The Study Of External Field Controlled Surface/Interface Electronic State And CO₂ Photocatalytic Performance For Transition Metal Oxides

Energy demand and environmental demand are the key issues and long-term contradictions in the development of human society.The photocatalytic conversion of CO₂ simulates the photosynthesis in nature.From the environmental point of view,it can alleviate the current difficult greenhouse effect.From the energy point of view,it can turn waste into treasure land and convert CO₂ into high value-added low-carbon energy.Therefore,it has been widely concerned by scientists at present.However,the photocatalytic conversion of CO₂ is a complex,multi electron and multi-channel reaction.So far,the improvement of the yield of CO₂ photocatalytic products and the control of the selectivity of special products are still challenging scientific research topics in the world.In order to solve these problems,we need to design our catalysts from the perspectives of kinetics and thermodynamics.From the kinetic point of view,the coordination environment of the active atoms and the bond length of the catalyst all affect the adsorption mode of CO*which is an important intermediate of the catalyst.As a result,CO*either undergoes hydrogenation,or desorbs on the surface of the catalyst to form CO product,or CO*undergoes C-C coupling to form multi carbon products.On the other hand,from a thermodynamic point of view,the catalytic conversion of CO₂ competes with the hydrogen production of water.In this paper,transition metal oxides are taken as the research object.Focused on the use of new field precision synthesis means,such as magnetic field induced synthesis,we rationally design and control the electronic states（electron orbital control,crystal defect control,crystal facet and crystal phase control）at the surface of transition metals.By means of synchrotron radiation,in-situ infrared,theoretical calculation and other methods,we build bridge of the electronic structure and CO₂ catalysis performance.The study explained the structure-activity relationship from the atomic level,which provided a new synthesis method for the accurate synthesis of inorganic catalysts and more theoretical guidance for the mechanism of CO₂ photocatalytic conversion.The main contents of this paper are as follows:1、Design W₁₈O₄₉/Cu₂O{111}interface to inhibit CO*desorption in CO₂photocatalysisThe CO₂ photocatalytic conversion technology has the potential to simultaneously solve the greenhouse effect and the promoting of carbon resources.However,the long-term resistance of this technology is the diversity of conversion products caused by multiple intermediate reaction pathways.In this study,Cu₂O was selected as the research object,and the W₁₈O₄₉/Cu₂O{111}composite interface containing different Cu₂O{111}crystal facet exposure ratio was controllably synthesized through the hydrothermal synthesis method.The crystal structure and energy band structure of the composite interface can inhibit the key intermediate CO*desorption in CO₂photocatalytic conversion and realize the controllable adjustment of CO₂ photocatalytic products of CH₄ and CO,which improve the selectivity of CO₂ photocatalytic conversion to CH₄.The yield rate of the photocatalytic conversion of CO₂ to CH₄ was6.5μmol g^-1h^-1.In addition,we also used density functional theory（DFT）and insitu FTIR to clarify the pathway of the key intermediate CO*and the mechanism of CO₂photocatalytic conversion in the process of CO₂ photocatalytic conversion.This study confirms the versatility of interface engineering in regulating reaction pathways and provides a new idea for the realization of highly selective CO₂ photocatalytic conversion.2、Magnetic field assisted synthesis of low-coordinated Ti O₂{100}facets to realize C-C coupling in CO₂ photocatalysisElectromagnetic field as a kind of special energy can directly reach the atomic scale which is expected to realize the precise synthesis of materials at the atomic scale.In this study,a strong magnetic field is introduced into the crystal facet control of Ti O₂for the first time.By control the splitting degree of the high-angle quantum orbits and low-angle quantum orbits of Ti atoms,Ti-O bonds was changed during the formation process and finallly the formed Ti O₂{100}crystal facets with more low-allocation Ti atoms was obtained.In addition,This material can solve the problem of C-C coupling in CO₂photocatalytic conversion.Through characterization techniques such as electron paramagnetic resonance（EPR）and X-ray absorption spectroscopy（XAS）,we found that the strong magnetic field lead to the directional splitting of the electron orbits of Ti atoms,which cause the stretching and reconstruction of the Ti-O bond,and finally the formation of more low coordination Ti O₂{100}structure of is achieved.Using density functional theory（DFT）calculations and in-situ fourier transform infrared spectroscopy（insitu FTIR）,we found that the material enable the key intermediate CO*have a new adsorption mode in the CO₂ photocatalysis process,which promotes the collision and coupling of the CO*intermediate,and finally enables the material to convert CO₂ to C₂H₅OH with a high yield of 6.16μmol g^-1h^-1,which is 22 times that of the original Ti O₂.This research pioneered the engineering of crystal facet regulation under a magnetic field and provided an effective method for highly selective and highly active CO₂ photocatalytic conversion into multi-carbon products.3、Magnetic field assisted synthesis of two-dimensional Fe_0.942O/Cu interface to promote C-C coupling in CO₂ photocatalysisIt needs more energy to break the barrier of chemical bond or phase boundary for synthesizing two-dimensional materials from bulk or second phase materials than to break the van der Waals force to get two-dimensional materials.Electromagnetic field as a kind of special energy that can directly reach the atomic scale can change the way of electron spin acting on atoms and is expected to achieve accurate synthesis at the atomic level.In this study,a strong magnetic field was introduced for the first time in the bulk stripping two-dimensional material technology.The high-spin-state transition of the Fe atoms under the action of a strong magnetic field was used to synthesize two-dimensional Fe_0.942O/Cu,and this material can change the current situation and bottleneck of CO₂ reduction to C₁ products promoting the coupling of C-C to bring C₂₊products.A series of experimental data and characterization confirmed that the magnetic field causes more electrons of Fe atoms to be excited to the d orbital to form a high-spin state during the synthesis process,and finally form a two-dimensional Fe_0.942O/Cu material.In situ fourier transform infrared spectroscopy（insitu FTIR）results show that the material can make CO*have a variety of adsorption modes on it during the CO₂ photocatalytic conversion process,which promotes the C-C coupling from energy and space perspective,and finally the yield rate and selectivity of CO₂photocatalysis to C₂H₅OH can be as high as 9.69μmol g^-1h^-1 and 67.64%,respectively.This research introduces the special energy of magnetic field into the synthesis of two-dimensional materials,and designs catalysts from the perspectives of atomic physics and quantum mechanics,which is expected to achieve precise synthesis chemistry of two-dimensional materials at the atomic level.On the other hand.In the field of catalysis,this material solves a major problem in CO₂ photocatalysis,C-C coupling,and provides more theoretical guidance for the catalytic conversion of CO₂ to multi-carbon energy products.