Oxygen — Catalysed and heat treatment effect on ZnO nanoparticles properties synthesized via precipitation techniques

Abstract

Zinc oxide (ZnO) semiconductor has been the focus of current research interest due to its versatile application in advanced functional device including short wavelength light emitting diode, ultra violet (UV) laser diode, piezoelectric device, gas sensor, catalyst, transparent conductor and field emission display. The diversify applicability of ZnO is owing to its unique properties which possess direct wide band gap (3.37 eV), large exciton binding energy (60 meV), chemically stable and is bio-compatibility. ZnO is also a material which has the richest family of nanostructures including nanoparticles, nanoneedles, nanorods, nanoflakes, nanotowers and nanotetrapod. As the structures are in nanometer scale, ZnO exhibit properties that are different from their bulk counterpart and their performance are enhanced resulting from the high surface to volume ratio properties. Among diverse morphology of ZnO nanostructures, ZnO nanoparticles have received enormous attention in recent years since it offers wide area of application such as chemical sensor, photocatalyst, transparent UV protection film, bio-imaging and drug delivery. Resulting from the widespread ZnO nanoparticles applicability, many methods to produce ZnO nanoparticles have been develop via solution chemical route and physical vapor deposition (PVD). For example; sol gel, colloid, hydrothermal, microemulsion, chemical bath deposition and precipitation are the routes under solution chemical method whereas spray pyrolysis, sputter deposition, template assisted growth and chemical vapor deposition are among the routes that are employed to synthesis ZnO nanoparticles under physical vapor deposition (PVD). Comparing the PVD and solution chemical route, PVD requires extreme condition such as high temperature and pressures, complicated equipments, expensive raw materials and long deposition times whereas solution based method are less expensive and produce high output volume thereby become the favored route in this work. Among the solution based techniques, precipitation is easier to control, capable of mass production, simple and versatile. However, it possesses some limitations where longer calcinations process [1] is required for removal of impurities thereby raise the production cost as more energy is consume. Furthermore, the particles tend to agglomerate during reaction which will reduce particles surface area, thus lowering ZnO sensing sensitivity. However, this limitation can be minimized by employing capping agent or surfactant (i.e. diethanolamine (DEA), polyvinyl alcohol (PVA), ethylene glycol (EG)) in the reaction, albeit their reaction are slower. The addition of catalyst will however help to speed up the nucleation process.