Defluorination of water solutions and glass industry wastewater using a magnetic pineapple hydrochar nanocomposite modified with a covalent organic framework

Abstract

This study investigates the development and use of a novel magnetic composite, PAH/MnFe₂O₄/COF, synthesized from pineapple hydrochar (PAH) and modified with a covalent organic framework (COF) for Fluoride (Flu) elimination from water and industrial wastewater. Fluoride contamination poses serious health risks, making its removal essential. The composite was analyzed using scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and other methods, confirming its successful synthesis with a surface area of 102.960 m²/g and a saturation magnetization of 19.548 emu/g. The adsorption efficiency was modeled using a second-order polynomial, with a high R² value of 0.9958, indicating excellent predictive accuracy. Optimal conditions for 99.54% Flu removal included a pH of 3.5, an adsorber mass of 1 g/L, a temperature of 50 °C, an adsorption time of 60 min, and a Flu concentration of 5 mg/L. The adsorption followed a pseudo-second-order model, indicating rapid chemical adsorption, while thermodynamic analysis revealed a spontaneous, endothermic process, supported by negative Gibbs free energy (ΔG°) values and an enthalpy (ΔH°) of 95.253 kJ/mol. The intraparticle diffusion model indicated multiple mechanisms were involved, including intraparticle diffusion and external surface adsorption. The composite showed a high adsorption capacity of 40.629 mg/g, outperforming the unmodified hydrochar. Additionally, the composite effectively reduced Flu ions, biochemical oxygen demand (BOD₅), chemical oxygen demand (COD), and total dissolved solids (TDS) levels in industrial wastewater. These findings demonstrate that the PAH/MnFe₂O₄/COF composite is an efficient and promising adsorber for addressing the defluorination of water, offering a potential solution to environmental and public health issues.