Study On The Controlled Synthesis Of Mesocrystal TiO₂-Based Micro-nanostructured Materials And Its Photocatalytic Hydrogen Production

In order to promote the application of solar water splitting hydrogen production technology,it is particularly important to build an efficient photocatalytic hydrogen production system.Ti O₂ has attracted much attention of researchers due to its excellent reactivity and stability under illumination,besides low toxicity and low price.However,its wide band gap is difficult to be excited by visible light,serious photogenerated carrier recombination,and high overpotential defects limit the further development and application of Ti O₂.Compared with traditional Ti O₂ materials,Ti O₂ mesocrystals,as a new type of porous material,not only retains the advantages of traditional Ti O₂,but also have good crystal plane orientation and high specific surface area of mesocrystal structure,and have more research potential in the field of photocatalysis.Supporting metal cocatalysts on semiconductor materials is an important means to improve their photocatalytic performance,and bimetallic cocatalysts have better synergistic effects,which can not only reduce the preparation cost but also have better photocatalytic hydrogen production activity than single metal cocatalysts,has recently received much attention.However,the simultaneous deposition method used by most bimetals is random,and close interfacial contact is usually not formed between metals.In this paper,a simple galvanic replacement method is used to deposit bimetallic cocatalysts on Ti O₂ mesocrystals step by step,and explore the the law of its photocatalytic hydrogen production activity,and the possible mechanism and hydrogen production mechanism were discussed in depth.The main research contents are as follows:（1）Using polyethylene glycol 400,H₂O and Ti Cl₃ as reactants,anatase Ti O₂mesocrystals with spindle morphology were prepared by solvothermal method,and their morphology and structural characteristics were explored through various characterizations.To further enhance its catalytic activity,Au-Pt bimetallic cocatalysts were deposited stepwise using chemical reduction and galvanic replacement methods,and XPS and TEM Mapping characterization results demonstrated the successful loading of the bimetallic structure.The optimal loading ratio of Au-Pt and the law of photocatalytic hydrogen production performance were explored,and the highest hydrogen production rate was21.0 mmol/g/h.The results showed that the Au-Pt bimetal had better catalytic activity than the single metal,and the performance was higher than that of the samples prepared by the simultaneous deposition method,which shows the advantages of bimetallic structure prepared by galvanic replacement method.Then,the photocatalytic hydrogen production mechanism was explored and analyzed through a series of photoelectrochemical characterizations.（2）Using the spindle-shaped anatase Ti O₂ mesocrystal as a carrier,in order to further improve the separation and transport efficiency of photogenerated carriers,Pt-Pd bimetals with high work function was deposited stepwise by chemical reduction method and galvanic replacement method.The successful loading of Pt-Pd was proved through a series of characterizations,and the optimal loading ratio and photocatalytic activity of Pt-Pd were explored,and the highest hydrogen production rate was 24.1 mmol/g/h.Photoelectrochemical tests showed that Pt-Pd/Ti O₂ has efficient charge transport and separation efficiency,effectively reducing the the recombination rate of photogenerated electrons and holes in Ti O₂ mesocrystal,and its photocatalytic mechanism was discussed.