A Z-Scheme Strategy that Utilizes ZnIn2 S4 and Hierarchical VS2 Microflowers with Improved Charge-Carrier Dynamics for Superior Photoelectrochemical Water Oxidation.

One of the major limiting factors for efficient photoelectrochemical water oxidation is the fast recombination kinetics of photogenerated charge carriers. Herein, we propose a model system that utilizes ZnIn2 S4 and hierarchical VS2 microflowers for efficient charge separation through a Z-scheme pathway, without the need for an electron mediator. An impressive 18-fold increase in photocurrent was observed for ZnIn2 S4 -VS2 compared to ZnIn2 S4 alone. The charge-transfer dynamics in the composite were found to follow a Z-scheme pathway, which resulted in decreased charge recombination and greater accumulation of the surface charge. Furthermore, slow kinetics of the surface reaction in the ZnIn2 S4 -VS2 composite correlated to an increased surface-charge capacitance. This feature of the composite material facilitated partial storage of the photogenerated charge carriers (e- /h+ ) under illumination and dark-current conditions, thus storing and utilizing solar energy more efficiently.

Effect of surface overlayer in enhancing the photoelectrochemical water oxidation of in situ grown one-dimensional spinel zinc ferrite nanorods directly onto the substrate.

Overlayer passivation minimizes surface defects and arrests the back transfer of electrons for an enhanced charge extraction. Surface passivation of ZnFe2O4 using alumina yields enhanced charge carrier density from 8.43 × 1020 cm-3 to 18.83 × 1020 cm-3 giving a record efficiency in this class of compounds.

Ordered-Disordered BaZrO3-δ Hollow Nanosphere/Carbon Dot Hybrid Nanocomposite: A New Visible-Light-Driven Efficient Composite Photocatalyst for Hydrogen Production and Dye Degradation.

Perovskites form an interesting class of photocatalytic compounds because of their chemical stability and exotic chemistry. Although barium zirconates have been known for a long time, their photocatalytic study in the literature is very limited. Herein, we have studied the effect of structural disorder, oxygen vacancies and carbon dots (CDs) on photocatalytic activity of BaZrO3-δ (BZO) hollow nanospheres. High alkaline conditions during hydrothermal synthesis lead to the formation of disordered states as well as oxygen vacancies in BZO and create midgap states within the band gap of BZO. The midgap states further shift its absorption onset toward visible light and their presence and effects have been proved by ultraviolet-visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, and electron spin resonance analysis. A composite that consists of CDs shows upconversion photoluminescence and charge-carrier transfer properties to enhance the light absorption of a photocatalyst and its activity. The photocatalytic efficiency of the compounds were examined by H2 evolution and the degradation of methylene blue (MB) dye. In this study, loading of 3 wt% CDs on BZO shows the highest hydrogen evolution efficiency (670 µmol/h/g) with an apparent quantum yield of ∼4% and the highest MB dye degradation efficiency (∼90%) among all synthesized composites. The synergistic effect of increased visible light absorption along with enhanced photogenerated charge-carrier transfer efficiency in the presence of CDs and oxygen vacancies in BZO contributes to the enhanced photocatalytic efficacy of hybrid nanomaterials under visible light irradiation.

Modulating the electronic structure of lanthanum manganite by ruthenium doping for enhanced photocatalytic water oxidation.

To the best of our knowledge this is the first report in which ruthenium doped polycrystalline lanthanum manganite, LaMn1-xRuxO3 (x = 0.0-0.4), having high efficacy for oxygen production from water without the use of any sacrificial reagent or co-catalyst and as an efficient photocatalyst for dye degradation is reported. Ruthenium doping alters the crystal structure of the parent LaMnO3 (LMO) due to the induced chemical pressure of the larger Ru4+ ion, which facilitates a bond angle of 180° in the Mn3+-O-Mn4+ plane resulting in the easy extraction of a photo-generated charge carrier population leading to enhanced photocatalytic activity. Rietveld refinements reveal that the parent compound LMO crystallizes in the rhombohedral phase, while upon an increase in the doping concentration of ruthenium, the phase of the compounds changes from the rhombohedral to the cubic phase. The percentage contribution of each phase has been estimated using the sixth-order polynomial and pseudo-Voigt function. Typically, all the compositions, LaMn1-xRuxO3 (x = 0.0-0.4), were prepared by a conventional solid state route and studied for their photocatalytic activity. The synthesized compounds were investigated by powder X-ray diffraction (PXRD), UV-visible diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) analysis. The structure-property correlation of the compound is presented based on Rietveld refinement combined with the experimental data. The as-prepared compounds show efficient photocatalytic oxygen gas production from water without the use of any co-catalyst or sacrificial reagents. Among the five compositions, LaMn0.7Ru0.3O3 shows the highest O2 production efficiency (4.73 mmol g-1 h-1) with an apparent quantum yield (AQY) of 7.43%. These ruthenium doped compositions also exhibit superior dye degradation properties, studied by taking the industrial dye methyl orange (MO) as the model compound.