Propane oxidative dehydrogenation over unpromoted and Nb promoted NiO loaded calcium-hydroxyapatite catalysts

Nickel loaded calcium-hydroxyapatite (xNi/CaHAp) and niobium promoted xNi/CaHAp catalysts were synthesized and characterised by X-ray, FTIR, U.V-visible-NIR spectroscopies and temperature programmed reduction (H2-TPR). X-ray diffraction patterns of xNi/CaHAp showed that for nickel loadings above 5 wt.% Ni, diffraction lines belonging to bulk NiO start to appear. The average size of those nickel oxide particles is equal to 16, 23, and 35 nm for x = 10, 15 and 20 Wt.%, respectively. U.V-visible and TPR showed that the loaded nickel is hosted by octahedral and pseudo-octahedral sites.Calcium-hydroxyapatite loaded with different amounts of nickel and niobium promoted xNi/CaHAp catalysts were tested in oxidative dehydrogenation propane (ODH). The best performance was achieved with a nickel loading of x = 10%. The corresponding stationary conversion of propane is equal to 22% with a propylene yield of 13%.Addition of niobium to xNi/CaHAp decreases the global conversion but enhances the propylene selective and the stability of the catalyst with time on stream. The best results were obtained with 0.15 wt.% Nb. The propylene yield at stead state reaches 14% at 425°C

Adsorption and Sustained Delivery of Small Molecules from Nanosilicate Hydrogel Composites

Two-dimensional nanosilicate particles (NS) have shown promise for the prolonged release of small-molecule therapeutics while minimizing burst release. When incorporated in a hydrogel, the high surface area and charge of NS enable electrostatic adsorption and/or intercalation of therapeutics, providing a lever to localize and control release. However, little is known about the physio-chemical interplay between the hydrogel, NS, and encapsulated small molecules. Here, we fabricated polyethylene glycol (PEG)-NS hydrogels for the release of model small molecules such as acridine orange (AO). We then elucidated the effect of NS concentration, NS/AO incubation time, and the ability of NS to freely associate with AO on hydrogel properties and AO release profiles. Overall, NS incorporation increased the hydrogel stiffness and decreased swelling and mesh size. When individual NS particles were embedded within the hydrogel, a 70-fold decrease in AO release was observed compared to PEG-only hydrogels, due to adsorption of AO onto NS surfaces. When NS was pre-incubated and complexed with AO prior to hydrogel encapsulation, a >9000-fold decrease in AO release was observed due to intercalation of AO between NS layers. Similar results were observed for other small molecules. Our results show the potential for use of these nanocomposite hydrogels for the tunable, long-term release of small molecules

The Synthesis and Characterization of Low-cost Mesoporous Silica SiO2 from Local Pumice Rock

Pumice is a porous volcanic rock containing a significant proportion of silica and alumina, and which has a low iron content. This natural, silica-rich material attracts wide attention because of its applications in adsorption process‐ es, heterogeneous catalysis and nanotechnology. In this contribution, the white amorphous silica nanoparticles were extracted using an optimized alkaline treatment and an acid-precipitation process using grey pumice powder. The isolated amorphous silica SiO2 was characterized via X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Transmission Electronic Microscopy (TEM-EDS), N2 adsorption/desorption measurements and simultaneous Thermal Gravimetry/Differential Thermal Analysis (TG/DTA). The obtained results indicated that the nanosilica powder was successfully prepared via the acid- base route with a predominantly amorphous mesoporous structure having a high surface area (422m2/g). The TEM images exhibited relatively homogeneous dispersed nanosilica particles with small sizes about 5–15 nm, in accordance with XRD data. Thermal analysis of the silica powder under air atmosphere showed total mass losses of 6.5%, with endothermic effects corresponding to the removal of water molecules and the OH of silanol groups contained in the material. The investigations performed in this work have indicated that there is great scope for pumice exploitation as a raw material in the production of amorphous silica nanopowder on large scale

Silicate Clay-Hydrogel Nanoscale Composites for Sustained Delivery of Small Molecules

Hydrogels have been widely used for therapeutic delivery applications due to their tunability and biocompatibility, although delivery of small molecules is difficult due to high burst release and rapid diffusion from the device. Nanosilicate clays (nanoclays) have shown the adsorption potential of small molecules, offering a lever to prolong the release kinetics of hydrogel delivery devices. However, further characterization of small molecule–nanoclay interactions and their effect on molecule release is needed to allow for the custom design of tunable nanocomposite hydrogel delivery devices. Here, we have characterized the adsorption of small molecules onto three nanoclays, Laponite, montmorillonite, and halloysite, and monitored their release in various conditions. The layered structures of Laponite and montmorillonite led to cationic exchange of the small molecules into the interlayer space, whereas the small molecules were adsorbed onto the surface of the tubular halloysite. The addition of nanoclays to polyethylene glycol (PEG) hydrogels significantly slowed the release of small molecules, especially from Laponite (500-fold decrease) and montmorillonite (∼3000-fold decrease) composite gels. Cationic small molecules were shown to be released significantly slower from nanocomposite hydrogels than anionic ones. The incubation time of small molecules with nanoclays prior to hydrogel encapsulation also played a key role in determining their release rate, with montmorillonite showing near-immediate adsorption while halloysite exhibited a higher dependence on incubation time due to slower adsorption kinetics. Release buffer salt concentration and pH were shown to affect release kinetics due to modulation of nanoclay–small molecule interactions. These results show the potential for formation of a highly tunable nanocomposite hydrogel delivery device for a greatly prolonged release of small molecules compared to traditional hydrogels