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.