Element doping adjusted the built-in electric field at the TiO2/CdS interface to enhance the photocatalytic reduction activity of Cr(VI)

TiO2-based heterojunction photocatalyst is promising for photocatalytic reaction due to its extensive spectral absorption and effective separation of photogenerated carriers. In this study, a simple modification method, element doping (N, I, Fe and Ce) was utilized to modify TiO2/CdS. Results of photocatalytic reduction experiments of Cr(VI) reveal that the photocatalytic activity follows the order of I-TiO2/CdS > Fe-TiO2/CdS > N-TiO2/CdS > TiO2/CdS > Ce-TiO2/CdS, and the kinetic rate parameter values of I-TiO2/CdS is about 29.0 and 2.7 times higher than that of TiO2 and TiO2/CdS, respectively. Meanwhile, the peaks of Ti 2p and Cd 3d exhibit the maximum shift of + 0.51 and –1.18 eV after coupling I-TiO2 with CdS, respectively. DFT calculations and electrochemical test reveal that high-electronegativity I doping can increase the difference of Fermi level between TiO2 and CdS, and I-TiO2/CdS heterostructure presents lower charge migration resistance and higher carrier separation behavior, suggesting that the improvement mechanism of I doping is largely attributed to the enhanced strength of built-in electric field at the interface between TiO2 and CdS. This work presents a simple but effective method to develop heterojunction with high photocatalytic activity via facilitating interface migration of photogenerated carriers.