Molecular-scale investigation of fluoride sorption mechanism by nanosized hydroxyapatite using 19F solid-state NMR spectroscopy
| Autor: | Wei Li, Chao Ren, Zhiwu Yu, Junfeng Ji, Bingcai Pan, Hongtao Wang, Brian L. Phillips |
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| Rok vydání: | 2019 |
| Předmět: |
Chemistry
Fluorapatite Sorption 02 engineering and technology Fluorine-19 NMR Nuclear magnetic resonance spectroscopy 010402 general chemistry 021001 nanoscience & nanotechnology 01 natural sciences 0104 chemical sciences Surfaces Coatings and Films Electronic Optical and Magnetic Materials Biomaterials chemistry.chemical_compound Colloid and Surface Chemistry Solid-state nuclear magnetic resonance Proton NMR 0210 nano-technology Fluoride Nuclear chemistry Solid solution |
| Zdroj: | Journal of Colloid and Interface Science. 557:357-366 |
| ISSN: | 0021-9797 |
| DOI: | 10.1016/j.jcis.2019.09.039 |
| Popis: | Hydroxyapatite (Hap) has been shown to be an excellent sorbent for F− removal of elevated levels of fluoride in groundwater worldwide; however, the molecular mechanisms of this process have not been clearly addressed. Herein, we used 19F solid-state NMR spectroscopy to investigate F− sorption mechanisms by nanosized Hap combined with 1H NMR and 1H{19F} Rotational Echo DOble Resonance (REDOR) technology in addition to other characterization methods such as Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD) and Nanoscale Secondary Ion Mass Spectroscopy (NanoSIMS). Our experimental results showed that F− sorption mechanisms depend on solution pH and fluoride concentration ([F−]). At pH 7 and [F−] ≤ 50 mM, a single 19F NMR peak at −103 ppm was observed, which could be assigned to fluorapatite [Ca5(PO4)3F] (Fap) or fluoro-hydroxyapatite solid solution [Ca5(PO4)3Fx(OH)1−x; x = 0–1] (F-Hap). A simultaneous formation of fluorite (CaF2) precipitates (δF-19 = −108 ppm) was observed at higher [F−] (e.g., 100 mM), which was further confirmed by TEM and XRD analysis. The NanoSIMS and 1H{19F} REDOR analyses indicated that a dissolution-precipitation process was involved in the F− sorption on Hap. Our results strongly support the efficacy of Hap for F− removal even after several instances of regeneration, making it a cost-effective strategy for fluoride treatment. |
| Databáze: | OpenAIRE |
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