Green-Synthesized Iron Oxide-Chitosan Nanocomposite for Chromium and Nanoplastics Remediation

<title>Abstract</title> This study presents the eco-friendly synthesis and application of iron oxide nanoparticles (IO-NPs) and a chitosan-based iron oxide nanocomposite (IO-NPs+C) for removing chromium (Cr) ions and nanoplastics (NPs) from contaminated water. For the first time, Aspergillus iranicus, a fungal isolate from the Indian Sundarbans mangrove ecosystem, was employed for the green synthesis of superparamagnetic iron oxide nanoparticles (SPIONs), aligning with sustainable chemistry principles. TEM and XRD analyses confirmed their spherical morphology and size range of 10–50 nm. The nanocomposite exhibited significantly enhanced adsorption efficiency compared to IO-NPs alone, achieving equilibrium capacities of 195.20 mg/g (Cr) and 190.50 mg/g (NPs) under optimal conditions (pH 2, 35°C, 100 mg/L dosage, 120 min contact). Langmuir isotherm fitting suggested monolayer adsorption, with maximum capacities exceeding 500 mg/g (Cr) and 250 mg/g (NPs). Process optimization through Response Surface Methodology (RSM) and Artificial Neural Networks (ANN) revealed a highly efficient removal (92.68% Cr and 97.89% NPs) at optimized conditions of 99.98 mg/L IO-NPs+C, pH 6.8, and 35°C. Field validation using groundwater near a Chromite Ore Processing Residue (COPR) site (Cr: 12.68 ± 1.2 mg/L, spiked NPs: 20 mg/L) showed 93.39% removal of both contaminants with 100 mg/L of IO-NPs+C at pH 7.6 and 313 K within 120 minutes. The IO-NPs+C outperformed IO-NPs alone, establishing its promise as a sustainable and high-performance solution for simultaneous Cr and NP remediation in wastewater treatment.