Ecological synthesis, characterization and application of iron oxide of tangerine nanoparticles for arsenic removal from aqueous solutions

Water pollution represents a critical global challenge affecting human health and natural ecosystems. Among the most hazardous contaminants are heavy metals, particularly arsenic (As), which is frequently detected at elevated concentrations in water bodies as a consequence of anthropogenic activities such as agriculture, mining, and metallurgical processes. In this study, magnetic iron oxide nanoparticles synthesized via a green route using tangerine (Citrus reticulata) peel extract (FeNPs-CR) were developed and evaluated for As removal from aqueous solutions. The nanoparticles were synthesized through a coprecipitation method employing 75 g of pulverized peel extract and characterized by scanning electron microscopy (SEM), FT-IR spectroscopy, UV–Vis spectroscopy, and dynamic light scattering (DLS). SEM analysis revealed quasi-spherical particles with primary sizes ranging from 70 to 300 nm, while DLS measurements indicated larger hydrodynamic diameters due to particle agglomeration in aqueous media. Adsorption experiments were conducted using hydride generation atomic absorption spectroscopy, evaluating the effects of contact time, adsorbent dosage, pH, temperature, and initial As concentration. Removal efficiencies exceeding 99% were achieved at 20 mg/L As within 10–30 min, while concentrations of 50–120 mg/L showed removal efficiencies above 95%. Adsorption kinetics were best described by the pseudo-second-order model, indicating a physicochemical adsorption mechanism. Equilibrium data were better fitted by the Freundlich isotherm (R² = 0.97), suggesting heterogeneous multilayer adsorption, with a maximum adsorption capacity (qmax) of 227.27 mg/g. Thermodynamic analysis revealed negative Gibbs free energy (ΔG° = −7.66 to −11.14 kJ/mol), confirming the spontaneous and exothermic nature of the adsorption process. Optimal performance was observed under acidic conditions (pH 1–3) and temperatures below 35 ℃. These findings demonstrated that FeNPs-CR synthesized from citrus waste constitute an efficient, sustainable, and low-cost adsorbent for As removal, with promising potential for large-scale water treatment applications.