Aqueous-phase fabrication of cellulose-mineral composites with enhanced Cd(II) adsorption and mechanistic insights

In this study, a green and sustainable synthesis strategy was developed to fabricate cellulose-based composite adsorbents by replacing the organic dispersion system previously used with an aqueous medium. Two inorganic fillers, sepiolite and TiO₂, were respectively incorporated to prepare cellulose-sepiolite (CgS(H₂O)) and cellulose-TiO₂ (CgT(H₂O)) composites, aiming to investigate the influence of mineral type and dispersion phase on Cd(II) adsorption performance and mechanism. Compared to the earlier reported CAT material synthesized in organic media, both aqueous-phase composites showed enhanced porosity, surface functionality, and carboxyl group distribution. CgS(H₂O) exhibited a fluffy, porous network structure with high micro/mesopore connectivity, achieving a maximum Cd(II) capacity of 239.45 mg/g. CgT(H₂O), with higher surface area and Ti–O active sites, demonstrated the highest capacity of 368.82 mg/g, significantly surpassing CAT (105 mg/g). Kinetic and isotherm analysis revealed that CgS(H₂O) followed multilayer chemisorption, while CgT(H₂O) conformed to monolayer Langmuir-type adsorption. Density functional theory (DFT) simulations further indicated stronger binding affinities and more active carboxyl-dominant sites in CgT(H₂O), while CgS(H₂O) benefited from networked carboxyl groups and Si–O-based interaction domains. These findings collectively highlight that the aqueous dispersion strategy, combined with targeted mineral selection, enhances not only environmental friendliness but also material structure and adsorption efficiency, offering a versatile platform for efficient heavy metal removal from water.