Search for: silica
0.012 seconds
Total 382 records

    A mild and efficient oxidation of benzylic alcohols without solvent using iodic acid supported on wet montmorillonite K10 or silica gel under microwave irradiation

    , Article Acta Chimica Slovenica ; Volume 52, Issue 1 , 2005 , Pages 86-87 ; 13180207 (ISSN) Hashemi, M. M ; Rahimi, A ; Karimi Jaberi, Z ; Ahmadibeni, Y ; Sharif University of Technology
    Iodic acid supported on wet silica gel and K10 clay are used for the efficient oxidation of benzylic alcohols under microwave irradiation and solvent free condition  

    Europium-doped yttrium silicate nanoparticles embedded in a porous SiO 2 matrix

    , Article Nanotechnology ; Volume 15, Issue 11 , 2004 , Pages 1549-1553 ; 09574484 (ISSN) Taghavinia, N ; Lerondel, G ; Makino, H ; Yao, T ; Sharif University of Technology
    Europium-doped yttrium silicate nanoparticles were grown inside a porous silicon oxide matrix by chemical impregnation of porous silicon layers, followed by heat treatments. The average size of the nanoparticles is 50 nm and they are dispersed almost uniformly within the whole porous layer. Local composition measurements demonstrate that Y and Eu are found only in nanoparticles, indicating a good phase separation efficiency. There is indirect evidence that yttrium silicate nanoparticles are nucleated around Eu ions. The crystalline phase of the particles is pure α-Y2Si2O7, with no trace of Y2O3 or Y2SiO5 or other Y2Si2O7 polymorphs. Structural purity is an advantage for this method, as in... 

    Influence of external mass transfer limitation on apparent kinetic parameters of penicillin G acylase immobilized on nonporous ultrafine silica particles

    , Article Journal of Bioscience and Bioengineering ; Volume 93, Issue 2 , 2002 , Pages 125-129 ; 13891723 (ISSN) Kheirolomoom, A ; Khorasheh, F ; Fazelinia, H ; Sharif University of Technology
    Society of Fermentation and Bioengineering  2002
    Immobilization of enzymes on nonporous supports provides a suitable model for investigating the effect of external mass transfer limitation on the reaction rate in the absence of internal diffusional resistance. In this study, deacylation of penicillin G was investigated using penicillin acylase immobilized on ultrafine silica particles. Kinetic studies were performed within the low-substrate-concentration region, where the external mass transfer limitation becomes significant. To predict the apparent kinetic parameters and the overall effectiveness factor, knowledge of the external mass transfer coefficient, kLa, is necessary. Although various correlations exist for estimation of kLa, in... 

    Determination of very low levels of dissolved mercury(II) and methylmercury in river waters by continuous flow with on-line UV decomposition and cold-vapor atomic fluorescence spectrometry after pre-concentration on a silica gel-2-mercaptobenzimidazol sorbent

    , Article Talanta ; Volume 55, Issue 6 , 2001 , Pages 1141-1150 ; 00399140 (ISSN) Bagheri, H ; Gholami, A ; Sharif University of Technology
    Elsevier  2001
    A new, simple and sensitive method for the simultaneous determination of mercury(II) and methylmercury chloride at sub-ng 1-1 levels in river waters is described. Inorganic and organic mercury were preconcentrated from fresh water samples simultaneously on a laboratory-made column containing 2-mercaptobenzimidazol loaded on silica gel and then quantitatively eluted with 0.05 M KCN solution and 2.0 M HCl to desorp inorganic and methylmercury species, respectively. After irradiation with an intensive UV source, MeHg+ was decomposed and mercury vapours were generated from inorganic and organic mercury using an acidic SnCl2 solution in a continuous flow system and were subsequently determined... 

    Synthesis and application of silica aerogel-MWCNT nanocomposites for adsorption of organic pollutants

    , Article Scientia Iranica ; Volume 17, Issue 2 F , 2010 , Pages 122-132 ; 10263098 (ISSN) Bargozin, H ; Amirkhani, L ; Moghaddas, J. S ; Ahadian, M. M ; Sharif University of Technology
    Silica aerogel-multi wall carbon nanotube composites were synthesized successfully with a waterglass precursor and an ambient pressure drying method. Pure silica aerogels are so fragile that they cannot be used easily. Carbon nanotubes (MWCNT) were used as reinforcements to strengthen the mechanical properties of pure silica aerogels. Results show that inserting small amounts of MWCNT causes silica aerogels to monolith. By addition of MWCNT, monolith nanocomposites were produced with 800 m2/g surface area and a 140° contact angle. Results show that the silica aerogels and reinforced composites have an excellent adsorption property for the removal of organic pollutants from water. The average... 

    Chemical durability of metallic copper nanoparticles in silica thin films synthesized by sol-gel

    , Article Journal of Physics D: Applied Physics ; Volume 41, Issue 23 , November , 2008 ; 00223727 (ISSN) Akhavan, O ; Sharif University of Technology
    In this study, chemical durability of metallic copper nanoparticles dispersed in sol-gel silica thin films was investigated by exposing the films to air after a reduction process. At first, heat treatment in air for 1 h produced silica films containing crystalline cupric oxide nanoparticles agglomerated on the film surface. Subsequently, reduction of the oxidized films in a reducing environment of N2-H2 for another 1 h at temperatures of 400, 500 and 600 °C resulted in the formation of crystalline metallic Cu nanoparticles diffused in the silica matrix. The time evolution of the surface plasmon resonance absorption peak of the reduced Cu nanoparticles was studied after the reduction... 

    Low temperature self-agglomeration of metallic Ag nanoparticles on silica sol-gel thin films

    , Article Journal of Physics D: Applied Physics ; Volume 41, Issue 19 , 2008 ; 00223727 (ISSN) Akhavan, O ; Azimirad, R ; Moshfegh, A. Z ; Sharif University of Technology
    A facile sol-gel synthesis for self-agglomeration of metallic silver nanoparticles, with fcc crystalline structure, on the silica surface in a low annealing temperature has been introduced. X-ray photoelectron spectroscopy (XPS) revealed initial agglomeration (∼30 times greater than the nominal concentration of Ag) of the nanoparticles on the surface of the dried film (100 °C) and also their oxidation as well as easy diffusion (with 0.08 eV required activation energy) into the porous silica thin films, by increasing the annealing temperature (200-400 °C). By raising the Ag concentration from 0.2 to 1.6 mol% in the sol, the average size of the Ag nanoparticles increased from ∼5 to 37 nm... 

    α-Amylase Immobilization on Nanocomposite Magnetic Silica Particles and Characterization of the Prepared Nanobiocatalysts

    , M.Sc. Thesis Sharif University of Technology Sayyahmanesh, Maryam (Author) ; Mashayekhan, Shohreh (Supervisor) ; Arpanaei, Ayyoob (Supervisor)
    Enzymes are widely used in industry, however, the expensive cost, low stability, and the limited activity in a certain range of temperature and pH, have limited the usage of such bio-catalists. In addition to increasing and preserving their activity under different conditions, the enzyme immobilization can improve its stability in different pH, temperature values and increase its thermostability, storage stability and the possibility of their recycling. Meanwhile, utilizing the super-magnetic systems could be very helpful as well. For instance, separation of the the magnetic nano-particles like Fe3O4 from reaction system using an external magnetic field is easily possible. In this study,... 

    Design of Drug Nanocarriers Based on Mesoporous Silica Nanoparticles Coated with Smart Polymers

    , Ph.D. Dissertation Sharif University of Technology Mazaheri Tehrani, Zahra (Author) ; Pourjavadi, Ali (Supervisor)
    Mesoporous silica nanoparticles have broad application in drud delivery systems due to their porous structure, functionalization, biocompatibility, high surface area and pore volume. Neverthless, pure mesoporous silica nanoparticles without functionality were not smart material and could not release drug in triggered and controlled manner. For this reason, using smart polymeric coating would be considered. Polymer shells also provide colloidal stability, improved blood circulation lifetime and reduced toxicity which are crucial for efficient in vivo drug delivery. Inflammatory and tumor tissue have low pH and high temperature as compared to health tissue. Therefore, using pH and... 

    The Study of Function of Lipase Biocatalyst Immobilized on Silica Nanoparticles Used for Biodiesel Production

    , M.Sc. Thesis Sharif University of Technology Kalantari, Mohammad (Author) ; Kazemini, Mohammad (Supervisor) ; Arpanaei, Ayyoob (Supervisor) ; Tabandeh, Fatemeh (Co-Advisor)
    Superparamagnetic core/shell nonporous (S1) and core/shell/shell mesoporous (S2 and S3) nanocomposite magnetite/silica particles with a magnetite cluster core of 130±30 nm, a nonporous silica shell of 90±10 nm thickness, and a mesoporous silica shell of 70±15 nm thickness were prepared thorough a simple method. Mesoporous particles were prepared with two BJH pore sizes (2.44 for S2 and 3.76 nm for S3 particles, respectively). The fabricated S1, S2 and S3 particles present high saturation magnetization values of 20, 13 and 17 emu/g, respectively. As a biological application, the lipase from Pseudomonas cepacia was successfully immobilized onto the amino-functionalized nanocomposite particles... 

    Modeling of Crumb Rubber Concrete for a Structural Column by Evaluating the use of FRP

    , M.Sc. Thesis Sharif University of Technology Ghaznavi Doozandeh, Soheil (Author) ; Khaloo, Alireza (Supervisor)
    The research shows that the compressive strength of concrete reduced by replacing crumb rubber in concrete mix design compared to normal concrete mix design. However, there have been a couple of utilizations investigated to date for the structural utilization of these materials. Crumb rubber is usually provided from recycled rubber from automotive and truck scrap tires. During the recycling process steel and triviality are removed, leaving tire rubber with a granulose cohesiveness. The additional crumb-rubber aggregate has a significant effect on concrete mix porosity which affects both the plastic state workability and hardened state mechanical properties. This research depicts an... 

    Study of 131I Adsorption Behavior on Nanoporous Silicates Modified with Elements of Ag, Cu, Zn, Ni

    , M.Sc. Thesis Sharif University of Technology Rohani, Ramezan (Author) ; Sayf Kordi, Ali Akbar (Supervisor) ; Sepehrian, Hamid (Supervisor)
    One of the common methods used for treatment of gaseous radioactive wastes in nuclear waste management is adsorption process. Nanoporous materials have found great utility as sorption media because of their large internal surface area and more adsorption sites than other adsorbents, which caused the increasing attention of researchers to use them in the nuclear waste management. Hence in this study, the surface of nanoporous silicates of SBA-15 and MCM-41 modified with d-block elements of the periodic table such as silver, copper, zinc and nickel by wet impregnation method. After characterization by different techniques such as X-ray diffraction, nitrogen gas porosimetry, Fourier... 

    Design of Methods for Synthesis and Immobilization of Nitrogen Ligands Such as Pyridine onto the Mesoporous Silica Nanoparticles and Design of Pharmaceutical Structures Based on Amino Acids and Carbohydrates to Inhibit Polymerase Η for the Treatment of Leukemia and their Applications In Resins and Ionic Liquids

    , Ph.D. Dissertation Sharif University of Technology Kalhor, Sepideh (Author) ; Matloubi Moghaddam, Firouz (Supervisor) ; Fattahi, Alireza (Supervisor)
    1- Mesoporous silica materials have been found to possess pore sizes ranging from 2 -10 nm alongside 2D-hexagonal and 3D-cubic structural features. The specific properties of nanoparticles of the mesoporous silica family, such as the collected size, porosity, morphology, and high chemical stability, make them among the best drug delivery systems and catalysts. Designing the catalysts with advanced structures that effectively locate the transition metals and create active centres onto the surfaces of mesoporous silica materials has attracted extraordinary attention. According to many studies, mesoporous silica materials without organic functional groups cannot be used as catalysts in chemical... 

    Investigation of the effect of water based nano-particles addition on hysteresis of oil and-water relative permeability curves

    , Article Society of Petroleum Engineers - SPE International Oilfield Nanotechnology Conference 2012 ; June , 2012 , p. 267-277 Parvazdavani, M ; Masihi, M ; Ghazanfari, M. H ; Sherafati, M ; Mashayekhi, L ; Sharif University of Technology
    It has been shown that one kind of poly silicon particles with sizes ranging from 10-500 nm, can be used in oilfields to enhance the oil recovery of water injection by 15-20%. The contributing mechanism might be reducing the interfacial tension which appears through improving relative permeability of the oil-phase. However, fundamental understanding of how hysteretic behavior of relative permeability curves affected by nanosilica particles remains a topic of debate in the literature. In this study, water as well as water dispersed nanosilica particles floods was performed on sandstone rock sample saturated by light crude oil supplied from one of Iranian oil reservoir, and the relative... 

    In situ preparation and property investigation of polypropylene/fumed silica nanocomposites

    , Article Polymer Composites ; Vol. 35, issue. 1 , January , 2014 , pp. 37-44 ; ISSN: 02728397 Azinfar, B ; Ahmad Ramazani, S. A ; Jafariesfad, N ; Sharif University of Technology
    We present the preparation of polypropylene (PP)/fumed silica (FS) nanocomposites via in situ polymerization in this article. The approach includes preparation and utilization of a bisupported Ziegler-Natta catalytic system in which magnesium ethoxide and FS are used as conjugate supports of the catalyst. Catalyst preparation and polymerization processes are carried out in the slurry phase and under argon atmosphere. Scanning electron microscopy images show a good dispersion of the FS throughout the PP matrix. Results from differential scanning calorimetry reveal that the crystallization temperature of prepared nanocomposites increases by increasing FS loading. Also, crystal content of... 

    Study on the catalytic activity and theoretical modeling of a novel dual acidic mesoporous silica

    , Article RSC Advances ; Volume 4, Issue 32, 2014 , 2014 , Pages 16647-16654 ; ISSN: 20462069 Vafaeezadeh, M ; Fattahi, A ; Sharif University of Technology
    A novel mesoporous silica-functionalized dual Brønsted acidic species has been introduced as an efficient catalyst for solvent-free esterification of fatty acids with ethanol. The structure of the catalyst has been characterized by FT-IR spectroscopy, thermal gravimetric analysis (TGA), TEM and N2 adsorption-desorption. TGA of catalyst 1 showed no weight loss before 200 °C, indicating a high degree of hydrophobicity of the surface of the mesoporous silica. TEM images and nitrogen adsorption-desorption showed no noticeable changes to the structure of the catalyst before and after acid treatment. pH metric analysis was performed for the catalyst to determine the loading of the acidic sites.... 

    Simple and green oxidation of cyclohexene to adipic acid with an efficient and durable silica-functionalized ammonium tungstate catalyst

    , Article Catalysis Communications ; Vol. 43 , 5 January , 2014 , pp. 169-172 Vafaeezadeh, M ; Mahmoodi Hashemi, M ; Sharif University of Technology
    A novel silica-functionalized ammonium tungstate interphase catalyst has been reported as a non-nitric acid route for adipic acid production from one-pot oxidative cleavage of 30% hydrogen peroxide and catalytic amounts of p-toluenesulfonic acid (PTSA). The catalyst has been simply prepared by commercially available starting material. The structure of the catalyst has been investigated using FT-IR spectroscopy, atomic absorption, TEM, SEM and XRD analysis. The catalyst has shown good to high activity even up to 10 runs of reaction. Simple preparation of the catalyst, avoids using harmful phase transfer catalyst (PTC) and/or chlorinated additives are among the other benefits of this work  

    Mesoporous silica-functionalized dual Brønsted acidic ionic liquid as an efficient catalyst for thioacetalization of carbonyl compounds in water

    , Article Catalysis Communications ; Volume 41 , 2013 , Pages 96-100 ; 15667367 (ISSN) Vafaeezadeh, M ; Dizicheh, Z. B ; Hashemi, M. M ; Sharif University of Technology
    A novel silica-functionalized dual Brønsted acidic ionic liquid (ionic liquid with two Brønsted acidic species) has been reported as a highly efficient catalyst for thioacetalization of carbonyl compounds. The reaction was efficiently performed in water as an environmentally benign solvent with good to high yields. Thermal gravimetric analysis showed that the catalyst is stable at least up to 350 C. Furthermore, the catalyst can be recycled and reused for six runs of reaction without appreciable loss of activity. The structure of the catalyst is modelized to gain more realistic structural insight about the functionalized ionic liquid  

    Design of silica supported task-specific ionic liquid catalyst system for oxidation of cyclohexene to adipic acid with 30% H 2O 2

    , Article Catalysis Communications ; Volume 26 , September , 2012 , Pages 54-57 ; 15667367 (ISSN) Vafaeezadeh, M ; Hashemi, M. M ; Shakourian Fard, M ; Sharif University of Technology
    Elsevier  2012
    1-Butyl-3-methylimidazolium tungstate ([BMIm] 2WO 4) ionic liquid supported onto silica sulphamic acid demonstrated desirable performance for oxidation of cyclohexene to adipic acid. Simple experimental procedure, easy product isolation, catalyst recovery and reusability are some attractive features of this protocol  

    Silver nanoparticles supported on silica-coated ferrite as magnetic and reusable catalysts for oxidant-free alcohol dehydrogenation

    , Article RSC Advances ; Volume 5, Issue 29 , Jan , 2015 , Pages 22503-22509 ; 20462069 (ISSN) Bayat, A ; Shakourian Fard, M ; Ehyaei, N ; Mahmoodi Hashemi, M ; Sharif University of Technology
    Royal Society of Chemistry  2015
    Silver (0) nanoparticles supported on silica-coated ferrite were synthesized to be used as an efficient and recyclable heterogeneous catalyst for oxidant-free dehydrogenation of alcohols to the corresponding carbonyl compounds. The catalyst can be easily recovered and reused for 8 reaction cycles without considerable loss of activity. The facile recovery of the catalyst is carried out by applying an external magnetic device. The catalyst was fully characterized by the techniques of TEM, SEM, XRD, EDS, ICP-AES, and VSM. This journal is