Phytotoxicity Mitigation and Malachite Green Removal from Wastewater Using Superparamagnetic Activated Carbon

This study addresses the removal of malachite green (MG) dye from water utilizing magnetic activated carbon prepared from flowers of Spathodea campanulata (SCMAC). The prepared SCMAC displayed an exceptional specific surface area (1012.9 m²/g) with mesopores (2.97 nm) and confirmed the superparamagnetism even after MG adsorption. FESEM revealed a highly porous structure with uniformly distributed Fe₃O₄nanoparticles (40.84 nm). XPS analysis revealed shifts in the C 1s, O 1s, and Fe 2p binding energies after MG adsorption, indicating the involvement of π–π interactions, hydrogen bonding, and surface complexation between MG molecules and the oxygenated functional groups and Fe²⁺/Fe³⁺sites on SCMAC. Batch adsorption studies revealed optimal conditions for MG removal (pH 4, 15 mg/L MG dye, 0.15 g/L SCMAC). Adsorption kinetic data obeyed the pseudo-second-order kinetics, and the Freundlich isotherm fitted well. The thermodynamic analysis demonstrated endothermic and spontaneous adsorption. Spiking studies demonstrated the practical applicability of SCMAC in industrial groundwater, achieving an adsorption capacity of 82.54 mg/g. Desorption studies showed 66.3% efficiency retention after six cycles. Phytotoxicity assessments revealed that after MG adsorption treatment with SCMAC, the germination index of Solanum lycopersicum seeds increased to 71.42%, underscoring its practical and ecological benefits. These findings establish the synthesized SCMAC as an efficient, sustainable, and reusable adsorbent, offering a practical and environmentally safe solution for wastewater treatment and remediation.