The ZnO/Bentonite composite for sustainable tetracycline removal from water: Adsorption and photocatalysis for effective wastewater treatment

Pharmaceutical pollutants such as tetracycline (TC) pose serious environmental concerns because of their persistence and potential to promote antibiotic resistance. In this study, a ZnO/bentonite composite was developed and applied for the efficient removal of TC from aqueous solutions under simulated solar irradiation via a synergistic adsorption–photocatalysis mechanism. The bentonite component enhanced adsorption by drawing TC molecules closer to the ZnO active sites, where the reactive oxygen species (ROS) generated by ZnO facilitated degradation. SEM, XRD, FTIR, and UV–Vis characterization confirmed the composite's structure and optical properties. Under optimal conditions (pH 8.5, 25 °C, 0.1 g/100 mL catalyst, 40 ppm TC), the system achieved 87 % removal, with complete mineralization validated by HPLC, total organic carbon (TOC), and Fourier transform infrared (FTIR) spectroscopy. The degradation followed pseudo-first-order kinetics with a rate constant of 0.015 min⁻¹, and the point of zero charge (pHpzc = 9.4) influenced the pH-dependent performance. The catalyst retained 77 % of its initial efficiency after five cycles, highlighting its low cost, reusability, and eco-friendly potential for antibiotic-contaminated wastewater treatment.