Adsorption Properties Of CO₂-Derived Carbon For Aromatic Compounds And Its Value-Added Reutilization

Molten salt CO2 capture and electrochemical transformation technology（MSCC-ET）is an emerging green technology,which can produce high value-added carbon products,realizing the capture and conversion of CO2 emissions at the same time.With its unique physical and chemical properties,CO2 transformed carbon materials（EC）have the great application prospect in the fields of energy storage and environmental remediation.Based on the previous understanding of the surface properties of EC and the primary exploration of their adsorption applications,this paper further studied the adsorption performance and mechanism of EC toward simple aromatic organic pollutants.More importantly,the reuse of exhausted EC adsorbent in oxygen reduction catalysis was investigated to solve the intractable tasks of post-treatment of adsorbent.We are trying to realize the continuous value-added utilization of waste CO2 from the environment to the energy field,providing an idea to alleviate environmental problems and energy crisis.The main conclusions of this paper are as follows:（1）Taking aniline as the model adsorbent of aromatic organic pollutants,the effects of adsorption time,temperature,solution p H,dosage and initial pollutant concentration on the adsorption performance of EC were investigated in detail.It was found that in a wide p H range（5-9）,the adsorption capacity of EC to aniline is high and the adsorption rate is fast.In the first 1min,the adsorption capacity reached about 67%of the equilibrium adsorption capacity,and the adsorption equilibrium could be reached within 60 min.The whole adsorption process conforms to the pseudo-second-order kinetic model,which is mainly controlled by external diffusion and internal diffusion.The analysis shows that the excellent adsorption performance for aniline is attributed to the high micropore area and reasonable mesoporous distribution of EC.In the study of adsorption isotherm,the adsorption process fits the Freundlich model well.Thermodynamic results show that the sorption is a spontaneous endothermic process.In addition,the adsorption capacity for aniline can be increased by 1.7 times through removing the acid oxygen-containing functional groups on the surface of EC.The adsorption capacity of EC to three kinds of aromatic organic pollutants（aniline,phenol,nitrobenzene）containing different functional groups was compared before and after treatment,and it was proved that the adsorption mechanism of EC to simple aromatic organic pollutants isπ-πinteraction.（2）After adsorption of aniline,EC was reutilized to prepare the N-doped carbon material（EC-N）,which was used as the catalyst for oxygen reduction reaction（ORR）.The results show that N atoms are doped into carbon skeleton of EC and serve as active sites for ORR catalysis.Moreover,with the increase of preparing temperature,the ORR catalytic activity of EC-N improve gradually,owing to the increase of the specific surface area,the defect degree,and the content of graphite-N.In addition,CAC-N-800was prepared under the same condition of EC-N-800 by changing EC to commercial activated carbon in 800 ^oC.Comparing with CAC-N-800,EC-N-800 makes significantly better catalytic performance because of the reasonable distribution of pore structures and larger electrochemical active surface area.In 0.1 M KOH electrolyte,the onset potential and limiting current density of EC-N-800 is 0.9 V and 5.28 m A/cm²,closing to that of 20%Pt/C.At the same time,EC-N-800 also shows the high stability and tolerance to methanol.As a cathode catalyst for zinc-air batteries,EC-N-800 also has a similar open circuit potential and discharge time with 20%Pt/C,showing great development potential in practical applications.（3）EC was used to simultaneously adsorb metal ions(Cu²⁺/CO²⁺)and aniline in aqueous solution,then was pyrolyzed to successfully prepare metal/N co-doped carbon materials（Co-N-EC and Cu-N-EC）.It was found by LSV tests that the obtained Co-N-EC and Cu-N-EC have obvious ORR catalytic activity.The preparation temperature significantly affected the catalytic performance of metal/N co-doped carbon materials.under the pyrolysis temperatures of 800 ^oC,Co-N-EC and Cu-N-EC showed the highest catalytic activity with the onset potential of 0.82 V,0.96 V and limiting current density of 3.4 m A/cm²,4.6 m A/cm²,respectively.