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 Kα 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.