Tightly Interfaced Heterojunction of In2O3@TiO2: A Facile Synthesis of MOF-on-MOF Derived In2O3@TiO2 and their Enhanced Performance in Photodegrading Tetracycline Under Visible Light Irradiation

To address the challenges of titanium dioxide's low utilization of visible light, easy recombination of photogenerated charges, and insufficient interfacial contact when integrated with other semiconductors to form heterojunctions, a novel, simple, and easy hybrid MOF template-directed method was developed to enhance the interaction between oxide and support, thereby constructing In 2 O 3 @TiO 2 - x (IT- x ) composites with tightly contacted heterojunction interfaces. After 120 minutes of exposure to visible light, the IT-30% realized a 91.98% degradation rate for tetracycline in wastewater with an initial concentration of 30 mg/L, which is 1.46, 3.39, and 2.07 times higher than that of bare TiO 2 , bare In 2 O 3 , and Degussa-P25, respectively. After 5 cycles (10 h), the IT-30% photocatalyst still maintained high photocatalytic activity with a 14.47% decline in tetracycline degradation efficiency. The experiments on free radical trapping and electromagnetic spin resonance (ESR) revealed that the superoxide radical is the primary active substance in the tetracycline photocatalytic degradation. SEM, HRTEM, and XRD characterization techniques were utilized to demonstrate the successful preparation of hollow composites. The results of BET, UV-Vis DRS, XPS, photoluminescence (PL), and electrochemical impedance spectroscopy (EIS) indicate that the high photocatalytic activity of the prepared IT-30% composite is ascribed to its large specific surface area, strong capacity for visible light absorption, generate abundant oxygen vacancies generated in the composites, and efficient separation and migration of photogenerated carriers. In addition, a possible degradation pathway for tetracycline was proposed according to the HPLC-MS test results of intermediate products.