Investigation of the Ag species and synergy of Ag-TiO2 and g-C3N4 for the enhancement of photocatalytic activity under UV–Visible light irradiation

Herein, UV–visible light-responsive g-C3N4/Ag-TiO2 photocatalysts were successfully synthesized. The Ag species in the composites before and after photocatalysis were investigated by X-ray absorption near edge structure (XANES) spectroscopy and X-ray photoelectron spectroscopy (XPS). The Ag species in the Ag-TiO2 were all metallic Ag, while a combination of metallic Ag and Ag+ attributed to Ag2O was found in the composites. In addition, the change of Ag0/Ag+ oxidation after photocatalysis was conspicuously explored. The composite with optimal ratios of g-C3N4 to Ag-TiO2 at 2 to 1 (2CN:1ST) exhibited photocatalytic efficiencies for the degradation of rhodamine B (RhB, cationic dye) and methyl orange (MO, anionic dye) of 95.01 % and 98.13 % and 72.92 % and 92.82 % under UV and visible light irradiation, respectively. The results suggested that Ag-TiO2 is a predominantly UV-responsive photocatalyst, whereas g-C3N4 can effectively promote photocatalytic degradation under visible light irradiation. Therefore, the synergy of the synthesized g-C3N4 and Ag-TiO2 photocatalysts results in high-performance cationic and anionic dye degradation under both UV and visible light irradiation. In addition, the ability of Ag0/Ag+ to switch oxidation states under irradiation is advantageous to the suppression of recombination.