Showing papers on "Silica gel published in 2010"

Silica aerogel: synthesis and applications

Abstract: Silica aerogels have drawn a lot of interest both in science and technology because of their low bulk density (up to 95% of their volume is air), hydrophobicity, low thermal conductivity, high surface area, and optical transparency. Aerogels are synthesized from molecular precursors by sol-gel processing. Special drying techniques must be applied to replace the pore liquid with air while maintaining the solid network. Supercritical drying is most common; however, recently developed methods allow removal of the liquid at atmospheric pressure after chemical modification of the inner surface of the gels, leaving only a porous silica network filled with air. Therefore, by considering the surprising properties of aerogels, the present review addresses synthesis of silica aerogels by the sol-gel method, as well as drying techniques and applications in current industrial development and scientific research.

Nitrogen-Enriched Nanocarbons with a 3-D Continuous Mesopore Structure from Polyacrylonitrile for Supercapacitor Application

Abstract: A kind of polyacrylonitrile-based carbon with a 3-D continuous mesopore structure was prepared by using silica gel as a template. Both the mesopore structure and the nitrogen content could be easil...

Hydrogenation of Nitrobenzene to Aniline over Silica Gel Supported Nickel Catalysts

Abstract: Nanosized silica gel supported Ni catalysts that have average Ni particle size of 3.7, 11.4, and 11.8 nm were prepared by facile impregnation of different Ni precursors and used for hydrogenation of nitrobenzene (NB). These catalysts were characterized by N2 adsorption, X-ray diffraction, and transmission electron microscopy. It was found that Ni dispersed highly on the surface of silica gel in the catalyst prepared via Ni(en)3(NO3)2, and the detected average Ni particle size was 3.7 nm. On the 3.7 nm sized Ni catalyst, the selectivity of aniline (AN) reached 99% with a 100% conversion of NB in 5.5 h at 90 °C, 1.0 MPa, and NB:Ni = 305 (mole ratio). But, the activities of 11.8 nm sized Ni catalysts and commercial Raney Ni catalyst are quite lower. The reaction network and mechanism of NB hydrogenation on 3.7 nm sized Ni catalyst were discussed on the basis of products distributions at different temperatures and pressures. The calculated activation energy of NB hydrogenation on Ni-5/SiO2-EN catalyst is 54.5...

Amphiphobic Nanofibrous Silica Mats with Flexible and High-Heat-Resistant Properties

Abstract: In this study, for the first time, we fabricated flexible, high-heat-resistant, and amphiphobic mats by (fluoroalkyl)silane (FAS) modification of electrospun pure silica nanofibrous mats. The inorganic silica nanofibrous mats were obtained via electrospinning the blend solutions of poly(vinyl alcohol) (PVA) and silica gel, followed by calcination to remove the organic component. The PVA/silica and silica fibers were found to be randomly oriented as nonwoven mats with fiber diameters in the range of 150−500 nm. After the FAS modification, the surface wettability of the silica mats was converted from amphiphilic to amphiphobic. The fluorinated mat with the bead-on-string structure showed the highest water contact angle (WCA) of 154° and oil contact angle (OCA) of 144°. Additionally, the fluorinated inorganic fibrous mats exhibited a high heat resistance; they kept their hydrophobicity (WCA of 138°) and oleophobicity (OCA of 132°) even after the annealing treatment at 450 °C for 30 min. Potential application...

Highly dispersed Pt nanoparticle catalyst prepared by atomic layer deposition

Abstract: Nanoparticulate platinum has been well dispersed onto large quantities of micron-sized mesoporous silica gel using atomic layer deposition in a fluidized bed reactor (i.e. ALD-FBR). Transmission electron microscopy (TEM) cross-sectional investigations showed that the Pt nanoparticles were homogeneously distributed throughout primary 30–75 μm silica gel particles, including the inner surfaces comprising 5–7 nm pores. The Pt catalyst loading level was tightly controlled by the number of coating cycles. An extremely low Pt loading with 3.1 × 10 −6 mg Pt/cm 2 (0.10 atom/nm 2 ), 4.8 × 10 −6 mg Pt/cm 2 (0.15 atom/nm 2 ) and 2.9 × 10 −5 mg Pt/cm 2 (0.91 atom/nm 2 ) was prepared with 3, 5 and 10 coating cycles, respectively. The average Pt particle size is approximately 1.2 nm for 3 cycles. For 5 and 10 coating cycles, the Pt particle size is measured to be 1.9 nm and 2.3 nm, respectively. The sample with a 3.1 × 10 −6 mg Pt/cm 2 loading exhibits the highest metal dispersion of 90%. Thermal stability studies indicated an initial sintering of the Pt particles during the first 4 h of heat treatment at 450 °C in an air environment. After that, there was no noticeable change of the particle size during the following heat treatment process. Carbon monoxide oxidation demonstrated nearly 100% conversion of CO to CO 2 over 20 mg of 4.8 × 10 −6 mg Pt/cm 2 loaded silica gel particles at 180 °C for 100 sccm flow rate of 1% CO in argon.

HILIC behavior of a reversed-phase/cation-exchange/anion-exchange trimode column

Abstract: The hydrophilic interaction liquid chromatography behavior of a novel trimodal stationary phase with reversed-phase/cation-exchange/anion-exchange characteristics was studied. This material is based on nanopolymer silica hybrid technology and provides reversed-phase, strong cation-exchange and weak anion-exchange properties at the same time. It is constructed with high-purity porous spherical silica particles coated with charged organic polymer nano-beads (d(p) approximately 100 nm). The inner-pore area of the silica gel is covalently modified with an organic layer that provides both reversed-phase and weak anion-exchange properties. The outer surface is modified with strong cation-exchange functionality. This chemistry ensures distinctive spatial separation of the anion-exchange and cation-exchange regions, which allows both retention mechanisms to function simultaneously and provides more flexibility in selectivity control. The new phase exhibits hydrophilic interaction liquid chromatography characteristics: at high acetonitrile levels, the retention for charged analytes is governed by an ion-exchange process, accompanied by hydrophilic interaction (partitioning mechanism). This feature provides good flexibility in pharmaceutical method development such as simultaneous separation of hydrophilic drug molecule and its counterions (e.g. penicillin G potassium salt).

Profiling of lipids in Leishmania donovani using hydrophilic interaction chromatography in combination with Fourier transform mass spectrometry

Abstract: There is evidence from our current research on resistance to stibigluconate and from some previous observations that lipid composition may be altered in resistant Leishmania donovani and in order to explore this we required a comprehensive lipidomics method. Phospholipids can be analysed by direct infusion into a mass spectrometer and such methods can work very well. However, chromatographic methods can also be very effective and are extensively used. They potentially avoid ion suppression effects, associate lipid classes with a retention time range and deliver good quantitative accuracy. In the current study three chromatography columns were compared for their ability to separate different classes of lipid. Butylsilane (C-4), Zic-HILIC and a silica gel column were compared. The best results were obtained with a silica gel column used in hydrophilic interaction chromatography (HILIC) mode with a mobile phase gradient consisting of (A) 20% isopropyl alcohol (IPA) in acetonitrile (v/v) and (B) 20% IPA in 0.02 M ammonium formate. Using these conditions separate peaks were obtained for triglycerides (TG), phosphoinositols (PI), inositol phosphoceramides (IPC), phosphatidylethanolamines (PE), phosphatidylserines (PS), phosphatidylcholines (PC), sphingosines (SG), lysophosphatidyethanolamines (LPE) and lysophosphatidylcholines (LPC). The methodology was applied to the analysis of lipid extracts from Leishmania donovani and by coupling the chromatography with an LTQ Orbitrap mass spectrometer. It was possible to detect 188 lipid species in the extracts with the following breakdown: PC 59, PE 38, TG 35, PI 20, CPI 13, LPC 11, LPE 2 and SG 10. The fatty acid composition of the more abundant lipids was characterised by MS2 and MS3 experiments carried out by using an LCQ Deca low-resolution ion trap instrument coupled with the silica gel column. The separation of lipids into well-defined groups gives extra confidence in their identification and minimises the risk of ion suppression effects. High-resolution mass spectrometry was necessary in order to be able to differentiate between acyl- and acyl-alkyl-lipids. Copyright C) (C) 2010 John Wiley & Sons, Ltd.

Investigating Mechanical Behaviors of Silica Nanoparticle Reinforced Composites

Abstract: The research is aimed to investigate the mechanical behaviors of epoxy-based nanocomposites reinforced with spherical nanoparticles. Five differ- ent contents of silica nanoparticles 5, 10, 15, 20, and 40 wt% were introduced in the samples. Through a solgel technique, the silica particles with a diameter of 25 nm were exfoliated uniformly in the epoxy matrix. Experimental results obtained from tensile tests indicate that the modulus of nanocomposites increases with the increment of particulate inclusions, and the enhancing behavior is coincided with the model predictions obtained from the MoriTanaka micromechanical model. In addition, the fracture tests conducted on single-edge-notch bending specimens reveal that the inclusion of nanoparticles can effectively increase the fracture tough- ness of the nanocomposites. Furthermore, the extent of the enhancement is more appreciable in the brittle matrix system rather than in the ductile matrix system. Subsequently, by inserting the silica epoxy mixture into the unidirectional glass fiber through a vacuum hand lay-up process, the glass fiber/silica/epoxy composite samples were fabricated. Results depicted that the in-plane shear strength increases until the increment of particle loadings are up to 10 wt%. In addition, results obtained from the compression tests revealed that the glass/epoxy specimens with 20 wt% silica loading exhibit superior compressive strengths than those that do not contain any silica particles.

Adsorption Kinetics and Thermodynamics of Methylene Blue onto p-tert-Butyl-calix[4,6,8]arene-Bonded Silica Gel

Abstract: New-style adsorbents of p-tert-butyl-calix[4,6,8]arene-bonded silica gel—CnABS (C4ABS, C6ABS, C8ABS)—were prepared by bonding p-tert-butyl-calix[4,6,8]arene to the silica gel surface through the coupling reagent, 3-glycidoxypropyltrimethoxysilane. The products were characterized by FTIR, thermogravimetry, elemental analysis, and scanning electron microscopy. The adsorption of methylene blue from aqueous solution by CnABS was studied. Kinetic studies showed that the adsorption of the dye onto CnABS fit a first-order kinetic model. The equilibrium adsorption data were interpreted using the Langmuir and Freundlich models. The adsorption of methylene blue onto CnABS was better represented by the Langmuir equation. The saturation adsorption quantity monotonically increased with the number of phenolic units in the calixarene ring. The thermodynamic parameters for the adsorption reaction were calculated through a van’t Hoff analysis. The whole adsorption process was endothermic, which resulted in an increase of ...

Nanocomposites of ionic liquids confined in mesoporous silica gels: preparation, characterization and performance

Abstract: A series of nanocomposites of ionic liquids (ILs) were prepared via a modified sol–gel method. The ILs were physically confined in mesoporous silica gels with 5–40% content. ILs from imidazolium, thiophenium and ammonium with different anions were prepared and used. Characterization using the Brunauer–Emmett–Teller (BET) method, Fourier transform infrared (FT-IR) spectroscopy, temperature-programmed desorption (TPD), differential scanning calorimetry (DSC), inverse gas chromatography (IGC), temperature-controlled Raman and fluorescence emission spectroscopies was conducted to explore any confinement effects. BET results showed that, depending on the ILs and their contents, the average pore diameter of the pure silica gel was 3–12 nm after the confined ILs were removed completely. It was suggested that ILs aggregated on the nanoscale in the mesoporous silica gel. In comparison with bulk ILs and ILs coated onto silica gels (IL/sg), IL nanocomposites (IL–sg) displayed remarkably low specific heat capacities (Cp was in the range 0.3–1.2 J g−1 K−1), disordered vibrational conformations (without phase transitions in the range −100–200 °C), greater interactions with hydrocarbon solutes (adsorption capacities of 0.3–0.4 g per 100 g for confined ILs with CO2 gas), and greatly enhanced fluorescence emission (up to 200 times stronger than bulk ILs). Furthermore, Based on the specific solubility of different compounds, the nanocomposites could also be applied to the separation of CO2 from CO2/N2 mixtures and thiophene from thiophene/octane mixtures.

The use of metal piece additives to enhance heat transfer rate through an unconsolidated adsorbent bed

Abstract: The effects of metal piece additives on effective thermal conductivity and diffusivity of an unconsolidated adsorbent bed in which adsorbent is silica gel were investigated. The metal piece additives were copper, brass, aluminum and stainless steel with two different sizes as 1.0–2.8 mm and 2.8–4.75 mm. The effective thermal conductivity and diffusivity of the mixed bed were predicted by comparison of the experimental results with the solution of dimensionless heat conduction equation for the bed. The performed experiments showed that the addition 15wt% of aluminum pieces with sizes between 1.0 and 2.8 mm enhances the effective thermal diffusivity and conductivity of a pure silica gel bed by 157% and 242%, respectively.

Selective removal of 2,4-dichlorophenoxyacetic acid from water by molecularly-imprinted amino-functionalized silica gel sorbent

Abstract: A molecularly-imprinted amino-functionalized sorbent for selective removal of 2,4-dichlorophenoxyacetic acid (2,4-D) was prepared by a surface imprinting technique in combination with a sol-gel process. The 2,4-D-imprinted amino-functionalized silica sorbent was characterized by FT-IR, nitrogen adsorption and static adsorption experiments. The selectivity of the sorbent was investigated by a batch competitive binding experiment using an aqueous 2,4-D and 2,4-dichlorophenol (2,4-DCP) mixture or using an aqueous 2,4-D and 2,4-dichlorophenylacetic acid (DPAC) mixture. The largest selectivity coefficient for 2,4-D in the presence of 2,4-DCP was found to be over 18, the largest relative selectivity coefficient between 2,4-D and 2,4-DCP over 9. The static uptake capacity and selectivity coefficient of the 2,4-D-imprinted functionalized sorbent are higher than those of the non-imprinted sorbent. The imprinted functionalized silica gel sorbent offered a fast kinetics for the extraction/stripping of 2,4-D, 73% of binding capacity (200 mg/L 2,4-D onto 20 mg of imprinted sorbent) was obtained within 5 min and the adsorbed 2,4-D can be easily stripped by the mixture solution of ethanol and 6 mol/L HCl (V:V = 1:1). In a test of five extraction/stripping cycles, the adsorption capacity of the sorbent was all above 93% of that of the fresh sorbent. Experimental result showed the potential of molecularly-imprinted amino-functionalized sorbent for selective removal of 2,4-D.