Amir Vahid | Northwestern University (original) (raw)

Papers by Amir Vahid

Synthesis and application of mesoporous silicate nanoparticles are important areas of research in... more Synthesis and application of mesoporous silicate nanoparticles are important areas of research in many fields such as drug delivery, medicine, catalysis, and optic. The method of synthesis strongly affects the properties of a product. In this work, the mesoporous silica nanoparticles were synthesized by means of a hydrogel. The obtained product was characterized by X-ray diffraction, scanning electron microscopy, and nitrogen physisorption. The results show that highly ordered mesoporous silica nanoparticles were synthesized by means of a hydrogel.

Sorption of drugs in nano-scale materials such as single-wall carbon nanotubes is a very interest... more Sorption of drugs in nano-scale materials such as single-wall carbon nanotubes is a very interesting research in nanomedicine. Nitroglycerin is one of drugs that can be used medically as a vasodilator to treat heart conditions. It is one of the oldest and most useful drugs for treating heart disease by shortening or even preventing attacks of angina pectoris. Nitroglycerin can be used to help destroy prostate cancer as well as being used as a heart medicine. Therefore, the study of capability of delivery of nitroglycerin as a drug may be useful in nano-sacle medicine. We apply Monte Carlo simulations to predict the sorptivity of single-wall carbon nanotubes for nitroglycerin at room temperature and varying pressure. The isotherm diagrams for nitroglycerin sorption report to find mechanism of this fluid sorption in single-wall carbon nanotubes. The sorption isotherms show that nitroglycerin can diffuse inside the single-wall carbon nanotubes while their diameter is larger than 10 Å ....

In the present work MCM-41 material was synthesized by a rapid method. The calcined material was ... more In the present work MCM-41 material was synthesized by a rapid method. The calcined material was characterized using XRD, scanning electron microscopy and nitrogen physisorption. The XRD pattern of calcined sample shows five well-defined peaks that indicates highly ordered MCM-41 material was synthesized. The SEM image reveals that the sample particles are in nanometer range. The isotherm of Nitrogen demonstrates a nearly reversible behavior which implies highly ordered MCM-41 material was synthesized by this method. The BET specific surface area of the sample is about 910 m3g-1. This method is also rapid and simple and results in high quality MCM-41 material.

International journal of Environmental Science and Technology

In the present work, H2S of crude oil was removed via a two-step method including stripping follo... more In the present work, H2S of crude oil was removed via a two-step method including stripping followed by adsorption. First, ZnO/MCM-41 adsorbents containing 5, 17.5 and 30 wt% of zinc were synthesized and characterized using XRD and nitrogen physisorption. Then, these materials were used as adsorbents for the removal of the H2S stripped from crude oil. At second step, the H2S of crude oil was extracted to gas phase by hot stripping. The obtained extract was collected in a storage tank for the subsequent H2S adsorption process. A three-factor Box–Behnken design with five center points and one response was performed for the optimization of adsorption of H2S. The influence of process parameters and their interactional effects on the adsorption of H2S were analyzed using the obtained adsorption experimental data. A model including three important factors, i.e., temperature, space velocity and amount of supported zinc and their interactions, was developed to generate the optimum condition...

Journal of Environmental Health Science and Engineering, 2015

Solid State Sciences, 2011

(2-Hydroxyethyl)-trimethylammonium hydroxide Mesoporous silicate material Highly ordered hexagona... more (2-Hydroxyethyl)-trimethylammonium hydroxide Mesoporous silicate material Highly ordered hexagonal structure MCM-41synthesis Characterization a b s t r a c t MCM-41material was synthesized using various ratios of (2-Hydroxyethyl)-trimethylammonium hydroxide and sodium hydroxide. The calcined samples were characterized by powder XRD, scanning electron microscopy, nitrogen physisorption, 29 Si MAS NMR spectroscopy and transmission electron microscopy. The XRD pattern of all calcined samples shows at least four distinct peaks that indicates long range order of them. The nitrogen adsorption/desorption isotherm of all samples exhibits type IV isotherm which is the typical characteristic of mesoporous materials. When (2-Hydroxyethyl)-trimethylammonium hydroxide was used alone as a base for the synthesis of MCM-41, the highest value of surface area was obtained. Results also reveal that the pore size distribution of this sample is so narrow. The SEM images show that wiry MCM-41 samples were obtained when (2-Hidroxyethyl)-trimethylammonium hydroxide was used in the synthesis process. 29 Si MAS NMR spectroscopy proves that the presence of pure organic base in synthesis medium improves framework condensation of MCM-41. TEM images illustrate well-ordered hexagonal array of mesopores in all samples.

Microporous and Mesoporous Materials, 2013

ABSTRACT In this work the synthesis of two sulfonic acid-functionalized mesoporous silica-based m... more ABSTRACT In this work the synthesis of two sulfonic acid-functionalized mesoporous silica-based materials (SBA-15-propyl-SO3H and SBA-15-phenyl-SO 3H) through a co-condensation method is reported. The samples were characterized by means of SAXS, N2-adsorption/desorption isotherms, FTIR spectroscopy and thermogravimetric analysis. In addition, the surface acidity of the samples was investigated through ammonia adsorption microcalorimetry. We found that both the number and the strength of acid sites of SBA-15-phenyl-SO3H catalyst are higher than those of SBA-15-propyl-SO3H. The total number of acid sites was 808 μmol/g and 122 μmol/g for SBA-15-phenyl-SO3H and SBA-15-propyl-SO 3H, respectively. The two materials were then used as acid heterogeneous catalysts for the interesterification of extra virgin olive oil with ethyl acetate to produce biodiesel. We found a higher catalytic activity of SBA-15-phenyl-SO3H respect to SBA-15-propyl-SO3H in agreement with the microcalorimetric acidity measurements. Phenyl-sulfonic acid-functionalized SBA-15 seems to be a promising acid heterogenous catalyst for the preparation of biodiesel through the interesterification of triglycerides with ethyl acetate.

Journal of Non-Crystalline Solids, 2011

In the present work, mesoporous silica nanoparticles (MSNs) with well-ordered hexagonal structure... more In the present work, mesoporous silica nanoparticles (MSNs) with well-ordered hexagonal structure were synthesized using Sodium Carboxy Methyl Cellulose. The MSNs were characterized by scanning electron microscopy, dynamic light scattering, powder XRD, nitrogen physisorption and Transmission electron microscopy. The MSNs were also functionalized with thiol groups and its capacity toward adsorption of a large cation, i.e. lead was investigated. Scanning electron microscopy reveals that MSNs have semi-spherical shapes. The XRD pattern of the calcined sample shows at least five well-defined peaks which point out that silicate nanoparticles have hexagonal array of pores as MCM-41 structure. The nitrogen adsorption isotherm displays a type IV isotherm according to the IUPAC classification. A sharp inflection in capillary condensation/ evaporation step specifies that well-ordered MCM-41 nanoparticles were synthesized. TEM image shows the well-ordered hexagonal structure of MSNs. The adsorption capacity of functionalized MSNs was higher than functionalized MCM-41 in which one reason for such behavior might be explained by higher accessibility of pores of functionalized MSNs. This approach was carried out using relatively low-cost and nonhazardous reactants in concentrated reaction medium and also the yield of this approach was high up to 96% by weight.

Journal of Molecular Liquids, 2013

ABSTRACT Three types of imidazolium based ionic liquids, 1-hexyl-3-methylimidazolium tetrafluorob... more ABSTRACT Three types of imidazolium based ionic liquids, 1-hexyl-3-methylimidazolium tetrafluoroborate ([HMIM] 26 [BF4]), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([EMIM][NTf2]) and 1-butyl-3- 27 methylimidazolium methylsulfate ([BMIM][MeSO4]) were prepared and a variety of their fundamental prop- erties such as kinematic (ν) and dynamic (η) viscosities, thermal stability, surface tension (σ ), refractive index (nD), pH and density (ρ) were investigated as a function of temperature. The coefficients of thermal expansion (αp) of the pure liquids were also calculated from the experimental values of the density at different temperatures. Electrochemical studies of these pure fluids asmedia were also studied at screen printed glassy carbon electrode (SP-GCE). Themeasurements were performed on a single drop of ionic liquids at surface of a screen-printed three electrode cell. The results showed an ideal wide range of potential windows for studies of electrochemical behavior of some species such as hydrogen sulfide and thiols in the lipophilic and hydrophilic ionic liquids. These properties were studied for special purposes such as development of electroanalytical methods for trace determination of organosulfur compounds in petroleum and its products.

Journal of Hazardous Materials, 2011

In this contribution, different amounts of nickel were incorporated into the mesopores of MCM-41 ... more In this contribution, different amounts of nickel were incorporated into the mesopores of MCM-41 via an in situ approach. A hydrophobic nickel precursor was incorporated into the nanochannels of mesoporous silica by manipulation of solvent-solute interaction. The synthesized material was characterized using Xray diffraction, nitrogen physisorption, temperature programmed reduction, and transmission electron microscopy. The results implicate the formation of MCM-41 with well-ordered hexagonal structure and establish also the presence of nickel nanoparticles inside the nanochannels of mesoporous silica. Adsorptive desulfurization of gas oil was conducted using the nickel-incorporated MCM-41 samples. The effects of nickel concentration, temperature of process and feed flow rate on the desulfurization process were examined. The MCM-41 containing 6 wt.% of nickel had both the highest breakthrough sulfur adsorption capacity and total sulfur adsorption capacity, which were 0.69 and 1.67 mg sulfur/g adsorbent, respectively. The breakthrough sulfur adsorption capacity was almost regained after reductive regeneration of spent adsorbent. The obtained results suggest that the method applied for the synthesis of Niy/MCM resulted in formation of well-dispersed, accessible and small nickel nanoparticles incorporated into the pores of MCM-41 which might be an advantage for adsorption of refractory sulfur compounds from low sulfur gas oil.

Fuel Processing Technology, 2013

ABSTRACT In this work, a novel in-situ synthesis route was applied for preparation of an adsorben... more ABSTRACT In this work, a novel in-situ synthesis route was applied for preparation of an adsorbent, i.e. palladium containing MCM-41. At fi rst, a hydrophobic palladium precursor was added to the ethanolic micellar solution followed by vac- uum distillation of ethanol which decreases the hydrophobic characteristic of the solution. Distillation caused diffu- sion of hydrophobic palladium precursor into the hydrophobic core of the micelles. Then, tetraethyl orthosilicate was added to the above solution and the silicate spices arranged around the palladium containing micelles. The XRD, N 2 physisorption and TEM studies revealed that 4 wt.% palladium loading was achieved without considerable loss of pore ordering. H 2 -TPR showed that the palladium nanoparticles were accessible for hydrogen molecules. Ad- sorptive desulfurization of low sulfur diesel fuel was then investigated using synthesized samples. The effect of three valuable parameters, i.e., temperature (25, 75, 150 and 200 °C), concentration of palladium (2, 4 and 5 wt.%) and feed fl ow rate (0.3 and 1 mL/min) were tested using a fi xed-bed fl owing device. The highest sulfur break through adsorption capacity and total sulfur adsorption capacity obtained at 200 °C, 0.3 mL/min of feed fl ow rate and 4 wt.% of palladium concentration were 1.67 and 2.35 mg sulfur/g adsorbent, respectively.

Chemistry of Materials, 2005

The application of nanomaterials in medical and biological fields has drawn great research intere... more The application of nanomaterials in medical and biological fields has drawn great research interest in recent years. 1 Currently, nanoparticles have been used in many biological fields, such as sensors, fluorescent markers in vitro and in vivo, clinical diagnosis, drug delivery, and MRI contrast agents. [8] Mesoporous materials, especially MCM-type silica, have many unique properties, such as ordered porous structure, extremely high surface area (>1000 m 2 g -1 ), large pore volume, and well-defined and tunable pore size (1.5-10 nm). It is proposed that mesoporous materials can act as a convenient reservoir for drugs and biomolecules. The drug adsorbing and releasing behavior of porous silica has been extensively studied using ibuprofen as a model drug. 9 Lin and co-workers 10 used CdS as a gate to demonstrate the stimuli-responsive controlled release in and Tanaka et al. 11 demonstrated photocontrolled releasing of cholestane from coumarin-modified MCM-41. A mesoporous silica-based gene transfection system where the average particle size was 250 nm was also reported very recently. 12 Mesoporous silica is thus believed to have great potential to be a new controlled-release system. At the same time, the extensive internal structure may be utilized for carrying non-releasing molecular imaging agents, such as fluorophore or magnetic resonance imaging (MRI) contrast agent. Previously, we reported gadolinium (Gd) incorporated nanosized mesoporous silicas as a new MRI contrast agent. In this paper, we will functionalize nanosized mesoporous silicas to be used as a fluorescence cell tag. Because of the protection of the mesopores, the embedded fluorophores are expected to be stable against enzymatic digestion and thus good for long time cell tracking.

Chemistry Letters, 2003

... Because of the unique properties of high-connectivity, large porosity, and well-dispersion, t... more ... Because of the unique properties of high-connectivity, large porosity, and well-dispersion, thenano-sized mesoporous silica could be used for the synthesis of the high-performancenano-catalysts,10 and mesoporous silica-polymer nanocomposites and for other appli-cations ...

ABSTRACT In the present work, three different porous supports, i.e. MCM-41, SBA-15 and UVM-7 were... more ABSTRACT In the present work, three different porous supports, i.e. MCM-41, SBA-15 and UVM-7 were synthesized and functionalized with three different aminosilanes (C9H23NO3Si, C8H22N2O3Si and C10H27N3O3Si). All the synthesized samples were characterized using XRD, nitrogen physisorption, elemental analysis and acid/base titration, SEM and TEM. The obtained results revealed that all the samples have well-ordered structure and amine groups successfully grafted on their pore surface. Then, the ability of amine-functionalized samples toward adsorption of H2S was investigated. In case of MCM-41 change of aminosilane functional group did not changed tbp (the time at which the outlet concentration of H2S reaches its maximum admissible value in the effluent, denoted as tbp). SBA-15 functionalized with C8H22N2O3Si showed enhanced tbp in comparison with C9H23NO3Si but, C10H27N3O3Si showed very low tbp (even lower than C9H23NO3Si) which might be attributed to pore blocking originated from very large size of C10H27N3O3Si. UVM-7 had the highest tbp for all the three aminosilane functional groups. This might be attributed to very large pore size of UVM-7 with respect to those of SBA-15 and MCM-41. In addition, nanosize particles of UVM-7 facilitate adsorption of H2S for this type of adsorbent which should be due to the unconstrained diffusion of H2S within the mesopores of UVM-7. Efficiency of aminosilane functional group strongly depends on pore size of support rather than its surface area.

ABSTRACT Mixtures of hydrocarbons have been simulated with discontinuous potential models to char... more ABSTRACT Mixtures of hydrocarbons have been simulated with discontinuous potential models to characterize the Helmholtz energy of the repulsive reference fluids (A0) as functions of density and composition. A previous study focused on methane, ethane, propane, n-butane, n-hexane, n-heptane, n-decane, and benzene.[1] Unfortunately, a slight inconsistency was encountered when the trend observed for these small molecules was extrapolated to the long chain limit. In the present work, we extend the analysis to methane with C10, C20, and C40 molecules of: nalkanes, ethyl-styrenes, and ethyl-propylenes. Compositions varied from 0.1 to 0.9 mole fraction for each binary mixture. Packing fractions varied from 0.3 to 0.5. The goal of the present study was to develop a general strategy for interpolating the perturbation contributions between simulations of individual state points in order to facilitate usage of molecular simulation results in engineering applications. We find that the athermal entropy of mixing deviates significantly from ideality, but still follows the van der Waals mixing formula. This leads to an accurate characterization of the entropic contribution for mixtures of all sizes and shapes. A general rule is developed for predicting the athermal entropy of mixing based on knowledge of the volume ratios of the constituent molecules. The simulations are compared to several theories, including the MCSL theory for hard spheres,[2] the SAFT model,[3] and the Guggenheim-Staverman theory.[4] Keywords: Thermodynamic properties, molecular simulation, polymers, entropy, mixtures, phase equilibria. Reference: 1. Gray, N. H.; Elliott, J. R. In Quadratic Mixing in Perturbation Theory, AIChE Fall National Meeting, Austin, TX, 2004; Austin, TX, 2004; p 160e. 2. Mansoori, G. A.; Carnahan, N. F.; Starling, K. E.; Leland, T. W., Equilibrium Thermodynamic Properties of the Mixture of Hard Spheres. J. Chem. Phys 1971, 54, 1523-1525. 3. Chapman, W. G.; Gubbins, K. E.; Jackson, G.; Radosz, M., SAFT: Equation of State Solution Model for Associating Fluids. Fluid Phase Equilib. 1989, 52, 31. 4. Abrams, D. S.; Prausnitz, J. M., Statistical Thermodynamics of Liquid Mixtures: A New Expression for the Excess Gibbs Energy of Partly or Completely Miscible Systems. AIChE J. 1975, 21, 116.

is modified in this research. The proposed modification estimates the specific volume of polar an... more is modified in this research. The proposed modification estimates the specific volume of polar and hydrogenbonded liquids and vapor pressure of pure substances with greater accuracy while maintaining the ability of PRFR EOS in predicting critical compressibility factor of pure compounds. The proposed model is applied to correlate and predict the experimental data of vapor-liquid equilibria (VLE) and liquid densities of various binary nonideal and polar solutions. For this purpose eight mixing rules (van der Waals, HVO, WS, MHV1, MHV2, MHV, LCVM and HVOS) were used. Among the mixing rules considered in this work, only the WS and the MHV are the best predictive tools. In the G ex part of the proposed model the NRTL and the UNIQUACtype models were used, respectively. NRTL model has weak predictive capabilities due to its temperaturedependent parameters.

In this research, the capabilities of PRSV (Peng-Robinson-Stryjek-Vera) and PRRF (Peng-Robinson-R... more In this research, the capabilities of PRSV (Peng-Robinson-Stryjek-Vera) and PRRF (Peng-Robinson-Rahdar-Feyzi) EOS + excess free energy (G ex) mixing rules in representing the behavior highly polar solutions are compared. The PRRF equation of state overcomes the shortcomings of PRSV and related EOS in predicting and correlating the phase behavior of polar solutions. The combined EOS + G ex models need to reproduce the excess Gibbs free energy models as closely as possible in order to represent low-pressure vapor-liquid equilibrium behavior of polar mixtures accurately and also to make the vapor-liquid predictions at higher temperatures and pressures accurate using only low-pressure information. The proposed model is applied to correlate and predict the experimental data of vapor-liquid equilibria (VLE) for various binary nonideal and polar solutions. For this purpose six mixing rules (HVO, WS, MHV1, MHV2, LCVM and HVOS) were used with each equation of state (PRSV and PRRF). The perfo...

Scarcity of water resources is becoming an increasing challenging problem in the world. This call... more Scarcity of water resources is becoming an increasing challenging problem in the world. This calls for new means of water utilization, including seawater. Entropy generation has been implemented in designing a new device for desalination process based on nonequilibrium thermodynamics and interfacial/electro chemistry concepts. The efficiency of the new proposed device is almost twice of the previous apparatus proposed in the literature and therefore it is classified as a new generation membrane-free machines for the desalination process required for purification of the natural seawater used as drinking water and in related chemical and biological applications.

Free energy and extent of the reaction (yield) are predicted by a thermodynamically guided approa... more Free energy and extent of the reaction (yield) are predicted by a thermodynamically guided approach based upon estimation of free energies of compounds. The non-ideality of the system and the effect of solvent are taken into account through the fugacity coefficient calculated by Perturbed-Chain Induced-Polar Statistical Associating Fluid Theory (PCIP-SAFT) molecular theory. A structure-based formulation is defined for the Gibbs free energy and the yield is obtained from the relationship between the free energy of reaction and equilibrium constant considering temperature effects. The model is trained using a database containing 10000 cited reactions. Regression of computed Gibbs free energy and yield of reaction versus experimental values resulted in a coefficient of determination (R2) of about 0.95. The absolute average deviation of the predicted yield is ~0.15 that has been validated against sets of 2000 reactions. Finally, the proposed theory is implemented to predict retrosynthet...