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Ytterbium-doped titanium dioxide (Yb-TiO 2 )/diatomite composite materials with different Yb concentrations were prepared by sol–gel method. The phase structure, morphology, and chemical composition of the as-prepared composites were well characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), and ultraviolet–visible (UV–vis) diffuse reflection spectroscopy. The XRD and Raman spectroscopy analysis indicated that the TiO 2 existed in the form of pure anatase in the composites. The SEM images exhibited the well deposition and dispersion of TiO 2 nanoparticles with little agglomeration on the surfaces of diatoms. The UV–vis diffuse reflection spectra showed that the band gap of TiO 2 could be narrowed by the introduction of Yb species, which was further affected by doping concentration of Yb. The photocatalytic activity of synthesized samples was investigated by the degradation of methylene blue (MB) under UV light irradiation. It was observed that the photocatalytic degradation followed a pseudo-first-order kinetics according to the Langmuir–Hinshelwood model. Compared to TiO 2 and TiO 2 /diatomite, the Yb-TiO 2 /diatomite composites exhibited higher photocatalytic activity toward degradation of MB using UV light irradiation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Co2+-doped ZnO nanoarrays was first grown on substrate and used as photocatalyst. • Co2+ was doped to improve the photocatalytic activity under visible-light induction. • Co2+-doped ZnO efficiently remove organic pollutants for environmental protection. In order to remove the organic pollution from water environment, Co2+-doped ZnO nanoarray photocatalyst was prepared through a hydrothermal process. The influences of Co2+ doping amount and hydrothermal temperature on the nanostructure and photocatalytic performance of Co2+-doped ZnO nanoarray were discussed in detail. The standard ZnO structure and nanoarray morphology of Co2+-doped ZnO samples were achieved and the absorption of visible light was also realized through Co2+ doping. The 2% Co2+-doped ZnO nanoarray prepared at 95 °C exhibited excellent photocatalytic activity and could degrade 96% of methylene blue solution within 120 min under visible light. Furthermore, the as-prepared 2% Co2+-doped ZnO nanoarray still maintained 91% for removal rate after 3 cycles of photocatalytic degradation, showed good photocatalytic activity and recyclability. All results indicate that ZnO nanoarray with Co2+ doping has a potential application in visible light photocatalysis for environmental protection and pollution control. [ABSTRACT FROM AUTHOR]