The formation of materials (TiO2, SnO2, and g-C3N4) was confirmed by wide typical analyses such as XRD pattern, FTIR spectra, TEM, and SEM. All characterizations were reported in refs. . Besides, other characterizations include: the DRS spectra were recorded using a Jasco V-670 spectrometer using an integrated sphere method; Mott-Schottky plots were conducted for the semiconductor films and recorded with an electrochemical workstation (BioLogic SP-240). Therein, the semiconductor film is a working electrode, and two electrodes including a Pt wire couter electrode, and Ag/AgCl reference electrode (3M KCl, 0.21 V vs. NHE); PL spectra were recorded at room temperature by a Horiba Jobin-Yvon Nanolog spectrophotometer equipped with a Xe lamp as the excitation source wavelength of 325 nm; XPS with an Al Ka monochromatic beam (1486.6 eV, ESCALAB250, Theta Probe XPS system) and UPS characterization with a He (I) beam source (21.21 eV) were measured to investigate the oxidation states and VBM of the materials, respectively.