Preparation Of Nitrogen-doped Coal Tar Pitch-based Porous Carbon And Its Adsorption Capacity For Chlortetracycline

The problems of ecosystem and human health caused by antibiotic pollution need to be solved urgently.Activated carbon has attracted extensive attention in the field of pollutant treatment due to its advantages of high efficiency,green and simple operation.The morphology and pore structure of carbon from coal tar pitch which has high carbon content and certain fluidity at high temperature can be controlled directional by template agent.In this study,the template coupling KOH was used to prepare the coal tar pitch based nitrogen-doped porous carbons by adding nitrogen-containing compounds.The materials were characterized by SEM,BET,XPS,FTIR,Zeta potential and UV-VIS,and the adsorption performance of the porous carbons for chlortetracycin was investigated.The main conclusions are as follows:（1）Nanoporous carbon materials(CC₆₀₀,CC₇₀₀,CC₈₀₀)were prepared by pyrolysis of coal tar pitch,potassium hydroxide and magnesium oxide at 600,700,800℃.The specific surface area of CC₈₀₀is up to 2480 m²/g,and the specific surface area of micropores is up to 2102 m²/g.The material is enriched and folded nanosheets with a large number of honeycomb pore structures.The content of oxygen-containing functional groups on CC₈₀₀surface is the least.When p H value reaches 3.33,the material surface changes from positive to negative.The equilibrium adsorption capacity of CC₈₀₀to chlortetracycline was 1089 mg/g.The adsorption capacity of the three materials changed under different p H values and ion concentrations.（2）Three nitrogen-doped porous carbons(MCC_0.5,MCC_2.0,MCC_4.0)were prepared by adjusting the ratio of melamine as nitrogen source and coal tar pitch,potassium hydroxide and magnesium oxide as raw materials.The specific surface area of MCC_0.5can reach 2574 m²/g,and the surface is rich in a large number of pores and accompanied by accumulation of folded lamellar,while the surface of MCC_2.0and MCC_4.0is characterized by irregular massive accumulation with few pore structures.The C=C bond C=N group tensile vibration of naphthalene ring or phenyl group appeared in MCC_0.5in FTIR.XPS analysis showed that the MCC_0.5has the highest pyridine N content..The adsorption capacity of the three materials for chlortetracycline is more than 620 mg/g,which accords with Langmuir adsorption isotherm model.At different p H values,the surface chemical properties of adsorbents and adsorbents changed,and the interactions between MCC_0.5and chlortetracycline,and electrostatic adsorption were dominant.High salt ion concentration will shield the charge on the surface of the adsorbent and reduce the chemisorption capacity.After five cycles of regeneration test,the adsorption performance decreased by only 10.5%.（3）Three nitrogen-doped porous carbons(DCC_0.5,DCC_2.0,DCC_4.0)were prepared from coal tar pitch,potassium hydroxide and magnesium oxide using 2-methylimidazole as nitrogen source.The specific surface area of DCC_0.5,DCC_2.0and DCC_4.0materials was2589,2969 and 2706 m²/g,and the porous carbon layers were stacked.The tensile vibration of C=C bond C=N group was obviously different from CC₈₀₀in FTIR spectra.DCC_2.0has the highest content of C=O,-OH with pyrrole N,pyridine N bonds.The saturated adsorption capacities of Chlortetracycline for DCC_0.5,DCC_2.0and DCC_4.0were1340,1228 and 880 mg/g,respectively,which fit Langmuir adsorption isotherm model.Pseudo-second-order kinetic model can describe the adsorption process of chlortetracycline on porous carbons.Under different p H value and ion concentration conditions,the adsorption properties of the materials have obvious changes.After five cycles of regeneration,the adsorption capacity of DCC_2.0decreased by 12.4%,indicating that DCC_2.0is a renewable green adsorbent.