Preparation,Modification And Properties Of Bismuth Oxide Formate Photocatalyst

Given that photocatalytic technology can simultaneously solve energy crisis and environmental pollution,the removal of pollutants via photocatalysis has attracted tremendous attention.It is of great significance to find a simple,green and low-cost photocatalyst synthesis method and to modify the existing photocatalyst effectively.In this paper,the layered green catalyst bismuth oxide formate（BiOHCOO,donated BiOR）was selected as the research object,and its synthesis and modification were studied.The main research contents are as follows:（1）Using bismuth nitrate pentahydrate（Bi（NO₃）₃·5H₂O）and sodium formate（HCOONa）as raw materials,for the first time,BiOR nanomaterials with different morphologies were prepared by adding the morphology regulator or a surfactant and changing the volume ratio of glycol to water under room temperature solution method.The experimental results show that different morphology BiOR materials all have good degradation efficiency to the dye Rhodamine B（RhB）under ultraviolet light.Among them,the tubular BiOR sample prepared by stirring for 5 h at room temperature in pure water solution has the best photocatalytic activity under visible light irradiation.In addition,from the perspective of environmental protection,this sample is selected as the basis for subsequent modification.（2）BiOR could not respond to visible light due to its wide-band-gap energy.Potassium bromide（KBr）or potassium iodide（KI）and HCOONa were added to the uniformly dispersed Bi（NO₃）₃·5H₂O aqueous solution and then stirring 5 h through room temperature co-precipitation method.The results displayed that when Br^-/Bi³⁺=0.6,the tubular S-scheme heterojunction BiOBr/BiOR-0.6 was obtained.The sample showed excellent photocatalytic activity for a variety of pollutants malachite green（MG）,RhB and tetracycline（TC）under visible light irradiation.The improvement of photodegradation efficiency of heterojunction samples is mainly due to the formation of solid solution BiORBr-x,which could broaden the visible light absorption rangemore,importantly,the suitable Br content in the solid solution could optimize the energy band structure and induce the transition from the traditional type I heterojunction of BiOBr/BiOR to the S-scheme heterojunction of BiOBr/BiORBr-x,thus leading to excellent photocatalytic activity for multiple pollutants degradation under visible light.Moreover,the tightly contacted interfaces between BiOBr and tube-like hierarchitecture BiORBr-x also facilitated the rapid transfer of the photo-generated electron-hole pairs.Similarly,when I^-/Bi³⁺=0.6,BiOI/BiOR p-n heterojunction was obtained.The construction of p-n junction successfully improved the transfer rate of the photo-carriers and its photocatalytic activity.（3）Based on the previous study,KBr,KI and HCOONa were added in one step to the uniformly dispersed Bi（NO₃）₃·5H₂O aqueous solution through the same method.The synergistic effect of the two halogens’modification was realized by fixing the molar ratios of Br^-/Bi³⁺and I^-/Bi³⁺respectively.It showed that when Br^-/Bi³⁺=0.6 and I^-/Bi³⁺=0.2,the as-obtained composite photocatalyst BiOBr/BiORI_0.2Br_0.6 has the highest photodegradation efficiency for TC driven by visible light,surpassing the composite samples modified by single halogen.This is mainly due to that the composite sample BiOBr/BiORI_0.2Br_0.6not only has a higher matching band structure,it also has a large specific surface area because of the addition of KI,which could contribute to the improvement of photocatalytic activity.