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Selective capture of thiols from a synthetic hydrogen sulfide containing mixture using supported nanogold materials has been explored for the potential removal of thiols from sour gas production fluids. In this research, TiO2-, Al2O3-, SiO2-, and ZnO-supported gold nanoparticles have been studied for their usage as regeneratable adsorbents to capture CH3SH, C2H5SH, and i-C3H7SH. Au/TiO2 and Au/Al2O3 showed promising properties for removing the thiols efficiently from a gas-phase mixture; however, Au/Al2O3 did catalyze some undesirable side reactions, e.g., carbonyl sulfide formation. It was found that a mild temperature of T = 200 °C was sufficient for regeneration of either Au/TiO2 or Au/Al2O3 adsorbent. The metal oxide mesopores played an important role for accommodating gold particles and chemisorption of the thiols, where smaller pore sizes were found to inhibit the agglomeration/growth of gold particles. The nature of thiol adsorption and the impact of multiple adsorption-desorption cycles on the adsorbents have been studied using electron microscopy, XPS, XRD, GC, and physi/chemiadsorption analyses.

For the first time, high surface area nanofibers were synthesized using aluminum isopropoxide monomer with acetic acid as the polycondensation agent in the green solvent, supercritical carbon dioxide (scCO(2)). It was found that the synthesis temperature, pressure, concentration, and acid/alkoxide ratio had a large effect on fiber formation. By optimizing the experimental conditions at 80 degrees C and 6000 psi of scCO(2) using aluminum isopropoxide at a concentration of 0.3 mmol/mL and acid/alkoxide ratio of 10, alumina nanofibers were formed ranging from 11 to 22 nm in diameter and 500 to 1000 nm in length, and with surface areas up to 580 m(2)/g. Lower temperatures gave irregular shaped nanoparticles, while a lower acid/alkoxide ratio (5:1) resulted in the formation of low surface area alumina bars. Increasing pressure led to better separation of the nanofibers and higher surface areas. In addition to the synthesis conditions, the influence of calcination temperature on the structural, textural, and morphological properties of the materials was examined using various physicochemical techniques including electron microscopy, TGA/DTA, powder XRD, FTIR, XPS, and nitrogen adsorption/desorption analysis. The long fibers with high aspect ratios were found to be thermally stable even after calcining at up to 1050 degrees C. The mechanism of fiber formation in scCO(2) is proposed based on a [Al(OH)(CH(3)CO(2))(2)](n) polycondensate backbone.

Direct sol-gel reactions in supercritical CO2 (scCO2) have attracted significant interest for synthesizing nanomaterials by reacting alkoxides with a carboxylic acid. In this study, the hydrolysis of silicon alkoxides (TEOS or TMOS) was carried out using scCO2 as the solvent to generate silica nanoparticles within the matrix of polyethylene for the synthesis of polymeric nanocomposites. This methodology provides advantages of combining the sol-gel reactions and drying into a one-step process for producing polymer nanocomposites. The synthesized polymer silica composites were characterized by SEM, FTIR, and XPS. When the TEOS loading was below 10 wt % Si content, nanometer-sized silica particles were formed that were well dispersed within the polyethylene matrix. The mechanism of the silicon alkoxides reacting with acetic acid in scCO2 was further studied using online GC-MS and offline 13C NMR. Oligomer structures with a bridging methoxyl group between the two silicon atoms and the acetate monodentate were observed. This study suggests a new sol-gel pathway in scCO2 that is different from the hydrolysis-condensation reactions using the conventional sol-gel process.

Inorganic-polymer nanocomposites are of significant interest for emerging materials due to their improved properties and unique combination of properties. Methacrylic acid (MA), a functionalization agent that can chemically link TiO2 nanomaterials (n-TiO2) and polymer matrix, was used to modify the surface of n-TiO2 using a Ti-carboxylic coordination bond. Then, the double bond in MA was copolymerized with methyl methacrylate (MMA) to form a n-TiO2-PMMA nanocomposite. The resulting n-TiO2-PMMA nanocomposite materials were characterized by using thermal analysis, electron microscopy, and elemental analysis. The dynamic mechanical properties (Young's and shear modulus) were measured using an ultrasonic pulse technique. The electron microscopy results showed a good distribution of the nanofillers in the polymer matrix. The glass transition temperature, thermal degradation temperature, and dynamic elastic moduli of the nanocomposites were shown to increase with an increase in the weight percentage of nanofibers in the composite. The resulting nanocomposites exhibited improved elastic properties and have potential application in dental composites and bone cements.

The objective of the present study was to synthesize porous ZrO2 aerogels with a nanostructure via a direct sol-gel route in the green solvent supercritical carbon dioxide (scCO2). The synthesis involved the coordination and polycondensation of a zirconium alkoxide using acetic acid in CO2, followed by scCO2 drying and calcination. Either a translucent or opaque monolith was obtained, which was subsequently characterized by electron microscopy, X-ray diffraction, thermal analysis, N2 physisorption, and infrared spectroscopy analysis. The electron microscopy results showed that the translucent monolithic ZrO2 exhibited a well-defined mesoporous structure, while the opaque monolith, formed using added alcohol as a cosolvent, was composed of loosely compacted nanospherical particles with a diameter of ca. 20 nm. After calcination at 400 and 500 degrees C, X-ray diffraction results indicated that the ZrO2 exhibited tetragonal and/or monoclinic phases. In situ infrared spectroscopy results showed the formation of a Zr-acetate coordinate complex at the initial stage of the polycondensation, followed by further condensation of the complex into macromolecules.

In this letter, we present a new method to synthesize titania nanofibers with nanocrystallites via a sol-gel route in supercritical CO2. The nanofibers were formed by the esterification and condensation of titanium alkoxides using acetic acid as the polymerization agent in supercritical CO2 from 40 to 70 degrees C and 2500 to 8000 psia. The TiO2 nanofiber morphology was characterized by means of SEM and HRTEM, which indicated that the diameters ranged from 9 to 100 nm. N2 physisorption, and powder XRD showed that the nanofibers exhibited relatively high surface areas up to 400 m2/g and anatase and/or rutile nanocrystallites were formed after calcination.