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

Abstract

In this study, an 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 using 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 resulted in 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 compared with 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_α is 0.02597 min⁻¹, and the transient photocurrent density of ST-30 was up to 34.35 μA cm⁻², 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.