Adsorption Efficiency And Mechanism Of Tetracycline Antibiotics And Arsenic By Copper-manganese Binary Oxide

In recent years,the pollution of livestock and poultry has received more and more attention,especially the environmental problem caused by tetracycline antibiotics（TCs）and arsenic which needs to be solved urgently.In the research of this paper,based on the previous results of the research group,copper-manganese binary oxide（CMBO）has been synthesized,which has a good adsorption capacity for TCs and arsenic.In addition,the mechanism and adsorbent of CMBO were discussed.The main works and results are as follows.1.CMBO powder（Cu:Mn=3:1）prepared by two-step methodis chosen as adsorbent for experimental studies.2.Using the methods of SEM-EDS,TEM,BET,FTIR,XRD and XPS to investigating the characteristics of the surface of CMBO.The results showed that CMBO has large specific surface（67.738m²/g）and pore size（16.87nm）,and the constituent elements mainly consist of Cu,Mn,C,O.The isoelectric point of CMBO(pH_pzc)was 7.82.Obvious crystal structure and rich hydroxyl groups,which is favorable for the adsorption of tetracycline antibiotics and arsenic.The adsorption capacity is higher than other equivalent adsorbents under the same conditions.3.The kinetic data fit the second-order kinetics model well at low TCs concentration,it shows that the adsorption is chemical adsorption mainly,at high concentration,the Elovich model can describe the adsorption process well,indicating that it is a heterogeneous adsorption.Temkin isotherm can well describe the adsorption of TCs,indicating that there is a correlation between adsorbent and adsorbate.The saturated adsorption of TC,OTC and CTC is 2.901,4.145 and 2.195 mmol/g respectively.The adsorption capacity of TCs increased first and then decreased with the pH increased,it has a large amount of adsorbed TCs in the pH range of 6 to 9,while the adsorption amounts were decreased obviously in the acid and alkaline conditions.The presence of calcium ions or silicate could bring adverse effects on the adsorption of TC and OTC,because of the complexation and competitive adsorption mechanisms.The carbonate and silicate could promote the adsorption of CTC.This is because the carbonate and silicate can be attracted to adsorbent which increasing the adsorption of CTC.4.The second-order kinetic model can describe the kinetic data of As（III）/As（V）,which showed that the adsorption process is dominated by chemical adsorption.The adsorption of As（III）by CMBO is in accordance with the Langmuir isotherm,which indicates that the adsorption process takes place on the monolayer chemisorption of the adsorbent surface,while the adsorption of As（V）conforms to the Sips isotherm model,and the separation constant R_L is between 0¹,indicates that the adsorption is favorable.The saturated adsorption capacity of As（III）/As（V）was 64.17 and 84.87 mg/g respectively,it shows that CMBO has better adsorption effect on As（V）than As（III）.The adsorption of As（III）/As（V）decreased with increasing pH,but the reaction mechanism was different.The adsorption of As（III）by CMBO with the increase of pH,the oxidation of As（III）weakened,and the competitive adsorption of OH and Mn（II）will lead to the decrease of As（III）adsorption.The effect of As（V）is mainly due to the Coulomb force.Ca²⁺,Mg²⁺can promote the adsorption of As（III）/As（V）on CMBO,because the cations can effectively compensate the negative charge due to adsorption of As.Anions could bring inhibitory effect on the adsorption because the competitive adsorption mechanisms.In the same concentration,the Order of influence was PO₄^3->SiO₃^2->CO₃^2->Cl^-≈SO₄^2-.5.The adsorption mechanism of CMBO is due to the complexation and ion exchange reaction between TCs and the hydroxyl and other ions on the surface of the adsorbent,which is the main mechanism of adsorption.TCs have a strong affinity for Cu（II）and a complexation reaction occurs between them,which make the adsorption capacity of CMBO better than other adsorbents.The adsorption mechanism of As on the adsorbent is also due to its surface complexation and ion exchange reaction with the hydroxyl groups and ions on the surface of the adsorbent.Simultaneously in the adsorption process,with the As（III）oxidation to As（V）.