Preparation Of The Modified BiVO₄ Photocatalyst To Improved Visible-light Photocatalytic Performance For Glyphosate

Glyphosate is a highly efficient,broad-spectrum andlow toxic herbicide,which itsoutput is largest in the world.Glyphosate can cause pollution in the process of production and use,and glyphosate with high concentrationhas been detected in natural lakes.Studies have shown that glyphosate can affect the physiological metabolism of fish and other aquatic organisms,amphibians,algae,soil organisms,humans and other mammals.Therefore,it has become a hot topic to study the high efficient and low cost technology to remove glyphosate from the water.Organic compounds can be degraded intocarbon dioxide,water and other inorganic ions using photocatalysis,no secondary pollution.BiVO₄ has attracted more attention because of its ability to absorb visible light,chemical stability and low cost.In this paper,the performance of BiVO₄ has been effectively improved through the surfactant/chelator modification,semiconductor heterostructure,quantum dot doping,and PDA surface modification.The main contents of this paper are as follows:?1?BiVO₄ samples were preparedby precipitation method using acetic acid and nitric acid,respectively.Using hydrothermal method,BiVO₄ samples were modified byethylene diamine tetraacetic aciddisodium,sodium dodecyl sulfate and sodium oleate,respectively.XRD results showed that the BiVO₄ sample modified by sodium oleate was amorphous,and other BiVO₄ samples were monoclinic.In addition,the?040?surface of the BiVO₄ sample modified by EDTA was more exposed than other BiVO₄ samples.SEM resultsshowed that the two BiVO₄ samples prepared by precipitation method were irregular and small,the morphology of the BiVO₄samples prepared by hydrothermal method were varied and large.The BiVO₄samplesprepared using acetic acid and modified by EDTA showed the highest photocatalytic activityin the precipitation method and hydrothermal method,respectively.?2?BiVO₄,g-C₃N₄and BiVO₄/PDA/g-C₃N₄were prepared by precipitation method,high temperature calcination method and ultrasonic assisted method,respectively.XRD,SEM,TEM and XPS results showed that the BiVO₄/PDA/g-C₃N₄ structure was BiVO₄dispersed in the PDA/g-C₃N₄ surface and folds.BiVO₄/PDA/g-C₃N₄ showed the best photocatalytic activity,which completely degraded 500mLof 10^-4mol/L glyphosate solution in 2.5h.PDA was used as the binder to combine BiVO₄ and g-C₃N₄ to enhance the stability of BiVO₄/PDA/g-C₃N₄.Reusability and XPS results showed that BiVO₄/PDA/g-C₃N₄ has good stability and photocorrosion resistance.The radical experiment indicated that the photogeneratedelectrons?e^-?and holes?h⁺?played the important role in the process of glyphosatedegradation.The effective separation of electrons and holes in the BiVO₄/PDA/g-C₃N₄heterojunction is the main factor to improve the degradation efficiency of glyphosate.?3?BiVO₄ prepared by precipitation method was dispersed in PDA solution,and then the BiVO₄/PDA/PbSsample was synthesized by ultrasonic assisted impregnation method.The structure of BiVO₄/PDA/PbS is PDA uniformly wrapped around the surface of BiVO₄,PbS loadedon the PDA.The degradation experiment results showed that BiVO₄/PDA/PbS exhibited better degradation rate than BiVO₄,BiVO₄/PDA and BiVO₄/PbS.The PL,I-t and EIS results showed that BiVO₄/PDA/PbS has excellent photoelectric properties,indicating that the modification of PDA and PbS can enhance the separation of photogenerated electron-hole pairs.Finally,for the transfer and separation processof electrons and holes,PbS is used as donor multiexciton,andPDA is used as the electron acceptor,which the photogenerated electron is tranfered from BiVO₄ to PbS via PDA.Thus,the highly efficient charge separation improved the photocatalytic performance.?4?L-cysteine as sulfur source and template,BiVO₄ and Bi₂S₃-BiVO₄ samples were synthesized by hydrothermal method.The TEMresults revealed that BiVO₄ grew along L-cysteine and then formed gradually starfish shaped BiVO₄.With the increase of L-cysteine,the BiVO₄ samples grew along the?040?crystal and finally formed similar peony shaped BiVO₄.The degradation experimentresults showed that the glyphosate degradation over the Bi₂S₃-BiVO₄ samples increasedfirstly and then decreased with the increase of L-cysteine.The degradation performace of the Bi₂S₃-BiVO₄ samples isproportional to the ratio of I_?040?/I_?121?.The results show that the Bi₂S₃-BiVO₄heterojunction was beneficial to the separation of electrons and holes,and the photocatalytic activity enhanced due to the increase of electron transfer efficiency.