Synthesis And The Photocatalytic Performances Of Bismuth-based Heterojunction

Semiconductor heterojunction structures,consisting of two or more components,have played an important role in modern material physics and chemistry since they often present enhanced properties due to the synergies between the components.Heterojunction photocatalysis has attracted great interest because it provides a promising pathway for solving energy supply and environmental pollution problems.In recent years,it has become an important research topic to develop a new type of visible light response photocatalyst with high efficiency and high stability.Therefore,we mainly design and synthesize bismuth-based heterojunction photocatalysts in this thesis.The main contents of this thesis are summarized as follows:1.One-dimensional?1D?Bi₂O₂CO₃-Bi?OHC₂O₄?·2H₂O heterostructure was synthesized by low temperature solution method using Bi?OHC₂O₄?·2H₂O nanorods as template.Bi₂O₂CO₃ nanosheets vertically grew onto the Bi?OHC₂O₄?·2H₂O rods along the long axial direction.Its adsorption capacity for organic pollutants was evaluated using methyl orange?MO?as model.The results showed that Bi?OHC₂O₄?·2H₂O-Bi₂O₂CO₃ heterostructure had excellent adsorption capacity of 95.78 mg/g and repeatability for MO.The adsorption isotherm accords with Langmuir model.Bi₂O₂CO₃-Bi?OHC₂O₄?·2H₂O heterostructure also excellent photocatalytic activity to degrade dyes?RhB,MB and MO?under solar/UV light irradiation.20 mg/L of RhB,30mg/L of MB and 75 mg/L of MO could be completely degraded by Bi₂O₂CO₃-Bi?OHC₂O₄?·2H₂O photocatalyst in 15,25 and 120 min,respectively.This superior adsorptive and photocatalytic performance is ascribed to the synergistic effect of big BET surface area and the formation of numbers of junctions in Bi₂O₂CO₃-Bi?OHC₂O₄?·2H₂O heterostructure.The trapping experiment of active species during the photocatalytic degradation was carried out,and the result indicatesthat ·O₂-radical and h+ play a major role in the photocatalytic degradation process.This study provides a general and effective method to fabricate unique 1D Bi₂O₂CO₃-Bi?OHC₂O₄?·2H₂O heterostructure with both photocatalytic and adsorptive performance on a large scale.2.One-dimensional Bi₂O₃-Bi₂O₂.33 heterostructure was synthesized by calcining 1D Bi₂O₂CO₃-Bi?OHC₂O₄?·2H₂O heterostructure.Compared with pure Bi₂O₃ and Bi₂O₂.33,this heterojunction exhibited superior photodegradation efficiency of methyl orange?MO??100 %?in 30 min and 80 min under solar/visible light irradiation.This enhanced photocatalytic performance was ascribed to the high separation rate of photo-generated carriers in the internal electric field due to the formation of heterostructure.More importantly,1D heterostructure is beneficial for transport of photo-generated electron-hole pairs and further improving the rate of photocatalytic reaction.Radical scavenger experiments revealed that h+ and ·O₂-were primarily active species in the photocatalytic system.This work would offer a new insight into the design and fabrication of heterostructure for photocatalytic applications.3.AgI/Bi₄O₅I₂ heterostructures were synthesized by a facile photology process using Bi₄O₅I₂ nanosheets and Ag NO₃ solution as raw materials.The Ag I nanoparticles dispersed on the surface of Bi₄O₅I₂ nanosheets.The obtained products were characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,X-ray photoelectron spectroscopy?XPS?,N2-sorption/desorption and Brunauer-Emmett-Teller surface area?BET?.The photocatalytic activity of the samples was assessed for degradation of Rhodamin B?RhB?and phenol under visible light irradiation.The result demonstrates that the AgI/Bi₄O₅I₂ heterostructures display higher photocatalytic activity than single Bi₄O₅I₂ nanosheets.As the content of AgI increases,the photocatalytic activity of AgI/Bi₄O₅I₂ heterojunction enhanced and the optimal sample was S2?cAgNO₃ = 4 mmol/L?.The enhancement of the photocatalytic activity of the AgI/Bi₄O₅I₂ heterostructures structures canbe ascribed to the larger number of surface active sites and faster spatial charge transfer.This work provides some insights into the rational design and development of high-performance photocatalysts.