Phytic acid-engineered TiO₂/cellulose composite hydrogels featuring multidentate phosphate sites for efficient...

The development of polysaccharide-based hydrogels for selective metal recovery is often hindered by insufficient stability and poor spatial organization of functional binding sites, especially in competitive aqueous environments. Here, this paper presents an inorganic-anchored site-engineering strategy to address this gap by in situ embedding phytic acid-modified TiO₂ hybrid nanoparticles into a carboxymethyl cellulose/poly(acrylic acid) three-dimensional network. This approach yields a composite hydrogel (CAPT-gel) that integrates renewable polysaccharide scaffolds with robust, accessible, and well-dispersed multidentate phosphate binding sites, stabilized through Ti-phosphate interactions. The resulting material achieves high adsorption capacities of 223.25 mg/g for Cu(II) and 313.52 mg/g for La(III), with a pronounced selectivity toward La(III) in coexisting-ion systems. CAPT-gel also maintains over 80% capacity retention after five adsorption-desorption cycles, demonstrating good reusability. Spectroscopic analyses and DFT calculations reveal that adsorption arises from interfacial interactions, including multidentate phosphate coordination, carboxylate-driven electrostatic effects, and inner-sphere surface complexation. The interconnected transport pathways within the hydrogel facilitate efficient solute access and thereby promote the formation of such complexes. This work provides a green and effective route to engineer phosphate-rich binding environments in cellulose-based hydrogels for selective capture and recovery of heavy-metal/rare-earth ions, expanding the utility of polysaccharide-derived materials in environmental remediation and resource recycling.