A novel magnetic Fe₃O₄/cellulose nanofiber/polyethyleneimine/thiol-modified montmorillonite aerogel for efficient removal of heavy metal ions: Adsorption behavior and mechanism study

To efficiently remove heavy metals from wastewater, designing an adsorbent with high adsorption capacity and ease of recovery is necessary. This paper presents a novel magnetic hybridized aerogel, Fe₃O₄/cellulose nanofiber/polyethyleneimine/thiol-modified montmorillonite (Fe₃O₄/CNF/PEI/SHMMT), and explores its adsorption performance and mechanism for Pb²⁺, Cu²⁺, and Cd²⁺ in aqueous solutions. The hybrid aerogel has a slit-like porous structure and numerous exposed active sites, which facilitates the uptake of metal ions by adsorption. Pb²⁺, Cu²⁺, and Cd²⁺ adsorption by the hybridized aerogel followed the second-order kinetics and the Langmuir isotherm model, the maximum adsorption of Pb²⁺, Cu²⁺, and Cd²⁺ at 25 °C, pH = 6, 800 mg/L was 429.18, 381.68 and 299.40 mg/g, respectively. The adsorption process was primarily attributed to monolayer chemical adsorption, a spontaneous heat-absorption reaction. FTIR, XPS and DFT studies confirmed that the adsorption mechanisms of Fe₃O₄/CNF/PEI/SHMMT on Pb²⁺, Cu²⁺, and Cd²⁺ were mainly chelation, coordination, and ion exchange. The lowest adsorption energy of Pb²⁺ on the hybrid aerogel was calculated to be -2.37 Ha by DFT, which indicates that the sample has higher adsorption affinity and preferential selectivity for Pb²⁺. After 5 cycles, the adsorption efficiency of the aerogel was still >85 %. The incorporation of Fe₃O₄ improved the mechanical properties of the aerogel. The Fe₃O₄/CNF/PEI/SHMMT has fast magnetic responsiveness, and it is easy to be separated and recovered after adsorption, which is a promising potential for the treatment of heavy metal ions.