Preparation And Property Characterization Of TiO₂ Catalyst For Solar Energy Photo-hydrolysis

Hydrogen energy is a clean, high effective and renewable energy. It is an important way among others to solve the global energy crisis worsening gradually by manufacture of hydrogen using the abundant accessible solar energy and water sources. In this article, the nano-TiO₂, a photocatalytic material of environment protective type with promising development prospect, was used as a photocatalyst in photo-hydrolysis. The catalytic properties were studied in order to provide a high effective and feasible method for generating hydrogen utilizing the solar energy.In the study of sample preparation, the nano-TiO₂ doped with Fe3+ was prepared using the Sol-Gel method and was loaded with the metal Pt. Modern analysis methods such as XRD, SEM, DTA and the like were used to study the relationship between the structure, composition and photocatalytic properties of the samples prepared and the preparation conditions.A light-yellow homogeneous transparent sol was obtained by the hydrolysis-polycondensation reaction using butyl titanate as the precursor, anhydrous ethanol as the solvent and nitric acid as the catalyst. The sol was further reacted to give an opaque gel after removing large portion of the ethanol solvent. Following the continuous warming and drying, the gel was heated to the designated temperature in a Muffle Furnace for 2 h to give TiO₂ particulates of different grain sizes.The XRD pattern analysis indicated that the roasting temperature has a decisive effect on the phase composition of the prepared sample. Among the samples roasted for 2 h at 400°C, 450°C and 600°C respectively, the sample obtained after roast at 400°C is a pure anatase nano-TiO₂, the XRD pattern of which has only the diffraction peaks of the anatase; in the XRD pattern of the sample obtained after roast at 450°C, the diffraction peaks of the rutile appear indicating that a portion of the anatase nano-TiO₂ has been converted into the rutile nano-TiO₂; and for the sample obtained after roast at 700°C, most of the diffraction peaks are from the rutile indicating that most of the anatase TiO₂ have been converted into the rulile nano-TiO₂.The doped ion Fe3+ promotes the phase conversion of the nano-TiO₂ from the anatase into the rutile. Furthermore, the small amount of Fe3+doping has a inhibition effect on the growth of grain particle size.SEM analysis showed, after the doping of 1% Fe3+, the sample particulates are largely in the shape of sphere and have good dispersity. With the increasing of the ion concentration of the doped Fe3+, the particulate reunion phenomenon increases obviously. The laser analysis of particle size showed that the range of the particle size distribution widens as the doped Fe3+ concentration increases, and the minimum range of the nano-TiO₂ particle size distribution was obtained when doping 1% Fe3+, which is mainly between 0.5 and 0.7μm.Proper amount loading of Pt may achieve the formation of micro-electrode on the nano-TiO₂ particulate surface which facilitates the improvement of the catalytic properties. However, if overloading, the particulate surface might be covered, thereby affecting the catalytic properties.The parameters of preparation process have a great influence on the photocatalytic properties. The orthogonal test showed the maximum catalytic activity of the nano-TiO₂ was obtained at 400°C with doping 3% Fe3+ and loading 2% Pt. The hybrid crystalline form of anatase and rutile has a higher activity than that of the pure rutile nano-TiO₂.The photocatalytic property of the TiO₂ modified by optimizing the doping-loading ratio is improved remarkably. The utilization efficiency of light energy is increased greatly. This study is successful in that the hydrogen generated under the same test conditions within the same time period is ten times more that generated using untreated TiO₂.