Anticorrosion performance of polyaniline nanostructures on mild steel

Different one-dimensional nanostructured polyanilines were synthesized in sulfuric acid solutions by conventional polymerization, interfacial polymerization and direct mixed reaction, respectively. The products were characterized with SEM, UV-vis and FTIR and the anticorrosion performance of products on mild steel were studied using electrochemical measurement in 3.5% NaCl aqueous solution. Results showed that the polyaniline nanofibers synthesized by direct mixed reaction have uniform morphology with diameters of 60-100 nm and more excellent protective properties than conventional aggregated polyaniline. Comparative studies revealed that the nanostructure and morphology of polyaniline could influence its anticorrosion performance. (C) 2010 Elsevier B.V. All rights reserved.

Epoxidation of propylene with dilute H2O2 over titanium silicalite containing trace aluminum

Titanium silicalite (TS-1) was successfully synthesized by using TPABr as the template and silica sol as silicon source in a 100 l stainless steel autoclave. IR, XRD, UV--vis, elemental analysis, and (2)7Al and (3)1P MAS NMR were used to characterize the synthesized products. The results show that the synthesized material has an MFI structure with high crystallinity and large crystal size and two kinds of titanium species. Trace aluminum in silica sol is also incorporated into the zeolite framework. The synthesized TS-1 exhibits high activity in the epoxidation of propylene with dilute H2O2 with high selectivity to methyl mono-ethers and low selectivity to propylene oxide (PO). The low selectivity toward PO is due to the residual acidity onto TS-1. The selectivity of PO can reach up to 90% through adjusting the pH of the reaction mixture. Extra amounts of base decrease the H2O2 utilization and the H2O2 conversion. However, in over acid-treated TS-1 in which part removal of extra-framework titanium takes place, the utilization of H2O2 is quite different: for the low Si/Ti ratio of TS-1, the H2O2 utilization increases. But the utilization of H2O2 does not change for the high Si/Ti ratio TS-1. Thermal analysis shows that the as-synthesized TS-1 exhibits high activity and thermal stability in the calcined range 540-900 degreesC.

Direct synthesis and characterization of titanium-substituted mesoporous molecular sieve SBA-15

Ti-substituted mesoporous SBA-15 (Ti-SBA-15) materials have been synthesized by using a new approach in which the hydrolysis of the silicon precursor (tetramethoxysilane, TMOS) is accelerated by fluoride. These materials were characterized by powder X-ray diffraction patterns (XRD), X-ray fluorescence spectroscopy (Y-RF), N-2 sorption isotherms, diffuse-reflectance UV-visible (UV-vis) and UV-Raman spectroscopy, Si-29 MAS NMR, and the catalytic epoxidation reaction of styrene. Experiments show that Ti-SBA-15 samples of high quality can be obtained under the following conditions: F/Si greater than or equal to 0.03 (molar ratio), pH less than or equal to 1.0, aging temperature less than or equal to 80 degreesC, and Ti/Si less than or equal to 0.01. It was found that the hydrolysis rate of TMOS was remarkably accelerated by fluoride, which was suggested to play the main role in the formation of Ti-SBA-15 materials of high quality. There is no stoichiometric incorporation of Ti, and the Ti contents that are obtained are quite low in the case of the approach that is proposed. The calcined Ti-SBA-15 materials show highly catalytic activity in the epoxidation of styrene.

The active sites in different TS-1 zeolites for propylene epoxidation studied by ultraviolet resonance Raman and ultraviolet visible absorption spectroscopies

The titanium species in four kinds of titanium-containing MFI zeolites have been studied by ultraviolet (UV)-Raman and ultraviolet visible (UV-Vis) absorption spectroscopies and by the epoxidation of propylene with diluted H2O2 solution (30%). UV-Raman spectroscopy is proved to be a suitable means to estimate qualitatively the framework titanium in TS-l zeolites. Based on the comparison of the relative intensity ratio I-1125/I-380 of UV-Raman spectra, the TS-1(conv.) sample synthesized hydrothermally by the conventional procedure shows the highest amount of framework titanium. UV-Vis spectroscopy reveals that besides minor anatase. titanium species are mainly tetrahydrally coordinated into the framework for TS-l(conv.) or the Ti-ZSM-5 sample prepared by gas-solid reaction between deboronated B-ZSM-5 and TiCl4 vapor at elevated temperatures. For the TS-1(org.) and TS-1(inorg.) samples synthesized hydrothermally using tetrapropylammonium bromide (TPABr) as template and tetrabutylorthotitanite (TBOT) and TiCl3 as titanium source, respectively, the presence of mononuclear and isolated TiOx species which are proposed to bond to the zeolite extraframework is observed. In addition to the framework titanium species, these isolated TiOx species are assumed to be also active for propylene epoxidation.

Titanium species in titanium silicalite TS-1 prepared by hydrothermal method

The titanium species existing in titanium silicalite TS-1, which is prepared by hydrothermal method, were investigated using chemical analysis, XRD, FT-IR, Si-29 MAS NMR, UV-VIS, ESR. It has been observed that several kinds of titanium species may exist in titanium silicalite. The form that titanium atoms incorporate into the framework of titanium silicalite synthesized using tetrapropylammonium bromide (TPABr) as template differs from that using the classical method. But, the symmetry of titanium silicalite, changes from monoclinic to orthorhombic with the increase of titanium content in both methods. The Ti-O-2(-) originated from framework titanium and H2O2 has the moderate stability and may be active site in oxidation reaction. TS-1 synthesized using TPABr as template does not contain anatase, but contains a kind of partly condensed titanium species with six-fold coordination. The titanium species may correspond to 270-280 mn band in UV-VIS spectra and also can form Ti-O-2(-). But, this kind of Ti-O-2(-) is very stable and cannot be catalytic active site. So, the six-fold coordination titanium species may be inactive in both the oxidation reaction and the decomposition of H2O2. The hypothesis has been further proved by the phenomena that the titanium species is easily washed off using acid, and acid treating will not influence the catalytic performance of TS-1. (C) 2001 Elsevier Science B.V. All rights reserved.

Direct synthesis of highly ordered Fe-SBA-15 mesoporous materials under weak acidic conditions

Iron-substituted SBA-15 (Fe-SBA-15) materials have been synthesized via a simple direct hydrothermal method under weak acidic conditions. The powder X-ray diffraction (XRD), NZ sorption and transmission electron microscopy (TEM) characterizations show that the resultant materials have well-ordered hexagonal meso-structures. The diffused reflectance UV-vis and UV resonance Raman spectroscopy characterizations show that most of the iron ions exist as isolated framework species for calcined materials when the Fe/Si molar ratios are below 0.01 in the gel. The presence of iron species also has significant salt effects that can greatly improve the ordering of the mesoporous structure. Different iron species including isolated framework iron species, extraframework iron clusters and iron oxides are formed selectively by adjusting the pH values of the synthesis solutions and Fe/Si molar ratios. (c) 2005 Elsevier Inc. All rights reserved.

Size-controllable synthesis of monodispersed SnO2 nanoparticles and application in electrocatalysts

Size-controllable tin oxide nanoparticles are prepared by heating ethylene glycol solutions containing SnCl2 at atmospheric pressure. The particles were characterized by means of transmission electron microscopic (TEM), X-ray diffraction (XRD) studies. TEM micrographs show that the obtained material are spherical nanoparticles, the size and size distribution of which depends on the initial experimental conditions of pH value, reaction time, water concentration, and tin precursor concentration. The XRD pattern result shows that the obtained powder is SnO2 with tetragonal crystalline structure. On the basis of UV/vis and FTIR characterization, the formation mechanism of SnO2 nanoparticles is deduced. Moreover, the SnO2 nanoparticles were employed to synthesize carbon-supported PtSnO2 catalyst, and it exhibits surprisingly high promoting catalytic activity for ethanol electrooxidation.

Post-grafting preparation of large-pore mesoporous materials with localized high content titanium doping

A new post-grafting process, consisting of two steps of substrate preparation and sol - gel post-grafting, has been developed to prepare titanium-doped mesoporous SBA-15 material with a double-layered structure and locally concentrated titanium content at the inner pore surface. With this novel technique, the single phased and originally ordered mesostructures can be well conserved; in the conventional direct synthesis they can be partially damaged when the frameworks are doped with high content heteroatoms. Titanium species exist in an isolated, tetrahedral structure and are localized at the pore surface; this is beneficial to both reactant access and product release. Characterization with XRD, N-2 adsorption/desorption isotherms, HREM/ EDS, ICP, UV - Vis, and the newly developed UV - Raman spectroscopy confirm these results. Preliminary catalytic tests with the selective epoxidation of cyclohexene show good catalytic activity. Among them, sample TiSBA-15-10 with a Si : Ti molar ratio of 10 shows a TON value of 75 and a highest product ( epoxide) yield of 55%.

Characterization of interaction property of multicomponents in Chinese Herb with protein by microdialysis combined with HPLC

Interaction of traditional Chinese Herb Rhizoma Chuanxiong and protein was studied by microdialysis coupled with high performance liquid chromatography. Compounds in Rhizoma Chuanxiong, such as ferulic acid, senkyunolide A and 3-butylphthalide, were identified by HPLC, HPLC-MS and UV-vis. Microdialysis recoveries and binding degrees of compounds in Rhizoma Chuanxiong with human serum albumin (HSA) and other human plasma protein were determined: recoveries of microdialysis sampling ranged from 36.7 to 98.4% with R.S.D. below 3.1%; while binding to HSA ranged from 0 to 91.5% (0.3 mM HSA) and from 0 to 93.5% (0.6 mM HSA), respectively. Compared with HSA, most of compounds bound to human blood serum more extensively and the results showed that binding of these compounds in Rhizoma Chuanxiong was influenced by pH. Two compounds were found to bind to HSA and human blood serum. their binding degrees were consistent with ferulic acid and 3-butylphthalide, the active compounds in Rhizoma Chuanoxiong. (c) 2005 Elsevier B.V. All rights reserved.