Qin-Qin Xu

CONTROLLED GROWTH OF COPPER NANOPARTICLES AND NANORODS IN THE CHANNELS OF SBA-15 BY SUPERCRITICAL FLUID DEPOSITION

Copper nanoparticles and nanorods were prepared in the one-dimensional channels of SBA-15 supported by a modified supercritical fluid deposition (SCFD) method. In this approach, cheap and widely available copper nitrate, which is insoluble in supercritical CO2 (scCO2), was used as the copper source and ethanol as the co-solvent, thus avoiding the employment of expensive and less available scCO2-soluble precursors. The deposition was carried out at the pressure of 21–25 MPa and temperature of 50°C, followed by calcinations at 500°C and H2 reduction at 500°C. The results showed that highly dispersed Cu nanoparticles or nanorods were obtained controllably just by varying the deposition time, as characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). On the other hand, when Cu(acac)2 was used as the precursor and without any co-solvent, only nanoparticles were formed in the channels of SBA-15 no matter how long the deposition time.

Systematical study of depositing nanoparticles and nanowires in mesoporous silica using supercritical carbon dioxide and co-solvents: morphology control, thermodynamics and kinetics of adsorption

AgNO3 was successfully deposited into mesoporous silica including SBA-15 and KIT-6 using supercritical carbon dioxide as the solvent, ethanol or a mixture of ethanol and ethylene glycol as the co-solvent, followed by calcination after depressurization. A large number of experiments were conducted to find out the most important parameters influencing the metal loading and the morphology of the nanostructure. The morphology was found to vary a lot according to the deposition time, which is interesting, i.e. small nanoparticles, short nanorods, continuous nanowires, and big nanoparticles appeared in succession as the deposition time increased. Besides, the co-solvent was also found to influence significantly the deposition results. The samples prepared using the mixture of ethanol and ethylene glycol as the co-solvent presented the morphology of nanowires, while those prepared using only ethanol as the co-solvent presented a mixed morphology of both nanoparticles and nanowires. The role of ethylene glycol was discussed and a mechanism model demonstrating the formation of Ag nanowires or nanoparticles was proposed. Finally, the adsorption of AgNO3 (adsorbate) from supercritical carbon dioxide and co-solvent (solvent) on the SBA-15 support (adsorbent) was investigated by both experimental and simulating methods. It was found that the adsorption isotherm was well fitted by the Langmuir model, and the kinetic investigation based on a mass differential equation showed that the adsorption reached equilibrium after 10 000 s (about 2.8 h) which was consistent with our experimental result (2.5 h).

Nanocasting Synthesis of Mesostructured Co3O4 via a Supercritical CO2 Deposition Method and the Catalytic Performance for CO Oxidation

We demonstrate a supercritical CO2 (scCO2) deposition method to synthesize mesostructured Co3O4 with crystalline walls using SBA-15 as the hard template. By variation of the scCO2 pressure, randomly organized nanorods or a highly ordered mesoporous structure of Co3O4 is obtained after only one filling operation. The catalytic tests show that the randomly organized Co3O4 nanorods display excellent activity for CO oxidation with the complete conversion of CO even at room temperature, while neither the ordered mesoporous nor bulk Co3O4 is active at this low-temperature, demonstrating the important role of Co3O4 morphology in catalysis.Graphical Abstract

Impregnation of ionic liquids in mesoporous silica using supercritical carbon dioxide and co-solvent

Ionic liquids (ILs) have been considered to be attractive alternatives for CO2 capture. The impregnation of ILs on porous substrates can significantly reduce the ILs consumption, enhance the mass transfer of CO2 in the ILs and make their recycling easier. However, due to the high viscosity of the ILs, the impregnated ILs were often poorly dispersed on the substrates or blocked the nanochannels when the traditional impregnation method was used. In this study, a new, effective and environmentally benign technique to impregnate ILs onto mesoporous substrates was proposed. The impregnation of [Bmim]BF4 on SBA-15 was successfully achieved using supercritical carbon dioxide (scCO2) as the solvent and methanol as co-solvent. The ILs were proved to be impregnated into the nanochannels rather than on the outside of the substrate by N2 adsorption–desorption and SEM analysis. The operating pressure, temperature and time were investigated to find out the optimum parameter to synthesis these nanocomposites. Finally, the CO2 adsorption capacity of the ILs@SBA-15 composites was performed on a dynamic adsorption apparatus.

Direct growth of highly dispersed MnCl2 · 4H2O nanostructures with different morphologies on graphene in supercritical CO2

Willow leaf-like Mn3O4 nanoplates@graphene nanocomposites were synthesized using graphene instead of graphene oxide as initial materials with the assistance of supercritical CO2. The near-zero surface tension and the gas-like viscosity of supercritical CO2 favored the intercalation and dispersion of precursors among the graphene nanosheets. In addition, MnCl2 4H2O ultra-small nanoparticles with diameter of 1–3 nm were supported on graphene using MnCl2 4H2O as precursor, supercritical CO2 as solvent and methanol as co-solvent under very moderate conditions. It was also found that the specific capacitance of the MnCl2 4H2O ultra-small nanoparticles@graphene with a metal loading of only 12.4% was twice that of pure graphene. In addition, the capacitance retention ratio of the MnCl2 4H2O ultra-small nanoparticles@graphene composite decreased by only 5.4% when the cycle number increased from 200 to 1000.

Molecular dynamics simulations of CO2 permeation through ionic liquids confined in γ-alumina nanopores

Abstract CO2 permeation through imidazolium-based ionic liquids (ILs, [BMIM][Ac], [EMIM][Ac], [OMIM][Ac], [BMIM][BF4], and [BMIM][PF6]) confined in 1.0, 2.0, and 3.5 nm γ-alumina pores was investigated using molecular dynamics simulation. It was found that the nanopore confinement effect influenced the structure of confined ILs greatly, resulting in a layered structure and anisotropic orientation of ILs. In the center of 2.0-nm pore, the long alkyl chain of [BMIM]+ tended to be parallel to the wall, providing a straight diffusion path benefiting the CO2 permeation. The CO2 diffusion coefficients in confined [EMIM][Ac], [BMIM][Ac], and [OMIM][Ac] were 2.3–4.1, 2.4–6.4, and 14.4–21.7 × 10−10 m2 s−1, respectively. This order was opposite to that in the bulk ILs, because the longer alkyl chain led to a more ordered structure, facilitating CO2 diffusion. In addition, the CO2 solubilities were 445–722 mol m−3 MPa−1 for the five ILs confined in 1.0 nm pore, which were larger than those in 2.0 and 3.5 nm pores (196–335 mol·m−3 MPa−1), due to the larger free volume. Both parallel orientation of alkyl chain and large free volume could increase the CO2 permeability in confined ILs.