Loading...
Search for: silica
0.005 seconds
Total 422 records

    The effect of water-cement ratio in compressive and abrasion strength of the nano silica concretes

    , Article World Applied Sciences Journal ; Volume 17, Issue 4 , 2012 , Pages 540-545 ; 18184952 (ISSN) Shamsai, A ; Rahmani, K ; Peroti, S ; Rahemi, L ; Sharif University of Technology
    2012
    Abstract
    Development and construction of hydraulic structures like dams, the concrete durability in these kinds of structures has gained special attention. One of the crucial factor in concrete technology is it durability in hydraulic structures. Concrete has to resist against abrasion due to the crash of particles carried by water. To enhance the abrasion resistance of concrete different methods have been offered. In the present stud, the role of water-cement ratio in compressive and abrasion strength of nano silica concrete was investigated. The constructed concrete samples with 3% nano silica and water-cement ratios of 0.33, 0.36, 0.40, 0.44 and 0.50 were experimented. Other design features... 

    Investigations for gas-phase deprotonation of the silica-propyl-SO3H catalyst using cage-like nanocluster modeling technique

    , Article Journal of the Iranian Chemical Society ; Volume 12, Issue 11 , November , 2015 , Pages 1991-1997 ; 1735207X (ISSN) Vafaeezadeh, M ; Hashemi, M. M ; Sharif University of Technology
    Springer Verlag  2015
    Abstract
    Exploring deprotonation properties of silica-functionalized propylsulfonic acid catalyst (silica-propyl-SO3H) is the subject of various experimental and theoretical researches. In the current study, the structure of the silica-propyl-SO3H has been simulated using density functional theory (DFT) methods by mimicking the surface of the silica in the form of cubic cage-like nanoclusters of silicon and oxygen. The values of ΔHacidity for gas-phase deprotonation are calculated considering various possible interactions of the propylsulfonic acid on the surface of the silica. Our investigations indicate that interactions of sulfonic acid (-SO3H) head... 

    The effect of protein corona on doxorubicin release from the magnetic mesoporous silica nanoparticles with polyethylene glycol coating

    , Article Journal of Nanoparticle Research ; Volume 17, Issue 4 , April , 2015 ; 13880764 (ISSN) Pourjavadi, A ; Tehrani, Z. M ; Mahmoudi, N ; Sharif University of Technology
    Kluwer Academic Publishers  2015
    Abstract
    In the present work, biocompatible superparamagnetic iron oxide nanoparticles coated by mesoporous silica were used as drug nanocarriers for doxorubicin (Dox; an anticancer drug) delivery. In biological media, the interaction of protein corona layer with the surface of nanoparticles is inevitable. For this reason, we studied the effect of protein corona on drug release from magnetic mesoporous silica nanoparticles (MMSNs) in human plasma medium. Besides, we used hydrophilic and biocompatible polymer, polyethylene glycol (PEG), to decrease protein corona effects. The results showed the increased Dox release from PEGylated MMSNs compared with bare MMSNs. This result indicated that the coating... 

    Design and calibration procedure of a proposed V-band antenna array on fused silica technology intended for MIMO applications

    , Article International Journal of Microwave and Optical Technology ; Volume 13, Issue 4 , 2018 , Pages 317-329 ; 15530396 (ISSN) Salarpour, M ; Farzaneh, F ; Staszewski, R. B ; Sharif University of Technology
    International Academy of Microwave and Optical Technology (IAMOT)  2018
    Abstract
    A coplanar-fed wideband antenna array system to characterize MIMO channels in the 60 GHz band is proposed. The array consists of six U-slot patch elements with half-wavelength separation and is fed independently by individual transceivers. The system is designed and simulated on fused silica substrate to be integrated easily with RFICs and to achieve fine fabrication resolution (1um) for accurate mm-wave measurements. It can provide 11dBi peak gain at broadside and beam steering up to ±40° tilted from broadside over 57-63 GHz band. A new on-wafer calibration technique is developed to balance the amplitude and phase of all transceivers at the input of the array system which realizes high... 

    Analysis of the effect of kevlar fibers on abrasion resistance, flexural strength and hydraulic conductivity coefficient of silica fume concretes

    , Article Iranian Journal of Science and Technology - Transactions of Civil Engineering ; Volume 44, Issue 2 , 2020 , Pages 669-674 Rahmani, K ; Piroti, S ; Ghameian, M ; Sharif University of Technology
    Springer  2020
    Abstract
    Reinforcing fiber and silica fume of concrete can be considered as one of the most widely used additives. In this study, with a review of the history and advantages of using silica fume and polypropylene fibers in concrete, 380 concrete laboratory samples were constructed, of which 25 mixing designs with water–cement ratio of 0.35 and fiber content of 0.2, 0.3, 0.4 and 0.5 of concrete volume and 7% silica fume were prepared according to the ACI standard in their manufacturing. In the present research, samples of Kevlar fiber containing silica fume were tested under flexural strength, abrasion resistance and hydraulic conductivity coefficient. According to achieved results, the optimum amount... 

    BF3.SiO2: An efficient heterogeneous alternative for regio-chemo and stereoselective Claisen-Schmidt condensation

    , Article Journal of the Iranian Chemical Society ; Volume 5, Issue 4 , 2008 , Pages 694-698 ; 1735207X (ISSN) Sadeghi, B ; Mirjalili, B. F ; Hashemi, M. M ; Sharif University of Technology
    Iranian Chemical Society  2008
    Abstract
    Under solvent free conditions between 40-50 °C, BF3.SiO 2, a mild solid acid catalyst, is applied to regio-chemo and stereoselective Claisen-Schmidt condensation. The procedure is very simple and the products are isolated with an easy workup in good to excellent yields  

    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
    2005
    Abstract
    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
    2004
    Abstract
    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
    Abstract
    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
    Abstract
    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... 

    Deep eutectic solvent functionalized mesoporous silica SBA-15 based mixed matrix polymeric membranes for mitigation of CO2 (Extended Version)

    , Article Journal of Engineering Research (Kuwait) ; Volume 10 , 2022 ; 23071885 (ISSN) Saif-Ur-Rehman ; Zaman, M. K. U ; Waseem, M. A ; Mehdi, M. S ; Rafiq, S ; Zaman, S. U ; Farooq, U ; Jamal, M ; Saeed, U ; Sharif University of Technology
    University of Kuwait  2022
    Abstract
    The carbon dioxide (CO2) separation can be enhanced by using modified materials like a deep eutectic solvent (DES) modified mesoporous silica SBA-15 in polymeric support i.e polysulfone via mixed matrix membranes (MMMs). The pure SBA-15 and DES are potential candidates for the CO2 capturing and their combination has not been reported yet. In this work, a fresh DES was synthesized by combining equal concentrations of Decanoic acid and choline chloride by mass. MMMs were fabricated by DES functionalized SBA-15 (DES-SBA) filler. The DES-SBA-based polymeric MMMs of different compositions, from 5% to 20% with the difference of five each, were developed and subjected to the gas permeation analysis... 

    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
    Abstract
    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
    2008
    Abstract
    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
    2008
    Abstract
    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)
    Abstract
    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)
    Abstract
    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)
    Abstract
    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)
    Abstract
    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)
    Abstract
    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)
    Abstract
    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...