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

Abstract

Humic acid and L-cysteine-codecorated magnetic Fe 3 O 4 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 Hg 2+ in a wide pH range. The adsorption capacity of HA/LC-MNPs for Hg 2+ can reach 206.5 mg/g, and the chemisorption was attributed to the major adsorption form. In competitive adsorption, HA/LC-MNPs preferentially adsorbed Hg 2+ with an affinity order of Hg 2+ > > Pb 2+ > Cu 2+ ≫ Zn 2+ > Cd 2+ . In total, 93.91% of Hg 2+ can be quickly captured in the presence of a 6000 times higher concentration of competing metal ions (Pb 2+ , Cu 2+ , Cd 2+ , and Zn 2+ ) 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 Hg 2+ because of the complexing abilities of the multiple thiol, amino, and carboxyl groups in sorbents with Hg 2+ , 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 Hg 2+ from polluted water.

Functionalization of Defective Zr-MOFs for Water Decontamination: Mechanistic Insight into the Competitive Roles of −NH2 and −SH Sites in the Removal of Hg(II) Ions

“…The N(1s)-core XPS of the −NH 2 -functionalized Gly@UiO-66 framework before Hg(II) shows two peaks. The first is centered at 399.49 eV and assigned to the neutral form of amine −NH 2 , and the second peak at 401.37 eV is assigned to the protonated amine sites (−NH 3 + ) (Figure a). − It is clear that the majority ratio (71%) of amine sites of the as-synthesized Gly@UiO-66 framework are protonated. Also, a full-range XPS survey of as-synthesized Gly@UiO-66 confirms the presence of chloride ions (Figure S14).…”

Functionalization of Defective Zr Metal–Organic Frameworks for Water Decontamination: Mechanistic Insight into the Competitive Roles of -NH2 and -SH Sites in Removal of As(III) Species

“…The results of XPS show that there are two peaks at different binding energies for the as-synthesized sample of Gly@UiO-66 (Figure a). The peak at 399.49 eV is related to the free -NH 2 sites, while the second peak at 401.37 eV originates from the presence of protonated amine (-NH 3 + ) sites. − According to the area under each peak, the amine groups of glycine are 29% in the free -NH 2 state and 71% in the -NH 3 + state while the XPS spectra of Gly@UiO-66 after the removal process display only one peak, 399.83 eV at pH 5 (Figure b) and 399.88 eV at pH 7 (Figure c). These peaks lie in the free -NH 2 region of energy. − This observation shows that the protonated -NH 3 + sites are deprotonated during removal to be coordinated to As­(III) species just like free -NH 2 sites.…”

Magnetic Adsorbents for Wastewater Treatment: Advancements in Their Synthesis Methods

“…Recently, more complex hybrid adsorbents have been synthesized using the co-precipitation method. Wan et al [ 91 ] reported the results of a humic acid/L-cysteine-codecorated magnetite that has complex properties, resulting from functional groups, ion exchange, and negatively charged surfaces. In another study, Amini et al [ 87 ] reported a novel composite, GO/Fe 3 O 4 /OPO 3 H 2 /PCN-222, that can extract U(VI) in 3 min, with a capacity of 416.7 mg/g.…”