The influence of Fe2O3 doping on the pore structure and mechanical strength of TiO2-containing alumina obtained by freeze-casting

This work investigated TiO/FeO doped alumina prepared by the freeze-casting technique and using camphene as the solvent. Dendritic pores were formed in the TiO doped alumina, a structure conferred by the frozen camphene. Contrary to this trend, further FeO doping of TiO-containing alumina resulted in the formation of non-dendritic structures. This behavior was attributed to the higher density of α-FeO (5.24 g cm) when compared to α-AlO (3.95 g cm) and anatase TiO (3.89 g cm), which reduced critical solidification front velocity, thus forming material with different pore shape. FeO doping also improved the densification of TiO-alumina and inhibited the formation of cracks, reflected by superior mechanical strength with best results ∼150% higher for 10% FeO loaded samples as compared to TiO-alumina samples

Effect of titania addition on the properties of freeze-cast alumina samples

This work investigated the behavior of TiO2-containing α-Al2O3 samples prepared by the freeze-casting technique. Camphene and liquid nitrogen were used as the solvent and cooling fluid, respectively. Camphene resulted in the formation of dendritic pores, in the direction of the freeze-casting cold front during sample preparation. The formation of β-Al2TiO5 phase occurred at 1300°C, and became more evident as the sintering temperatures reached 1500°C. The TiO2 loading did not affect the sample porosity at a given temperature, but it was detrimental in the case of mechanical properties under certain conditions. For instance, the flexural strength slightly improved with increasing the TiO2 loading and sintering temperature from 1100 to 1300°C. This effect was attributed to the occurrence of a more effective sintering of alumina. However, as the heat treatment temperature was raised from 1300 to 1500°C, the flexural strength did not increase as a function of the TiO2 loading, even though the densification occurred with loss of porosity. The loss of mechanical strength was found to be associated with the formation of microcracks which stemmed from the formation of β-Al2TiO5 phase for TiO2 loadings in excess of 4wt% at these high sintering temperatures

On the structural, mechanical, and biodegradation properties of HA/β-TCP robocast scaffolds

International audienceHydroxyapatite/β-tricalcium phosphate (HA/β-TCP) composite scaffolds have shown great potential for bone-tissue engineering applications. In this work, ceramic scaffold with different HA/β-TCP compositions (pure HA, 60HA/40β-TCP, and 20HA/80β-TCP) were fabricated by a robotic-assisted deposition (robocasting) technique using water-based hydrogel inks. A systematic study was conducted to investigate the porosity, mechanical property, and degradation of the scaffolds. Our results indicate that, at a similar volume porosity, the mechanical strength of the sintered scaffolds increased with the decreasing rod diameter. The compressive strength of the fabricated scaffolds (porosity ≈ 25–80 vol %) varied between ∼3 and ∼50 MPa, a value equal or higher than that of human cancellous bone (2–12 MPa). Although there was a slight increase of Ca and P ions in water after 5 month, no noticeable degradation of the scaffolds in SBF or water was observed. Our findings from this work indicate that composite calcium phosphate scaffolds with customer-designed chemistry and architecture may be fabricated by a robotic-assisted deposition method

Development of a flexible nanocomposite TiO2 film as a protective coating for bioapplications of superelastic NiTi alloys

International audienceAn experimental procedure to coat superelastic NiTi alloys with flexible TiO2 protective nanocomposite films using sol-gel technology was developed in this work to improve the metal biocompatibility without deteriorating its superelastic mechanical properties. The coatings were characterized by scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and glazing incidence X-ray diffraction. The elasticity of the film was tested in coated specimens submitted to three-point bending tests. A short densification by thermal treatment at 500 degrees C for 10 min yielded a bilayer film consisting of a 50 nm-thick crystallized TiO2 at the inner interface with another 50-nm-thick amorphous oxide film at the outer interface. This bilayer could sustain over 6.4% strain without cracking and could thus be used to coat biomedical instruments as well as other devices made with superelastic NiTi alloys. (C) 2016 Elsevier B.V. All rights reserved

Synthesis, characterization, and use of nanocast LaMnO3 perovskites in the catalytic production of imine by the gas-phase oxidative coupling of benzyl alcohol to aniline

We report here a green methodology for the synthesis of imine from a gas-phase oxidative coupling of benzyl alcohol to aniline in a continuous-flow system. These reactions were performed using LaMNO3 perovskites as heterogeneous catalysts. The catalytic performance of these materials was 98% and remained stable for 8 h of reaction. The prepared catalysts were successfully regenerated and reused in five successive catalytic cycles. No organic solvents were used in this process, which represents an important advantage in terms of the environment, simplicity, and safety. Moreover, this approach reduces the need for subsequent physicochemical extraction and purification steps

Tailoring the pore architecture and crystalline structure of UiO-66 for the selective adsorption of anionic species in aqueous media

International audienceMicropollutants such as organic dyes and pharmaceuticals have received much attention in recent years due to their harmful effects on humans and wildlife, high stability against natural degradation, and difficult removal in conventional water treatment plants. In this work, we have optimized the adsorption of organic pollutants on UiO-66 metal-organic frameworks by changing some synthesis parameters, which allowed the tuning of their crystal structure and pore architecture. Samples with an extended microporous structure and specific surface areas over 1300 m 2 .g − 1 were prepared by a solvothermal approach, which favored the access of the pollutant molecules to active adsorption sites. The specific surface areas measured in this study are among the highest ever reported for UiO-66. In batch adsorption tests conducted using aqueous solutions containing low initial concentrations (20 mg.L-1) of acid orange (AO7), ibuprofen (IBU), and methylene blue (MB), the materials tested in this study exhibited preferential adsorption of the anionic species AO7 (192 mg.g − 1) and IBU (173 mg.g − 1), resulting in AO7/MB and IBU/MB selectivities of 9.6 and 8.7, respectively. The primary adsorption mechanism is most likely a combination of electrostatic and Lewis acid-base interactions involving Zr-(-SO 3 −) for AO7 and Zr-(-CO 2 −) for IBU. Subsequent tests with moderately higher concentrations of AO7 (50 mg.L-1) showed even higher adsorption capacities, exceeding 340 mg.g − 1. These results demonstrate that the optimized UiO-66 structure prepared in this study exhibits high-performance adsorption capabilities for the removal of anionic pollutants from aqueous media, thereby expanding the knowledge on the use of Zr-based MOFs for water remediation

Structural investigation of cobalt-doped silica derived from sol-gel synthesis

This work investigates the structural properties of cobalt doped silica samples prepared by sol-gel synthesis. Air calcination led to the formation of Co3O4 particles as evidenced by XRD and FTIR tests, although these features were no longer apparent for hydrogen-reduced samples. This behavior suggests the formation of metallic Co and CoO in the reduced samples. The variation of the cobalt content embedded in the silica matrix resulted in a change in texture of the prepared materials from microporous to mesoporous. This was attributed to the agglomeration of particles as observed in TEM micrographs, which led to larger particles and pores. The latter was associated with the formation of hysteresis loop in the nitrogen adsorption isotherms as a function of the [Co/(Si + Co)] molar ratio. This effect was more remarkable for reduced samples, leading to a further broadening of the hysteresis loop that stemmed from the reduction or loss of oxygen from cobalt oxide particles

Post-synthetic modification of aluminum trimesate and copper trimesate with TiO2 nanoparticles for photocatalytic applications

International audienceOrganic pollutants have been a significant source of concern in recent years due to their facile dissemination and harmful effects. In this work, two different metal–organic frameworks (MOFs) were initially prepared by hydrothermal treatment, namely aluminum trimesate (MIL-100(Al)) and copper trimesate (HKUST-1). These materials were subsequently submitted to a post-synthetic modification step to grow titania nanoparticles on their surface. Anatase nanoparticles with sizes around 5 nm were successfully anchored on MIL-100(Al), and the concentration of TiO2 in this sample was about 68 wt.%. This is the first time that this composite (TiO2@MIL-100(Al)) is reported in the literature. It showed an improved photocatalytic activity, removing 90% of methylene blue (kapp = 1.29 h−1), 55% of sodium diclofenac (kapp = 0.21 h−1), and 62% of ibuprofen (kapp = 0.37 h−1) after four hours of illumination with UV-A light. A significant concentration (14 µM) of reactive oxygen species (ROS) was detected for this composite. HKUST-1 showed a structural collapse during its post-synthetic modification, leading to a non-porous material and providing fewer sites for the heterogeneous nucleation of titania. This behavior led to a low concentration of rutile nanoparticles on HKUST-1 (9 wt.%). However, the obtained composite (TiO2@HKUST) also showed an improved photoactivity compared to HKUST-1, increasing the photodegradation rates evaluated for methylene blue (0.05 h−1 vs. 0.29 h−1), sodium diclofenac (negligible vs. 0.03 h−1), and ibuprofen (0.01 h−1 vs. 0.02 h−1). This work brings new insights concerning the preparation of photocatalysts by growing semiconductor nanoparticles on trimesate-based MOFs