Study On The Morphology Control Of Novel Photocatalyst And Their Photocatalytic Hydrogen Production

Nowadays, the people are facing serious energy and environmental problems, and develope a clean and sustainable energy is an effective way to solve such problems. Hydrogen gas as an environmentally friendly fuel has been considered as one of the most important alternative energy carrier to replace fossil fuels. Photocatalytic hydrogen production from water splitting under solar irradiation is an attractive process to alleviate the global energy and environmental problems. However, many semiconductors (such as TiO2, CdS) are not efficient for water splitting due to the reasons such as large band gap, photocorresion and low quantum efficiency. To overcome these drawbacks, techniques such as doping, surface modification or exploring different hybrid semiconductor heterostructure have been used to improve the photocatalytic activity of these semiconductor materals. However, the problems such as narrow light response and low quantum efficiency still exist. Moreover, most photocatalytic water-splitting requires noble metal co-catalysts for photocatalytic hydrogen generation because noble metals can promote effective charge separation. However, using noble metals increases the cost of the catalyst and makes it unsuitable for large-scale production and application. Therefore, the direction of the photocatalytic water splitting is to develop a novel photocatalyst with high photocatalytic activity, which can perform an excellent hydrogen production under the condition of no noble metal.Due to the morphology of the photocatalyst play an important role in the photocatalytic acitivity, so the morphology control is a major aspect by the researcher. In recent years, the research on the morphology, crystal phase, electron lifetime, band gap, electron structure, defects and surface state of photocatalyst has caused great concern. The nano-materials with low-dimension structure and special morphology have caused the great interest of people due to it perform great activity in many fields. Therefore, developing a micro-nano materials with controlled morphology and dimension is an effective way to improving the efficiency of photocatalytic water splitting. In this paper, we prepared some photocatalysts with special morphology and efficient photocatalytic water splitting by different methods, and deeply discussed the preparation mechanism, the formation mechanism of the morphology and the connection between the morphology and the photocatalytic activity. The above analysis can provide the theoretical support for the developing a novel catalyst with enhanced catalytic activity. The following is the main research result.(1) It is discovered that the titanium phosphate with special morphology are capable of enhanced hydrogen evolution from solar water splitting under the condition of no noble metal cocatalyst. The content of phosphoric acid plays an important role in crystal phase and morphology of titanium phosphate. We have successfully prepared titanium phosphate with special morphology and different dimension, such as fibrous (one-dimension), layered (two-dimension) and flower like (three-dimension) titanium phosphate. The morphology formation mechanism and the photocatalytic water splitting mechanism have been deeply analyzed.(2) A novel ZnO/TiO2amorphous/crystalline heterostructure has been fabricated using a facile low-temperature (120℃) synthetic method, and this novel amorphous-based composite photocatalyst exhibits outstanding H2generation from solar water splitting in the absence of any noble metal co-catalyst. Moreover, the crystal structure of the ZnO/TiO2composite catalyst can be easily controlled by just adjusting the experimental parameters. For example:the crystal structure of the ZnO/TiO2composites will undergo an amorphous, amorphous/crystalline and crystalline transition by modifying the Ti/Zn ratio; The multiplicity of the ZnO/TiO2amorphous/crystalline heterostructure can be controlled by just adjusting the pH value, the amorphous increases with the increasing of the pH value; The BET surface area of the ZnO/TiO2amorphous/crystalline heterostructure can be controlled by adjusting the amorphous multiplicity, the BET surface area increases with the increasing of the amorphous. When the amorphous/crystalline heterostructure is the most obvious, the BET surface area can reach358m2g-1, and the photocaltalytic activity of the sample is the best.(3) A flower-like ZnO microsphere has been prepared in the room temperature by a normal temperature precipitation method; a columnar ZnO has been prepared by hydrothermal treatment. The photocatalytic activity of the flower-like ZnO microspheres is better than the columnar ZnO when the two kinds of ZnO used in the photocatalytic water splitting. The formation mechanism and the photocatalytic water splitting mechanism have been deeply discussed.