Sandström Dan E, Jarlbring Mathias, Antzutkin Oleg N, Forsling Willis
Department of Chemical Engineering and Geoscience, Division of Chemistry, Luleå University of Technology, SE-97187 Luleå, Sweden.
Langmuir. 2006 Dec 19;22(26):11060-4. doi: 10.1021/la0602158.
Assignments of the protolytic speciation at the calcium hydroxyl surface sites of synthetic fluorapatite and the chemical interactions between fluorapatite-maghemite and fluorapatite-Fe2+ ions have been studied by means of 1H and 31P single-pulse and 31P CP MAS NMR. Three possible forms of calcium hydroxyl surface sites have been suggested and assigned to [triple bond] CaOH, [triple bond]Ca(OH)2-, and [triple bond]CaOH2+, and their mutual ratios were found to vary as a function of pH. Due to their paramagnetic properties, iron species and Fe2+ ions adsorbed at the fluorapatite surface display a broad spinning sideband manifold in the single-pulse 31P MAS NMR spectra. The resonance lines in the 31P CP MAS NMR spectra originating from the bulk phosphate groups PO4(3-) and phosphorus surface sites [triple bond]POx and [triple bond]POxH decrease with increasing Fe2+ ion adsorption. When iron species originating from maghemite are adsorbed at the fluorapatite surface, no 31P NMR signal is detected, which supports the hypothesis that surface reactions occur between the phosphorus surface sites of fluorapatite and iron species.
通过¹H和³¹P单脉冲以及³¹P交叉极化魔角旋转核磁共振（CP MAS NMR）研究了合成氟磷灰石钙羟基表面位点的质子化形态以及氟磷灰石 - 磁赤铁矿和氟磷灰石 - Fe²⁺离子之间的化学相互作用。已提出钙羟基表面位点的三种可能形式，并将其指定为[三键]CaOH、[三键]Ca(OH)₂⁻和[三键]CaOH₂⁺，发现它们的相互比例随pH值变化。由于其顺磁性质，吸附在氟磷灰石表面的铁物种和Fe²⁺离子在单脉冲³¹P MAS NMR光谱中显示出宽的旋转边带多重峰。³¹P CP MAS NMR光谱中源自本体磷酸根基团PO₄³⁻以及磷表面位点[三键]POₓ和[三键]POₓH的共振线随着Fe²⁺离子吸附的增加而降低。当源自磁赤铁矿的铁物种吸附在氟磷灰石表面时，未检测到³¹P NMR信号，这支持了氟磷灰石的磷表面位点与铁物种之间发生表面反应的假设。
