Rajesh Adhikari

The long term stability of photoelectrochemical (PEC) devices based on colloidal quantum dots (QDs) for hydrogen production is a major challenge. The degradation is often caused by the self-oxidation of QDs induced by the excess accumulation of holes in the valance band. Here, we use heterostructured “giant” core/alloyed-shell CdSe/Pb_xCd_1−xS/CdS QDs to sensitize TiO₂ mesoporous films for PEC hydrogen production. Transient fluorescence analysis results show that the use of a Pb_xCd_1−xS gradient layer leads to a three-fold increase in the hole transfer rate compared to a pure CdS shell with similar shell thickness. The as-prepared PEC cell using alloyed shell “giant” QDs exhibits an enhanced photocurrent density of 10.2 mA cm⁻² (97 mL per cm² per day) under one sun illumination (100 mW cm⁻²). The PEC cell based on alloyed shell “giant” QDs shows an enhanced PEC device stability, with retention of ∼94.9% of its initial photocurrent after 2 h under one sun illumination. This finding provides unique insights to improve the stability and functional performance of PEC devices in which the photoanode is sensitized using colloidal “giant” QDs.

Ag–BaMoO4 co-doped with Er3+/Yb3+ microcrystals were synthesized by the microwave hydrothermal process. The crystal structures and particle morphology were observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. XRD patterns indicate the tetragonal scheelite structure of BaMoO4. Elemental composition was analyzed by X-ray photoelectron spectroscopy (XPS). UV-Vis diffuse reflectance spectra, Raman spectra and photoluminescence spectra were analyzed by UV-Vis diffuse reflectance spectroscopy, Raman spectroscopy and photoluminescence spectroscopy, respectively. Two strong green emission peaks (526 nm and 554 nm) and a weak red emission peak (661 nm) were identified, which were associated to the 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of the Er3+ ions, respectively. Moreover, two photonic processes were observed. The surface plasmon resonance (SPR) with upconversion luminescence behavior of the Ag–BaMoO4: Er3+/Yb3+ samples were clearly described.

Bismuth tungstate photocatalyst was synthesized by facile microwave hydrothermal method and the morphology evolution was investigated under wide range of microwave irradiation time. Structural, morphological, compositional and optical properties were analyzed by means of X-ray Diffraction (XRD), Raman Spectroscopy, Scanning Electron Microscopy (SEM), and UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) methods. Photocatalytic activity was performed by the decomposition of Rhodamine B (Rh B) under visible light irradiation. Results revealed that the microwave irradiation time is crucial in order to control the morphology of bismuth tungstate nanoparticles. Different morphologies were obtained under different microwave irradiation time and the best conditions of microwave irradiation time for the best photocatalytic activity under visible light were investigated which proves that the microwave could induce various morphology of bismuth tungstate photocatalyst to exhibit the best photocatalytic activity under visible light.

This paper reports the microwave hydrothermal synthesis of TiO₂ nanotubes and their characterization. Structural properties of the as synthesized materials were investigated by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Raman Spectroscopy. Results revealed that the TiO₂ nanotubes consists of different layers of titanates (Na₂Ti₄O₉, H₂Ti₅O₁₁ H₂O, ZnTiO₃). Raman results indicate that there is a definite phase change observed between the samples analysed, which can be attributed to alterations in the morphology and subsequent phase of the samples.

This Paper reports the photocatalytic activity of g-C₃N₄/NaTaO₃ hybrid composite photocatalysts synthesized by ball-mill method. The g-C₃N₄ and NaTaO₃ were individually prepared by Solid state reaction and microwave hydrothermal process, respectively. The g-C₃N₄/NaTaO₃ composite showed the enhanced photocatalytic activity for degradation of rhodamine B dye (Rh. B) under simulated solar light irradiation. The results revealed that the band-gap energy absorption edge of hybrid composite samples was shifted to a longer wavelength as compared to NaTaO₃ and the 50 wt% g-C₃N₄/NaTaO₃ hybrid composite exhibited the highest percentage (99.6%) of degradation of Rh. B and the highest reaction rate constant (0.013 min⁻¹) in 4 h which could be attributed to the enhanced absorption of the hybrid composite photocatalyst in the UV-Vis region. Hence, these results suggest that the g-C₃N₄/NaTaO₃ hybrid composite exhibits enhanced photocatalytic activity for the degradation of rhodamine B under simulated solar light irradiation in comparison to the commercial NaTaO₃.