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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]