Construction Of BiOCl-based Nanomaterials And Their Photocatalytic CO₂ Reduction

Since the industrial revolution,due to the accelerated development of heavy industry,mankind has faced serious environmental pollution and exhaustion of natural resources.Among them,the large-scale use of fossil fuels with high energy density leads to an explosive increase in CO2 emissions to the atmosphere,which is considered to be the main cause of global warming.How to effectively slow down and control CO2 emissions and make further use of them to achieve "carbon neutrality" has become an urgent problem for all countries in the world.Solar energy is widely regarded as a kind of clean,abundant and free renewable energy,providing about 120,000 TW of energy to the earth every year.Collecting and storing solar energy in the form of abundant CO2 as a chemical fuel can not only solve the problem of carbon emissions,but also meet energy needs,which is of great significance to the development of society.Therefore,CO2 photoreduction that mimics natural photosynthesis represents a clean,carbon-neutral and sustainable strategy.Bismuth oxychloride(BiOCl)is a typical ?-?-? ternary compound,which has application value in many fields.In recent years,as one of the most intensively studied photochemical materials,BiOCl has made outstanding contributions in the field of photocatalysis due to its unique layered structure and optical properties.However,such a cheap and abundant material still has great limitations,such as a wide band gap,resulting in insufficient visible light response and unable to make full use of sunlight,greatly reducing the application value of the material.In order to solve this problem,this paper uses a variety of methods to modify BiOCl,and studies the relationship between the properties and the internal structure of the material.The specific work is as follows:(1)Using the bubble template method to synthesize BiOCl nanospheres stacked from many nanosheets,use sodium borohydride to treat them,introduce oxygen vacancies and load Au nanoparticles,and prepare a series of Au/BiOCl heterojunction photocatalysts with different proportions.Under visible light irradiation,the yields of CO and CH4 on the 1.0%-Au/BOC composite photocatalyst can reach 13.02 and 1.90 ?mol·g1·h-1,respectively,which are 8 and 5 times than that of BOC(CO:1.56?mol·g-1·h-1,CH4:0.34?mol·g-1·h-1).Using Au nanoparticles to absorb visible light,the high-energy hot electrons generated by the SPR effect can increase the number of electrons participating in the CO2 reduction reaction,thereby increasing the utilization rate of light and speeding up the reaction rate.Calculating the work function of BiOCl and Au by DFT theory can verify the formation of ohmic contact,which is beneficial to the separation of photogenerated carriers.Through in situ FTIR spectroscopy,the reaction mechanism of CO2 reduction is proposed.(2)A series of Ag/Ag2O/BiOCl photocatalysts were prepared by loading Ag/Ag2O onto BiOCl nanospheres through chemical reduction method and introducing oxygen vacancies.Under simulated sunlight,the yields of CO and CH4 over the 4-Ag/Ag2O/BOC composite photocatalyst can reach 30.69 and 15.98 ?mol·g-1·h-1,respectively.It is 4.7 and 5.3 times of BOC(CO:1.56 ?mol·g-1·h-1,CH4:0.34 ?mol·g-1·h-1).In addition to using the SPR effect of Ag nanoparticles to enhance the visible light absorption capacity of the photocatalyst,an Ag2O/BOC p-n heterojunction was also synthesized,which not only increases the number of electrons participating in the reaction,but also improves the separation capability of photogenerated carriers.Through in situ FTIR spectroscopy,the reaction mechanism of CO2 reduction is proposed.(3)A series of Bi0/OVs-BOC photocatalysts were prepared by heat-treating BiOCl in N2 atmosphere to generate OVs and Bi0 nanoparticles in situ from the BiOCl lattice.The synergistic effect of non-noble metal Bi0 nanoparticles and OVs makes the Bi0/OVsBOC photocatalytic rate significantly increase.Especially BOC-250 performs best in CO generation(24.82 ?mol·g-1·h-1),which is almost four times than that of BOC.In addition,no CH4 generation is detected,and the selectivity to CO reaches 100%,Due to the presence of OVs and Bi0 nanoparticles,the light utilization efficiency and charge separation ability of the photocatalyst have been significantly improved.Through DFT calculation,it can be concluded that the reaction energy of Bi0/OVs-BOC is reduced,the adsorption energy of CO is weakened,and the suitable adsorption energy of H and OH leads to the highly selective formation of CO.