Influence of Synthetic and Processing Parameters on the Surface Area, Speciation, and Particle Formation in Copper Oxide/Silica Aerogel Composites

Abstract

A systematic study of the effects of pH, precursor salt, and temperature on the surface area, particle size, and copper speciation in 3 wt % CuO in silica aerogels and xerogels has been conducted. The materials were synthesized by copolymerization sol−gel reactions, followed by either supercritical solvent extraction using CO2 (aerogels) or conventional drying (xerogels) and annealing in air. Among the six different copper precursors examined, copper(II) acetate was found to be the best in terms of its stability, solubility, and binding capacity of copper in the silica matrix. Aerogels prepared with copper(II) acetate were found to have considerably higher surface areas than the corresponding xerogels, and the observed formation of CuO particles occurred at higher temperatures (900 vs 650 °C, by TEM analysis). X-ray diffraction of gels annealed at 900 °C likewise revealed the presence of nanocrystalline CuO, with larger particles observed in acid-catalyzed aerogels vs base-catalyzed aerogels (∼26 vs ∼15 nm, respectively). Additionally, in 900 °C annealed acid- and base-catalyzed xerogels, the silica matrix crystallized as crystobalite and quartz, respectively. EPR data suggest that the Cu2+ environment goes through a series of structural changes upon annealing. These changes are significantly different in acid- vs base-catalyzed systems because of differences in the internal structures and pore distributions of the materials. In both cases, a broad isotropic component, attributed to CuO, is observed upon heating. By 900 °C, the hyperfine peaks originally attributed to dispersed Cu2+ are absent in base-catalyzed systems, but they are still present as a small fraction in acid-catalyzed systems, suggesting incomplete transformation in the latter case.

Recovery of high surface area mesoporous silica from waste hexafluorosilicic acid (H2SiF6) of fertilizer industry

“…tion isotherms. The physisorption isotherms exhibited hysteresis loop with type IV isotherms which are generally observed for the mesoporous materials due to capillary condensation in the mesopores [18][19][20]. Fig.…”

Characterization of thermally stable gamma alumina fibres biomimicking sisal

“…The first would be indicative of a more uniform nanostructure and better pore connectivity [23,71] and the second suggests a complete filling of pores, characteristics of a material with a porous structure more organized and with a limited range of pore sizes. In fact, H1 hysteresis type is associated with porous materials consisting of agglomerated particles with a certain compactness and even, it has been associated with cylindrical mesopores open at both ends [72], while the H3 type, without an adsorption limit at high P/P 0 , is typical of poorly aggregated materials or plate-like particles living rise to slit-shaped pores [70]. The main results of the textural analysis performed are listed in Table 2.…”

Preparation of CuO-CoO-MnO/SiO2 nanocomposite aerogels as catalyst carriers and their application in the synthesis of diphenyl carbonate

“…These features are important for heterogeneous catalysis, gas sensing and separation science [1][2][3][4][5][6] . Unique structural and morphological properties, including open porosity, large pore volume, and excellent temperature stability [7] , render aerogels promising materials for catalytic applications [8] . Altering the chemical composition of the aerogel framework to generate catalytically selective high surface area materials is an area of current topical interest.…”