Study Of Mn-Fe-Based Peroxidase Activity And Catalytic Degradation Of Bisphenol A

Compared with natural enzymes,peroxidase-like enzymes have low cost,easy synthesis,good stability,high resistance to change,adjustable catalytic activity,acid and alkali resistance,reusable,easy to scale up,etc.,which show superior enzymatic activity,and are widely applied in bioanalytical testing,cancer diagnosis and treatment,and pollutant removal,etc.At present,BPA has been detected in water,soil,and food.Reports confirmed that it can cause obesity,diabetes,metabolic diseases,and cancer,and may be cause the teratogenic neurotoxicity and reproductive toxicity.Under the natural conditions,it is extremely difficult to remove BPA completely.Therefore,the development of efficient and stable peroxidase-liked catalysts is of great importance for treating bisphenol A wastewater.In this study,Mn-Fe-based composites（Mn₃O₄microspheres,iron oxides,and iron-metal organic framework materials）were complexed with metal oxides,metal sulfides,and graphene oxide,respectively,and were used as peroxidase-like catalysts to investigate their enzymatic activities and to the catalysis degradation of simulated bisphenol A wastewater.The details of the study are as follows:1.Mn₃O₄-FeS₂/Fe₂O₃composite was synthesized by the solvothermal method,their morphology and structural composition were morphologically characterized and analyzed using XRD,SEM,ICP-OES,FT-IR,N₂adsorption-desorption,and particle size distribution.Their enzyme-like activities were determined systematically.Mn₃O₄-FeS₂/Fe₂O₃catalyzes the oxidation of 3,3,5,5-Tetramethylbenzidine（TMB）by H₂O₂to form the blue oxidation product of ox TMB.The steady-state kinetics were simulated by the Michaelis-Menten equation in buffer solution of p H=4.5.The Lineweaver-Burk constants for TMB and H₂O₂（K_m）are 0.54 mmol/L and 2.52 mmol/L,respectively,indicating that Mn₃O₄-FeS₂/Fe₂O₃has good catalytic activity as a peroxidase-like enzyme.The reactive species burst experiments demonstrated that the reactive radicals generated by the reaction are mainly hydroxyl radicals（·OH）and superoxide radicals（·O₂^-）.2.The catalytic degradation of BPA by Mn₃O₄-FeS₂/Fe₂O₃was systematically investigated.Under the conditions of temperature at 25°C and H₂O₂（30%）dosage of70μL,10 mg of Mn₃O₄-FeS₂/Fe₂O₃can catalyze the degradation of 50 m L of 50mg/L BPA totally within degradation time of 60 min.After five cycles,the degradation rate can still reach 85.80%,The possible mechanism of catalytic degradation of BPA by Mn₃O₄-FeS₂/Fe₂O₃was analyzed.The intermediate products of degradation analyzed by LC-MS includes p-methanol,5-methyl-phenylhexane,4-isopropyl phenol,4-isopropylphenol,2,3-dihydrobenzofuran,4-hydroxybenzoxime,acetyl benzene,4-hydroxybenzoic acid,terephthalene,benzaldehyde,benzoquinone,maleic acid,CO₂and H₂O.3.Two-step solvothermal method was used to prepare Mn₃O₄/GO-MIL-88B（Fe）composite.The morphological characterization and analysis were carried out by XRD,SEM,ICP-OES,FT-IR,N₂adsorption-desorption,TEM,and Raman spectra.The enzyme-like activities were discussed.Mn₃O₄/GO-MIL-88B（Fe）catalyzes the oxidation of 3,3,5,5-tetramethylbenzidine（TMB）in the presence of H₂O₂to form a blue oxidation product（ox TMB）.The Lineweaver-Burk constants（K_m）for TMB and H₂O₂are 1.46mmol/L and 2.34 mmol/L,respectively,obtained by the steady-state kinetics simulation of Michaelis-Menten equation in the buffer solution of p H=3.5,revealing that Mn₃O₄/GO-MIL-88B（Fe）can be as peroxidase-like composite with good substrate affinity.The reactive species burst test proved that the reactive radicals generated by the reaction are mainly consisted of hydroxyl radicals（·OH）and superoxide radicals（·O₂^-）.4.The conditions for the Mn₃O₄/GO-MIL-88B（Fe）-like peroxidase catalyzed degradation of BPA were explored systematically and the mechanism of its possible catalysis degradation was discussed.The 100 m L of BPA with an initial concentration of50 mg/L could be degraded completely within 75 min by adding 5 mg of Mn₃O₄/GO-MIL-88B（Fe）at a system temperature of 25℃and 40μL of H₂O₂（30%）.The intermediate products of the degradation process were analyzed by LC-MS which include 4-（2-hydroxyisopropyl）acetophenone,p-methylbenzyl alcohol,5-methyl-1-phenylhexane-1,3-dione,4-isopropylphenol,4-isopropenyl phenol,4-hydroxybenzoic acid,acetyl benzene,phenol,acetic acid,CO₂and H₂O.The BPA degradation rate was still up to 71.26%when recycled and used five times,which has good stability and can rapidly degrade BPA in wastewater with fewer dosage.