| As the environmental pollution and energy crisis become more and more serious,it is urgent to develop sustainable and renewable clean energy to replace traditional fuels.Photocatalytic hydrogen evolution reaction is the decomposition of water to produce clean hydrogen energy through the photocatalysis,which converts sustainable solar energy into chemical energy.Hence,it is expected to solve global energy and environmental problems.However,the hydrogen evolution efficiency of photocatalysts is low at present,which cannot meet the needs of practical applications.Therefore,the development of photocatalysts with efficient hydrogen production has important significance.Since 1972,titania has been considered as a photocatalytic material with great potentials.However,titania has the shortcomings of low light utilization and easy recombination of electron-hole pairs.In order to solve these problems,I modified the titania nanospheres by adjusting the morphology,doping transition metals and compounding with semiconductors in this thesis,and studied their photocatalytic hydrogen evolution performance.The specific research contents are as follows:（1）A simple method for preparing mesoporous titania nanospheres（mTiO2）was developed,and the principle of forming mesoporous structure and the performance of photocatalytic H2 production about mTiO2 were investigated.Under hydrothermal conditions at 180℃,hexadecylamine is continuously decomposed,causing a large number of pores in the solid titania nanospheres（TiO2）and thereby giving rise to mesoporous structures.It increases the specific surface area of the nanospheres and provides more active sites for photocatalytic reaction.Moreover,the prepared mTiO2 has good crystallinity,high light utilization and photo-generated carriers separative efficiency.When 3 wt.%Pt is used as the co-catalyst,the photocatalytic hydrogen production rate of mTiO2 can reach 13.8 mmol g-1 h-1,which is 14.9 times that of TiO2.（2）Transition metal（M:Fe,Co,Ni,Cu）doped mesoporous TiO2 nanospheres（MmTiO2）were successfully prepared by solvothermal method,and their performance of photocatalytic hydrogen production was studied.The prepared M-mTiO2 has a mesoporous structure and the doped metal elements are evenly distributed.Cu-mTiO2 has the highest photocatalytic H2 production rate of 3.68 mmol g-1 h-1,which is 27.3 folds that of pure mTiO2.Cu+ is the active site of photocatalytic hydrogen production of CumTiO2.Further study indicated that the superior photocatalytic performance of Cu-mTiO2 originates from the special photoactivation process.During photoactivation,Cu+ is reduced and Ti4+ is reduced to Ti3+.The reduction of metal ions facilitates the adsorption of hydrogen atoms,which greatly improves the performance of photocatalytic hydrogen evolution.（3）I prepared titania nano-shell（h-TiO2）and graphite carbon nitride（CN）composite materials（h-TiO2/CN）were prepared,and demonstrated the enhancing photocatalytic performance by use of the field enhancement effect of the dielectric resonator.The high refractive index TiO2 can generate strong electric and magnetic field enhancement inside and at the near region of surface.The nano-shell structure can maximize the application of the field enhancement.The h-TiO2/CN is obtained by the polymerization of dicyandiamide molecules inside and outside h-TiO2 to form CN,and its highest photocatalytic hydrogen production rate can reach 6.3 mmol g-1 h-1,which is about 3 times that of pure CN.The study found that the Z-scheme structure cannot be formed and the separated efficiency of photogenerated carriers has not been improved in h-TiO2/CN,so neither of them is the reason for improvement of photocatalytic efficiency.Further,the mechanism of photocatalytic efficiency improvement is proposed through experiments and theoretical calculations.The strong electric and magnetic field enhancement of the hTiO2 dielectric resonator improves the light absorption of CN and the utilization rate of light for CN. |
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