Efficient fluoride removal from water and industrial wastewater using magnetic chitosan/β-cyclodextrin aerogel enhanced with biochar and MOF composites

Abstract

Fluoride ion (Fl) is essential for human and environmental health but can cause serious health issues at high levels. This study developed chitosan/β-cyclodextrin (CS/β-CD) aerogels, enhanced with coconut shell biochar (CSBC) and a magnetic composite (MnFe₂O₄/Al-La MOF), to assess their efficiency in eliminating Fl from water and industrial wastewater. Structural analysis confirmed that CS/β-CD/CSBC/MnFe₂O₄/Al-La MOF had the highest surface area (9.232 m²/g) and a saturation magnetization of 5.32 emu/g, enabling efficient adsorption and magnetic separation. Under optimal conditions (pH 6, 50 °C, 0.9 g/L adsorbent, 70 min), it achieved a 99.41 % removal rate, with a maximum sorption capacity of 38.59 mg/g. Adsorption followed Freundlich isotherm and pseudo-second-order kinetics, indicating heterogeneous surface interactions and chemical bonding. The value of the Gibbs free energy parameter (ΔG°) for the adsorption of Fl ion using the aforementioned samples was determined to be in the range of −4.619 to −14.669 kJ/mol, indicating that the adsorption process is physical and spontaneous. The enthalpy (ΔH°) parameter value for the adsorption of Fl ion using CS/β-CD aerogel, CS/β-CD aerogel/CSBC, and CS/β-CD aerogel/CSBC/MnFe₂O₄/Al-La MOF samples was determined to be 21.213, 45.549, and 65.816 kJ/mol, respectively, indicating that the process is endothermic. Also, the results showed that the aforementioned adsorbents have a good ability to remove Fl ions from industrial wastewater and can be used as effective adsorbents in cleaning industrial wastewater.