Oxygen-Deficient Zirconia (ZrO2-x): A New Material for Solar Light Absorption

Here, we present oxygen-deficient black ZrO2-x as a new material for sunlight absorption with a low band gap around ∼1.5 eV, via a controlled magnesiothermic reduction in 5% H2/Ar from white ZrO2, a wide bandgap(∼5 eV) semiconductor, usually not considered for solar light absorption. It shows for the first time a dramatic increase in solar light absorbance and significant activity for solar light-induced H2 production from methanol-water with excellent stability up to 30 days while white ZrO2 fails. Generation of large amounts of oxygen vacancies or surface defects clearly visualized by the HR-TEM and HR-SEM images is the main reason for the drastic alteration of the optical properties through the formation of new energy states near valence band and conduction band towards Fermi level in black ZrO2-x as indicated by XPS and DFT calculations of black ZrO2-x. Current reduction method using Mg and H2 is mild, but highly efficient to produce solar light-assisted photocatalytically active black ZrO2-x.1

Green fabrication of 3-dimensional flower-shaped zinc glycerolate and ZnO microstructures for p-nitrophenol sensing

The solvent or reaction medium always plays a lead role in synthesis chemistry. Glycerol has been studied as a green solvent for different organic transformations and is also expected to give interesting control in material synthesis. In this study, we use aqueous glycerol to synthesize zinc glycerolate and the corresponding ZnO micro-flower structures with an intention to encourage the utilization of glycerol as a green reaction medium in material synthesis. A zinc ammonium complex is used as a source of zinc, which converts to zinc glycerolate in the presence of glycerol. Glycerol plays a dual role as a reactant to form zinc glycerolate and as a solvent to control the morphology. The unreacted glycerol is recovered after the reaction and reused further. The flower-structured zinc glycerolate and ZnO are then used for the first time to modify a glassy carbon electrode to make a binder-free non-enzymatic amperometric chemical sensor for p-nitrophenol that is a brutal environmental pollutant. The modified electrode is found to be an excellent alternative for the purpose with respect to sensitivity, selectivity and stability. © 2015 The Royal Society of Chemistry.1

A new approach to prepare highly active and stable black titania for visible light-assisted hydrogen production

In spite of their remarkable enhancement in visible light absorption, black TiO2 materials have failed to demonstrate expected photocatalytic activity in visible light due to the presence of a high number of recombination centers. In this report, a new controlled magnesiothermic reduction has been developed to synthesize reduced black TiO2 under a 5% H2/Ar atmosphere. The material possesses an optimum band gap and band position, oxygen vacancies, surface defects, and charge recombination centers and shows significantly improved optical absorption in the visible and infrared region. The synergistic effects enable the black TiO2 material to show an excellent hydrogen production ability in the methanol-water system in the presence of Pt as a co-catalyst. The maximum hydrogen production rates are 43 mmol h-1 g-1 and 440 μmol h-1 g-1, along with remarkable stability under the full solar wavelength range of light and visible light, respectively, and these values are superior to those of previously reported black TiO2 materials. © 2015 The Royal Society of Chemistry.1

High capacity and exceptional cycling stability of ternary metal sulfide nanorods as Li ion battery anodes

Ternary spinel NiCo<inf>2</inf>S<inf>4</inf> nanorods are tested for the first time as anode electrodes for Li ion batteries. When the electrode is fabricated using the carboxymethyl cellulose-polyacryl amide composite binder, it is found to restrict or suppress the formation of a polymeric gel passivation layer. As a result, the electrode not only delivers excellent specific capacity, but also an outstanding rate and cyclic stability with almost no decay up to 100 charge-discharge cycles. © The Royal Society of Chemistry 2015.

Sub 10 nm CoO nanoparticle-decorated graphitic carbon nitride for solar hydrogen generation: via efficient charge separation

Solar hydrogen generation is one of the most compelling concepts in modern research to address both the energy and environmental issues simultaneously for the survival of the human race. A Type II heterojunction (CoO-GCN) was fabricated by decorating sub 10 nm CoO nanoparticles (NPs) on the graphitic carbon nitride (GCN) surface. It exhibited improved absorption of UV-VIS light and efficiently separate the photogenerated electrons and holes in opposite directions. A maximum hydrogen generation rate of 9.8 mmol g-1 h-1 was recorded using CoO-GCN from 10% aqueous triethanolamine under simulated sunlight in the presence of 1 wt% Pt. The rate is 3.8 times higher than that of bare GCN. Furthermore, it showed excellent stability for up to five repeated uses. Interestingly, the study also revealed that untreated seawater could replace the deionized water. The cooperative participation of the uniform shape and size of CoO NPs firmly grafted on GCN resulted in remarkable performance for solar hydrogen generation. This journal is © 2020 The Royal Society of Chemistry.1

Fabrication of defective mesoporous cerium oxide nanostructure for promoting an efficient and stable electrocatalytic oxygen evolution reaction

The development of renewable energy technologies, such as fuel cells, electrolysersand metal-air batteries, relies heavily on the availability of highly efficient electrocatalysts for the anodic oxygen evolution reaction (OER). Defected ceria (D-CeO2) has a high potential to compete with the activity of RuO2 based OER catalysts. We have synthesiseda mesoporous nanostructure ceria (CeO2) with induced defects using a simple and economical approach at a relatively low temperature. The observed catalytic activity of the prepared D-CeO2 porous nanostructure was found to be remarkable. Additionally, the nanostructure exhibited a high tolerance to methanol and demonstrated durability towards OER in alkaline media. During the experiment, it was observed that the catalyst exhibited noteworthy activity in the OER compared to the commercially available RuO2 catalyst, as this is evident by a higher current density and more negative onset potential. The catalyst's remarkable OER activity is attributed to the synergistic effect resulting from the combination of defect sites and the porous structure of CeO2. CeO2 mesoporous nanostructures serve as excellent electrocatalysts for OER due to their elevated surface area, robust catalytic activity, and stability. Furthermore, their mesoporous configuration enhances mass transport, expedites oxygen transfer, mitigates electrode polarisation, and enhances the overall electrochemical performance

H-doped TiO2-x prepared with MgH2 for highly efficient solar-driven hydrogen production

Efficient utilization of visible light with high stability remains a critical challenge for solar-driven photochemical generation of hydrogen (H2) using particulate photocatalysts. Black TiO2 was introduced with remarkable enhancement of visible light absorption, but its efficiency in the visible light has not reached the desired level for real-world applications. Here we report a gold-colored H-doped TiO2-x (H:TiO2-x) nanoparticles prepared by controlled reduction via simultaneous presence of [Mg] and [H], which are obtained from the decomposition of MgH2. The H-doped TiO2-x exhibits a significant activity (16.1 mmolg−1h−1) and remarkable stability after Pt deposition for solar-driven H2 generation from methanol-water. The excellent photoactivity of H-doped TiO2 can be attributed to oxygen vacancies and H doping at the reduced TiO2-x surface generated by [Mg] and [H]. The H-doped TiO2 is also producing H2 from methanol-seawater with a rate of 6.1 mmolg−1h−1 under simulated sunlight. © 2018 Elsevier B.V.1

Efficient solar light photoreduction of CO2 to hydrocarbon fuels via magnesiothermally reduced TiO2 photocatalyst

Elevated atmospheric CO2 levels are recognized as a key driver of global warming. Making use of sunlight to photoreduce CO2, in turn fabricating hydrocarbon fuels compatible with the current energy infrastructure, is a compelling strategy to minimize atmospheric CO2 concentrations. However, practical application of such a photocatalytic system requires significant efforts for improved photoreduction performance and product selectivity. Herein, we investigate the performance of our newly developed reduced TiO2, prepared by a reduction process using Mg in 5% H2/Ar, for photoconversion of CO2 and water vapor to hydrocarbons, primarily CH4. Using Pt nanoparticles as a co-catalyst, under simulated solar light irradiation the reduced anatase TiO2 exhibits a relatively stable performance with a threefold increase in the rate of CH4 production (1640.58 ppm g−1 h−1, 1.13 μmol g−1 h−1) as compared to anatase TiO2 nanoparticles (546.98 ppm g−1 h−1, 0.38 μmol g−1 h−1). The improved photocatalytic performance is attributed to enhanced light absorption, suitable band edge alignment with respect to the CO2/CH4 redox potential, and efficient separation of photogenerated charges. Our results suggest that the Pt-sensitized reduced TiO2 can serve as an efficient photocatalyst for solar light CO2 photoreduction. © 2017 Elsevier B.V

Hydrogenated MoS2 QD-TiO2 heterojunction mediated efficient solar hydrogen production

Herein, we report the development of a hydrogenated MoS2 QD-TiO2 (HMT) heterojunction as an efficient photocatalytic system via a one-pot hydrothermal reaction followed by hydrogenation. This synthetic strategy facilitates the formation of MoS2 QDs with an enhanced band gap and a proper heterojunction between them and TiO2, which accelerates charge transfer process. Hydrogenation leads to oxygen vacancies in TiO2, enhancing the visible light absorption capacity through narrowing its band gap, and sulfur vacancies in MoS2, which enhance the active sites for hydrogen adsorption. Due to the band gap reduction of hydrogenated TiO2 and the band gap enhancement of the MoS2 QDs, the energy states are rearranged to create a reverse movement of electrons and holes facilitated the charge transfer process which enhance life-time of photo-generated charges. The photocatalyst showed stable, efficient and exceptionally high noble metal free sunlight-induced hydrogen production with a maximum rate of 3.1 mmol g-1 h-1. The developed synthetic strategy also provides flexibility towards the shape of the MoS2, e.g. QDs/single or few layers, on TiO2 and offers the opportunity to design novel visible light active photocatalysts for different applications. © 2017 The Royal Society of Chemistry.1

TiO2/ZrO2 Nanoparticle Composites for Electrochemical Hydrogen Evolution

Composites of different semiconductors are found to show much improved electronic conductivity and decreased charge transfer resistance. In this work, this hypothesis is tested by preparing composite heterostructures of chemically and structurally dissimilar and wide-bandgap semiconductors, titania (TiO2) and zirconia (ZrO2). Herein, the underpotential hydrogen generation ability of the composite nanoparticles is studied for the first time. The dissimilarity in coordination can create charge imbalance once the composite of these two materials is formed, which in turn can increase the surface acidity and the active sites for proton adsorption as proved through various analytical techniques. The composite of separately incompetent hydrogen evolution reaction (HER) catalysts shows improved HER activity due to improved charge transfer between the composite catalyst and reactant caused by the generation of the new electronic states. To improve the electronic conduction, we have performed the reduction of TiO2/ZrO2 binary metal oxide composite, which results in oxygen vacancies in the composite. The reduced counterpart of the composite is found to possess semimetallic properties and shows outstanding high stability and 7 times increase in HER current density at -0.6 V along with a very small overpotential of only ∼160 mV penalty to have a HER current density of 10 mA/cm2 Copyright © 2020 American Chemical Society.1