Synthesis of functionalized magnetic Fe₃O₄ nanocomposites for efficient capture and recover Ag(I) from e-waste

The recovery of silver from secondary resources by adsorption technology is of vital importance to environmental protection and sustainable development. Herein, a series of magnetic Fe₃O₄ nanocomposites (Fe₃O₄@SiO₂-LCYS, Fe₃O₄@SiO₂-EDA, Fe₃O₄@SiO₂-TSC, Fe₃O₄@SiO₂-AMP and Fe₃O₄@SiO₂-AP) were constructed using l-cysteine (LCYS), ethylenediamine (EDA), thiosemicarbazide (TSC), aminomethylpyridine (AMP) and aminopyridine (AP) as functional groups. The adsorption behavior of the nanocomposites for Ag(I) was evaluated and their application for recovering Ag(I) from e-waste was determined. The nanocomposites exhibit good adsorption performance for Ag(I). The optimal adsorption pH value is 6. The adsorption for Ag(I) by the above nanocomposites can reach saturation at 180, 200, 180, 240 and 240 min, respectively. The adsorption capacity of the nanocomposites for Ag(I) can be promoted by raising temperature and Ag(I) concentration. The adsorption isotherm and kinetic process can be fitted by Langmuir and pseudo-second-order models. The maximum adsorption capacity of Fe₃O₄@SiO₂-LCYS, Fe₃O₄@SiO₂-EDA, Fe₃O₄@SiO₂-TSC, Fe₃O₄@SiO₂-AMP and Fe₃O₄@SiO₂-AP for Ag(I) are 2.95, 1.71, 1.42, 1.41 and 1.30 mmol g^-1. The nanocomposites display excellent adsorption selectivity and great potential for recovering Ag(I) from e-waste. The recovery rate of Fe₃O₄@SiO₂-LCYS for Ag(I) is 100 % in e-waste leaching solution. The functional groups of SH, -NH-, C=O, NH₂, C=N and C=S are proved to participate in the adsorption, and the nanocomposites exhibit good regeneration property. The work provides a simple strategy for constructing adsorbents to recover Ag(I) efficiently from aqueous solution, which exhibit great potentials in environmental remediation and resources recycling.