Study On The Mechanism Of Absorbing Heavy Metals And Degrading Atrazine By Bixbyte BioMn₂O₃

Manganese oxides are excellent adsorbents and oxidants and are ubiquitous in the natural environment.Microbial activity is closely linked to the formation of manganese oxides in natural conditions.Currently,the mechanism of biomineralization to form manganese oxides comes from three phylogenetically bacteria isolated from the aqueous phase.Their mineralization products are predominantly birnessite with low crystallinity and high valence.In this study,the manganese-oxidizing bacteria isolated by the research group were used to prepare and purify manganese oxides by mediated mineralization of Mn（II）;at the same time,manganese oxides were chemically synthesized.The purified biological manganese oxides and synthetic manganese oxides were characterized by scanning electron microscopy-energy dispersive spectroscopy（SEM-EDS）,powder X-ray diffraction（XRD）,high-resolution transmission electron microscopy-selected-area electron diffraction（HRTEM-SAED）,N₂adsorption/desorption,and X-ray photoelectron spectroscopy（XPS）,and applied them to the study of heavy metal adsorption and pesticide degradation.The main results are as follows:1.The results show that the purified biological manganese oxides are irregular granular,with a pore size of 2-50 nm,and are weakly crystalline bixbyite-type minerals with a specific surface area（SSA）of6.68 m²/g,and the valence state is mainly Mn³⁺.The synthetic manganese oxide is a regular nanoscale particle with a pore size distribution between2 and 50 nm.It is a strongly crystalline single crystal bixbyite-type mineral with a specific surface area of 4.62 m²/g.2.Under the conditions of p H 6 and ion concentration of 1 mmol/L,the adsorption of heavy metals by bixbyite Bio Mn₂O₃reached the maximum value,which were Pb（II）（240.17 mg/g）and Cd（II）（109.21mg/g）,Cu（II）（89.89 mg/g）,Zn（II）（83.73 mg/g）and Ni（II）（78.32 mg/g）,respectively.The adsorption of heavy metals by bixbyite Bio Mn₂O₃manganese oxide is monolayer adsorption,and the adsorption process is controlled by chemical adsorption.3.X-ray absorption spectroscopy（XAS）analysis of the crystal structure of bixbyite Bio Mn₂O₃—a low-valence biomanganese oxide composed of distorted and regular manganese-oxygen octahedra.The Mn1-O interatomic length of the regular Mn1O6 octahedron is 1.990（?）,and the Mn-O interatomic length of the distorted Mn2O6 octahedron is1.808（?）,2.069（?）and 2.232（?）,respectively.4.The degradation of atrazine at concentrations of 0.1,1 and 10mg/L by purified biogenic manganese oxides was 63.87%,47.22%and35.37%respectively.Six intermediate degradation products were identified during the removal of atrazine by bixbyite Bio Mn₂O₃,including deethylatrazine（DEA）,hydroxyatrazine（HA）,deethylhydroxyatrazine（DEHA）,Ammeline,cyanuric acid and5-methylhexahydro-1,3,5-triazine-2-thione（MTT）.At the same time,Mn（II）ions were released from bixbyite-type Bio Mn₂O₃and the content of hydroxyl O species increased at the expense of the lattice and water O species on the surface of bixbyite-type Bio Mn₂O₃,but the basic crystal structure of this Mn oxide remained unchanged.Furthermore,no dissociative Mn（III）was found to be involved in the degradation of atrazine.