Sharif Digital Repository

In this paper, the sorption of uranium onto nanoporous silica adsorbent in the presence of nitrate, sulfate, chloride, fluoride and phosphate was studied. The effect of contact time between the nanoporous sorbent and aqueous solution, pH and initial concentration of uranium was also investigated. Uranium sorption onto nanoporous silica adsorbent is a very fast process as sorption rate increases with pH increment. Optimum pH for uranium sorption was 4-8. Experimental sorption isotherm is successfully described by Langmuir and Freundlich models. The results obtained by batch experiments showed that the presence of high concentration of nitrate, sulfate, chloride and phosphate anions alone had... 

The water desalination process using nanoporous single-layer graphene membranes is simulated through classical molecular dynamics. The effect of nanopores shapes on the capacity of the membrane for filtration of water is investigated. According to the results, the geometry of the nanopores considerably affects the performance of the membrane and can completely change the water flow rate and salt rejection. The results reveal that the effective area of the nanopores plays a critical role and for a better understanding of the impact of this parameter, aspect ratio and the equal diameter of noncircular pores based on different methods such as equal area, equal perimeter, and hydraulic diameter... 

This study aimed to prepare nanoporous anodic alumina on AA3003-H14 aluminum alloy using a mild anodization process with minimal working voltage and treatment time. The microstructural features, mechanical properties, and tribocorrosion behavior of the coatings were assessed to determine the optimum conditions for the fabrication of nanoporous anodic alumina on AA3003-H14 alloy. The microstructural analysis showed both uniform and nonuniform pore nucleations during anodization in H2SO4/C2H2O4, H2SO4/H2CrO4, and EG/H2O/NH4F electrolytes, where the optimal nanoporous structure with an average thickness, porosity, pore diameter, and interpore distance of 382 nm, 19%, 16 nm, and 35 nm,... 

Finite element (FE) method is used to model radial deformation of single-walled carbon nanotube (SWCNT) under hydrostatic pressure. Elastic deformation of the nanostructure is simulated via elastic beams. Properties of the beam element are calculated by considering the stiffness of the covalent bonds between the carbon atoms in the hexagonal lattice. By applying the beam elements in a three-dimensional space, elastic properties of the SWCNT in transverse direction are obtained. In this regard, influences of diameter and tube wall thickness on the radial and circumferential elastic moduli of zigzag and armchair SWCNTs are considered. It is observed that there is a good agreement between the... 

We use an efficient molecular theory approach to study electrokinetic flow within a pH-responsive nanopore grafted with a polyelectrolyte (PE) brush. The flow rate, migration and convective conductance, electric potential and velocity fields, species distributions and the degree of ionization of the weak PE functional groups and nanopore selectivity are obtained and interpreted while considering pH-induced surface charges. The theory is generally based on writing the overall free energy of the system including the entropies arising from the conformations of flexible, excluded volume chains, the mixing of mobile species, electrostatic contribution, and the free energy due to the chemical... 

The electrokinetic energy conversion, electroviscous effect, and induced internal and external magnetic fields in a smart polyelectrolyte grafted "soft"nanopore with pH responsiveness are studied here using an efficient molecular theory approach. The analysis is based on writing the total free energy of the system, including the conformational entropy of the flexible, self-avoiding polymer chains and the translational entropy of the mobile species, the electrostatic interactions, and the free energy due to chemical equilibrium reactions. Then, the free energy is minimized, while satisfying the necessary constraints to find the equilibrium state of the system. The predictions of the model are... 

Exploring bi-functional electrocatalysts with excellent activity, good durability, and cost-effectiveness for electrochemical hydrogen and oxygen evolution reactions (HER and OER) in the same electrolyte is a critical step towards a sustainable hydrogen economy. Three main features such as high density of active sites, improved charge transfer, and optimized electronic configuration have positive effects on the electrocatalyst activity. In this context, understanding structure–composition–property relationships and catalyst activity is very important and highly desirable. Herein, for the first time, we present the design and fabrication of novel MOF-derived ultra-small Ru/RuO2 nanoparticles... 

Nowadays, achievement to easy, fast, reliable and cost-effective techniques and tools is one of the most important challenges in detection of microorganisms. Salmonella typhimurium is one of the most important pathogenic bacteria that affect the human health and environmental infections. In this work we report a new, stable, biocompatible and cost-effective platform for construction of an aptasensor based on nanoporous gold (NPG) for detection of S. typhimurium. Nanoporous gold is electrochemically synthesized using Au-Cu alloy at the surface of Au/GCE. Thiol functionalized aptamer is used for effective linking to the surface of NPG/Au/GCE via self-assemble monolayers (SAMs) formation.... 

This article presents a novel armchair graphene nanoribbon (AGNR) field-effect transistor with engineered nanopores for resonant tunneling. Two rectangular nanopores are punched to create two potential barriers and one quantum well. Channel and source and drain contacts are AGNR, indicating structure homogeneity. Nonequilibrium Green's function and Poisson's equations are used for structural analysis. The input variables are well width (WW), drain voltage (VD), and barrier width (BW). The effects of repositioning nanopores and AGNR type (i.e., semiconductor and semimetal) are also studied. The impact of the parameters on the density of states, transmission probabilities, peak current (IP)... 

A temperature-induced degenerate p-type graphene nanopore/reduced graphene oxide (GNP/rGO) heterojunction-based nanodevice was prepared and studied for the first time, showing a robust negative differential resistance (NDR) feature. In this regard, cellulose-based perforated graphene foams (PGFs), containing numerous nanopores (with an average size of ∼2 nm surrounded by nearly six-layer rGO walls) were synthesized using bagasse as a green starting material. The PGFs with an essential p-type semiconducting property showed a band gap energy of ∼1.8 eV. The observed two-terminal NDR peak could present stable and reversible features at high temperatures of 586-592 K. It was demonstrated that... 

Carbon nanotubes are widely used in the design of nanosensors and actuators. Any defect in the manufactured nanotube plays an important role in the natural frequencies of these structures. In this paper, the effect of vacancy defects on the vibration of carbon nanotubes is investigated by using an atomistic modeling technique, called the molecular structural mechanics method. Vibration analysis is performed for armchair and zigzag nanotubes with cantilever boundary condition. The shift of the principal frequency of the nanotube with vacancy defect at different locations on the length is plotted. The results indicate that the frequency of the defective nanotube can be larger or smaller or... 

In this paper, an atomistic–continuum homogenization multiscale method is developed to study the nonlinear behavior of heterogeneous nanomaterials. The atomistic representative volume element (RVE) with vacancy and/or void defects are analyzed by employing the fully atomistic method, in which the nucleation, migration, and elimination of dislocation, as well as the dislocation-vacancy interaction, are captured. The coarse-scale material domain is modeled within the framework of the nonlinear finite element method, and the impression of nanoscale material defects is investigated by upscaling the stress tensor and tangent modulus from the atomistic RVE based on the Hill-Mandel principle. The... 

Submicron sized polyacrylamide particles were prepared via modified precipitation polymerization method. Experimental design based on Taguchi approach was employed to study the influence of the polymerization composition including monomer (acrylamide), crosslinker (methylenebisacrylamide), initiator (azobisisobutyronitrile), and modifier (polyvinylpyrrolidone, K-30), on the size and morphology of the particles. Varying the polymerization composition, submicron-particles with sizes ranging between 100 and 600 nm were achieved. In all the cases, polydispersity index (PDI) of the particle size was found to be almost 1 indicating uniformity of the particle size. The concentration of crosslinker... 

We conduct an experimental investigation on the pool boiling enhancement in DI water on nanoporous surfaces. The surfaces are modified by anodic oxidation, and cavities with 2 mm diameter and pitches between 2.5 and 5 mm applied on them using EDM method filled with a two-part epoxy with low thermal conductivity properties. The capillary wicking action of the superhydrophilic nanoporous oxide layer enhances the rewetting and spreading of the liquid to dry-spots during boiling. The epoxy disks remain wet and prevent merging bubbles during the pool boiling experiment and a 2-D microflow is induced toward dried regions with synergic effects of nanoporous surface absorption, create a considerable... 

In this research convective heat transfer coefficient enhancement of nanofluids prepared from high surface area graphene has been investigated in laminar flow in the developing region. The nanofluid has been prepared from nanoporous graphene with high surface area and with concentration of 0.025 to 0.1 wt.%. Deionized water has been used as the base fluid and a type of Ter-Polymer has been utilized as the surfactant. The results indicate that thermal conductivity of nanofluid with concentration of 0.1 wt.% remains quite constant, with only 3.8% enhancement, while convective heat transfer coefficient improves significantly, with 34% enhancement. The behavior of this enhancement related to the... 

Adsorption and recovery of uranium by nanoporous MCM-41 from aqueous solutions (synthetic solution and uranium conversion facility liquid waste) were investigated by use of a fixed-bed column (1.2 cm diameter and 3.0 cm height). Adsorption was carried out at flow rates 0.2 and 0.5 mL min-1, which correspond to retention times of 10 and 6 min. The maximum breakthrough capacity for uranium ions was achieved by use of nanoporous MCM-41 at the optimum pH of 3.6 and flow rate 0.2 mL min-1 (61.95 μg g-1). The Thomas and Yan models were applied to the experimental data, by use of linear regression, to determine the characteristics of the column for process design. The breakthrough curves calculated... 

Mechanical properties of a material near the surfaces and interfaces are different from those of the same material far from the surfaces/interfaces. The effect of this difference on the effective mechanical properties of heterogeneous materials becomes significant when the size of inhomogeneities is at the scale of nanometers. In this article, within a micromechanical framework, the effects of surface residual stress and surface elasticity are taken into account to obtain a macroscopic size-dependent yield function for nanoporous materials containing aligned cylindrical nanovoids. Based on the modified Hill's condition, the strains are decomposed into two parts, a part due to the external... 

Water desalination methods on the basis of newly developed graphene-based membrane have been introduced as a more efficient alternative for the conventional water purification technologies such as classical thermal desalination and reverse osmosis (RO). However, the increase of water permeation rate and ion rejection are still the main subjects in this field. In this study, a new method based on using oscillating electric field is proposed to improve the performance of nanoporous graphene. The effects of the amplitude and oscillation frequency of the electric field and the pore size of the membrane on the water permeation and salt rejection are studied by conducting molecular dynamics... 

Graphene, due to its unique excellent properties, is proposed as a developing method with high efficiency compared to classical water desalination methods. In this regard, charging the membrane is considered a promising and effective approach to enhance the performance of the graphene membrane. In this research, by using molecular dynamics simulations, the water desalination by charged multilayer graphene is evaluated and the influence of electric charge amount and geometric parameters, including the pore diameter and the interlayer distance, are investigated. According to the results, the multilayer nanoporous graphene with 16.35 Å pore diameter, in which the electric charge is distributed... 

Nanocrystalline TiO2-AgO thin films and powders were prepared by an aqueous particulate sol-gel route at the low temperature of 573 K (300 °C). Titanium tetraisopropoxide and silver nitrate were used as precursors, hydroxypropyl cellulose was used as a polymeric fugitive agent in order to increase the specific surface area. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the phase composition of the mixed oxide depends upon the annealing temperature, being a mixture of TiO2 and AgO in the range 573 K to 773 K (300 °C to 500 °C) and a mixture of TiO2, AgO, Ag2O at 973 K (700 °C). Furthermore, one of the smallest crystallite sizes was obtained for TiO...