GREEN SYNTHESIS OF IRON OXIDE NANOPARTICLES FOR ENVIRONMENTAL REMEDIATION APPLICATIONS

Abstract

The discharge of toxic heavy metals (Pb2+, Cd2+, Ni2+, Cu2+, Cr) and recalcitrant synthetic dyes from textile and printing industries have increased the need for low-cost and sustainable water treatment technologies as conventional precipitation, ion exchange, and adsorption methods are limited by high energy demand and secondary-waste generation (Akintelu et al., 2021; Osman et al., 2024). Iron oxide nanoparticles, notably magnetite (Fe3O4) and maghemite (γ-Fe2O3), have received persistent interest owing to their superparamagnetism, chemical stability, low toxicity, and magnetic recoverability that allow for multifunctional adsorbent and Fenton-like photocatalyst applications (Priya et al., 2021; Tan et al., 2023). However, traditional chemical/physical synthesis uses toxic reductants like NaBH₄ and energy-consuming solvent pathways, leading to the requirement of plant extract mediated green synthesis where polyphenols, flavonoids, terpenoids, tannins and proteins serve as in-situ reductants and capping agents (Akintelu et al., 2021; Haider et al., 2024; Priya et al., 2021). Biogenic IONPs are generally characterised by cubic spinel phases, quasi-spherical/polyhedral shapes (5–30 nm), high BET surface area (80–160 m² g −1) and saturation magnetisation of 10–80 emu g −1 (Akintelu et al., 2021; Khadka et al., 2024; Priya et al., 2021). Langmuir maxima of 105.93 mg g-1 (Cd2+) and 118.76 mg g-1 (Pb2+) have been reported on cyanobacteria-derived IONPs (Kaleem et al., 2023) and 100 % Cd2+/Ni2+ removal on clove/green-coffee-derived material (Mohamed et al., 2023). Methylene-blue degradation efficiencies of 87 % under UV (Bibi et al., 2022) and >80 % under simulated sunlight (Khadka et al., 2024) have been demonstrated through ROS-driven Fenton-like and photocatalytic pathways (Alshehri et al., 2017; Hassaan et al., 2023). The uptake was consistently described by pseudo-second-order kinetics and Langmuir/Freundlich models (Akintelu et al., 2021; Kaleem et al., 2023; Mohamed et al., 2023) with a capacity retention of 80–88 % for five regeneration cycles (Alshehri et al., 2017; Kaleem et al., 2023). Despite this, batch-to-batch phytochemical variability, lack of good manufacturing practices (GMP)-grade standardisation and limited ecotoxicological profiling continue to hinder commercialisation (Akintelu et al., 2021; Haider et al., 2024; Priya et al., 2021; Tan et al., 2023). These have resulted in new strategies including FeNP/rGO/TiO2 hybrids, machine-learning-assisted phytochemical screening, extremophile-mediated biosynthesis and continuous-flow photoreactor integration (Akhtar et al., 2024; Bolade et al., 2019; Kapoor et al., 2021; Osman et al., 2024).