A weak-light-responsive TiO₂/g-C₃N₄ composite film: photocatalytic activity under low-intensity light irradiation

A TiO₂/g-C₃N₄ composite photocatalytic film was prepared by in situ synthesis method and its photocatalytic capability under weak-visible-light condition was studied. The co-precursor with different ratio of melamine and TiO₂ sol-gel precursor were treated using ultrasonic mixing, physical deposition, and co-sintering method to form the smooth, white-yellow, and compact TiO₂/g-C₃N₄ composite films. The prepared TiO₂/g-C₃N₄ materials were characterized by SEM, TEM, EDS, XRD, BET, VBXPS, and UV-vis diffuse reflectance spectra. The results of composite showed that TiO₂ and g-C₃N₄ have close interfacial connections which are favorable to charge transfer between these two semiconductors with suitable band structure, g-C₃N₄ retard the anatase-to-rutile phase transition of TiO₂ significantly, the specific surface area were increased with g-C₃N₄ ratio raised. Under weak-light irradiation, composite films photocatalytic experiments exhibited RhB removal efficiency approaching 90% after three recycles. Powders suspension degradation experiments revealed the removal efficiency of TiO₂/g-C₃N₄ (90.8%) was higher than pure TiO₂ (52.1%) and slightly lower than pure g-C₃N₄ (96.6%). By control experiment, the enhanced photocatalysis is ascribed to the combination of TiO₂ and g-C₃N₄, which not only produced thin films with greater stability but also formed heterojunctions that can be favorable to charge transfer between these two semiconductors with suitable band structure. This study presents the potential application of photocatalytic film in the wastewater treatment under weak-light situation.