Papers by Keyword: Mesoporous Silica

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Authors: Laszlo Lizkay, C. Corbel, P. Perez, P. Desgardin, Marie France Barthe, Toshiyuki Ohdaira, Ryoichi Suzuki, P. Crivelli, Ulisse Gendotti, A. Rubbia, M. Etienne, A. Walcarius
Abstract: Positron annihilation gamma energy distribution, lifetime spectroscopy and time-of-flight method were used to study surfactant-templated mesoporous silica films deposited on glass. The lifetime depth profiling was correlated to Doppler broadening and 3γ annihilation fraction measurements to determine the annihilation characteristics inside the films. A set of consistent fingerprints for positronium annihilation, o-Ps reemission into vacuum, and pore size was directly determined. The lifetime measurements were performed in reflection mode with a specially designed lifetime spectrometer mounted on a slow positron beam system. The intensity of the 142 ns vacuum lifetime component was recorded as a function of the energy of the positron beam. In a film with high porosity a reemission efficiency of as high as 40 % was found at low positron energy. Positron lifetime in samples capped by a thin silica layer was used to determine the pore size. The energy of the reemitted o-Ps fraction was measured by a time-of-flight detector, mounted on the same system, allowing determination of both o-Ps re-emission efficiency and energy in the same sample. We demonstrate the potential of the simultaneous use of different positron annihilation techniques in the study of thin porous films.
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Authors: Lei Zu, Yu Yuan Zhi, Kai Gu, Hui Qin Lian, Xiu Guo Cui
Abstract: The poly(pseudo)rotaxanes formed by β-CD and F127 was used as the template to prepare the mesoporous silica. The specific surface area, pore size distribution and pore volume of the mesoporous silica could be controlled by simply changing the poly(pseudo)rotaxanes forming time. A series of samples with different template forming time were prepared to investigate the various specific surface area and pore size of the mesoporous silica. The morphology, composition, specific surface area and pore size of the mesoporous silica particle were investigated by the scanning electron microscopy, Fourier transformation infrared spectroscope, and N2 adsorption–desorption measurement.
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Authors: Salasiah Binti Endud, Nadirah Zawani Binti Mohd Nesfu
Abstract: The Claisen–Schmidt condensations stand out to be important reaction in carbon–carbon bond formation as well as in the preparation of fine chemicals and intermediates with the presence of base catalyst such as NaOH. However, only few studies concern the synthesis and catalytic activity of mesoporous silica containing bimetallic compound as catalyst for aldol condensation of bulky aldehydes. The advantages of mesoporous systems with respect to zeolites are the improved reactant accessibility to the active sites and enhanced catalyst stability. Mesoporous silica with exceedingly high surface area (> 800 m2/g) and very high concentration of surface silanol groups fulfill most of the criteria for catalyst support. In this contribution, we report on the incorporation of Nb and Cs, alone or together, into the mesoporous silica with cubic mesostructure and the investigation of their catalytic properties in the Claisen-Schmidt condensation of acetophenone with benzaldehyde to produce chalcone, an aromatic ketone that forms the active sites for important biological compounds with antibacterial activities.
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Authors: Jeong Ho Chang, Jun Liu
Abstract: This work describes chemically functionalized nanoporous silica as a novel catalyst for the rapid hydrolysis of a phenyl ester. Work demonstrates a very simple and flexible approach to control surface reactivity on the nanometer scale using a self-assembled organic monolayer consisting of polar, (dihydroxyl, carboxyl, ethylene-diamine, and dihydroimidazole), and non-polar (isobutyl) groups. All five functional groups are an essential requirement in preparing an enzymelike catalyst because of the synergistic effect and hydrophobic partitioning, which has been verified by a 13C CP- MAS solid-state NMR technique. Catalytic activities were obtained from the catalytic efficiency constant and specificity constant using Michaelis-Menten kinetics. Catalytic activities were close to those of a natural enzyme when 12% of the surface was covered by hydrophobic isobutyl silane. The rate of enzyme catalyzed activity was dependent on the energy of the transition state as defined in terms of an energy barrier derived from the relationship between transfer free energy and specificity constant.
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Authors: Zhi Dong Han, Feng Xu, Li Jiang, Zheng Quan Jiang, Peng Wang
Abstract: MCM-41 mesoporous silica was prepared by hydrothermal method. 2-carboxyethyl phenyl phosphinic acid (CEPPA) was loaded on MCM-41 by solution method. The structure of MCM-41 and its supported CEPPA was studied by X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscopy (SEM) coupled with energy dispersive spectrometer (EDS). The results revealed that CEPPA was successfully loaded on MCM-41 with Si/P molar ratio of about 20:1. The XRD spectrum of MCM-41 supported CEPPA was different from MCM-41, indicating the structure of MCM-41 was changed after loading of CEPPA. CEPPA molecule moved into the mesoporous structure and filled in the mesopores, leading to the disappearance of characteristic diffraction peaks of MCM-41. The interaction between hydroxyl group of CEPPA and silanol of MCM-41 made it stable for CEPPA to be in the mesopores and on the surface of MCM-41. MCM-41 supported CEPPA also showed the similar mesoporous structure with long-range order to MCM-41 when observed by TEM. SEM provided further evidences of the similar particle size and different morphology.
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Authors: Richard Yeboah Abrokwah, Vishwanath G. Deshmane, Sri Lanka Owen, Debasish Kuila
Abstract: We have synthesized mesoporous SiO2 (MCM-41) and TiO2 encapsulated bimetallic Cu-Ni nanocatalysts using an optimized one-pot hydrothermal procedure. The catalysts were characterized using BET, XRD, TGA-DSC and HRTEM techniques. While bimetallic Cu-Ni/MCM-41catalysts have high surface area- 634-1000 m2/g, Cu-Ni/TiO2 yields surface area of 250-350 m2/g depending on the metal loading (5-10 wt%). The XRD studies confirmed a long range ordered structure in Cu-Ni/MCM-41 and the presence of the catalytically active anatase phase in the crystalline Cu-Ni/TiO2. The results from HRTEM studies were consistent with the mesoporosity of both supports. These catalysts were tested for methanol conversion and H2/CO selectivity via steam reforming of methanol (SRM) reactions in a fixed bed reactor. There is a distinct difference in the performance of these two supports. Bimetallic 3.33%Cu6.67%Ni/TiO2 catalyst showed an impressive 99% H2 selectivity at as low as 150°C and a maximum conversion of 92% at 250 °C but 3.33%Cu6.67%Ni/MCM-41 catalyst did not show any H2 selectivity at 150°C and only ~12% conversion at 250°C. The effect of each support and relative metal loadings on the activity and selectivity of the SRM reaction products at different temperatures is discussed.
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Authors: Ming Zhang, Wen Shuai Zhu, Meng Li, Yan An Li, Suhang Xun, Rong Xiang Qin, Hua Ming Li
Abstract: Tungsten-containing functional mesoporousW-SiO2 have been successfully synthesized by an one-pot and facile room-temperature procedure. These materials presented a high dispersion of tungsten species and excellent catalytic activity on the removal of sulfur compounds without any organic solvents as extractants. The catalytic performance on sulfur compounds was investigated in detail. After recycling for 8 times, the removal of the oxidation desulfurization system could still reach 92.0%.
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Authors: Go Kawamura, Ikuo Hayashi, Rahmat Ali Fitrah, Hiroyuki Muto, Junichi Hamagami, Atsunori Matsuda
Abstract: Gold nanorods (GNRs) were deposited in ordered mesoporous silica SBA-15 by a liquid-phase synthesis. The X-ray diffraction pattern of GNRs-deposited SBA-15 (GNRs/SBA-15) confirmed that the mesoporous structure of the SBA-15 was maintained even after depositing GNRs in the SBA-15 pores. Laser irradiation and heat treatment for GNRs/SBA-15 were carried out to check the effect on the GNRs morphology alteration. These treatments were found to shorten the length of the GNRs in SBA-15, leading to a blue shift of the surface plasmon resonance wavelength of the GNRs. Especially, heat treatment at high temperatures, e.g. at 500 °C, showed unique result that the inner wall of SBA-15 was collapsed by the overgrowth of gold nanoparticles.
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Authors: Y. Kim, B.G. Song, Soo Ryong Kim, Kwang Jin Kim
Abstract: Porous hydroxyapatite coated with mesoporous silica has been utilized as the matrix for controlled drug delivery. TEM observation confirms the pore size of mesoporous silica scatters about 50 Å. Porous hydroxyapatite was coated with mesoporous silica via sol-gel process. Ibuprofen and was loaded into the pores of mesoporous silica, and controlled release profiles were studied by soaking the samples in a simulated body fluid using a UV-VIS spectrophotometer.
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Authors: Sara Faiz Hanna Tasfy, Maizatul Shima Shaharun, Noor Asmawati Mohd Zabidi, Duvvuri Subbarao
Abstract: Cupper/zinc oxide catalyst supported on mesoporous silica (SBA-15) prepared at different sol acidity have been synthesized. The influence of preparation conditions on the textural properties and morphology of the mesoporous silica were investgated. The morphology and textural properties of the SBA-15 synthesized through the acidic route was found to be strongly influence by the pH of the synthesis sol. The effects of supported Cu/ZnO catalyst in CO2 hydrogenation was investigated in a three-phase reactor system at 483K, 22.5bar, and H2/CO2 of 3. The catalytic preformance was found to be strongly affected by the morphology of SBA-15. The maximum in the methanol synthesis activity (57.8 %) and methanol selectivity (66.4) was attained for the catalyst supported by SBA-15 synthesized at lower acidity (pH of 2).
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