Decontamination of levofloxacin from water using a novel chitosan–walnut shells composite: linear, nonlinear, and optimization modeling

Abstract

Chitosan–walnut shells (Ch–W) composite was tested for the removal of levofloxacin from water. Various experimental factors were examined at different contact time intervals. The prepared composite exhibited maximum uptake capacity of 7.43 mg g−1 for levofloxacin with 0.5 g L−1 Ch–W dose at 45 min and pH = 7. Linear and nonlinear isotherm/kinetic models have been investigated, and the pertinency of the models was confirmed by correlation coefficients (R2) and error functions. Consequently, the adsorption of levofloxacin could be more accurately described by the nonlinear pseudo-second-order and Langmuir as well as Temkin models (R2 ˃ 0.98). Optimization modeling of levofloxacin was performed using a central composite design. The independent parameters; initial concentration, pH, and Ch–W dose, were selected while levofloxacin removal was the response. The maximum levofloxacin removal was 75.7% and 94.2% at concentrations of 4 mg L−1 and 2 mg L−1, respectively. Furthermore, 3D surface plots with the interaction effects of the investigated factors are presented. The developed model was reliable for further study and prediction owing to the closeness between the experimental and predicted values. The individual and interacting factors were found to be significant except for “concentration x dose” based on the ANOVA. The models confirmed the experimental results with R2, R2adjusted, and R2predicted values ˃ 0.939. The continuity adsorption cycles were tested for reuse and revealed that the removal of levofloxacin was decreased ~ 23% after six cycles. Hence, the prepared composite has the potential to remove antibiotics from water.