Study Of Reaction Time On Microstructure And Properties Of TiO₂Thin Films Prepared By Hydrothermal Method

TiO2is an important wide band gap semiconductor which has a broad range of applications in photocatalysis, solar cells, water photoelectrolysis, self-cleaning and so on. For many of these applicatios, big specific surface area is crucial. Among these applications, the surface morphology of TiO2has direct and determined influences. So preparing different structures of TiO2has received considerable attention of current researches.In this study, TiO2thin films with different morphologies were prepared without any templates by hydrothermal method. The microstructure, composition, photoluminescence (PL), Raman properties and optoelectronic properties were investigated with X-ray diffractometer (XRD), scanning electron microscope (SEM),3D digital microscope, X-ray photoelectron spectrometer (XPS), micro-Raman spectroscope system and ultraviolet-visible spectroscope (UV-Vis). Methyl orange was used as a typical dye pollutant to estimate the photocatalytic activities of TiO2thin films. The influences of reaction time on microstructure, surface morphology, surface chemical composition, photoluminescence properties, Raman properties, transmission spectra, the values of band gap and photocatalytic activitivies were studied respectively. The main results are as follows:As the reaction time increases, anatase structure and brookite structure of TiO2films respectively increases and decreases, corresponding to surface morphology changes from irregular structure to regular geometrical shape structure then to one-dimensional nanowire structure, two-dimensional sheet structure, and three-dimensional nuts structure. These surface morphology changes are accompanied by significant variations of optical properties and photocatalytic properties including a widening of the band gap from2.86eV to3.24eV, photocatalytic degradation efficiency first decreases from96.59%to92.80%then increases to97.11%last decreases to96.41%and photocatalytic degradation rate first decreases from0.0436min-1to0.0350min-1then increases to0.0459min-1last decreases to0.0416min-1. Among all samples, TiO2film with6h reaction time shows the best photocatalytic properties and can be used as a promising photocatalyst for the practical application in photocatalytic decolorization of organic contaminants. Compositional analysis indicates that TiO2surface layer contains Ti and O elements, the ratio of Ti:O is1:2.28which is close to the atom ratio of TiO2.The PL spectra results reveal that TiO2thin films show strong luminescence in the visible area and the intrinsic luminescence is suppressed. The Raman spectra results display that the characteristic peaks of1h and2h TiO2films are mainly brookite structure, the characteristic peaks of3h TiO2film begins to show anatase structure, the characteristic peaks of4h,6h,12h and24h TiO2films are mainly anatase structure. It further improves that anatase structure and brookite structure of TiO2films respectively increases and decreases with increasing reaction time.The main innovations of this paper are as follows:1. This paper systematically studied the influences of reaction time on the microstructure, surface morphology and other properties TiO2thin films. It provides conditions to find the optimal process parameters.2. The surface morphology of TiO2films shows obvious changes with increasing reaction time and its formation mechanism is analyzed. It lays the foundation for subsequent modification of quantum dots sensitized work.