Anium dioxide nanotubes were produced on the surface of titanium metal foil by electrochemical anodic oxidation, and the tube diameter and wall size of the nanotubes were controlled by adjusting the anodic oxidation voltage and time, and the microscopic morphology of the TiO2 nanotube arrays obtained under different preparation conditions was observed by scanning electron microscopy (SEM), and the effects of oxidation voltage and time on the morphology of the TiO2 nanotube arrays of the nanotubes were examined; the crystalline shape of the titanium dioxide nanotubes was adjusted using a heat treatment process, and the sample crystal shape was characterised by X-ray diffraction (XRD). The crystal shape of TiO2 nanotubes was adjusted, and the sample crystal shape was characterised by X-ray diffractometer (XRD). The results showed that the TiO2 nanotubes were neatly ordered when oxidised with 0.5% ammonium fluoride in aqueous ethylene glycol solution as the electrolyte at 40 V for 30 min; after heat treatment at 450 ℃ for 2 h, the crystalline shape of the TiO2 nanotubes was transformed from the amorphous state to anatase-type TiO2, and the nanotubes appeared to have a small portion of collapsed.
TiO,nanotubes are a kind of semiconductor material with the characteristics of non-toxic, chemically stable, biocompatible, easy to prepare, and good photocatalytic, etc., which are widely used in the fields of biomedicine, wastewater treatment, solar cells, and national defence due to their excellent properties"-. Until now, there have been more studies on titanium dioxide nanotubes in China, and the main research areas are related to surface modification of implants5, photocatalytic hydrogen production in dye-sensitised solar cells, and precious metal catalyst carriers, etc., but there are fewer studies on metal catalyst carriers for automotive applications. Lin Xiaoxia et al. conducted a study on the effect of electrolyte temperature on nanotube arrays and photovoltaic properties.4 They mainly investigated the effect of electrolyte temperature on the inner diameter, wall and crystal shape of the nanotubes, and the photovoltaic properties of the nanotube arrays formed at different temperatures. Xiao Tongxin used a modified secondary anodic oxidation to prepare neat and orderly titanium dioxide nanotube arrays on the surface of titanium foil, and the modified nanotubes had better degradation efficiency for methyl orange compared with the conventional primary anodic oxidation. Ning Chengyun IV et al. investigated the effects of electrolyte concentration, anodic oxidation voltage and anodic oxidation time on the size and morphology of titanium oxide nanotube arrays. It was shown that neat and orderly nanotube arrays could be prepared under the condition of anodic oxidation voltage of 20V and HF electrolyte concentration of 0.5%.
1. Introduction
The titanium dioxide nano-arrays prepared by anodic oxidation of titanium flakes are mainly used in the medical field, photovoltaic hydrogen production and dye-sensitised solar cells.Roman Ioan et al. prepared titanium dioxide nanotubes by anodic oxidation of titanium dioxide nanotubes on different substrates (titanium, Ti6A14V and Ti6AI7Nb alloys) using ethylene glycol and glycerol as raw materials, and analysed the effects of the applied potentials and the processing time on the diameters and lengths of the nanotubes. MohamecAhmmed ElRuby et al. prepared titanium dioxide nanotubes by anodic oxidation in different viscous electrolytes such as glycerol and ethylene glycol, and investigated the effects of anodic oxidation voltage, oxidation time, chemical composition of electrolyte and pH on the anodic oxidation. It is shown that 5% or higher water content in glycerol electrolyte is the key to prepare nanotubes: H value of 6 is favourable for the preparation of highly ordered and continuous nanotube arrays with lengths up to 900 nm. XiaoPeng et al. prepared titanium dioxide nanotube (TNT) arrays by the anodic oxidation of iron foils in different electrolytes, and burned them with kilodrying ammonia at different temperatures to study the conductivity of the nanotube arrays before and after the calcination. The conductivity and capacitance of the nanotube arrays were investigated before and after calcination. Generally speaking, TiO nanotubes produced by anodic oxidation are in amorphous state and can be transformed into anatase or rutile by heat treatment. However, if the heat treatment temperature is too high, the Ti0 nanotubes will collapse. However, there are many potential applications that require TiO nanotubes of a certain diameter to maintain their morphology intact, as well as a specific crystal shape. To date, there are few systematic studies on the control of TiO nanocrystallites and morphology on the surface of titanium foils. In addition, most of the studies on Ti0,nanotubes are still in the basic research stage in the laboratory, and few of them have been applied in a wide range of practical production, mainly because the problems of solid loading of the nanotubes and the later product moulding have not been well solved. Therefore, the author intends to prepare TiO nanotubes with controllable morphology and crystal shape on the surface of titanium foil, which is very easy to be processed and shaped, by anodic oxidation method and changing the gasification voltage, time and heat treatment process, so as to provide the corresponding reference for its application in the later stage.
2. Test
Titanium foil (0.05mmx10mmx15 mm) with 99.9% purity was washed with acetone, anhydrous ethanol and deionised water for 10 min to remove surface stains. After cleaning, the titanium sheets were dried and set aside. The electrolysis was carried out using a WYK-6005K DC power supply, with titanium as the anode and stone chips as the cathode, with a spacing of about 30 mm, and the electrolyte was an aqueous ethylene glycol solution containing 0.5% ammonium fluoride. The anodising voltages were 20, 30, 40 and 50 V, and the oxidation times were 0.5, 1, 2 and 4 h. After the reaction, the samples were taken out immediately, rinsed with a large amount of deionised water and dried naturally, and then left to be used. The anodised samples were heated to 450 ℃ in a muffle furnace for 2 h, cooled naturally to room temperature, and then taken out for use.
The surface of the samples was analysed by Gemini field emission electron scanning electron microscope (BRUKER, Germany) for morphology and dimensional characteristics, and the samples were characterised by D8-Advance x-ray diffractometer (BRUKER, Germany) for physical phase.
Test results and discussion
Effect of oxidation voltage on the surface morphology of TiO nanotubes
The microscopic morphology of TiO nanotubes prepared by anodic oxidation of TiO nanotubes in an aqueous solution of ethylene glycol containing 0.5% ammonium fluoride (4:1, v/v) for 4 h at different oxidation voltages (20, 30, 40, 50 V). It can be seen that the surface of titanium foil oxidised for 4h at different voltages produces a layer of uniform and regular nanotubes, which are vertically distributed on the titanium substrate. The nanotubes generated on the titanium substrate under the oxidation voltage of 20V have the smallest diameter. About 40~70 nm, the surface is covered with many broken nanotubes, probably because the electrolysis time is too long, the dissolution time of the pits increases, the length of nanotubes increases, and the nanotubes are biased or even broken due to the nanotube wall is too thin to support a certain length of the nanotubes. There is a ring at the mouth of the tube, which may be due to the high concentration of F and slow diffusion in the glycol organic electrolyte, so that the nanotube microporous F diffusion is not sufficient, the dissolution rate is not consistent, resulting in the mouth Ti0, began to dissolve, forming a ring structure. That is, in this system oxidation voltage at 20, 30, 40V, oxidation time 4h are generated nanotubes, with the increase of voltage, nanotube diameter increases, the structure becomes neat and orderly. When the voltage reaches 50V, no nanotube structure can be observed, which is because the nanotubes collapse due to the high voltage, forming a sponge-like porous structure. This shows that in the electrolyte of 0.5% ammonium fluoride in aqueous ethylene glycol solution (4:1, v/v), the magnitude of the oxidation voltage directly affects the formation of TiO nanotube structures. If the voltage is too high, the dissolution rate is accelerated and sponge-like structure is formed.
3 Conclusion
The anodic oxidation method, combined with heat treatment, can be used to achieve a controlled preparation of TiO nanotube morphology and crystal shape. The anodic oxidation voltage, oxidation time and heat treatment process have an important effect on the morphology and crystalline shape of TiO nanotubes. Under the same oxidation time, the diameter of nanotubes increases with the increase of voltage, and the wall of nanotubes decreases with the increase of voltage: under the same oxidation voltage, the wall of nanotubes decreases with the increase of oxidation time, and the diameter of nanotubes is basically unchanged. When the oxidation voltage is 20V and the oxidation time is 0.5h, the nanotube diameter is the smallest; when the oxidation voltage is 40V and the oxidation time is 0.5h, the nanotube diameter is the largest. The nanotubes were partially collapsed after heat treatment, and the heat treatment mainly affected the structure of the nanotubes, and the anatase-type titanium dioxide was obtained at 450 ℃.
