Green-synthesized magnetite-maghemite nanocomposites for the removal of lead and cadmium from water: competitive adsorption behavior and mechanism studies.

Abstract

The environment and human health are at risk when industrial waste leaks into aquatic environments. Green-synthesized magnetite-maghemite nanocomposites (GSMMNs) were developed in this study as bio-synthesized adsorbents for removing heavy metals from water. The XRD, TEM, FT-IR, SEM-EDS, BET, VSM, and XPS analyses characterized the nanocomposites. The average particle size was 13.76 nm by TEM analysis with a surface area of 158 m²/g. The functional groups (C = O) and mixed Fe²⁺/Fe³⁺ states contribute to the adsorption confirmed by FT-IR and XPS. Batch studies showed optimal adsorption at pH 6.5, 1.5 g/L dose, 30 °C, and 20-30 min contact time (initial concentration 5 mg/L). Pb(II) and Cd(II) have maximal adsorption capacities of 35 mg/g and 15 mg/g, respectively, which decrease to 19 mg/g and 8.1 mg/g as a result of their antagonistic effects. The single and binary systems are followed by Langmuir and Sip models, respectively with a pseudo-second-order kinetic model (R² = 0.99). An antagonistic effect was observed in the binary solution of Pb(II) and Cd(II), based on mathematical modeling. Co-existing ions and ionic strength have an impact on the adsorption following the sequence (PO₄³⁻ > CO₃²⁻ > SO₄²⁻ > Ca²⁺ > NO₃⁻ > Cl⁻ > K⁺). In a real water matrix, the adsorbent showed performance following the sequence: deionized water > tube well water > tap water > river water. The GSMMNs showed promising potential as a cost-effective adsorbent with five regeneration cycles.