Abstract
In this paper, ZnO electrodeposition was studied with the presence of graphene oxide (GO) exploited as a possible structure-directing agent. The effect of deposition potential and duration on the morphology and structure of ZnO was analyzed. The morphology and structure of the hybrids was analyzed by Raman spectroscopy, X-ray diffraction (XRD), and Scanning Electron Microscopy (SEM). The Raman results indicate a successful modification of ZnO with GO sheets and a hybridization threshold of 10 mg L−1 by the evolution of the defect related band of ZnO at 580 cm−1. The morphology results show that a low GO content only slightly influences the morphology and orientation of ZnO nanostructures while a high content as 10 mg L−1 changes the morphology in nanoplates and growth orientation to lateral. The results show that while GO participated in the deposition reaction, it has a two-fold role, also by structure-controlling ZnO, indicating that the approach is valid for the use of GO as a structure-directing agent for the fabrication of ZnO nanostructures by electrodeposition with varying morphologies and orientations.
Highlights
IntroductionZinc oxide (ZnO) is an n-type semiconductor highly employed in different devices, such as sensors, biosensor, solar cells, supercapacitor and catalysis fields [1,2,3,4] thanks to its interesting properties, including its wide band gap of 3.37 eV [4], resistivity control, high electrochemical stability, good electron transfer features and transparency in the visible wavelength region [1] in addition to being an abundant non-toxic and low-cost material.It is well known that properties of materials at nano-scale are markedly dependent on their size, shape or morphology; the control of features such as porosity, surface area or specific orientation has attracted much interest for improving the performance of ZnO-based devices [5].In this respect, ZnO morphology is highly versatile as it encompasses nanorods, nanowires, nanotubes, nanowalls, nanocups nanobelts, nanorings, nanosprings, nanobowls, nanoflowers, nanohelices and nanoparticles [1,6,7,8]
The electrodeposition of Zinc oxide (ZnO) takes place by a reaction mechanism based on the reduction of oxygen molecules and the formation of Zn(OH)2 which dehydrates at the applied temperature condition to form ZnO [11] and simultaneous graphene oxide (GO) reduction according to [42]: GO + aH+ + be− → rGO + cH2 O
A higher GO content in the electrolytic bath resulted in a negligible shift in the reduction peak current and potential with respect to the ZnO electrodeposition in the absence of GO, which is due to the increased density of GO sheets in the electrolytic bath that result in an agglomeration and in the exposure of less oxygen groups that could be used for ZnO growth
Summary
Zinc oxide (ZnO) is an n-type semiconductor highly employed in different devices, such as sensors, biosensor, solar cells, supercapacitor and catalysis fields [1,2,3,4] thanks to its interesting properties, including its wide band gap of 3.37 eV [4], resistivity control, high electrochemical stability, good electron transfer features and transparency in the visible wavelength region [1] in addition to being an abundant non-toxic and low-cost material.It is well known that properties of materials at nano-scale are markedly dependent on their size, shape or morphology; the control of features such as porosity, surface area or specific orientation has attracted much interest for improving the performance of ZnO-based devices [5].In this respect, ZnO morphology is highly versatile as it encompasses nanorods, nanowires, nanotubes, nanowalls, nanocups nanobelts, nanorings, nanosprings, nanobowls, nanoflowers, nanohelices and nanoparticles [1,6,7,8]. A large range of techniques such as magnetron sputtering, spray pyrolysis, electrodeposition, sol-gel, chemical bath deposition, thermal methods pulsed laser ablation in liquid or gas environment or chemical vapor deposition have been applied for the synthesis of ZnO nanostructures and its composites [11,12,13,14,15,16] Amongst these techniques, electrodeposition represents a great alternative as it provides excellent coating of varying geometries of substrates, it allows the control of morphology, thickness and crystallite size and aspect ratio of the deposit by varying the electrochemical parameters, including precursor concentration, bath temperature, deposition time or deposition potential/current [1,10] and it is a simple and cost- and time-efficient technique which does not require sophisticated experimental setups [1]. Morphologies such as platelets, nanowalls and nanorods were reported by adjusting the electrodeposition potential and bath temperature [10]
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