Hierarchical ZnO/SnO2 heterostructures via hydrothermally assisted electrospinning technique: synthesis and photocatalytic performances

Abstract

Hierarchical nanostructures with multiporous tin oxide nanofibers (SnO2- MPNFs) and zinc oxide nanorods (ZnO-NRs) have been synthesized by combining electrospinning technique and hydrothermal method. A solution containing uniformly distributed tin (Sn) and silicon (Si) species of precursors, as well as a sacrificial polymer (PVP) was electrospun using a single-nozzle spinneret to fabricate nanofibers. In virtue of the Kirkendall effect driven by calcination at 550 °C, the SiO2-cored SnO2 nanofibers (SnO2-SiO2-NFs) deliberated from PVP were formed and used as backbones for further hydrothermal growth of ZnO-NRs. By varying the hydrothermal reaction time (0.5–2 h) at the constant concentration of SnO2-SiO2-NFs, zinc (Zn) precursor, directing agent (hexamethylenetetramine, HMT) and aqueous ammonia, the density, length and thickness of ZnO-NRs were controlled. Nanofibers and ZnO-NRs/SnO2-MPNFs heterostructures are confirmed by X-ray diffraction (XRD), field-emission scanning electron microcopy (FE-SEM), energy dispersive spectrometer (EDS), transmission electron microscopy (TEM) and elemental mapping analysis. The hydrothermal treatment conducted at 90 °C in aqueous ammonia allowed: a) selective etching of SiO2 from the SnO2-SiO2-NFs core and SiO2 trapped between SnO2 particles, and b) effective growth of ZnO-NRs. The process resulted in ZnO-NRs/SnO2-MPNFs heterostructures with ZnO-NRs of 1–5 μm in length attached to SnO2-MPNFs, the shell of which was composed of ultra-fine SnO2 crystallites (~5 nm in size) and where the four porous channels create the core instead of SiO2. Photocatalytic performance of the heterostructures was investigated toward different organic azo-dyes (methylene blue, methyl orange) and obvious enhancement was demonstrated in degradation of the organic pollutant, compared to primary SnO2-based nanofibers.