Silica Gel Beads Research Articles

Continuous-flow photoreactor packed with titanium dioxide immobilized on large silica gel beads to decompose oxalic acid in excess water

A tubular continuous-flow photoreactor consisting of a pyrex glass tube 8 mm in diameter packed with titanium dioxide photocatalyst immobilized on 2 mm diameter silica gel beads was constructed to efficiently decompose water contaminants at high-flow rate. To fix titanium dioxide using sol–gel without destroying silica gel beads, the beads were exposed to ethanol vapor and then wetted with ethanol before being dipped into the TiO 2 precursor sol. Photoreactor performance was evaluated for how it decomposed aqueous oxalic acid solution as a model contaminant.

Glutathione oxidase-like activity of glass beads, silica gel and anion-exchange resin modified with cobalt(III)–tetrakis(4-carboxyphenyl)porphine

Silica gel and glass beads were modified by using acid chloride of metal–tetrakis(4-carboxyphenyl)porphine (M–TCPP) through a peptide bond, and an anion-exchange resin with M–TCPP by ion-exchange reaction and physical adsorption. The carriers modified with Co3+–TCPP proved to accelerate the redox reaction which is catalyzed by glutathione oxidase (GSHOx), while those modified with Mn3+–TCPP exhibited no activity. Formation of GS-SG and hydrogen peroxide was confirmed by means of mass spectroscopy and colored reaction, respectively. The silica gel modified with Co3+–TCPP exhibited the strongest activity among the tested carriers, and was expected to be useful practically as a solid catalyst for the determination of glutathione.

Determination of manganese in natural water and effluent streams using a solid-phase lead(IV) dioxide reactor in a flow-injection system

The determination of manganese(II) in natural water and effluent streams, using a solid-phase reactor incorporated into a flow-injection system, was investigated. Mn 2+-ions in samples injected into a carrier stream, were oxidised by solid lead(IV) dioxide suspended on silica gel beads to form MnO 4 −-ions which were detected spectrophotometrically at 526 nm. The linear range of the system is between 1 to 5 mg l −1 with a detection limit of 0.56 mg l −1. The proposed system is suitable for the determination of manganese(II) in natural water and effluent streams with a relative standard deviation of better than 1.8%.

Preparation and characterization of swelling porous carbon beads

Porous carbon beads have been prepared by two replica methods, Ester and CVD methods. The Ester method consists of esterification of silica gel beads with alcohol or phenol, pyrolysis of the esterified silica gel, and dissolution of the silica gel with HF solution, yielding porous carbon beads with specific surface area ranging 1100–2000 m 2 g −1. On the other hand the CVD method consists of pyrolysis of benzene vapor on silica gel beads and dissolution of the silica gel with HF solution, yielding porous carbon whose specific surface area is 640 m 2g −1. Porous carbon beads made from 4-phenyl-1,2-dihydroxybenzene by the Ester method showed enormously large expansion on adsorbing benzene (their apparent volumes doubled) and contracted to the original size on desorption. These dimensional changes were reproducible, and expansion and contraction completed in a few tens of seconds. The extent of dimensional changes was influenced by the kinds of adsorbates and decreased in the following order: toluene > xylene, benzene > chloroform > carbon tetrachloride > 1-butanol > 1-propanol, octane > heptane > cyclohexane, ethanol, hexane > pentane > methanol > water. On the contrary the porous carbon made by the CVD method did not show any dimensional change. A mechanism for the dimensional change of the porous carbon beads was proposed based on strain energy of carbon films, capillary force at menisci in the pores, and interfacial energy of carbon films.

Adsorption of Enzymes at Silica-Gel with Amphiphilic Block Copolymers

The amount of adsorbed catalase at silica-gel (Wakogel C-300) having an average pore size of 7 nm in aqueous solution at pH 7.0 significantly increased in the presence of the polymer aggregate prepared from an block copolymer (1) consisting of poly[(N-acetylimino)ethylene] and poly[(N-pentanoylimino)ethylene]. Amounts of adsorbed catalase and horseradish peroxidase (HRP) with an block copolymer (2) containing poly[(N-acetylimino)ethylene] and poly[(N-nonanoylimino)ethylene] at Micro bead silica gel (MB-800) having an average pore size of 80 nm were measured at various pH. In the absence of 2, the affinity of a silica surface for catalase in aqueous solutions decreased almost three orders of magnitude when pH in the solutions was raised over pH 7.0. The amount of adsorbed catalase and HRP with 2 was not dependent on pH. The adsorbed amount of catalase on silica surface with 2 in alkaline condition (pH 8.0) was more than 10 times that in the absence of the block copolymer. The thermal stabilities of adsorbed catalase with and without the block copolymer (2) were studied in aqueous solution, and the immobilization of catalase on silica-gel with 2 increased thermal stability.

Using Silica Gel Beads to Dispense Indicators and Reagents

Silica gel beads which have adsorbed certain chemical reagents such as acid-base indicators, detecting reagents, color-producing metal ions, and organic dyestuffs can be used in classrooms and field studies either as teaching aids or for students' laboratory work. These beads are light and unbreakable and can be easily carried to any place or used simply on the spot without spillage.

Mixed Retention Mechanism in Gas-Liquid Chromatography of Hydrocarbons and Dialkyl Ethers on Tricresyl Phosphate-Coated Silica Gel Column

A mixed retention mechanism was studied in gas-liquid chromatography of some hydrocarbons and dialkyl ethers using packed columns of silica gel beads coated with different amounts of tricresyl phosphate (TCP). Two adsorption equilibria, on solid surface of silica gel and on organic surface of a monolayer of TCP dominantly contribute to solute retention until the silica gel surface is completely covered with a monolayer of TCP. For hydrocarbons, adsorption on solid surface of silica gel is promoted by formation of a weak 1:1 solute-TCP adduct through lateral interaction between adsorbed solute and TCP molecules. An excess of TCP over an amount necessary for formation of the monolayer on the whole of silica gel surface forms a bulk liquid on the deactivated surface of silica gel, so that bulk solution partition concurrently contributes to solute retention, together with adsorption on the TCP monolayer. Distribution constants of these sorption equilibria could be calculated as reasonable values for any solute.

Enhanced microbial cell lysis by the use of lysozyme immobilized on different carriers

Lysozyme was immobilized on chitosan and silica gel by adsorption, on cross-linked polystyrene divinylbenzene matrix (Deacidite KMP) by ionic binding and on non-porous glass beads by covalent attachment to improve the lytic activity towards complex substrates such as Micrococcus luteus. The lysozyme immobilization yields decreased on decreasing the amount of enzyme loaded, whereas the activation yields (defined as percentage ratio of immobilized active enzyme to immobilized enzyme) increased. Chitosan, silica gel, Deacidite KMP and non-porous glass bead preparations showed activation yields of 10%, 13·20%, 26·67% and 12·77%, respectively.

Glucose determination using immobilized polyphosphate glucokinase

Polyphosphate glucokinase (EC 2.7.1.63, polyphosphate:glucose phosphotransferase) was covalently coupled to collagen-coated silica gel beads. The immobilized enzyme, as a packed-bed reactor, was used to determine glucose in serum and other samples. The method was based on a spectrophotometric measurement of NADPH produced by two consecutive reactions, similar to the hexokinase method. The described approach takes advantage of the greater stability of polyphosphate compared to that of ATP, the greater specificity of polyphosphate glucokinase versus that of hexokinase, and the reusability of the immobilized enzyme. Linearity, precision, and accuracy of the method were tested and found to be very good. The results were linear between 10 and 50 nmol of glucose in a 50-μl sample and the coefficient of variation was less than 4% in five successive determinations. The recovery of glucose was about 100% after calibration of the method. The results of the measurements correlated well with those obtained with soluble polyphosphate glucokinase ( r = 0.997, y = 1.036 x − 0.016). The immobilized-enzyme reactor showed good operational stability during a month of use, losing about 12% of its initial activity.

TRANSITION OF FLOW REGIME IN FLUIDIZED BEDS WITH SLANTING BLADE BAFFLES

A flow model is proposed to investigate the transition of flow regime from bubbling to turbulent fluidization postulating that the flow in the emulsion phase follows the Richardson-Zaki equation. Void fraction of the whole bed εf and the mean velocity of bubbles Ub were measured in fluidized beds of 0.3 and 0.5 m ID, in which slanting blade baffles were positioned. Mo-catalyst, silica gel, sand and glass beads with size between 135-443 μm were fluidized by air. Void fraction of the emulsion phase ε e was calculated on the basis of the above model. Correlating ε e with superficial gas velocity Uƒ, we found that ε e was very close to ε mƒ in the bubbling regime and that e, increased with increasing Uƒ in the turbulent regime. Calculated values of the volume fraction of bubble phase δ were correlated with Uƒ, from which apparent transition point from bubbling to turbulent regime was estimated. Combining information obtained, transition of flow regime in the above type of fluidized beds is discussed

Heavy Metal Removal Using Bound Macrocycles

Aza macrocycles bound to silica gel beads were found to selectively remove heavy metal cations such as Pb2+, Cd2+, Ag+, and Hg2+ from aqueous solutions. These bound macrocycles have a virtually infinite selectivity of binding with heavy metals over alkali and alkaline earth cations. The material is very stable and can be reused hundreds of times. Columns may be regenerated using an acidic eluent solution. Equilibrium constants were determined by column tests. Removal of heavy metals was demonstrated in bench scale tests using a synthetic contaminated water and in pilot scale tests using a naturally contaminated river water. Heavy metal concentrations could be effectively reduced to the µg/L level using the process.

Immobilization of enzymes to porous-bead polymers and silica gels activated by graft polymerization of 2,3-epoxypropyl methacrylate.

Three types of organic polymers and bead-shape silica gels were activated by graft polymerization of 2,3-epoxypropyl methacrylate; in some cases, epoxide groups on the support surface were modified to NH2 groups. Eight active matrices so obtained were assessed as supports for immobilized enzymes using peroxidase, glucoamylase and urease. The immobilization yield of protein and specific activities of enzymes were better with supports containing NH2 groups than with those containing epoxide spacer arms. Maximum enzyme immobilization and storage stabilities were obtained with silica-gel beads activated by graft polymerization of 2,3-epoxypropyl methacrylate. With all eight matrices tested, the immobilized enzymes showed good stability with not less than 82% of the original activity persisting after 28 days. The developed matrices have potential for use in process-scale biotechnological operations.

Dynamic quenching of europium(III) and terbium(III) luminescence: a potential detection method in ion chromatography

Indirect detection methods based on UV absorption and fluorescence measurements are well known in single-column ion chromatography’. The detector responds to the chromophoric or fluorophoric eluent ions; a negative signal is observed, as the eluting analyte displaces an equal amount of eluent at the detector. As a consequence, low detection limits are attainable only if the analytical separation is performed at low eluent concentrations. In our laboratory, we have developed an indirect detection method based on dynamic quenching of luminescence*+. Here displacement effects and therefore eluent concentrations play no role. A decrease in signal is observed for analytes able to reduce the luminescence quantum yield of a luminescing compound present in the detector cell. Previously we made use almost exclusively of the phosphorophore biacetyl, present as a solute in the eluent, and successful experiments have been reported2+. Unfortunately, the need to remove oxygen completely from the whole high-performance liquid chromatographic (HPLC) system makes the experimental set-up more complicated than for HPLC with W absorption or fluorescence detection. To reduce or even eliminate this problem we have followed two approaches. First we developed a detection technique based on an immobilized phosphorophore, covalently bound via an alkyl spacer on glass or silica gel bead@. As a second approach, reported here, we utilized rare earth metal ions as luminescent probes. Europium (III) and terbium (III) emit long-lived luminescence in fluid aqueous solutions that is hardly or not influenced by the presence of oxygen. Europium and other lanthanide ions have been applied as luminescence probes in studies on the structures of biological macromolecules7 and polymeric material@ and as NMR shift reagent@. Several non-radioisotopic immunoassays make use of Eu3 + chelates as luminescent markers lo.1 l. Because of their long luminescence lifetimes (1O-5-1O-3 s), the combination with time-resolved luminescence detection techniques results in very sensitive methods12. The use of Eu3 + and Tb3+ as detection luminophores in LC in a sensitized luminescence mode has been described by DiBella et ~1.‘~. The organic compounds are excited by UV radiation, energy transfer from the triplet state of the organic compound to an excited state of the lanthanide ion occurs and luminescence of the lanthanide is detected. Interesting results were ob-

Retention behaviour of disubstituted benzene derivatives on several β-cyclodextrin stationary phases

β-Cyclodextrin has been immobilized on silica gel beads via three kinds of spacers. The retention behaviour of several disubstituted benzene derivatives on these phases and on their modified derivatives was investigated, as well as on stationary phases without β-cyclodextrin. The β-cyclodextrin stationary phase obtained from succinamidopropyl silica (whose unreacted carboxyl groups are not modified) is more efficient than the other β-cyclodextrin phases in the liquid chromatographic separation of the ortho, meta and para isomers. The unreacted carboxyl groups of the spacer arms do not interact significantly with solutes having various functional groups. The effects of ionic strength and column temperature on the retention were also studied briefly.

Graft polymerization of triethoxyvinylsilane–styrene and triethoxyvinylsilane–methyl methacrylate binary monomers onto various silicates

Triethoxyvinylsilane–styrene and triethoxyvinylsilane–methyl methacrylate binary monomers were polymerized by chemical initiation or by γ-ray irradiation in the presence of silica gel, fire brick, quartz wool, and glass beads. The amount and composition of the polymers grafted to silicates were analyzed by using pyrolysis gas chromatography. When triethoxyvinylsilane alone was subjected to the reaction with silicates, condensation occurred irrespective of the initiating means, and the extent of the reaction was almost proportional to the specific surface area of the silicate. When binary monomer mixture was applied, incorporation of styrene or methyl methacrylate into the grafted polymer was observed whenever a monomer mixture of high styrene or methyl methacrylate content was submitted to the reaction. On each silicate, the relationship between the composition of polymer grafted on it and that of monomer showed a similar pattern in spite of the great difference of the specific surface area. Almost no participation of styrene or methyl methacrylate was observed when the silicate preirradiated in air or under vacuum was heated with the binary monomer mixture. It was concluded that triethoxyvinylsilane reacts with silicates by condensation and that some of the pendent vinyl groups on the silicates are incorporated into the copolymer with styrene or methyl methacrylate.

The subgenus Persicargas (Ixodoidea: Argasidae: Argas). 21. The effect of some factors in the process of mating on egg development and oviposition in A. (P.) arboreus Kaiser, Hoogstraal & Kohls.

Injection of male accessory gland and/or testis extracts into the hemocoel of fed, virgin female Argas (Persicargas) arboreus induced ova development and ovulation as in normally mated females. Ovulated eggs degenerated in the ovary lumen, oviduct, and uterus, and no oviposition occurred. Testis extract induced migration of 14–30% of the ovulated eggs to the uterus. Insertion of silica gel beads into the female uterus and copulation with male A. (P.) persicus did not mechanically stimulate ova development. In studies of oogenesis, oviposition, or virus survival in A. (P.) arboreus , the syringe needle should not injure the vagina; such injury stimulates ova development in virgin females and interferes with oviposition in mated females.

The Flow of Gas in a Fluidized Bed at Low Pressure

The mechanism of the flow of gas in a fluidized bed at low pressure could be presumed from the formal analogy to the flow of gas in a capillary, but there had been no work reported on it. In order to make a contribution to the studies on the behavior of the fluidized bed at low pressure, the present work was carried out experimentally with the apparatus whose schematic diagram is shown in Fig. 1. Sifted sand, silica gel and glass beads were used as material samples and the operating conditions covered the range of pressures from 1 to 760mmHg, and that of linear velocities of gas from 10 to 250cm/secThe results obtained may be summarized as follows:(1) The behavior of the fluidized bed at low pressure has a resemblance to that at atmospheric pressure.(2) It is more difficult to have a uniform fluidized bed at low pressure than at atmospheric pressure. χ, the ratio of ΔP to the gravitational force of the bed, falls between 0.85 and 0.95 as shown in Fig. 5.(3) The relation between the pressure drop and the flow velocity through the bed at low pressure can be correlated with modified friction factor, f'' (comprizing F(e), φ and the effect of slip-flow), in the experimental region of the present work, as shown in Figs. 7 and 8.(4) The minimum flow rate for fluidization is found to decrease proportionally with the decrease in operating pressure as shown in Eq. (1); however, at a pressure lower than 100mmHg or so, no such linear relationship is found. Consequently, the corrected relation between the minimum flow rate for fluidization and pressure is proposed as given by Eq. (8), where the correction factor, J, has been obtained by correlating the conductance of capillary in the medium vacuum region. The experimental results from which Eq. (7) and J value for dpP have been obtained are shown in Figs. 9 and 10.