Construction of SnS2/TiO2 S-scheme heterostructure photocatalyst for highly efficient photocatalytic degradation of tetracycline hydrochloride

In this study, the S-scheme heterostructure photocatalyst of SnS2/TiO2 (denoted as ST) ultrathin nanosheet-nanorod arrays with high efficiency for the degradation of tetracycline hydrochloride (TC-HCl) was successfully prepared by a two-step hydrothermal method. By expanding the light absorption area and hindering the reorganization of light-generated e--h+ pairs, the binding of TiO2 to SnS2 prepared photocatalysts with highly efficient photocatalytic activity and long-term stability. The results showed that the optimized photocatalyst samples all contributed to the degradation efficiency of tetracycline hydrochloride within 90 min than the photocatalytic degradation of pure TiO2 (41.1%). Among them, the ST loaded with 30 mM SnS2 exhibited the highest photocatalytic degradation efficiency of TC-HCl (93.4%). The reaction rate constant K is 0.02597 min-1, and the transient photocurrent density of ST-30 was up to 34.35 A/cm2, which were 5.78 and 10.54 times higher than that of unmodified TiO2. At the same time, the effects of photocatalysts on the degradation efficiency of TC-HCl under different conditions (pH values, inorganic anions and antibiotic concentrations) were systematically investigated. The inhibition of the degradation efficiency of tetracycline hydrochloride by SnS2/TiO2 heterojunction with the addition of different free radical scavengers indicated that ·O2- and ·OH were the main active substances involved in the degradation process. In addition, two environmentally friendly degradation pathways were proposed based on the analysis of liquid chromatography-mass spectrometry (LC-MS) results and the toxicity assessment of various intermediates in the degradation process. Finally, the photocatalytic mechanism of SnS2/TiO2 heterojunctions was proposed based on the optical and electrochemical properties of the photocatalysts as shown in the tests. These results indicate that the synthesized S-scheme heterostructure photocatalyst SnS2/TiO2 can significantly improve the light trapping ability and reduce the photoelectron-hole complexation rate, which is a promising approach to enhance the degradation efficiency of photocatalysts.