Simultaneous in situ synthesis and loading of magnetite for dye wastewater remediation: adsorption study and DFT calculations.

Synthesizing new materials for water treatment often involves resource- and energy-intensive processes to achieve the desired treatment performance. In this work, we propose for the first time a novel approach for the facile synthesis of a hybrid inorganic/organic adsorbent via in situ loading of magnetite nanoparticles with organic dyes commonly present in industrial wastewater, namely congo red (CR) and bromocresol green (BCG). The resulting dye-loaded magnetite was subsequently used to remove other dyes from synthetic wastewater, including methylene blue (MB) and methyl orange (MO). Derivative spectroscopy was employed to quantify the loading and removal capacities of magnetite in the examined multi-component systems. The results showed that >90% of both CR (92.7 mg g-1 as per D-R isotherm) and BCG (16.2 mg g-1 as per D-R isotherm) were successfully loaded onto magnetite, and the loaded magnetite subsequently adsorbed MB in single and binary systems with MO, with removal efficiencies exceeding 75% and 50%, respectively; MO exhibited 0% and 50% removal in its single and binary system, respectively. Adsorption was also successful in saline and tap water; however the adsorbent dose was increased to 10 g L-1. The loaded magnetite was reused for four cycles without loss of removal efficiency. DFT calculations were performed to investigate the adsorption mechanisms of the dyes on the magnetite surface and to calculate adsorption and dispersion energies. Theoretical results were compared against isotherm models derived from experimental data. Both experimental and DFT results suggested that dye adsorption on magnetite was mainly dominated by physisorption. Overall, the proposed approach enables simultaneous material synthesis and water treatment, offering a greener and simpler alternative to traditional adsorbent fabrication methods.