Sharif Digital Repository

Three-dimensional (3D) polyamide scaffolds were fabricated by applying a solvent bath as the collecting element. Electrospun nanofibers were immersed into the solvent bath to give a material with a laminated 3D texture. In parallel, 2D nanofibers were synthesized and utilized as microextractive phases in a needle trap device to compare the capabilities of 2D and 3D materials in terms of headspace extraction of various chlorobenzenes (chlorobenzene, 1,2-dichlorobenzene, 1,4-dichlorobenzene, 1,2,4-trichlorobenzene and 1,2,3,4-tetrachlorobenzene). The results demonstrate the superiority of 3D nanofibrous scaffolds over 2D mats. The porosity, morphology, and thermal stability of the 3D scaffolds... 

Nanocages (NCs) have emerged as a new class of drug-carriers, with a wide range of possibilities in multi-modality medical treatments and theranostics. Nanocages can overcome such limitations as high toxicity caused by anti-cancer chemotherapy or by the nanocarrier itself, due to their unique characteristics. These properties consist of: (1) a high loading-capacity (spacious interior); (2) a porous structure (analogous to openings between the bars of the cage); (3) enabling smart release (a key to unlock the cage); and (4) a low likelihood of unfavorable immune responses (the outside of the cage is safe). In this review, we cover different classes of NC structures such as virus-like... 

Metallic or ceramic micro/nanoporous materials have attracted particular attention due to some interesting structural and functional properties. There exist a variety of methods for producing porous materials by which optimized features can be reached. Spark plasma sintering (SPS) is one of these new-emerging approaches. This technique is often combined with conventional technologies and produce a variety of porous structures with tailorable microstructure and physicomechanical properties. This review addresses SPS and obtainable porous materials with nanoscale and microscale microstructural features. The processing methods, microstructural phenomena, and physicomechanical properties of... 

This paper reports on hydrogen sensing based graphene oxide hybrid with Co-based metal organic frameworks (Co-MOFs@GO) prepared by the hydrothermal process. The texture and morphology of the hybrid were characterized by powder x-ray diffraction, scanning electron microscopy and Brunauer-Emmett-Teller analysis. Porous flower like structures assembled from Co-MOFs and GO flakes with sufficient specific surface area are obtained, which are ideal for gas molecules diffusion and interactions. Sensing performance of Co-MOFs@GO were tested and also improved by sputtering platinum (Pt) as a catalyst. The Pt-sputtered Co-MOFs@GO show outstanding hydrogen resistive-sensing with response and recovery... 

Metallic foams are a class of lightweight materials that show high potentials for different industrial applications such as automotive and aerospace engineering. However, many factors have prevented metallic foams from being fully utilized in industrial applications. One main factor is that the influences of the porous structure on the mechanical properties of metallic foams are not well known yet. In this paper, a finite element model was used to analyze monodisperse closed cell aluminum foam in order to determine the relationship between its elastic modulus, porosity and pore diameter. A nonlinear relationship was found between the foams porosity, pore diameter and modulus of elasticity.... 

Exploiting of the nanostructure arrays as a promising candidate for excitation of neural cells has been analyzed. Based on the importance of the coupling effect between electrode and neuron, a multiphyscis modeling approach has been proposed. The model incorporates theoretically both structural effects (size, geometry) and electrophysiological effects. The system of equations for proposed model has been solved numerically using Finite Element Method for Poisson equation and Finite Difference Method for Cable equation. In this regards we have combined the system of equations in COMSOL platform with Matlab interface accordingly. We have analyzed the effect of excitation of neuron with an extra... 

Porous nanocomposite hydrogels were prepared using CaCO3 particles as solid porogens. The hydrogels were prepared by polymerization and grafting of acrylamide and 2-acrylamido-2-methylpropane sulfonic acid onto the starch in the presence of CaCO3 and graphene oxide. CaCO3 solid porogens were then removed by washing with acid and porous structures were obtained. The prepared hydrogels were used as adsorbents for methylene blue as a model cationic dye; and a very high adsorption capacity, up to 714.29 mg g-1, was obtained. Kinetics and isotherms of adsorption and the effect of porosity of hydrogel as well as other experimental conditions were also investigated. The prepared adsorbents were... 

In order to produce an inexpensive catalyst for the Fischer-Tropsch synthesis (FTS), zeolitized high silicon fly ash utilized as a catalytic support for cobalt nanoparticles. The ability of this new support in proper hosting of nanoparticles studied through various characterization methods such as X-ray diffraction, nitrogen sorption, transmission electron microscopy, energy-dispersive spectroscopic and temperature-programmed reduction. In addition, the catalytic properties for the FTS evaluated at 523 K and 20 MPa. The obtained results show remarkable influence of utilized support specifications upon the formation and catalytic behavior of cobalt nanoparticles in the FTS  

Three-dimensional reduced graphene oxide (3D-rGO) structures decorated with CuO particles (GCu) are synthesized through a simple and scalable method for detection of hydrogen sulfide (H2S) gas. For characterization and investigation of porous structure various techniques were employed. Decorated 3D structures demonstrated higher sensitivity and selectivity in comparison to pure structure. Optimized structure for sensing was obtained through introducing different amounts of CuO. The GCu heterostructures containing 35 μmol of CuO powder demonstrated reproducible response of about 30% to the concentration of 10 ppm at room temperature, while complete recovery was obtained through heating to 150... 

PANI/Pd/TiO2NTs electrodes with highly porous structures and good capacitive characteristics were prepared by electrodeposition of polyaniline on palladium nanoparticles loaded TiO2 nanotubes. The loading of small palladium nanoparticles was carried out by sonochemical reduction of Pd+2 onto TiO2NTs and affected the ordered growth of PANI, reducing the charge transfer resistance and increasing surface area of PANI. The specific capacitance and the stability of electrode showed improvements. The results illustrated that the specific capacitance of these electrodes was around 1060 F g-1 in 1.0 M H2SO4 electrolyte as measured at a constant current of 2.0 A g-1, whereas it was 210 F g-1 for the... 

In this study, copper oxide nano particles were synthesized by batchwise supercritical hydrothermal method. After preparation of CuO nano particles, they were immobilized into the porous matrix of sodium alginate. The drying process formed a very porous structure that is useful for enhancing of adsorption activity. Produced CuO particles were characterized by X-ray diffractometery (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and BET for measuring the surface area. The prepared materials were then used as adsorbent in the removal of toxic metal ions in aqueous solution. To optimize the adsorption system, the effect of various parameters such as adsorbent... 

V2O5-TiO2 nanostructured porous layers were grown through micro arc oxidation of titanium in vanadate containing electrolytes. This study sheds light on the effect of the electric current type on the photocatalytic performance of the layers. Surface morphology of the layers was investigated by SEM. The results revealed a porous structure with a pores size of 30-180 nm depending on the frequency and the duty cycle. A uniform porous structure was obtained under the pulse-DC regime. Topographical investigations revealed a rough surface which is favorable for catalytic applications. Our XRD and XPS results showed that the layers consisted of anatase, rutile, and vanadium oxide phases whose... 

Macroporous styrene-divinylbenzene copolymers with different degree of crosslinking were prepared by suspension polymerization in presence of different binary mixtures of toluene and heptane, as diluent. Specific surface area, bulk and apparent densities, and pore volume of the resulting beads were determined experimentally. Applying the least square method to the experimental data, correlations for prediction of these properties were obtained. Effects of divinylbenzene concentration, diluent to comonomer volume ratio, and composition of the diluent mixture were considered in developing the aforementioned correlations. The influence of the reaction recipe on porous structure of the samples... 

In this research, the possibility that nanostructured aluminium titanate (tialite) powder can be used as a chemical source for producing Al2O3 and Al3Ti precipitates in aluminium matrix composites has been investigated. Optical microscopy, FE-SEM, XRD, DSC and TGA examinations were used to characterize the synthesized specimens. The results showed that a porous structure and inferior mechanical properties were obtained in as-sintered samples. The further thermomechanical treatments i.e. cyclic rolling and hot extrusion improved the mechanical properties and led to a dense microstructure with a homogeneous distribution of Al2O3 and... 

In this study, sintered porous polymeric materials made of high density polyethylene (HDPE) were fabricated through controlling the chain interdiffusion time at the transition temperature of semicrystalline and melt states. At this intermediate state, where both crystalline and amorphous phases coexist, the interfacial welding of HDPE particles is facilitated thanks to interdiffusion caused by chain relaxation phenomena. Then, by assuming a spherical shape and a cubic packing configuration of particles, a geometrical model was developed to predict porosity variations as sintering progresses. Moreover, the HDPE used, as a broad molecular weight distributed polymer, has different family chains... 

A novel AC impedance study on three-dimensional hybrid structures of graphene sheets/MoS2 nanorose (GMS) toward ethanol vapor detection is presented in this work. These defective 3D hybrid porous structures are sensitive to the presence of different gases as a result of charge transfer with gas species, as well as a change in the effective capacitance of the system. The sensing behavior of the samples is investigated throughout time-dependent impedance measurement and electrochemical impedance spectroscopy (EIS). The sensor response is estimated at about 20% to 10 ppm ethanol vapor, with the response and recovery times about 3.2 s and 0.8 s, respectively. Sensing mechanism proposed to... 

A reinforced double network (DN) hydrogel as a candidate for skin scaffold was prepared. It consists of O-carboxymethyl chitosan, polyvinyl alcohol, honey, CaCl2, and graphene oxide. The various concentrations of CaCl2, namely, 30, 45, and 60 wt% were investigated. Besides, the GO content was studied as 3, 5, and 10 wt%. The structure of the DN was characterized by Fourier-transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, energy dispersive X-ray and Brunauer-Emmett-Teller were evaluated. The mechanical properties were studied, too. It showed that the DN with 45 wt% CaCl2 was optimized. Also, swelling mechanism was investigated.... 

In this investigation, a reactor model for prediction of the deactivation behavior of MTO's porous catalyst in a fixed bed reactor is developed. Effect of coking on molecular transport in the porous structure of SAPO-34 has been simulated using the percolation theory. Thermal effects of the reaction were considered in the model and the temperature profile of the gas stream in the reactor was predicted. The predicted loss in catalyst activity with time-on-stream was in very good agreement with the experimental data. The resulting coke deposition and gas temperature profiles along the length of reactor suggested a reaction front moving toward the outlet of the fixed bed reactor at the... 

TiO2 layers were grown via pulse type microarc oxidation process under different applied voltages, frequencies, and duty cycles. Surface chemical composition and phase structure of the synthesized layers were studied utilizing X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Furthermore, scanning electron microscope (SEM) and atomic force microscope (AFM) were employed to investigate surface morphology and topography of the layers. It was revealed that the layers had a porous structure with both anatase and rutile phases. The anatase relative content in the layers increased with the applied frequency; meanwhile, it decreased with duty cycle at low applied voltages, but... 

Hydrogen storage capacities of raw, oxidized, purified and Fe-doped multi-walled carbon nanotubes (MWCNTs) were studied by electrochemical method. Based on transmission electron microscopy and Raman spectroscopic data, thermal oxidation removed defective graphite shells at the outer walls of MWCNTs. The analysis results indicated that the acid treatment dissolved most of the catalysts and opened some tips of the MWCNTs. Thermal gravimetric analysis and differential scanning calorimetry results illustrated that by oxidation and purification of MWCNTs, the weight loss peak shifts toward a higher temperature. N2 adsorption isotherms of the purified and oxidized MWCNTs showed an increase in N2...