Wei Shan

Zeolite nanoparticle modified microchip reactor for efficient protein digestion.

An enzymatic microreactor has been fabricated based on the poly(methyl methacrylate) (PMMA) microchchip surface-modified with zeolite nanoparticles. By introducing the silanol functional groups, the surface of PMMA microchannel has been successfully modified with silicalite-1 nanoparticle for the first time due to its large external surface area and high dispersibility in solutions. Trypsin can be stably immobilized in the microchannel to form a bioreactor using silica sol-gel matrix. The immobilization of enzyme can be realized with a stable gel network through a silicon-oxygen-silicon bridge via tethering to those silanol groups, which has been investigated by scanning electron microscopy and microchip capillary electrophoresis with laser-induced fluorescence detection. The maximum proteolytic rate constant of the immobilized trypsin is measured to be about 6.6 mM s(-1). Using matrix assisted laser desorption and ionization time-of-flight mass spectrometry, the proposed microreactor provides an efficient digestion of cytochrome c and bovine serum albumin at a fast flow rate of 4.0 microL min(-1), which affords a very short reaction time of less than 5 s.

Zeolite nanoparticles with immobilized metal ions: isolation and MALDI-TOF-MS/MS identification of phosphopeptides

Metal-ion-immobilized zeolite nanoparticles have been applied for the first time to isolate phosphopeptides from tryptic beta-casein digest; the phosphopeptides enriched on the modified zeolite nanoparticles could be effectively identified by MALDI-TOF-MS/MS.

Fabrication of zeolite coatings on stainless steel grids

During the last decade considerable research enthusiasm has been aroused for the preparation of zeolite coatings on various substrates, which might be used as catalysts, adsorbents, chemical sensors, selective electrodes and corrosion-resistant films [1–7]. Stainless steel is one of the ideal supports for preparing such kinds of materials due to its low cost, high thermal stability, good thermal conductivity, mechanical strength, facility of forming arbitrary shape and resistance to chemical corrosion [4–7]. The zeolite coatings on stainless steel have generally been prepared using in situ crystallization [4–6] and seed film [7] method. However, these methods can hardly control over the zeolite particle size, film thickness and are difficult to avoid the concurrently crystallizing of zeolites in the synthesis solution [5]. Recently, many endeavors have been paid to developing the layer-by-layer (LbL) zeolite assembly technique, which can easily control the zeolite film composition, structure and thickness by alternately electrostatic adsorbing zeolite nanocrystals and polyelectrolytes [8–10]. By this convenient and versatile approach the zeolite coatings on latex spheres [8, 9] and carbon fibers [10] have been successfully prepared. In this paper, the LbL zeolite assembly technique was first used to fabricate zeolite coatings on stainless steel grids. Because of the unique features of steel grids and the controllability of thickness and composition of the nanozeolite films, the novel materials are expected to have even more favorable conditions for mass transfer, thermal conductivity and lessening pressure drop. Furthermore, these kinds of materials can also be applied as the monolithic catalysts in de-NOx , dehydrogenation, catalytic distillation and other important catalytic processes if the corresponding active nanozeolites were used as the building blocks. Nanocrystals of silicalite-1 (80 ± 10 nm and 300 ± 40 nm), TS-1 (80 ± 10 nm), ZSM-5 (80 ± 10 nm) and beta (40 ± 5 nm) were prepared as described in the literature [11–15], and characterized by means of XRD, IR and SEM. The products were purified by repeated centrifugation and washing, then dispersed in distilled water to form a stable zeolite suspension with a concentration of approximately 1.0 wt% at pH 9.5 (adjusted with NH4OH) In order to provide a smooth and positively charged surface to aid subsequent adsorption of nanozeolites, the stainless steel grids (wire diameter of ∼22 μm and mesh size of ∼5 μm as shown in Fig. 1a) were precoated with three layers of polyelectrolytes of cationic poly(diallyldimethylammonium chloride) (PDDA) and anionic poly(styrene-sulfonate, sodium salt) (PSS) in the order of PDDA/PSS/PDDA. Then, the nanozeolites and PDDA were alternately deposited on the surface of the modified steel grids to form homogeneous nanozeolite/PDDA multi-layer films (20 min each adsorption step). After each adsorption step was completed, the grids were rinsed with 0.1 mol/L NH4OH solution for four times to remove the excess nanozeolites or PDDA. After certain deposition cycles had attained, the nanozeolite-coated grids were calcined at 823 K (heating rate 5 K/min) for 5 h in air to remove the organic species. The proper electrostatic interaction between substrate and zeolite particles is crucial to forming the perfect zeolite coatings on stainless steel grids by LbL method. Thus the charge character of nanozeolite, which may be scaled by zeta potential, is the fundamental parameter that affects the LbL process. The curves of the zeta potential of the 80 nm silicalite-1 colloids vs. pH value and salt concentration were shown in Fig. 2. We could find that, if positively charged steel grids were used as substrates, it was prerequisite to make the nanozeolite particles oppositely charged (i.e., negatively) by keeping the deposition solution in basic condition. At pH 9.5 and 0.1 mol/L salt concentration, the coatings on the grid surface were very uniform and dense after one layer of nanozeolites was deposited. However, uncovered regions could be observed on the grids at the same pH value but without adding salts (Fig. 1b), which may be explained as the fact that too high negative zeta potential on the zeolite particles would lead to the mutual repulsion among them. On the other hand, if the zeta potential of the nanosilicalite-1 particles was not high enough, e.g., at pH near 7, zeolite particles preferred to coalesce and form aggregates in the solution. These phenomena indicate that appropriate amount of surface charge of the nanozeolites determines the density of zeolite coating. To further study the effect of electrostatic attraction, the pH value of the dipping solution was also adjusted below the isoelectric point, e.g. pH = 3.0, where the particle surface is positively charged. Only few particles were deposited on the positively charged grids after one nanosilicalite-1 deposition step. However, when

A novel catalyst with high activity for polyhydric alcohol oxidation: nanosilver/zeolite film

A novel catalyst of silver nanoparticles over a zeolite film-coated copper grid (SZFC) has been fabricated via an in situ electrolytic method; it exhibited high catalytic activity and selectivity at a relatively low temperature for the partial oxidation of 1,2-propylene glycol to methyl glyoxal.

The application of zeolite/fac composites in protein separation

Abstract The aim of this research is to develop a novel zeolite/fly ash cenosphere (FAC) composite as inorganic stationary substrate in immobilized metal ion affinity chromatography (IMAC) for protein separation. After immobilization of metal ions by ion-exchange process, two model proteins, Bovine Serum Albumin (BSA) and Chicken Egg Albumin (CEA), which contain different sequences of histidine residues, could be successfully identified by IMAC method using Zn 2+ -exchanged ZSM-5/FAC composite as the packing sorbent. It was found that the separation effect of this type of packing substrate depended on the various interactions between the proteins and the immobilized metal ions in the zeolite substrate. Among Cu 2+ , Zn 2+ and Co 2+ ions, Zn 2+ ion, which possesses the suitable interactions with both the zeolite framework and the guest proteins, exhibited the best separation performance for the two model proteins. Due to its high chemical and mechanical stability, abundant and uniform pores, as well as its ion-exchange ability, this composite, compared with traditional soft gel matrix, is of great promise as a novel and ideal IMAC sorbent for biomolecular separation, especially under high pressure.