查看更多>>摘要：The polyvinyl acetal sponge modified by chitosan was prepared by adding chitosan/polyvinyl alcohol (PVA) solution during the acetalation reaction of PVA and formaldehyde.The effect of vesicant and chitosan to the pore morphology,water absorption ratio,water absorption rate,expansion time and mechanical properties were studied.The polyvinyl acetal sponge modified by chitosan was used as a hemostatic packing material for the injured rabbit nasal tissue.The hemostatic effect and the healing effect of the modified sponge on the nasal mucosa after nasal surgery were studied.The results indicated that the polyvinyl acetal sponge modified by chitosan has an interconnected pore structure and the wall between large pores also has small pores.The chitosan adhered on the inner surface of the pores.The increased content of vesicant led to an increase in pore diameter,in the water absorption ratio and in expansion time.However,there was only a small change in the water absorption rate and a decrease in tensile strength and compression strength were noted.With an increase in chitosan content,the pore diameter and interconnection of the sponge was reduced.Water absorption ratio,expansion time and water absorption rate decreased,but tensile strength and compression strength improved.Observation of the rabbit nasal tissue after surgical operation suggested that polyvinyl acetal sponge modified by chitosan has an anti-inflammatory,hemostatic and antiadherent characteristic and could promote the healing and functional recovery of rabbit nasal mucosa.
查看更多>>摘要：To study the bioactive constituents from Andrographis paniculata,two compounds were isolated and purified by column chromatography on AB-8 macroporous adsorption resin and polyarnide.Their structures were determined by various spectroscopic methods,including UV,FABMS,1H-NMR,13C-NMR,DQFCOSY,TOCSY,HMQC,HMBC,and NOESY.The 1H-NMR and 13C-NMR signals of the two compounds were assigned.The structures of the two compounds were elucidated as 5,4'-dihydroxy-7-methoxyflavone-6-yl-β-D-glucopyranoside and 5,4'-dihydroxy-7-methoxyflavone- 8-yl-β-D-glucopyranoside,respectively.
查看更多>>摘要：The thermal decomposition of CeO2 nanocrystalline precursor prepared by chemical precipitation method was investigated using thermo-gravimetric/differential scanning calorimetry (TG/DSC) and X-ray powder diffraction (XRD).In particular,the differential thermal analysis curves for the decomposition of CeO2 nanocrystalline precursor were measured at different heating rates in air by a thermal analyzer (NETZSCH STA 449C,Germany).The kinetic parameters of the thermal decomposition of CeO2 nanocrystalline precursor were calculated using the Kissinger method and the Coats-Redfern method.Results show that the apparent active energy E of the reaction is 105.51 kJ/mol,the frequency factor lnA is 3.602 and the reaction order n is 2.This thermal decomposition process can be described by the anti-Jander equation and a threedimensional diffusion mechanism.
查看更多>>摘要：A small molecule (GMS-SA2) with one alkyl chain and two terminal carboxyl groups was synthesized successfully by the reaction of glyceryl monostearate (GMS) with excess succinic anhydride (SA).Then,GMSSA2 was used as a coupling agent to condensate with polyethylene glycols (PEG) of different molecular weight or polyethylene glycol monomethyl ether (PEGm) in the presence of stannous octoate as catalyst and diphenyl ether as azeotropic agent.The AB2 star-shaped miktoarm copolymers were obtained successfully and were characterized by 1H-NMR,DSC,GPC,XRD,FTIR and polarizing microscopy.The results of DSC and XRD measurements indicate that the crystallization temperature and the melting temperature of the AB2 star-shaped miktoarm copolymers are different from those of the corresponding linear PEGs,because the existing of GMS-SA2 alters their crystalline growth velocity and the perfect degree of crystals.It is very important to control the crystal morphology of star-shaped copolymers by introducing the miktoarm into the starshaped polymers and adjusting its content in star-shaped polymers.
查看更多>>摘要：Nanometer MgO was prepared via a sol-gel auto-combustion technique using magnesium nitrate as raw material and citric acid as chelating agent.IR spectra of the dried gel were used to investigate the structure of the precursors.By studying the different TG curves of magnesium citrate gel prepared by different methods,we found that a combustion process occurred and the nitrate ions acted as an oxidant in the combustion process.TEM photographs of synthesized powders from the sol-gel auto-combustion showed that the crystallites were uniform in size.In addition,the XRD pattern of this sample showed that the particle size was 8.9 nm.The BET curves,in turn,showed that the specific surface of the sample was 26.34 m2/g.The mechanism of the frothing process in restraining agglomeration is discussed.
查看更多>>摘要：A nano-alumina with high specific area was prepared using a homogeneous precipitation method with titanium dioxide and barium oxide as modifying additives.Results showed that 5 wt% TiO2 or BaO added in the alumina gels can decrease the particle size and increase the specific area,but excessive TiO2 or BaO could deteriorate the properties of α-Al2O3.
查看更多>>摘要：An improved ion chromatographic (IC)method was developed to determine trace levels of perchlorate in environmental water samples.Perchlorate was separated in the hydroxide selective column IonPac AS 16 using NaOH as an eluent with an organic modifier.To eliminate the coelution of perchlorate and 4-chlorobenzene sulfonate (4-CBS),an organic solvent as modifier was added to the eluent.Of four organic solvents studied,acetonitrile proved to be the most efficient based on the retention time of perchlorate and 4-CBS.To improve the method sensitivity,a concentrator column (AGI9) was used to concentrate perchlorate online.With the adoption of a preconcentration step,the sensitivity of our method was improved and the method detection limit (MDL) was reduced to 0.1 μg/L.The linear range was from 0.2 μg/L to 200/.μg/L with a linear correlation coefficient of 0.9989 and the relative standard deviation (RSD) of peak area for eleven successive injections of 0.5 μg/L perehlorate was 4.2%.The method had been applied to the determination of perchlorate in some real environmental water samples and recovery was between 93% and 113%.
查看更多>>摘要：A water-soluble polysaccharide (CPS-0) was obtained from the root of Cudrania tricuspidata (Carr.)Bur.,by hot water extraction (70℃),deproteination using enzymolysis and Sevag method,precipitation with ethanol,and fractionation through DEAE-Sephadex A-50 chromatography.The purity of CPS-0 was determined by HPLC and the structure was elucidated by monosaccharide composition analysis,methylation analysis,GC,GC-MS,NMR spectral (1H-NMR,13C-NMR,HMQC),UV,IR,and elemental analysis.The CPS-0 was found to contain glucose residues only.The average repeating unit is a decasaccharide having a backbone consisting of 1,41inked α-D-glucopyranosyl residues to which the side chain consisting of terminal and 1,4-1inked α-D-glucopyranosyl residues was attached at position 6 of the branching residues.
查看更多>>摘要：Nanocrystalline nickel with an average diameter of about 16 nm and a face-centered cubic (fcc)structure was uniformly attached to the surface of carbon nanotubes (CNT) by wet chemistry.The sample was characterized by X-ray powder diffraction and transmission electron microscopy (TEM).A glass carbon electrode modified with nickel-modified multi-wall carbon nanotubes (MWCNTs-Ni/GCE) was prepared.The electrochemical behavior of the MWCNTs-Ni/GCE and the electrocatalytic oxidation of methanol at the MWCNTsNi/GCE were investigated by cyclic voltammetry in 1.0 mol/L NaOH solution.The cyclic voltammograms showed that the electron transfer between β-Ni(OH)2 and β-NiOOH is mainly a diffusion-controlled quasireversible process,and that the electrode has high catalytic activity for the electrooxidation of methanol in alkaline medium,revealing its potential application in alkaline rechargeable batteries and fuel cells.
查看更多>>摘要：The effect of pH value on the electrostatic layer-by-layer self-assembly and the photo-responsive behavior of Poly{2-[4-(4-ethoxyphenylazo)phenoxy]ethyl acrylate-co-acrylic acid} (PEAPE) was studied.Results show that in the studied pH value range,the lower the pH value is,the higher is the UV-vis absorbance and the larger is the thickness of the multilayer films.FTIR studies indicate that the azo polyelectrolyte exhibits a different ionization degree in solutions with different pH values.The higher absorbance and the larger thickness of the layer-by-layer films can be attributed to the low ionization degree and the shrinkage conformation of PEAPE in the solution with low pH values.FTIR analysis also confirms that the driving force for layer-by-layer self-assembly of PEAPE and PDAC is the electrostatic interaction.
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