Adsorption of perfluorooctanoic acid from aqueous matrices onto chitosan-modified magnetic biochar: Response surface methodology-based modeling, performance, and mechanism

Perfluorooctanoic acid (PFOA) removal has gained significant attention due to its environmental stability and potential toxicity. This study aims to synthesize a chitosan-modified magnetic biochar (CS_MBC) for efficient PFOA removal from aqueous solutions. Various CS loading ratios (0.25:1, 0.5:1, and 1:1) were explored to determine the optimal adsorbent, with preliminary experiments exhibiting superior performance of CS1_MBC. To explore the impact of various experimental conditions (pH, adsorbent dose, time, and initial PFOA concentrations) on PFOA removal and optimize these parameters, central composite design of response surface methodology was applied. Statistical analysis of variance was conducted to assess the model's adequacy, which demonstrated a strong correlation between experimental results and the model. The predicted optimal conditions for achieving maximum PFOA removal (similar to 94%) were pH 4, 120 mg/L dose, 60 min time, and 20 mg/L PFOA concentration. The kinetics and isotherm studies revealed that the pseudo-second-order (R-2 = 0.9996) and Redlich-Peterson (R-2 = 0.999) models better described PFOA adsorption, with Langmuir maximum adsorption capacity of similar to 517 mg/g. Thermodynamic study confirmed the spontaneous, endothermic, and physisorptive nature of PFOA adsorption, with electrostatic and hydrophobic interactions and hydrogen bonding governing the process. Further, the fixed-bed column experiment was conducted to evaluate the effectiveness of CS1_MBC for practical applications, which demonstrated the maximum experimental adsorption capacity of 39.63 mg/g. The breakthrough data showed an excellent fit with both the Thomas and Yoon-Nelson models, with a high correlation coefficient (R-2 = 0.99). Therefore, this research underscores the potential of CS_MBC as an efficient adsorbent for mitigating PFOA contamination in aqueous environments.