Synthesis, Characterization and Catalytic Activity of Ternary Oxide Catalysts Using the Microwave-Assisted Solution Combustion Method.

Ni-Co-Al, Ni-Cu-Al and Co-Cu-Al ternary oxide catalysts, with a fixed 5 wt% transition metal loading, were prepared by the microwave-assisted solution combustion method and tested in CO oxidation. The bulk and surface properties of the catalysts were investigated, using XRD, N2 adsorption-desorption, SEM, XPS and TEM techniques. XRD, XPS and TEM results revealed that nickel and cobalt were present as spinels on the surface and in the bulk. Differently, copper was preferentially present in "bulk-like" CuO-segregated phases. No interaction between the couples of transition metal species was detected, and the introduction of Cu-containing precursors into the Ni-Al or Co-Al combustion systems was not effective in preventing the formation of NiAl2O4 and CoAl2O4 spinels in the Ni- or Co-containing catalysts. Copper-containing catalysts were the most active, indicating that copper oxides are the effective active species for improving the CO oxidation activity.

Effect of the Compositions on the Biocompatibility of New Alumina-Zirconia-Titania Dental Ceramic Composites.

Dental implant biomaterials are expected to be in contact with living tissues, therefore their toxicity and osseointegration ability must be carefully assessed. In the current study, the wettability, cytotoxicity, and genotoxicity of different alumina-zirconia-titania composites were evaluated. The surface wettability determines the biological event cascade in the bioceramic/human living tissues interface. The measured water contact angle indicated that the wettability strongly depends on the ceramic composition. Notwithstanding the contact angle variability, the ceramic surfaces are hydrophilic. The cytotoxicity of human gingival fibroblast cells with materials, evaluated by an (3-(4,5 methylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) test, revealed an absence of any cytotoxic effect. A relationship was found between the cell viability and the wettability. It was subsequently deduced that the cell viability increases when the wettability increases. This effect is more pronounced when the titania content is higher. Finally, a comet test was applied as complementary biocompatibility test to detect any changes in fibroblast cell DNA. The results showed that the DNA damage is intimately related to the TiO2 content. Genotoxicity was mainly attributed to ceramic composites containing 10 wt.% TiO2. Our research revealed that the newly developed high performance alumina-zirconia-titania ceramic composites contain less than 10 wt.% TiO2, and display promising surface properties, making them suitable for dental implantology applications.

Preparation and characterization of photocatalytic Gd-doped TiO2 nanoparticles for water treatment.

In recent years, the photocatalytic process by using TiO2 nanoparticles (NPs) has produced a great interest in wastewater treatment due to its interesting features such as low-cost, environmental compatibility, and especially capacity to eliminate persistent organic compounds as well as microorganisms in water. In the present work, the photocatalytic activity of Gd-doped TiO2 nanopowders, with different doping amount 0.1, 1, and 5 mol% synthesized by the sol-gel method, was studied under UV/Visible irradiation for water treatment application. The Gd-doped TiO2 nanoparticles were investigated for their photocatalytic degradation of methylene blue (MB) dye and antibacterial activities against two bacterial strains namely Stenotrophomonas maltophilia (S. maltophilia) and Micrococcus luteus (M. luteus). MB dye was used as a pollutant model to estimate reactive oxygen species (ROS) generation and to correlate killing action of nanoparticles with the generation of ROS. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Raman spectroscopy were used to characterize the as-synthesized nanomaterials. Photocatalytic, as well as antibacterial tests, showed that doping with an appropriate amount of Gd could reduce the radiative recombination process of photogenerated electron-hole pairs in TiO2 and induce a significant enhancement in photocatalytic and consequently antibacterial activity. The experimental sequence of bactericidal activity and photocatalytic degradation efficiency exhibited by the different gadolinium-doped nanoparticles was the following: 0.1 mol% Gd-doped TiO2 > 1 mol% Gd-doped TiO2 > 5 mol% Gd-doped TiO2 > pure titania.

Binary Oxides Prepared by Microwave-Assisted Solution Combustion: Synthesis, Characterization and Catalytic Activity.

Three different alumina-based Ni, Cu, Co oxide catalysts with metal loading of 10 wt %, and labeled 10Ni⁻Al, 10Co⁻Al and 10Cu⁻Al, were prepared by microwave-assisted solution combustion. Their morphological, structural and surface properties were deeply investigated by complementary physico-chemical techniques. Finally, the three materials were tested in CO oxidation used as test reaction for comparing their catalytic performance. The 10Cu⁻Al catalyst was constituted of copper oxide phase, while the 10Ni⁻Al and 10Co⁻Al catalysts showed the presence of "spinels" phases on the surface. The well-crystallized copper oxide phase in the 10Cu⁻Al catalyst, obtained by microwave synthesis, allowed for obtaining very high catalytic activity. With a CO conversion of 100% at 225 °C, the copper containing catalyst showed a much higher activity than that usually measured for catalytic materials of similar composition, thus representing a promising alternative for oxidation processes.

Tricalcium phosphate-Fluorapatite as bone tissue engineering: Evaluation of bioactivity and biocompatibility.

Biocomposites consisting of ß Tricalcium phosphate (ß-TCP) with 26.52% Fluorapatite (Fap) were elaborated and characterized in order to evaluate it potential application in bone graft substitute. Bioactivity was determined with in vitro tests by immersion of samples in simulated fluid body for several periods of times. The SEM, EDS and Atomic Absorption Spectroscopy showed the deposition of apatite layer on the surface of samples showing a good bioactivity. However, after 6days of soaking, the dissolution rate of Ca2+ and PO43- decreased which due probably to the improvement of crystallization of the apatite layer. These findings agree with those observed after 6weeks postimplantation of prepared macroporous scaffolds in rabbits. All histological observations of the preliminary in vivo study in the tibia of rabbits proved the biocompatibility and the resorption of the investigated bioceramic. In contrast, the implantation period will have to be optimized by further extensive animal experiments.

Manufacture and optimization of low-cost tubular ceramic supports for membrane filtration: application to algal solution concentration.

Low-cost tubular macroporous supports for ceramic membranes were elaborated using the extrusion method, followed by curing, debinding, and sintering processes, from a powder mixture containing kaolin, starch, and sand. The obtained substrates were characterized using mercury intrusion porosimetry, water absorption test, water permeability, scanning electron microscopy, and three-point bending test to evaluate the effects of the additives on the relevant characteristics. According to experimental results, adding the starch ratio to the kaolin powder shows a notable impact on the membrane porosity and consequently on the water permeability of the tubular supports, whereas their mechanical strength decreased compared to those prepared from kaolin alone. It has been shown that the addition of an appropriate amount of starch to the ceramic paste leads to obtaining membrane supports with the desired porosity. Indeed, the water permeability increased significantly from 20 to 612 L h-1 m-2 bar-1 for samples without and with 20 wt% of starch, respectively, as well as the open porosity, the apparent porosity, and the pore size distribution. The bending strength decreased slightly and reached about 4 MPa for samples with the highest starch amounts. On the other hand, the incorporation of sand in a mixture of kaolin + 10 wt% starch increased the mechanical strength and the water permeability. The samples containing 3 wt% of sand exhibited a bending strength four times higher than the supports without sand; the water permeability measured was about 221 L h-1 m-2 bar-1. These elaborated tubular supports for membrane are found to be suitable for solution concentration; they were applied for algal solution and are also easily cleaned by water.

Alumina-fluorapatite composite coating deposited by atmospheric plasma spraying: An agent of cohesion between bone and prostheses.

In order to remedy the poor biological and tribological properties of 316L stainless steel (SS), plasma sprayed bio-ceramic coatings have been widely investigated. In the present study, a small amount of fluorapatite (Fap) was introduced into alumina in order to enhance its bioactivity. The powder feedstock was sprayed on 316L substrate by Atmospheric Plasma Spraying (APS) technology. The roughness profiles and average roughness values were determined using 3D profilometry. The cross sectional morphologies of the coatings were examined by scanning electron microscopy (SEM). Adhesive strength, micro-hardness and tribological properties were also examined. Experimental results revealed that Al2O3/Fap coating showed a good microhardness property revealing that the calcium aluminates were quite effective in improving the Fap mechanical behavior. The tribological characteristics of both alumina and alumina-Fap coating were also compared to those of classical hydroxyapatite (Hap) coatings as reported in the literature. The main finding of this work was that Fap coating can contribute to the cohesion between bone and prostheses and thus ensure a more durable and reliable prostheses.

Synthesis, characterization and bioactivity of a calcium-phosphate glass-ceramics obtained by the sol-gel processing method.

In this work, a calcium-phosphate glass-ceramics was successfully obtained by heat treatment of a mixture of 26.52 in wt.% of fluorapatite (Fap) and 73.48 in wt.% of 77S (77 SiO214 CaO9 P2O5 in wt.%) gel. The calcium phosphate-glass-ceramics was prepared by sol-gel process with tetraethyl orthosilicate (TEOS), triethyl phosphate (TEP), calcium nitrate and fluorapatite. The synthesized powders were characterized by some commonly used tools such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), 31P magic angle spinning nuclear magnetic resonance (MAS-NMR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and thin-film X-ray diffraction (TF-XRD). The obtained results seemed to confirm the nucleation and growth of hydroxyapatite (Hap) nano-phase in the glass. Moreover, an in-vitro evaluation of the glass-ceramic was performed. In addition, to assess its bioactive capacity, it was soaked in simulated body fluid (SBF) at different time intervals. The SEM, EDS and TF-XRD analyses showed the deposition of hydroxyapatite on the surface of the specimens after three days of immersion in SBF solution. The mechanical properties of the obtained material such as rupture strength, Vickers hardness and elastic modulus were measured. In addition, the friction coefficient of calcium phosphate-glass-ceramics was tested. The values of the composite of rupture strength (24MPa), Vickers hardness (214Hv), Young's modulus (52.3GPa), shear modulus (19GPa) and friction coefficient (0.327) were obtained. This glass-ceramics can have useful applications in dental prostheses. Indeed, this material may have promising applications for implants because of its content of fluorine, the effective protector against dental caries.

Sintering and mechanical properties of the alumina-tricalcium phosphate-titania composites.

The objective of this study was to determine the effect of the content of titania and the sintering process on the transformation phase, the densification, the rupture strength and the microstructures of the alumina-10 wt.% tricalcium phosphate composites. After the sintering process, the samples were examined by using (31)P and (27)Al magic angle scanning nuclear magnetic resonance, X-ray powder diffraction and scanning electron microscopy analysis. The Brazilian test was used to measure the rupture strength of the samples. The present results provide new information about solid-state reactivity in the ternary system α-alumina-ß-tricalcium phosphate-anatase-titania. The differential thermal analysis of the α-alumina-ß-tricalcium phosphate-titania composites shows two endothermic peaks, at 1360 °C and at 1405 °C, which are caused by the reactions between titania/alumina and titania/tricalcium phosphate, respectively. Thus, the presence of titania in the alumina-10 wt.% tricalcium phosphate leads to the formation of ß-Al2TiO5 at 1360 °C. At 1600 °C, the alumina-10 wt.% tricalcium phosphate-5 wt.% titania composites displayed the highest rupture strength (74 MPa), compared to the alumina-10 wt.% tricalcium phosphate composites (13.5 MPa). Accordingly, the increase of the rupture strength is due to the formation of the new ß-Al2TiO5 phase.

Effect of fluorapatite additive on densification and mechanical properties of tricalcium phosphate.

Tricalcium phosphate and synthesized fluorapatite powder were mixed in order to elaborate biphasic composites. The samples were characterized by X-ray diffraction, differential thermal analysis, infrared spectroscopy, scanning electron microscopy and by an analysis using (31)P nuclear magnetic resonance. The sintering of tricalcium phosphate with different percentages of fluorapatite (13.26 wt%; 19.9 wt%; 33.16 wt% and 40 wt%) indicates the evolution of the microstructure, densification and mechanical properties. The Brazilian test was used to measure the rupture strength of the sintered biphasic composites. The mechanical properties increase with the sintering temperature and with the addition of fluorapatite additive. The mechanical resistance of beta tricalcium phosphate-33.16 wt% fluorapatite composites reached its maximum value (13.7 MPa) at 1400 ( composite function)C, whereas the optimum densification was obtained at 1350 ( composite function)C (93.2%). Above 1400 ( composite function)C, the densification and mechanical properties were hindered by the tricalcium phosphate allotropic transformation and the formation of both intragranular porosity and cracks. The (31)P magic angle spinning nuclear magnetic resonance analysis of composites as sintered at various temperatures or with different percentages of fluorapatite reveals the presence of tetrahedral P sites.

Rheological behavior of organic suspensions of fluorapatite.

A fluorapatite suspension prepared in the azeotrope methyl ethyl ketone-ethyl alcohol (MEK:EtOH) in the presence of the phosphoric ester was investigated. Electrical conductivity, adsorption isotherms, and sedimentation technique showed that the amount of phosphoric ester adsorbed on the fluorapatite surface was equal to, or higher than, 1 wt%. This dispersant concentration led to a good particle packing. The rheological properties of fluorapatite suspensions were studied as a function of phosphoric ester concentration. The data obtained from the viscosity measurements and those previously collected correlated well. In the case of suspensions prepared with 60 wt% in fluorapatite, the dispersion was optimal for a phosphoric ester content of about 1.3 wt%.