Search for: rate-constants
Total 96 records
Solvent effects on kinetics of an heteroatomic nucleophilic substitution reaction in ionic liquid and molecular solvents mixtures, Article Russian Journal of Physical Chemistry A ; Volume 87, Issue 12 , December , 2013 , pp 1969-1975 ; 1531-863X ; Pedervand, M. (Mohsen) ; Sadeghzadeh-Darabi, F. (Faramarz) ; Gholami, M. R. (Mohammad Reza) ; Sharif University of Technology
Rate constants, k A, for the aromatic nucleophilic substitution reaction of 2-chloro-3,5-dinitropyridine with aniline were determined in different compositions of 2-propanol mixed with hexane, benzene, and 2-methylpropan-2-ol and 1-ethyl-3-methylimidazolium ethylsulfate ([Emim][EtSO4]) with dimethyl sulfoxide at 25°C. The obtained rate constants of the reaction in pure solvents are in the following order: 2-methylpropan-2-ol > dimethyl sulfoxide > 2-propanol > hexane > benzene > [Emim][EtSO4]. Molecularmicroscopic solvent parameters corresponding to the selected binary mixtures were utilized to study the kinetics of a nucleophilic substitution reaction in order to investigate and compare the...
Article Macromolecules ; Volume 51, Issue 11 , 2018 , Pages 3941-3952 ; 00249297 (ISSN) ; Abdekhodaie, M. J ; Chau, Y ; Sharif University of Technology
American Chemical Society 2018
We describe here a theoretical framework to model the bulk degradation of hydrogels, which are prepared by chemical cross-linking of pendant functional groups on long polymer chains. The random order of the cleavage of degradable bonds was described by stochastic Monte Carlo simulation. The events of bond cleavage were related to the macroscopic changes of hydrogel by the Bray-Merrill equation. Next, the time for the gel to disintegrate was predicted by considering the relation between the recursive nature in breaking the cross-link nodes and gel-to-sol transition. To start the simulation, initial network properties including the number of active functional groups on the polymer chain and...
Article Journal of Physical Organic Chemistry ; Volume 21, Issue 9 , 2008 , Pages 783-788 ; 08943230 (ISSN) ; Habibi Yangjeh, A ; Gholami, M. R ; Sharif University of Technology
The second-order rate constants for cycloaddition reaction of cyclopentadiene with naphthoquinone were determined spectrophotometrically in various compositions of 1-(1-butyl)-3-methylimidazolium terafluoroborate ([bmim]BF4) with water and methanol at 25°C. Rate constants of the reaction in pure solvents are in the order of water > [bmim]BF 4 > methanol. Rate constants of the reaction decrease sharply with mole fraction of the ionic liquid in aqueous solutions and increase slightly to a maximum in alcoholic mixtures. Multi-parameter correlation of logk 2 versus solute-solvent interaction parameters demonstrated that solvophobicity parameter (Sp), hydrogen-bond donor acidity (α) and...
Solvent effects on kinetics of the reaction between 2-chloro-3,5- dinitropyridine and aniline in aqueous and alcoholic solutions of [bmim]BF 4, Article International Journal of Chemical Kinetics ; Volume 39, Issue 12 , December , 2007 , Pages 681-687 ; 05388066 (ISSN) ; Habibi Yangjeh, A ; Gholami, M. R ; Sharif University of Technology
Rate constants, kA. for the aromatic nucleophilic substitution reaction of 2-chloro-3,5-dinitropyridine with aniline were determined in different compositions of 1-(1-butyl)-3-methylimidazolium terafluoroborate ([bmim]BF4) mixed with water, methanol, and ethanol at 25°C. The obtained rate constants of the reaction in pure solvents are in the following order: water > methanol > ethanol > [bmim]BF4. In these solutions, rate constants of the reaction decrease with the mole fraction of the ionic liquid. Single-parameter correlations of log kA versus normalized polarity parameter (ETN), hydrogen bond acceptor basicity (β), hydrogen bond donor acidity (α), and dipolarity/polarizability (π*) do not...
Article International Journal of Hydrogen Energy ; Volume 32, Issue 12 , 2007 , Pages 1755-1761 ; 03603199 (ISSN) ; Jafarian, M ; Gobal, F ; Heli, H ; Mahjani, M. G ; Sharif University of Technology
The mechanism and kinetics of the hydrogen evolution reaction (HER) on tin electrode in 0.1 M H2SO4 solution were studied using the methods of steady-state polarization and electrochemical impedance spectroscopy. The simulation of the data obtained from these two methods, using nonlinear fitting procedure allowed us to determine the rate constants of Volmer, Heyrovsky and Tafel steps associated with the mentioned reaction. The kinetic results indicate that HER mechanism at low negative potentials is a serial combination of Volmer step and parallel Tafel and Heyrovsky steps. At high negative potentials where the hydrogen coverage reaches its limiting value, a Tafel line with the slope of -...
Article Journal of Applied Electrochemistry ; Volume 36, Issue 8 , 2006 , Pages 913-918 ; 0021891X (ISSN) ; Moghaddam, R. B ; Mahjani, M. G ; Gobal, F ; Sharif University of Technology
The electro-catalytic oxidation of methanol on a Ni-Cu alloy (NCA) with atomic ratio of 60/40 having previously undergone 50 potential sweep cycles in the range 0-600 mV vs. (Ag/AgCl) in 1 m NaOH was studied by cyclic voltammetry (CV), chronoamperometry (CA) and impedance spectroscopy (EIS). The electro-oxidation was observed as large anodic peaks both in the anodic and early stages of the cathodic direction of potential sweep around 420 mV vs. (Ag/AgCl). The electro-catalytic surface was at least an order of magnitude superior to a pure nickel electrode for methanol oxidation. The diffusion coefficient and apparent rate constant of methanol oxidation were found to be 2.16 × 10-4 cm2 s-1 and...
Solvent effects on kinetics of an heteroatomic nucleophilic substitution reaction in ionic liquid and molecular solvents mixtures, Article Russian Journal of Physical Chemistry A ; Volume 87, Issue 12 , 2013 , Pages 1969-1975 ; 00360244 (ISSN) ; Pedervand, M ; Sadeghzadeh Darabi, F ; Gholami, M. R ; Sharif University of Technology
Rate constants, k A, for the aromatic nucleophilic substitution reaction of 2-chloro-3,5-dinitropyridine with aniline were determined in different compositions of 2-propanol mixed with hexane, benzene, and 2-methylpropan-2-ol and 1-ethyl-3-methylimidazolium ethylsulfate ([Emim][EtSO4]) with dimethyl sulfoxide at 25 C. The obtained rate constants of the reaction in pure solvents are in the following order: 2-methylpropan-2-ol > dimethyl sulfoxide > 2-propanol > hexane > benzene > [Emim][EtSO4]. Molecularmicroscopic solvent parameters corresponding to the selected binary mixtures were utilized to study the kinetics of a nucleophilic substitution reaction in order to investigate and compare the...
Kinetics and electrocatalytic behavior of nanocrystalline CoNiFe alloy in hydrogen evolution reaction, Article International Journal of Hydrogen Energy ; Volume 32, Issue 12 , 2007 , Pages 1686-1693 ; 03603199 (ISSN) ; Azizi, O ; Gobal, F ; Mahjani, M. G ; Sharif University of Technology
Electrocatalytic activity of electrodeposited nanocrystalline CoNiFe alloy in hydrogen evolution reaction (HER) was studied in 1 M NaOH solution. The steady-state polarization measurement and electrochemical impedance spectroscopy were used to determine the Tafel slope, the exchange current density and the activation energy. The simulation of the data obtained from these two methods, using a nonlinear fitting procedure, allowed us to determine the surface coverage and the rate constants associated with the mentioned reaction. The ac-impedance spectra measured at various overpotentials in the HER region exhibited three semicircles in the complex plane plots. The high-frequency semicircle was...
Solvent parameters effects on the second-order rate constants of the reaction of 2-chloro-3,5-dinitropyridine with aniline in aqueous solutions of alcohols, Article Progress in Reaction Kinetics and Mechanism ; Volume 31, Issue 2 , 2006 , Pages 117-127 ; 14686783 (ISSN) ; Masumpour, M. S ; Gholami, M. R ; Sharif University of Technology
Science Reviews Ltd 2006
Aromatic nucleophilic substitution reaction kinetics of 2-chloro-3,5-dinitropyridine with aniline was studied in aqueous solutions of methanol, ethanol, and 2-propanol at room temperature. The obtained results for aqueous solutions indicate that the second-order rate constants are in order of 2-propanol>ethanol>methanol with a maximum at water mole fraction of 0.9. The influence of solvent parameters including normalized polarity (E TN), dipolarity/polarisability (π*), and hydrogen bond donor acidity (α) on the second-order rate constants were investigated and multiple regressions gave much better results with regard to single parameter regressions. Dipolarity/polarisability and hydrogen...
A study on mutual interaction between atomistic and macroscopic phenomena during electrochemical processes using coupled finite difference - Kinetic Monte Carlo model: Application to potential step test in simple copper sulfate bath, Article Journal of Electroanalytical Chemistry ; Volume 588, Issue 2 , 2006 , Pages 267-284 ; 15726657 (ISSN) ; Sharif University of Technology
A novel method is used to link a 2D kinetic Monte Carlo code to a 1D finite difference code to construct a more realistic and efficient tool for simulating various electrochemical processes. This multiscale model is able to simulate the long-scale mass transfer of electroactive species in bath along with electrode surface phenomena at atomic scale simultaneously. An embedded atom method (EAM) has been used to evaluate the barrier energies of diffusion and redox reactions on electrode surface. The FD code provides the ion concentration on OHP for KMC code, while the KMC code provides the surface activity and rate constants of redox reactions as an input data for FD code. The electrochemical...
Theoretical investigation of the hydrogen abstraction reaction of the OH radical with CH3CHF2 (HFC152-a): A dual level direct density functional theory dynamics study, Article Journal of Physical Chemistry A ; Volume 109, Issue 36 , 2005 , Pages 8158-8167 ; 10895639 (ISSN) ; Parsafar, G. A ; Sabzyan, H ; Sharif University of Technology
The hydrogen abstraction reaction of the OH radical with CH 3CHF2 (HFC152-a) has been studied theoretically over a wide temperature range, 200-3000 K. Two different reactive sites of the molecule, CH3 and CHF2 groups have been investigated precisely, and results confirm that CHF2 position of the molecule is a highly reactive site. In this study, three recently developed hybrid density functional theories, namely, MPWB1K, MPW1B95, and MPW1K, are used. The MPWB1K/6-31+G(d,p) method gives the best result for kinetic calculations, including barrier heights, reaction path information and geometry of transition state structures and other stationary points. To refine the barrier height of each...
Solute-solvent interaction effects on second-order rate constants of reaction between 1-chloro-2,4-dinitrobenzene and aniline in alcohol-water mixtures, Article International Journal of Chemical Kinetics ; Volume 37, Issue 2 , 2005 , Pages 90-97 ; 05388066 (ISSN) ; Gholami, M. R ; Sharif University of Technology
The second-order rate coefficients for aromatic nucleophilic substitution reaction between 1-chloro-2,4-dinitrobenzene and aniline have been measured in aqueous solutions of ethanol and methanol at 25°C. The plots of rate constants versus mole fraction of water show a maximum in all-aqueous solutions. The effect of four empirical solvent parameters including hydrogen bond donor acidity (α), dipolarity/polarizability (π*). normalized polarity (ETN), and solvophobicity (Sp) has been investigated. This investigation has been carried out by means of simple and multiple regression models A dual-parameter equation of log k2 versus Sp and α was obtained in all-aqueous solutions (n = 41, r = 0.962,...
Article International Journal of Chemical Kinetics ; Volume 44, Issue 11 , 2012 , Pages 712-721 ; 05388066 (ISSN) ; Jafarian, M ; Forouzandeh, F ; Gobal, F ; Sharif University of Technology
Nickel-modified glassy carbon electrode (GC/Ni) prepared by galvanostatic deposition was used for the electrocatalytic oxidation of glucose in alkaline solutions where different electrochemical methods were employed. In cyclic voltammetry studies, in the presence of glucose an increase in the peak current of the oxidation of nickel hydroxide is followed by a decrease in the corresponding cathodic current. This suggests that the oxidation of glucose is being catalyzed through mediated electron transfer across the nickel hydroxide layer comprising nickel ions of various valence states. Under the chronoamperometric regime, the reaction followed a Cottrellian behavior and the diffusion...
Article RSC Advances ; Volume 5, Issue 84 , Aug , 2015 , Pages 68378-68384 ; 20462069 (ISSN) ; Faraji, M ; Sharif University of Technology
Royal Society of Chemistry 2015
The present work describes the preparation and electrochemical characterization of RuO
2/MWCNT/Stainless Steel Mesh (SSM) electrode as compared with a MWCNT/SSM electrode in the positive half-cell of a Vanadium Redox Flow Battery (VRFB). The electrochemical characterization of prepared electrode was carried out using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge procedures. The electrochemical activity of MWCNT/SSM modified with RuO 2 as positive electrode in a VRFB was notably improved. The RuO 2-included electrodes demonstrated high peak current ratio, small peak potential difference and high electron...
(WO3)x-(TiO2)1-x nano-structured porous catalysts grown by micro-arc oxidation method: Characterization and formation mechanism, Article Materials Chemistry and Physics ; Volume 124, Issue 1 , 2010 , Pages 203-207 ; 02540584 (ISSN) ; Moshfegh, A. Z ; Golestani Fard, F ; Molaei, R ; Sharif University of Technology
Very recently, we fabricated (WO3)x-(TiO 2)1-x layers via micro-arc oxidation process under different applied voltages. Morphological and topographical studies, accomplished by SEM and AFM techniques, revealed that the pores size as well as the surface roughness increased with the voltage. Phase structure and chemical composition of the layers were also investigated by XRD and XPS and the results showed the grown layers consisted of titanium and tungsten oxides. It was found that WO3 dispersed in the TiO2 matrix and also doped into the TiO2 lattice. In addition, optical properties of the synthesized layers were studied employing a UV-vis spectrophotometer. Band gap energy of the layers was...
Preparation, physiochemical and kinetic investigations of V2O5/SiO2 catalyst for sulfuric acid production, Article International Journal of Engineering, Transactions B: Applications ; Volume 29, Issue 11 , 2016 , Pages 1478-1488 ; 1728144X (ISSN) ; Kazemeini, M ; Fattahi, M ; Vafajoo, L ; Sharif University of Technology
Materials and Energy Research Center 2016
V2O5/SiO2 catalyst utilized to oxidize the SO2 to SO3 species in the presence of oxygen mainly for producing sulfuric acid. For this catalyst, the active phase was a mixture of vanadium pentoxide and basic sulfate/pyrosulfate material. This active phase at the reaction temperature behaved as a liquid filling up the pores of the silica support. On the other hand, amounts of the SO3 and V5+ species in the catalyst necessarily varied with the concentration of the feed material and temperature rendering complexity to the kinetics of the SO2 oxidation reaction. In the current research, the catalyst preparation with different amounts of such materials was undertaken. Purified Diatomaceous earth of...
Preparation and characterization of a new CdS–NiFe2O4/reduced graphene oxide photocatalyst and its use for degradation of methylene blue under visible light irradiation, Article Research on Chemical Intermediates ; Volume 44, Issue 10 , 2018 , Pages 5953-5979 ; 09226168 (ISSN) ; Kaveh, R ; Ozkar, S ; Akbayrak, S ; Sharif University of Technology
In this paper, CdS nanoparticles as a visible light active photocatalyst were coupled by NiFe2O4 and reduced graphene oxide (rGO) to form CdS–NiFe2O4/rGO nanocomposite by facile hydrothermal methods. The CdS–NiFe2O4/rGO nanocomposite shows enhanced photocatalytic activity for the degradation of methylene blue (MB) under visible light illumination. In addition to improved photocatalytic performance, this prepared nanocomposite shows increased photostability and is magnetically separable from the aqueous media. The degradation rate constant (kapp) of the optimized photocatalyst, i.e. CdS–NiFe2O4 (0.05)/rGO 25 wt% nanocomposite, was higher than the corresponding CdS and NiFe2O4 nanoparticles by...
Long-term deactivation of a commercial CoMo-Al2O3 catalyst in hydrodesulfurization of a naphtha stream, Article Industrial and Engineering Chemistry Research ; Volume 48, Issue 7 , 2009 , Pages 3331-3340 ; 08885885 (ISSN) ; Hoseini, M ; Sharif University of Technology
Long-term deactivation of a commercial CoMoγ-Al2O3 catalyst used in the hydrodesulfurization of a naphtha stream was studied using 35 months of operating data of an industrial HDS fixed bed reactor. The major sulfur-containing species of the naphtha feed was identified as 2-ethyl-4-methylthiophene (2E4MT) based on GC-MS analysis. The characterization of the industrial catalysts was performed by BET, XRD, XRF, and HCN Leco analyses. The reaction rate constant of the gas-phase hydrodesulfurization reaction was calculated by fitting the industrial reactor conversion data to the Hougen-Watson rate equation, assuming that the surface reaction between the sulfur-containing species and adsorbed...
Fabrication of modified TiO 2 nanoparticle carbon paste electrode for simultaneous determination of dopamine, uric acid, and l-cysteine, Article Journal of Solid State Electrochemistry ; Volume 13, Issue 9 , 2009 , Pages 1433-1440 ; 14328488 (ISSN) ; Talebi, A ; Naeimi, H ; Nejati Barzoky, M ; Taghavinia, N ; Sharif University of Technology
A carbon paste electrode, modified with 2, 2″-[1,7- hepthandiylbis(nitriloethylidyne)]-bis-hydroquinone and TiO 2 nanoparticles, was used for the simultaneous determination of dopamine (DA), uric acid (UA), and l-cysteine. The study was carried out by using cyclic voltammetry, chronoamperometry, and square wave voltammetry (SWV) techniques. Some kinetic parameters such as the electron transfer coefficient (α) and heterogeneous rate constant (k s) were also determined for the DA oxidation. A dynamic range of 8.0-1400 μM, with the detection limit of 8.4∈×∈10 -7 M for DA, was obtained using SWV (pH∈=∈7.0). The prepared electrode was successfully applied for the determination of DA, UA, and...
Preparation of nitrogen-doped aluminium titanate (Al2TiO5) nanostructures: Application to removal of organic pollutants from aqueous media, Article Advanced Powder Technology ; Volume 31, Issue 8 , 2020 , Pages 3328-3341 ; Zekavat, M ; Soltaninejad, M ; Bakhshandeh, F ; Reza Madaah Hosseini, H ; Kashani, S ; Amutha, C ; Khatiboleslam Sadrnezhaad, S ; Ramakrishna, S ; Sharif University of Technology
Elsevier B.V 2020
Recently, aluminum titanate (Al2TiO5)-based nanostructures have been proved to serve as an efficient photocatalytic material with satisfactory photodegradation capacity. In this study, the citrate sol–gel method was used to synthesize these nanostructures and inspect the significant impacts of nitrogen-doping-originated crystalline defects on their photocatalytic performance in some details for the first time. The results indicated that the penetration of nitrogen atoms into AT crystal lattice, depending on the nitriding time and temperature, can induce a great deal of the residual stress and result in propagating the existing cracks and breaking down the particles. The XPS and FTIR results...