Presence Of Silica Gel Research Articles

Integral Membrane Properties of Polysulfone/Chitosan/Polyvinyl Alcohol Blend Incorporated with Rice Husk Ash Silica Gel

In this study, silica gel was extracted from rice husk ash using a modified acid-leaching process. The gel was then characterized using an X-ray Diffractometer (XRD) and an X-ray Fluorescence (XRF). At different loadings of 0, 0.05 and 0.10 wt.%, silica gel was used as a cross-linker in the membrane formulation. Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) were used to characterize the membranes, while their performance was determined by pure water flux. XRD and XRF results revealed that the gel contained 76.85% silica. The presence of silica gel in membranes results in optimal water flux, indicating that the membranes have achieved good integral stability via the cross-linking process. Based on these positive findings, the applications of the membranes in the water-oil separation process will be evaluated in future work.

Silica gel-assisted synthesis of benzo[b]thiophenes from o-(alkylsulfanyl)(ethynyl)benzenes

A variety of 2-substituted benzo[b]thiophenes were prepared from o-(alkylsulfanyl)(ethynyl)benzenes in the presence of silica gel under thermal conditions. Tertiary alkyl-substituted sulfanyl derivatives gave good results. Methylsulfanyl-substituted precursors also afforded benzo[b]thiophenes at higher temperature. Effect of modified silica gel was evaluated and the mechanism of this method was discussed. This method was also applied to preparation of 2-substituted thieno[3,2-b]thiophenes, which gave moderate yields.

Silica gel and microwave-promoted synthesis of dihydropyrrolizines and tetrahydroindolizines from enaminones.

A wide range of N-(ethoxycarbonylmethyl)enaminones, prepared by the Eschenmoser sulfide contraction between N-(ethoxycarbonylmethyl)pyrrolidine-2-thione and various bromomethyl aryl and heteroaryl ketones, underwent cyclization in the presence of silica gel to give ethyl 6-(hetero)aryl-2,3-dihydro-1H-pyrrolizine-5-carboxylates within minutes upon microwave heating in xylene at 150 °C. Instead of functioning as a nucleophile, the enaminone acted as an electrophile at its carbonyl group during the cyclization. Yields of the bicyclic products were generally above 75%. The analogous microwave-assisted reaction to produce ethyl 2-aryl-5,6,7,8-tetrahydroindolizine-3-carboxylates from (E)-ethyl 2-[2-(2-oxo-2-arylethylidene)piperidin-1-yl]acetates failed in nonpolar solvents, but occurred in ethanol at lower temperature and microwave power, although requiring much longer time. A possible mechanism for the cyclization is presented, and further functionalization of the newly created pyrrole ring in the dihydropyrrolizine core is described.

Gaseous environment modulates volatile emission and viability loss during seed artificial ageing

Main conclusionModulation of the gaseous environment using oxygen absorbers and/or silica gel shows potential for enhancing seed longevity through trapping toxic volatiles emitted by seeds during artificial ageing.Volatile profiling using non-invasive gas chromatography–mass spectrometry provides insight into the specific processes occurring during seed ageing. Production of alcohols, aldehydes and ketones, derived from processes such as alcoholic fermentation, lipid peroxidation and Maillard reactions, are known to be dependent on storage temperature and relative humidity, but little is known about the potential modulating role of the gaseous environment, which also affects seed lifespan, on volatile production. Seeds of Lolium perenne (Poaceae), Agrostemma githago (Caryophyllaceae) and Pisum sativum (Fabaceae) were aged under normal atmospheric oxygen conditions and in sealed vials containing either oxygen absorbers, oxygen absorbers and silica gel (equilibrated at 60% RH), or silica gel alone. Seeds of A. githago that were aged in the absence of oxygen maintained higher viability and produced fewer volatiles than seeds aged in air. In addition, seeds of A. githago and L. perenne aged in the presence of silica gel were longer lived than those aged without silica, with no effect on seed moisture content or oxygen concentration in the storage containers, but with silica gel acting as a volatile trap. These results indicate that the use of inexpensive oxygen absorbers and silica gel could improve seed longevity in storage for some species and suggests a potential, and previously unidentified, role for silica gel in ultra-dry storage.

P-Terphenyls From Aspergillus sp. GZWMJZ-055: Identification, Derivation, Antioxidant and α-Glycosidase Inhibitory Activities.

One new (1) and fifteen known (2–16) p-terphenyls were isolated from a solid culture of the endophytic fungus Aspergillus sp. GZWMJZ-055 by adding the leaves of its host Eucommia ulmoides. Furthermore, nine p-terphenyls (17–25) were synthesized from the main compounds (5–7), among which derivatives 18, 19, 21, 22, and 25 are new p-terphenyls. Compounds 15 and 16 were also, respectively, synthesized from compounds 6 and 7 by oxidative cyclization of air in the presence of silica gel. These p-terphenyls especially those with 4,2′,4″-trihydroxy (4–7, 20, 21) or 4, 4″-dihydroxy-1,2,1′,2′-furan (15, 16) substituted nucleus, exhibited significant antioxidant and α-glucosidase inhibitory activities and lower cytotoxicity to caco-2 cells. The results indicated their potential use as lead compounds or dietary supplements for treating or preventing the diabetes.

Characterization of the Effect of ɤ-Radiation Absorbed Dose on the Electrical Conductivity of Aqueous Urea Solutions in the Presence of Silica Gel :A Preliminary Dosimetric Study

ɤ-radiolysis of 6M- aqueous urea solutions, in the presence of silica gel (SG), significantly, increases the values of electrical conductivity (RIC) of the solutions, relative to that in the absence of SG. Some dosimetric characteristics were studied, such as the effects of absorbed dose, absorbed dose rate, and post-irradiation storage time on the RIC of the irradiated 6M- aqueous urea solutions in the presence of SG (>0.16mm - 0.2mm). A linear relationship between the RIC of the solutions and the absorbed dose (R2 = 0.998) was observed from 0.240 to 17.670 kGy. The uncertainty in the dose-response function was found to be in the range 0.040-0.320 at 95% confidence level. As dose rate increases the RIC-decreases in the range of 0.298 -1.19 kGy/h. The stability of the response (RIC) of the irradiated solutions is acceptable during post irradiation storage (14 days at 0 oC), where, the response (RIC) decreased at the end of the storage period, 0.49-2.8%%. The effective atomic number of this solution (7.08) was found to be compatible with biological tissues. The results show that the studied system can be considered as a promise dosimeter for low dose applications in the range 0.240 to 17.670 kGy, such as medical and food irradiation.

Particle size effect of silica gel on the ɤ-radiation induced electrical conductivity of urea aqueous solutions

Different concentrations (0.1, 3, 6 M) of urea aqueous Solutions (UAS) have been irradiated with 60Co- ɤ-rays in the presence of silica gel (SG) with different particle size (0.1-0.5mm) at room temperature. The radiation induced electrical conductivity (RIC) of the irradiated solutions was measured. The RIC values of the 0.1 M solutions increase as the particle size of SG decreases i.e., the particle surface area increases. This observation points to a radiation induced chemical reactions, which are catalyzed by SG. These reactions, probably, yield products, which increase the RIC such as urea peroxide (UP). On the other hand, different behavior was observed in the case of 3, 6 M solutions, where, the RIC increases as particle size increase. So, the mechanism of production of the species which increase the RIC of 0.1 M samples is different than that in the case of 3, 6 M. In all irradiated samples the pH values tend to increase slightly as particle size increases. A mechanism was proposed to explain the obtained data.

New Insight into Phase Transitions of Porous Glass-Based Ferroelectric Nanocomposites.

The results of XRD, FTIR and differential scanning calorimetry (DSC) studies of empty porous silica matrices filled with binary mixtures of K1–xAgxNO3 (x = 0.05, 0.10) are reported in comparison with those obtained for bulk salts in the temperature range of structural phase transitions. Scanning electron microscopic data of the studied empty macroporous and microporous glasses confirmed differences in the pore morphology associated with the presence of silica gel. Accordingly, XRD and FTIR samples contain crystalline phase of KNO3 and AgNO3. The results of calorimetric investigation of porous glasses filled with binary mixtures of K1–xAgxNO3 (x = 0.05, 0.10) are presented. The results show that in the K1–xAgxNO3 nanocomposites, anomalies associated with phase transitions were detected. An influence of the mean value of pores sizes on the ferroelectric phase transition temperatures of K1–xAgxNO3 nanocrystals embedded into the porous matrices was determined. The impact of pore space structure on the phase transitions of ferroics nanocomposites was discussed.

Enhancement of gas and aromatics by in-situ catalytic pyrolysis of biomass in the presence of silica gel

The aim of this study was to investigate the role of SiO2 in the in-situ pyrolysis of wheat straw. The maximum yields of CO, CH4 were 62.43 mL g−1, 9.19 mL g−1, and monocyclic aromatics, such as BTX (benzene, toluene, and xylene), PC (phenol, cresol), and naphthalene were, 8.67%, 12.14%, and 2.36%, respectively. High yields of gaseous products and light aromatics were obtained, which indicated that SiO2 exhibited catalytic activity in the pyrolysis of biomass. Char characterization by XRD, TEM-EDS, SEM, FT-IR, ICP, and BET revealed that SiO2 acted as a dispersant due to the porous structure of SiO2 increased the average pore diameter and total pore volume to promote the dispersion of metallic particles such as K, Fe, and Ca on the biomass ash. This resulted in improving quantity and quality of light aromatics of bio-tar and enhanced CH4 yield.

A possible ɤ- radiation Dosimeter based on the radiation induced changes in Electrical conductivity of water in the presence of silica gel

ɤ-Irradiation induces electrical conductivity (RIC) in water. But, the RIC values of water can be more than twofold higher in the presence of silica gel (SG) with particle size in the range >0.16–0...

Silica gel-modified electrode as an electrochemical sensor for the detection of acetaminophen

In the present work, an inexpensive and highly reproducible carbon-based sensor in the presence of silica gel was introduced to determine acetaminophen, a pain killer drug. From the experimental results, an appreciable increment on the oxidation current was seen at the surface of the modified sensor due to the cavity structure of the sensor and also effective adsorption of acetaminophen. Hence, the silica gel electrode was used as an electrochemical sensor for the cyclic voltammetric and differential pulse voltammetric detection of acetaminophen. The surface morphology of the electrode was investigated with the help of atomic force microscopy. The effects of various experimental parameters were explored. The differential pulse voltammograms exhibited acceptable analytical performances in terms of linearity and limit of detection. The proposed technique was sensitive, specific, and could be admissible for the resolution of acetaminophen in pharmaceutical originations and spiked human urine.

Laboratory investigation of aerosol coating and capillarity effects on particle ice nucleation in deposition and condensation modes

In this work, the ice nucleating effectiveness of Arizona Test Dust (ATD), bare and coated with NaCl, not examined in previous published papers, was investigated. The ATD, NaCl coated ATD, and NaCl aerosols were generated by nebulizing water suspensions of bare ATD, ATD-NaCl and NaCl solution. Dried aerosols were sampled on black-gridded cellulose nitrate membrane filters for ice nuclei assessment through a Dynamic Filter Processing Chamber device (DFPC). After water evaporation ATD-NaCl droplets gave rise to ATD particles coated with NaCl.Processing of filters was performed at −22 °C and − 18 °C, under sub- and super-saturated conditions (water saturation ratio Sw < 1 and Sw > 1, respectively). Additional experiments were performed by modifying the storage conditions of the filters to simulate variation of atmospheric conditions, i.e. air temperature and relative humidity. For this purpose, the filters were housed in Petri dishes, with silica gel, at +10 °C and −10 °C. As silica gel can desorb water from the aerosol capillary at low temperatures, storage conditions with and without silica gel can simulate the aerosol pre-activation atmospheric process. The highest activated fraction (AF) and ice-active surface site density (ns) values were obtained for ATD at −22 °C and Sw = 1.02. Results showed a decrease in the AF and ns between bare and ATD coated with NaCl both at Sw = 1.02 and Sw = 0.96 and for filters stored in the presence of silica gel. The results obtained show the great influence exerted by NaCl coated insoluble aerosol on the ice nucleation.

Flocculation of flotation tailings in presence of silicate gel and polymer

Flotation tailings were successfully flocculated in the presence of cationic polyacrylamide and silica gel. The effects of various parameters such as polymer weight, charge density, and pH on the rate of flocculation were also investigated in the current study. The flocculation mechanism of the flocculant on tailings was investigated using zeta potential and Fourier transform infrared (FTIR) measurements. The results obtained reveal that 1) sodium silicate gel, used as a binder for the consolidation of tailings form primary flocs, acts as an anchor and the adsorption of polymer flocculant on these anchors results in the formation of larger flocs and, consequently, enhanced settling rate; 2) flocculation in the presence of silica gel and polymer has a faster settling rate than single-polymer flocculation owing to the mechanisms of charge neutralization and bridging as identified using zeta potential and FTIR measurements. A pilot level study was conducted to investigate the influence of processed water on the flotation of scheelite. The results show that the proposed tailing disposal method could improve scheelite recovery by 2% (approximately) and could reduce the daily operation costs of the plant by approximately 108.57 USD.

Synthesis of dioxolanes and oxazolidines by silica gel catalysis

Ethylene glycol condensed with carbonyl compounds in the presence of silica gel or alumina, without solvent and under pressure, affords 1,3-dioxolanes. 2-Amino-2-methylpropanol also condensed with carbonyl compounds in the presence of silica gel or an acid-activated clay, without solvent and under pressure, produces oxazolidines. To explain these results, we propose that the glycol and the aminopropanol react with Bronsted (H+) and Lewis acid sites (Si and Al) located on the surface of the catalysts, leading to the products via various ionic intermediates.

Assessing the role of silica gel in the degradation of p -nitrophenol via Zn(0)-activated persulfate

Abstract In this study, silica gel (SG) was utilized as an assistant to improve the degradation efficiency of p-nitrophenol (PNP) via persulfate (PS) activated with zero-valent zinc (Zn(0)). The effects of various parameters such as the dosages of SG, PS, Zn(0), and the initial pH on PNP degradation via Zn(0)/SG/PS were investigated through batch experiments. The results demonstrated that SG exhibited a strong synergistic role in the decomposition of PNP via Zn(0)-activated PS due to the dispersion and buffering character of SG. The degradation efficiency of PNP was strongly related to the dosage of SG, PS, or Zn(0). A low pH favored of the degradation of PNP. Nevertheless, PNP could be efficiently removed in a pH range of 3 to 9. The radicals of SO4•− and •OH were verified to be responsible for the oxidative degradation of PNP. Nevertheless, the contribution of SO4•− to the degradation of PNP was much larger than that of •OH. Based on the analyses of HPLC-MS data, it could be determined that C6H7NO, C6H6O2, and C12H7N3O8 were the main intermediates generated from the degradation of PNP via Zn(0)/SG/PS. Furthermore, the possible mechanism and the degradation pathways of PNP via Zn(0)/SG/PS were proposed. PS activated with Zn(0) in the presence of SG could be concluded as a promising approach for the degradation of PNP in aqueous solution.

S-O acetyl rearrangement in 6-thio-D-glucose derivatives

The solvolytic reaction of 1,2-O-isopropylidene-3,6-di-O-(p-toluenesulphonyl)- ?-D-glucofuranose (2), as well as that of 6-chloro-6-deoxy-1,2-O-isopropylidene-3-O-(p-toluenesulphonyl)-?-D-glucofuranose (3), in the presence of potassium thioacetate unexpectedly gave the 6-S-acetyl-5-O-acetyl derivative 5 as the main reaction product. A possible mechanism of these transformations was postulated whereby the main role was ascribed to a neighbouring group participation process, involving hydrogen thio-orthoester formation as an intermediate. The regiospecific monosubstitution of the 6-tosyloxy group in compound 2 was successfully achieved with potassium thioacetate, in presence of 2,3-benzo-15-crown-5 as a catalyst. The corresponding 6-S-acetyl derivative 7 was obtained representing a possible intermediate in the mentioned solvolytic reactions. Compound 7 was shown to be very reactive, since it fully transformed into the corresponding mercaptan 8 in the presence of silica gel. This transformation occurred via the same thio-orthoester 7a as in the mentioned solvolytic reactions of furanoses 2 and 3. The synthesized compounds are key intermediates in the planned synthesis of selected natural products and their analogues.

An Improved Rapid and Mild Deoxygenation of Amine N‐oxides

An improved mild and selective method for the deoxygenation of a variety of amine N‐oxides has been carried out in the presence of silica gel under mild conditions at room temperature to afford corresponding amines in relatively good yields without purification. The reaction is tolerant of a variety of functional groups such as hydroxyl, ester, acid, carbonyl, and cyano groups, as well as halogens. This method would be of great utility to synthesize various pyridines and amines easily.

Conducting macroporous carbon foams derived from microwave-generated caramel/silica gel intermediates

The current work reports the preparation of macroporous carbon/silica foams using sucrose as precursor in the presence of silica gel and water. After a preliminary fast transformation of sucrose into caramel by MW irradiation, the carbon/silica materials are obtained by thermal treatment at 800 °C under nitrogen atmosphere. In contrast to carbon/clay materials prepared by the same synthetic route, the use of microporous silica gel as inorganic support for the chemical transformation of sucrose gives rise to foam-like materials without requiring the addition of blowing agents. The resulting materials are low-density monoliths (0.17 g cm−3) that show several populations of macropores centered at 150 and in the range of 30–5 µm, as well as mesopores around 5–6 nm. The porosity is close to 97%, as determined from helium pycnometry, which gave a skeletal density value of 6.08 g cm−3. The resulting foams show electrical conductivity values around 3 mS cm−1 due to the generated graphene-like materials, as corroborated by Raman spectroscopy. A preliminary evaluation of these macroporous materials as adsorbents of aromatic pollutants was carried out using methylene blue (MB) as a model dye. The regeneration of the MB-loaded foams to make possible their application in successive adsorption cycles was assessed by solid–liquid extraction and electrochemical regeneration. In both cases, the treatment produced an increase in the uptake capacity, which could be due to an increment in porosity and specific surface area, from 360 to 440 m2 g−1, as determined from mercury porosimetry and N2 adsorption measurements. In addition, the electrochemical method allowed a partial degradation of the pollutant, as determined by UV–Vis and HPLC–MS. Thus, the carbon/silica materials here developed are promising adsorbents for treatment of polluted effluents.

Silica gel-promoted new one-pot procedure for the synthesis of 1,3-oxathiolan-5-one

ABSTRACTA highly selective two-component silica gel-promoted synthesis of 1,3-oxathiolan-5-one derivatives in N,N-Dimethylformamide (DMF) is presented. The reaction was carried out using aromatic aldehyde and mercaptoacetic acid in the presence of silica gel in DMF with heating. The reactions were worked up by separating the silica gel and recovering the solid product after adding water in excellent yields without any chromatographic purification. Structures of the compounds were satisfactorily confirmed by 1H NMR and LCMS spectral analysis.

A useful ring transformation route to novel thiazepino[7,6-b]indoles from monochloro-β-lactam-fused 1,3-thiazino[6,5-b]indoles, analogues of cyclobrassinin

The Staudinger ketene-imine cycloaddition reactions of cyclobrassinin phytoalexin analogues 2-aryl-4,9-dihydro-1,3-thiazino[6,5-b]indoles with chloroacetyl chloride as a ketene source were investigated under different conditions. Both β-lactam ring formation and the N-chloroacetylation of the indole moiety took place. The indole N-chloroacetyl group can be easily removed by treatment in the presence of silica gel in methanol at reflux temperature. The selective β-lactam formation can be also achieved in certain cases under milder Staudinger conditions. The treatment of azeto[2,1-b]thiazino[6,5-b]indole-1-one derivatives with sodium ethoxide in ethanol provided the novel thiazepino[7,6-b]indole ring systems in a one-step ring transformation. The structures of the new ring systems were determined by means of IR and NMR spectroscopy.