In this paper, we report a suitable method for extracellular synthesis of copper oxide nano particles by using Phormidium cyanobacterium. We hypothesize that synthesis of copper oxide nano particles is believed to occur by extracellular hydrolysis of the cationic copper by certain metal chelating anionic proteins/reductase secreted by bacteria under simple experimental conditions like aerobic environment, neutral pH and room temperature. Proteins not only reduce Cu (II) into copper oxide nano particles (CONPs) but also plays significant role in stabilization of formed nanoparticles at room temperature. Further TEM, SEM, XRD and FTIR analysis have confirmed the synthesis of nano particles through microbial route. Extracellular induction of metal chelating proteins/reductase was analyzed by SDS-PAGE.   Keywords: Synthesis, copper oxide nano particles, Phormidium cyanobacterium

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KTaO3 was doped with Sr cations, and its photocatalytic activity for the overall water splitting was investigated. By doping with Sr, a Sr-rich shell was formed over a Sr-poor core. Extended X-ray absorption fine structure spectroscopy revealed the simultaneous occupation of the K sites and Ta sites by Sr cations. A concentration gradient of Sr cations occupying the Ta sites was suggested to be produced after doping with Sr. The concentration gradient of Sr cations simultaneously induced an energy gradient of the conduction band edge bottom. Hence, photoexcited electrons are separated, which are driven away to the bulk by the energy gradient, from the complementary holes present on the surface. The higher the Sr cation concentration, the higher the energy gradient produced. Thus, the electron-hole separation is improved and the electron population accordingly increases with the increase in the Sr cation concentration. Nevertheless, the increase in the Sr cation concentration led to the decrease in the water splitting activity. The highest water splitting activity was observed for bare KTaO3. The decreased water splitting activity was proposed to be primarily due to the blockage of the electron transfer to the cocatalysts by the Sr-rich shell and the poor O2 evolution ability of the Sr-rich shell.

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The atomic-scale structure of a NaTaO3 photocatalyst doped with La3+ and Cr3+ for visible light sensitization is successfully revealed.

Understanding the science behind highly active materials is essential for advancement in the field of photocatalytic water splitting for solar energy harvesting. Sodium tantalate (NaTaO 3 ) doped with La cations is one of the best engineered materials for efficient water splitting to evolve hydrogen. In this study, physical insights into the sensitivity of the watersplitting activity to the spatial La distribution are discussed. The spatial distribution of La cations placed at the Na site was found to dictate the energy gradient of the conduction band bottom (CBB), resulting in a tunable electron population and hence water-splitting activity. A less homogeneous sample with a sufficiently large CBB gradient exhibited higher water-splitting activity. The mechanism of gradient tuning of the CBB through controlling the spatial dopant distribution is expected to be applicable to a broad range of metal oxide perovskites for artificial photosynthesis.

Perovskite-structured tantalates, NaTaO3 in particular, have been at the forefront of solar energy conversion to generate hydrogen fuel via photocatalytic water splitting. However, their application as a photocatalyst remains impractical due to their inability to absorb long-wavelength light. One promising scheme for extending the material response to long-wavelength light is via the charge compensation of doped cations with lanthanum and a transition metal. In this research, NaTaO3 is doubly doped with lanthanum and manganese, a 3d-block transition metal, for visible-light sensitization. Following the double doping, the light absorption is extended to the near-infrared region. The doubly doped samples not only strongly absorb visible light but also produce electrons under visible-light irradiation (420 < λ < 740 nm). EDX confirms the one-to-one ratio of dopant incorporation, and nanometer-resolution elemental mapping with TEM demonstrating that La and Mn are incorporated at approximately the same location in the particles. EXAFS furthermore reveals that La occupies the Na site, while Mn occupies the Ta site. These findings suggest that La pairs with Mn at the neighboring site to form a LaMnO3–NaTaO3 solid solution.

N-doped ZnO (N-ZnO) and N-doped ZrO2 (N-ZrO2) are synthesized by novel, simple thermal decomposition methods. The catalysts are evaluated for the degradation of rhodamine 6G (R6G) under visible and UV light. N-ZnO exhibits higher dye degradation under both visible and UV light compared to N-ZrO2 due to possessing higher specific surface area, lower crystalline size, and lower band gap. However, it is less reusable than N-ZrO2 and its photocatalytic activity is also deteriorated at low pH. At the same intensity of 3.5 W/m(2), UVC light is shown to be a better UV source for N-ZnO, while UVA light is more suitable for N-ZrO2. At pH 7 with initial dye concentration of 10 mg/L, catalyst concentration of 1 g/L, and UVC light, 94.3 % of R6G is degraded by N-ZnO within 2 h. Using UVA light under identical experimental conditions, 93.5 % degradation of R6G is obtained by N-ZrO2. Moreover, the type of light source is found to determine the reactive species produced in the R6G degradation by N-ZnO and N-ZrO2. Less oxidative reactive species such as superoxide radical and singlet oxygen play a major role in the degradation of R6G under visible light. On the contrary, highly oxidative hydroxyl radicals are predominant under UVC light. Based on the kinetic study, the adsorption of R6G on the catalyst surface is found to be the controlling step.