In-situ formation of Cu metal crystals within nanostructured ZnO electrospun fibers

a r t i c l e i n f o The in-situ synthesis of Cu/ZnO crystalline nanofibers is presented. The composite nanofibers are formed through the calcination and reduction of as-electrospun fibers consisting of poly(vinyl pyrrolidone) as well as Cu and ZnO precursors. The crystal structure and morphology of the synthesized fibers were characterized using X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. The presence of well crystallized Cu and ZnO phases within the fiber was verified using XRD spectra and HRTEM images. To the best of our knowledge, this analysis confirms the first successful in-situ synthesis of a metal nanocrystal and ceramic polycrystalline electrospun fiber hybrid. Since the discovery of one-dimensional (1D) carbon nanotubes, extensive research investigations have been focused on the preparation of 1D nanostructures with well-controlled morphology. Due to their unique physical and chemical properties, 1D nanostructures act as novel building blocks for the hierarchical manufacturing of optics, catalysts, solar cells, super-capacitors, and other microscale devices [1–5]. Zinc oxide (ZnO) is a well-known Würtzite structured semiconducting oxide material with a large exciton binding energy and large band-gap energy. One-dimensional ZnO fibers are particularly useful in the manufacturing of small devices because a high surface area and large plate-like ratio increase chemical and physical interaction. The pure and doped forms of ZnO nanomaterials have been used for a wide range of applications including as active elements in photocatalysis, gas sensing, and hydrogen production [6–9]. Recently, the sensing and catalytic performance of ZnO has been enhanced significantly through the production of ZnO-based heterostructures or composites in the presence of Cu metal elements [10,11]. Capitalizing on the unique properties of these heterostructures requires a method capable of organizing 1D micro-and nanoscale fibers, rods, and tubes into macroscale functional structures. The top-down approach of electro-spinning has been widely utilized to fabricate organic and inorganic 1D structures, ranging in size from tens of nanometers to hundred of micrometers, due to its cost effectiveness, rapid fabrication time, and versatility [12,13]. Previous electrospinning studies have reported the synthesis of several single-component, composite, and doped fibers with various physical and chemical properties [14–16]. In this letter, we report the preparation of polycrystalline fibers consisting of Cu nanocrystals and ZnO grains through an electrospinning, calcination, and reduction process. The synthesis of this kind of nanostructured polycrystalline fiber offers the potential to modify and tailor physical characteristics such as thermal conductivity, electrical conductivity, and …