Study On The Preparation Of Functionalized Porous Materials And Their Application To Photoelectrocatalytic Reduction Of CO₂

Human productivity has been greatly improved with the development of the world economy,meanwhile,it has led to many negative problems such as environmental pollution,ecological destruction and energy shortage,which have severely restricted the development of mankind and future generations.More than 80 per cent of global energy consumption comes from fossil fuels such as coal,oil and natural gas.However,the excessive consumption of fossil fuels causes a large amount of CO2 emissions,leading to climate warming and other serious environmental problems.Therefore,the development of clean,renewable energy is the basic strategy and fundamental approach to solve the human crisis and the world economy development.Solar energy is the most important basic energy among all kinds of renewable energy and the most abundant energy available to human beings.On the basis of maintaining the balance of carbon cycle,solar energy can be effectively utilized to promote the conversion of carbon dioxide to hydrocarbons,achieve sustainable carbon recycling and turn waste into treasure,which is undoubtedly a strategic breakthrough to solve the energy crisis and environmental pollution.Photoelectrocatalytic reduction of CO2 to valuable hydrocarbons is one of the most efficient way to not only mitigate the greenhouse effect and reduce CO2 emissions,but also ensure the balance of the global carbon cycle by utilizing the inexhaustible solar energy resources.Developing efficient and reasonable catalysts is the key to achieve this target.In recent years,researchers have invested a lot of spirits in the development and utilization of catalysts.Functionalized porous materials have been widely used in various catalytic fields because of their large specific surface area,regular pore structure and efficient catalytic activity.At present,the utilization of porous materials mainly focuses on the capture and storage of CO2,and the application in the CO2 reduction is very limited.Based on the above analysis,this thesis intends to design and synthesis of new effective functional porous materials applied to the photoelectrocatalytic reduction of CO2.So different types of porous materials were prepared,using its structure characteristics,through the surface modification,skeleton doping,organic functionalization methods introducing the catalytic active component,improve its catalytic activity,in order to develop the performance of CO2 reduction catalysts,improve the efficiency of photoelectrocatalytic reduction of carbon dioxide.(1)Covalent organic framework COFs crystal porous material:In this chapter,a series of novel and efficient porphyrin-COFs deposited with copper are designed and prepared.The structure and properties of these materials are characterized by various means,and the catalytic efficiency of these materials in photoelectrocatalytic reduction of CO2 is investigated.The results show that Cu@porphyrin-COFs/CF photocathode shows a three-dimensional structure and excellent catalytic activity.The introduction of hydroxyl group and the deposition of copper increase the migration rate of photogenerated electrons and effectively inhibit the recombination of photogenerated electron-hole pairs.When the applied voltage is-0.8V(vs.SCE),the AFE of Cu@[OH]H2P-COF/CF is 452.75%.On the other hand,DFT calculation shows that intramolecular hydrogen bond is formed in[OH]-H2P-COF,which makes the molecule more stable,thus improving the catalytic performance of photocathodes.(2)Functionalized Ti-MCM-41 ordered mesoporous materials:In this chapter,a series of titanium-doped Ti-MCM-41 with different Si/Ti ratios were designed and prepared,APTES and salicylaldehyde were functionalized into the inner and outer surfaces of Ti-MCM-41 by post-grafting method.The functionalized mesoporous materials were applied in the study of photoelectrocatalytic catalytic reduction of CO2 and their performance were investigated.The results showed that the functionalized mesoporous materials S-Ti-MCM-41-X with different titanium contents showed excellent catalytic activity for photoelectrocatalytic reduction of CO2 and produced valuable C2+ products such as ethanol and acetone,which effectively promoted C-C coupling.At the applied voltage of-1.2V(vs.SCE),the total hydrocarbons formation rate of S-Ti-MCM-41-50 is 193 ?m·cm-2·h-1.At the applied voltage of-1.0V(vs.SCE),the selectivity of C2+ hydrocarbons of S-Ti-MCM-41-20 is 88%.(3)Functionalized SBA-15 ordered mesoporous materials:In this chapter,by adjusting the reaction conditions and surfactant,mesoporous materials SBA-15 with different morphology and channel structure have been synthesized.By appling surface grafting functional assembly,the organic functionalized mesoporous materials NH2SBA-15 and S-SBA-15 have been prepared.The organic functionalized mesoporous materials apply to the study of photoelectrocatalytic reduction of CO2,explores the morphology and structure of the channel's influence on the catalytic reduction of CO2.The results showed that the fibrous functionalized mesoporous material SBA-15(r)with the characteristics of bimodal pore systems promoted the diffusion and transport between CO2 molecules and reactants by its large specific surface area,abundant pore space and catalytic active center,and effectively improved the efficiency of CO2 reduction.When the applied voltage is-0.6 V(vs.SCE),the AFE of S-SBA-15(r)is 152.18%,the C2 hydrocarbons formation rate of NH2-SBA-15(r)is 51.9 ?M·cm-2·h-1,and the selectivity of C2 hydrocarbons is 86.57%.The source of the above products was confirmed by 13C labeling experiment,and they were all from the products of CO2 reduction rather than external introduction.It is proved that the functional porous materials have high catalytic activity in photoelectrocatalytic reduction of CO2,which is a kind of catalytic materials with signifcantly potential.This work provides a new method and approach for its application.