Showing papers on "Silica gel published in 2018"

Hydroxyl Radical Based Photocatalytic Degradation of Halogenated Organic Contaminants and Paraffin on Silica Gel

Abstract: Photochemical materials are of scientific and practical importance in the field of photocatalysis. In this study, the photochemistry of several organic contaminants, including decabromodiphenyl ether (BDE-209), halogenated phenols (C6 X5OH, X = F, Cl, Br) and paraffin, on silica gel (SG) surface was investigated under simulated solar irradiation conditions. Photolysis of these compounds at the solid/air interface proceeds with different rates yielding various hydroxylation products, and hydroxyl radical was determined as the major reactive species. According to density functional theory (DFT) calculations, the reaction of physically adsorbed water with reactive silanone sites (>Si═O) on silica was indispensable for the generation of •OH radical, where the required energy matches well with the irradiation energy of visible light. Then, the BDE-209 was selected as a representative compound to evaluate the photocatalytic performance of SG under different conditions. The SG material showed good stability in the photodegradation process, and was able to effectively eliminate BDE-209 under natural sunlight. These findings provide new insights into the potential application of SG as a solid surface photocatalyst for contaminants removal.

Metal–organic framework@silica as a stationary phase sorbent for rapid and cost-effective removal of hexavalent chromium

Abstract: A one-pot synthesis in quantitative yield is described to construct a composite of the amino-derivative Zr carboxylate metal–organic framework (MOF) and silica gel (UiO-66-NH2@silica). The silica gel was utilized as a porous solid support to enable enhanced column packing efficiency and increase the sorbent–solute contact time. The control experiment conducted on bare silica unambiguously established the active role of the amino-functionalized MOF as the ion-exchange element in the novel composite. The column prepared from this composite shows excellent hexavalent chromium uptake (Cr2O72− uptake of 277.4 mg g−1). Remarkably, this ion exchange column is capable of eliminating Cr(VI) ions even in the presence of competing anions including chloride, bromide, nitrate and sulphate, thus indicating its potential for applications in municipal as well as industrial waste water treatment.

Sol-gel Silica Nanoparticles in Medicine: A Natural Choice. Design, Synthesis and Products.

Abstract: Silica is one of the most abundant minerals in the Earth’s crust, and over time it has been introduced first into human life and later into engineering. Silica is present in the food chain and in the human body. As a biomaterial, silica is widely used in dentistry, orthopedics, and dermatology. Recently amorphous sol-gel SiO2 nanoparticles (NPs) have appeared as nanocarriers in a wide range of medical applications, namely in drug/gene target delivery and imaging diagnosis, where they stand out for their high biocompatibility, hydrophilicity, enormous flexibility for surface modification with a high payload capacity, and prolonged blood circulation time. The sol-gel process is an extremely versatile bottom-up methodology used in the synthesis of silica NPs, offering a great variety of chemical possibilities, such as high homogeneity and purity, along with full scale pH processing. By introducing organic functional groups or surfactants during the sol-gel process, ORMOSIL NPs or mesoporous NPs are produced. Colloidal route, biomimetic synthesis, solution route and template synthesis (the main sol-gel methods to produce monosized silica nanoparticles) are compared and discussed. This short review goes over some of the emerging approaches in the field of non-porous sol-gel silica NPs aiming at medical applications, centered on the syntheses processes used.

Extraordinary water adsorption characteristics of graphene oxide

Abstract: The laminated structure of graphene oxide (GO) confers unique interactions with water molecules which may be utilised in a range of applications that require materials with tuneable hygroscopic properties. The precise role of the expandable interlayer spacing and functional groups in GO laminates has not completely been understood to date. Herein, we report the experimental and theoretical investigations on the adsorption and desorption behaviour of water in GO laminates as a function of relative pressure. We observed that GO imparts high water uptake capacity of up to 0.58 gram of water per gram of GO (g g−1), which is significantly higher than silica gel as a conventional desiccant material. More interestingly, the adsorption and desorption kinetics of GO is five times higher than silica gel. The observed extraordinary adsorption/desorption rate can be attributed to the high capillary pressure in GO laminates as well as micro meter sized tunnel-like wrinkles located at the surface.

Elucidating the accelerated carbonation products of calcium silicates using multi-technique approach

Abstract: This article features an investigation of the accelerated carbonation products of four calcium silicate phases, namely monoclinic-tricalcium silicate (3CaO·SiO2 or C3S), γ-dicalcium silicate (2CaO·SiO2 or γ-C2S), tricalcium disilicate (3CaO·2SiO2 or C3S2, rankinite), and monocalcium silicate (CaO·SiO2 or CS, wollastonite). During the carbonation reaction, the calcium silicate minerals form calcium carbonate and Ca-modified silica gel. These reaction products were examined using thermogravimetric analysis (TGA), X-ray powder diffraction (XRD), 29Si magic angle spining (MAS) nuclear magnetic resonance (NMR), 13C {1H} cross polarized (CP)/MAS NMR, and dynamic vapor sorption (DVS) techniques. Along with the crystalline forms of CaCO3 (i.e., calcite, vaterite, and aragonite), amorphous calcium carbonate (ACC) was also found to be present in the carbonated calcium silicate systems. Based on the experimental results, it is proposed that the ACC particles were stabilized by the deposition of silica layers on their surfaces. Presence of ACC also affected the pore size distribution of the matrixes, which eventually influenced the diffusion based carbonation rate of the matrixes. Moreover, the degree of carbonation of CS was found to be most effective compared to other calcium silicates in terms of the percentage of the phase reacted for the experimental conditions used in this study.

Novel Approach for Enhanced Scandium and Titanium Leaching Efficiency from Bauxite Residue with Suppressed Silica Gel Formation.

Abstract: The need of light weight alloys for future transportation industry puts Sc and Ti under a sudden demand. While these metals can bring unique and desired properties to alloys, lack of reliable sources brought forth a supply problem which can be solved by valorization of the secondary resources. Bauxite residue (red mud), with considerable Ti and Sc content, is a promising resource for secure supply of these metals. Due to drawbacks of the direct leaching route from bauxite residue, such as silica gel formation and low selectivity towards these valuable metals, a novel leaching process based on oxidative leaching conditions, aiming more efficient and selective leaching but also considering environmental aspects via lower acid consumption, was investigated in this study. Combination of hydrogen peroxide (H2O2) and sulfuric acid (H2SO4) was utilized as the leaching solution, where various acid concentrations, solid-to-liquid ratios, leaching temperatures and times were examined in a comparative manner. Leaching with 2.5 M H2O2: 2.5 M H2SO4 mixture at 90 °C for 30 min was observed to be the best leaching conditions with suppressed silica gel formation and the highest reported leaching efficiency with high S/L ratio for Sc and Ti; 68% and 91%; respectively.

The removal and capture of CO2 from biogas by vacuum pressure swing process using silica gel

Abstract: In this study, silica gel was employed as adsorbent in a vacuum pressure swing adsorption process for the removal and capture of CO2 from biogas. Adsorption isotherms of CH4 and CO2 on silica gel were measured experimentally, meanwhile a series of breakthrough experiments were also performed on a fixed bed packed with silica gel. In order to design experiments of VPSA process more reasonable, Central Composite Design Methodology was employed to implement the design of experiments, while Response Surface Methodology was used to analyze experimental results. Experimental results showed that the biogas simulated by 55% CH4 balanced with CO2 could be concentrated to an enriched CH4 stream with CH4 purity higher than 98%, after most of the CO2 had been depleted from feed gas by VPSA process. Moreover, dynamic and transient behaviors, such as temperature profiles and concentration profiles in adsorption bed, were revealed by numerical modeling. A good consistency between experimental data and simulation results was observed. Furthermore, an industrial scale dual pressure swing adsorption unit was designed and evaluated by numerical simulation to achieve the goal of CH4 enrichment and CO2 capture simultaneously. Simulation results indicated that the simulated biogas could be separated to an enriched CH4 stream at 98.01% CH4 purity and 97.31% CH4 recovery, as well as a concentrated CO2 stream at 96.74% CO2 purity and 97.58% CO2 recovery.

Sturdy, Monolithic SiC and Si3N4 Aerogels from Compressed Polymer-Cross-Linked Silica Xerogel Powders

Abstract: We report the carbothermal synthesis of sturdy, highly porous (>85%) SiC and Si3N4 monolithic aerogels from compressed polyurea-cross-linked silica xerogel powders. The high porosity in those articles was created via reaction of core silica nanoparticles with their carbonized polymer coating toward the new ceramic framework and CO that escaped. Sol–gel silica powder was obtained by disrupting gelation of a silica sol with vigorous agitation. The grains of the powder were about 50 μm in size and irregular in shape and consisted of 3D assemblies of silica nanoparticles as in any typical silica gel. The individual elementary silica nanoparticles within the grains of the powder were coated conformally with a nanothin layer of carbonizable polyurea derived from the reaction of an aromatic triisocyanate (TIPM: triisocyanatophenyl methane) with the innate −OH, deliberately added −NH2 groups, and adsorbed water on the surface of silica nanoparticles. The wet-gel powder was dried at ambient temperature under vacuu...

Adsorption of congo red dye from aqueous solution onto amino-functionalized silica gel

Abstract: This study investigates the potential use of amino-functionalized silica gel as an adsorbent for the recovering of congo red dye from aqueous solution. The effects of pH, contact time, and temperature were determined and evaluated. Equilibrium isotherms were also studied. The adsorption kinetics was modeled by pseudo-first order and pseudo-second order. Furthermore, desorption of congo red was preliminarily studied. The pH range from 4.5 to 7.0 was favorable for the adsorption of congo red onto amine modified silica at 25oC. Higher adsorption capacity was obtained at 50oC. Langmuir and Freundlich models were fitted to the adsorption equilibrium data. The best fittings were obtained with the pseudo-second order and Langmuir model for kinetics and equilibrium, respectively. Desorption studies suggest that ion exchange might be the major mode of adsorption. KOH solution was the best desorbing agent for recovering the adsorbed dye.

Glycopolymer Grafted Silica Gel as Chromatographic Packing Materials

Abstract: The modification of the surface of silica gel to prepare hydrophilic chromatographic fillers has recently become a research interest. Most researchers have grafted natural sugar-containing polymers onto chromatographic surfaces. The disadvantage of this approach is that the packing structure is singular and the application scope is limited. In this paper, we explore the innovative technique of grafting a sugar-containing polymer, 2-gluconamidoethyl methacrylamide (GAEMA), onto the surface of silica gel by atom transfer radical polymerization (ATRP). The SiO₂-g-GAEMA with ATRP reaction time was characterized by Fourier infrared analysis, Thermogravimetric analysis (TGA), and elemental analysis. As the reaction time lengthened, the amount of GAEMA grafted on the surface of the silica gel gradually increased. The GAEMA is rich in amide bonds and hydroxyl groups and is a typical hydrophilic chromatography filler. Finally, SiO₂-g-GAEMA (reaction time = 24 h) was chosen as the stationary phase of the chromatographic packing and evaluated with four polar compounds (uracil, cytosine, guanosine, and cytidine). Compared with unmodified silica gel, modified silica gel produces sharper peaks and better separation efficiency. This novel packing material may have a potential for application with highly isomerized sugar mixtures.

Zn(II), Pb(II), and Cd(II) adsorption from aqueous solution by magnetic silica gel: preparation, characterization, and adsorption

Abstract: A novel magnetic silica gel adsorbent (Fe3O4-Si-COOH) was successfully prepared by introducing carboxyl group in situ to improve the performance for Pb(II), Zn(II), and Cd(II) adsorption Infrared spectroscopy (IR), scanning electron microscope (SEM), transmission electron microscope (TEM), thermo-gravimetric analyzer (TGA), the Brunauer-Emmett-Teller (BET) surface area, X-ray diffraction (XRD), and vibrating sample magnetometer (VSM) characterizations suggested that Fe3O4-Si-COOH has been successfully prepared The adsorption performance was evaluated by batch experiments with different initial concentrations, ionic strength, contact time, and pH The adsorption kinetics data followed pseudo-second-order model and exhibited a three-stage intraparticle diffusion mode Isothermal adsorption equilibrium data were best fitted by the Freundlich model and the adsorption capacity were 155, 110, and 93 mg/g (initial concentration 210 mg/L) for Pb(II), Zn(II), and Cd(II), respectively The result of X-ray photoelectron spectroscopy (XPS) survey spectrum suggested that the main adsorption mechanism is that the H+ of carboxyl groups exchanged with heavy metal ions in the adsorption processes In addition, the adsorbed Fe3O4-Si-COOH could be regenerated and the adsorption capacity of reused Fe3O4-Si-COOH could maintain 803% after five cycles Hence, the Fe3O4-Si-COOH could be a kind of potential material for removing Pb(II), Zn(II), and Cd(II) from wastewater

Silica Gel Coated Spherical Micro resonator for Ultra-High Sensitivity Detection of Ammonia Gas Concentration in Air.

Abstract: A silica gel coated microsphere resonator is proposed and experimentally demonstrated for measurements of ammonia (NH3) concentration in air with ultra-high sensitivity. The optical properties of the porous silica gel layer change when it is exposed to low (parts per million (ppm)) and even ultra-low (parts per billion (ppb)) concentrations of ammonia vapor, leading to a spectral shift of the WGM resonances in the transmission spectrum of the fiber taper. The experimentally demonstrated sensitivity of the proposed sensor to ammonia is estimated as 34.46 pm/ppm in the low ammonia concentrations range from 4 ppm to 30 ppm using an optical spectrum analyser (OSA), and as 800 pm/ppm in the ultra-low range of ammonia concentrations from 2.5 ppb to 12 ppb using the frequency detuning method, resulting in the lowest detection limit (by two orders of magnitude) reported to date equal to 0.16 ppb of ammonia in air. In addition, the sensor exhibits excellent selectivity to ammonia and very fast response and recovery times measured at 1.5 and 3.6 seconds, respectively. Other attractive features of the proposed sensor are its compact nature, simplicity of fabrication.

Nanoporous silica gel structures and evolution from reactive force field-based molecular dynamics simulations

Abstract: Nanoporous silica-rich gel formed on silicate glass surfaces during dissolution in aqueous environment is critical in elucidating the corrosion mechanisms and the long-term residual dissolution behaviors. Silica gel models were created using two types of methods with reactive force field-based molecular dynamics simulations. The results show that the remnant silica gels created from the ISG bulk structure have a more isolated and closed pore morphology and slightly higher glass network connectivity. This contrasts with the gel structures created by hydrogarnet defect formation that exhibit more connected pore morphologies. The remnant gel structures show lower water diffusivity which was explained by the nano-confinement effect of water molecules due to frequent interactions of water molecules with adjacent silica walls and the more isolated pore morphology in the remnant gel structures. These results reveal the complexity in terms of micro and atomic structures of these silica gels, and both structure features have impact on water transport in the gel layer hence the passivating effect that controls the long-term dissolution behavior of these glasses. Theoretical models that mimic the interfacial silica gel layers created during the dissolution of silicate glasses have been developed. The formation of these nanoporous silica gels is important in many fields, including biomaterials, catalysis, and nuclear-waste storage, and understanding their structures and properties is important for ultimately understanding how they corrode. Now, taking advantage of recent advances in computational chemistry methods, Jincheng Du and J.M. Rimsza from the University of North Texas have developed two atomistic silica gel models, one imitates the proposed experimental mechanism for gel formation by removing the dissolvable species of an International Simplified Glass, the second mimics the formation of a prevalent defect structure. Their data lead to critical insights into the silica structures formed during silicate dissolution, highlighting the importance of water diffusion, pore-connectivity, and microstructure.

New heterogeneous Rh-containing catalysts immobilized on a hybrid organic-inorganic surface for hydroformylation of unsaturated compounds

Abstract: Anchoring Rh complexes to the surface of a silica polyamine composite, which has a poly(allylamine) covalently grafted to the surface of amorphous silica gel, yielded a material that proved to be an effective and novel heterogeneous catalyst for hydroformylation of unsaturated compounds. Surface amino groups of the material were modified with phosphines by covalent and ionic coupling. The modified materials were then treated with Rh(acac)(CO)2, giving the catalysts K-1 and K-2. Catalysts were characterized by solid-state NMR spectroscopy, IR spectroscopy, XPS, TEM, and elemental analysis. The activity and stability of K-1 and K-2 were then studied for the hydroformylation of selected unsaturated compounds. Hydroformylation of terminal double bonds occurred selectively in the presence of internal double bonds. Characterization of the catalysts and the problems encountered with the supported catalysts are discussed. Catalyst K-1 is reusable and can be applied to the hydroformylation of linear olefins, styrene, 4-vinylcyclohexene, and dienes, as well as representative terpenes and other unsaturated hydrocarbons in a batch reactor.