Study On Photocatalysis Of TiO₂ Film And Its Application In COD Determination

On the basis of the study of photo-catalytic ability of TiO₂, people are very interested in its application in the environmental treatment. Since the early seventies of the last century, the research has been started in this field, and many methods have been used to treat environmental problems. Among them, the photo-catalysis of TiO₂ which functions as the advanced oxidation technique has many unique advantages. Firstly, heterogeneous photo-catalysis in which TiO₂ is the photo-catalyst can occur completely under relatively gentle conditions. Secondly, solar power can be used to stimulate photo-catalysis directly in order to make redox take place. The wide application of photo-catalysis of TiO₂ in the environmental treatment has led to a revolution which is being used in many aspects such as the water treatment, quality detection of water, air decontamination, sterilization, and etc.Water pollution is a significant aspect of environmental pollution. Whether the polluted water can be discarded or not depends on the index of pollution. The most important one is the value of COD (chemical oxygen demand) which is defined as the number of oxygen equivalents consumed in the oxidation of organic compounds by strong oxidizing agents(mg l^₁). The accuracy of COD measurement is determined by the extent of the oxidation of the organics or other reductants. Due to the stimulation of photo-catalytic TiO₂ by light, strong oxidants including oxygenic radicals such as HO· are formed to mineralize the organic pollutants deeply. This principle provides a basis for the quick and instantaneous measurement of organic pollutants. Meanwhile, the determination of total pollutants in the water can be achieved.The way in which photo-catalytic TiO₂ film was prepared and characterized was described in the paper. The mechanism of the photo-catalytic oxidation of organic substances by TiO₂ film was discussed and the brand new concept applied in the detection of COD by photo-catalytic oxidation was also offered. Furthermore, novel COD analyzer was developed. Totally, there are five chapters in this paper. The first chapterIn this part, four parts, that is, the development of the TiO₂ and their application and development in the environmental analysis. the oxidizing and catalytic mechanism of the nano-semiconductor and the research on the measurement of the oxygen containing radicals and the current circumstances of the development of the fast COD detector in the waste water system were discussed and a detail outline and review of the development in the current area was introduced.The second chapterThe method of Ti/TiO₂ photoelectrode prepared by using laser calcination method instead of oven calcination process was introduced. The prepared TiO₂ film was observed with AFM and XRD. Photoelectrocatalytic degradation of rhodamine B using this electrode was investigated, and anodic potential and pH were optimized. The laser power applied in this electrode preparation was also discussed, and it indicated that TiO₂ particle prepared with high laser power was crystallized adequately and the photoelectrocatalytic ability was satisfactory. RB degradation was investigated under different conditions, and it showed that photoelectrocatalytic degradation could achieve efficient and complete mineralization of organic pollutant. The photoelectrocatalytic oxidation using the Ti/TiO₂ electrode calcinated by laser was compared with that of the electrode calcinated by furnace, and it showed that the reaction rate of RB degradation using the electrode by laser was faster than that by furnace.The third chapterA Ti/TiO₂ mesh electrode by laser calcination was prepared in this article. The resulting TiO₂ film was investigated by X-ray diffraction (XRD) and electrochemical impedance spectroscopy (EIS), and it illuminated that the prepared electrode mainly consisted of anatase TiO₂ nanoparticles on its surface and exhibited a superior photocatalytic activity. The photodegradation of methylene blue (MB) using the proposed electrode under different experimental conditions was investigated in terms of both UV absorbance at 664 run and chemical oxygen demand (COD) removal. The electrical bias applied in photoelectrocatalytic (PEC) oxidation was also studied. Through the comparison between photocatalytic (PC) oxidation and photoelectrocatalytic (PEC) oxidation, it was found that PEC oxidation was a convenient and effective way to mineralize the organic matters and that laser- treated photoelectrode exceeded the oven-treated one.The fourth chapterIn this chapter, a COD measurement by a photocatalytic oxidation method using nano TiO₂ film was studied. TiO₂ was deposited on a quartz support, which could avoid the filtration and provide higher quantum yields than TiO₂ in powder form. In addition, K₂Cr₂O₇ was used as electron scavenger, which could inhibit the recombination of electrons and holes and enhance the oxidation of organic compounds. The change in Cr(III) concentration produced by the photocatalytic reduction was measured by a colorimetric method. It was considered that the value obtained by the proposed method could be reliably correlated with the COD obtained by using the conventional methods.The fifth chapterIn this chapter, Ti/TiO₂ electrode was prepared by using laser-assisted sol-gel method, which could shorten the time of electrode preparation. And it was examined through characterization with XRD and photoelectrochemical behavior study with EIS and amperometry. The proposed electrode was developed as a sensor for the determination of COD. This method was proved to be simple, rapid and environmentally friendly. Additionally, the COD values obtained by the proposed method were well correlated with those obtained from the conventional method.The sixth chapterIn this chapter, photoelectro-synergistic catalysis oxidation of organics in the water on Ti/TiO₂/PbO₂ electrode was investigated by the method of electrochemistry. Furthermore, the results were compared with those obtained from photocatalysis and electrocatalysis. The method proposed was applied to determine the chemical oxygen demand (COD) value, Ti/TiO₂/PbO₂ electrode functioning as the work electrode during the process. It was shown that the method of photoelectro-synergistic catalysis had lower detection limit and wider linear range than the methods of electroassisted photocatalysis and electrocatalysis. The results obtained by the proposed method and conventional one were compared by carrying out the experiment on Wastewater samples. The correlation of the results using different methods was satisfactory and the relative bias was below ± 6.0 %. The seventh chapterA fast COD flow injection analysis (FIA) instrument by means of electroanalysis which was developed according to the photoelectro-synergistic catalysis theory of the Ti/TiO₂/PbO₂ electrode. This instrument has such advantages as the short detective time of the single sample, convenient operation, high precision, good consistency with the standard COD analytical method,less second pollution and the capability of fast COD analysis.