g-C3N4/TiO2 composite microspheres: in situ growth and high visible light catalytic activity

Abstract

The morphology, structure and composition of a photocatalyst are the key factors affecting its photocatalytic activity. Herein, g-C₃N₄ nanosheets were successfully grown in situ on the surface of TiO₂ microspheres, and then a three-dimensional (3D) flower-like g-C₃N₄/TiO₂ composite microsphere photocatalyst (FCTM) was formed with the self-assembly of TiO₂ nanosheets. The effects of g-C₃N₄ nanosheets on the growth process, physical adsorption and photocatalytic activity of FCTM samples were studied. Compared with pure TiO₂, the 3D flower-like g-C₃N₄/TiO₂ composite microsphere photocatalyst had a larger specific surface area, and the specific surface area of FCTM-20 was 239.75 m² g⁻¹. Additionally, the addition of g-C₃N₄ nanosheets also changed the surface charge of TiO₂ microspheres, resulting in the improvement of the physical adsorption capacity of FCTM-20. The degradation rates with FCTM-20 of MO and MB solutions were 51.7% and 92.5% after visible light irradiation for 5 h, which were 41.6% and 111.2% higher than those with pure TiO₂ microspheres, respectively. During the photocatalytic process, FCTM-20 exhibited the best adsorption and degradation of MB solution. This is because the chromophoric groups of MO and MB lead to different energy requirements for FCTM-20 in the degradation process. Furthermore, the self-assembled 3D flower-like morphology of FCTM-20 provided more active sites for the degradation of MO and MB, and the heterojunction structure formed between TiO₂ and g-C₃N₄ was more conducive to the transmission of photogenerated carriers.