Synthesis and field electron emission properties of waste cooking palm oil-based carbon nanotubes coated on different zinc oxide nanostructures

Abstract

Carbon nanotubes (CNTs) from waste cooking palm oil were synthesised on different zinc oxide (ZnO) nanostructures including nanorods (ZNRs), nanoflowers (ZNFs) and nanorods-nanoflakes (Al:ZNRs-FLs) via thermal chemical vapour deposition method. The ZnO nanostructures were controllably synthesised by sonicated sol–gel immersion method. The morphologies and crystal structures of the nanostructures were observed using field emission scanning electron microscopy, photoluminescence spectroscopy, X-ray diffractometer and micro-Raman spectroscopy. The diameter and density of CNTs were affected by the presence of ZnO nanostructures. Moreover, the morphology of ZnO nanostructures was modified during the synthesis of CNTs. The presence of ZnO reduced the barrier layer between CNTs and substrate, thus enhanced the field electron emission (FEE) properties of CNTs. Among the ZnO nanostructured prepared, the growth of CNTs on ZNFs gave the best FEE performance with the lowest turn-on field (0.8 V/μm at 1 μA/cm2). The ZNFs trapped more iron (Fe) elements and promote the tip and body-emission processes in the sample. Moreover, the presence of Fe elements also reduced the work function of ZNFs/CNTs nanocomposite and acted as additional electrons. Therefore, the significant FEE performance enhancement was observed.