Lysine-functionalized hydrated zirconium oxide hybrid material: Molecular-scale design for enhanced adsorption and sustainable removal of Cr(VI) and phosphate from wastewater

Chromium (Cr(VI)) and phosphate contaminants in wastewater pose severe threats to ecosystems and human health. To address this challenge, we engineered a novel molecular-scale organic-inorganic hybrid material (Lys-HZO) through facile integration of lysine (Lys) with hydrated zirconium oxide (HZO). The uniform anchoring of Lys within the HZO framework significantly enhances the material’s hydrophilicity, improving the accessibility of adsorption sites both internally and externally, thus overcoming the structural limitations of traditional HZO materials. The amino and hydroxyl groups in the material create a synergistic effect through multiple mechanisms, including electrostatic attraction, ligand exchange, and redox interactions, which collectively drive the adsorption process. Batch adsorption experiments showed that the material’s adsorption capacities for Cr(VI) and phosphate were 15 and 10 times higher, respectively, than those of pure HZO. Kinetic and isothermal adsorption analyses confirmed that adsorption is primarily governed by chemisorption, while thermodynamic studies indicated the adsorption process’s spontaneous and endothermic nature. In cyclic fixed-bed column experiments under competitive ion conditions, Lys-HZO demonstrated high adsorption capacity, treating 2532 bed volumes (BV) of phosphate-containing wastewater (3 mg P/L) and 726 BV of Cr(VI)-contaminated effluent (3 mg Cr(VI)/L). The treated effluent concentrations remained below regulatory limits: < 0.5 mg P/L and < 0.2 mg Cr(VI)/L, respectively. The innovative design strategy of "molecular-scale hybridization and site synergistic activation" proposed in this study not only fully unlocks the adsorption potential of HZO materials, but also provides novel insights for developing amino acid-functionalized metal oxide hybrid materials in the field of water treatment.