研究目的
To investigate and clarify the mechanism that controls the growth orientation of anodic TiO2 nanotubes fabricated by anodization, specifically verifying whether they grow vertically to the local Ti substrate surface and understanding the underlying factors.
研究成果
The growth orientation of anodic TiO2 nanotubes is predominantly determined by the local electric field around the nanotube bottom, which is regulated by the initial nano-scale local Ti substrate surface. For flat surfaces, nanotubes are vertical, circular, and straight; on convex surfaces, some nanotubes detach due to decreasing interface area; on concave surfaces, Y-branched nanotubes form to avoid vacancies. This mechanism provides insights for controlling nanotube morphology in applications.
研究不足
The study is limited to specific anodization conditions (e.g., voltage, electrolyte composition) and substrates (Ti foil and wire); long anodization times may lead to uneven dissolution and 'nanograss' formation; the model may not account for all variations in nanotube growth under different experimental setups.
1：Experimental Design and Method Selection:
The study uses electrochemical anodization to fabricate TiO2 nanotubes on rotated Ti foil and thin Ti wire to investigate growth orientation. The field-assisted oxidation and dissolution model is employed to explain the mechanism.
2：Sample Selection and Data Sources:
Flat Ti foil (purity
3：99%, dimensions 30 mm*25 mm*3 mm) and thin Ti wire (purity 99%, diameter 127 mm) are used as anodes. List of Experimental Equipment and Materials:
Equipment includes a Zahner electrochemical workstation (Zennium, Germany) as power source, HITACHI SU8200 and Fei NNS 450 field emission scanning electron microscopes (FE-SEM) for morphological characterization, and Leica EM TIC 3X ion beam milling system (FIB system) for axis section revelation. Materials include ethylene glycol, NH4F, H2O for the organic electrolyte, with specific concentrations (e.g.,
4：3wt% NH4F + 5vol% H2O in ethylene glycol). Experimental Procedures and Operational Workflow:
Two-electrode configuration with stainless steel cathode; anodization performed at room temperature (~22°C) with distance between electrodes of 2 cm; Ti foil rotated at angles (0°, 30°, 60°, 90°) relative to cathode; thin Ti wire partially immersed to avoid short-circuit; current density-time curves recorded; after anodization, samples rinsed with deionized water and dried in air.
5：Data Analysis Methods:
SEM images analyzed for nanotube morphology, length, diameter, and orientation; current density profiles examined; growth orientation model based on local electric field and initial nano-scale local Ti substrate surface shape.
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