Fig. 8. Reusability studies; repeated adsorption/desorption of Pb²⁺ by Fe₃O₄@DHAQ_GO nanocomposite (a). The consecutive adsorption capacities (mg g⁻¹) of Fe₃O₄@DHAQ_GO nanocomposite for Pb(ii), Cu(ii), Ni(ii), Co(ii), and Cd(ii) ions during the five adsorption/desorption cycles (b). C₀ ≃ 50 mg L⁻¹, adsorbent dosage = 0.4 g L⁻¹, pH 7, contact time 30 min, desorption agent: EDTA-2Na 0.01 N.