This study elucidates the adsorption mechanism of fluoride removal by thermally treated eggshells (ES-800) using advanced surface characterization techniques. X-ray photoelectron spectroscopy (XPS) analysis was conducted before and after fluoride adsorption to identify chemical changes on the surface. In the untreated ES-800, the Ca2p peak at 346.2 eV corresponded to CaCO₃, while a second peak at 347.1 eV was attributed to Ca(OH)₂. The C1s spectrum showed peaks at 285.0 eV (C–H/C–C) and 289.3 eV (CO₃²⁻), and O1s exhibited a dominant signal at 531.2 eV, consistent with carbonate species. Notably, no F1s signal was detected in the pre-adsorption sample.
After fluoride exposure, significant spectral changes were observed. The Ca2p region developed new peaks at 347.8 eV and 351.4 eV, characteristic of CaF₂, indicating successful formation of calcium fluoride. Concurrently, the intensity of the Ca(OH)₂ peak diminished, and the CaCO₃ signal decreased, suggesting consumption of calcium compounds in the reaction.Laropiprant custom synthesis No notable shifts were observed in the C1s or O1s spectra, confirming that organic components remained largely unaffected. The F1s peak appeared at 684.8 eV, matching the binding energy of fluorine in CaF₂.
Complementary X-ray diffraction (XRD) analysis confirmed the presence of crystalline CaF₂ on the surface of fluoride-loaded ES-800, with distinct diffraction peaks absent in the original material. This provides direct evidence that fluoride removal occurs primarily through precipitation rather than surface adsorption alone. The transformation of Ca(OH)₂ and CaO into CaF₂ is driven by the high reactivity of these phases formed during thermal treatment above 800 °C. The dissolution of calcium ions from the solid matrix facilitates the formation of insoluble CaF₂, which precipitates out of solution.
These results conclusively demonstrate that fluoride removal by ES-800 is governed by a precipitation mechanism involving calcium-based compounds.3-Methyl-2-cyclohexen-1-one medchemexpress The structural and chemical evolution induced by thermal activation enables the conversion of stable calcite into reactive calcium hydroxide and oxide, which readily react with fluoride ions to form CaF₂.PMID:34464866 This process not only explains the high adsorption capacity but also highlights the importance of thermal treatment in unlocking the functional potential of eggshell waste. The findings validate ES-800 as a chemically active, sustainable material for effective defluoridation.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com