High-surface thermally stable mesoporous gallium phosphates constituted by nanoparticles as primary building blocks

In constant, search for micro/mesoporous materials, gallium phosphates, have attracted continued interest due to the large pore size reported for some of these solids in comparison with analogous aluminum phosphates. However up to now, the porosity of gallium phosphates collapsed upon template removal or exposure to the ambient moisture. In the present work, we describe high-surface thermally stable mesoporous gallium phosphates synthesized from gallium propoxide and PCl3 and different templating agents such as amines (dipropylamine, piperidine and aminopiperidine) and quaternary ammonium salts (C16H33(CH3)3NBr and C16PyCl). These highly reactive precursors have so far not been used as gallium and phosphate sources for the synthesis of gallophosphates. Conceptually, our present synthetic procedure is based on the fast formation of gallium phosphate nanoparticles via the reaction of gallium propoxide with PCl3 and subsequent construction of the porous material with nanoparticles as building blocks. The organization of the gallophosphate nanoparticles in stable porous structures is effected by the templates. Different experimental procedures varying the molar composition of the sol-gel, pH and the pretreatment of gallium precursor were assayed, most of them leading to satisfactory materials in terms of thermal stability and porosity. In this way, a series of gallium phosphates with surface are above 200 m(2) g(-1), and narrow pore size from 3 to 6 nm and remarkable thermal stability (up to 550 degrees C) have been prepared. In some cases, the structure tends to show some periodicity and regularity as determined by XRD. The remarkable stability has allowed us to test the catalytic activity of gallophosphates for the aerobic oxidation of alkylaromatics with notable good results. Our report reopens the interest for gallophosphates in heterogeneous catalysis. (C) 2010 Elsevier Inc. All rights reserved.

Thick titania films for semiconductor photocatalysis

A brief overview of work carried out by this group on thick (> 1 mu m), optically clear, robust titania films prepared by a sol-gel method, as well as new results regarding these films, are described. Such films are very active as photocatalysts and able to destroy stearic acid with a quantum yield of 0.32%. The activity of such films is largely unaffected by annealing temperatures below 760 degrees C, but is drastically reduced above this temperature. The drop in photocatalyst activity of such films as a function of annealing temperature appears to correlate well with the change in porosity of the films and suggests that the latter parameter is very important in deciding the overall activity of such films. The importance of porosity in semiconductor photocatalysed cold combustion may be due to the effect it has on access of oxygen to the active sites, rather like the effect the position of a fire grate (open or closed) has on the rate of burning, i.e., hot combustion, that takes place in a fireplace.

Diagenetic Alterations and Reservoir Quality Evolution of Lower Cretaceous Fluvial Sandstones: Nubian Formation, Sirt Basin, North-Central Libya

Lower Cretaceous meandering and braided fluvial sandstones of the Nubian Formation form some of the most important subsurface reservoir rocks in the Sirt Basin, north-central Libya. Mineralogical, petrographical and geochemical analyses of sandstone samples from well BB6-59, Sarir oilfield, indicate that the meandering fluvial sandstones are fine- to very fine-grained subarkosic arenites (av. Q91F5L4), and that braided fluvial sandstones are medium- to very coarse-grained quartz arenites (av. Q96F3L1). The reservoir qualities of these sandstones were modified during both eodiagenesis (ca. <70oC; <2 km) and mesodiagenesis (ca. >70oC; >2km). Reservoir quality evolution was controlled primarily by the dissolution and kaolinitization of feldspars, micas and mud intraclasts during eodiagenesis, and by the amount and thicknessof grain-coating clays, chemical compaction and quartz overgrowths during mesodiagenesis. However, dissolution and kaolinitization of feldspars, micas and mud intraclasts resulted in the creation of intercrystalline micro- and mouldic macro-porosity and permeability during eodiagenesis, which were more widespread in braided fluvial than in meandering fluvial sandstones. This was because of the greater depositional porosity and permeability in the braided fluvial sandstones which enhanced percolation of meteoric waters. The development of only limited quartz overgrowths in the braided fluvial sandstones, in which quartz grains are coated by thick illite layers, retained high porosity and permeability (12-23 % and 30- 600 mD). By contrast, meandering fluvial sandstones underwent porosity loss as a result of quartz overgrowth development on quartz grains which lack or have thin and incomplete grain-coating illite (2-15 % and 0-0.1mD). Further loss of porosity in the meandering fluvial sandstones occurred as a result of chemical compaction (pressuredissolution) induced by the occurrence of micas along grains contacts. Otherdiagenetic alterations, such as the growth of pyrite, siderite, dolomite/ankerite and albitization, had little impact on reservoir quality. The albitization of feldspars may have had minor positive influence on reservoir quality throughthe creation of intercrystalline micro-porosity between albite crystals.The results of this study show that diagenetic modifications of the braided and meandering fluvial sandstones in the Nubian Formation, and resulting changes in reservoir quality, are closely linked to depositional porosity and permeability. They are also linked to the thickness of grain-coating infiltrated clays, and to variations in detrital composition, particularly the amounts of mud intraclasts, feldspars and mica grains as well as climatic conditions.

The effect of simvastatin on bone formation and ceramic resorption in a peri-implant defect model

Experimental use of statins as stimulators of bone formation suggests they may have widespread applicability in the field of orthopaedics. With their combined effects on osteoblasts and osteoclasts, statins have the potential to enhance resorption of synthetic materials and improve bone ingrowth. In this study, the effect of oral and local administration of simvastatin to a 0 tricalcium phosphate (beta TCP)-filled defect around an implant was compared with recombinant human bone morphogenetic protein 2 (rhBMP2). On hundred and sixty-two Sprague-Dawley rats were assigned to treatment groups: local application of 0.1, 0.9 or 1.7 mg of simvastatin, oral simvastatin at 5, 10 or 50 mg kg(-1) day(-1) for 20 days, local delivery of I or 10 mu g of rhBMP2, or control. At 6 weeks rhBMP2 increased serum tartrate-resistant acid phosphatase 5b levels and reduced PTCP area fraction, particle size and number compared with control, suggesting increased osteoclast activity. There was reduced stiffness and increased mechanical strength with this treatment. Local simvastatin resulted in a decreased mineral apposition rate at 6 weeks and increased fibrous area fraction, PTCP area fraction, particle size and number at 26 weeks. Oral simvastatin had no effect compared with control. Local application of rhBMP2 increased resorption and improved mechanical strength whereas simvastatin was detrimental to healing. Oral simvastatin was ineffective at promoting either ceramic resorption or bone formation. The effect of statins on the repair of bone defects with graft substitute materials is influenced by its bioavailability. Thus, further studies on the optimal delivery system are needed. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Quantification of all-ceramic crown margin surface profile from try-in to 1-week post-cementation

To use profilometry to assess the margin surface profile of all-ceramic crowns (ACC’s) at try-in and 1-week after cementation with dual-cured resin (DC, RelyX ARC, 3 M ESPE, St. Paul, MN, USA), self-adhesive dual-cured resin (SADC, RelyX Unicem, 3 M ESPE), light-cured resin (LC, RelyX Veneer, 3 M ESPE) or chemically cured resin-modified glass ionomer (RMGI, RelyX Luting Plus, 3 M ESPE) luting cement. Methods: Forty, sound, extracted, human, premolar teeth underwent a standardised preparation for ACC’s. IPS Empress (Ivoclar-Vivadent, Liechtenstein) crowns of standard dimensions were fabricated and 10 luted with each cement and stored in water for 7 days. Three groups of serial profiles were taken, the first of the tooth preparation, the second of the crown margins at try-in and lastly of the crown margins after cementation and 7 days water storage. Results: There were no significant differences in the crown margin surface profile between the four cement groups at try-in. The change in crown margin position between try-in and post-cementation was significantly greater for DC than for LC and RMGI. SADC was not significantly different to the other cements. There were no significant differences in the crown margin extensions between the four cement groups, however most of the IPS Empress ACC’s in this study were underextended but this was not statistically significant. Conclusions: IPS Empress ACC’s seated more fully with LC and RMGI than with DC cement

The control of porosity at nano scale in resorcinol formaldehyde carbon aerogels

Organic aerogels were synthesized by sol–gel polymerization of resorcinol (R) with formaldehyde (F) catalyzed by sodium carbonate (C) followed by vacuum drying. The influence of the resorcinol/sodium carbonate ratio (R/C) on the porous structure of the resultant aerogels was investigated. The nitrogen adsorption–desorption measurements show that the aerogels possess a well developed porous structure and mesoporosity was found to increase with increasing the R/C ratio. Carbon aerogels were obtained by carbonization of RF aerogels. The carbonization temperature impacts the microstructure of the aerogels by pore transformations during carbonization probably due to the formation of micropores and shrinkage of the gel structure. The results showed that a temperature of 1073 Kis more effective in the development of the pore structure of the gel. Activated carbon aerogels were obtained from the CO2 activation of carbon aerogels. Activation results in an increase in the number of both micropores and mesopores, indicative of pore creation in the structure of the carbon. Activation at higher temperatures results in a higher degree of burn off and increases the pore volume and the surface area remarkably without change of the basic porous structure, pore size, and pore size distribution.

Preparation of controlled porosity carbon-aerogels for energy storage in rechargeable lithium oxygen batteries

Porous carbon aerogels are prepared by polycondensation of resorcinol and formaldehyde catalyzed by sodium carbonate followed by carbonization of the resultant aerogels in an inert atmosphere. Pore structure of carbon aerogels is adjusted by changing the molar ratio of resorcinol to catalyst during gel preparation and also pyrolysis under Ar and activation under CO2 atmosphere at different temperatures. The prepared carbons are used as active materials in fabrication of composite carbon electrodes. The electrochemical performance of the electrodes has been tested in a Li/O2 cell. Through the galvanostatic charge/discharge measurements, it is found that the cell performance (i.e. discharge capacity and discharge voltage) depends on the morphology of carbon and a combined effect of pore volume, pore size and surface area of carbon affects the storage capacity. A Li/O2 cell using the carbon with the largest pore volume (2.195cm3/g) and a wide pore size (14.23 nm) showed a specific capacity of 1290mAh g-1.