Electrochemical enzymatic biosensor with long-term stability using hybrid mesoporous membrane.

An acetylcholinesterase-immobilized sensor unit was successfully prepared by encapsulating the enzyme within hybrid mesoporous silica membranes (F127-MST). Through a novel combination with tetracyanoquinodimethane, both acetylcholine and organophosphorus pesticides were successfully detected with high sensitivity. Furthermore, we manufactured the working prototype of an enzyme sensor with this sensor unit for detecting dichlorvos, aldicarb and parathion. At present, the detection limit in this working prototype either equaled or surpassed that of others. Also, we have the advantage of increased stability of the enzyme against the outer environment by encapsulation of the enzymes into a silica nanospace. Consequently, acetylcholinesterase immobilized in F127-MST is a practical sensor with high sensitivity, reusability, and storage stability.

Preparation of plate-like mesoporous material from layered silicate RUB-15.

A plate-like mesoporous material was formed from the lamellar structure of layered silicate RUB-15. RUB-15 was synthesized by a hydrothermal method, as reported previously. TMA (tetramethylammonium) ions exist in the interlayer of RUB-15 were exchanged with C16 TMA (hexadecyl-trimethyl-ammonium) ions, and TEOS (tetraethylorthosilicate) was then intercalated in between the layers. After steaming, the obtained powder was calcined and characterized by XRD, N2 gas adsorption, and scanning electron microscopy (SEM). The XRD patterns and N2 adsorption-desorption isotherms of the finally obtained powders indicated the presence of mesopores in the sample. The morphology of powders was plate-like which originates from the structure of the starting material. Cross-sectional FE-SEM images of the final obtained powders revealed existence of mesopores between the layers. The morphology of the final obtained mesoporous materials was affected by their remaining layered structure due to the starting material RUB-15.

A one-step conversion of benzene to phenol with a palladium membrane.

Existing phenol production processes tend to be energy-consuming and produce unwanted by-products. We report an efficient process using a shell-and-tube reactor, in which a gaseous mixture of benzene and oxygen is fed into a porous alumina tube coated with a palladium thin layer and hydrogen is fed into the shell. Hydrogen dissociated on the palladium layer surface permeates onto the back and reacts with oxygen to give active oxygen species, which attack benzene to produce phenol. This one-step process attained phenol formation selectivities of 80 to 97% at benzene conversions of 2 to 16% below 250 degrees C (phenol yield: 1.5 kilograms per kilogram of catalyst per hour at 150 degrees C).

Importance of the support material in thin palladium composite membranes for steady hydrogen permeation at elevated temperatures.

Hydrogen permeation performance of palladium membranes supported on porous alpha-alumina and yttria-stabilized zirconia (YSZ) was studied at 300-850 degrees C. The hydrogen permeation flux across the palladium-alpha-alumina membrane decreased markedly during permeation tests conducted at >600 degrees C. The SEM and XPS studies of the post-test membrane revealed the presence of aluminium in the palladium layer. Such migration of aluminium was not observed by heating the palladium-alpha-alumina membrane under an argon atmosphere, indicating that hydrogen is responsible for this phenomenon. Hydrogen-induced strong metal-support interaction might be related to this considerable loss of the hydrogen flux. Reduction of alumina to Al(0) by active hydrogen at the membrane-support interface and subsequent migration of Al(0) into the palladium layer represents the most plausible mechanism for the aluminium diffusion. Actually, Al(0) that migrated into the palladium membrane layer generated less hydrogen-permeable palladium-aluminium alloy or inter-metallic compound phase. In contrast, no such strong interaction was found between the YSZ support and the palladium membrane. This composite membrane exhibited a steady permeation of hydrogen at 650 degrees C for 336 h. Having a remarkably high reduction potential, Y(III) is unlikely to be reduced to Y(0), although Zr(IV) has a comparable reduction potential to that of Al(III). A binary phase diagram shows a liquid alloy phase present for the Pd/Al couple at temperatures greater than 615 degrees C (eutectic point), while an inter-metallic compound or liquid alloy phase in the Pd-Zr binary system is not apparent at temperatures less than 750 degrees C. Consequently, inter-diffusion of zirconium with palladium did not occur during operations at 650 degrees C.

Selective adsorption of bacterial cells onto zeolites.

Zeolites adsorb microbial cells on their surfaces and selective adsorption for specific microorganisms was seen with certain zeolites. Tests for the adsorption ability of zeolites were conducted using various established microbial cell lines. Specific cell lines were shown to selectively absorb to certain zeolites, species to species. In order to understand the selectivity of adsorption, we tested adsorption under various pH conditions and determined the zeta-potentials of zeolites and cells. The adsorption of some cell lines depended on the pH, and some microorganisms were preferentially adsorbed at acidic pH. The values of zeta-potentials were used for calculating the electric double layer interaction energy between zeolites and microbial cells. There was a correlation between the experimental adsorption results and the interaction energy. Moreover, we evaluated the surface hydrophobicity of bacterial cells by using the microbial adherence to hydrocarbon (MATH) assay. In addition, we also applied this method for zeolites to quantify relative surface hydrophobicity. As a result, we found a correlation between the adsorption results and the hydrophobicity of bacterial cells and zeolites. These results suggested that adsorption could be explained mainly by electric double layer interactions and hydrophobic interactions. Finally, by using the zeolites Na-BEA and H-Y, we succeeded in clearly separating three representative microbes from a mixture of Escherichia coli, Bacillus subtilis and Staphylococcus aureus. Zeolites could adsorb each of the bacterial cell species with high selectivity even from a mixed suspension. Zeolites can therefore be used as effective carrier materials to provide an easy, rapid and accurate method for cell separation.

Formation of cage-like hollow spherical silica via a mesoporous structure by calcination of lysozyme-silica hybrid particles.

Calcination of lysozyme-silica hybrid hollow particles gives novel cage-like hollow spherical silicas with differently patterned through-holes on their shell structure.

A reactivity index study to monitor the role of solvation on the interaction of the chromophores with amino-functional silanol surface for colorimetric sensors.

Amino-functional silanol surface are mostly used for the immobilization of inorganic ions, molecules, organic or biochemical molecules onto the mesopore surface. In analytical chemistry, the metal ion uptake was visualized through colorimetric sensors using chromophore molecules. One needs to know the structure-property correlation between the chromophore and silylating agent while choosing chromophore, which is very important to design the sensors. We have used two chromophores representative of hydrophobic and hydrophilic type. We used density functional calculation on all the interacting molecules in both the unsolvated phase and solvated medium within the domain of hard soft acid base principle (HSAB) to look at the localized activity of the interacting atoms of these reacting molecules to formulate a priori rule to choose of the best chromophore. We have as well postulated the mechanism of interaction between chromophore and the silylating agent. The results were compared with experiment and it is observed that solvation plays a detrimental role in the binding of chromophore with silylating agent. The results also show that, the range of reactivity index can be used as a suitable property to scale activity of chromophore molecules suitable for the sensing process. It is observed that the hydrophobic chromophore binds stronger with both the metal and the silylating agent; whereas for the hydrophilic one, it binds only with the silylating agent when solvated and in all cases the metal ion binding is weaker compared to that of the hydrophobic one.

A method for the molecular imprinting of hemoglobin on silica surfaces using silanes.

A new molecular imprinting technique using covalently immobilized hemoglobin (Hb) is described for creating Hb-specific recognition cavities on silica. Two kinds of organic silane (3-aminopropyltrimethoxysilane: APTMS, and trimethoxypropylsilane: TMPS) were polymerized on a surface of porous silica after the Hb template was covalently immobilized by forming imine bonds, and their influence was analyzed. The results showed that not only the silane amount but also the relative proportions play an important role in protein imprinting. Pore size distribution on Hb imprinted silica was determined by nitrogen adsorption/desorption after removing the template Hb. The Hb-imprinted silica using covalently immobilized Hb (MIPi) as a template proved superior to silica using free Hb (MIPf) regarding displacement of template Hb, and selective re-adsorption as compared with other non-template proteins. The results suggested the capacity for selective adsorption of MIPi to be not only based on the isoelectric point (pI) and protein molecular weight, but also the characteristics of protein recognition cavities imprinted on base silica.

Effects of water on the structure and bonding of resorcinol in the interlayer of montmorillonite nanocomposite: a periodic first principle study.

Resorcinol forms a novel nanocomposite in the interlayer of montmorillonite. This resorcinol oligomer is stable inside the clay matrixes even above the boiling point of the monomer. A periodic ab initio calculation was performed with hydrated and nonhydrated montmorillonite before and after intercalation of resorcinol. For the most feasible dimer and tetramer shaped oligomer of resorcinol, the intramolecular and intermolecular hydrogen bonding feasibility has been tested using the DFT-BLYP approach and the DNP basis set in the gas phase and in the presence of aqueous solvent. After locating the active site through Fukui functions within the helm of the hard-soft acid-base principle, the relative nucleophilicity of the active cation sites in their hydrated state has been calculated. A novel quantitative scale in terms of the relative nucleophilicity and electrophilicity of the interacting resorcinol oligomers before and after solvation is proposed. Besides that, a comparison with a hydration situation and also the strength of the hydrogen bridges have been evaluated using mainly the dimer and cyclic tetramer type oligomers of resorcinol. Using periodic ab initio calculations, the formation mechanism was traced by the following two ways: (1) resorcinol molecules combine without any interaction with water or (2) resorcinol oligomerizes through water. Both the mechanism is compared and the effect of water on the process is elucidated. The results show that resorcinol molecules combine after hydration only and hence they are stable at higher temperature. The fittings of the oligomers were also tested as well by periodic calculation to compare the stability of the oligomers inside the newly formed clay nanocomposite.

General and simple approach for control cage and cylindrical mesopores, and thermal/hydrothermal stable frameworks.

Highly ordered cage and cylindrical mesoporeous silica monoliths (HOM) with 2- and 3-dimensional (2D and 3D, respectively) structures, mesopore/micropore volumes, and thick-walled frameworks were successfully fabricated by instant direct templating of lyotropic phases of copolymer (EO(m)-PO(n)-EO(m)) surfactants. Large cage-like pores with uniform constriction sizes up to 10 nm and open cylindrical channel-like mesopores can be easily achieved by this simple and efficient synthesis design. Our results show that the cage-like pores could be fabricated at relatively lower copolymer concentrations used in the lyotropic phase domains at copolymer/TMOS ratios of 35 wt %. These ordered cage pore architectures underwent transition to open-cylindrical pores by increasing the copolymer concentration. High EO/PO block copolymers, in general, were crucially affected on the increase of the interior cavity sizes and on the stability of the cage mesopore characters. However, for F108 (EO(141)PO(44)EO(141)) systems, the fabrication of ordered and stable cage pore monoliths was achieved with significantly higher copolymer concentrations up to 90 wt %. Interestingly, the effective copolymer molecular nature was also observed in the ability to design various ordered mesophase geometries in large domain sizes. Our findings here show evidence that the synthetic strategy provides realistic control over a wide range of mesostructured phase geometries and their extended long-range ordering in the final replicas of the silica monolith frameworks. In addition, the HOM silica monoliths exhibited considerable structural stability against higher thermal temperature (up to 1000 degrees C) and longer hydrothermal treatment times under boiling water and steam. The remarkable structural findings of 3D frameworks, transparent monoliths, and micropores combined with large cage- and cylindrical-like mesopores are expected to find promising uses in materials chemistry.

Synthesis of protein-silica hybrid hollow particles through the combination of protein catalysts and sonochemical treatment.

Hollow spherical particles with protein-silica hybrid shell structures have been synthesized through a combination of the catalytic activity of the protein and sonochemical treatment; the morphologies of the particles were controlled by varying the protein concentration.

Structure and property correlation for Ag deposition on alpha-Al2O3--a first principle study.

The nature of bonding at the interface between deposited silver and (001) surface of alpha-Al2O3 for both Al-terminated and OH-terminated has been investigated using a periodic ab initio method. Substantial inter-planar relaxations within the alumina were found at both the interfaces and the bulk. The periodic calculation with Ag deposition shows that 10% of Ag loading on alumina results maximum stability. Now, this is known that, the clean alumina surface only exists at UHV condition and normally the alumina surface prefers to stay hydroxylated. We have therefore compared the silver bonding over hydroxylated alumina surface and confirmed the fact that the hydroxylated surface binds silver weakly in comparison to the clean surface and it recommends that the silver cluster over the hydroxylated surface begins to join in to form three-dimensional nuclei. The deposited Ag forms a cluster on top of the alumina surface. The Ag atomic packing was monitored to rationalize the role of packing on activity of silver. Three low-index Ag surfaces (100), (110) and (111) are investigated via the ab initio density functional calculations with ultrasoft potentials. We have monitored the relation between Ag atomic packing and its electronic properties. The results show that the structural and electronic property of Ag deposited on alumina surface depends significantly on atomic packing. Ag110 over clean alumina surface shows highest surface energy and smallest work function, whereas for the OH-terminated surface it is the Ag111. The results are discussed in view of the existing experimental data and models of metal-oxide interface.

A highly photoreflective and heat-insulating alumina film composed of stacked mesoporous layers in hierarchical structure.

An alumina film with highly photoreflective and heat-insulating properties can be simply synthesized using a sol of fibrous boehmite with an additive. The entangled fibers bring about mesopores among them and form stacked 2D nonwoven-like nanosheets. The porosity and the layered structure of alumina accompanying the heat resistivity provide the upper properties that are usually difficult to realize simultaneously.

2,3,7,8-Tetrachloro dibenzo-p-dioxin can be successfully decomposed over 2:1 dioctahedral smectite-a reactivity index study.

2:1 Dioctahedral smectite family has shown its capability to decompose 2,3,7,8-tetrachloro dibenzo-p-dioxin (TeCDD) using the active hydroxyl hydrogen attached with the central octahedral aluminum, as monitored using density functional theory (DFT). From the values of the local softness and the charge on the hydrogen atom of the bridging/structural (occurring on the surface) hydroxyl attached to octahedral/tetrahedral metal site present in smectite used as a first approximation to the local hardness, it is concluded that the local acidities of the inorganic material systems are dependent on several characteristics which are of importance within the framework of hard-soft acid-base (HSAB) principle. The first step in this process of decomposition is the abstraction of chlorine bound to TeCDD using surface hydrogen of smectites. This results in non-chlorinated dibenzo-p-dioxin (NCDD), which is less toxic than TeCDD. The second step is the formation of a dative bond between oxygen of NCDD and hydroxyl proton of smectite, with the breaking of Cz.sbnd;O bond of NCDD. The reaction mechanism is postulated within the helm of DFT using Fukui functions for all possible chlorinated and non-chlorinated dioxin varieties along with clay clusters. The material is identified to act for the decomposition of dioxin.

A Novel Layered Silicate with a Helical Morphology.

Helices composed of stacked layers are present in the novel silicate obtained from a silica sol and NaOH by hydrothermal synthesis in the presence of tetramethylammonium (TMA) hydroxide and 1,4-dioxane. The helical morphology is evident in scanning electron micrographs (see picture). The TMA and sodium ions of the silicate are readily replaced by protons, and on heating to 200°C a reversible phase transition occurs in which water molecules are lost from between the layers.

An enzyme-encapsulated microreactor for efficient theanine synthesis.

A flow-type microreactor containing glutaminase-mesoporous silica composites with 10.6 nm pore diameter (TMPS10.6) was developed for the continuous synthesis of theanine, a unique amino acid. High enzymatic activity was exhibited by the local control of the reaction temperature.

Heterogeneous nucleation of protein crystals on fluorinated layered silicate.

Here, we describe an improved system for protein crystallization based on heterogeneous nucleation using fluorinated layered silicate. In addition, we also investigated the mechanism of nucleation on the silicate surface. Crystallization of lysozyme using silicates with different chemical compositions indicated that fluorosilicates promoted nucleation whereas the silicates without fluorine did not. The use of synthesized saponites for lysozyme crystallization confirmed that the substitution of hydroxyl groups contained in the lamellae structure for fluorine atoms is responsible for the nucleation-inducing property of the nucleant. Crystallization of twelve proteins with a wide range of pI values revealed that the nucleation promoting effect of the saponites tended to increase with increased substitution rate. Furthermore, the saponite with the highest fluorine content promoted nucleation in all the test proteins regardless of their overall net charge. Adsorption experiments of proteins on the saponites confirmed that the density of adsorbed molecules increased according to the substitution rate, thereby explaining the heterogeneous nucleation on the silicate surface.

Increasing particle size of a synthetic smectite for polymer nanocomposites using a supercritical hydrothermal treatment.

We have studied the effect of a supercritical hydrothermal process on the structural and surface morphological properties of synthetic smectite clay, stevensite (ST), in terms of the particle size, in order to enhance the functionality of the synthetic smectites as an inorganic filler for transparent clay/polymer nanocomposites. The ST aqueous suspensions were treated in a flow reactor system at 673 K and 25 MPa. The structural characterizations revealed that the ST retained a layered structure composed of polymeric sheets of SiO(4) tetrahedra after the treatment. The treated ST possessed a particle size of 71 nm, approximately twice that of the original ST (36 nm) for the 0.1 wt.% suspension using an operation condition at a flow rate of 0.085 g s(-1). SEM observation revealed that an enlarged particle was formed from cohesive aggregates, suggesting that the increase in size of the particles was caused by the cohesion of the microcrystallites or primary particles of ST. The treated ST was subsequently used to prepare nanocomposites with carboxymethylcellulose sodium salt (CMC Na) to evaluate the effect of the supercritical treatment. The treated ST nanocomposite films retained their transparency which is very similar to the original ST nanocomposite films. Furthermore, the nanocomposite films, which had a high CMC Na ratio ranging from 40 to 90 wt.%, showed improved oxygen barrier properties when compared with those of original ST. The tortuous model revealed that this improvement was mainly due to the increase of the particle size. Consequently, the supercritical treatment successfully brought about the growth of the ST particles, leading to the development of functional synthetic clays for clay/polymer nanocomposites.