Kazuhiko Kandori

Surface silanol groups of mesoporous silica FSM-16

The surface structure of mesoporous silica crystals FSM-16 with a narrowly distributed pore size has been studied by FTIR, measurement of SiOH number and adsorption of N2 and H2O. IR spectra of FSM-16 outgassed at temperatures above 170 °C showed a sharp band at 3740 cm–1 due to free SiOH and a broad shoulder at 3600–3500 cm–1 due to hydrogen-bonded SiOH. The SiOH number, determined by a weight-loss method, amounted to 3.3 groups nm–2, which is less than that of mesoporous silica gels. The amount of H2O adsorbed on FSM-16 decreased with calcination above 800 °C, owing to the dehydroxylation of SiOH. On treating with alcohol, the number of free SiOH decreased, leading to a decrease in H2O adsorption. The crystallinity of FSM-16 was lowered by pressing. With increasing pressure the specific surface area decreased and the SiOH number increased, up to 9.5 groups nm–2.

Preparation and characterization of magnesium–calcium hydroxyapatites

Magnesium–calcium hydroxyapatite (MgCaHAP) solid solutions have been prepared by a wet method from aqueous solutions with different molar ratios, Mg/(Mg + Ca), ranging from 0 to 0.5. The MgCaHAP particles formed were characterized by XRD, FTIR, TEM, TCP, TG-DTA and gas adsorption techniques. The Mg/(Mg + Ca) ratios of the formed MgCaHAP particles were less than those of the starting solutions. With increasing Mg content, the particles became less crystalline and agglomerates of the fine crystals and finally the products were amorphous at Mg/(Mg + Ca)>0.31. The amount of irreversible adsorption of CO2 and CH3OH showed a minimum at a molar ratio (Mg + Ca)/P of ca. 1.56, less than the stoichiometric ratio of 1.67.

Surface structure and composition of calcium hydroxyapatites substituted with Al(III), La(III) and Fe(III) ions

Abstract Synthetic calcium hydroxyapatite (CaHap) particles were modified by ionexchange with Al(III), La(III) and Fe(III) by the coprecipitation and immersion methods. The growth of CaHap particles was observed on substituting with these metal ions by coprecipitation. The exchange ratios of Ca(II) with the metal ions revealed that Fe(III) replaces Ca(II) as hydroxo ions and the substitution with La(III) accompanies OH − -deficiency. In the substitution with immersion the exchange ratios for all the metal ions were less than 1.5 of the theoretical ratio, verifying the exchange with metal hydroxo ions. IR spectra of the CaHap particles substituted with Al(III) by both the methods gave rise to several bands due to surface Al-OH besides the surface P-OH bands, whereas the CaHap substituted with La(III) showed no surface La-OH band. The surface Fe-OH was found on the CaHaps substituted by the coprecipitation but not on those substituted by the immersion.

FTIR STUDY ON INCORPORATION OF CO2 INTO CALCIUM HYDROXYAPATITE

Calcium hydroxyapatite (CaHAP) particles were prepared by precipitation reactions of Ca(OH)2 and H3PO4 at different pH. Incorporation of CO2 into CaHAP during the preparation was investigated mainly by FTIR spectroscopy. The amount of CO32− ions contained in the formed CaHAP was increased by raising the solution pH. IR bands of the CO32− ions incorporated into CaHAP were assigned by means of CO2 adsorption. The 1414, 1447 and 1500 cm−1 bands were assignable to CO32− ions in OH− sites of the CaHAP crystals and the 1457 and 1550 cm−1 bands to CO32− ions in PO43− sites. This assignment is different from those in the literature. FTIR results demonstrated that the inclusion of CO32− ions in PO43− sites is maximum for CaHAP formed at pH 5.94 and that in OH− sites increases as the solution pH rises.

Surface composition of calcium hydroxyapatite modified with metal ions

Abstract Colloidal calcium hydroxyapatite (CaHAP) particles were modified with Ni 2+ , Cu 2+ , Co 2+ and Cr 3+ ions by ion-exchange and coprecipitation. The CaHAPs doped with these ions were characterized by various methods including FTIR, XPS, TEM and ICP. The atomic ratio, metal/(Ca+metal), of the surface phase ( X s ) of the particles modified with Ni 2+ and Cu 2+ by coprecipitation was much less than the atomic ratio of the whole particle ( X w ), while X s of the particles modified with Cr 3+ approximated to their X w . In the modification by ion-exchange, X s was larger than X w except for the Ni 2+ -substituted samples where X s was identical to X w . The surface P–OH groups were decreased by cation-exchange of the protons of the P–OH groups with Ni 2+ , Cu 2+ and Co 2+ in both the modification methods. On the other hand, Cr 3+ ions were doped in the surface phase by anion-exchange of the surface phosphate ions with hydrated chromium hydroxide anions.

Adsorption of bovine serum albumin onto synthetic calcium hydroxyapatite: influence of particle texture

Abstract Calcium hydroxyapatites (CaHAPs), with particle lengths varying from 27 to 103 nm but similar widths of about 15 nm, were synthesized, and the adsorption behavior of bovine serum albumin (BSA) on these synthetic CaHAPs was investigated at pH 6.0 and 15°C. The size of the synthetic CaHAP particles increased on increasing the concentration of H 3 PO 4 in the aging solution. The adsorption isotherms of BSA on CaHAPs were pseudo-Langmuir type. The saturated amounts of adsorbed BSA ( n s ), which are the plateau values of the adsorption isotherms, increased with an increase in particle length of the CaHAPs. However, no relationship was found between n s and the molar ratio of calcium to phosphorus in CaHAP particles. These results suggest that the particle texture is significant in the adsorption of BSA. The large rod-like particles with flat surfaces are advantageous for the adsorption of negatively charged BSA by the large number of positively charged adsorption sites on the exposed ac or bc crystal faces.

Formation of magnetite in the presence of ferric oxyhydroxides

Abstract The products of the reactions of ferric oxyhydroxides ( α -, β - and γ -FeOOH) with ferrous species in O 2 -free aqueous systems containing Cl − were characterized by XRD, FTIR and TEM. The reactions using all the FeOOH gave Fe 3 O 4 at 25–100°C and a wide pH range from 3 to 13, accompanying a depletion of FeOOH. The yield of Fe 3 O 4 depended on the molar ratio of OH\Fe(II) in the suspensions, showing a maximum at OH\Fe(II) = 2. The maximum yield of Fe 3 O 4 was in the order of β -FeOOH> γ -FeOOH≫ α -FeOOH. It was revealed that Fe 3 O 4 is formed by the reactions of the dissolved species of Fe(OH) 2 with those of FeOOH.

Study on the particle texture dependence of protein adsorption by using synthetic micrometer-sized calcium hydroxyapatite particles

Abstract Rod-like calcium hydroxyapatites (Hap) with micrometer size were produced by supplying Ca(CH 3 COO) 2 and NH 4 H 2 PO 4 solutions into a CH 3 COONH 4 solution by varying their feeding rate at 85±5 °C and pH 7.4±0.2 under nitrogen atmosphere and vigorously stirring. The size of the Hap particles was increased with increase in feeding time ( t F ) of the solutions; with increase in the t F the mean particle width and lengths were increased from 0.02 to 0.47 μm and from 0.12 to 5.21 μm, respectively. All these particles were highly crystallized and exhibited a single crystal and Ca-deficient natures with Ca/P atomic ratios of 1.50–1.59. TG and chemical analyses indicated that the chemical composition of the particles can be expressed to Ca 10− x − y (HPO 4 ) x (PO 4 ) 6− x (OH) 2− x −2 y  ·  n H 2 O. The amount of adsorbed bovine serum albumin (BSA) onto the synthesized micrometer-sized Hap particles is strongly dependent upon their mean particle length ( L p ), while that of lysozyme (LSZ) onto the Hap particles exhibited a minor dependence on the L p . This protein adsorption behavior observed in the present paper provided a definitive evidence that the C sites exposed on ac or bc crystal faces are the adsorption sites for BSA.

Influences of metal ions on the formation of β-FeOOH particles

Abstract β-FeOOH particles were synthesized from aqueous FeCl 3 solutions added with different metal ions of Ti(IV), Cr(III), Cu(II) and Ni(II) at varied atomic ratios (metal/Fe) of 0–0.1. Ti(IV) was much more incorporated into the formed particles than Cr(III), Cu(II) and Ni(II). Ti(IV) drastically influences the crystallization and particle growth of β-FeOOH, whereas the other metal ions exhibited no marked effect. This result is available for interpretation of the function of Ti in raising resistance to atmospheric corrosion of steels in chloride environments.

Surface modification of calcium hydroxyapatite with hexyl and decyl phosphates

Abstract The surface of synthetic calcium hydroxyapatite Ca10(PO4)6(OH)2 (CaHAP), modified by monohexyl phosphate (HP) and monodecyl phosphate (DP) in acetone at 25°C, has been examined by various methods. The X-ray diffraction (XRD) patterns of the materials modified with HP at less than 0.10 mol dm−3 or DP at less than 0.15 mol dm−3 were almost the same as that of the unmodified material. The particle morphology was not changed by the modification. The number of alkyl groups of the modified materials was about two groups per nm2. These alkyl groups were removed by outgassing above 300°C. After this treatment the modified materials exhibited a larger number of surface POH groups and a higher negative electrophoretic mobility compared with the unmodified material. The materials with alkyl groups adsorbed much less H2O and CO2 than the unmodified material.