| The issues of energy and environment are the basic problems of the recent years. The wide bandgap semiconductor, TiO2 plays an important role in both pollution treatment and energy using areas, because of its advantages of chemical stability, non-toxic, low cost and biocompatibility. The TiO2 nanotube arrays can provide efficient ways for the conducting of electrons, increase the efficiency of catching the photon, and advance the separation of photo-induced carriers, due to its high specific surface area, highly orientation and excellentmechanical strength among all stuff of nano-TiO2 materials. For the nano materials, the performance was greatly influenced by morphology of materials. Thus, it is important to optimize the morphology of TiO2 nanotube arrays to improve its performance of photoelectricity and increase its photocatalytic activity and light current.In this study, re-anodize method has been used in the watered glycol-NHUF system in order to prepare TiO2 nanotube arrays. VHX-600ESO super depth of the field 3D display system, scanning electron microscope (SEM), X ray diffractometer (XRD) and ultraviolet and visible spectrophotometer (UV-Vis) have been utilized to analyze the microstructure, component, surface appearance and UV-Vis transmission spectrum of the samples. The result shows that the re-oxidation can improve the flatness of surface, while the nanobube opening rate and the consistency of length are obviously better than the TiO2 produced by one-step oxidation. There are drapes connecting the tube walls. The section diameters of the tubes appear wider on the top and narrower on the bottom. So this method can improve the stability of nanotube arrays.Learning from the results of XRD of the samples before and after annealing, we find that the nanotube arrays prepared via re-oxidation have more exposed crystal faces, better crystallization and more and stronger peaks after annealing. The UV-Vis transmission spectrum shows that the absorbance of the reoxidized sample is better than which of samples oxidized once, and the absorption edge is hardly changed.The SEM,XRD, X-ray photoelectron emission microscope (XPS), UV-Vis and photocatalytic:test system are used to study the influence of the decorated CdS quantum dots, produced by Successive Ionic Layer Adsorptionand Reaction (SILAR) among the microstructure. surface appearance. UV-Vis transmission spectrum, optical band gap and photocatalytic properties of the nanotube arrays. The results of microstructure and surface appearance show that the nanotube arrays modified by CdS quantum dots through 5 times sedimentary-cycling have the best surface appearance, which the pipe orifices are still open, and the quantum dots are uniform distributed in and on the walls of nanotubes without block or gathered. The (111) and (220) crystal faces of blend CdS appear in the XRD result, while in the TEM analysis, there are interplanar crystal spaces of 0.352 and 0.336nm, corresponding the (101) crystal face of TiO2 and the (111) of CdS. The Ti2p, Ols, Cd3d, S2p, Ti2p are existing in the XPS consequence, Because the Ti2p and Ols binding energy of the nanotube have been changed after CdS-doping,which means that CdS-sensitization changes of the microstructure of TiO2 nanotubes. The element ratios of O:Ti and Cd:S are 2.34:1 and 1.34:1, which are close to the theoretical element ratios. The ultraviolet-visible spectrums of the series of the quantum modified nanotue arrays are all red shifted, which declare that the absorbance of light are exposed to the visible part. Among all the samples, the one through 5 times SILAR cyclic has the best uniformity, so the sample can prevent composition of photon-generated carrier efficiently, and generate more hydroxyl through photocatalytic reaction, which leads to the highest catalytic efficiency.The CdSe quantum dots deposited on TiO2 nanotube arrays by cyclic voltammetry (CV) have been studied, whose charge capacity has been controlled by adjusting the frequency of cyclic voltammetry. The result of SEM shows that the surface appearance of 5-time cycled sample is the best. Compared to the unmodified nanotubes, there is a peak of the (220) crystal face of CdSe appeared in the XRD result. Also, the wider peak proves that CdSe exists in the form of small grain. Considering the TEM photos, it is shown that the grain size of the uniform distributed quantum dots is 5-10nm. Analyzed by the UV-Vis, the whole series of the samples have different levels of red shift, which explains that the CdSe can help the nanotube to expand its light absorbance to visible part. The sample deposited 5 times has the largest absorbance of light,as its open tube mouth and moderation quantum, dots. The photoresponse result shows the current can reach 1.853μA/cm2., so;this-sample-shows :the highest catalytic efficiency (88.20%) among the series.Choosing the nanotube arrays prepared by re-oxidation as basement; we use SILAR method to deposit two kinds of quantum dots, ZnS and CdS, onto the samplessuccessively. The analyses of SEM, XRD and TEM indicate that two kinds of quantum dots distribute regularly, and the pipe orifices are open, while the diffraction peaks of CdS (111) and ZnS (220) crystal faces are shown in the XRD. From the UV-Vis absorption spectrum of one sample, the red shift is occur after the sedimentation of the two quantum dots, which proves that the double modification can expand the absorption to 650nm. Among all specimens, the sample produced by co-deposition has the highest speed of catalytic efficiency. In the test of photocatalysis repetition, it is proved that the passivation layer of ZnS can slow down the photocorrosion of quantum dots in the electrolyteeffectively.The innovation points of this academic dissertation are:1.This research deeply studied the effects of the method of re-oxidation to product the TiO2 nanotube arrays on the microstructure, surface appearance and optical properties. It summarized the producing ways of highly consistent orientation and smooth nanotubes under the constant voltage system. The conditions of experiment are easy to operate. The special structure and surface morphology have been observed, and the basement of quantum dots modification has been prepared.2. The producing method of CdS or CdSe quantum dots modified nanotube arrays under room temperature has been studied. The light absorption is been observed, in order to get a conculsion of the discipline about how the quantum dots affect the absorption edge. The photocatalysis and light current have also been tested, and a reasonable explain about its mechanism has been given.3.The conditions and means of co-doping TiO2 nanotube arrays have been studied. The photocatalysis properties have been researched and explained. So this study has potential application prospect in optical devices, pollution dealing and anode material of solar cells. |
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