Operando Nuclear Magnetic Resonance Study Of Surface Photocatalytic Processes On The Surface Of Solid Photocatalyts And Development Of Novel Materials And Devices For Photocatalysis

The energy crisis and environmental pollution are regarded as two major social problems facing humanity in today's world.The semiconductor-based photocatalysis has good prospects to produce clean energy sources and deal with environmental issues by using the inexhaustible solar energy.In this thesis,the photocatalytic mechanism,devices,and new materials were investigated.In Chapters 2 and 3,an operando NMR technique was employed to study the methanol reforming reaction on TiO₂.In Chapter4,we attempted to make TiO₂ photocatalytic devices.In Chapter 5,we designed a novel amorphous photocatalyst based on g-C₃N₄.The main contents are as follows:1.In Chapter 2,an operando NMR technique was proposed to systematically study the effects of photon flux and photon energy on TiO₂ and Pd/TiO₂-based photocatalytic methanol reforming reactions.The photon flux had different effects on the productivity of the methanol oxidation reaction based on TiO₂ and Pd/TiO₂ catalysts within a limited range of optical power density.In the wavelength range of 350-400 nm,it was found that short wavelengths?higher photon energy?can accelerate the methanol reforming reaction.Meanwhile,a significantly enhanced activity in CH₃OH oxidation was found at 380 nm compared to that at 365 nm.This enhanced oxidation activity can be attributed to the surface plasmon resonance?SPR?effect of the cocatalyst Pd.2.In Chapter 3,the strong metal-support interaction?SMSI?in Pt/TiO₂ catalyst was studied by the operando NMR technique.By introducing gas molecules,the active reaction sites on the TiO₂ and Pt/TiO₂ surfaces were explored in detail.It has been discovered that the gas molecules?H₂,N₂,and CO₂,etc.?can be absorbed at Ti_5c sites on the surface of TiO₂.After loading precious metal Pt,the adsorption and reaction sites of CH₃OH were transferred from Ti_5c to metal Pt or the interface between metal Pt and TiO₂,thereby maintaining the catalytic efficiency.3.In Chapter 4,the photocatalytic devices based on TiO₂-hydrogel were developed.The devices were prepared by dispersing the TiO₂ powder in the hydrogel.The introduction of hydrogel can not only provide the possibility of recycling photocatalyst,but also improve the adsorption capacity of organic dyes.The results showed that the TiO₂-hydrogel devices have good performances in the photodegradation of rhodamine B.Meanwhile,the regeneration process of the device is very simple.The strategy in this chapter may guide the design of recyclable photocatalytic devices.4.In Chapter 5,we attempted to prepare novel photocatalysts based on the understanding of the photocatalytic mechanisms.A series of amorphous,novel noble metal-free photocatalysts,C₃N₄Zn_xO_y?x,y=0.32-1.10?,were successfully synthesized.The crystallinity of the samples can be adjusted by changing the ratio of urea and ZnO.The results of FTIR,XPS,and ssNMR showed that with the increase of ZnO content,a structure similar to g-C₃N₄ existed in the amorphous sample.Under visible light irradiation,the degradation efficiency of tetracycline hydrochloride by the completely amorphous sample was greatly enhanced compared to the g-C₃N₄ sample.The results revealed that the improvement of the photocatalytic efficiency is related to the short-range ordered structures.In summary,in this thesis the operando NMR technique was used to systematically study the photocatalytic methanol reforming reactions on the surface of TiO₂.We discussed the effects of photon flux and photon energy on photocatalytic reactions,analyzed the relationship between the reaction sites and the products,and explained SPR and SMSI.Then we made TiO₂-hydrogel photocatalytic devices.Finally,we designed and prepared a novel highly efficient amorphous photocatalyst.The results in this thesis may help further understand the photocatalytic mechanisms,and can guide the design and development of novel photocatalysts and devices.