-of-care measurements of AHB that could enhance population-wide diabetes and prediabetes screening strategies.

Augmented Z scheme blueprint for efficient solar water splitting system using quaternary chalcogenide absorber material.

Photoelectrochemical hydrogen (H2) production from water is a key method of addressing energy needs using an environmentally friendly approach. In the last two decades we have witnessed the evolution of many different expensive catalysts, photoelectrodes and related technologies, especially those involving precious metals and use of acidic or basic electrolytes for hydrogen production. Cu2ZnSnS4 (CZTS) is a relatively new candidate in the category of efficient photocathodes, due to its high absorption coefficient and near optimal energy band gap. In this paper, we demonstrate photoelectrochemical viability of CZTS in combination with other photoanodes such as TiO2, BiVO4, and WO3 for H2 production with the use of an electrolyte of near neutral pH, a single redox mediator, and insignificant potential biasing. A systematic study was performed to understand CZTS performance with each photoanode, band energetics of CZTS with other photoanodes, impedance behavior of each photoelectrode, and utility of a CZTS photocell in place of a CZTS photocathode. Our assessment indicates that a protected CZTS photocell performs well when used in a Z-scheme containing TiO2 nanotubular array-CZTS or nanocrystalline WO3-CZTS. Preliminary experiments indicated that apart from band energetics, porosity and effective surface area of the photoanodes play a crucial role in determining the photoelectrochemical performance of the system.

Light emitting diodes based on carbon dots derived from food, beverage, and combustion wastes.

One important resource for material synthesis is waste. Utilization of waste as a resource for material synthesis is an environmentally responsible approach that reduces the need for virgin resources and subsequent processing. In this report a method to produce multicolored, luminescent carbon dots (CDs) and subsequent fabrication of light emitting diodes from food, beverage, and combustion wastes, is discussed. Apart from food and beverages, combustion exhaust was also utilized for CDs production. Optical characterization results suggest that CDs from waste food and beverages are more luminescent than those produced from combustion waste.