Construction Of Surface Modified Bi₂WO₆ And Its Photocatalytic Reduction Of CO₂

As the representative of Aurivillius compounds,Bi₂WO₆ crystals have a two-dimensional layered structure formed by stacking?WO₄?^2-and?Bi₂O₂?²⁺.It has strong built-in electric field,large specific surface area and large number of exposed surface reactivity sites,which are favorable for the migration of photogenic charge carriers due to the unique microscopic configuration.However,because of its weak visible light response capability and the inability of conducting band potential to meet reducing CO₂ electrode potential which are limited its application in the field of photoreduction of CO₂.Therefore,this paper used various surface modification methods to improve the photo responsiveness and photo reduction ability of Bi₂WO₆.This paper explored the differences between photoelectric properties and photoreduction CO₂ reaction which were modified with surface modification or not.By analyzing the material components,micromorphology and energy band structure,discussed the internal mechanism of catalytic reaction activity enhancement.As for Bi₂WO₆ photocatalyst,this paper mainly carried out work from the following three parts:?1?Graphene quantum dots?GQDs?,which were used as photosensitizer to modify Bi₂WO₆ by introducing oxygen vacancy?Vo?in coordination with alkali etching post-treatment.The band gap of Bi₂WO₆ that modified by GQDs and V_O was narrowed and the band position was more negative by using ultraviolet visible diffuse reflectance and X-ray photoelectron valence band energy spectra.The results of photoluminescent spectrum and photocurrent density test shows that the separation capacity of photocharge transfer has been enhanced after photosensitization and oxygen vacancy modification.The photoreduction CO₂ experiment results showed that the maximum yield of CH₄ and CO were 102.75?mol·g^-1·h^-1 and 46.68?mol·g^-1·h^-1.?2?Bi₂WO₆,which both with bismuth vacancy(V_Bi)and oxygen vacancy?V_O?,were prepared by hydrothermal method.Bismuth and oxygen vacancys were successfully introduced into Bi₂WO₆ photocatalyst by adjusting the concentration of the precursor and the mass of ethylene glycol.Electron paramagnetic resonance and X-ray photoelectron spectroscopy also showed that bismuth and oxygen vacancy were successfully introduced into the photocatalyst.The CO₂reduction experiment displayed that the maximum yield of CH₄ and CO were 91.64?mol·g^-1·h^-1 and 87.99?mol·g^-1·h^-1.The Bi_2-xWO_6-y photocatalyst,not only maintain high conversion rate of CH₄,but also have better CO conversion rate and selectivity.Moreover,with the formation of CH₃OH,the yield reached 193.89?mol/g cat for 5h of illumination.?3?Cu₂O containing lewis acid-base pair that was successfully compounded to the surface of Bi₂WO_6-x by liquid phase synthesis method.It was proved by X-ray diffraction?XRD?.The photoresponse capacity of the composite photocatalyst was improved,more and more CO₂ molecules were adsorbed to participate in the subsequent reaction X-ray photoelectron spectroscopy?XPS?test proved that the surface of Cu₂O was rich for ites oxygen defects and Cu¹⁺species,which contributed to the transmission and separation of photogenic electrons.CO₂ catalytic reduction data display that the maximum yield of CH₄ and CO were 72.87?mol·g^-1·h^-1 and91.58?mol·g^-1·h^-1.The total amount of CH₃OH was 308.21?mol/g cat after 5h of illumination.