An inverse opal TiO₂/g-C₃N₄ composite with a heterojunction for enhanced visible light-driven photocatalytic activity

A TiO2/g-C3N4 composite photocatalyst with an inverse opal structure and heterojunction has been successfully prepared by a relatively facile approach. The catalyst was characterized by a combination of XRD, SEM, HRTEM, XPS, PL, EIS and DRS techniques and applied for the photocatalytic degradation of organic pollutants represented by Rhodamine B, phenol and levofloxacin. The results of RhB degradation showed that the rate constant of inverse opal TiO2/g-C3N4 with the best compound ratio is 0.184 min-1, which is 2.7 times faster than that of normal TiO2/g-C3N4 and 4.2 times faster than that of inverse opal TiO2. The enhancement of photocatalytic activity may be attributed to the matched overlapping band structure and the interaction between inverse opal g-C3N4 and TiO2. The inverse opal structure of g-C3N4 has improved the optical absorption properties of g-C3N4 and the interaction between inverse opal g-C3N4 and TiO2 creates more interfaces for the efficient transfer of photogenerated electron-hole pairs to restrict the recombination, which was proved from the photoluminescence spectra (PL). Moreover, a possible photocatalytic mechanism has been tentatively proposed according to the experimental results. All in all, both the inverse opal structure and heterojunction construction play significant roles in the excellent photocatalytic degradation performance according to the mechanism investigation.