Synthesis of CeO₂/Bi₂MoO₆ nanocomposites and their enhanced photocatalytic degradation performance

A series of CeO₂/Bi₂MoO₆ nanocomposites were prepared by hydrothermal method. The effect of pH value (2~9) and Ce/Bi molar ratio (3 %~10 %) on the photocatalytic performance of the prepared composites were investigated. The composition, structure and photoelectric properties of the catalyst were characterized by X-ray powder diffraction, scanning electron microscopy, infrared spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, photoluminescence spectroscopy and transient photocurrent-time response spectrum, etc. The results showed that the morphology of Bi₂MoO₆ (BMO) crystals was needle-like at pH 6, and it became thick after recombination with CeO₂. At the same time, the specific surface area reduced and the crystal particles enlarged. Photocatalytic activity of the catalyst was tested by photocatalytic degradation of Rhodamine B (RhB), methylene blue (MB) and phenol, respectively, under simulated sunlight irradiation (a 300 W Xenon lamp). The results showed that the optimal composite containing 5 % CeO₂ could achieve the maximum photocatalytic degradation rate. Under the same experimental conditions, reaction rate constants of photocatalytic degradation of RhB, MB and phenol by 5 % CeO₂/BMO were 0.037, 0.016 and 0.007 min^-1, respectively, which were 3.19, 1.70 and 4.58 times higher than pure BMO, respectively. The enhanced photocatalytic performance was attributed to the formation of heterojunctions between CeO₂ and Bi₂MoO₆, which were beneficial to the efficient separation of photogenerated electrons and holes. This, as a result, increased the content of active free radicals. Free radical trapping experiments showed that superoxide ion radical (O^2-)、hydroxyl radical (OH) and holes (h⁺) all participated in the photocatalytic degradation, and their influence was in the order of O^2->OH>h⁺.