Preparation Of Metal-doped BiFeO₃ And Its Degradation Of Analgesics In Water By Vis/PMS System

Non-steroidal anti-inflammatory analgesic drugs are one of the most widely used drugs in the world.They are difficult to biodegrade,durable and biotoxic,and pose potential safety risks to the ecological environment and human health.Photocatalysis and persulfate oxidation are both cutting-edge technologies in the field of wastewater treatment,and the selection of efficient,stable and safe catalytic materials is the key to these two technologies.Bismuth ferrite（BiFeO₃）has unique microstructure and physical and chemical properties,which endures its catalytic versatility.As a semiconductor material,BiFeO₃has a good ability to response to visible light.As Fenton-like catalyst,BiFeO₃has excellent catalytic performance,it has great potential in the field of environmental governance.In view of the traditional water treatment technology is difficult to effectively remove non-steroidal anti-inflammatory analgesic drugs,this work using rare earth metal La and transition metal Mn doping modification was carried out on the ferrite bismuth,so as to enhance the visible light catalytic activity and activate persulfate ability.The two kinds of metal doped ferrite bismuth materials’s crystal structure,morphology characteristics and optical properties were characterized,to explore the mechanism of Mn and La doping affecting the degradation performance of bismuth ferrite.The visible light catalytic/activated persulfate synergistic system（vis/PMS）was established with metal-doped bismuth ferrite as the catalyst.The degradation efficiency and characteristics of the system were studied with the non-steroidal anti-infalmmatory analgesic drug-meloxicam as the target pollution.The effects of PMS dosage,initial p H,humic acid concentration and common inorganic anion interference on its degradation performance were investigated.The active species involved in the degradation of pollutants in the vis/PMS system were identified by radical quenching experiment.The mineralization and intermediate products of meloxicam in the vis/PMS system were analyzed by HPLC-MS.The possible degradation pathways were identified to further clarify the degradation mechanism of the vis/PMS system.The main conclusions are as follows:（1）The doping of Mn and La metal has obvious changes on the structure,morphology,chemical environment and optical properties of bismuth ferrite.A proper amount of doping of Mn or La element is beneficial to improve the photocatalytic activity of bismuth ferrite and the activation efficiency of persulfate.However,the mechanism of the two kinds of metal doping on the improvement of bismuth ferrite performance is different.（2）Whether Mn or La doping bismuth ferrite materials,under the vis/PMS system,the degradation efficiency of meloxicam were significantly higher than that of single by photocatalytic oxidation or persulfate oxidation,proved that Mn or La doping bismuth ferrite materials can effectively combine two kinds of advanced oxidation technologies,more efficiently eliminate the non-steroidal anti-inflammatory analgesic drugs.In addition,after four repeated experiments,the degradation rate of meloxicam remained at a high level in vis/PMS system,indicating that the two materials have good catalytic stability.（3）With the increase of PMS dosage,the removal rate of meloxicam by vis/PMS system increased,but the increase was obviously weakened,and excessive PMS dosage even showed inhibitory effect.Vis/PMS system has a wide range of p H adaptation,and the removal efficiency does not change significantly when the initial p H is 3～9.Humic acid can promote the degradation of vis/PMS at low concentration,but it can inhibit the degradation of vis/PMS at high concentration.Among the four inorganic anions,Cl^-has a relatively obvious promoting effect on the reaction of vis/PMS system,while NO₃^-,H₂PO₄^-and HCO₃^-show different inhibitory effects,and the inhibitory degree is H₂PO₄^->HCO₃^->NO₃^-.（4）The active species involved in meloxicam degradation in the vis/PMS system were dominated by SO₄^·-,and·OH,·O₂^-,h⁺and so on were involved in the degradation of pollutant.It is speculated that during the reaction process,the C-N bond and enol structure of meloxicam molecular structure were damaged by the oxidation of various active groups,and were decompose into 2-amino-5-methylthiazole（C₄H₆N₂S）and other small molecular organic compounds,which were eventually mineralized into H₂O,CO₂,SO₄^2-,NH₄⁺and so on.