Mechanical, pH and Thermal Stability of Mesoporous Hydroxyapatite

The stability of mesoporous hydroxyapatite (HAP) powder was studied following treatments of ultrasound, pH and heating. HAP was found to be mechanically stable up to (and including) 1 h continuous ultrasonic treatment in water. The HAP structure was also stable to pH, evidenced by practically identical XRD and FTIR spectra over the pH range 2–12. The surface area increased progressively with increasing acidity, reaching a maximum of 121.9 m 2 g −1 at pH 2, while alkaline conditions decreased the surface area to a minimum of 55.4 m 2 g −1 at pH 12. Heating in air had a significant influence on the structural and morphological properties of HAP, which underwent dehydroxylation to form oxyhydroxyapatite (OHAP) at temperatures ≥ 650 °C, and β-tricalcium phosphate (β-TCP) ≥750 °C. The surface area decreased at elevated temperatures due to agglomeration of HAP crystals by sintering, which was associated with an increased particle size

Methane emission management in a dual-fuel engine exhaust using Pd and Ni hydroxyapatite catalysts

© 2017 Elsevier Ltd While dual-fuel engines reduce transportation costs and CO 2 emissions by using alternative energy sources e.g. natural gas, the exhaust streams often contain quantities of emissions that exceed limits and therefore require removal. Pd- and Ni-hydroxyapatite (HAP) catalysts were prepared using a soft-templating method and tested in the dry reforming of methane (DRM) in a fixed bed reactor that simulates an exhaust from a diesel-natural gas dual-fuel engine. XRD revealed the characteristic HAP crystal structure of all the prepared materials. The HAP phase was further confirmed by TEM, which also showed the presence of submicron sized particles. The BET surface areas of HAP prepared using a single surfactant was 27.7 m 2  g −1 and increased to 84.9 m 2  g −1 when mixed surfactants were used. Active metals were added to HAP using either incipient wetness impregnation, ion-exchange or solid dispersion. All the catalysts tested were active in DRM with the optimal samples converting over 85% of methane at 650 °C

Sum-frequency generation as a vibrational and electronic probe of the electrochemical interface and thin films

International audienceStandard vibrational sum-frequency generation (SFG) spectroscopy is performed to probe the electrochemical cyanoacetylene/ Au(1 1 1) interface, enlightening a 20 cm À1 /V Stark shift of the free CN vibration mode of this cyanopolyynes-class molecule. SFG data suggest an orientation for the adsorbed molecules with the CN moiety pointing out in a direction perpendicular to the metal surface. A newly developed two-colour SFG (2C-SFG) setup based on the CLIO free electron laser synchronized with a tuneable visible laser source is used to probe simultaneously the vibrational and electronic fingerprint of a thiophenol/Ag(1 1 1) interface. Structural information on the adsorbed self-assembled monolayer is put in evidence as a function of the immersion time of the silver substrate in the thio-phenol solution (24 h or 5 days). With a longer immersion time, the molecular packing is of better quality and more compact, with the carbon rings less tilted with respect to the surface normal. This new experimental setup combines the advantages to have a higher spectral and temporal resolution with higher power energies at far infrared wavelengths than these presently available from tabletop infrared optical parametric oscillators

Magnetic molecules - Chirality and magnetism shake hands

The synthesis of chiral magnetic molecules allows the first observation of strong magneto-chiral dichroism, where unpolarized light is absorbed differently for parallel and antiparallel propagation with respect to an applied magnetic field