Charge Separation Mechanism And Photoelectric Application Of Low-Dimensional Carbon Composites

In recent years,with the rapid development of nanomaterial synthesis technology,composite nanocatalytic materials have been prepared,which are represented by carbon-metal oxide composite nanoparticles.Carbon material is rich in resources,environmentally friendly,stable,and has high carrier mobility.By controlling the synthesis route,a special structure carrier can be obtained to meet the needs of different catalytic reactions.Another widely studied carbon composite nanomaterial is based on graphene.Multi-layer two-dimensional materials are stacked together by van der Waals（vdW）forces to form a vdW heterojunction.Since this type of heterojunction can form a steep barrier at the interface,higher charge separation efficiency can be achieved even without lattice matching,and is often used to prepare high-efficiency photovoltaic devices.The above-mentioned photocatalysts based on carbon composite nanomaterials and photoelectrically responsive devices based on two-dimensional van der Waals heterojunctions rely heavily on charge separation efficiency.Charge separation is a process that such materials must undergo.It is of great academic value and practical significance to study the motion process of excited state carriers and the transport of interface charges in carbon composite nanomaterials.Based on this scientific problem,this work starts with the experiment and theory of carbon composite nanomaterials,and studies the mechanism of charge separation and its application in catalysis and optoelectronic devices.The main contents of the paper are as follows:1.The dynamic of carrier in carbon composite nanomaterials with cuprous oxide nanoparticles as photosensitive materials was studied in this paper.The source of the transient absorption signal was determined using the electron sacrificed methyl viologen(MV²⁺).When the cuprous oxide is excited,the electrons are quickly trapped by the defect state,which is detrimental to charge separation and catalytic reaction.It is further found that the use of nitrogen-doped porous carbon-coated cuprous oxide and nitrogen-doped carbon framework-supported cuprous oxide composite nanoparticles can effectively improve the charge separation efficiency.2.This paper studies the effect of doping on the excited state carrier dynamic under the condition of using titanium dioxide as a photosensitive material.It was found that nitrogen doping can not only increase the concentration of hole in TiO₂,but also increase the probability being captured by shallow defect levels above the valence band and improve the catalytic efficiency.It is demonstrated that the loading of the nitrogen-doped carbon framework can promote the transfer of electrons from the titanium dioxide conduction band to the carbon framework.It has been further found in the study of titanium dioxide having different crystal facets that electrons tend to aggregate on the surface of titanium dioxide（101）.For the graphene-loaded titanium dioxide composite nanoparticles,the low surface potential of the（101）plane may lead to back electron,and the charge separation efficiency is low.After the（100）crystal plane contacts graphene,the charge separation time can be effectively extended to several microseconds（>4.2?s）3.In this paper,graphene nanosheets with stacked structure were prepared by using graphene oxidized as precursor and solvothermal cutting method.The idea of the presence of inter-band heterojunctions in stacked graphene nanosheets is proposed.Due to its nearly 100%charge separation efficiency,UV luminescence at 307 nm was observed for the stacked graphene nanosheets.It has further been found that the few layer graphene nanosheet can be exfoliated into a monolayer graphene nanosheet by ultraviolet light irradiation in a polar solvent;and long-time ultraviolet light irradiation can activate the graphene edge and integrate it horizontally into a large size.4.This paper applies the new carbon composite nanomaterials to the photocatalytic reaction of“Cross Dehydrogenative Coupling”and“amine oxidation”,achieving a product formation rate of up to 99%.It exhibits excellent photocatalytic performance.On this basis,a photoresponsive device based on graphene nanosheets was prepared,which proved that the layered graphene nanosheet optoelectronic device can be used as a high-performance solar-responsive material for solar blind regions with a switching current ratio of 5.2.