The dissolution kinetic and structural behaviour of natural hydroxyapatite (N-HA) and synthetic hydroxyapatite (S-HA) was
studied vs. sintering temperature and using ‘in vitro’ experiments. Obtained results highlight the chemical stability of N-HA. Any structural
modification was observed until 1200°C. In the fact S-HA undergoes some modifications. XRD diagrams show the tricalcium phosphate
(TCP) phase formation between 800 and 1100°C and tetracalcium phosphate (TetCP) phase formation at 1200°C. The ‘in vitro’
assay shows that the dissolution was occurred more in N-HA than in S-HA. The formed TCP activated the dissolution kinetic
and then the precipitation phenomena when a continuous dissolution of TetCP leaded to slow down the kinetic precipitation. 相似文献
Two birds with one auric stone : The title system acts as a highly efficient heterogeneous catalyst for the one‐pot tandem synthesis of imines or oximes from alcohols and the corresponding amines under mild conditions (see scheme; HAP= hydroxyapatite).
An approach for the sensitive and selective determination of Ag+, Cu2+ and Hg2+ ions was developed based on the fluorescence quenching of mercaptopropionic acid (MPA) capped CdTe quantum dots in the existence of hydroxyapatite (HAP) nanoribbon spherulites. Among various metal ions investigated, it was found that the fluorescence of CdTe QDs was only sensitive to Ag+, Cu2+ and Hg2+ ions. The addition of HAP into the CdTe system could bring forward a sensitivity improvement of about 1 to 2 orders of magnitude in the detection of Ag+ and Cu2+ compared with the plain CdTe system without the existence of HAP; while there was no sensitization effect for Hg2+. Under optimal conditions, the detection limits for Ag+, Cu2+ and Hg2+ were 20, 56 and 3.0 nmol·L?1, respectively, and the linear ranges were 0.02–50, 0.056–54 and 0.003–2.4 µmol·L?1, respectively. Mechanisms of both QDs fluorescence quenching by metal ions and the sensitization effect by HAP were also discussed. 相似文献
Calcium hydroxyapatite powder was prepared by sol-gel method using calcium acetate and PO(OC2H5)3 as initial compounds, and alcohol (methyl, ethyl, and propyl-alcohol) as solvent. Homogeneous solution and gels were prepared
using a molar ratio of Ca/P=1.67. The evolution of the structure was detected by X-ray diffraction, IR, and FT-n(=1,2,3)D-EPR spectroscopy. The dried gels exhibit a signal characterized by a central line and two satellites. The 2D spectrum
(ESEEM vs. field sweep) showed the same modulation for the central line. The FT-EPR spectrum vs. field sweep 2D-spectrum indicated
that the satellites are due to an hfs splitting with water. The central region of this 2D spectrum is influenced by P and
H in a concentration ratio of [H]/[P]=2.5. The ESEEM spectrum was simulated assuming the equation Vmod=Vmod(P)mVmod(H)n for two spin systems S=1/2 and I=1/2. This simulation gave form andn the values of 2 and 5, respectively. This finding suggests the structure:
for the unpaired state. It appears that one ethyl group does not hydrolyse in the gelation process. The ESEEM spectra of
hydroxyapatite exhibit a modulation generated by P, H and Ca atoms. 相似文献
Sol-gel-derived hydroxyapatite (HA) precursors were calcined by two thermal processings, a rapid-thermal-calcine (RTC) heating at 100–600°C/min and a conventional-furnace-calcine (CFC) heating at 1.67°C/min, respectively. X-ray diffraction patterns revealed that the onset temperature of HA crystallization is lower in RTC, 350°C, as compared to 600°C in CFC. Pyrolytic-GC/MS programs showed that the evolved gases out of a sample subjected to RTC are mainly H2O, N2O and ethylamine, while those of a sample subjected to CFC are CO2 and small organic molecules. The results leads to models that RTC can quickly remove organic portion of the gel networks, leading to a porous surface morphology and a collapse of gel networks at local areas, so that HA crystallite nucleation is facilitated due to intimate contacts among inorganic species at lower temperatures. On the other hand, slow evolution of organics during CFC leads to carbonaceous residues that isolate the inorganic species and inhibit nucleation of HA crystallites until at a higher temperature. 相似文献
Novel heterogeneous catalysts, which were designed with atomic precision, easy to prepare, and recyclable, have been developed using a unique inorganic support hydroxyapatite, Ca10(PO4)6(OH)2. The introduction of a Ru cation into the apatite framework can generate a stable monomeric phosphate complex, which exhibits prominent catalytic performances for various oxidation reactions using molecular oxygen as a primary oxidant. Treatment of the RuHAP with an aqueous solution of AgX affords cationic Ru phosphate complexes as Lewis acid catalysts, promoting Diels–Alder and aldol reactions under mild and neutral conditions. Furthermore, two classes of heterogeneous Pd catalysts were synthesized with both stoichiometric and Ca-deficient hydroxyapatites, which show specific functions for aerobic oxidation of alcohols and carbon–carbon bond-forming reactions with extremely high turnover numbers. The catalytic systems described here are simple, efficient, and general for practical organic syntheses; thus meeting the increasing demands for environmentally-benign chemical processes. 相似文献
IR spectroscopy was used to study the modification of hydroxyapatite by potassium ferrocyanide and the interaction of transition metal ions with the modified adsorbent. The structural changes of hydroxyapatite upon the adsorption of Zn2+ ions were studied by X-ray phase analysis. Potassium ferrocyanide was found to interact with the surface hydroxyl groups of hydroxyapatite through the nitrogen unshared electron pair. Co2+, Ni2+, and Zn2+ ions were found to eliminate outer-sphere K+ ions of adsorbed ferrocyanide to give Fe2+— CN—M2+— NC—Fe2+ bridging structures. Zn2+ cations additionally eliminate a part of the Ca2+ ions from structural positions of hydroxyapatite, which leads to the appearance of a two-phase hydroxyapatite–sholzite system with heterogeneous distribution of the Ca2+ ions in the mot her mineral phase, while the Zr2+ ions are found in the new sholzite phase. 相似文献