In this study, fundamental experiments on the adsorption behavior of proteins on synthesized magnesium-doped calcium hydroxyapatite particles (MgHap) at various Mg/(Ca + Mg) molar ratios (abbreviated as X_Mg : 0–0.3) were examined. Rod-like calcium hydroxyapatite particles, with a width of 24 nm and length of 180 nm, were obtained in the absence of Mg²⁺ (X_Mg = 0). With the increase in X_Mg up to 0.10, the width and length of MgHap particles decreased to ~10 and 50 nm, respectively. Agglomerates of small thin particles were obtained at X_Mg ≥ 0.15. All of the synthesized particles exhibited single phase of calcium hydroxyapatite particles (CaHap). The X_Mg values for the particles precipitated at X_Mg ≥ 0.04 were less than those of the corresponding solutions. Hence, almost all of the MgHap particles are deficient in magnesium. We propose that to compensate for the cation deficiency, PO₄^3- is incorporated as HPO₄^2- and H₂PO₄^- and thus decreases the particle negative charge. In addition, all of the adsorption isotherms of typical acidic and basic proteins such as bovine serum albumin (BSA) and lysozyme (LSZ) were compared. The isotherms obtained from a 1 × 10⁻⁴ mol/dm³ KCl solution were of the Langmuirian type. The saturated amount of adsorbed BSA (n_s^BSA) strongly depended on the particle length rather than on the X_Mg value. At a particle length of greater than 150 nm, n_s^BSA values abruptly increased. This result strongly suggests that the effects of the C sites produced on the ac and bc faces are advantageous for BSA adsorption. In other words, the adsorption of BSA on MgHap particles was considerably dependent on the length at a critical value of greater than 150 nm. However, the saturated amount of adsorbed LSZ (n_s^LSZ) exhibited no remarkable variation with the particle length.

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Hydroxyapatite (HAp)/zeolite composite (HZc) was prepared by a simple immersion method, and it was then modified with Cu²⁺ and 3-aminoplopyltriethoxysilane (APES) to produce a novel adsorbent for unpleasant odors such as NH₃, H₂S and CH₃CHO gases. The obtained materials were characterized by SEM-EDS, XRD, FT-IR, TG-DTA and ninhydrin reaction test. Nano-sized order HAp was observed distributed on zeolite for HZc, and modification of HZc with Cu²⁺ and APES maintained the original framework structure of HZc. Introduced amount of Cu²⁺ and APES after the modification was 3.6 mol% and 12.6 mg·g^-1, respectively. The adsorption ability evaluated via a gas bag-detection tube method showed that Cu²⁺-modified HZc increased NH₃ and H₂S adsorption ability, and APES-modified HZc enhanced CH₃CHO adsorption ability in comparison to unmodified one, respectively. Sequential modification of HZc with Cu²⁺ and APES also maintained H₂S and NH₃ adsorption ability, but decreased CH₃CHO adsorption ability. This suggests that adsorption sites for CH₃CHO were impeded in case of formation of Cu-N coordinate bond derived from direct interaction between Cu²⁺ and amino groups of APES. Therefore, use of HZc individually modified with Cu²⁺ and APES is recommended to capture multiple unpleasant odors.

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Zinc chloroapatite (ZnClAp), a promising material for bone treatment, was synthesized by a mechanochemical method. The effect of synthesis condition on its crystallinity was investigated. Starting materials (i.e., calcium monohydrogen phosphate dihydrate, calcium oxide, zinc oxide and calcium chloride) were kneaded with water at four kinds of water/solid ratios in a planetary ball-mill. Thus obtained products were analyzed by a powder X-ray diffractometry (PXRD) and an attenuated total reflection - infrared (ATR-IR) spectroscopy. The PXRD and ATR-IR results indicate that ZnClAp has successfully been synthesized by the present method. PXRD results indicate that the crystallinity of ZnClAp increases with the water/solid ratio of the kneaded paste for the synthesis. This finding is supported by a principal component analysis (PCA) that is applied to the ATR-IR spectra. The present mechanochemical method is simple, economy, and is useful for the synthesis of ZnClAp.

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Photo-Fenton reaction as an advanced oxidation process for water purification was investigated in water by using a heterogeneous iron-apatite hybridized catalyst, Fe(III)-treated hydroxyapatite (HAP-400-Fe), which was further modified with humic substance, Wako humic acid (WHA), Nordic aquatic humic acid (NHA), or Nordic aquatic fulvic acid (NFA). The substrates employed in the reaction were organic dyes, methyl orange (MO) and alizarin red S (ARS), and an herbicide, atrazine (ATZ). HAP-400-Fe catalyst modified with NHA or NFA, HAP-400-Fe-NHA or HAP-400-Fe-NFA, considerably enhanced substrate consumptions in comparison with the raw HAP-400-Fe. Particularly, HAP-400-Fe-NFA indicated complete consumptions (>99%) of all the three substrates for 24 h, and exhibited higher mineralization values of MO (41%) and ARS (68%). After the reaction, it was found that the surface NFA modifier on HAP-400-Fe had been subjected to oxidative degradation to some extent, and that catalytic activity of HAP-400-Fe-NFA had been lowered to the same activity as the raw HAP-400-Fe: The modifier can afford catalytic acceleration involving its own oxidative structural degradation, namely self-sacrifice. However, the deteriorated HAP-400-Fe-NFA could be remediated by re-adsorption treatment with NFA, and the remediated catalyst could feature the same effective catalytic activity as HAP-400-Fe. The catalyst recycling through remediation and reusing was extended to at least 4 times under the same photo-Fenton condition. A kinetic investigation based on Michaelis-Menten theory also elucidated that NFA modification improves affinity and kinetic ability of HAP-400-Fe. As a predominant oxidizing species, hydroxyl radical •OH was confirmed by a control test using a •OH scavenger, 2-propanol.

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We analyzed the electrical properties of human bone in comparison with the electrically polarized and nonpolarized bone specimens and discussed the role of an organic and inorganic matrix of bone in bone piezoelectricity. Femoral neck bone was scanned to evaluate the cancellous bone structures using micro-computed tomography, and we quantified the carbonic acid by attenuated total reflection spectra to estimate carbonate apatite. The stored electrical charge in the electrically polarized and nonpolarized bone specimens were calculated using thermally stimulated depolarized current (TSDC) measurements. Each TSDC curve had 3 peaks at 100°C, 300°C and 500°C, which may be attributed to collagen, carbonate apatite and hydroxyapatite, respectively. It is suggested that organic substances are more effectively electrically polarized than apatite minerals and that the stored charge in bone may be affected by total bone mass and bone quality, including 3-dimensional structure and structural composition.

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This paper reports the application of ultrasound irradiation in the synthesis of ultrafine hydroxyapatite (HAp) with a high specific surface area of 300 m²/g. We examined the effects of initial temperature, horn diameter and suspension concentration on the powder properties, especially specific surface area, of ultrafine HAp. Amorphous calcium phosphate (ACP), which is a precursor of HAp, was formed in the early stage of the reaction, and then rapidly crystallized to form HAp. In the case of an initial temperature at 30 °C, the largest specific surface areas of 250 m²/g and 300 m²/g were obtained using horn diameters of 19 mm and 6 mm, respectively. Based on particle size distribution measurements, the mode and average diameters of the HAp powders were found to be 5.0 and 6.3 nm, respectively. These values were well-agreed with the average diameter calculated from the specific surface area.

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Hydroxyapatite (HAp) samples were prepared from precursor solutions with different Ca/P molar ratios. The HAp samples were utilized as catalysts for the oxidative dehydrogenation (ODH) of isobutane. Also, the HAp samples were characterized by N₂ and H₂O adsorption-desorption measurements, X-ray diffraction, inductively coupled plasma optical emission spectrometry, thermogravimetry-differential thermal analyses, and temperature-programmed oxidation (TPO). The Ca/P molar ratio of the precursor solution had a major influence on the catalytic activity and coking resistance ability. The HAp catalyst prepared from the stoichiometric precursor solution [HAp (1.67)] showed the highest isobutene yield. Furthermore, the white color of HAp (1.67) remained unchanged during the ODH of isobutene, indicating the absence of coke on the surface of HAp (1.67) after the reaction and its higher coking resistance ability. The results of the TPO measurements showed that the HAp (1.67) catalyst possesses the strongest oxidation ability which is likely related to its higher coking resistance ability.

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Phosphonylation of kojic acid has been achieved using inorganic diphosphonate (DP) in aqueous solution. The optimum condition for the phosphonylation of kojic acid with DP is kojic acid : DP = 0.1 mol/L : 0.5 mol/L, pH 9 and 25 °C. 2-Phosphonylmethyl-kojic acid was synthesized with the yield of 45 %. The reaction mechanism of kojic acid with DP was discussed. We have successfully introduced the phosphonate group in kojic acid. Phosphonylated kojic acid is expected that the permeability of kojic acid into the skin will be increased by introducing a phosphonate group.

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