| Among all kinds of semiconductor materials, TiO2 nanotube arrays is considered as the most effective and environment friendly photocatalyst because of its superior photocatalytic activity, non-toxicity, high chemical stability, unique tube structure and high specific surface area. However, there are still two drawbacks that limit the wide use of TiO2 photocatalyst. One is the quick recombination of photon induced charge carriers and the other is that the band gap of TiO2 is so wide (3.2 eV) that its activation is only limited in the UV region. Thus it is a reasonable approach to enhance its photocatalytic performance by inhibiting the recombination of eletron-hole pairs and widening its photoresponse range.In this thesis, TiO2 nanotube arrays fabricated via anodization was modified by various ways, and characterized by SEM, XRD, XPS, TEM and other technological means. The photocatalytic performance under visible light of the modified TiO2 nanotube arrays was also studied. The following conclusions could be drawn:(1) In the process of anodization, the diameter and length of TiO2 nanotube arrays were influenced by anodization voltage, the concentration of NH4F and water content in the electrolyte. With the increase of voltage, the diameter and length of TiO2 nanotube arrays also increased. When the the concentration of NH4F in the electrolyte increased, the diameter went up first and later came down, while the length increased to a certain degree and then keep almost the same. The gap between nanotubes appeared and became larger when the water content in the electrolyte increased. And the diameter also increased with the water content from 124 nm at 2 vol% to 180 nm at 10 vol%, while the length decreased, from 29 μm at 2 vol% to 8.4 μm at 10 vol%.(2) CdS nanoparticles modified TiO2 nanotube arrays got enhanced photocatalytic performance under visible light (λ≥400 nm), which could totally degradate methyl orange in 3 h. CdS nanoparticles distributed more uniformly on TiO2 nanotube arrays whose diameter and intertube space were larger, and the photocatalytic performance was better. Higher precursor concentration or more deposition cycles lead to more CdS nanoparticles formed on TiO2 nanotube arrays. With the increasing amount of CdS nanoparticles, the photocatalytic performance of the corresponding samples increased first, then dereased.(3) The photocatalytic performance of CdS/CdSe nanoparticles co-modified TiO2 nanotube arrays under visible light (λ≥ 400 nm) was excellent, the degradation rate towards methyl orange was up to 95.1% in 2 h. It’s highly enhanced compared with only CdS or CdSe nanoparticles modified TiO2 nanotube arrays.(4) Organic semiconductor g-C3N4 modified TiO2 nanotube arrays prepared by solid sublimation method had good photoelectrocatalytic performance under blue light (λ= 460 nm). As the amount of precursor urea increased, more g-C3N4 formed and the photoelectrocatalytic performance also enhanced. The highest photocurrent density was up to 65 μA/cm2, which is almost as ten times high as pure TiO2 nanotube arrays. With a bias voltage of 0.5 V, its photoelectrocatalytic degradation rate towards methyl blue was 55% under blue light illumination for 10 h.(5) SrTiO3 nanocubes modified TiO2 nanotube arrays was prepared by hydrothermal method. In the hydrothermal process, with the increase of reaction time, the SrTiO3 grew more and bigger, the photocurrent of the samples increased to a maximum and then decreased. The photoresponse range of g-C3N4/SrTiO3 co-modified TiO2 nanotube arrays was broadened to 430 nm visible light region. Under the illumination of visible light (λ≥ 420 nm), its photocurrent density was as high as 150 μA/cm2, and the degradation rate towards methyl blue reached 82% under a 0.5 V bias potential in 2 h. |
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