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Title: Synthesis of amorphous calcium phosphate using various types of cyclodextrins

Abstract

Amorphous calcium phosphate (ACP) was synthesised in aqueous solution at room temperature using cyclodextrins. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and thermal analysis (DTA/TGA) were performed on the calcium phosphate precipitates obtained from solutions. We observed that only {beta}-CD could stabilise the amorphous phase in the mother solution because of the lower solubility of {beta}-CD in water and the ACP remained stable in aqueous solution for more than 24 h at room temperature. The ACP particle has an initial particle size of less than 40 nm, Ca/P molar ratio of 1.67 and {beta}-CD absorbed on its surface. The mechanism for the stabilisation of ACP is proposed.

Authors:
 [1];  [1];  [2]
  1. Singapore-MIT Alliance, School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore)
  2. Singapore-MIT Alliance, School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore). E-mail: mkctam@ntu.edu.sg
Publication Date:
OSTI Identifier:
21000628
Resource Type:
Journal Article
Resource Relation:
Journal Name: Materials Research Bulletin; Journal Volume: 42; Journal Issue: 5; Other Information: DOI: 10.1016/j.materresbull.2006.08.027; PII: S0025-5408(06)00355-2; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; AMORPHOUS STATE; AQUEOUS SOLUTIONS; CALCIUM PHOSPHATES; CHEMICAL PREPARATION; DIFFERENTIAL THERMAL ANALYSIS; FOURIER TRANSFORMATION; INFRARED SPECTRA; NANOSTRUCTURES; PARTICLE SIZE; PARTICLES; PRECIPITATION; SOLUBILITY; TEMPERATURE RANGE 0273-0400 K; THERMAL GRAVIMETRIC ANALYSIS; TRANSMISSION ELECTRON MICROSCOPY; X-RAY DIFFRACTION; X-RAY SPECTROSCOPY

Citation Formats

Li Yanbao, Wiliana, Tjandra, and Tam, Kam C. Synthesis of amorphous calcium phosphate using various types of cyclodextrins. United States: N. p., 2007. Web.
Li Yanbao, Wiliana, Tjandra, & Tam, Kam C. Synthesis of amorphous calcium phosphate using various types of cyclodextrins. United States.
Li Yanbao, Wiliana, Tjandra, and Tam, Kam C. Thu . "Synthesis of amorphous calcium phosphate using various types of cyclodextrins". United States. doi:.
@article{osti_21000628,
title = {Synthesis of amorphous calcium phosphate using various types of cyclodextrins},
author = {Li Yanbao and Wiliana, Tjandra and Tam, Kam C.},
abstractNote = {Amorphous calcium phosphate (ACP) was synthesised in aqueous solution at room temperature using cyclodextrins. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and thermal analysis (DTA/TGA) were performed on the calcium phosphate precipitates obtained from solutions. We observed that only {beta}-CD could stabilise the amorphous phase in the mother solution because of the lower solubility of {beta}-CD in water and the ACP remained stable in aqueous solution for more than 24 h at room temperature. The ACP particle has an initial particle size of less than 40 nm, Ca/P molar ratio of 1.67 and {beta}-CD absorbed on its surface. The mechanism for the stabilisation of ACP is proposed.},
doi = {},
journal = {Materials Research Bulletin},
number = 5,
volume = 42,
place = {United States},
year = {Thu May 03 00:00:00 EDT 2007},
month = {Thu May 03 00:00:00 EDT 2007}
}
  • The mobility of uranium in subsurface environments depends strongly on its redox state, with U IV phases being significantly less soluble than U VI minerals. This study compares the oxidation kinetics and mechanisms of two potential products of U VI reduction in natural systems, a nanoparticulate UO 2 phase and an amorphous U IV–Ca–PO 4 analog to ningyoite (CaU IV(PO 4) 2·1–2H 2O). The valence of U was tracked by X-ray absorption near-edge spectroscopy (XANES), showing similar oxidation rate constants for U IVO 2 and U IV–phosphate in solutions equilibrated with atmospheric O 2 and CO 2 at pH 7.0more » (k obs,UO2 = 0.17 ± 0.075 h -1 vs. k obs,U IV PO4 = 0.30 ± 0.25 h -1). Addition of up to 400 μM Ca and PO 4 decreased the oxidation rate constant by an order of magnitude for both UO 2 and U IV–phosphate. The intermediates and products of oxidation were tracked by electron microscopy, powder X-ray diffraction (pXRD), and extended X-ray absorption fine-structure spectroscopy (EXAFS). In the absence of Ca or PO 4, the product of UO 2 oxidation is Na–uranyl oxyhydroxide (under environmentally relevant concentrations of sodium, 15 mM NaClO 4 and low carbonate concentration), resulting in low concentrations of dissolved U VI (<2.5 × 10 -7 M). Oxidation of U IV–phosphate produced a Na-autunite phase (Na 2(UO 2)PO 4·xH 2O), resulting in similarly low dissolved U concentrations (<7.3 × 10 -8 M). When Ca and PO 4 are present in the solution, the EXAFS data and the solubility of the UVI phase resulting from oxidation of UO 2 and UIV–phosphate are consistent with the precipitation of Na-autunite. Bicarbonate extractions and Ca K-edge X-ray absorption spectroscopy of oxidized solids indicate the formation of a Ca–UVI–PO 4 layer on the UO 2 surface and suggest a passivation layer mechanism for the decreased rate of UO 2 oxidation in the presence of Ca and PO 4. Interestingly, the extractions were unable to remove all of the oxidized U from partially oxidized UO 2 solids, suggesting that oxidized U is distributed between the interior of the UO 2 nanoparticles and the labile surface layer. Accounting for the entire pool of oxidized U by XANES is the likely reason for the higher UO 2 oxidation rate constants determined here relative to prior studies. In conclusion, our results suggest that the natural presence or addition of Ca and PO 4 in groundwater could slow the rates of U IV oxidation, but that the rates are still fast enough to cause complete oxidation of U IV within days under fully oxygenated conditions.« less
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