Studies On The Dye Photodecolorization Using Ba/Urea Doped TiO₂ Film

Dyeing wastewater from textile industry is large volumes of heavily pollutive wastewaters with high colority and high organic content, containing complicated components, which has caused serious problems to the environment and people. TiO₂ can deeply decolor dyeing wastewater and deal with larger quantities of nonbiodegradable pollutants using a stream of clean solar energy. However, TiO₂ has a low utilization ratio of solar energy. The holes and electrons easily recombine. The negative factors limit the practical application of TiO₂. The paper prepares Ba²⁺ and urea doped TiO₂ sol and films. The catalyst's photoactivity is improved and expected to decolor the dyeing wastewater.Ba²⁺/TiO₂ sol is prepared by adding alkaline earth Ba²⁺ in absence of alcohol using sol-gel method at room temperature. The effects of amount of doped Ba²⁺ on the particle size, UV/vis absorption spectra, crystal form, FI-IR spectra and photocatalytic activity of the sol are discussed. The results indicate that particle size decreases with adding 0.01%Ba²⁺ then increases as the mass continue to increase. With increased amount of doped Ba²⁺, the absorption wavelength edge shifts to long wave direction, which leads to an increase in optical absorption intensity in the visible-light region. XRD spectra show that 0.01%Ba²⁺ doped doesn't change the anatase phase of TiO₂, but makes the diffraction peak widen. The crystallite size is reduced from 22.4nm to 20.1nm. Doped Ba²⁺ makes the vibration absorption peaks of Ti-O bond appear a red shift from 485cm-1 to 627cm-1.The changes of TiO₂ properties, such as particle size, absorption spectra, improve UV and visible light photocatalytic activity. The decolorization of 0.05% doped under UV light and 0.01% doped under visible light are 89.1% and 93.1%, respectively.Ba²⁺/TiO₂ film is prepared by spin coating method at room temperature. The effects of amount of doped Ba²⁺, spin speed, film layers, spin time and recycle times on the photocatalytic activity of Ba²⁺/TiO₂ film are discussed. The film spinned 3 times, each time for 30s, in rotation speed of 2500rpm has relatively good photoactivity. The catalytic activity of Ba²⁺/TiO₂ film doesn't have an obvious decrease after cycle using for 5 times. The effects of doped Ba²⁺ on adhesion, hydrophily, morphology structure, light transmission performance and photocatalytic activity of Ba²⁺/TiO₂ film are investigated. The results indicate that the film is properly adherent proved by tap water erosion test and the scotch tape test. The appropriate amount Ba²⁺ decreases contact angle and improves the hydrophilicity of the film, which is beneficial to adsorb more dye molecules. The film basically contains ball particles and the balls disperse uniformly. 0.01% doped Ba²⁺ can effectively restrain the agglomeration of particles and formation of second particle. 0.01% and 0.05% doped Ba²⁺ also leads to an increase in optical absorption intensity in the ultraviolet light region. The film reduces transmission and increases light absorption with the increase in film layers. The moderate doping can improve the activity of the catalyst and the decolorization of the film with 0.01% Ba²⁺ doped reaches 86.1%. Ba²⁺/TiO₂ film is used to decolor the dye solution. The effects of the initial concentration of dyes, light intensity, irradiation time and dye structure on the photocatalytic activity of the film are investigated. The results indicate that high initial concentration can reduce the light transmittance of the reaction solution, which leads to decrease the decolorization performance. The activity of film presents a trend of rise first to 100W then unchangeableness as light intensity increases. The photodecoloriation increases with the increased irradiation time. Ba²⁺/TiO₂ film has remarkable decolorization ability for both of selected azo and anthraquinone dyes. Among these dyes, the decolorization of acid green GS reaches 86.3%.The urea/TiO₂ sol is prepared by adding nonmetal urea using sol-gel method at room temperature in absence of alcohol. The effects of amount of doped urea on the particle size, UV/vis absorption spectra, crystal form, FI-IR spectra and photocatalytic activity of the sol are investigated. The results indicate that the effect of doped urea on the particle size would be modest. The mean particle size of the sol is around 30-40nm.The doping of urea doesn't make the absorption threshold wavelength have an obvious red-shift. However, it leads to an increase in optical absorption intensity. The characteristic peak of urea doesn't appear in the XRD spectra. 0.01% urea doped makes the diffraction peak widen. FI-IR spectra indicate that urea involves in the hydrolysis process of tetrabutyl titanate and forms a new covalent bond with TiO₂. 0.01% doped urea can improve the photoactivity of the catalyst from 87.2% to 95.2%, from 89.2% to 92.8% under UV and visible light, respectively. Absorption spectra changes of the dye solution in the process of decolorization show that the absorption peak rapidly decreases to almost disappear. No new absorption peak and new organic pollutant are generated.The effects of doped urea on adhesion, hydrophily, morphology structure, light transmission performance and photocatalytic activity of urea/TiO₂ film are discussed. The results indicate that the film is properly adherent. 0.01% doped urea improves the hydrophilicity of the film resulting in adsorbing more dye molecules. 0.01% urea can effectively restrain the agglomeration of particles and formation of second particle. The gap between the particles exists. Doped urea also leads to an increase in optical absorption intensity in the ultraviolet and visible light region. The moderate doping can improve the activity of the catalyst. 0.01% urea doped makes the decolorization improves from 85.6% to 91.6%.Nylon 6/urea-TiO₂ fiber film is prepared by electro-spinning method at room temperature based on nylon 6. The film has high specific surface area, which is beneficial to improve the photoactivity. The FI-IR spectra, morphology structure, photocatalytic activity and cycle using performance of the fiber film are discussed. The characteristic absorption peaks of nylon 6 and urea/TiO₂ exist in the FI-IR spectra. The surface of the fiber film is even. When spinning solution contains 15% and 20% urea/TiO₂ catalyst, the fiber becomes thinner between 80nm and 200nm and specific surface area increases, resulting to the strengthen of adsorptive capacity of the fiber film. The film can absorb about 5% dye. The photocatalytic decolorization of the film containing 20% catalyst reaches 93.7%. The film can be reused. Nylon 6/urea-TiO₂ fiber film has remarkable decolorization ability for both of selected azo and anthraquinone dyes. According to the analysis of FI-IR spectra of dye solution before and after the reaction, the dye structure has changed. The azo bond is cleaved and benzene ring is destroyed.Doping Ba²⁺ and urea can effectively improve the photoactivity of TiO₂. The catalyst films prepared by spin coating and electro-spinning methods are even, uniform and adherent. The films with high photocatalytic activity and good reused performance can decolor many kinds of dyes and have potential applicability in treating dyeing wastewater.