Fabrication Of Electrospun Inorganic Nanofiber Materials And Their Functionalization Research

Electrospinning is an effective, straightforward, and convenient method to process thematerials into one-dimensional （1D） structureal nanofibers with controllable compositions,diameters, and porosities for a variety of applications, including textiles, filters, tissueengineering, drug delivery, sensor, optoelectronics, photocatalysis, catalysis, and so forth. Inthis dissertation, the valuable explorations have been focused on the design and synthesis offunctional1D inorganic nanofiber materials via combining of electrospinning technique andother synthesis approach. The physical and chemical properties and the practical applicationsof the as-prepared functional1D inorganic nanofiber materials are also investigated. The mainresearches are list as follow:（1） Carbon nanofibers with controllable nanoporous structures were fabricated viaelectrospinning technique. In the first step, for the preparation of porous polyacrylonitrile（PAN） nanofibers as the template, two kinds of polymers of PAN and polyvinylpyrrolidone（PVP） were used as electrospun precursor materials, and then the bicomponent nanofibers ofPAN and PVP were extracted with water to remove the PVP in the composite polymernanofibers. Afterward, by using the porous PAN nanofibers as structures directing templateand through heat treatment, the porous carbon nanofibers with the high specific surface areaand large length-to-diameter ratio were obtained. Notably, by altering the ratio of PAN/PVP inthe electrospun precursor materials, the pore size and pore distribution of porous carbonnanofibers could be easily controlled. Such carbon nanofibers with controllable nanoporousstructures are of interest for a broad range of applications in areas such as sensors, lithium ionbatteries, filter technologies, solar cells, and so on.（2） ZnO hollow nanofibers with diameters of120-150nm were fabricated byelectrospinning the precursor solution consisting of PAN, PVP, and zinc acetate compositethrough a facile single capillary, followed by thermal decomposition for removal of the abovepolymers from the precursor fibers. The investigation indicated that, during theelectrospinning process, there occurred phase separation between the electrospun compositematerials, while the obtained precursor nanofibers of PAN, PVP, and zinc acetate compositemight possess a core/shell structure （PAN as the core and PVP/zinc acetate composite as theshell）. Furthermore, the composite nanofibers with core/shell structure could play a structuraldirecting template role for preparing ZnO hollow nanofibers during the calcination process.Because of the large length-to-diameter ratio and the high surface-to-volume ratio of the ZnOhollow nanofibers, excellent sensing properties to ethanol, with short response and recoverytime were exhibited. （3） The well-designed1D electrospun nanofibers of SnO₂/ZnO n-n heterojunction withthe matchable band gap and low lattice mismatch were fabricated via electrospinningtechnique. The as-electrospun SnO₂/ZnO nanofibers with diameters of100-150nm wereconsisted of rutile SnO₂and wurtzite ZnO nanoparticles. The photocatalytic activity of theSnO₂/ZnO nanofibers for the degradation of rhodamine B （RB） was much higher than that ofZnO, SnO₂, and TiO₂electrospun nanofibers, which could be attributed to the increasing theelectron-hole pair separation efficiency based on the photosynergistic effect of the ZnO-SnO₂heterojunction and the high specific surface area of the SnO₂/ZnO nanofibers. Notably, theSnO₂/ZnO nanofibers could be easily recycled without the decrease of the photocatalyticactivity due to their1D nanostructural property.（4） The well-designed1D electrospun nanofibers of NiO/ZnO p-n heterojunction withthe Ni/Zn molar ratio of0.5or1were fabricated via electrospinning technique. Theas-electrospun NiO/ZnO nanofibers with diameters of50-70nm were consisted of cubicstructure NiO and hexangular structure ZnO nanoparticles. The photocatalytic activity of theas-electrospun NiO/ZnO nanofibers for the degradation of rhodamine B （RB） was muchhigher than that of ZnO, NiO, and TiO₂electrospun nanofibers, which could be ascribed to theformation of p-n heterojunctions in the NiO/ZnO nanofibers. In particular, the NiO/ZnO p-nheterojunction nanofibers with the Ni/Zn molar ratio of1exhibited the best catalytic activity,which could be attributed to their high separation efficiency of photogenerated electrons andholes. Notably, the electrospun nanofibers of NiO/ZnO p-n heterojunctions could be easilyrecycled without a decrease of the photocatalytic activity due to their1D nanostructuralproperty.（5） Tubular nanocomposites of gold nanoparticles （AuNPs）/silica nanotubes （SNTs） withthe nearly uniform diameters of250–350nm were fabricated by combining the singlecapillary electrospinning technique （for SNTs as the supports） and an in situ reductionapproach （for AuNPs）. The small size （3-5nm） and highly dispersed AuNPs were assembledon the inner and outer surface of SNTs through the in situ reduction of Ag+by Sn2+ions. Thecatalytic activities of the as-prepared tubular nanocomposites were evaluated by using amodel reaction based on the reduction process of4-nitrophenol （4-NP） into4-aminophenol（4-AP） in the presence of NaBH4as the reductant. The results indicated that the tubularnanocomposites exhibited excellent catalytic activities because the small size and highlydispersed AuNPs were exposed on the inner and outer surface of electrospun SNTs, allowingeffective contact with the reactants and catalysis of the reaction. Those tubular catalysts couldbe easily recycled without a decrease of the catalytic activities due to their1D nanostructuralproperty.（6） Tubular nanocomposites of silver nanoparticles （AgNPs）/silica nanotubes （SNTs）with the nearly uniform diameters of250–350nm were fabricated by combining the single capillary electrospinning technique （for SNTs as the supports） and an in situ reductionapproach （for AgNPs）. The highly dispersed AgNPs were assembled on the inner and outersurface of SNTs through the in situ reduction of Ag+by Sn²⁺ions. It is interesting to note thatthe size of AgNPs on the surface of SNTs could be controlled by appropriately adjusting theamount of ammonia solution during the above in situ reduction reaction. The catalyticactivities of the as-prepared tubular nanocomposites were evaluated by using a model reactionbased on the reduction process of4-nitrophenol （4-NP） into4-aminophenol （4-AP） in thepresence of NaBH4as the reductant. The results indicated that all the tubular nanocompositescatalysts with high specific surface area （185–250m²g-1） exhibited excellent catalyticactivities because the highly dispersed AgNPs were exposed on the inner and outer surface ofelectrospun SNTs, allowing effective contact with the reactants and catalysis of the reaction.In particular, the tubular nanocomposite catalysts containing small size AgNPs had highercatalytic activities than those containing the large size ones, which was attributed to thesize-dependent Ag redox potential and surface-to-volume ratio influencing interfacial electrontransfer from AgNPs surface to4-NP in the presence of highly electron injecting BH4-ions.Those tubular catalysts based on AgNPs/SNTs nanocomposites could be easily recycledwithout a decrease of the catalytic activities due to their1D nanostructural property...