Development of AC/ZnO/Fe2O3 for efficiently adsorptive removal of Tetracycline from water environment: isotherm, kinetic and thermodynamic studies and adsorption mechanism

The present study deals with the adsorptive removal of tetracycline (TC) from liquid phase by different adsorbents of AC (activated carbon), AC/ZnO, and AC/ZnO/Fe2O3. Scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and Brunauer-Emmett-Teller (BET) analyses guarantee the desirable synthesis of the adsorbents. Vibrating-sample magnetometer (VSM) analysis confirms the proper magnetic property of AC/ZnO/Fe2O3 and thermal gravimetric analysis (TGA) indicates the sustainable thermal stability of AC/ZnO/Fe2O3. The optimization examinations of the adsorption process declared that the maximum removal efficiency of TC is dependent to pH, adsorbent dosage, TC concentration, and mixing time for all three adsorbents. The effect of interfering coexisting ions decreased the efficiency of TC adsorption in the order: PO4-3 > SO4-2 > CO3-2 > NO3-1 > Cl-1. Reusability study elucidated no significant change in the adsorption capacity of AC/ZnO/Fe2O3 after five successive cycles. The findings demonstrated that adsorption data were better correlated with Freundlich adsorption and pseudo-first-order kinetic models, and thermodynamic values of increment G, increment S, and increment H indicated that the process of TC uptake by AC, AC/ZnO, and AC/ZnO/Fe2O3 was exothermic and spontaneous in nature. In conclusion, the results of this study disclose that modification of AC with nanometals like ZnO and Fe2O3, not only increases the adsorption capacity of AC to some extent but also minimizes the separation cost of AC/ZnO/Fe2O3 using magnetic field, improves the reusability of AC/ZnO/Fe2O3, and keeps its adsorption potential in the existence of interfering ions. The findings of this study can provide valuable data for future studies dealing with full-scale applications of these adsorbents for the removal of drug contaminants from water matrices.