Obviously boosting charge separation efficiency and photocatalytic activity of CdS by a simple fluorination method

In this work, CdS is prepared by a simple molten salt method (CdS-MS), and CdS-MS is halogenated to obtain F-doped CdS (F-CdS) under solvothermal condition. The samples are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), ultraviolet–visible diffuse reflection spectroscopy (UV–Vis DRS), photoluminescence (PL) spectrum, photocurrent, electrochemical impedance spectroscopy (EIS); and the photocatalytic activity is estimated by the degradation of RhB. The results show that after the fluorination treatment, the photoluminescence decreases, the photocurrent increases from 50 to 160 mA/cm2, and the electrical resistance decreases from 3.588 to 0.7 Ω, although the band gap does not change. Under visible light irradiation (λ ≥ 420 nm) for 90 min, 83.8% of RhB is degraded by F-CdS-2, while only 52% is degraded by CdS-MS. The higher activity is mainly attributed to the enhanced charge separation efficiency. Besides, we also study the effect of pH on the degradation reaction. The results show that over F-CdS-2, the degradation efficiency of RhB is 93.1% in 20 min at pH = 2, which is 3 times as much as that at pH = 7. The masking experiment results show that at pH = 7, ·O2– and holes have been identified as the main active oxidative species, but ·O2– is the main active oxidative species at pH = 2. The results indicate that H+ may promote the activated of oxygen. The simple fluorination method could be extended to the other photocatalysts. This work conducted extensive experiments on the photocatalytic degradation of RhB, and the results showed that fluorine modification can significantly improve the efficiency and stability of CdS and the method can be applied to other photocatalysts either. In addition, this work also studied the mechanism of F-CdS in photocatalytic reactions, revealing the photocatalytic process and influencing factors of halogenated photocatalysts, providing a novel and effective strategy for improving the performance of photocatalysts.