Preparation Of Lanthanide Perovskite For Degradation Of Cresol

Cresol is the main component of wastewater from coking and oil refining industries,which can cause animal death,interfere with endocrine,threaten human health and disrupt ecosystems.Therefore,there is an urgent need to develop a technology for efficient degrading cresol pollutants in water.The article intends to take the three isomers of cresol（o-cresol,m-cresol and p-cresol）as the target pollutants,and use the citric acid-sol-gel method to prepare the perovskite-type material La Fe_1-xCu_xO₃（x=0.1,0.2,0.3,0.4 and 0.5）and La Fe_1-xMn_xO₃（x=0.9,0.7,0.6,0.5 and 0.4）to activate peroxymonosulfate（PMS）to degrade target pollutants.The effects of different Fe/Cu and Fe/Mn ratios,material dosages,PMS concentration and initial p H on degradation performance were examined,the active sites of heterogeneous activation of PMS were analyzed and the activation mechanism of the system was inferred.The main conclusions are as follows:（1）The perovskite-type material La Fe_0.8Cu_0.2O₃（x=0.1,0.2,0.3,0.4 and 0.5）was prepared by the sol-gel method.SEM results showed that the materials with different Fe/Cu ratios were nano-particle agglomerates with uniform morphology,and the particle size was between 40-70 nm.XPS results showed that the doping of Cu makes the valence states of Fe and Cu into Fe（III）/Fe（II）,Cu（II）/Cu（I）mixed valence states.The degradation rate of B-site doped Cu p-cresol increased from 30%to more than 80%.When 2.5 g/L La Fe_0.8Cu_0.2O₃ was added and 5 mmol/L PMS was added dropwise,the degradation rate of 100 mg/L p-cresol could reach 88.75%within 20 minutes.Under the same conditions,the removal rates of o-cresol and m-cresol were 72.3%and 80.5%,respectively.After La Fe_0.8Cu_0.2O₃ was reused three times,the degradation rate of p-cresol could reach about 85%.The degradation process of p-cresol conforms to the pseudo first-order reaction kinetics.The reaction system produces active components such as SO₄^-·,HO·and singlet oxygen,of which SO₄^-·plays a major role.The mechanism of La Fe_0.8Cu_0.2O₃ activation of PMS mainly has the following three ways:firstly,PMS was oxidized by Fe（III）and Cu（II）on the surface of the material to generate free radicals;secondly,the doping of Cu will cause more oxygen vacancies to be formed on the surface of the material.Vacancies would also react with PMS to generate free radicals;finally Fe（II）and Cu（II）would combine with the hydroxyl groups on the surface of the material to form complexes,and PMS would react with these electron-obtained complexes to generate free radicals.（2）The perovskite-type material La Fe_1-xMn_xO₃（x=0.9,0.7,0.6,0.5 and 0.4）was prepared by the sol-gel method.SEM results showed that the morphologies of materials with different Fe/Mn ratios were all honeycomb porous structures.FITR and XRD results showed that the doping of Mn did not change the original crystal structure of the perovskite La Fe O₃.XPS results showed that the doping of Mn makes the valence states of Fe and Mn into Fe（III）/Fe（II）,Mn（IV）/Mn（III）/Mn（II）mixed valence states,which not only facilitates the recycling of active metals,but also promotes the generation rate of free radicals.The degradation rate of B-site doped Mn o-cresol was increased from 28%to over 80%,and the degradation performance was significantly improved.When 2.5 g/L La Fe_0.1Mn_0.9O₃ was added and 5 mmol/L PMS was added dropwise,the degradation rate of 100 mg/L o-cresol can reach 86.25%within 30 minutes.As the added La Fe_0.1Mn_0.9O3 increases,the PMS concentration increases,and the removal rate of o-cresol will also increase.However,the excessively high concentration of PMS has a certain inhibitory effect on the degradation of o-cresol.The initial p H in the range of 3.00-9.00 can quickly degrade o-cresol.The La Fe_0.1Mn_0.9O₃/PMS system degrades o-cresol,and the rate constant within 20 minutes was1.45 times than that of the La Fe_0.8Cu_0.2O₃/PMS system.The La Fe_0.1Mn_0.9O₃/PMS system degrades m-cresol,and p-cresol with the degradation rates 88.03%,and 91.87%,respectively.The active components that play a major role in the reaction system are SO₄^-·and singlet oxygen.Mn in La Fe_0.1Mn_0.9O₃ not only has a variety of valence states,but also generates more oxygen vacancies,promoting the generation of singlet oxygen,and has more ways to activate PMS.