Rui Zhai

Zhengzhou University, Cheng, Henan Sheng, China

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Publications (5)4.02 Total impact

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    ABSTRACT: Inorganic nanostructures and their assemblies play important roles in immobilizing biomolecules. Herein, we developed a facile and green methodology to assemble natural halloysite nanotubes (1D building blocks) into nest-like porous microspheres (3D architecture). We further modified the microspheres with dopamine to form a biomimetic entity. The interconnected and hierarchical pores within the microspheres provide larger pore volume to entrap biomolecules, and the abundant functional groups on the pore surface bond covalently with enzyme to enhance the immobilization ability. The porous microspheres showed excellent loading capacity for laccase immobilization as high as 311.2 mg/g, around 30 times higher than the individual halloysite nanotubes (11.3 mg/g). The specific activity above 80% was retained for the immobilized laccase compared to the free laccase. In addition, the immobilized enzyme exhibited remarkable thermal and recycle use stability. The biomimetic microspheres are expected to be biologically safe and chemically stable microcapsules for immobilizing a variety of biomolecules because of their natural and biofriendly characteristics.
    ACS Sustainable Chemistry & Engineering. 08/2013; 2(3):396–403.
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    ABSTRACT: Hierarchical MnO₂ nanostructures were prepared through the reaction between KMnO₄ and oleic acid at room temperature in the surfactant-free microemulsion system. The obtained samples were characterized by powder X-ray diffraction, N₂ adsorption, scanning electron microscopy, and transmission electron microscopy. The results indicated that the flowerlike nanospheres were three-dimensional (3D) porous microstructures consisting of nanoplates. The surface area of the sample was 171.5 m(2)/g and the distribution of pore diameter lay within the range of 5-15 nm. The prepared hierarchically structured MnO₂ showed excellent adsorption capacity and rapid adsorption rate for methylene blue ions in water. The maximum adsorption capacity of methylene blue was as high as 273.9 mg/g and 97.5% of the dye was removed within initial 5 min of contact time. Compared with other adsorbents, the synthesized hierarchical MnO₂ nanostructures displayed a faster adsorption rate and higher adsorption capacity, which implied potential application for removing dye pollutants from waste water.
    Water Science & Technology 01/2012; 65(6):1054-9. · 1.10 Impact Factor
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    ABSTRACT: In this study, we use natural halloysite nanotubes as novel support materials to immobilize enzymes. Two typical industrial enzymes (α-amylase and urease) with different sizes were immobilized in channels of the nanotubes through simple physical adsorption. After 60 min heating, both immobilized enzymes retained more than 80% activity. Stored for 15 days, the immobilized enzymes still showed more than 90% activity. More than 55% initial activity of the enzyme was retained after 7 cycles. The immobilized enzymes exhibited thermal stability, good storage stability and reusability, which indicate that halloysite is a promising support material for enzyme immobilization.Graphical AbstractResearch Highlights►Using natural halloysite nanotube as novel support materials for immobilization of enzymes. ►Two typical enzymes were immobilized on the nanotubes through simple physical adsorption. ►Immobilized enzymes retain a high fraction of their native activity. ►Low cost, the improved stability and reusability render halloysite potential support materials.
    Catalysis Communications 01/2010; 12(4):259-263. · 2.92 Impact Factor
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    ABSTRACT: Chitosan–halloysite hybrid-nanotubes were synthesized through the assembly of chitosan onto halloysite, a natural nanotubular aluminosilicate. Nitrogen adsorption–desorption measurement, Fourier-transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy analysis were employed to elucidate the structure of the hybrid-nanotubes. The results indicated that the hybrid-nanotubes could form three-dimensional (3D) nanocomposites with hierarchically porous structure. As-prepared structure showed excellent capacity for horseradish peroxidase (HRP) immobilization through cross-linking by glutaraldehyde. The maximum enzyme loading reached as large as 21.5 mg/g, higher than 3.1 mg/g of raw halloysite. After 35 days storage, the immobilized HRP did not undergo any activity loss while the free HRP only retained 27% of its original activity. Phenol removal efficiency by the immobilized HRP was also explored. The result showed the immobilized HRP exhibited overall high removal efficiency for phenol from wastewater.
    Chemical Engineering Journal. 214:304–309.
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    ABSTRACT: The halloysite nanotube (HNT) has already been extensively investigated to remove various organic pollutants and metal ions, and how to prepare the beads with excellent absorbability, stability, and reusability is critical to its practical application. In this study, we prepared a new kind of porous beads by immobilizing halloysite nanotubes with alginate (Alg). The as-prepared product was characterized by scanning electron microscope (SEM). The SEM image shows that hybrid bead is a porous structure comprised of accumulated halloysite nanotubes. Besides, the batch and column adsorption experiments of methylene blue (MB) were applied to evaluate its adsorption performance. In batch adsorption, the influences of pH, contact time and temperature on its adsorption capacity were investigated. The adsorption kinetic and isotherm models were established, and the maximum adsorption capacity of about 250 mg/g at 308 K can be deduced from the model. After 10 successive adsorption–desorption cycles, the removal efficiency of MB could be kept above 90%. Furthermore, the results of column experiments indicate that the removal efficiency could maintain above 90% after 1500 bed volumes of waste-water were treated. The obtained results indicated that the Alg–HNT hybrid beads could be an effective adsorbent in practical application for dye removal.
    Chemical Engineering Journal. 187:210–216.