Optimization of photocatalytic degradation of amoxicillin by ZnO-TiO2 heterojunction under UV-Visible irradiation

This study aims to evaluate the efficiency of the ZnO/TiO₂ heterojunction in a photocatalytic process under UV-Visible irradiation for the degradation of amoxicillin (AMX), an antibiotic commonly detected as a pharmaceutical contaminant in water. The photocatalyst was synthesized by sol-gel method and characterized by various techniques such as XRD, FT-IR, SEM/EDX, MET and UV-vis DRS, in order to evaluate its physicochemical properties. Optimization of several experimental parameters, such as the initial concentration of AMX, the nature of the photocatalyst, the catalyst dose and the initial pH of the solution, was carried out to maximize photocatalytic performance. XRD revealed the presence of the wurtzite phase for ZnO, while TiO₂ showed the rutile and anatase phases, finely dispersed in the ZnO matrix. FT-IR analysis confirmed the presence of the characteristic ZnO and TiO₂ bands, and UV-vis DRS analysis also confirmed significant energy absorption in the UV-vis range. In addition, evaluation of photocatalytic efficiency under different experimental conditions showed that alkaline conditions were more conducive to degradation due to the significantly higher hydroxyl ion content. Under optimal experimental conditions (AMX concentration of 40 mg/L, pH of approx. 10, catalyst dose of 100 mg/L and Zn²⁺/Ti⁴⁺=4 molar ratio), the ZnO-TiO₂ heterojunction reached 94% after 210 minutes of exposure to UV-vis irradiation, guaranteeing an optimum balance between light penetration and photocatalytic activity. In addition, the photocatalyst demonstrated high regeneration capacity and photostability, maintaining high regeneration capacity after five cycles. These results underline the strong potential of the ZnO-TiO₂ heterojunction for concrete applications in the treatment of polluted water.