Novel 3DOM BiVO4/TiO2 nanocomposites for highly enhanced photocatalytic activity

Abstract

Novel 3DOM BiVO₄/TiO₂ nanocomposites with intimate contact were for the first time synthesized by a hydrothermal method in order to elucidate their visible-light-driven photocatalytic performances. BiVO₄ nanoparticles and 3DOM TiO₂ inverse opal were fabricated respectively. These materials were characterized by XRD, XPS, SEM, TEM, N₂ adsorption–desorption and UV-vis diffuse (UV-vis) and photoluminescence spectroscopies. As references for comparison, a physical mixture of BiVO₄ nanoparticles and 3DOM TiO₂ inverse opal powder (0.08 : 1), and a BiVO₄/P25 TiO₂ (0.08 : 1) nanocomposite made also by the hydrothermal method were prepared. The photocatalytic performance of all the prepared materials was evaluated by the degradation of rhodamine B (RhB) as a model pollutant molecule under visible light irradiation. The highly ordered 3D macroporous inverse opal structure can provide more active surface areas and increased mass transfer because of its highly accessible 3D porosity. The results show that 3DOM BiVO₄/TiO₂ nanocomposites possess a highly prolonged lifetime and increased separation of visible light generated charges and extraordinarily high photocatalytic activity. Owing to the intimate contact between BiVO₄ and large surface area 3DOM TiO₂, the photogenerated high energy charges can be easily transferred from BiVO₄ to the 3DOM TiO₂ support. BiVO₄ nanoparticles in the 3DOM TiO₂ inverse opal structure act thus as a sensitizer to absorb visible light and to transfer efficiently high energy electrons to TiO₂ to ensure long lifetime of the photogenerated charges and keep them well separated, owing to the direct bandgap of BiVO₄ of 2.4 eV, favourably positioned band edges, very low recombination rate of electron–hole pairs and stability when coupled with photocatalysts, explaining the extraordinarily high photocatalytic performance of 3DOM BiVO₄/TiO₂ nanocomposites. It is found that larger the amount of BiVO₄ in the nanocomposite, longer the duration of photogenerated charge separation and higher the photocatalytic activity. This work can shed light on the development of novel visible light responsive nanomaterials for efficient solar energy utilisation by the intimate combination of an inorganic light sensitizing nanoparticle with an inverse opal structure with high diffusion efficiency and high accessible surface area.