Search for: dissociation
0.007 seconds
Total 59 records

    First principles study of oxygen adsorption on nickel-doped graphite

    , Article Molecular Physics ; Volume 110, Issue 13 , Feb , 2012 , Pages 1437-1445 ; 00268976 (ISSN) Nahali, M ; Gobal, F ; Sharif University of Technology
    Density functional theory is used in a spin-polarized plane wave pseudopotential implementation to investigate molecular oxygen adsorption and dissociation on graphite and nickel-doped graphite surfaces. Molecular oxygen physisorbs on graphite surface retaining its magnetic property. The calculated adsorption energy is consistent with the experimental value of 0.1eV. It is found that substituting a carbon atom of the graphite surface by a single doping nickel atom (2.8% content) makes the surface active for oxygen chemisorption. It is found that the molecular oxygen never adsorbs on doping nickel atom while it adsorbs and dissociates spontaneously into atomic oxygens on the carbon atoms... 

    Adsorption and dissociation of hydrogen peroxide on small Pd xM3-x (M = Pt, Cu; X = 1-3) clusters: A hybrid density functional study

    , Article Molecular Physics ; Volume 109, Issue 14 , May , 2011 , Pages 1797-1804 ; 00268976 (ISSN) Nahali, M ; Gobal, F ; Arab, R ; Sharif University of Technology
    The adsorption and dissociation of H2O2 on small PdxM3-x (M=Pt, Cu; x = 1-3) clusters is investigated using the B3PW91 hybrid density functional method. Natural bond orbitals are analysed to obtain partial charges on atoms, dipole moments, bond orders, and hybrid orbitals of the PdxM3-x-H2O2 systems. The calculated adsorption energies are in the range of -0.32 to -2.12 eV. Generally, H2O2 adsorbs on top positions through one of its oxygen atoms and only in a few cases reacts with the cluster through both oxygen and hydrogen sides. In the latter case the cluster sites which are negatively charged interact with the hydrogen atoms. Interestingly, on the triplet Pd2Pt cluster, H2O2 dissociates... 

    Adsorption of carbon monoxide on SixGe4-x(x = 0-4) nano-clusters: A hybrid meta density functional study

    , Article Molecular Physics ; Volume 108, Issue 10 , 2010 , Pages 1317-1327 ; 00268976 (ISSN) Nahali, M ; Gobal, F ; Sharif University of Technology
    Theoretical study of carbon monoxide adsorption on SixGe4 - x(x = 0-4) nano-clusters has been carried out using advanced hybrid meta density functional method of Truhlar (MPW1B95). MG3 semi-diffuse (MG3S) and correlation consistent valence basis sets with relativistic core potential were employed to improve the results. The agreement of the calculated ionization and dissociation energies with experimental values validates the reported structures of nano-clusters and justifies the use of hybrid meta density functional method. The geometry, adsorption energy, charge distribution, and vibrational frequency of CO adsorption on all possible structures were investigated. The maximum vibrational... 

    Theoretical aspects of the enhancement of metal binding affinity by intramolecular hydrogen bonding and modulating p: K a values

    , Article New Journal of Chemistry ; Volume 41, Issue 24 , 2017 , Pages 15110-15119 ; 11440546 (ISSN) Motahari, A ; Fattahi, A ; Sharif University of Technology
    Royal Society of Chemistry  2017
    Polyols were used as model ligands for Mg2+, Ca2+, and Zn2+ complexes to study the role of the hydrogen bond network on the metal binding affinity and modulation of successive pKa values using density functional theory. The results confirm that the acidity of polyols dramatically increases upon metal complexation in the order Zn2+ > Mg2+ > Ca2+. For example, the three H-site positions in the hydroxyl groups of the heptaol, bound to Zn2+, are 11.2, 29.9, and 30.9 pKa units (in methanol) more acidic than those of pure heptaol. This acidity enhancement leads to making polyols as good ligands toward complexation. For instance, the formation constants of the heptaol in the presence of Zn2+, Mg2+,... 

    The formation and dissociation energy of vacancies in cementite: A first-principles study

    , Article Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms ; Volume 502 , 2021 , Pages 157-163 ; 0168583X (ISSN) Mehrdad Zamzamian, S ; Amirhossein Feghhi, S ; Samadfam, M ; Sharif University of Technology
    Elsevier B.V  2021
    Because of the possibility of various types of vacancies in cementite due to its crystalline structure, the focus of this paper was only on vacancies. In this regard, the formation energies of single, two, three and four vacancies of over than 120 different cases were calculated using first-principles method. For the case of single vacancy, the results were in three values of ~1.63, 1.39 and 0.78 eV according to iron vacancies at general positions, iron vacancies located on mirror planes and carbon vacancies in the interstitial positions, respectively. The results for the case of two, three and four vacancies were between from 2.10 to 3.34 eV, from 3.92 to 5.10 eV and from 4.77 to 6.33 eV,... 

    Single-hydrogen dissociation paths for upright and flat acetophenone adsorbates on the Si(001) surface

    , Article Journal of Physical Chemistry C ; Volume 118, Issue 41 , 16 October , 2014 , Pages 23682-23689 ; ISSN: 19327447 Mehdipour, H ; Sharif University of Technology
    Using cluster-based density functional theory we investigate adsorption configurations of an acetophenone molecule on a Si(001) surface and their follow-up proton transfer processes. We examine two possible types of dative-adsorption configurations, up-right standing and flat, as well as compute their follow-up kinetically preferable on-dimer, interdimer, and inter-row proton transfers. Energetics of possible conversions between the achieved adsorption configurations are computed as well. Using all the data obtained, we theoretically illustrate reaction pathways leading to detached hydrogen positions captured in STM imaging of a Si(001) surface exposed to acetophenone vapor at room... 

    Super-hydrophilic characteristic of thermochemically prepared CdS nanocrystals

    , Article Physica E: Low-Dimensional Systems and Nanostructures ; Vol. 58 , April , 2014 , pp. 146-152 ; ISSN: 13869477 Marandi, M ; Taghavinia, N ; Babaei, A ; Sharif University of Technology
    CdS nanocrystals were thermochemically (thermally activated) synthesized thorough the reaction between CdSO4 and Na2S 2O3 in an aqueous solution. Thioglycolic Acid (TGA) was used as the capping agent and catalyst of the reaction. The method was based on heat activated dissociation of Na2S2O3 and controllable release of S and free electrons in the solution. CdS NCs were formed by heating the sample solution at 96 C for 1 h. The results of optical spectroscopy and transmission electron microscopy demonstrated round shape NCs with sizes about 3.0 nm. The nanocrystals were also luminescent and represented a broad emission with a peak located at 515 nm and FWHM of 160 nm. Several samples were... 

    Origin of the correlation of the rate constant of substrate hydroxylation by nonheme iron(IV)-oxo complexes with the bond-dissociation energy of the C-H bond of the substrate

    , Article Chemistry - A European Journal ; Volume 15, Issue 27 , 2009 , Pages 6651-6662 ; 09476539 (ISSN) Latifi, R ; Bagherzadeh, M ; De Visser, S ; Sharif University of Technology
    Wiley-VCH Verlag  2009
    Mononuclear nonheme iron containing systems are versatile and vital oxidants of substrate hydroxylation reactions in many biosystems, whereby the rate constant of hydroxylation correlates with the strength of the C-H bond that is broken in the process. The thermodynamic reason behind these correlations, however, has never been established. In this work results of a series of density functional theory calculations of substrate hydroxylation by a mononuclear nonheme iron(IV)-oxo oxidant with a 2 His/ 1Asp structural motif analogous to aketoglutarate dependent dioxygenases are presented. The calculations show that these oxidants are very efficient and able to hydroxylate strong C-H bonds,... 

    Thermal stability and strain sensitivity of nanostructured aluminum titanate (Al2TiO5)

    , Article Materials Chemistry and Physics ; Volume 223 , 2019 , Pages 202-208 ; 02540584 (ISSN) Keyvani, N ; Azarniya, A ; Madaah Hosseini, H. R ; Abedi, M ; Moskovskikh, D ; Sharif University of Technology
    Elsevier Ltd  2019
    In the present work, nanostructured aluminum titanate (Al2TiO5 or AT) was synthesized by the sol-gel method and potential effects of mechanical strain on its phase analysis, morphology, and thermal stability were investigated in some details for the first time, because the thermal instability of AT is beneficial to the fabrication of in-situ aluminum matrix composites. To characterize the particle distribution, microstructure and thermal durability of AT after the strain induction, field-emission scanning electron microscope (FE-SEM), differential scanning calorimetry (DSC), and x-ray diffraction analysis (XRD) were utilized. The experimental results showed that a 3-h ball milling process... 

    Electronic structure of some thymol derivatives correlated with the radical scavenging activity: Theoretical study

    , Article Food Chemistry ; Vol. 165, issue , Dec , 2014 , p. 451-459 Jebelli Javan, Ashkan ; Jebeli Javanb, M ; Sharif University of Technology
    Molecules acting as antioxidants capable of scavenging reactive oxygen species (ROS) are of upmost importance in the living cell. Thymol derivatives exhibit various antioxidant activities and potential health benefits. Exploration of structure-radical scavenging activity (SAR) was approached with a wide range of thymol derivatives. To accomplish this task, the DPPH experimental assay along with quantum-chemical calculations were also employed for these compounds. By comparing the structural properties of the derivatives of interest, their antioxidant activity was explained by the formation of an intramolecular hydrogen bond and the presence of unsaturated double bond (–CHdouble bond; length... 

    Theoretical investigation on antioxidant activity of bromophenols from the marine red alga Rhodomela confervoides: H-atom vs electron transfer mechanism

    , Article Journal of Agricultural and Food Chemistry ; Volume 61, Issue 7 , 2013 , Pages 1534-1541 ; 00218561 (ISSN) Javan, A. J ; Javan, M. J ; Tehrani, Z. A ; Sharif University of Technology
    Bromophenols are known as antioxidant radical scavengers for some biomolecules such as those in marine red alga. Full understanding of the role played by bromophenols requires detailed knowledge of the radical scavenging activities in probable pathways, a focus of ongoing research. To gain detailed insight into two suggested pathways, H-atom transfer and electron transfer, theoretical studies employing first principle quantum mechanical calculations have been carried out on selected bromophenols. Detailed investigation of the aforementioned routes revealed that upon H-atom abstraction or the electron transfer process, bromophenols cause an increase in radical species in which the unpaired... 

    Preparation of Ni/MeAl2O4-MgAl2O4 (Me=Fe, Co, Ni, Cu, Zn, Mg) nanocatalysts for the syngas production via combined dry reforming and partial oxidation of methane

    , Article Renewable Energy ; Volume 149 , April , 2020 , Pages 1053-1067 Jalali, R ; Rezaei, M ; Nematollahi, B ; Baghalha, M ; Sharif University of Technology
    Elsevier Ltd  2020
    In this paper, a comprehensive study was conducted on the application of various MeAl2O4 spinels (Me = Fe, Co, Ni, Cu, Zn, Mg) as the catalyst support for the preparation of nickel-based catalysts in the combined dry reforming and partial oxidation. These supports were synthesized by a novel facile sol-gel method using propylene oxide as the gelation agent and nickel was deposited on these supports by the deposition-precipitation method. The prepared samples were characterized by N2 adsorption/desorption, XRD, TPR, TPO, CO2-TPD, SEM, and TEM techniques. In addition, the temperature-programmed methane dissociation (TPMD) was performed to evaluate the effect of nickel-support interaction on... 

    Investigation of intense femto-second laser ionization and dissociation of methane with time-dependent density-functional approach

    , Article Chemical Physics Letters ; Vol. 604 , 2014 , Pages 60-67 ; ISSN: 00092614 Irani, E ; Sadighi Bonabi, R ; Anvari, A ; Sharif University of Technology
    Three dimensional calculations of electronic dynamics of CH4 in a strong laser field are presented with time-dependent density-functional theory. Time evolution of dipole moment and electron localization function is presented. The dependence of dissociation rate on the laser characters is shown and optimal effective parameters are evaluated. The optimum field leads to 76% dissociation probability for Gaussian envelope and 40 fs (FWHM) at 10 16 W cm-2. The dissociation probability is calculated by optimum convolution of dual short pulses. By combining of field assisted dissociation process and Ehrenfest molecular dynamics, time variation of bond length, velocity and orientation effect are... 

    The effect of intense short pulse laser shapes on generating of the optimum wakefield and dissociation of methane molecule

    , Article Laser and Particle Beams ; Volume 30, Issue 3 , May , 2012 , Pages 357-367 ; 02630346 (ISSN) Irani, E ; Zare, S ; Navid, H. A ; Dehghani, Z ; Sadighi Bonabi, R ; Sharif University of Technology
    The optimum convolution of dual short pulse for producing the maximum wakefield and the highest dissociation probability of CH4 has been investigated. By using three fundamental shapes of pulses though four different arrangements, the generated wake are considered in plasma. It is found that when the first and second pulses were rectangular-triangular and sinusoidal pulse shapes, respectively, the resultant wakefield amplitude is the highest. This effect opens up a new novel way by pulse shaping mechanism in the photo dissociation dynamics of molecules and controlling of chemical reactions in the desired channels by short pulse intense lasers for reducing the computation time of genetic... 

    Dissociative ionization of methane in an elliptical pulse shaped laser field

    , Article Journal of Molecular Structure ; Volume 1079 , January , 2015 , Pages 454-459 ; 00222860 (ISSN) Irani, E ; Sadighi Bonabi, R ; Anvari, A ; Sharif University of Technology
    Elsevier  2015
    The effect of strong femto-second laser pulses on the dissociation probability of methane has been investigated analytically in various arrangements. The ellipticity dependence of the dissociation probability at intensities from 1014 W cm-2 to 1016 W cm-2 for Ti:Sapphire laser is presented. A reliable calculation of the dissociation probability based on 3D time-dependent Schrodinger equation with an improved model of time-dependent density-functional theory is presented. These calculations are carried out for three different cases of elliptically polarized laser pulse, optimum convolution of dual short pulses, and two-color mixed nonresonant laser pulses. It is found that the rescattering... 

    Multielectron dissociative ionization of methane and formaldehyde molecules with optimally tailored intense femtosecond laser pulses

    , Article Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy ; Volume 185 , 2017 , Pages 298-303 ; 13861425 (ISSN) Irani, E ; Anvari, A ; Sadighi Bonabi, R ; Monfared, M ; Sharif University of Technology
    The multielectron dissociative ionization of CH4 and CH2O molecules has been investigated using optimum convolution of different dual tailored short laser pulses. Based on three dimensional molecular dynamics simulations and TDDFT approach, the dissociation probability is enhanced by designing the dual chirped-chirped laser pulses and chirped-ordinary laser pulses for formaldehyde molecule. However, it is interesting to notice that the sensitivity of enhanced dissociation probability into different tailored laser pulses is not significant for methane molecule. In this presented modifications, time variation of bond length, velocity, time dependent electron localization function and evolution... 

    Selective photo-dissociative ionization of methane molecule with TDDFT study

    , Article Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy ; Volume 171 , 2017 , Pages 325-329 ; 13861425 (ISSN) Irani, E ; Anvari, A ; Sadighi Bonabi, R ; Sharif University of Technology
    Elsevier B.V  2017
    Three dimensional calculation of control dynamics for finding the optimized laser filed is formulated using an iterative method and time-dependent density functional approach. An appropriate laser pulse is designed to control the desired products in the dissociation of methane molecule. The tailored laser pulse profile, eigenstate distributions and evolution of the efficient occupation numbers are predicted and exact energy levels of this five-atomic molecule is obtained. Dissociation rates of up to 78%, 80%, 90%, and 82% for CH2 +, CH+, C+ and C++ are achieved. Based on the present approach one can reduce the controlling costs. © 2016 Elsevier B.V  

    Modified carrageenan. 1. H-CarragPAM, a novel biopolymer-based superabsorbent hydrogel

    , Article Journal of Bioactive and Compatible Polymers ; Volume 20, Issue 5 , 2005 , Pages 475-490 ; 08839115 (ISSN) Hosseinzadeh, H ; Pourjavadi, A ; Mahdavinia, G. R ; Zohuriaan Mehr, M. J ; Sharif University of Technology
    A novel kappa-carrageenan (κC)-based superabsorbing hydrogel was synthesized through graft copolymerization of acrylamide (AAm) onto a κC substrate in the presence of a crosslinking agent. The crosslinked κC-poly(AAm) polymer graft was partially hydrolyzed in alkaline medium to yield a superabsorbent resin, H-carragPAM. The resin structure was confirmed using FTIR spectroscopy. The variables of graft copolymerization (monomer, initiator, polysaccharide and crosslinker concentration, reaction temperature and time as well as stirrer speed) that affected on the ultimate water-swelling capacity were optimized. The time-temperature variation of the copolymerization was investigated in terms of... 

    Carbon dioxide reforming of methane by pulsed glow discharge at atmospheric pressure: the effect of pulse compression

    , Article Journal of Applied Physics ; Volume 101, Issue 12 , 2007 ; 00218979 (ISSN) Ghorbanzadeh, A. M ; Modarresi, H ; Sharif University of Technology
    Methane reforming by carbon dioxide in pulsed glow discharge at atmospheric pressure is examined. The plasma pulse is compressed to less than 50 ns. This compression enables one to work at higher frequencies, over 3 kHz, without glow-arc transition. The main products of the reaction are synthetic gases (H2, CO) and C2 hydrocarbons. Approximately 42% of plasma energy goes to the chemical dissociation, when the reactant ratio is C O2 C H4 =1. At this point, the energy expense is less than 3.8 eV per converted molecule while reactant conversions are relatively high reaching to 55% (C H4) and 42% (C O2). The reactor energy performance even gets better at higher C O2 C H4 ratios. While energy... 

    High energy efficiency in syngas and hydrocarbon production from dissociation of CH4-CO2 mixture in a non-equilibrium pulsed plasma

    , Article Journal of Physics D: Applied Physics ; Volume 38, Issue 20 , 2005 , Pages 3804-3811 ; 00223727 (ISSN) Ghorbanzadeh, A. M ; Norouzi, S ; Mohammadi, T ; Sharif University of Technology
    The efficient production of syngas from a CH4+CO2 mixture in an atmospheric pulsed glow discharge, sustained by corona pre-ionization, has been investigated. The products were mainly syngas (CO, H2) and hydrocarbons up to C4, with acetylene having the highest selectivity. The energy efficiency was within 15-40% for different experimental conditions, which demonstrates a comprehensive improvement relative to the achievements of other types of non-equilibrium plasma. These values are, however, comparable with the efficiencies obtained by gliding arc plasmas but this plasma operates at near room temperature. Furthermore, it has been shown that the energy efficiency is increased by decreasing...