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A pressing problem in supported-metal-nanoparticle heterogeneous catalysis--despite the long history and considerable fundamental as well as industrial importance of such heterogeneous catalysts--is how to monitor such catalysts' formation more routinely, rapidly, and in real time. Such information is needed to better control the size, shape, composition, and thus resultant catalytic activity, selectivity, and lifetime of these important catalysts. To this end, a study is reported of the formation of supported Pt(0)(n) nanoparticles by H(2) reduction of H(2)PtCl(6) on Al(2)O(3) (or TiO(2)) to give 6 equivalents of HCl plus supported Pt(0)(n)/Al(2)O(3) (or Pt(0)(n)/TiO(2)), all while in contact with a solution of EtOH and cyclohexene. The HCl and Pt(0)(n) products were confirmed, respectively, by the stoichiometry of HCl formation using pH(apparent) measurements, appropriate standards, and by TEM and EDX measurements. The hypothesis of this research is that the kinetics of formation of this supported heterogeneous catalyst could be successfully monitored by a fast cyclohexene hydrogenation catalytic reporter reaction method first worked out for monitoring transition-metal nanoparticle formation in solution (Watzky, M. A. and Finke, R. G. J. Am. Chem. Soc. 1997, 119, 10382-10400). Significantly, sigmoidal kinetics of Pt(0)(n)/Al(2)O(3) catalyst formation were in fact successfully monitored by the catalytic hydrogenation reporter reaction method and then found to be well fit to the Finke-Watzky (hereafter F-W) 2-step, slow continuous nucleation and then autocatalytic surface growth mechanism, A --> B (rate constant k(1)) and A + B --> 2B (rate constant k(2)), respectively, in which A is the H(2)PtCl(6) and B is the growing, catalytically active Pt(0) nanoparticle surface. The finding that the F-W mechanism is applicable is significant in that it, in turn, suggests that the > or = 8 insights from studies of the mechanisms of soluble nanocluster formation can likely also be applied to supported heterogeneous catalyst synthesis, including a recent equation that gives nanocluster size vs time in terms of k(1), k(2), [A](o) and other parameters (Watzky, M. A., Finney, E. E. and Finke, R. G. J. Am. Chem. Soc. 2008, 130, 11959-11969 ). Also presented are the use of the catalytic reporter reaction to reveal H(2) gas to-solution mass-transfer-limitations (MTL) in the system of H(2)PtCl(6) on TiO(2), results relevant to a recent communication in this journal. The use of the F-W 2-step nucleation and autocatalytic growth kinetic model to fit 3 literature examples of heterogeneous catalyst formation, involving H(2) reduction of both supported or bulk M(x)O(y) (i.e., and in gas-solid reactions), are also presented as part of the Supporting Information. A conclusion section is then provided summarizing the insights and caveats from the present work, as well as some needed future studies.
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PMID:Monitoring supported-nanocluster heterogeneous catalyst formation: product and kinetic evidence for a 2-step, nucleation and autocatalytic growth mechanism of Pt(0)n formation from H2PtCl6 on Al2O3 or TiO2. 1937 11

In this study, we report a new phenomenon dealing with the size-dependent behavior of the wall thickness of block copolymer vesicles, especially the decrease in wall thickness with decreasing vesicle size. Four vesicle-forming copolymers from the polystyrene-b-poly-(acrylic acid) (PS-b-PAA) family (i.e., PS(500)-b-PAA(50), PS(310)-b-PAA(28), PS(240)-b-PAA(15), and PS(412)-b-PAA(46)) were chosen for study. The sizes and wall thicknesses of the vesicles after quenching were determined from the TEM micrographs, and plots were made of the wall thickness versus size for each family of vesicles made from each of the various blocks. First, the effect of the length of the PAA block on the relationship between the wall thickness and the size was examined. In the vesicles prepared from PS(500)-b-PAA(50), the copolymer with the longest PAA block that yields the smallest vesicles, the wall thickness decreases strongly with decreasing size. By contrast, in the case of vesicles made from PS(240)-b-PAA(15), for which a wide size distribution is obtained, only a weak size dependence of the wall thickness is seen. For vesicles made from the copolymer with intermediate PAA block length (i.e., PS(310)-b-PAA(28)), both strong and weak behavior regions are observed depending on the vesicle size range. We suggest that this new phenomenon of the size dependence of the wall thickness can be considered to be another stabilization mechanism for very small vesicles, under conditions where chain segregation is insufficient to stabilize the size. The vesicles can be stabilized by decreasing the wall thickness for very small vesicles, resulting in the increase in area per corona chain, thus decreasing the corona repulsion on the inside. The effects of additives such as NaCl, HCl, or NaOH on the relationship between the wall thickness and the size were also investigated. By shielding the electrostatic repulsion among corona chains in the presence of NaCl, the strong behavior of the vesicles prepared from PS(412)-b-PAA(46) changes to a weak one as the width of the vesicle size distribution increases. In a NaCl concentration region around 10 mM, an opposite effect is seen relative to that observed in small vesicles in that the wall thickness decreases with increasing vesicle size for vesicles larger than ca. 300 nm, an effect ascribed to corona repulsion among the external corona chains. The addition of HCl also drives the relationship to be weaker through the protonation of the carboxylate groups of PAA chains, in an effect similar to that of NaCl. The presence of NaOH is expected to strengthen the relationship via the deprotonation of PAA, which increases the corona repulsion. However, because of the very short length of PAA chains in the system where a weak effect is seen, no significant effect of NaOH addition was observed because the size distribution remained broad.
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PMID:Relationship between wall thickness and size in block copolymer vesicles. 1942 64

Yellowish (Fe, N)-doped nanocrystalline TiO2 powders have been prepared using TiOSO4, CO(NH2)2, Fe(NO3)3.9H2O and CN3H5.HCl as precursors by hydrothermal method. The as-synthesized powders were anatase in phase and the grain size was about 10 nm according to the TEM photos. The ratio of Fe/Ti is 2.2 at% and N/O is 0.8 at% respectively. TiO2 powders were mixed with organic silicon and acrylic syrup to test their antibacterial performance by the colony counting method. The results show that the sterilization ratio of E. coli by the heat-treated (Fe, N)-doped nanocrystalline TiO2 powders is reached up to 94.5% while that of the powders without any heat treatment is 91.1% by 8 hours-400 lux-Visible-light irradiation with humidity of 55% RH.
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PMID:Preparation of (Fe, N)-doped TiO2 powders and their antibacterial activities under visible light irradiation. 1944 63

Mesoporous silica, SBA-15 was successfully functionalized with quinoline moiety, and was applied as a matrix in the MALDI-TOF-MS analysis of small molecules. The modified SBA-15 material [SBA-15-8-(3-(triethoxysilyl)propoxy) quinoline, SBA-15-8QSi] was obtained by using calcined SBA-15 and 8-hydroxy quinoline. The structure of the functionalized mesoporous material was systemically characterized by TEM, the N(2) adsorption-desorption isotherm technique and FT-IR spectra. Compared with DHB and SBA-15, SBA-15-8QSi demonstrated several advantages in the analysis of small molecules with MALDI-TOF-MS, such as less background interference ions, high homogeneity, and better reproducibility. Based on these results, the various analytical parameters were optimized. The ideal operating conditions were (1) methanol used as the dissolving solvent; (2) sample first dropping method; (3) a ratio between the analyte and the matrix of 3.5:10. Under these optimization conditions, a low detection limit (8 pmol for L-Arginine-HCl) and high reproducibility (< or = 29%) were obtained. This technique was successfully applied to the analysis of various types of small molecules, such as saccharides, amino acids, metabolites, and natural honey.
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PMID:MALDI-TOF-MS analysis of small molecules using modified mesoporous material SBA-15 as assisted matrix. 1976 53

Aqueous well-dispersed and phase-pure anatase TiO(2) truncated octahedron nanoplatelets (NPLs) were prepared via controlled hydrolysis of titanium tetrachloride (TiCl(4)) in ethylene glycol at 240 degrees C. Two shapes, square and hexagon, were observed by microscopy, exactly corresponding to the truncated octahedron NPLs. Ethylene glycol was found to produce water in situ that reacts with TiCl(4) to produce TiO(2) and HCl-the latter promoting TiO(2) colloid peptization. TiO(2) truncated octahedron NPLs are formed under the stabilizing action of ethylene glycol thermolysis derivatives, such as aldehydes. Crystal growth of the TiO(2) NPLs was affected by the reaction temperature that determines the water production rate and HCl-assisted peptization. TGA and FT-IR results showed approximately 1.2% ethylene glycol thermolysis derivatives are attached to the surface of the TiO(2) NPLs, which prevents their agglomeration, hence making them easily dispersible in aqueous media. HR-TEM and SAED results showed that the TiO(2) NPLs are well crystallized and that the SAED patterns of the single TiO(2) NPL changes with its size and shape. XRD patterns showed that the TiO(2) NPLs are phase-pure anatase and the percentage of the [101] plane in the TiO(2) NPLs to be only 18%-a structural feature that renders the TiO(2) NPLs with enhanced UV absorption and reactivity properties.
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PMID:The synthesis of aqueous-dispersible anatase TiO2 nanoplatelets. 1995 13

Nanometer size biphasic calcium phosphate (BCP) powders with various Ca/P molar ratios satisfied with appropriate phase ratios of HA/beta-TCP were prepared by high temperature flame spray pyrolysis process. The BCP powders had spherical shapes and narrow size distributions irrespective of the ratios of Ca/P. The mean size of the BCP powders measured from the TEM image was 38 nm. The composition ratio of Ca/P was controlled from 1.500 to 1.723 in the spray solution, and required phase ratios of HA/TCP are controlled systematically. The calcium dissolution of the pellets obtained from the BCP powders directly prepared by flame spray pyrolysis in buffer solution increased with the decrease of Ca/P ratios except with the Ca/P ratio of 1.713. The pellet surface with Ca/P ratio of 1.500, which consisted of beta-TCP, was eroded dramatically for 7 days. On the other hand, the pellet surface with Ca/P ratio of 1.667 was stable and did not disintegrate after immersion in Tris-HCl buffer solution based on the SEM observation.
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PMID:Synthesis of nano-sized biphasic calcium phosphate ceramics with spherical shape by flame spray pyrolysis. 2005 21

At the room temperature, a novel and environmental friendly approach for synthesizing polyaniline (PANI) nanofibers on a large scale is presented firstly in the aqueous phase by ultraviolet (UV)-assisted polymerization using cetyltrimethylammonium bromide (CTAB) as the "soft-template." It is obvious that the polymerization process can be accelerated under the illumination of UV light and the preliminary mechanism has been pointed out. Furthermore, it also can be noted that the lower concentrations of CTAB and HCl are helpful for the fabrication of smooth and uniform PANI nanofibers. As observed with FE-SEM and TEM, the as-synthesized PANI nanostructures under the appropriate conditions are composed of uniform nanofibers with the average diameter of about 100 nm and the length of several micrometers. Subsequently, the synthesized PANI nanostructures are characterized with UV-vis, FT-IR, XRD spectra, and the typical physical and chemical properties of PANI are displayed. In addition, the conductivity of the synthesized PANI nanofibers was also measured with the four probe method and the excellent conductivity was presented. In summary, the procedure presented here only involving exposure of an acidic aqueous solution of aniline to UV light illumination is so simple and the needed equipment is so low cost, from the viewpoint of technological applications, that the large-scale UV-assisted polymerization of PANI nanofibers from the monomer solution is feasible and promising.
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PMID:Fabrication of one dimensional polyaniline nanofibers by UV-assisted polymerization in the aqueous phase. 2035 39

Polyaniline (PAni) nanofibers doped with HCl and CSA have been irradiated with 90 MeV O(7+) ions with fluence of 3 x 10(10), 3 x 10(11) and 1 x 10(12) ions cm(-2). TEM micrographs show a decrease in the fiber diameter with increasing irradiation fluence, which has been explained on the basis of the Coulomb explosion model. XRD analysis reveals a decrease in the crystalline domain length and an increase in the strain. The increase in d-spacing for the (100) reflection with increasing irradiation fluence is ascribed to the increase in the tilt angle of the polymer chain, which is also evident from micro-Raman spectra. UV-vis spectra of the PAni nanofibers exhibit blue-shift in the absorption bands attributed to pi-pi* band transitions indicating a reduction in particle size after SHI irradiation; as also observed in TEM micrographs. Micro-Raman spectra also reveal a transition from the benzenoid to quinoid structures in the PAni chain as the fluence is increased. Although the quinoid unit has no hydrogen for DPPH scavenging, the antioxidant activity of PAni nanofibers is found to increase with increasing fluence. This has been attributed to the availability of more reaction sites as a result of fragmentation of the PAni nanofibers which compensates for the benzenoid to quinoid transition after irradiation. The biocompatibility of the PAni nanofibers is also found to increase with increasing irradiation fluence, indicating the possibility of employing swift heavy ion irradiation as an effective technique in order to modify conducting polymer nanostructures for biomedical applications.
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PMID:Swift heavy ion irradiation induced enhancement in the antioxidant activity and biocompatibility of polyaniline nanofibers. 2035 8

Spherical-like Pt-MCM-41 meso-materials, including Pt-MCM-41, Pt-Al-MCM-41, and Pt-La-MCM-41, as well as MCM-41, were synthesized by a "one-step" approach with orthosilicate (TEOS) as silica source and cetyltrimethylammonium bromide (CTAB) as a template in the presence of suitable H(2)SO(4) (or HCl) at 0 degrees C. The samples were characterized by XRD, N(2) sorption, FTIR, SEM, TEM, ICP-AES, and XPS techniques. The results show that the metallic cations (such as Al(3+) and La(3+)) were hard to be incorporated into the synthesized samples under strong acidic conditions. However, H(2)PtCl(6) can be introduced almost 100% in the as-synthesized Pt-containing meso-materials, and H(2)PtCl(6) in the samples can be decomposed mostly into metallic Pt accompanied by part Pt(2)Si and few Pt oxides during the calcination at 550 degrees C to remove the template. In the catalytic hydrogenation of nitrobenzene, the calcined Pt-MCM-41 meso-materials, like the corresponding reduced samples, exhibit high catalytic activities with an excellent selectivity to aniline, which are much better than those of the reduced Pt/MCM-41 prepared by the incipient wetness method.
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PMID:Synthesis of spherical-like Pt-MCM-41 meso-materials with high catalytic performance for hydrogenation of nitrobenzene. 2038 12

In this article, we report in situ fabrication of meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) nanostructures with excitonic absorption on glass substrate. The exposure of TPPS thin film coated on a glass plate to HCl vapor resulted in the formation of nanostructures of TPPS. The formed TPPS nanostructures on glass plate were characterized by UV-vis, steady state emission spectral techniques, atomic force microscopy, and high resolution transmission electron microscopy (HR-TEM). A new sharp and intense absorption band (excitonic band) at 490 nm was observed for TPPS nanostructures on glass plate. Protonation of tertiary nitrogen atoms of TPPS ring by HCl molecules leads to the formation of nanostructures of J-aggregates of TPPS on glass surface. The height of the TPPS nanostructures was found to be 50-170 nm with an average width of 100 nm. HR-TEM images showed that the formed TPPS J-aggregates consist of tiny nanorods. The size of the nanostructures was tuned successfully by varying the concentration of TPPS used for thin film preparation.
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PMID:In situ fabrication of meso-tetrakis(4-sulfonatophenyl)porphyrin nanostructures with excitonic absorption on glass substrate. 2104 55

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