Preparation of Humic Acid/<scp>l</scp>-Cysteine-Codecorated Magnetic Fe₃O₄ Nanoparticles for Selective and Highly Efficient Adsorption of Mercury

Abstract

Humic acid and l-cysteine-codecorated magnetic Fe₃O₄ nanoparticles (HA/LC-MNPs) were synthesized using a coprecipitation method. Humic acid fractions abundant with carboxyl and hydroxyl groups can be selectively coated on the surface of MNPs during synthesis. HA/LC-MNPs with abundant heteroatoms (N, S, and O) show excellent removal capacity, great selectivity, and also fast trapping of Hg²⁺ in a wide pH range. The adsorption capacity of HA/LC-MNPs for Hg²⁺ can reach 206.5 mg/g, and the chemisorption was attributed to the major adsorption form. In competitive adsorption, HA/LC-MNPs preferentially adsorbed Hg²⁺ with an affinity order of Hg²⁺ > > Pb²⁺ > Cu²⁺ ≫ Zn²⁺ > Cd²⁺. In total, 93.91% of Hg²⁺ can be quickly captured in the presence of a 6000 times higher concentration of competing metal ions (Pb²⁺, Cu²⁺, Cd²⁺, and Zn²⁺) within 30 min. The adsorption mechanism was analyzed using X-ray photoelectron spectroscopy (XPS). It suggested that the HA/LC-MNPs enhanced the adsorption capacity of Hg²⁺ because of the complexing abilities of the multiple thiol, amino, and carboxyl groups in sorbents with Hg²⁺, the ion exchange ability of the carboxyl group, and the negative charge surface. All in all, HA/LC-MNPs are a potentially useful and economic material for the selective removal of Hg²⁺ from polluted water.