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Fe-Ti mixed oxide nanoparticles with different atomic ratios in Ti/(Fe + Ti) from 0 to 1.0 have been prepared by hydrolysis of aqueous solutions containing Fe(III) and Ti_(IV) ions and a freezing method with liquid N_2, which inhibits crystallization and particle growth. The particles produced were poorly crystalline according to XRD and the product, in the absence of Ti_(IV), was assigned to 2-line ferrihydrite. The products had a high specific surface area of 369-460 m^2 g^(-1), corresponding to a mean particle size of 3-4 nm. These nanosized particles were composed of crystallites of about 1 nm size. It was found by Mossbauer spectroscopy that the particles produced were superparamagnetic and their blocking temperature and inner electric field decreased with increasing Ti_(IV) content.

The effects of chloride ions on the morphology and structure of hematite particles, produced from a forced hydrolysis reaction of acidic Fe(III) solution, were investigated. Spherical hematite particles were precipitated under all conditions employed which changed the molar fraction of coordinative Cl^- to non-coordinative N0_3^- ions to Fe(III) ions in the solutions. The size of the particles was increased with increase in the molar fraction of FeCl_3, FeCl_3/[FeCl_3 + Fe(N0_3)_3 (X_(FeCl_3)) although no remarkable change was observed in varying that of HCl, HCI/(HCl + HNO_3) (X_(HCI)). TEM and XRD measurements suggested that the hematite particles formed at X_(FeCl_3) < 0.2 exhibited a single-crystal nature, although those produced at X_(FeCl_3) > 0.4 are polycrystalline with an enlarged c edge length in a unit cell possessing OH^- ions in the lattice. The rate of phase transformation from Beta-FeOOH to hematite decreased with increase in X_(FeCl_3) and was closely related to the crystal lattice distortion. The results obtained were explained by an aggregation mechanism taking into account the difference in the coordination properties of Cl^- and N0_3^- ions to Fe(III) ions. The hydrolysis reaction of Fe(III) was slowed in the presence of Cl^- by its strong coordination to produce electrically neutral, extremely low molecular weight polynuclear (PN) species, [Fe0_(2/3)(OH)_(4/3)(H_2O)_xCl_(l/3))_p. Therefore, this system gave a large spherical particle through the aggregation of the neutral small PNs with less mutual electrostatic repulsion force. In contrast, N0_3^- ions exhibited a fast hydrolysis reaction owing to their non-coordinative nature and produced positively charged, high molecular weight PNs, [Fe0_(2/3)(OH)_(4/3)(H_20)_X)^(p/3)+_p,resulting in less aggregated small hematite particles owing to their repulsion force. This aggregation mechanism was further confirmed by gas adsorption, TEM and addition of NaCI.

Synthetic calcium hydroxyapatite, Ca_10(PO_4)_6(OH)_2 (CaHap), prepared by a wet method was evacuated at various temperatures up to 900 C and the influence of thermal treatment on the structure of this material was investigated by FTIR, determination of concentration of surface P-OH groups, adsorption of H_2O and heat of mersion in water. The number of surface P-OH groups was 2.6 groups nm^(-2) and the ionic ratio of surface (PO_4)^(2-) - to H_2PO_4 - was 31: 69. The surface P-OH groups were essentially dehydroxylated by outgassing above 400 C to produce surface P-O-P species. The heat of rehydroxylationper one P-O-P group was determined to be 1.43 x 10^(-16) J group^(-1). When outgassed above 600 C, CaHap was rehydrated via the reaction: (1- x)Ca_10(P0_4)_6(OH)_2 + 3xbeta-Ca_3(P0_4)_2 + xH_2O → Ca_l0-x(P_2O_7)_x(P0_4)_6-2x(OH)_2.

The adsorption of myoglobin (MGB) onto various kinds of colloidal synthetic hydroxyapatite[X_10(PO_4)_6(OH)_2, noted CaHap, SrHap and CaSrHap for X = Ca, Sr and Ca + Sr, respectivelyJ particles was investigated at 15 °C in a 1 x 10^(-4) mol dm^(-3) KCl solution of pH 6.0. The adsorption rate of MGB onto CaHap was comparable to that of lysozyme (LSZ) and was faster than that of bovine serum albumin (BSA). This distinction was explained by the difference in the molecular mass of these proteins (MGB: 17800 Da, LSZ: 14600 Da, BSA: 67 200 Da); the diffusion rates of the smaller MGB and LSZ molecules to the CaHap surface are faster than that of the larger BSA. The adsorption isotherms of MGB onto these synthetic hydroxyapatites (Haps) exhibited the Langmuir type and the surface charge of the MGB-covered Haps showed almost constant negative value and was independent of the MGB concentration for all the Haps. The values of the saturated amounts of adsorbed MGB for CaHap were independent of the Ca : PO_4 molar ratio of the materials, supporting less importance of an electrostatic interaction between MGB and Haps because MGB molecules are electrostatically neutral at pH 6. It was presumed that MGB molecules are adsorbed onto phosphate ions exposed on ac and bc crystal faces by the van der Waals attractive force without taking advantage of the electrostatic interaction.

Lead hydroxyapatite (PbHAP) particles were prepared by a homogeneous precipitation reaction of Pb(NO 3 ) 2 and (NH 4 ) 2 HPO 4 using acetamide (AA) in aqueous media. The particles obtained under different conditions were examined by various methods, including XRD, FTIR, SEM, ICP, TG-DTA and N 2 adsorption. The crystal phase of the products depended on the concentration of AA ([AA]) and the ageing period (t a ). Large highly crystalline needle-like PbHAP particles were formed by ageing at [AA]=0.4-1.6 mol dm –3 and t a ≥1 day. At [AA]≥3.2 mol dm –3 a mixture of PbHAP and α-Pb 3 (PO 4 ) 2 was generated. The transformation of α-Pb 3 (PO 4 ) 2 to PbHAP in solution at [AA]≥3.2 mol dm –3 was hindered by CH 3 COOH, produced by hydrolysis of AA.

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.

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.

δ-FeOOH particles have been prepared by oxidation of Fe(OH)2 with H2O2. The Fe(OH)2 precursors precipitated from a concentrated FeSO4 solution were aged at different temperatures from 40 to 110 °C. The δ-FeOOH particles obtained were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and N2 adsorption. The δ-FeOOH particles are tetradecahedra and the particle size increases from ca. 0.1 to 1 µm with increasing ageing temperature. The tetradecahedral δ-FeOOH particles are less crystalline. The N2 adsorption t-plots show the microporous structure of the δ-FeOOH particles obtained by ageing Fe(OH)2 at a higher temperature. The tetradecahedral α-Fe2O3 particles formed by outgassing these δ-FeOOH particles above 150 °C have micropores with sizes ranging from 0.8 to 2 nm.

Colloidal particles of homogeneous solid solutions of strontium and calcium hydroxyapatites (SrCaHAP) have been synthesized in different mole fractions, Sr/(Ca + Sr) ranging from 0 to 1. The crystallite size of the SrCaHAP particles obtained was a minimum around Sr/(Ca + Sr)= 0.3, whereas the specific surface area was maximum around the same Sr/(Ca + Sr). The morphology of the SrCaHAP particles became irregular as Sr/(Ca + Sr) increased up to 0.5. The irreversible adsorption of CO2 per unit surface area was a minimum at (Ca + Sr)/P = 1.56, less than the stoichiometric value of 1.67. These results suggest that there are two kinds of irreversible adsorption site for CO2 on SrCaHAP.

The surface and pore structures of the materials resulting on outgassing the colloidal δ-FeOOH particles at different temperatures in the range 50–300 °C have been investigated by a variety of techniques. The FTIR spectrum of the particles outgassed at 100 °C has a weak broad band at 3650 cm–1 and a strong band at 3150 cm–1 which are assigned to the surface and bulk OH groups of δ-FeOOH, respectively. When outgassed above 150 °C three bands appear at 3665, 3635 and 3400 cm–1. The former two bands and the latter one can be assigned to the surface OH groups and the H2O molecules adsorbed in the micropores, respectively. Increasing the outgassing temperature develops the microporosity of the products. The t-plots of the samples treated above 150 °C indicate the formation of micropores with a 0.8 nm width as confirmed by transmission electron microscopy (TEM).

The adsorption isotherms of H2O, CCl4, n-C6H14 and CH3OH on the synthetic γ-FeOOH particles have been measured at different temperatures from –5 to 35 °C. The isotherms of H2O, CCl4 and n-C6H14 exhibited a step below their monolayer adsorption capacity, while no step appeared in the isotherm of CH3OH. The isosteric heats of adsorption of H2O, CCl4 and n-C6H14 showed a maximum at an adsorption coverage of 0.6, 0.8 and 0.75, respectively. The surface fractal dimension was close to 2, indication that the γ-FeOOH surface is homogeneous. It can be concluded that the step-like isotherms reflect the two-dimensional condensation of these molecules on the chemically and geometrically homogeneous surface of γ-FeOOH.

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.

Calcium hydroxyapatite (CaHAP) particles synthesized by a wet method have been modified by treating them with water-acetone solutions of ethyl phosphates (EP). The modified CaHAP particles were characterized by various means.XRD patterns of the modified CaHAP particles showed a strong peak at d = 1.40 nm in addition to the peaks characteristic of CaHAP. With increasing EP concentration the XRD peaks of CaHAP were weakened while the new strong peak grew rapidly. The original particles were modified by EP, with no formation of new particles. These results indicate that treatment with EP induces the formation of a layered structure in the surface layer of the particles. The H_2O and C_2H_5 groups present in the modified particles were removed by heating above 350°C in air, which resulted in the immediate disappearance of the XRD peaks due to the layered structure, so that only the CaHAP peaks were observed. Outgassing of the modified materials above 300°C gave mesoporous CaHAP particles.

The surface of colloidal strontium hydroxyapatite (SrHAP) particles with different Sr : P molar ratios from 1.51 to 1.71 has been characterized by means of an FTNIR spectrometer. The IR spectra of the Sr-deficient SrHAP gave rise to 3684, 3662 and 3640 cm–1 bands, which are assigned to surface P—OH groups. The Sr-rich SrHAP exhibited a band at 3710 cm–1 in addition to the three surface P—OH bands. The amount of irreversible adsorption of CO2 on the Sr-rich SrHAP was larger than that on the Sr-deficient samples. The change in the spectra after CO2 adsorption by the sample proved that the irreversible adsorption sites of CO2 on the Sr-deficient SrHAP are the less-acidic surface P—OH groups giving the 3640 cm–1 band and those on the Sr-rich SrHAP are surface OH– ions. The mechanism of irreversible adsorption of CO2 is discussed.

Monodispersed spherical and cubic haematite particles prepared by forced hydrolysis have been characterized by various techniques. Electron microscopy and X-ray diffraction measurements indicated that these two kinds of particles were formed through the recrystallization of β-FeOOH to haematite accompanying the dissolution of β-FeOOH. The relationship between the absorbance of the IR band due to the inner OH groups and the weight loss by heating in vacuo suggested that the monodispersed cubic haematite particles are polycrystalline and constructed by the aggregation of fine hydrous iron(III) oxide particles during dehydration. This mechanism was supported by the formation of micropores in cubic haematite particles that were outgassed in vacuo at 150 and 200 °C. On outgassing at 300 °C, the particles became non-porous or less porous but the inner OH bands were observed above 400 °C. A similar mechanism of formation was confirmed regarding the formation of spherical haematite particles, although the spherical haematite particles were more crystalline than the cubic particles.

Fourier-transform infrared spectra and surface properties of colloidal α-, β- and γ-ferric oxide hydroxides [Fe(O)OH], which were synthesized and aged in this laboratory, have been studied. The spectrum of the α phase has a strong absorption band at 3150 cm–1 and two weak ones at 3485 and 3661 cm–1. That of the β phase has a strong band at 3480 cm–1, a weak band at 3659 cm–1 and two very weak bands at 3686 and 3723 cm–1. That of the γ phase has a strong band at 3160 cm–1, a weak band at 3624 cm–1 and a very weak band at 3528 cm–1. The changes of these bands by the adsorption of heavy water, water and methyl iodide molecules and cupric ions have been studied in detail and the various bands were assigned to various OH groups with respect to the crystal structures of these materials.

The surfaces of α-, β- and γ-iron(III) oxide hydroxides have been characterized mainly through the adsorption behaviour of water and methanol by means of F.t.i.r. spectroscopy. In the α-phase two kinds of surface hydroxyl groups with bands at 3485 and 3661 cm–1 are active for the adsorption of these molecules. In the β-phase two surface hydroxyl groups with bands at 3686 and 3723 cm–1 are active for the adsorption of both molecules, but that at 3659 cm–1 is less active. The hydroxyl groups of the γ-phase with a band at 3624 cm–1 are active for water and methanol adsorption. There seem to be reactive adsorption sites other than surface hydroxyl groups.