Application Of Modified TiO₂Nanotube Arrays In Determination And Removal Of Environmental Pollutants

Nowadays, with outstanding development of industry, environment becomesseriously contaminated, which directly affects people’s health. Determination andremoval of organic pollutants, therefore, draw a great deal of attentions. We can’t solvethese entirely, of course, but we can hope to take a small part for general scence. In thisthesis, some basic researchs have been carried out based on using the modified titaniumdioxide nanotube arrays for analysis and removal of some organic pollutants. Base onthe optical/electrical activity of the titanium dioxide nanotube arrays, new titaniumdioxide nano-composite materials were fabricated by modification of the titaniumdioxide nanotube arrays for detetermination and removal of organic pollutants inenvironment.TiO₂nanotube arrays, which were synthesized for the first time in2001, have beenused in many fields, including photocatalysis and sensor due to their highly orderedorientation, uniform surface morphology, adjustable pore size, length; and specialelectrical, and optical properties. On the other hand, TiO₂nanotube arrays were greatlyused due to its low cost, widespread availability, non-toxicity, high photocatalyticactivity, and excellent chemical stability. However, as is commonly known,photocatalytic application of TiO₂is limited by its relatively large bandgap of3.0eV forrutile and3.2eV for the anatase phases, which limits photoactivity to the ultravioletregion. Moreover, the recombination of the photogenerated electron-hole pairs can leadto reduce the photoconversion efficiency. With the modification of TiO₂, the functionalnano-TiO₂composite materials would be with enhanced absorption in visible light andphotoconversion efficiency. Those are our research goals and the contents are as belows:To enhance conductivity and also reduce recombination of photogeneratedelectron-hole pairs within TiO₂, we have chosen appropriate narrow-band semiconductormaterials such as ZnSe and Cu-Zn-S to decorate TiO₂. The decorated TiO₂semiconductor can be excited under solar light. When the conduction band of a selectednarrow-band semiconductor is more negative than that of TiO₂, the photogeneratedelectrons of the narrow-band semiconductor will transfer to the conduction band of TiO₂or vice versa, and then participate in reduction. Whereas, the photogenerated holes ofTiO₂formed at the valence band may transfer to the narrow-band semiconductor andtake part in oxidation. This is why functionaized nano-TiO₂composite materials can promote the photo-carriers separation and absorb visible light, leading to enhancedoptical properties of the composite materials. Based on this theory, we fabricated novelfunctional nano-TiO₂composite materials by decoration of TiO₂nanotubes withnarrow-band binary or ternary semiconductor heterostructures （ZnSe/TiO₂andCu-Zn-S/TiO₂）. ZnSe nanoparticles-sensitized TiO₂nanotube arrays show higherphotocatalytic ability by35%compared with that of non-sensitized TiO₂nanotubearrays for photocatalytic degradation of pentachlorophenol. Moreover, they exhibit asignificantly increased capability for photocatalytic degradation of this compound withsupport of the photo-Fenton system which is investigated as oxidants. Cu-Zn-S ternarysemiconductor sensitized TiO₂nanotube arrays exhibits high photoelectrocatalyticdegradation capability to2,4-dichlorophenoxyacetic acid and anthracene-9-carboxylicacid. This photoelectrocatalytic degradation capability of Cu-Zn-S/TiO₂toward2,4-dichlorophenoxyacetic acid and anthracene-9-carboxylic acid is higher than that ofthe non-sensitized TiO₂nanotube arrays by48.2%and31.5%, respectively.The good photoelectrical, chemical, and physical properties of TiO₂nanotubesoffer a good chance for using the TiO₂nanotubes as the substrate of photoelectricalsensors. Photoelectrochemical sensors were therefore prepared by modifyingmolecularly imprinted polymer on the TiO₂nanotube arrays （MIP@TiO₂NTAs）. Theproposed sensor is highly sensitive to perfluorooctane sulfonate （PFOS） in watersamples with a limit of detection of86ng/mL. Moreover, the PFOS MIP@TiO₂NTAphotoelectrochemical sensor exhibits outstanding selectivity. These results affirm thatsemiconductor is a good choice for application in the analytical field, especially indetermination of organic pollutants.In conclusion, we have fabricated, modified, and applied the compositenano-materials based on TiO₂nanotube arrays. These researches have been continuousdeveloped the photoelectrocatalytic and photoelectrochemical analysis based onsemiconductor materials.