Chitosan-graft-poly(N‑tert‑butylacrylamide) Copolymer: Synthesis, Characterization and Optimization of Tetracycline Removal Using RSM

In the present study, a graft copolymer was synthesized in accordance with the free radical method using N-tertiary butylacrylamide monomer on chitosan, which is an environmentally friendly polymer. The chemical structure and surface morphology of the newly synthesized graft copolymer were determined by Fourier transform infrared spectroscopy, scanning electron microscopy and X-ray diffraction. Moreover, the thermal behavior was analyzed by thermogravimetric analysis. The chitosan-graft-poly(N‑tert‑butylacrylamide) graft copolymer was used as an adsorbent for the rapid removal of tetracycline from aqueous solutions in order to investigate its applicability. Response surface methodology (RSM) was employed for the optimization of the study conditions, namely adsorbent dosage (0.01–0.04 g 100 mL−1), reaction time (10–90 min) and initial tetracycline concentration (10–100 mg 100 mL−1). The effects of these conditions on tetracycline uptake capacity were examined and the results were statistically analyzed. The RSM results showed that the maximum tetracycline uptake capacity of 104.81 mg g−1 was achieved under the following conditions: adsorbent dose of 0.03 mg 100 mL−1, reaction time of 51.12 min and initial tetracycline concentration of 97.99 mg L−1. ANOVA based on central composite design combined with RSM showed a good agreement between the experimental values and quadratic model estimates, thus resulting in a coefficient (R2) of 0.9118 for tetracycline uptake. The kinetics, isotherms, and thermodynamics of adsorption were examined, and results showed that equilibrium data fitted the Freundlich isotherm model, and the adsorption kinetics of tetracycline followed pseudo-second-order model. Thermodynamic parameters like the enthalpy − 10.39 kJ mol−1 (ΔH°), entropy 0.044 kJ mol−1 K−1 (ΔS°) and Gibbs free energy − 23.26 kJ mol−1 (ΔG°) were evaluated and also, ΔG° shows a negative values indicating that the adsorption process was exothermic and spontaneous. The findings demonstrated that the chitosan-graft-poly(N‑tert‑butylacrylamide) copolymer is an effective adsorbent for pharmaceutical wastewater treatment.