| Due to its large specific surface area, high mobility of charge carrier, high degree of order and convenient recycling, the anodic TiO2 nanotube (TNT) array has been widely used in photocatalysis, solar cell, gas sensor and biomedicine fields. However, the low utilization of sunlight and quantum efficiency of TiO2 greatly limit the practical application of TNT array. Therefore, to optimize the preparation of TNT array and reasonable modifications are of great significance for the development of photocatalytic materials with wide spectral response and high quantum efficiency.In this paper, a modified organic electrolyte was used to prepare TNT array, and the effect of preparation conditions on the performance of the photocatalytic degradation of pollutant was investigated for system optimization. CdS quantum dots (CdS QDs) were as the sensitizers to expand the absorption range of TNT array and enhance the visible-light activity. A large area graphene (GR) film was deposited on TNT array via an electrochemical process to increase the adsorption ability and enhance the transport and separation of charge carriers. Alternate growth of GR and CdS QDs on TNT array was conducted to obtain many three-component TNT-GR-CdS, TNT-CdS-GR and TNT-CdS-GR-CdS composite films, then the effect of different structure order on the photoelectrochemical and photocatalytic properties was investigated, and the charge carriers transfer and photocatalytic reaction mechanism in Z-scheme composite film were discussed. The TNT array and its composite films were further used in photoelectrocatalysis, then the difference and relation between photocatalysis and photoelectrocatalysis were discussed, and the mechanism of the photoelectric synergistic effect was revealed. The main conclusions are as follow:(1) The uniform and highly ordered TNT array was successfully prepared, the samples annealed at 400-500℃ were the anatase crystal phase, and the photocatalytic activity of TNT400-20V2h (the TNT anodized at 20 V for 2 h and annealed at 400℃) was the best;(2) The partical size of CdS QDs grew on inner surface of TNT was about 5 nm, the edge of absorption was gradually red shifted with the increase of cycle times, and many more CdS QDs were coupled to TNT with the increases of anodic voltage, dipping concentration and cycle times, thus the better photoelectric response and activity were obtained under visible light;(3) The controllable fabrication of folded and smooth GR on TNT array was successfully realized via a detailed mechanism of reduction and deposition, the obtained TNT-GR composite films have shown the enhanced light absorption, photoelectric response, dye adsorption and photocatalytic activity, and the improvement effect of smooth GR was higher than that of folded GR;(4) The three-component TNT-GR-CdS composite film in Z-scheme has been successfully constructed showing the highest photoelectrochemical and photocatalytic performances, this was because that the electrons of the conduction band of TNT were transferred to the valence band of CdS through GR film in a Z-scheme mechanism, which not only made the spatial separation of electron and holes, but also efficiently restrained the photocorrosion of CdS;(5) In the two-electrode and three-electrode systems, the photoelectrocatalytic activities of TNT array and TNT-GR-CdS were both efficiently enhanced, and the fast and complete mineralization was relized, this was due to the separation effect of photogenerated charge carriers resulted from the difference of electrode potential or from the external voltage, which facilitated that the quantum efficiency of photoelectrocatalysis was further enhanced.The features and innovations of this thesis are as follows:(1) The effects of preparaton conditions of TNT-CdS on its photocatalytic activity were demonstrated; (2) The detailed mechanism of one-step electrochemical fabrication of large smooth GR on TNT was revealed; (3) The three-conponent TNT-GR-CdS in Z-scheme with enhanced activity and stability was firstly constructed, and its photocatalytic mechanism was elaborated; (4) The effect of different electrode system on the photoelectrocatalysis of TNT was investigated, and the TNT-GR-CdS was used in the photoelectrocatalytical area. |
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