Immobilization of TiO2 Nanoparticles over Mesoporous MCM-41 Adsorbent toward Treatment of Tetracycline Antibiotic-Contaminated Water

The goal of this study is to synthesize TiO2(10)/MCM-41 nanocomposite via the hydrothermal-impregnation method and compare its performance with bare TiO2 nanoparticles with the aim of assessing the role of silica support in the removal of tetracycline antibiotics. The physicochemical properties of synthesized photocatalysts were investigated using various analyzes. The results of XRD and EDX analyses indicated the successful synthesis of TiO2(10)/MCM-41 nanocomposite. FESEM and EDX images showed the existence of nanosized small surface particles with uniform size distribution and dispersion over the structure of TiO2(10)/MCM-41. FESEM images also revealed that nanoparticles size decrease and the formation of agglomerations are prevented as a result of nanoparticle immobilization. The PL and DRS techniques confirmed that the TiO2 immobilization results in a decrease in electron-hole recombination and surface nanoparticle size. The N2 adsorption-desorption analysis showed that the synthesized nanocomposite has a high specific surface area (972 m2/g). According to the performance results, the tetracycline degradation over TiO2(10)/MCM-41 was 67.7% higher than that of the bare TiO2 nanoparticles. This enhancement can be due to the suitable crystalline structure of TiO2, smaller size and uniform distribution of TiO2 nanoparticles, high specific surface area, the decrease of charge carriers recombination, and prevention of photocatalyst aggregation as a result of the existence of MCM-41. Based on the kinetics consideration, the degradation rate of pollutants over immobilized nanoparticles is higher and follows the second-order reaction. Also, a degradation efficiency of 68% was obtained under operation conditions of 20 mg/L tetracycline concentration, 1.5 g/L photocatalyst dosage, and 2 h irradiation. The relatively high and constant activity after the first cycle of reuse refers to the suitable separation and thereupon, appropriate reusability of TiO2(10)/MCM-41 sample. Therefore, it can be concluded that in addition to easier and better separation, TiO2 immobilization over MCM-41 improves the optical and structural properties, and finally, increases the performance of the photocatalyst.