Study On AuNPs Size Effect Of Hot Electron Injection Efficiency Of Au/TiO₂

Hot electron injection refers to the process in which the electrons in the noble metal micro-nano structure absorb external energy and move to higher-order energy levels,cross the Schottky barrier created by the contact between the noble metal and the semiconductor,and reach the conduction band of the semiconductor.The hot electron injection effect can not only broaden the light response range of traditional semiconductors,but also suppress the recombination of electron-hole pairs in semiconductors.Therefore,the hot electron injection effect is widely used in research fields such as photocatalysis and photodetection devices.Research on how to improve the injection efficiency of hot electrons is of great significance to the development of these fields,among which the size of the noble metal nanoparticles is an important influencing factor.In this thesis,taking Au-TiO₂ photocatalyst as an example,the influence of AuNPs size on the hot electron injection efficiency and surface potential difference is studied from two aspects:simulation calculation and KPFM surface potential characterization.In addition,this thesis also studied the effect of AuNPs size effect on the photocatalytic performance of plasma photocatalyst TiO₂-ZnO-Au.The specific work is as follows:First,based on the classic Fowler theoretical model,considering the hot electron lifetime theory,a set of calculation model for quantifying the hot electron injection process was established,and the effect of AuNPs size on the hot electrons of Au-TiO₂ is simulated.The results show that the hot electron injection efficiency decreases as the size of AuNPs increases.Using finite element software to obtain the surface electric field distribution of AuNPs with different particle sizes under visible light,combining and improving the theory of Schottky junction solar cells,the simulation calculated the influence of AuNPs size effect on the contact potential difference between Au and TiO₂.It is found that AuNPs with a radius of 5 nm have the highest potential difference of the gold half-contact.Secondly,AuNPs solutions of different particle sizes were synthesized by the sodium citrate reduction method,and Au-TiO₂ samples with gold nanoparticles of different particle sizes were prepared by the 3-mercaptopropionic acid solution self-assembly method.KPFM was used to characterize and analyze the surface potential of Au-TiO₂samples with gold nanoparticles with different diameters under visible light.The results show that gold nanoparticles with a radius of 25 nm have the highest surface potential（～200 m V）.Finally,TiO₂ and ZnO sol were synthesized by sol-gel method,and then spin-coating method and self-assembly methods were used to prepare TiO₂-ZnO-Au plasma photocatalyst samples with gold nanoparticles of different sizes.The effect of AuNPs size on the photocatalytic performance of the plasma photocatalyst was further explored through the photocurrent response test and the visible light degradation experiment of methylene blue.The results show that the TiO₂-ZnO-Au sample with gold nanoparticles with a radius of 5 nm has the best photocatalytic performance（degradation rate reached 73% in 10.5 hours）.