Evaluation of the effectiveness of silver-coated alkali-activated ceramic for removal of fluoride ions in water

Fluoride contamination in drinking water is a major public health concern, common within deprived communities where groundwater supplies routinely exceed the limit of 1.5 mg/L recommended by the World Health Organization. Long-term exposure to high fluoride concentrations is linked to dental and skeletal fluorosis, neurological impacts, and other chronic health disorders, making the development of effective low-cost water treatment materials a necessity. This study investigated a novel silver-coated alkali-activated ceramic adsorbent (AgAACA) for fluoride removal from water. AgAACA exhibited favorable adsorption properties, including a high water-holding capacity (3.69 g/g). Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDX) analyses confirmed the aluminosilicate ceramic structure and silver surface modification. In batch adsorption experiments, AgAACA demonstrated rapid and effective fluoride uptake, achieving an equilibrium removal rate of 89.95% and a capacity of 22.49 mg/g under optimal conditions (pH of 8 and 298 K). Kinetic studies indicated that the adsorption process is surface-controlled and was best described by the pseudo-second-order kinetic model. The Elovich model (with a determination coefficient of 0.995) further suggested the presence of heterogeneous binding sites. Equilibrium data aligned most closely with the Freundlich isotherm, while the Langmuir model estimated a maximum monolayer capacity of 66.65 mg/g. Thermodynamic parameters (with enthalpy of −53.83 kJ/mol, entropy of −0.176 kJ/(mol·K), and negative Gibbs free energy values at low temperatures) indicated that the adsorption process is exothermic and spontaneous, dominated by chemisorption at Ag-functionalized sites.