Chemical Imaging Of Cuprous Oxide Single Particle Based On Dark Field Scattering

Cuprous oxide(Cu₂O),as a non-stoichiometric p-type semiconductor,has good application prospects in the fields of antibacterial,photocatalysis,gas sensing,solar photolysis of water,carbon monoxide oxidation,solar conversion,lithium-ion battery cathode materials and chemical templates.To improve its performance,it is important to understand the physicochemical properties of Cu₂O.Single particle research can provide more detailed information at the level of single particles that it can more clearly and accurately grasp the structure-activity relationship of materials.It provides better theoretical support for the development and design of high-efficiency materials.In this dissertation,according to the Mie scattering theory,Cu₂O microcrystals with different morphologies and sizes were controllably prepared to meet the imaging requirements of dark-field optical microscopy(DFM),and on this basis,some important properties of single Cu₂O microparticles were studied.The main research contents and results are as follows:1.In order to study the chemical process of Cu₂O single particles in situ,according to the Mie scattering theory,the particle size must be at least 400 nm.At the same time,in order to clarify the structure-activity relationship of Cu₂O participating in the reaction,its morphology must be effectively controlled.Firstly,the factors affecting the morphology and size of Cu₂O microparticles,including sodium tartrate concentration,temperature,and reaction solution concentration,were studied by solution reduction method.Sodium tartrate is more easily adsorbed on the Cu₂O{1 1 1}surface and hinders its growth,resulting in the formation of Cu₂O microcube exposing only the{1 0 0}surface.Low temperature is conducive to the growth of crystals.Smaller crystals can be obtained at lower concentration of reactants.Therefore,by adjusting the amount of sodium tartrate and the concentration of the reaction solution,Cu₂O crystals with different morphologies and sizes can be controllably synthesized,which lays a good foundation for the study of Cu₂O single particle imaging.2.After successfully preparing Cu₂O crystals with different morphologies and sizes,in situ imaging observations were made to observe some important chemical processes involved in Cu₂O.Among them,oxygen vacancy can effectively control the electronic,geometric structure and light absorption of semiconductors,and plays an important role in performance regulation.Herein,the distribution of oxygen vacancies in single Cu₂O crystal were observed directly by DFM,and the factors affecting the growth of Cu₂O-Ag heterojunction were tested.Ag⁺can be reduced by oxygen vacancy in Cu₂O crystal and make Ag nanobelts grow longitudinally,which can be observed directly by DFM.The amount of oxygen vacancy in Cu₂O crystal was adjusted by acid and organic reagent,which further confirmed the recognition ability of Ag⁺to its oxygen vacancy.There are obvious differences in oxygen vacancies between particles.Ag nanobelts are easier to grow longitudinally on the{1 0 0}surface due to relatively low electron density.The discovery of these phenomena has important implications for a deeper understanding of vacancy theory and the design of Schottky heterojunctions.3.The synthesis of micro\nano materials with special structure and function through ion exchange reaction is a very effective preparation method.Herein,the ion exchange process between S^2-/Cl^-and single Cu₂O microparticles was studied by DFM.The factors affecting the anion exchange reaction were investigated,including the morphology,size,crystal surface,p H value and exchange ion concentration of Cu₂O particles.It is found that there is obvious heterogeneity between particles.Cu₂O particles with large specific surface area,low p H value and high ion exchange concentration can promote the anion exchange process,but there is no significant correlation between Cu₂O surface and reaction rate.Based on the pseudo-first order and pseudo-second-order kinetic model,the reaction rate and diffusion coefficient were estimated at the single particle level.Moreover,a single particle visual sensing method is constructed by using the special response of single Cu₂O microparticles to S^2-,which has good selectivity and linearity.4.Wastewater containing radioactive iodine(I^-)seriously threatens the life safety of modern and future people because of its high mobility and long half-life.Understanding the adsorption mechanism of solid-phase adsorbents for I^-is of great significance for the preparation of high-performance adsorbents.Here,the adsorption process of I^-on single Cu₂O microparticles was studied by DFM.It is found that in the process of adsorbing I^-the Cu₂O microparticles obviously become larger and the scattering intensity increases.According to these changes,the adsorption capacity of I^-in single Cu₂O microparticles can be quantitatively analyzed.The adsorption selectivity,particle heterogeneity,p H dependence,adsorption reaction kinetics and isothermal adsorption model were studied.It is found that I^-can be absorbed into Cu₂O microparticles even in the presence of other anions.There was no obvious adsorption heterogeneity between particles.The adsorption process is more consistent with the pseudo-first order kinetic and Dubinin Radushkevich isothermal adsorption model.We believe that the Kirkendall effect induced by acid activation is the main factor to increase the adsorption capacity of I^-in Cu₂O microparticles.5.Nitrogen oxides(NO_x),as a major air pollutant,seriously affects the ecological environment.Cu₂O is an effective adsorption and degradation material,but its degradation mechanism is not clear,which hinders the development of high-performance materials.Here,the interaction between NO_x gas and Cu₂O microparticles is studied by DFM.It is found that the interaction is not continuous but oscillatory.This random and dynamic oscillation phenomenon leads to significant heterogeneity among particles,and the average value of several particles can mask this phenomenon.In addition,this oscillation phenomenon is easier to be observed in high pressure NO_x and Cu₂O{1 1 1}surface.Through a series of related characterization tests,it is speculated that this oscillation phenomenon is controlled by the cyclic formation and falling off of Cu₂(NO₃)(OH)₃ on the surface of Cu₂O microparticles.The smooth progress of the above research work has broadened the field of single particle research of DFM,and provided a better understanding and theoretical support of the chemical process involved in Cu₂O microparticles,the design and synthesis of micro/nano materials with special structures and functions,and the preparation of high-efficiency environmental pollutant.