Optimizing the fluoride removal from drinking water through adsorption with mesoporous magnetic calcite nanocomposites

Abstract

Fluoride (F−) contamination in groundwater is a global concern arising from natural processes and human activities. This study investigates the adsorption of F− using surface-activated magnetic calcite nanocomposites (NCs) synthesized via co-precipitation assisted wet-impregnation (CP-WI). Various Fe3O4 loadings and calcination temperatures (300 °C and 500 °C) were explored to optimize synthesis parameters. Batch adsorption experiments were conducted to assess the performance of synthesized nanoparticles (NPs) and nanocomposites (NCs). BET, FTIR spectroscopy, X-ray diffraction, and SEM characterization techniques were employed to analyze the physicochemical properties, including surface functional groups, crystallite size, and morphology. The adsorption process was investigated using RSM statistical design with adsorbent dose (A) and F− concentration (B) as independent variables. 0.5Fe-C-NC-5, calcined at 500 °C, exhibited superior adsorption capacity (7.81 mg/g) compared to Fe3O4 and calcite NPs (6.57 mg/g and 6.81 mg/g, respectively). Maximum F− adsorption occurred within 10 min of contact time. NPs and NCs that were exposed to higher calcination temperatures, reaching up to 500 °C, showed an increase in crystallite development while experiencing a reduction in surface area and an enlargement of pore size compared to those treated at lower temperatures. The BET analysis revealed a narrow, slit-like mix of microporous and mesoporous surface with a type IV isotherm and H3 hysteresis loop, indicating multilayer adsorption followed by capillary condensation. The SEM images displayed columnar shapes of CaCO3 polymorph in the prepared Fe3O4-calcite NP and Fe–C NP, which can be attributed to lower calcination or synthesis temperatures.

Keywords

• Magnetic nanoparticles
• Fluoride
• Calcite nanocomposites
• Response surface methodology
• Groundwater contamination
• Batch adsorption