Modification Of TiO₂ Nanotube Arrays Light Catalyst System And Research Of Pollutant Degradation Function

TiO₂ as a kind of inorganic photosensitive semiconductor materials, due to its low cost, chemical stability, low toxicity, no pollution, high catalytic activity, completely oxidating organic pollutants under atmospheric pressure, etc, has been considered as one of the best photocatalyst, and has become one of the hot spot research in recent years. TiO₂ nanotubes have special tubular structure, larger specific surface area, especially TiO₂ nanotube arrays, with highly ordered nanotube array structure, has significant effect of quantum size and orientation. Under the light irradiation, photoproduction electronic can quickly transfer from the conduction band of TiO₂ nanotubes into the conductive substrate, and composite of photo-induced carriers is obviously reduced, thus TiO₂ nanotube array shows good photoelectric activity, and has a very broad application prospects in many fields. In this paper, double-sided preparation of TiO₂ nanotube arrays was prepared by anodic oxidation method, and the further studies of Ag nanoparticles modified on the surface of the TiO₂ nanotube arrays, and N doping modification technology were performed. Finally the photocatalytic oxidation degradation experiments of azo dyes methyl orange and low boiling point ethanol and acetic acid were studied by using the as-prepeared-TiO₂, Ag/TiO₂ photocatalyst.In the process of the preparation of double-side TiO₂ nanotube arrays, 0.5 mm thick, 2 cm×12 cm, Ti plate as the anode, graphite as the cathode. The conditions of effect on the TiO₂ nanotube growth, apparent structure, the influence of crystal configuration and light catalytic activity, such as anodic oxidation voltage, concentration of ammonium fluoride, volume ratio of glyceryl alcohol and water, anode oxidation time, calcination temperature, etc, were investigated. The results were showed that the optimal conditions found are as follows: 0.25 mol/L NH4 F, 2︰1 volume ratio of glyceryl alcohol and water, 20 V anodic oxidation voltage, time for 2 h, the calcination temperature at 450℃ for 5h. the as-prepeared-TiO₂ nanotube arrays are clear and integrated, orderly, the nanotube diameter and nanotube wall thickness evenly distributed, on average between 120 nm to 150 nm in diameter, wall thickness for an average of 12 nm to 15 nm. XRD spectra analysis indicated that the crystal type of TiO₂ nanotubes arrays was anatase.After the calcinations, the process of modification of Ag nanoparticles on the surface of TiO₂ nanotubes consists of two continuous processes. The results shown that Ag nanoparticles could be evenly dispersed on the surface of TiO₂ nanotubes, and had the highest photocatalytic activity, under the conditions of the concentration of silver nitrate at 2.0 g/L, ethanol and water volume ratio of 1:4, the time of ultraviolet light reduction for 30 min. SEM showed that TiO₂ nanotube diameter was about 120 nm, the length was about 1700 nm Ag nanotubes, the Ag particle size was about 10 nm. XRD analysis indicated that the modified process of Ag nanoparticles did not change TiO₂ anatase configuration, XPS spectra analysis indicated that the average atom fraction of Ag was 1.11%.The sodium nitrate and urea under acid condition can emit nitrogen at room temperature, using the reaction, sodium nitrite and urea were both added into the electrolyte of anodic oxidation, the solution acidity was adjusted with hydrochloric acid, so N-doped TiO₂ nanotubes was preparated by one-step anodic oxidation process. SEM spectra analysis showed that N-doped TiO₂ tubular structure become defect from clear and complete, and nanotube diameter become smaller than that of TiO₂. XRD analysis showed that after calcinated at the same temperature of 450 ℃, the crystal type of TiO₂ was still the anatase. XPS spectra analysis of N atom percentage was 3.41%. Photocatalytic activity study showed that the UV photocatalytic activity of N/TiO₂ was 18% higher than TiO₂, while the visible light photocatalytic activity of xenon lamp is increased by 38%..Ethanol and acetic acid are low boiling point organic pollutants, and are the main pollution compositions of condensed water. The optimum conditions of TiO₂ based catalysts on the photocatalytic degradation of acetic acid and ethanol was: anodic oxidation time was 120 min, the concentration of NH4 F was 0.25 mol/L, glycerol and water volume ratio of 2: 1, the UV light source is 11 w UV lamp. The degradation rate of ethanol and acetic acid by Ag/TiO₂ was 92% and 79% respectively. The thotocatalytic degradation dynamics model of acetic acid was discussed, using Langmuir-Hinshelwood dynamics model, the total rate equation of the photocatalytic reaction was established, and the expression of the rate constant K and the adsorption constant K was given.