| The increasing global consumption of fossil energy sources,including coal,oil and natural gas,has triggered an unprecedented energy crisis.At present,the energy provided by fossil fuels accounts for about 85%of the total energy consumption of human society,and it is the raw material for almost all types of chemical production.The gradual depletion of fossil fuel reserves has raised serious concerns about future energy supply from all walks of life.In addition,the use of fossil fuels continues to emit "greenhouse gases" into the atmosphere,especially carbon dioxide(CO2),leading to a gradual increase in global temperatures.Global warming seriously affects the ecological balance and triggers extreme climates.Therefore,in order to curb the dependence of the existing energy structure on fossil fuels and CO2 emissions,it is imperative to exlpore green and sustainable alternative energy sources.Solar energy is considered one of the most valuable green energy sources.The sun continuously radiates enormous amounts of energy to the earth,yet existing technologies cannot store and use it efficiently.Most plants and algae can store solar energy by converting CO2 into carbohydrates through photosynthesis.Inspired by this,the researchers proposed artificial photosynthesis,which aims to convert CO2 and H2O into carbon-based fuels and oxygen for the conversion and storage of solar energy to chemical energy.In the CO2 reduction process of artificial photosynthesis,the synthesis and control of photocatalysts are the key.At present,although a lot of work has been done on photocatalytic reduction of CO2,there are great challenges in terms of reduction efficiency and product selectivity.Based on the above problems,in this paper,two-dimensional BiOCl nanosheets with atomic thickness were prepared by liquid phase exfoliation method,and their surface was further modified and modified to study their photocatalytic CO2 reduction performance.Taking ultrathin BiOCl nanosheets as the research object,combined with first-principles calculations,the structure-activity relationship between the two-dimensional nanosheet structure and the photocatalytic CO2 reduction performance was explored,and the understanding of the photocatalytic CO2 reduction mechanism was deepened.The two-dimensional nanomaterial photocatalyst provides a new idea.The main contents of this paper include the following aspects:1.The preparation of atomic-thick BiOCl nanosheets and study of their photocatalytic CO2 reduction propertiesWe successfully prepared atomically-thick BiOCl nanosheets by liquid exfoliation,and used them as research objects to explore quantum confinement,the influence of entanglement factors(such as size effect and defects)generated by exfoliation on the activity and selectivity of photocatalytic CO2 reduction.The oxygen vacancies in a-BiOCl were neutralized by ultraviolet/ozone(UVO)treatment,and the entanglement factors affecting the photocatalytic reduction of CO2 were investigated in detail to explore the role of a-BiOCl oxygen vacancies in the photocatalytic process.The results demonstrated that Oxygen vacancies can not only increase the yield of photoreduction products,but also improve the selectivity to CO formation.Meanwhile,the photoreduction CO2 yield is linearly correlated with the oxygen vacancy concentration,indicating the photocatalytic CO2 yield in an oxygen vacancy concentration-dependent manner in the atomically thick BiOCl nanosheets.This work may inspire more excellent work on the design of atomically thin 2D vdW photocatalysts.2.The BiOCl 2D nanosheet electronic structure layer-dependent properties and the CO2RR first-principle studyWe constructed(001)as the main exposed crystal plane and(200)as the lateral exposure by calculating the surface energy of the atomically thick BiOCl nanosheets The bulk and 2-layer BiOCl analytical models.At the same time,calculating the chemical potentials of Bi,O and Cl,and analyzing the defect structure proved that the surface oxygen vacancies have the lowest formation energy and the most stable form in the(200)crystal plane.Based on the theoretical calculations,it is implied that the oxygen vacancies formed on the BiOCl side crystal plane(200)during the exfoliation process are the main reason for the excellent photocatalytic CO2 reduction performance of the catalyst.Further,the in situ FTIR spectroscopy of the photocatalyst indicates that the abundant CO*stable configuration formed in a-BiOCl,which is responsible for the high CO yield and selectivity.Combined with theoretical calculations,it is shown that the weak p-σ bond of Bi-CO-Bi geometry in atomically thick BiOCl nanosheets is responsible for the improved CO yield and selectivity.This work provides theoretical support for the design of two-dimensional photocatalysts for the next photocatalytic reduction of CO2.3.Promoted Photocarriers Separation in Atomically Thin BiOCl/Bi2WO6 Heterostructure for Solar-Driven Photocatalytic CO2 ReductionExploring efficient strategies to promote photocarrier separation remains a challenge in solar energy conversion processes.Herein,we construct a novel atomically thin BiOCl/Bi2WO6 heterostructure to enhance photocarriers separation via the internal electric field at the heterointerface.The resultant atomically thin BiOCl/Bi2WO6 heterostructure exhibits superior photocatalytic CO2 reduction activity with a CH4 evolution rate of ca.6.63 μmol g-1 h-1 and 82.9%in selectivity under simulated sunlight irradiation without sacrificial reagent.The experimental characterizations highlight that the atomically thin heterostructure endow BiOCl/Bi2WO6 with an enhanced CO2 uptake capability and improved interfacial charge transfer behavior.Further theoretical calculations demonstrate the charge separation in BiOCl/Bi2WO6 heterointerface,and confirm the generation of stable CO*adsorption geometry as well,which accounts for the photoreduction selectivity of CH4.This work is expected to provide inspiration for preparing other 2D atomically thin heterostructures employed in the solar energy conversion field. |
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