Preparation Of Bi₂O₂CO₃ Photocatalytic Materials And Photodegradation And Photoreduction Studies

Bismuth subcarbonate（Bi₂O₂CO₃）is an outstanding example of Bi Aurivillius oxide semiconductors,which is built up of alternating[Bi₂O₂]²⁺layers with[CO₃]^2-layers.Owing to its unique layered structure and promising physicochemical properties,Bi₂O₂CO₃has a wide range of applications in the fields of photocatalysis.In this study,we have synthesized various Bi₂O₂CO₃ nanostructures via different hydrothermal routes,including nanosheets,nanoplates,nanoparticles,nanosheet-assembled hierarchical nanotubes,pinecone-like hierarchical nanostructures,and carnation flower-like hierarchical nanostructures.The samples were characterized by a series of XRD,SEM,TEM and UV-vis DRS,and the photoelectrochemical,photocatalytic and photoreductive properties were tested,and finally the internal mechanism was analyzed.Specific research contents are as follows:1.Carnation flower-like Bi₂O₂CO₃ hierarchical structures prepared by hydrothermal method.Herein the Cr（VI）concentration was detect ed based on ultraviolet-visible absorption spectrum measurements by using 1,5-diphenylcarbazide as the chromogenic agent.In order to correctly determine the concentration of Cr（VI）,the effects of H₂SO₄concentration,DPC concentration,Cr（VI）concentration,reaction time t and reaction temperature T on the absorbance determination of Cr（VI）solution were systematically studied.The effects of H₂SO₄,Na OH,Cr（VI）concentration and catalyst dosage on photoreduction of Cr（VI）were explored in the photocatalytic experiments.The experimental results of simulating sunlight-driven Cr（VI）photoreduction show that the carnation flower-like Bi₂O₂CO₃ material has excellent photocatalytic ability to reduce Cr（VI）.Finally,the photoreduction mechanism is analyzed in detail.2.One-step hydrothermal method for the synthesis of Bi₂O₂CO₃ hierarchical nanotubes with ordered self-assembly from nanosheets under template-free conditions.The effect of reaction time on the structural/morphological evolution,light absorption properties,photoelectrochemical properties and photocatalytic activity of the prepared samples was investigated by controlling the reaction time.Among the products synthesized for different reaction times,the 3 h-derived Bi₂O₂CO₃ hierarchical nanotubes were identified to possess the highest photocatalytic activity.It is found that the reason for the excellent photocatalytic performance of 3h-BOC is the generation of oxygen vacancies during the formation process.However,with the prolongation of the reaction time,excessive oxygen vacancies will inhibit the photocatalytic performance of Bi₂O₂CO₃.The performance of 3h-BOC was evaluated by simulating sunlight-driven photodegradation of MO/Rh B/MB mixed solution,CIP,SMX,TC,and Cr（VI）photoreduction system.Finally,combined with DFT calculation,the involved photocatalytic mechanism is analyzed.3.Nanosheets,nanoplates,nanoparticles,nanosheet-assembled hierarchical nanotubes,pinecone-shaped hierarchical nanostructures,and carnation flower-shaped hierarchical nanostructures were synthesized in different hydrothermal routes.The properties of various nanostructures have been studied with the support of multiple characterisation techniques.Their photodegradation and photoreductive activities were systematically compared by degrading MB and reducing Cr（VI）ions under simulated-sunlight irradiation.Among various Bi₂O₂CO₃ nanostructures,the nanoparticles demonstrate the highest photodegradation activity for degrading MB,whereas the hierarchical nanotubes exhibit the highest photoreduction activity for reducing Cr（VI）ions.Based on the experimental data,several factors are proposed to explain the photocatalytic differences between Bi₂O₂CO₃ nanostructures.This work demonstrates that the photocatalytic activity of photocatalytic materials can be greatly optimized by controlling their morphology and size through different synthetic routes.