TiO2/carboxylate-rich porous carbon: A highly efficient visible-light-driven photocatalyst based on the ligand-to-metal charge transfer (LMCT) process

A novel visible-light-driven photocatalyst based on TiO₂/carboxylate-rich porous carbon composite (TiO₂/CRPC) was successfully synthesized by low temperature carbonization process in air. Sodium gluconate plays a crucial role in the formation of TiO₂/CRPC. Different functional groups of sodium gluconate play synergetic roles in the formation of TiO₂/CRPC. XRD and Raman spectra studies indicated that there are two different TiO₂ crystalline phases existing in TiO₂/CRPC, which are anatase and brookite, and the CRPC is amorphous. Via FT-IR and XPS spectra investigations, it was demonstrated that carboxylate group, the ligand-to-metal charge transfer (LMCT) forming functional group, was solidified into the CRPC and form the LMCT complex on TiO₂ surface through the fabrication of TiO₂/CRPC. Compared with the pure TiO₂, TiO₂/CRPC exhibit enhanced absorption in the UV and visible light region around 260–600 nm. The strong absorption in the visible light region gives TiO₂/CRPC advantages over pure TiO₂ for the degradation of organic pollutants. TiO₂/CRPC can activate O₂ in air under mild conditions and exhibit excellent visible-light-driven photocatalytic activities. However, TiO₂/C composite obtained by using glucose instead of sodium gluconate exhibits poor photocatalytic activity, which demonstrated that carboxylate–TiO₂ complexes are responsible for the prominent photocatalytic properties of TiO₂/CRPC under visible light irradiation.