In Situ Growth of ZnO Nanocrystals from Solid Electrospun Nanofiber Matrixes

Porous fiber membranes consisting of 1D assemblies of ZnO nanocrystal-supported poly(vinyl alcohol) (PVA) nanofibers are described. These hybrid nanofiber membranes were assembled by first electrospinning a ZnO precursor-containing PVA aqueous solution. Subsequently, the electrospun composite nanofibers were submerged in a basic ethanol solution. As a result, ZnO precursors in solid PVA matrixes were hydrolyzed to generate ZnO crystals residing on the fiber surfaces. Photoluminescence spectroscopy analysis demonstrated the as-hydrolyzed fiber membranes possess white luminescence. Furthermore, the ZnO-encapsulated PVA nanofibers were prepared by directly electrospinning a ZnO nanocrystal-containing PVA solution as the contrast of the as-hydrolyzed hybrid nanofibers. The surface photovoltage spectroscopy (SPS) confirmed that the as-hydrolyzed hybrid fiber membranes had a strong SPS response, but the directly spun fiber membranes did not have any SPS response. This can be attributed to the favorable structure of the hydrolyzed hybrid nanofibers, that is, the surface residence of ZnO permits ZnO crystals to make direct contact with ITO electrodes to transfer the photogenerated electron originating from ZnO to ITO electrodes. By contrast, the transfer of the photogenerated electron is limited by PVA matrixes in the directly spun fiber system.