Preparation Of Bismuth-based Photocatalytic Composites By In Situ Reaction Of Coal Pitch-based Carbon Quantum Dots And Their Properties

In recent years,bismuth-based photocatalysts,especially semiconductor photocatalysts containing bismuth oxides,have attracted wide attention due to their unique layered structure and band position,which show superior photocatalytic degradation performance of organic pollutants.Bismuth oxide formate also has the structural characteristics of bismuth-based semiconductors.At the same time,it does not contain toxic halogen elements,will not cause secondary pollution to the environment,so that it has more application potential.However,bismuth oxide formate is a photocatalyst that can only respond to ultraviolet light,which limits its use in converting solar energy.Carbon quantum dots?CDs?are a new type of zero-dimensional carbon nanomaterials that have gradually emerged in recent years.They have excellent optical properties and can be used as electron acceptors or electron donors after being compounded with other materials to promote charge separation in the interface area of the material and increase the concentration of charge carriers used in photocatalytic reactions to enhance the performance of photocatalysis.Further exploring the process of photocatalytic reaction,photocatalytic reaction mainly occurs on the active sites of the catalyst,and creating more active sites of the photocatalytic reaction is the most essential way to improve the performance of the photocatalyst.In the photocatalytic reaction,the active substance is its main reaction participant.Quantitative calculation and kinetic analysis can not only deeply understand the mechanism of the photocatalytic reaction,but also optimize the reaction process.In this paper,the in situ synthesis of coal pitch-based carbon quantum dots and bismuth oxide formate is used to form a heterojunction,which is then treated with sodium borohydride solution to undergo in situ phase transformation to form a new heterojunction.Degradation of organic pollutants to analyze their photocatalytic performance,quantitative detection of hydroxyl radicals generated during their photocatalytic reaction to further study the photocatalytic mechanism.The research content and research results of this paper mainly include the following aspects:?1?At room temperature,BiOCOOH was prepared by simple stirring of formic acid and bismuth nitrate pentahydrate.Similarly,using formic acid to etch coal pitch to prepare the remaining formic acid in the carbon quantum dots solution,and in situ synthesis with bismuth nitrate pentahydrate can obtain CDs@BiOCOOH heterojunction.Zeta potential test proves that CDs and BiOCOOH are easy to combine to form CDs@BiOCOOH heterojunction,and the valence bond structure and elemental analysis of the samples are performed by XRD test and XPS test.The UV-visible absorption test on the two samples shows that the composite carbon quantum dots can significantly enhance the absorption of visible light by the catalyst,and also have a better effect when photocatalytically degrading organic pollutants.The active substance capture experiment proves that the holes induced by light promote the degradation of organic pollutants through the direct charge transfer process,and hydroxyl radicals and superoxide radicals have a special selective effect on the degradation of organic pollutants.The introduction of carbon dots changed the energy band structure of BiOCOOH.The valence band of BiOCOOH changed from 2.27 eV to 2.14 eV,which was closer to the oxidation potential of hydroxyl radicals,which was beneficial to the photocatalytic reaction.The electrochemical test proves that after the composite carbon quantum dots,CDs@BiOCOOH has a smaller carrier transfer resistance and a stronger photocurrent response,and a better photocatalytic degradation effect is obtained.?2?At room temperature,the CDs@BiOCOOH powder prepared in the previous experiment and sodium borohydride solution were simply stirred to produce CDs@?BiO?₂CO₃ by in situ phase transformation.XRD test and XPS test prove that BiOCOOH in CDs@BiOCOOH is converted to?BiO?₂CO₃,and more carbon oxygen double bonds are generated.SEM test proved that after treatment with sodium borohydride solution,the sample morphology changed,and TEM test show that after conversion of CDs@BiOCOOH to CDs@?BiO?₂CO₃,many structural defects are formed and more active sites of photocatalytic reaction are created.The BET specific surface area test proves that CDs@?BiO?₂CO₃ has a larger specific surface area and a smaller pore volume.The ultraviolet-visible absorption test shows that it has a stronger response to visible light.When photocatalytically degrading organic pollutants,CDs@?BiO?₂CO₃ exhibited better degradation effects,The efficiency of degrading Rhodamine B and methylene blue is doubled compared to CDs@BiOCOOH,which simultaneously produced hydroxyl radicals and superoxide radicals.The change of phase structure also caused the change of CDs@BiOCOOH energy band structure,and the reduction of valence band was beneficial to the production of more hydroxyl radicals.After treatment with sodium borohydride solution,CDs@?BiO?₂CO₃ has a smaller carrier transfer resistance and a stronger photocurrent response,resulting in a better photocatalytic degradation effect.Finally,through the repeatability test of CDs@?BiO?₂CO₃ degrading Rhodamine B and the comparison experiment under different light intensity,it was found that the degradation of Rhodamine B using CDs@?BiO?₂CO₃ four times was basically inactivated,The photocatalytic degradation rate of CDs@?BiO?₂CO₃ is roughly linear with the light intensity,proving its good photocatalytic stability and practicality.?3?Taking the reaction of terephthalic acid and hydroxyl radical to generate2-hydroxyterephthalic acid as the reaction model,a kinetic detection method of hydroxyl radical was constructed.First,fit the relationship between the concentration of2-hydroxyterephthalic acid solution and the fluorescence intensity by fluorescence test:Y=0.13547X,so that the rate of change of the solution concentration can be obtained according to the rate of change of the fluorescence intensity of 2-hydroxyterephthalic acid,and the analogy is The rate of hydroxyl radical generation.Hydroxyl radical is an important active substance involved in the reaction.The rate of reaction with terephthalic acid to produce2-hydroxyterephthalic acid depends to a large extent on the concentration of terephthalic acid as a substrate.Refer to the enzymatic reaction process Michaelis-Menten equation:v=V_max[S]/?[S]+[K_m]?,expressing V_max as the maximum formation rate of2-hydroxyterephthalic acid to define the photocatalytic activity of degrading organic pollutants.This kind of kinetic detection for active substances analyzes the mechanism of the photocatalytic reaction process from a more essential perspective.Further,by comparing the rate of photocatalytic degradation of organic pollutants,this method has high reliability and sensitivity has been proved.