Self-Assembly Films Of Anatase TiO₂Nanocrystals From Organic Acid Peptization And Their Photoelectrochemical Properties

TiO2sols have been seen as one of the most useful inorganic materials since they can be more conveniently used than the solid TiO2nano-materials, such as TiO2nanoparticles and TiO2thin films. The stability and dispersity are always used to estimate the characteristics of the sols, which will affect their prosperities in the application. Therefore, the researches about TiO2sols still focus on the preparation of the highly dispersed TiO2sols. In this study, the anatase TiO2sols were synthesized by a peptization-hydrothermal process. Moreover, the TiO2thin films were prepared by self assembly technique through the "bottom-up" method. The applications of TiO2thin films in the fields about the determination of chemical oxygen demand (COD) and the fabrication of dye-sensitized solar cells (DSSCs) were systematically investigated as well.Anatase TiO2sols with high dispersity and stability were prepared by the peptization of amorphous precipitates in trifluoroactic acid (TFA) solution. The crystallite size of TiO2in the sols was tuned by the subsequently hydrothermal treatment. In order to investigate the photocataltic activities of the TiO2in sol and remove affection of the organics on the surface of the TiO2in photocatalysis. The dried TiO2sols were calcined at500℃for2h, and the degradation of phenol proved that the photocatalytic activities of the obtained TiO2nanoparticles. The nanoparticles obtained from the sample Ti/8TFA-2had shown a better photocatalytic activity than that of the commercial TiO2nanoparticles.The positive charged nanoparticles in the sol Ti/8TFA-2and the poly(styrene sulfonic acid) sodium salt (PSS) solution were used to prepare TiO2/PSS thin films by a layer-by-layer (LBL) self-assembly technique, and the compact TiO2thin films were obtained after calcination at500℃.The TiO2LBL thin films were introduced to be working electrodes in three-electrode photoelectrochemical cells. The15-layer TiO2thin film electrode showed the highest photoelectrochemical property and it was employed as a sensor for the chemical oxygen demand. The detection limit of1.0mg-L"1with a working range of0-130mg-L"1was achieved. The results demonstrated the practicability of the photoelectrocatalysis for COD determination through the LBL TiO2thin film electrodes.Since the TiO2nanocrystals in the sol were easy to sinter, the dried sol was calcined at300℃for1h to eliminate the organics over the surface of TiO2and increase the crystallite size of the TiO2nanocrystals (the special surface area of the calcined TiO2decreased from224.7m2/g to94.9m2/g) to prepare the paste for the porous layer of DSSCs. The compact layer was prepared by the diluted sol through the layer-by-layer self assembly technique to control its thickness. Compared with the DSSCs without the compact layer, the cells with the LBL compact layers showed improved photovoltaic properties. In order to further enhance the photovoltatic properties of the DSSCs, the photoanodes with compact films were also modified by the TiO2sol through the post treatment, and finally the photoelectron conversion efficiency of the modified DSSC had increased to7.87%. The treatment with the TiO2sol was a better way for the modification of DSSC photoanodes than the traditional treatment through a TiCl4solution, which also showed the great potential in the application of the preparation and modification for the DSSC photoanodes.The flexible transparent conductive oxide (TCO) substrates are always with a low thermal stability at high temperature, and the thin films can not prepared on them through the traditional methods.The all-nanoparticle self-assembly technique was used in this study to solve this problem. The all-nanoparticle TiO2thin film was prepared by the crystallized TiO2nanoparticles in sol and the commercial TiO2(P25) through the layer-by-layer self assembly method. The TiO2films were applied in water quality assessment and the fabrication of DSSC photoanodes. They had showed the high photocatalytic properties in water quality assessment, but the photoelectron conversion efficiencies of DSSCs with the all-nanoparticle TiO2thin film photoanodes were low. The highest photoelectron conversion efficiency of flexible DSSC with the all-nanoparticle TiO2thin film photoanode just arrived to1.09%. Moreover, the results demonstrated the practicability of the all-nanoparticle assembly technique in DSSC and presented a brand new way to fabricate the TiO2films on flexible TCO substrates.