Synthesis And Catalytic Performance Of Novel Multifunctional Nanocomposites

With the development of modern science and technology, the nanomaterials with a single performance can not meet the needs of the people. By the multiple functionality of two or more nanomaterials, and the complementation and optimization of their performance, the nanocomposites could be prepared with excellent properties. They will be gradually developed into one of the dominant materials of the21st century, due to their broad application prospects. Nanocomposites are the novel materials combined with two or more inorganic materials or organic materials in nanoscale, two or more phases of composites have strong interactions or form the interpenetrating network structures. The versatility of nanocomposites can overcome the limitations of single inorganic or organic materials, and they presents many new features in catalysis, therefore, nanocomposites have become an important research direction in the field of novel catalytic materials.Based on the research status and problems of nanocomposite catalysts, we focused our works on the design and modification of the surface of the inorganic silica and polyethylene fibers, synthesis of novel funcational and acid nanocomposite catalysts with simple methods and low-cost synthetic processes in order to promote their applications on immobilization of penicillin G acylase, catalytic oxidation of CO at low temperature and conversion of fructose. The meaningful results are summarized as follows:(1) Lanthanum or cerium was successfully incorporated into the framework of mesostructured cellular foams (MCF) by the direct hydrothermal synthesis method (pH-adjusting method) with citric acid complexation. The strong Lewis acid sites are produced on the surface of the generated La-MCF and Ce-MCF nanocomposite materials, which can significantly enhance the interactions between supports and enzyme molecules. Therefore, the operational stability of the immobilized penicillin G acylase (PGA/La-MCF and PGA/Ce-MCF) is improved remarkably. After10recycles, PGA/La-MCF and PGA/Ce-MCF still retain89%and91%of their initial activities, but only77%of the initial activity can be obtained over PGA/MCF.(2) A general in situ growth method was successfully employed to prepare metal salt nanoparticle-MCF nanocomposite materials (LnPO4-MCF and BaSO4-MCF) containing highly uniform lanthanide phosphate (Ln=La, Ce, and Eu) nanorods and layered BaSO4nanocrystals (5-8nm) using inorganic phosphate and organic sulfonate (sodium dodecyl-benzenesulfonate, SDBS) as precursors. Due to a unique interaction between gold nanoparticles and nanosized metal salt supports, the composite materials are identified as efficient supports to stabilize the Au nanoparticles. Even after calcination at300℃, the size of gold nanoparticles still remains in the range of2-4nm. Therefore, the resultant metal salt nanoparticle-MCF nanocomposites are used as novel supports with highly activity, good stability, strong practicability for gold catalysts for catalytic oxidation of CO at low temperatures.(3) The VPO-MCF nanocomposite material, possessing highly uniform vanadium phosphate (VPO) nanocrystals (5-7nm) coated on the surface of MCF, was synthesized by an in situ growth method using organic n-octadecylphosphonic acid as the phosphate source. A three-phase catalytic system, consisting of an aqueous phase, a hydrophobic ionic-liquid phase is developed for efficient conversion of biomass-derived fructose to5-hydroxymethylfurfural (HMF). It can significantly inhibit the side reactions of HMF with H2O by isolating the top aqueous phase from the bottom solid-acid catalyst, and leading to91mol%selectivity to HMF at89%of fructose conversion. Moreover, both the VPO-MCF nanocomposite catalyst and ionic-liquid can be utilized repeatedly in this three-phase catalytic system, and the large-scale application of this process is feasible due to the low cost of recycling.(4) The bifunctional nanocomposite catalysts, synthesized by surface-initiated atom transfer radical polymerization (ATRP) and an irradiation-induced method by growing acid polymer brushes outward from the surface of silica particles (about175nm) and polyethylene fiber, were employed as a reusable acid catalyst for dehydration of fructose to HMF solely in water. The catalysts’ brush structure can provide a unique organic solvation microenvironment for inhibiting the side reactions of HMF with H2O, thus significantly enhances the selectivity and yield of HMF from fructose solely in water.