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Buxing Han

Publications and source records attributed to Buxing Han.

At least 19 recordsLinked to original sources
PubMed2006

Effect of compressed CO2 on the critical micelle concentration and aggregation number of AOT reverse micelles in isooctane.

The effect of compressed CO2 on the critical micelle concentration (cmc) and aggregation number of sodium bis-2-ethylhexylsulfosuccinate (AOT) reverse micelles in isooctane solution was studied by UV/Vis and fluorescence spectroscopy methods in the temperature range of 303.2-318.2 K and at different pressures or mole fractions of CO2 (X(CO2)). The capacity of the reverse micelles to solubilize water was also determined by direct observation. The standard Gibbs free energy (DeltaGo(m)), standard enthalpy (DeltaHo(m)), and standard entropy (DeltaSo(m)) for the formation of the reverse micelles were calculated by using the cmc data determined. It was discovered that the cmc versus X(CO2) curve and the DeltaGo(m) versus X(CO2) curve for a fixed temperature have a minimum, and the aggregation number and water-solubilization capacity of the reverse micelles reach a maximum at the X(CO2) value corresponding to that minimum. These results indicate that CO2 at a suitable concentration favors the formation of and can stabilize AOT reverse micelles. A detailed thermodynamic study showed that the driving force for the formation of the reverse micelles is entropy.

Journal Article↗
PubMed2006

Decoration carbon nanotubes with Pd and Ru nanocrystals via an inorganic reaction route in supercritical carbon dioxide-methanol solution.

This work describes a method to decorate carbon nanotubes (CNTs) with metallic Pd and Ru nanocrystals via inorganic reactions in supercritical (SC) CO2-methanol solutions. In this route, PdCl2 or RuCl3.3H2O dissolved in SC CO2-methanol solution acted as a metal precursor and CNTs functioned as a template to direct the deposition of produced nanoparticles. Methanol served as the reductant for the precursors as well as cosolvent to enhance the dissolution of precursors in SC CO2. Dry products were readily obtained through in situ extraction with SC CO2 after reactions. The products were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. It was demonstrated that the loading content and particle size of the nanoparticles deposited on CNTs could be tuned by changing the weight ratio of the precursor to CNTs. This simple and efficient approach may also be utilized to synthesize other high-purity materials using inorganic salt precursors in SC CO2-based solution.

Journal Article↗
PubMed2006

Synthesis of ZrO2-carbon nanotube composites and their application as chemiluminescent sensor material for ethanol.

ZrO2-carbon nanotube (CNT) composites have been successfully synthesized via decomposition of Zr(NO3)4.5H2O in supercritical carbon dioxide-ethanol solution with dispersed CNTs at relatively low temperatures. The samples were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM), and energy-dispersive X-ray (EDX) analyses. It was demonstrated that CNTs were fully coated with an amorphous ZrO2 layer, and the coating layer was nominally complete and uniform. In addition, the thickness of the coating sheath could be readily controlled by tuning the Zr(NO3)4.5H2O/CNTs ratio used. Furthermore, the chemiluminescent sensor prepared from ZrO2-carbon nanotube composites exhibited dramatic sensitivity as well as high stability and selectivity to ethanol.

Journal Article↗
PubMed2006

Ti-Si mixed oxides prepared by polymer in situ sol-gel chemistry with the aid of CO2.

A method to prepare titania-silica binary oxides is proposed in this work. In this route, inorganic precursors tetraethyl orthosilicate (TEOS) and titanium isopropoxide (TIP) were simultaneously or sequentially impregnated into a polypropylene (PP) matrix using supercritical carbon dioxide as a swelling agent and carrier. Hydrolysis and condensation reaction of the precursors confined in a polymer network were induced by treating the composites in 1 mol.dm(-3) (1 M) HCl. Then the PP matrix was decomposed at higher temperature, and titania-silica binary oxides were obtained. The mixed oxides were characterized by X-ray diffraction and Raman, FTIR, and X-ray photoelectron spectroscopy. It was demonstrated that the structure of the oxides depended strongly on the procedure to impregnate the precursors. The simultaneous method, in which the TEOS and TIP were simultaneously impregnated into a PP matrix, resulted in mixed oxides with highly dispersed titanium oxide species in the SiO2 matrix, while the sequential method produced the mixed oxide with separate SiO2 and TiO2 phases which were connected by Ti-O-Si bands at the interface. The method described in this work provides a new route to control the texture of TiO2-SiO2 mixed oxide simply by the impregnation sequence.

Journal Article↗
PubMed2006

Synthesis and characterization of ZnS-montmorillonite nanocomposites and their application for degrading eosin B.

Nanocomposites of zinc sulfide (ZnS) and montmorillonite (MMT) were prepared via a hydrothermal route. In this method, the MMT treated with hexadecyltrimethyl ammonium bromide (HTAB) aqueous solution was dispersed in the aqueous solution of thiourea and Zn(OOCHCH(3))(2)2H(2)O, and heated at 170 degrees C for about 4 h, resulting in ZnS-MMT composites. The as-prepared nanocomposites were characterized with X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen sorption analysis. It was demonstrated that the interlayer space of MMT was enlarged from 0.98 to 3.77 nm after the treatment with HTAB aqueous solution, and the ZnS nanoparticles were deposited on the layers of MMT. Nitrogen sorption analysis demonstrated that the specific surface area of the samples decreased from 39.2 m(2)/g of the pristine MMT to 5.9 m(2)/g of the final ZnS-MMT composites. The resulting ZnS-MMT nanocomposites (50.0 mg) could degrade eosin B completely in aqueous solution (75 ml, 3.2x10(-5) M) within 20 min under UV irradiation.

Journal Article↗
PubMed2006

Synthesis of cross-linked enzyme aggregates (CLEAs) in CO2-expanded micellar solutions.

A new method to prepare the cross-linked enzyme aggregates (CLEAs) was developed. Through cross-linking the enzyme (Trypsin) aggregates, which was precipitated from the CO2-expanded reverse micellar solutions, dendritic CLEAs were obtained. The sizes of the CLEAs prepared by this new method were nanometer order of magnitudes and could be tuned by changing the water-to-surfactant ratio (w0) and the concentration of enzyme in the reverse micellar solution. The diameter of CLEAs increased with increasing w0 value of reverse micelles and the concentration of Trypsin. The activity of CLEAs obtained by this method is improved in contrast to those obtained by the conventional method. This method has some advantages in applications and can be easily applied to the synthesis of other cross-linked enzyme aggregates.

Carbon Dioxide↗
PubMed2006

Enhanced solubilization of bovine serum albumin in reverse micelles by compressed CO2.

The effect of compressed CO2 on the solubilization of bovine serum albumin (BSA) in water/sodium bis-(2-ethylhexyl) sulfosuccinate (AOT)/isooctane reverse micelles was studied by observing phase behavior and recording UV-visible spectra under different conditions. The pH values within the water cores of reverse micelles at different CO2 pressures were also determined. The solubilization capacity of the reverse micelles for the protein increased considerably as CO2 pressure increased within the low-pressure range, but decreased at higher CO2 pressures, so that the micelles eventually lost their ability to solubilize the protein. The effect of CO2 on the stability of the reverse micelles played an important role in the relationship between pressure and protein solubility. A "multicomplex" model was proposed to explain these effects. The different solublization capacities within different pressure ranges demonstrates the unique advantage of using compressed CO2 in the extraction of proteins with reverse micelles.

Carbon Dioxide↗
PubMed2006

Micropatterned polymer surfaces induced by nonsolvent.

In this work, we present a facile method for fabricating polymer thin films with micropatterned surfaces by evaporating polymer solution containing a small amount of nonsolvent of polymer in air. Poly(methyl methacrylate) (PMMA) and polystyrene (PS) films with densely packed micropores on the surfaces were fabricated. This method was also used to prepare three-dimensional PMMA films with micropatterned surfaces. The effects of nonsolvent content; evaporation temperature; and interactions between the polymer, solvent, and nonsolvent on the specific patterns were investigated, and the formation mechanism of the pores is discussed. This simple route can potentially be used, for example, in the large-scale production of patterned surfaces, three-dimensional painting, and hydrophobicity-enhancing coatings.

Journal Article↗
PubMed2006

Controlled synthesis of Ag/TiO2 core-shell nanowires with smooth and bristled surfaces via a one-step solution route.

Ag/TiO2 core-shell nanowires were synthesized via a one-step solution method without using a template. Interestingly, the shell morphologies can be controlled to be smooth or bristled by altering the reaction temperature. Moreover, the TiO2 shell thickness and bristle length can be tuned by changing the AgNO3 concentration. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), energy-dispersive X-ray analysis (EDS), X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used to characterize the resultant Ag/TiO2 core-shell nanowires. Moreover, the absorption peaks of our samples are significantly red-shifted compared with those of the uncoated pure silver nanowires, indicating that interaction between the core and shell occurred. On the basis of the experimental results, we proposed a template-induced Oswald ripening mechanism to explain the formation of the Ag/TiO2 core-shell nanowires.

Journal Article↗
PubMed2006

Synthesis of noble metal/carbon nanotube composites in supercritical methanol.

A simple and efficient route has been employed to deposit noble metal nanoparticles (Pt, Ru, Pt-Ru, Rh, Ru-Sn) onto carbon nanotubes (CNTs) in supercritical methanol solution. In this method, the inorganic metallic salts acted as metal precursors, and methanol as solvent as well as reductant for the precursors. The as-prepared nanocomposites were structurally and morphologically characterized by X-ray diffraction spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy, and X-ray photoelectron spectroscopy analyses. It was demonstrated that the CNTs were decorated by crystalline metal nanoparticles with uniform sizes and a narrow particle size distribution. The size and loading content of the nanoparticles on CNTs could be tuned by manipulating reaction parameters. Furthermore, the formation mechanism of the composites was also discussed.

Chromatography, Supercritical Fluid↗
PubMed2006

Microwave-assisted synthesis of pt nanocrystals and deposition on carbon nanotubes in ionic liquids.

In this work, a simple, fast and efficient route is presented for the metal (such as Pt, Rh, etc.) nanocrystal synthesis and deposition on carbon nanotubes (CNTs) in ionic liquids (ILs) via microwave heating. In this method, inorganic salts (such as H2PtCl6.4H2O, RhCl3.2H2O, etc.) dissolved in ILs, 1,1,3,3-tetramethylguanidinium trifluoroacetate or 1,1,3,3-tetramethylguanidinium lactate, were reduced to metal nanoparticles by glycol with the aid of microwave heating, and the produced metal nanoparticles could be decorated on CNTs in the presence of CNTs in ILs. The resulting nanomaterials were characterized by means of transmission electron microscopy and X-ray diffraction. It was demonstrated that the homogeneously dispersed Pt nanocrystals with the size of 2-3 nm were obtained using H2PtCl6.4H2O as precursor, and they deposited on CNTs with the similar size when CNTs was present in ILs. This technique also can be extended to fabricate other noble metal nanocrystals (including Rh, Au, etc.) and corresponding CNT composites.

Carbon↗
PubMed2006

Synthesis of polyaniline nanofibrous networks with the aid of an amphiphilic ionic liquid.

In this work, polyaniline (PANI) nanofibrous networks were prepared using ionic liquid (IL), 1-hexadecyl-3-methylimidazolium chloride (C16MIMCl), as a template through oxidative polymerization of aniline with ammonium persulfate. The resulting PANI was characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis, and FTIR. It was indicated that the as-prepared PANI was in the emeraldine form and its morphology strongly depended on the molar ratio of aniline/C16MIMCI. A possible mechanism for the formation of PANI nanofibrous networks was that the ordered micro-domains of the IL acted as template to direct the growth of the nanostructures.

Aniline Compounds↗
PubMed2005

Enhancing the rate of the Diels-Alder reaction using CO2 + ethanol and CO2 + n-hexane mixed solvents of different phase regions.

The reaction rate of the Diels-Alder reaction between N-ethylmaleimide and 9-hydroxymethylanthrance in CO2 + ethanol and CO2 + hexane mixed solvents of different compositions were determined by in situ UV/vis spectroscopy at 318.15 K and different pressures. The density of the mixed solvents at different pressures was also determined and the isothermal compressibility was calculated using the density data. The activation volume of the reaction was calculated based on the dependence of rate constant (kc) on pressure. It was demonstrated that the kc was very sensitive to the pressure in the mixed solvents near the critical region and the kc increased dramatically as pressure approached dew points, critical point, and bubble points of the mixed solvents. However, the kc in the mixed solvents outside the critical region or in pure CO2 was not sensitive to pressure. At suitable conditions, kc could be 40 times larger than that in acetonitrile. The activation volume of the reaction was nearly independent of pressure as the pressure was much higher than the phase separation pressure of the mixed solvents, while it increased considerably as pressure approached the bubble points, critical point, and dew points from high pressure. The clustering of the solvent molecules with the reactants and the activated complex in the reaction systems near the phase boundary in the critical region may be the main reason for the interesting phenomena observed. This work also shows that, using pure CO2 as the solvent, the reaction cannot be carried out in the critical region of the solvent due to the limitations of the reactants, while it can be conducted in the critical region of mixed solvents of suitable compositions, where the solvents are highly compressible and the reaction rate can be tuned effectively by pressure.

Anthracenes↗
PubMed2005

Effect of compressed CO2 on the chloroperoxidase catalyzed halogenation of 1,3-dihydroxybenzene in reverse micelles.

The effect of compressed CO2 on the specific activity of chloroperoxidase (CPO) to catalyze the chlorination of 1,3-dihydroxybenzene in cetyltrimethylammonium chloride (CTAC)/H2O/octane/pentanol reverse micellar solution was studied. The results show that the specific activity of the enzyme can be enhanced significantly by compressed CO2, and the specific activity can be tuned continuously by changing pressure. The mechanism for the specific activity enhancement of the enzyme by CO2 was also studied. We believe that compressed CO2 can be utilized to tune some other enzyme catalytic reactions in different reverse micellar systems with potential advantages.

Journal Article↗
PubMed2005

Carbon microspheres with supported silver nanoparticles prepared from pollen grains.

In this paper, we present a new method to fabricate carbon microspheres with supported silver nanoparticles on the surfaces. In this method, pollen grains were first treated with AgNO(3) aqueous solution, then preoxidized in air at 300 degrees C and carbonized in nitrogen at 600 degrees C, resulting in the silver/carbon nanocomposites. The silver/carbon nanocomposites were characterized by means of SEM, TEM, TG, and XRD. The size and distribution of the silver nanoparticles on the carbon microsphere surface could be controlled by tuning the AgNO(3) treatment conditions.

Journal Article↗
PubMed2005

Phase behaviors of AOT/longer chain n-alkanes reverse micelles in the presence of compressed ethylene.

It was found that, in a suitable pressure range, ethylene could increase the amount of solubilized water in reverse micelles of sodium bis-2-ethylhexylsulfosuccinate (AOT) in longer chain n-alkanes considerably, where the phase separation was induced by a micelle-micelle interaction mechanism. The microenvironments in the ethylene-stabilized reverse micelles were investigated by the UV-vis adsorption spectra using methyl orange (MO) as a probe. The maximum absorption of MO decreased with the increase of ethylene pressure at constant W0 value. Conductivity measurements demonstrated that the percolation temperature of the reverse micellar system increased considerably after compressed ethylene was added. The results of this work confirm that some small-molecule gases have the function of cosurfactants to stabilize reverse micelles.

Journal Article↗