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Cobalt-doped silica organic-inorganic (Co/SiO2) materials were prepared by sol-gel technique using tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) as silicon precursors and Co(NO3)2...

Two methyl-modified Al2O3/SiO2 xerogels, i. e. AIP-Al2O3/MSiO2 and ANN-Al2O3/MSiO2 xerogels, were prepared using aluminum isopropoxide and aluminum nitrate nonahydrate as the aluminum precursors, respectively. The appearance, density, viscosity, Gibbs activation energy for viscous flow and reaction rate constant of the sols were analyzed and compared. Their microstructures were characterized by means of powder X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and nitrogen adsorption–desorption measurements. The results show that the Al–O–Si bond is formed in the AIP-Al2O3/MSiO2 and ANN-Al2O3/MSiO2 xerogels. The ANN-Al2O3/MSiO2 sol has a smaller mean particle size and greater sol stability than the AIP-Al2O3/MSiO2 sol. Meanwhile, the ANN-Al2O3/MSiO2 xerogel has a smaller pore size and higher porosity. The total pore volume and specific surface area of the ANN-Al2O3/MSiO2 xerogel are 27.27% and 29.36% larger than those of the AIP-Al2O3/ MSiO2 sample, respectively. The saturated adsorption capacity of the ANN-Al2O3/MSiO2 xerogel to methylene blue is 7.15% larger than that of the AIP-Al2O3/MSiO2 xerogel.

With methyltriethoxysilane as hydrophobic precursors and aluminum isopropoxide as the aluminum source, the Al2O3/SiO2 sols and their gel materials were prepared. The effects of aluminum content (nA...

For a binary mixture of x N-methylimidazole (hereafter abbreviated as N-mim) + (1 − x) ethyl acetate (hereafter abbreviated as EAC), the density, sound velocity, viscosity and refractive index at (288.15, 298.15, 308.15, 318.15, and 328.15) K, mixing enthalpy at 298.15 K, and 1H NMR measurements combined with the ab initio calculations were carried out over a full molar fraction range. The density, sound velocity, isentropic compressibility, refractive index, viscosity, Gibbs energy of activation of viscous flow and the isobaric thermal expansivity were correlated with a polynomial well. The excess molar volume, excess isobaric thermal expansivity, isobaric thermal expansivity deviation, excess sound velocity, sound velocity deviation, excess isentropic compressibility, isentropic compressibility deviation, excess refractive index, refractive index deviation, excess logarithm viscosity, viscosity deviation, excess Gibbs energy of activation of viscous flow and the molar mixing enthalpy, were calculated and fitted to a Redlich-Kister polynomial. The activation parameters of viscous flow of the mixture, chemical shift changes of N-mim and EAC protons, interaction energy and second-order perturbation stabilization energy of 2-CH···O C, 2-CH···N and CH···O H-bonds were calculated. The mixing process of N-mim with EAC is an endothermic process with volume contraction. The energy to break the like molecular interactions is bigger than that to form dislike molecular interactions, and the volume contraction is mainly attributed to both the free volume difference and the more effective steric accommodation of molecules in the mixture. The 2-CH···O C and 2-CH···N H-bonds are approximately equivalent in dimers, 2-CH···O C H-bond in dimer (N-mim + EAC) is stronger and more stable than the CH···O H-bonds in EAC dimer. The amount of 2-CH···O C H-bond reaches a zenith at x ≈ 0.5. The formation of 2-CH···O C H-bond leads to the electron density rearrangement of the N-mim and EAC molecules, where the electron densities of the N-mim and EAC protons decrease and increase, respectively.

In order to evaluate the effect of Al on the enhancement of the sensor performance of SnO2 prepared at a low sintering temperature, the Al-doped SnO2 powder was prepared by a chemical co-precipitation method and sintered at a temperature of 400 °C. The gas-sensing response to ppm-level ethanol was investigated. The results showed that the gas-sensing response increased with an increase of the Al/(Al + Sn) molar ratio, and exhibited a maximum response at a molar ratio of 19%, then decreased drastically. A new possible influence mechanism is therefore proposed that, with the increase of Al/(Al + Sn) molar ratio, Al3+ ions form at first an interstitial solid solution in the SnO2 lattice, which causes a charge imbalance of the Al-doped SnO2 grains, and enhances the oxygen-adsorption onto the surface of SnO2 grains, thereby resulting in an improvement in the gas-sensing performance. At the molar ratio greater than 19%, excess Al3+ ions deposit on the surface of the SnO2 grains, which reduces the chance of contact between ethanol and the adsorbed oxygen, thereby reducing the gas-sensing performance.

SiO2 and Pd/SiO2 nanocomposites were prepared using sol–gel method and characterized by X-ray diffraction, Fourier transform infrared spectra, scanning electron microscopy and different heating rate thermogravimetric–differential thermogravimetric analysis. The apparent activation energies (Ea) were calculated using the Kissinger’s and Ozawa’s methods. The most probable kinetic mechanism functions were obtained by master plot method. The entropy (ΔS≠), enthalpy (ΔH≠) and activation free energy (ΔG≠) were calculated using three methods. The results demonstrated that the thermal decomposition processes of both materials are the three-step reactions. After thermal condition in air atmosphere, the introduced hydrophobic Si–CH3 group in Pd/SiO2 gel materials was completely decomposed into inorganic composition, and the Pd element was transformed into PdO and metallic Pd. The Ea values obtained by Kissinger’s method are close to those by Ozawa’s method. The Pd-doping can increase the thermal decomposition activation energies and improve the thermal stability of SiO2 material. The decomposition mechanisms for the three stages are the assumed random nucleation and its subsequent growth, irrespective of the Pd-doping. Compared with SiO2 material, the thermal decomposition of Pd/SiO2 requires more energy due to the increasing ΔH≠. The ΔH≠ values calculated by method II are nearly equal to the Ea values from the Kissinger’s and Ozawa’s methods, which indicated that the thermodynamic parameters obtained by method II are the most accurate.

Pd-doped SiO2 organic-inorganic hybrid materials were synthesized using sol-gel technique. The Pd-doped SiO2 samples were calcined at the temperature 350°C for several different time in air atmosph...

Pd-doped methyl-modified SiO2 membrane materials were prepared by sol-gel technique with tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) as silicon precursors, PdCl2 as pall...

For a binary mixture of xN-methylimidazole (hereafter abbreviated to N-mim) + (1-x) water, over a full molar fraction range, the mass density, sound velocity, refractive index, viscosity, mixing enthalpy, conductivity, and pH at (298.15, 308.15, 318.15) K and 0.1 MPa, and 1H NMR and 13C NMR at room temperature combined with Ab initio calculations, were measured and carried out. The excess molar volume (VmE), sound deviation (∆u), refractive index deviation (∆nD), viscosity deviation (∆η), excess Gibbs energy of activation of viscous flow (∆G⁎E), molar mixing enthalpy (∆mixHm), 1H NMR chemical shift changes of N-mim and water protons (∆δH), 13C NMR chemical shift change of N-mim (∆δC), sum of the chemical shift changes (∑∆δH(N-mim), ∑∆δC), and the interaction energy, hydrogen bond length, second-order perturbation stabilization energy, electron density, and the electronic energy density of the trimer hydrogen-bonded complexes were calculated. The values of VmE, ∆u, ∆nD, ∆η, ∆G⁎E, and ∆mixHm were fitted to a Redlich-Kister equation. The extreme positions of these quantities and the chemical shift changes were compared and discussed with regard to the intermolecular interaction between N-mim and water, and a possible molecular interaction scheme was suggested for N-mim added to water. There occurs an ionization process and hydrogen-bonded interactions between N-mim and water. The ionization process may not be neglected at an infinite dilution of water, and hydrogen bonds predominate the primary interaction in the mixture. The predominant hydrogen-bonded complex in the mixture transforms with increasing x, which is consistent with the calculation results.

As a further investigation on the binary mixtures containing 1-alkylimidazole, over the whole composition range and at atmospheric pressure, density, ρ, sound velocity, u, of binary system of x 1-ethylimidazole (abbreviated as 1-Eim) + (1-x) methanol, were measured at temperatures (293.15–328.15) K; refractive index, nD, and viscosity, η, of them were determined at temperatures (293.15–318.15) K; 1H NMR, δH, is measured at 288.15 K; isobaric thermal expansivity, αp, isentropic compressibility, κS, excess and deviation properties were calculated. The excess enthalpy and Gibbs free energy were predicted by COSMO-RS model. All the properties indicate that the real mixing process is a spontaneous enthalpy-driving process with liquid structure more ordered, and a lower temperature more benefits the process. There are stronger attractive interactions in the mixture than in pure liquids. The H-bonded interactions are the main attractive interactions in the mixture, followed by the electrostatic/misfit interaction and the Van der Waals force. A H-bonded network with a ration of methanol:1-Eim = 1:1 appears in the mixture, and reaches its maximum amount at x about 0.4; via the N···HO, the rearrangement of electron densities occurs where protons of 1-Eim and hydroxyl all show electron-donating abilities while methyl protons of methanol show electron-withdrawing ability.

In order to explore the properties and molecular interactions in the binary systems of 1-alkylimidazole with molecular solvents, the system of x 1-ethylimidazole (herein referred to as 1-Eim) + (1-x) water, in the temperature range (288.15–328.15) K, the density ρ, sound velocity u, viscosity η, refractive index nD, pH and conductivity κ, and the 1H NMR δH, were measured at atmospheric pressure; the excess molar enthalpy HmE, the excess molar Gibbs free energy GmE, and the excess molar entropy SmE were predicted from the COSMO-RS model. The experimental and predicted properties indicate that the H-bonded interactions are the predominant interactions over the whole composition range. 1-Eim protons share more electron densities than water protons via the H-bonds, which are stronger between dissimilar molecules than between similar ones. The stable H-bonded structure of water molecules breaks when x is about 0.1, while the stable H-bonded structure of 1-Eim molecules forms when x is about 0.9. Temperature affects the H-bonded interactions more in the case of dissimilar molecules than similar molecules, especially in the water-rich region. The real mixing process is an enthalpy-driving spontaneous process with the liquid structure more ordered. A lower temperature more greatly benefits spontaneous mixing.