Fabrication And Application Of Sheath-core Inorganic Nanofibers Membrane By Co-electrospinning

Compared with zero-dimensional nanoparticles, one dimensional nanomaterials have abetter electrical conductivity and mechanical property because of a larger aspect ratio, and haveattracted great research interest in the field of electrics, magnetics and optics. But the complexityof traditional preparation inhibit the development of one-dimensional nanomaterials.Electrospinning, developed in1930s, has disadvantages of simplicity, high versatility, low-costoperation and large-scale production in fabricating nanofibers, and recently have attracted moreand more inorganic nanomaterials researchers’ attentions. Coating was widely used to improvethe materials performance. But traditional coating methods can not meet the demand as a resultof uncontrollability, complexity et al. Thus, core-sheath nanofibers with different coatingmaterials and thickness were directly prepared by co-electrospinning, and then applied indye-sensitized solar cells (DSSC), photocatalysis and photoluminescence. The morphologies andstructures of core-sheath nanofibers were characterized by field emission scanning electronmicroscopy (FE-SEM), Thermo-gravimetric analysis (TGA), Fourier transform infrared spectra(FT-IR), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-rayphotoelectron spectroscopy (XPS). At last, the influences of different coating materials andthickness on the photo-electrical performance, photocatalytic and photoluminescent propertieswere also investigated.。SnO2/TiO2and MgO/TiO2sheath-core nanofibers, MgO and SnO2as the coating materials,were fabricated by the combination of co-electrospinning and calcination. Afterwards, theinorganic nanofibers were used as an photo-anode for dye-sensitized solar cells (DSSC) by aseries of processes. TEM photographs demonstrated that the core-sheath structures weresuccessfully obtained, and the sheath thicknesses were65nm and60nm, respectively. The XRDpatterns of samples revealed that crystal structure of core TiO2changed because of the migrationof Mg and Sn into TiO2crystal lattice. At last, SnO2and MgO coatings can prevent the oxidationreaction between electrons and oxidized dyes or electrolyte. Therefore, SnO2/TiO2and MgO/TiO2based DSSCs performed a larger efficiency than pure TiO2based DSSC(1.27%),which were1.64%and1.48%.SiO2/TiO2sheath-core nanofibers with different sheath thickness were prepared by acombination of co-electrospinning and calcination to investigate the effects of sheath thicknesson the catalytic performance of TiO2nanofibers. The results revealed that the phasetransformation of TiO2declined due to the migration of Si into TiO2crystal lattice duringcalcination. The obtained heterogeneous structure were useful for the separation of electron-hole.And BET results showed the core-sheath nanofibers also had a higher specific surface area thanpure TiO2nanofibers. That made the core-sheath nanofibers have a larger catalytical performancethan pure TiO2nanofibers. Besides, the catalytic performance of SiO2/TiO2sheath-corenanofibers did not show a linear relationship with sheath thickness. Because the bigger thesheath thickness was, the larger distance the electrons transport. So more electrons would quenchwith holes, leading to a less number of surface hydroxyl group.Core-sheath nanostructures representes one approach that has been researched to increasethe luminescence efficiency by removing surface quenching sites. However, there has been noreport about the influence of sheath thickness on nanofibers phosphors. Herein,Gd2O3/Y2O3:Eu3+sheath-core nanofibers with different sheath thickness were obtained by acombination of co-electrospinning and calcination. The smaller the sheath flow rate was, themore the migration number of Gd into Y2O3lattice. That would inhibit the growth of Y2O3grain,resulting in a larger quantity of quenching sites. When the sheath flow rate increased, Gd2O3sheath can effectively coat the Y2O3core. Finally, the surface defects can be passivated and theenergy transformation between surface hydroxy and Eu3+can also be reduced by coating, whichresulted in the enhancement of photoluminescent performance. But when the sheath thicknessexceeded a threshold value, more body defects would emerged. And the effect of quenchingmechanisms was greater than the effect of surface passivation. That may explain thephotoluminescent performance of Gd2O3/Y2O3:Eu3+sheath-core nanofibers was lower than thatof pure Y2O3:Eu3+nanofibers.