Alcohol solvents evaporation-induced self-assembly synthesis of mesoporous TiO_2−x−yC_xN_y nanoparticles toward visible-light driven photocatalytic activity

A one-step solvent evaporation-induced self-assembly (SEISA) process was demonstrated to prepare carbon and nitrogen co-doping mesoporous TiO₂ nanoparticles (MesoTiO_2−x−yC_xN_y-S) using an ionic liquid as carbon and nitrogen sources as well as mesoporous template. After the evaporation of different solvents (methanol, ethanol, and isopropanol) and subsequent calcinations at 773 K, the obtained MesoTiO_2−x−yC_xN_y-S samples were systematically characterized by a variety of spectroscopic and analytical techniques, including small- and large-angle X-ray diffraction (XRD), Raman, transmission electron microscopy (TEM), N₂ adsorption–desorption isotherms, Fourier transform infrared (FTIR), and X-ray photoelectron (XPS) spectroscopies. The results indicate that the solvents play an essential role on the chemical microstructure, doping elemental states, and photocatalytic performance of catalysts. The MesoTiO_2−x−yC_xN_y-I samples have the lowest band gap of ca. 2.75 eV and strongest absorbance of visible light in the range of 400–600 nm. Among the MesoTiO_2−x−yC_xN_y-S photocatalysts, the MesoTiO_2−x−yC_xN_y-M catalysts show superior photocatalytic activity of hydrogen generation in methanol aqueous solution under visible light irradiation as compared to MesoTiO_2−x−yC_xN_y-E, MesoTiO_2−x−yC_xN_y-I, and commercial Degussa TiO₂. This result could be attributed to the moderate C,N co-doping amounts on their developed mesoporous texture (pore size = 8.0 nm) and high surface area (107 m² g⁻¹) of TiO₂ (crystallite size = 9.9 nm) in the MesoTiO_2−x−yC_xN_y-M catalysts