Adsorption Characteristics Of Tetracycline In Water By Alfalfa And Corn Cob Biochar At Different Pyrolysis Temperatures

Tetracycline was frequently and widely used in livestock and poultry breeding,and constantly released into the water environment,was known as"persistent"organic pollutants.Tetracycline pollution had gradually aroused people’s common concern.Alfalfa biochar（HMBC600,HMBC700 and HMBC800）and corn cob biochar（HYBC600,HYBC700 and HYBC800）were prepared by using alfalfa and corn cob as raw materials at 600℃,700℃and 800℃respectively.The biochar was characterized by scanning electron microscopy,elemental analysis,Brunauer-Emmett-Teller,Fourier transform infrared spectroscopy,and X-ray diffraction.Tetracycline was used as the target pollutant,combining dynamics and thermodynamics method to explore the adsorption performance and mechanism of biochar.In this paper,main conclusions were as follows:（1）The results of scanning electron microscopy showed that both alfalfa and corn cob biochar had obvious carbon frame structure,and the surface of corn cob biochar was rougher.At higher pyrolysis temperature,the hydrophilicity,polarity and aromaticity of alfalfa biochar were stronger,while the hydrophilicity and polarity of corn cob biochar decreased,but the aromaticity increased.The Brunauer-Emmett-Teller results showed that increasing the pyrolysis temperature helped to increase the specific surface area of biochar.By Fourier transform infrared spectroscopy results,the types of functional groups on the surface of alfalfa and corn cob biochar were roughly the same,and the surface functional groups decrease or disappear when the pyrolysis temperature increases.X-ray diffraction results showed that alfalfa biochar contains Si O₂and Ca CO₃mineral components,corn cob biochar had multi-layer stable microporous graphite crystal,did not contain crystal mineral components.These differences may be the reasons for the different adsorption capacities of alfalfa and corn cob biochar.（2）The adsorption capacity of alfalfa and corn cob biochar for tetracycline in solution was investigated.The removal rate increased with the addition of biochar in the solution.With the initial concentration of tetracycline increasing,the adsorption capacity of biochar increased,and the removal rate showed a downward trend.The increase of ion concentration could decrease the adsorption capacity of biochar for tetracycline,and the effect of Mg²⁺on the adsorption efficiency was more significant than that of Na⁺.The optimal p H of alfalfa biochar for tetracycline adsorption was 7.0,while corn cob biochar had the best adsorption performance when p H was 3.0.The adsorption of tetracycline by biochar was more consistent with the pseudo-second-order and Langmuir adsorption isotherm model,which was a spontaneous endothermic process.The adsorption mechanism of tetracycline on biochar mainly included surface functional group interaction,electrostatic interaction andπ-πEDA interaction.（3）The adsorption capacity of biochar was enhanced by increasing the pyrolysis temperature.The adsorption capacity of corn cob biochar was up to 98.35 mg·g^-1,and that of alfalfa biochar was up to 73.56 mg·g^-1.The yield of corn cob biochar was higher than that of alfalfa biochar when the pyrolysis temperature increased.Alfalfa and corn cob biochar were environmentally friendly adsorbents with excellent adsorption performance and can be recycled.