Sharif Digital Repository

This study investigated the effects of combined utilization of wollastonite particles and recycled waste ceramic aggregate (RWCA) on high strength concrete (HSC) properties. Two groups of mixtures were manufactured: 1) concrete mixtures in which cement was partially replaced with wollastonite at values ranging from 10% to 50%, and 2) mixtures in which wollastonite was used at the aforementioned dosages and 50% of natural coarse aggregate was replaced with RWCA. In addition, 10% of cement weight micro-silica was added to all mixtures. The concrete behavior in terms of strength, durability, resistance against acidic environment, and performance under elevated temperatures ranging from 20 °C to... 

Novel organic-inorganic hybrid heterogeneous nanocatalysts were obtained by covalent anchoring of a molybdenum(vi) complex of salicylidene 2-picoloyl hydrazine, MoO2(sal-phz)(CH3OH), (1) on the surface of magnetic nanoparticles functionalized by one of two routes: in the first method, the surface of magnetic nanoparticles is directly modified with 3-chloropropyltrimethoxysilane yielding 1A. In the second method, magnetic nanoparticles were silica-coated with tetraethoxysilane and then with 3-chloropropyltrimethoxysilane yielding the intermediate 2B. Then complex 1 was grafted on the surface of 1A or 2B through covalent interaction yielding 2A or 3B, respectively. The nanocatalysts 2A and 3B... 

The current study describes design and synthesis of silica-coated zinc oxide nanoparticles containing Ponceau 4R food colorant (named as ZnO@SiO2@APTMS/P4R). The interactions of Ponceau 4R and ZnO@SiO2@APTMS/P4R with calf thymus-DNA were investigated It should be noted that the competitive binding experiment revealed that both Ponceau 4R and ZnO@SiO2@APTMS/P4R could release Hoechst 33258. As inferred from the results the binding of the Ponceau 4R and ZnO@SiO2@APTMS/P4R with DNA were surface binding, mainly due to groove binding. Furthermore, antibacterial properties of ZnO, Ponceau 4R and ZnO@SiO2@APTMS/P4R samples against gram-positive bacteria and gram-negative bacteria were examined and... 

In this study, a noble robust superhydrophobic and highly oleophobic polyurethane (PU)–SiO2 nanoparticle (NP) coating is specially designed using sol-gel process. For this purpose the effective parameters on surface tension and durability of the synthesized coating investigated and optimized. This new superhydrophobic and highly oleophobic coating exhibits good pensile hardness as high as 6H with adhesive force grade of 5B and repels water and oil with contact angles (CAs) of 159° and 140° respectively. The synthesized PU-SiO2 composite also retains an excellent amphiphobicity after a 7 days immersion in water with water and oil with CAs of 150° and 130°. Facile fabrication of PU–SiO2... 

In this work, solvent blending in combination with extruding are applied to provide polystyrene/silica nanocomposite specimens. Transmission electron microscope (TEM) and scanning electron microscope (SEM) show same nanoparticle dispersion in PS matrix in low to high filler loadings. Differential scanning calorimetry (DSC), dynamic mechanical thermal analyzer (DMTA) and thermogravimetric analyzer (TGA) were used to study the thermophysical characteristic of the nanocomposites in solid state. In addition, the melt state rheological behavior of the samples was investigated under constant and zero shear rates. Interestingly, different behaviors were detected in nanocomposites in low and high... 

Hyperbranched polyethyleneimine functionalized silica (PEI-SiO2) nanoparticles with considerable hydrophilicity were synthesized and incorporated into a polysulfone (PSF)/dimethylacetamide (DMA)/polyvinylpyrrolidone (PVP) membrane casting solution in five different ratios to fabricate PEI-SiO2/PSF nanocomposite membranes using nonsolvent-induced phase separation. The hydrophilic PEI-SiO2 nanoparticles were characterized by TEM, FTIR, TGA, and XPS analyses. Morphology, water contact angles, mean pore sizes, overall porosity, tensile strengths, water flux, antifouling and the dye separation performances of the PEI-SiO2/PSF membranes were also studied. The PEI-SiO2 nanoparticles were uniformly... 

We introduce highly antifouling Polymer-Nanoparticle-Nanoparticle/Polymer (PNNP) hybrid membranes as multi-functional materials for versatile purification of wastewater. Nitrogen-rich polyethylenimine (PEI)-functionalized halloysite nanotube (HNT-SiO2-PEI) nanoparticles were developed and embedded in polyvinyl chloride (PVC) membranes for protein and dye filtration. Bulk and surface characteristics of the resulting HNT-SiO2-PEI nanocomposites were determined using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). Moreover, microstructure and... 

A task-specific Brønsted acidic ionic liquid (BAIL), 1-benzyl-3-methylimidazolium hydrogensulfate ([BnMIm]HSO4), was prepared and confined onto the high surface area silica gel. The catalyst has shown extraordinary activity in comparison of homogeneous ionic liquid (IL) system for Fischer esterification of fatty acid with ethanol. The ester derivatives were synthesized in high yields and catalyst was easily separated from the reaction mixture by simple filtration. The structure of the catalyst is theoretically modelized to investigate the unusual catalytic activity. Hence, a hydroxylated cage-like nano-cluster, H6Si8O12(OH)2, was selected to mimic the surface of silica gel. The interactions... 

Silica gel-confined ionic liquid (IL) is a class of heterogeneous catalysts with broad catalytic applications. Leaching of the IL from the surface of the support is the major drawback of these catalysts, which reduce the catalyst efficiency during the chemical reactions. To investigate the effect of the hydrogen bonding on the leaching phenomena, the interaction between the 1-ethyl-3-methylimidazolium-based IL with various anions (Cl-, Br-, HSO4 -, NO3 -, BF 4 -, and PF6 -) and the surface of the silica gel were studied using density functional theory. Hence, a hydroxylated cage-like cluster of silica gel, Si4O6(OH), was selected to mimic the surface. The values of ÎEinteraction show that... 

A novel mesoporous silica-functionalized dual Brønsted acidic species has been introduced as an efficient catalyst for solvent-free esterification of fatty acids with ethanol. The structure of the catalyst has been characterized by FT-IR spectroscopy, thermal gravimetric analysis (TGA), TEM and N2 adsorption-desorption. TGA of catalyst 1 showed no weight loss before 200 °C, indicating a high degree of hydrophobicity of the surface of the mesoporous silica. TEM images and nitrogen adsorption-desorption showed no noticeable changes to the structure of the catalyst before and after acid treatment. pH metric analysis was performed for the catalyst to determine the loading of the acidic sites.... 

A novel silica-functionalized ammonium tungstate interphase catalyst has been reported as a non-nitric acid route for adipic acid production from one-pot oxidative cleavage of 30% hydrogen peroxide and catalytic amounts of p-toluenesulfonic acid (PTSA). The catalyst has been simply prepared by commercially available starting material. The structure of the catalyst has been investigated using FT-IR spectroscopy, atomic absorption, TEM, SEM and XRD analysis. The catalyst has shown good to high activity even up to 10 runs of reaction. Simple preparation of the catalyst, avoids using harmful phase transfer catalyst (PTC) and/or chlorinated additives are among the other benefits of this work  

A novel silica-functionalized dual Brønsted acidic ionic liquid (ionic liquid with two Brønsted acidic species) has been reported as a highly efficient catalyst for thioacetalization of carbonyl compounds. The reaction was efficiently performed in water as an environmentally benign solvent with good to high yields. Thermal gravimetric analysis showed that the catalyst is stable at least up to 350 C. Furthermore, the catalyst can be recycled and reused for six runs of reaction without appreciable loss of activity. The structure of the catalyst is modelized to gain more realistic structural insight about the functionalized ionic liquid  

1-Butyl-3-methylimidazolium tungstate ([BMIm] 2WO 4) ionic liquid supported onto silica sulphamic acid demonstrated desirable performance for oxidation of cyclohexene to adipic acid. Simple experimental procedure, easy product isolation, catalyst recovery and reusability are some attractive features of this protocol  

Exploring deprotonation properties of silica-functionalized propylsulfonic acid catalyst (silica-propyl-SO3H) is the subject of various experimental and theoretical researches. In the current study, the structure of the silica-propyl-SO3H has been simulated using density functional theory (DFT) methods by mimicking the surface of the silica in the form of cubic cage-like nanoclusters of silicon and oxygen. The values of ΔHacidity for gas-phase deprotonation are calculated considering various possible interactions of the propylsulfonic acid on the surface of the silica. Our investigations indicate that interactions of sulfonic acid (-SO3H) head... 

The overall behavior of rammed earth (RE) as a low embodied energy construction method can be enhanced by using stabilizers. Several studies have been performed on cement and lime stabilized RE. However, studies on other additives, especially the sustainable ones, are limited. In this research, the effect of stabilizers including cement, pozzolan, microsilica, fiberglass, guar gum and phase change material (PCM) was evaluated on the performance of RE mixtures. The mixtures were assessed by considering the durability, shrinkage, thermal conductivity, mechanical properties and their sensitivity to the humidity. Then, the correlations were determined between the mechanical properties and the... 

In recent years, pozzolana are being increasingly used in different types of concretes and mortars. This investigation aims to evaluate the effect of replacing 7, 14, 21, and 28% cement (by weight) with silica fume (SF), granulated blast furnace slag (GBFS), zeolite, and fly ash (FA) under elevated temperatures. Forty mix designs were built with various water-to-cement ratios and plasticizers. Three hundred and six specimens were prepared, and the flexural, uniaxial compression and tensile tests were performed on specimens after exposure to elevated temperatures between 25°C and 900°C. The X-ray diffraction (XRD) test was then performed on the two series of specimens. Accordingly, the... 

The preparation and characterization of a new type of nanocomposite polyelectrolyte membrane, based on DuPont Nafion/imidazole-modified nanosilica (Im-Si), for direct methanol fuel cell applications is described. Related to the interactions between the protonated imidazole groups, grafted on the surface of nanosilica, and negatively charged sulfonic acid groups of Nafion, new electrostatic interactions can be formed in the interface of Nafion and Im-Si which result in both lower methanol permeability and also higher proton conductivity. Physical characteristics of these manufactured nanocomposite membranes were investigated by scanning electron microscopy, thermogravimetry analysis,... 

This work develops a systematic uncertainty quantification framework to assess the reliability of prediction delivered by physics-based material models in the presence of incomplete measurement data and modeling error. The framework consists of global sensitivity analysis, Bayesian inference, and forward propagation of uncertainty through the computational model. The implementation of this framework on a new multiphase model of novel porous silica aerogel materials is demonstrated to predict the thermomechanical performances of a building envelope insulation component. The uncertainty analyses rely on sampling methods, including Markov-chain Monte Carlo and a mixed finite element solution of... 

The synthesis of plate-like silica particles, which are of importance for a variety of applications, are mainly based on the widely adopted method of the sol-gel reaction of silicon alkoxides in traditional batch-wise instrumentation. In this study, continuous-flow synthesis of amorphous plate-like silica particles is reported through combining droplet-based microfluidics and the sol-gel reaction of tetraethyl orthosilicate. The reaction was conducted at the surface of oil droplets, comprising tetraethyl orthosilicate (TEOS), suspended in acidic (HCl) water, resulting in silica particles on the surface of the droplets, leaving the device with outlet flow. The synthesized particles had... 

In this contribution, the effect of physical immobilization of methylene blue (MB) into silica nanocomposites was investigated on the conversion and selectivity of the photooxygenation of anthracene and dihydroartemisinic acid (DHAA). Physically immobilized photocatalysts were synthesized through a developed Stöber method and were thoroughly characterized by UV–Vis, FTIR, XRD, XPS, SEM, TEM, HR-TEM, BET-BJH, and EDX analyses. Based on the TEM and UV–Vis results, it was determined that enhancement of the MB concentration as an organocatalyst for the Stöber reaction led to an increase in the size of the nanoparticles from 54 to 183 nm and a 21 nm blue shift in their UV–Vis spectra. Moreover,...