Synthesis and characterization of Zn and Fe doped magnetic biochar from Acacia falcata leaves for Cr(VI) adsorption

Hexavalent chromium (Cr(VI)), a toxic pollutant extensively utilized across multiple industries, necessitates effective treatment using low-cost and sustainable materials. In this research, magnetic biochar (MBC) was prepared using Acacia falcata leaves through chemical treatment with ZnCl2 and incorporating Fe3O4 nanoparticles using FeCl3<middle dot>6H(2)O as a precursor. BET analysis revealed a specific surface area of 248.11 m(2)/g and FESEM images showed a highly porous structure with uniformly embedded Fe3O4 nanoparticles, which became smoother and more compact after Cr(VI) removal. XRD spectra confirmed the incorporation of Fe3O4 through distinct (311) and (440) peaks, matching the cubic spinel structure, while VSM data revealed a magnetic saturation of 5.44 emu/g. XPS analysis indicated the participation of carboxyl, hydroxyl, carbonyl, and Fe3O4 groups in Cr(VI) reduction and adsorption. Batch experiments identified an optimum pH of 2, a MBC dose of 0.4 g/L, and a contact time of 3 h. The adsorption data followed the Freundlich isotherm and pseudo-second-order kinetics. The maximum adsorption capacity was 25.62 mg/g at 303 K, and thermodynamic studies confirmed that Cr(VI) removal was spontaneous and endothermic. The enthalpy and entropy values for Cr(VI) adsorption were 17.71 kJ/mol and 63.22 J/mol<middle dot>K, respectively. Reusability studies, conducted at the optimum pH of 2 and a MBC dose of 1.4 g/L, demonstrated that MBC could be reused for up to five cycles. MBC effectively removed over 97.80% of Cr(VI) from various water sources, highlighting its potential for Cr(VI) remediation.