Heterojunctioned ZnO/Bi₂S₃ nanocomposites were prepared via a facile solvothermal method. The obtained photocatalysts were characterized by X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), High resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectroscopy (DRS), and Photoelectrochemical and Photoluminescence spectroscopy (PL), respectively. The results showed that ZnO/Bi₂S₃ composites exhibited the sandwiched-like structure, where ZnO nanoparticles were randomly embedded between Bi₂S₃ nanoflakes. The performance of photocatalytic Cr(VI) reduction under visible light indicated that ZnO/Bi₂S₃ composites exhibited high-efficiency photocatalytic activity in comparison with either Bi₂S₃ or ZnO. The 5%-ZnO/Bi₂S₃ photocatalyst removed 96% of Cr(VI) within 120 min at 20 mg/L initial concentration of Cr(VI). The enhanced performance of ZnO/Bi₂S₃ photocatalysts could be ascribed to the increased light harvesting and the effective separation and transfer of the photogenerated charge carriers across the heterojunction interface of the ZnO/Bi₂S₃ composite. This work could pave the way for the design of new hetero-structured materials and has great potential in environmental remediation.

Three dimensional (3D) ZnO/ZnAl₂O₄ nanocomposites (Zn_nAl-MMO) were synthesized by a simple urea-assisted hydrothermal process and subsequent high-temperature calcination. The as-prepared samples and their precursors were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), UV-Vis diffuse reflectance spectroscopy (DRS), and Photoluminescence spectra (PL). It was observed that the morphology of Zn_nAl-MMO nanocomposites could be tuned from cubic aggregates, hierarchically flower-like spheres to porous microspheres by simply changing the molar ratio of metal cations of the starting reaction mixtures. The photocatalytic performance of ZnO/ZnAl₂O₄ nanocomposites in the photoreduction of aqueous Cr(VI) indicated that the as-prepared 3D hierarchical sphere-like Zn_nAl-MMO nanocomposite showed excellent photocatalytic activity of Cr(VI) reduction under UV light irradiation. The results indicated that the maximum removal percentage of aqueous Cr(VI) was 98% within four hours at 10 mg/L initial concentration of Cr(VI), owing to the effective charge separation and diversion of photogenerated carriers across the heterojunction interface of the composite. Our study put forward a facile method to fabricate hierarchical ZnO/ZnAl₂O₄ composites with potential applications for wastewater treatment.

Bismuth nanoparticles (BiNPs) and Zinc Oxide photocatalysts (BiNPs/ZnO) with different Bi loadings were successfully prepared via a facile chemical method. Their morphology and structure were thoroughly characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), UV-Vis (Ultraviolet-Visible) diffuse reflectance spectroscopy (DRS), photoluminescence spectra (PL), and electrochemical impedance spectroscopy (EIS). The results showed that a modification of hexagonal wurtzite-phase ZnO nanoparticles with Bi is achievable with an intimate interfacial interaction within its composites. The performance of the photocatalytic Cr(VI) removal under visible light irradiation indicated that BiNPs/ZnO exhibited a superior removal performance to bare ZnO, Bi, and the counterpart sample prepared using a physical mixing method. The excellent performance of the BiNPs/ZnO photocatalysts could be ascribed to the synergistic effect between the considerable physical Cr (VI) adsorption and enhanced absorption intensity in the visible light region, due to the surface plasmon resonance (SPR) as well as the effective transfer and separation of the photogenerated charge carriers at the interface.

The potential extensive application of graphene oxide (GO) in various fields results in the possibility of its release into the natural environment with negative impacts on humans and the ecosystem. The UV-induced removal behavior of aqueous GO was evaluated in this study, and the effect of various parameters (including initial GO concentration, initial solution pH and co-existing ions) on removal rate of GO were investigated in detail. The results showed that UV-light induced a maximum removal rate of GO of 99.1% after 32 h irradiation without any additives, and that the photo-induced removal process in all cases fitted well with pseudo-first-order kinetics. Under optimal conditions, GO was completely removed, with initial GO concentrations of 10 mg/L while adjusting solution pH to 3 or adding Ca²⁺-containing salt. The GO and photoreduced graphene oxide (prGO) were characterized using High-resolution Transmission Microscopy (HRTEM), X-ray Photoelectron Spectroscopy (XPS), and Fourier-transform Infrared Spectroscopy (FT-IR). The radical species trapping experiments and Electron Spin Resonance (ESR) tests indicated that self-reduction of GO upon UV-light exposure could be achieved via photogenerated electrons from a GO semiconductor. Further mechanism study showed that the high efficiency of UV-induced GO removal came from UV-induced photoreduction, and pH-induced or cation-induced coagulation. This study provided a green and effective method to remove GO from aqueous solutions.