Carbon Silica Gel Research Articles

Nanotube-doped alginate gel as a novel carrier for BSA immobilization

In this paper different dopants, including carbon nanotubes (CNTs), silica nanotubes (SiNTs), graphite and silica gel, were incorporated into alginate (ALG) gel to form nanotube/alginate or nanoparticle/alginate composites used for bovine serum albumin (BSA) immobilization carrier. During encapsulation, first BSA was adsorbed on the dopants, and then BSA and dopants were suspended in alginate solution, followed by being added dropwise into the CaCl2 solution to form the biocomposites. The BSA leakage decreased significantly in these biocomposites as the following order: BSA-ALG-SiNT > BSA-ALG-CNT > BSA-ALG-SiO2 > BSA-ALG-graphite, which was mainly due to firstly the protein molecule adsorption on the dopants which could not be washed out easily and secondly, during the biocomposites formation, water loss in BSA-ALG-dopant biocomposites became less than that in BSA-ALG biocomposite. In addition, the mechanical properties of these biocomposites were remarkably reinforced in the same order as BSA leakage decrease.

탄소에어로젤 복합전극의 전기용량적 탈이온 공정 특성

전기화학적으로 이온을 흡착시켜 이온을 제거하는 capacitive deionization(CDI)공정용 전극으로 탄소에어로젤에 실리카젤이 첨가된 다공성 탄소에어로젤 복합전극을 사용하여 1,000ppm NaCl수용액에서 탈염 특성에 대한 충전과 방전시 시간에 따른 전류 변화, CDI효율을 조사하였다. Paste rolling법으로 제조된 <TEX>$10\times10cm^2$</TEX>다공성 탄소에어로젤 복합전극은 촉매 분야에서 활용되고 있는 다공성 지지체인 실리카젤을 첨가함으로써 CDI 반응진행에 대한 전극활물질 탈락이 없이 전극의 성형성이 크게 향상되었고, 친수성과 전극의 기계적 강도 증가 및 CDI 효율을 증가시킬 수 있었다. 이러한 45개의 전극을 하나의 묶음으로 네 개의 단을 직렬연결 하여, CDI 시스템을 구성하였고 충전 시에는 1.2V, 방전 시에는 0.001V를 각각 10분간 인가하여 실험한 결과 <TEX>$99\%$</TEX> 이상의 CDI 효율을 달성하였다. Porous-composite electrodes have been developed using silica gel, which reduce carbon aerogel usage with high cost. Silica gel powder was added to the carbon aerogel to simplify the manufacturing procedure and to increase the wet-ability, the mechanical strength and the CDI efficiency. Porous composite electrodes composed of carbon aerogel and silica gel powder were prepared by paste rolling method. Carbon aerosol composite electrodes with <TEX>$10\times10cm^2$</TEX> are placed face to face between spacers, and assembled the four-stage series cells for CDI process. Each stage is composed of 45 cells. Four-stage series cells (flow through cells) for CDI process are put in continuous-system reactor containing 1,000ml-NaCl solution bath of 1,000 ppm. The four-stage series cells with carbon aerogel electrodes are charged at 1.2V and are discharged at 0.001V, and then read the current. Conclusively, removal efficiencies of ions using the four-stage series cells composed of carbon aerogel composite electrodes show good removal efficiency of <TEX>$99\%$</TEX> respectively.

A method to circumvent the lot number of activated carbon affecting the performance of activated carbon silica gel columns used for cleanup of blood samples for analysis of 29 hazardous organochlorine compounds

We have previously described the use of a tandem simplified multilayer silica gel-activated carbon dispersed silica gel (TS-ML-AC) column for the cleanup of blood samples for the analysis of 29 hazardous organochlorine compounds (OCs)--the 17 major polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDDs/DFs) and 4 non-ortho- and 8 mono-ortho-polychlorinated biphenyls (PCBs). We noted that the performance of the activated carbon-silica gel (ACS) column (lower column) varied with the lot number of the ACS. In this study, we compared the elution profiles of OCs eluted on 5 ACS columns, each with a different ACS lot number, and found that only mono-ortho-PCBs #114 and #123 were affected by lot number. The problem was that the 50 ml of n-hexane required to elute all the OCs from the simplified multilayer silica gel (MLS) column (upper column) into the AC column (lower column) also eluted varying amounts of PCBs #114 and #123 from the ACS column by ACS lot number. Although we could prevent PCBs #114 and #123 from being eluted from the ACS column by reducing the n-hexane volume to 10 ml, this volume was not sufficient to elute all the OCs from the MLS column. We solved this by separating the two columns; the sample solution was eluted with 50 ml of n-hexane from the MLS column, this eluate was concentrated to about 0.3 ml using a rotary evaporator, and then the concentrated solution was cleaned up on the ACS column. The recovery rates of #114 and #123 from blood samples were above 70% and the relative standard deviations of their concentration were below 10%, irrespective of the lot number, compared with recovery rates of 45-79% for #114 and 59-89% for #123, and relative standard deviations of their concentration above 15% when 50 ml of n-hexane was run through the tandem column. Our modified method affords reliable and reproducible cleanup of blood samples for analysis of 29 OCs, irrespective of the ACS lot number.

Optimization of the purification method for dioxin analysis in human serum and temporal changes in background dioxin levels in the general population

To perform high quality and high throughput measurements, complicated purification procedure by two rounds of open column chromatography was simplified by appraising the components and adding a sufficient amount of adsorbents to the column. The procedure consists of two open column techniques using a multi-layer silica gel column and an active carbon dispersed silica gel column. This purification procedure is used in “Standard manual for dioxin analysis in human blood” published in 2000 (Ministry of Health and Welfare, Japan, 2000). Consequently, a purification procedure using only 1 g of 10% AgNO 3/silica gel can remove the matrix of blood serum as effectively as a multi-layer silica gel column. In addition, 0.1 g of carbon silica gel, equivalent to 1/10 the weight used currently in analyses, separates and recovers the dioxins in purified extract of blood serum. Furthermore, changes in the background level in the general population were clarified by monitoring the dioxin concentrations in human blood. The dioxin concentrations and ratios in blood in the general population remained at a tolerable level for three months. Therefore, the blood serum was available for the detection of a remarkable elevation in dioxins level considered to be indicative of contamination due to high-density exposure.

Electrochemical and catalytic investigation of carbon paste modified with Toluidine Blue O covalently immobilised on silica gel

Toluidine Blue O (TBO) was covalently bound on silica gel and mixed with graphite powder and paraffin oil to produce modified carbon paste electrodes. The formal potential ( E°′) of the covalently bound TBO was found to be −100 mV versus Ag|AgCl (KCl sat.) at pH 7.0 and the E°′ varied less than anticipated for a 2-electron–proton type mediator with pH. The bound TBO was found to act as an efficient electron acceptor for NADH as well as electron donor for oxidised horseradish peroxidase (HRP). The kinetics and the mechanism of the reaction between NADH and TBO were investigated with cyclic voltammetry and using a rotating disc electrode. Further experiments were done in the flow injection mode injecting different concentrations of NADH. Similar studies were done in the presence of hydrogen peroxide when HRP was adsorbed onto the TBO modified silica gel carbon paste electrodes.

Surface Properties of Mesoporous Carbon–Silica Gel Adsorbents

Carbon/silica (carbosil) samples prepared utilizing mesoporous silica gel (Si-60) modified by methylene chloride pyrolysis were studied by nitrogen adsorption, quasi-isothermal thermogravimetry, p-nitrophenol adsorption from aqueous solution, and 1H NMR methods. The structural characteristics and other properties of carbosils depend markedly on the synthetic conditions and the amount of carbon deposited. The changes in the pore size distribution with increasing carbon concentration suggest grafting of carbon mainly in pores, leading to diminution of the mesopore radii. However, heating pure silica gel at the pyrolysis temperature of 550°C leads to an increase in the pore radii. The quasi-isothermal thermogravimetry and 1H NMR spectroscopy methods used to investigate the water layers on carbosils showed a significant capability of carbosils to adsorb water despite a relatively large content of the hydrophobic carbon deposit, which represents a nonuniform layer incompletely covering the oxide surface.

Preparation of a silica gel–carbon black composite by the sol–gel process in the presence of polymer-grafted carbon black

This paper is concerned with the preparation of a silica gel–carbon black composite by the sol–gel process, which consists of tetraethoxysilane and polymer-grafted carbon black. Polymer-grafted carbon black was synthesized by three methods: (1) cationic polymerization of N-vinyl-2-pyrrolidone, (2) cationic ring-opening polymerization of 2-methyl-2-oxazoline, and (3) radical polymerization of glycidyl methacrylate followed by reaction of glycidyl groups in the grafted polymer chains with 3-aminopropyltriethoxysilane. The polycondensation of tetraethoxysilane proceeded under acidic conditions in the presence of polymer-grafted carbon black to give a deep black silica gel–carbon black composite. The more the content of untreated carbon black was increased, the more the gelation time was shortened. On the contrary, gelation was retarded by grafted polymer chains on the carbon black surface in the case of polymer-grafted carbon black. The scratch hardness of the resulting silica gel–carbon black composite was almost equal regardless of the carbon black content in the presence of untreated carbon black, whereas it was liable to decrease as the content of polymer-grafted carbon black increased. The solvent adsorption properties of the silica gel–polymer-grafted carbon black composite varied with the solubility of grafted polymer chains on the carbon black surface towards the immersion solvent. © 1998 Chapman & Hall

Study and application of a method for the determination of metallic elements by ICP-AES with preconcentration on an active carbon-silica gel microcolumn in a FI system

Using active carbon-silica gel as adsorbent and sodium diethyldithiocarbamate (NaDDTC) as chelating reagent in a flow injection system, an ICP-AES method has been developed for preconcentration and determination of trace metallic elements in high purity rare earth oxides. The experimental parameters such as pH, flow rate, amount of adsorbent, length of reaction coil and eluent acidity were optimized. At pH 4.6 Al,Cr,Cu,Fe,Pb,V,Zn could be preconcentrated, and subsequently determined by ICP-AES. This method can eliminate matrix effects. Its enrichment factors were 8.1–12.6 with detection limits in the ng/mL range and RSD of 2.3–5.0. This method was applied to the analysis of high purity of La2O3 and Eu2O3 with satisfactory results.

Carbon-silica xerogel and aerogel composites

High surface area carbon-silica xerogels and aerogels were prepared by adding various amounts of activated carbon particles during gelation of tetramethyoxysilane (TMOS). Surface areas and pore structure of the gels were determined by nitrogen and water adsorption and desorption measurements. Carbon increased the surface area of silica gel and the carbon-silica gel composites were found to be hydrophobic. The pore structure of xerogel composites was dominated by carbon whereas that of aerogel composites was apparently controlled by silica component.

Analytical methods for a national study of chemical residues in fish: I: Polychlorinated dibenzo-p-dioxins/dibenzofurans

Analytical Methods were developed to determine the concentration of PCDD/PCDF in fish tissue for a national survey conducted by EPA. The method was designed to achieve a relatively low cost per sample while maintaining adequate quality control. It utilizes a Soxhlet extraction, acid-celite, florisil and carbon-silica gel chromatography, and HRGC/HRMS analysis. The minimum level of detection for 2,3,7,8-TCDD is approximately 1 pg/g. Rigorous quality assurance/quality control criteria have been developed to assure the validity of the data.

On-line microcolumn preconcentration with desolvation and determination of trace elements by flow-injection inductively coupled plasma atomic emission spectrometry

A desolavation device was connected to a microcolumn (40 mm × 3.0 mm i.d.) in which 8-hydroxyquinoline-5-sulphonic acid was immobilized on the substrate of active carbon—silica gel. The analyte and 1.0 M sodium acetate—acetic acid buffer solution (pH 5.6) were mixed and pumped through the microcolumn. The analyte was then preconcentrated and eluted from the column with 2.0 M hydrochloric acid. The efficiency of desolvation, improvement in sensitivity and signal stability over the temperature range 70–120°C were studied in detail. It was found that aluminium, copper, cadmium, iron and manganese could be separated from various co-existing elements with a sample volume of 1.2. ml and a carrier flow-rate of 1.2 ml min −. The desolvation efficiency at a desolvation temperature of 120°C 73%. The column could be used more than 100 times. The detection limits for the above metal ions were 0.34–5.1 ng ml −1 and the relative standard deviations ( n=6) were 2.6–4.3%. The reliability of the method was confirmed for the analysis of human serum, and the results were in good agreement with those given by graphite furnace atomic absorption spectrometry.

Examination of Conditions for the Determination of Carbamate Pesticides in Soils

The procedure for the determination of carbamate pesticides in soil was optimized. The following factors affecting the final results were investigated: extracting solvent, extraction procedure, extract purification procedure, and soil type. Triple extraction with acetone and purification of the extract on a two-stage purification column containing an activated carbon-silica gel 1+1 mixture were found optimal. The extracts after treatment were analyzed by RP-HPLC with UV detection. The method developed allows carbamate pesticides in soil to be determined at concentrations in excess of 30 μg kg-1.

Effect of zirconium on preparation and sorption properties of complex carbon-mineral adsorbents

The use of complex carbon-mineral adsorbents is expected to grow and investigations will develop on their applications, not only in adsorption or in chromatography. Their complex structure determines their unique surface properties and the possibility of using them in wide area applications. In this paper, preparation, structure and sorption properties of complex adsorbents, i.e. zirconia-silica gel (ZrO 2/SiO 2), carbon-silica gel (C/SiO 2), carbon-zirconia (C/ZrO 2) and carbon-zirconia-silica gel (CZrO 2/SiO 2) have been presented. Complex carbon-mineral adsorbents were obtained by carburization of the starting adsorbents with methylene chloride, n-octanol, methylnaphthalene or α-methyl benzyl alcohol in an autoclave. The obtained adsorbents have been characterized by low-temperature nitrogen adsorption, diffractogram measurements, differential thermal analysis and imaging of the adsorbent surfaces with a scanning electron microscope. Values of the adsorption head and the adsorption isotherm of n-hexane, benzene and chloroform as well as the energy distribution function of chloroform were calculated. From these data, results show that the most interesting materials are adsorbents of the type ZrO 2/SiO 2 and C/ZrO 2/SiO 2. Zirconium ions present on a silica surface cause an increase in the degree of conversion of organic substances to carbon, a more uniform distribution on the surface and a growth of thermal endurance.

Calorimetric and Isosteric Heats of Adsorption of Substances with Molecules of Different Electronic Structure

Calorimetric heats of adsorption have been measured for iso- and cyclo-pentane on NaX(86) zeolite at 140°C and for acetonitrile on carbon black and silica gel at 150°C. These heats have been compared with the corresponding isosteric values, calculated from isotherms measured over temperature ranges whose average values correspond to the above temperatures. The isosteric heats of adsorption coincide well with the calorimetric values in those cases where no change occurs in the mechanism for adsorbate–adsorbent interaction within the temperature range over which the isotherms have been measured. If this condition is not observed, the difference between the two sets of values can be quite considerable.

Carbon-13 Nuclear Magnetic Relaxation Studies of Benzene Molecules Adsorbed on the Pillar Interlayered Montmorillonite

Abstract Carbon-13 nuclear magnetic relaxation times of 13C-enriched benzene have been determined in order to elucidate the adsorption properties of PILM (pillar interlayered montmorillonite) by varying temperatures and coverages. The activation energy of diffusion as small as 6.5 kJ mol−1 indicates that the majority of PILM adsorption sites exhibits a weak interaction with benzene. The pre-exponential factor of correlation time was exceptionally large, probably because the two-dimensional pore structure of PILM, in contrast to the three-dimentional zeolite or the open surfaces of graphitized carbon black and silica gel, restricts the chance for the adsorbate to diffuse. In the spin-lattice relaxation spectra at low temperatures, the internal and the external surfaces of PILM were discriminated, since the two adsorbed states on these surfaces give different T1 and chemical shift values.

Rheological properties of high-temperature lubricating greases

Reports results from an investigation of the rheological properties of high-temperature greases of the carbon black, silica gel, and phthalocyanine types, in which conventional test procedures were applied to model systems. Uses the petroleum oil MS-20 and the polymethylchlorophenylsiloxane fluid KhS-2-1VV as dispersion media. Investigates the variation of rheological properties of the plastic systems in the stage preceding steady-state flow. Finds that greases distinguished by a high degree of heat-hardening (phthalocyanine greases) cannot be used to lubricate components in which a limited starting torque is available, nor in sliding-contact bearings, owing to the difficulty of access of the grease to the working zone of the component. Recommends phthalocyanine greases, which are mechanically stable but harden when heated, for high-speed bearings operating at high loads and large shearing forces. Suggests that carbon black greases should be used in low-speed rolling-contact and sliding-contact bearings. Points out that of the nonsoap greases investigated, the greases based on the organic-modified silica gel AM-2 are outstanding.

High-Precision Gas Chromatography

A high-precision chromatograph has been used for determination of differential thermodynamic quantities of two gas-liquid systems. Individual α values and consequently Δ(ΔH°) were determined with a precision of ±0.02%. The precision in the measurement of Δ(ΔG°) was ±0.2%. These values represent an order of magnitude improvement over the best previously reported data. Heats of adsorption of hydrocarbons on carbon black and silica gel were also determined with a precision of ±0.6%.

Adsorption of Phenothiazines from Aqueous Solution. Approach to Understanding of Membrane Action

As an approach to an understanding of the membrane action of phenothiazines, the adsorption from solution was investigated using such adsorbents as carbon black (CB), graphite (GP), silica gel (SG) and polyethylene (PE), and relating the results with other physico-chemical and biological activities of the drugs. The adsorption isotherms by CB and GP were in accordance with Langmuir equation. In the case of SG, the phenomenon looked like a multilayer adsorption. Phenothiazines were considered to be classified into three groups according to the adsorbability by PE. The adsorbed amount was influenced by the molecular volume of R10'N at 9-position, sulfoxide group at 5-position, and the bulkiness of substituent at 2-position. The adsorbed amount increased with pH of buffer solution between 5 and 8, and it was considered that pH had influence on the hydrophobic and hydrophilic balance of the molecule. The decrease in adsorption with addition of urea demonstrated that the adsorption of phenothiazines proceeded on the hydrophobic interaction. The adsorbability of phenothiazines by CB increased with the surface tension lowering of solution and also with the partition coefficient in CHCl3-0.2N HCl. It was shown that the adsorbability have relation to the neuroleptic and the haemolytic activities.

The gas chromatographic separation of pairs of isotopic molecules by means of porous polymer beads

The separation of various isotopic molecules with deuterium substitutions is reported. Columns with porous polymer beads (Porapak Q) are employed. A comparison is made between this packing material and other adsorbents, as graphitized carbon black or silica gel. High separation factors are obtained. The working temperatures are usually higher with respect to the other materials, but the isotopic effects measured with the Porapak are more favourable for many of these separations.

Heats of preferential sorption from liquid mixtures

The construction and applications of an inexpensive calorimeter suitable for the determination of heats of preferential sorption from liquid mixtures on solid surfaces is described. The calorimeter is very sensitive and is capable of detecting the heat effects as low as 0.001 cal/g. The application of the calorimeter is illustrated by determinations of the heats of sorption for a number of liquids dissolved in n-heptane and benzene on solid adsorbents such as carbon black, silica gel, alumina, lithium stearate and Zeocarb solid-liquid chromatography.