Active Site Fabrication And Catalytic Mechansim Investigation Of Bismuth-Based Photothermal Catalyst For CO₂ Reduction

Solar-powered conversion of carbon dioxide（CO₂）into fuels and industrial feedstocks with H₂O as a proton/electron donor is deemed as one of the ideal strategies for addressing the problems of global warming and energy shortage.Developing the photocatalytic materials with photothermal effect can achieve thermally-assisted photocatalytic CO₂reduction reaction by the integration of thermocatalysis and photocatalysis through the broadband light absorption across the whole solar spectrum to,affording a green and sustainable strategy for CO₂conversion.In recent years,some achievements have been made on thermally-assisted photocatalytic CO₂conversion,but remarkable problems remain with respect to activity and product selectivity.Especially,the production of multicarbon(C₂₊)chemicals from CO₂photoreduction is greatly challenging.Therefore,it is crucial to develop the materials with both high photothermal conversion efficiency and excellent photocatalytic performance for enhancing the activity and selectivity towards C₂₊production.Some bismuth-based semiconductors present photochromic property（e.g.,Bi OCl）or intrinsic dark colors（e.g.,Bi₂S₃）,which have great potential for photothermal conversion.Moreover,the bismuth-based semiconductors are widely used in photocatalysis owing to their convenient synthesis,low cost and adjustable band structure.However,the CO₂reduction products from bismuth-based photocatalysts are generally limited to C₁compounds（e.g.,CO and CH₄）.The photothermal effect of these bismuth-based photocatalysts is often neglected in CO₂photoreduction.Based on the above problems,in this thesis,the specific active sites were constructed on Bi OCl and Bi₂S₃which have distinct photothermal conversion properties by introducing heteroatoms and constructing heterointerfaces,respectively,to improve the activity and selectivity of thermally-assisted photocatalytic CO₂reduction reaction,especially for the C₂H₄production with high selectivity.The main research contents of this thesis are summarized as follows:1.A sulfur-doped Bi OCl（S-Bi OCl）nanosheet photocatalyst was developed via a one-step solvothermal method,which could promptly develop a black color and reach a high temperature（～200°C）under the illumination of simulated sunlight.The thermally-assisted photocatalytic performance for H₂O-assisted CO₂reduction to CO was greatly improved on the S-Bi OCl catalyst,furnishing a CO production rate of49.76μmol g_cat^-1h^-1with 100%selectivity under simulated sunlight.The H₂O-assisted CO₂reduction reaction on S-Bi OCl catalyst was triggered by photoexcited charge carriers and meanwhile accelerated by the photothermal effect.The kinetic isotope experiments indicated that the sluggish H₂O dissociation affected the whole photocatalytic CO₂reduction process.Both experimental and theoretical investigations affirmed that oxygen vacancies could promote the adsorption and activation of H₂O molecules,and the doped S sites played a crucial role in boosting H₂O dissociation and accelerating the dynamic migration of hydrogen species.As a result,the ingenious integration of O_Vdefects,S sites and photothermal effect in S-Bi OCl catalyst conjointly contributed to the significant improvement in thermally-assisted photocatalytic CO₂reduction performance.This study provides some new insight into developing the efficient thermal assisted photocatalytic CO₂conversion by the reasonable construction of catalytic sites for H₂O assisted CO₂reduction reaction.2.On the basis of the significant improvement of the thermally-assisted photocatalytic CO₂reduction efficiency,it is more important to achieve the C₂₊production with high yield and selectivity.We developed the Bi₂S₃@In₂S₃heterostructure catalyst via one-step solvothermal synthesis.This catalyst exhibited a prominent light-harvesting ability in the whole solar spectrum and a high separation efficiency of photoinduced charge carriers.Bi₂S₃could serve as a photothermal material to increase the surface temperature of Bi₂S₃@In₂S₃catalyst under light irradiation and the unique In-S_V-Bi active centers were formed by the adjacent Bi and In atoms regulated with sulfur vacancies at the heterointerfaces.The high activity and selectivity of H₂O assisted CO₂conversion to C₂H₄were achieved on the Bi₂S₃@In₂S₃catalyst under a simulated sunlight without extra heat input,furnishing C₂H₄product with an evolution rate of 11.81μmol g_cat^-1h^-1and the selectivity near 90%.DFT calculations unveiled that the In-S_V-Bi active sites formed at the heterointerface of Bi₂S₃@In₂S₃catalyst were pivotal to the formation of*OCCO intermediate from*CO dimerization owing to the appropriate distance and asymmetric charge distribution between In and Bi atoms.A series of control experiments and in-situ spectroscopic analyses indicated that the CO₂conversion performance of Bi₂S₃@In₂S₃catalyst was attributable to the thermal-assisted photocatalysis where the photocatalysis triggered the reaction and the elevated temperature from photothermal effect kinetically promoted the C-C coupling for C₂H₄production.Therefore,the ingenious combination of In-S_V-Bi active sites and photothermal effect in Bi₂S₃@In₂S₃catalyst resulted in the high performance for CO₂conversion to C₂H₄.The findings shed some light on the construction of efficient photothermal catalyst for the solar-powdered conversion of CO₂into multicarbon products.