Comparative study of photocatalytic activities of Ca2Nb2O7 nanopolyhedra and TiO2: Degradations of benzene and methyl orange

Ca2Nb2O7 (CN) nanopolyhedra with relatively high surface area and small crystallites have been prepared by a microwave-assisted template-free hydrothermal method for the first time. The samples are characterized by powder X-ray diffraction (XRD), UV–vis diffuse reflectance spectra (UV–vis DRS), N2-adsorption, and Transmission electron microscopy (TEM). A comparative study on the photocatalytic degradations of methyl orange (MO) in aqueous solution and benzene in gas phase has been carried out between Ca2Nb2O7 nanopolyhedra and TiO2. Results show that the MO and benzene could be effectively degraded and mineralized over the CN samples. Due to the higher photoabsorption performance and concentration of OH radicals, TiO2 exhibit a superior photocatalytic activity for the degradation of MO compared with the CN samples. However, the weaker redox ability of the photogenerated hole–electron pairs induces the lower mineralization ratio of MO. Fourier transform infrared (FT-IR) analysis reveals that the photocatalytic active sites of TiO2 have been blocked by stable intermediates, leading to the deactivation of the photocatalyst. In contrast, although the CN samples exhibit a lower photocatalytic degradation rate of MO, they show a much higher mineralization ratio of MO and benzene compared with TiO2. Therefore, the CN samples maintain a clean surface during the photocatalytic process, resulting in a high and stable photocatalytic degradation performance. In addition, water plays a key role in the photocatalytic degradation of organic pollutants.

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► Ca2Nb2O7 nanopolyhydra were successfully prepared for the first time.
► Comparison on photocatalytic activities between TiO2 and Ca2Nb2O7 was carried out.
► Relationship between the bandgap and photocatalytic activity was investigated.
► Relationship between photocurrent and photocatalytic activity was investigated.
► Roles of H2O on the degradation of gaseous benzene were discussed.