Study On Microwave-Assisted Preparation Of BiFeO₃ And Properties Of Catalytic Oxidation On Emerging Contaminants BPA And PFOA

Emerging contaminants due to wide distribution,hard degradation,and accumulated toxicity have been become the focal point of global concern for pollution caused by ecological environment,human health.Photocatalysis and Fenton-like catalysis technology are used as the main method to degrade emerging contaminants.How to prepare catalysts with high efficiency,safe,stability and practicability is a pressing issue in application.In this paper,microwave assisted hydrothermal method was found to prepare Pb-BiFeO₃/rGO@NF catalytic material via Pb ions and rGO codoping in bismuth?Bi FeO₃?which nickel foam?NF?used as a carrier.Photocatalytic process and microwave?MW?enhanced Fenton-like process?MW-Fenton-like?were set up to degrade BPA and PFOA as target contaminants.The process parameters of MW-Fenton-like dynamic test were optimized.The mechanisms of how to remove emerging contaminants by Pb-BiFe O₃/rGO@NF in the photocatalytic system and the MW-Fenton-like system were also investigated.Base on MW irradiation technology,MW assisted hydrothermal method was used to prepare Pb-Bi FeO₃ catalytic material,which could solve the problem of long time consuming and poor catalytic performance via traditional hydrothermal method.The preparation processes were optimized by response surface method,the optimal process parameters are as follows:the molar ratio of Bi/Fe is 1,Pb²⁺doped and the dosage is1.88 wt%,dispersant is PEG6000 and the dosage 1.0 g/L,sodium hydroxide?NaOH?concentration is 3.26 g/L,microwave hydrothermal temperature is 190^oC,microwave hydrothermal time is 30 min.The Pb-BiFeO₃ catalyst is a perovskite crystal with an aperture of 7.8 nm and a specific surface area of 67.7 m²/g.When degrade 20 mg/L BPA using 1.0 g/L Pb-BiFeO₃ under 100 W UV light,the removal rate of BPA can reach98.5%.Through compared and analyzed the Pb-BiFeO₃ catalytic materials via microwave-assisted hydrothermal method and traditional hydrothermal method,the advantages of microwave-assisted hydrothermal method were analyzed by morphology,crystal form,specific surface area and functional groups.The results showed that microwave and incorporation of Pb²⁺significantly enhanced the crystalline form of BiFeO₃ nanoparticles,reduced the particle size and increased the specific surface area.Thereby the catalytic performance of Pb-BiFeO₃ catalytic materials were improved.In order to further improve the catalytic performance and practical application of Pb-BiFe O₃ nanomaterials,microwave assisted hydrothermal method was used to prepare Pb-BiFeO₃/rGO@NF catalysts.NF was used as the carrier,and rGO was incorporated into Pb-BiFeO₃ nanoparticles.The technological parameters are as follows:the dosage of rGO is 0.7 wt%,the mass ratio of Pb-BiFeO₃/rGO and NF is 1,the dosage of NaOH is 3.26 g/L,microwave hydrothermal temperature and hydrothermal time is190 ^oC and 30 min respectively.The Pb-BiFeO₃/rGO@NF catalytic materials were high catalytic properties,easy recovery,recycling and stability.Using Pb-BiFe O₃/rGO@NF as catalytic materials,BPA was removed in photocatalytic oxidation process and PFOA was removed in MW-Fenton-like process.When remove 20 mg/L BPA using 1.0g/L Pb-BiFe O₃/rGO@NF as catalysts,the removal ratio of BPA is 96.7%and TOC removal ratio is 64.8%in photocatalytic oxidation process.When remove 10 mg/L PFOA using1.2 g/L Pb-BiFeO₃/rGO@NF as catalysts,in 6 min the removal ratio of PFOA is 97.3%and TOC removal ratio is 63.3%in MW-Fenton-like process via added 34 mg/L H₂O₂.Base on the static experiments,dynamic experiments were set up to degrade PFOA in MW-Fenton-like process.The dosage of H₂O₂,microwave irradiation temperature,the dosage of catalytic materials and hydraulic retention time were optimized by response surface methodology.When the pH is 5,the dosage of H₂O₂ is 70 mg/L,the dosage of Pb-BiFe O₃/rGO@NF is 2.0 g/L,the aeration rate is 0.5 m³/h,the hydraulic retention time is 10 min,the PFOA removal ratio is 92.3%.The stability and cyclicity of Pb-Bi FeO₃/rGO@NF catalytic materials were investigated.After 6 cycles of tests,the concentration of metal ions of Pb-BiFe O₃/rGO@NF catalytic material was lower than 70?g/L,and the removal ratio of BPA was higher than 85%.The problems about improving the catalytic activity,immobilization and stability of catalytic materials were solved in photocatalytic process and MW-Fenton-like process.Meanwhile,the mechanisms on degradation of BPA in photocatalytic oxidation system and degradation of PFOA in MW-Fenton-like system were discussed via research on free radicals and reaction kinetics.The results were showed that·OH as the main offensive substance to remove BPA and PFOA.And more·OH were generated to participate in catalytic reaction with Pb²⁺and rGO codoped.In addition,the degradation paths of BPA and PFOA were speculated.In the photocatalytic system,OH attacked the isopropyl junction of BPA molecule to open the benzene to form phenol and benzene diketone.When the phenol was further attacked by·OH,H₂O and CO₂ were generated.PFOA is degraded via continuous fracture of long chain,and a CF₂ is removed at every fracture to form a short chain fluorinated compounds.And the short chain fluorinated compounds were degraded to form micro-molecular organics F^-,H₂O and CO₂.