Amino/thiol-functionalized silica from coal fly ash for Cu²⁺ removal

The pollution incurred by heavy metal Cu²⁺ jeopardizes ecology and human health by means of persistence and bioaccumulation. Hence, the pollution control necessitates the development of efficient and cost-effective adsorbent materials. In this study, mesoporous silica (MS) materials were prepared via sintering-acid leaching combined with the sol-gel method using power plant Coal fly ash (CFA). These substances were chemically grafted with 3-aminopropyltriethoxysilane (APTES) and (3-mercaptopropyl) trimethoxysilane (KH-590), yielding amino-functionalized (MS-NH₂) and thiol-functionalized (MS-SH) materials. The effects of dosage, pH, concentration, and contact time on adsorption were examined. Material structure and adsorption mechanisms were dissected by virtue of Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS), and Brunauer-Emmett-Teller (BET) characterization techniques. Kinetic and isotherm models were leveraged to delineate adsorption behavior patterns. As manifested by the results, the Si-O-Si framework structure of MS remained intact after modification. Under optimized conditions, the adsorption capacities of MS-NH₂ and MS-SH for Cu²⁺ attained 38.05 mg/g and 58.25 mg/g, respectively, accompanied by superior performance of MS-SH. Efficient Cu²⁺ removal was accomplished by the adsorption mechanism, involving synergistic complexation, electrostatic adsorption, and ion exchange processes. Kinetic fitting revealed that adsorption followed the pseudo-second-order model, whereas isotherm data conformed better to the Freundlich model. The theoretical maximum adsorption capacity of MS-SH (120.07 mg/g) was dramatically higher than that of MS-NH₂ (93.01 mg/g). This research delivers novel functional materials and theoretical foundations for exploiting Coal fly ash resources and remedying heavy metal-contaminated water.