Preparation of S-type heterojunction N-C₃N₄/BiOCl_xI_1-x with internal electric field and enhanced photocatalytic properties

N-C₃N₄/BiOCl_xI_1-x S-type heterojunctions were prepared by a facile one-step hydrothermal method. The crystal form, morphology, structure, elemental composition, surface functional groups and optical properties of the samples were characterized by XRD, XPS, SEM, TEM, FTIR and UV-Vis. The photocatalytic activity of N-C₃N₄/BiOCl_xI_1-x oxidation of organic pollutants and reduction of Cr(VI) was investigated. The results show that N-C₃N₄/BiOCl_xI_1-x sample exhibited the effective enhancement in light absorption. The charge carriers were generated by the transfer of the photoinduced electron from N-C₃N₄ to BiOCl_xI_1-x across the interface under irradiation, which inhibited the recombination of electron-hole pairs. Under visible light irradiation, 20%N-BiOCl_0.5I_0.5 exhibited high activity, the degradation rate of phenol reached 98.53% with 2.5 h of visible light irradiation. Meanwhile, the reduction rate of Cr(VI) of 20% N-BiOCl_0.5I_0.5 reached to 99.11% with 1 h of visible light irradiation. 20%N-BiOCl_0.5I_0.5 showed good stability after five cycles. The TOC removal rate of degradation phenol by 20%N-BiOCl_0.5I_0.5 within 3 hours was 80.21%. Combined with capture experiment, ESR and DFT calculation, the improvement activity of N-C₃N₄/BiOCl_xI_1-x was attributed to the formation of S-type heterojunction, the internal electric field based on different Fermi levels between N-C₃N₄ and BiOCl_xI_1-x, as well as band bending and Coulomb force, which together accelerated spatial separation of photogenerated carriers and orderly electron flow.