The UPS results of TiO2, g-C3N4, and TiO2/g-C3N4 in Figure From above analyses, the procedure of the derteming the band structure of semiconductor is illustrated in Figure . Therein, the DRS and PL measurements should be firstly conducted to estimate the bandgap of semiconductors. After that, the Mott-Schottky plots and UPS measurement are used to determine the CBM and VBM of semiconductors, respectively. The change of the bandstructure and charge transfer pathways of semiconductor after contacting, for instance, SnO2/TiO2 is also indicated as in Figure . By this approach, the photocatalytic mechanism of semiconductors is easily determined for detail case.