Preparation Of Nano-TiO₂ And Nano-zno By Anodization Method

Owing to their unique structures and excellent properties, nano-materials havevarious potential applications in nano-devices, sensing, photo-catalysis, lasers andbatteries. The properties of nano-materials depend on their morphology and sizes.Therefore, it is important to develop new techniques for fabrication of nano-materialswith desired structures. The size and morphology of the product can be easilycontrolled by changing the electrolyte composition, voltage of anodization anddifferent treatment time by anodization method. Moreover, according to the differentelectrolyte composition, various morphologies of nanomaterials can be prepared.More importantly, anodic oxidation method has many advantages, such as low cost,direct deposition of the product to the electrode, easy separation, so many researchershave investigated on anodization. In the present paper, preparation and properties ofnano-materials by anodization method have been investigated. The main contentsinclude:1. TiO₂ nanotube arrays have been successfully prepared by anodization in H2O /HF / ethylene glycol electrolyte system, the effects on the formation of TiO₂ nanotubearrays have been investigated. When anodizing voltage increases, TiO₂ nanotubediameter increases; before the balance, the length of TiO₂ nanotube increases withtime extension; the content of water is the main factor of the anodization rate, therebyaffecting the morphology of TiO₂ nanotube. TiO₂ nanotube arrays were prepared with avery smooth wall in HF / ethylene glycol electrolyte system; sources of F- can affectthe morphology of TiO₂ nanotube arrays, the length of more than 100μm of TiO₂nanotube arrays can be prepared in H2O / NH4F / ethylene glycol electrolyte system.2. Zn nano-pores have been successfully prepared in 80% ethanol aqueoussolution (v/v) with 0.08M salicylic acid at 40 V for 5 h with stirring byelectrochemical anodization of Zn foil. The formation mechanism of the Znnano-pores has been investigated. The concentration of salicylic acid determines theformation of Zn nano-pores, and too low concentration of salicylic acid can not formZn nano-pores. High salicylic acid concentration led to the failure of forming nano-pores, which may be due to the severe corrosion of the Zn foil. Applied potentialis also one of the factors determining the dissolution rate, the higher the voltage thefaster the dissolution rate, but it did not affect the diameter of Zn nano-pores. Znnano-pores were then oxidized in air and transformed into ZnO nano-wires, thelengths of ZnO nano-wires range from 2 to 5μm, the diameters of nano-wires range from 40 to 70 nm.3. ZnO nanoparticles size between 60nm and 80nm has been successfullyprepared by electrochemical anodization of Zn foil in oxalic acid solution. The effectsof applied potential and content of oxalic acid on the formation of ZnO nanoparticleshas been investigated. As the applied potential increased, the size of ZnOnanoparticles became smaller; as the concentration of oxalic acid increased, the sizeof ZnO nanoparticles became smaller.4. ZnO nanosheet has been successfully prepared by electrochemical anodizationof Zn foil in acetic acid alcohol solution. The main effect on ZnO nanosheetmorphology is the content of water, water is the main factor of the anodization rate,thereby affecting the formation of ZnO nanosheet. Finally the effect of appliedpotential on the formation of ZnO nanosheet has been investigated. The formationprocess of the ZnO nanosheet has been described.