Enhanced Adsorption Of Methylene Blue And Metronidazole On Hard Carbon By Coating-CO₂ Activation Carbonization

The problem of water environment pollution is directly related to food security and human health and safety,which is a key issue of social concern in recent years.The discharge of wastewater containing dyes and antibiotics into the environment will directly lead to the deterioration of water quality and even cause great negative effects on the water supply ecosystem.It is urgent to solve the problem of pollutants.Adsorption is one of the most important methods in many removal methods because of its simple operation,low cost and high efficiency.Biochar has become a hot material for research and development due to its loose porosity and low price.The hard biochar obtained by pyrolysis of nut shell or hardwood is hard and granular,which is conducive to loading,separation,recovery and recycling in the process of sewage treatment.China is rich in apricot plant resources.A large number of almond shells are often formed after processing almonds and apricot meat,which have been made into hard biochar.However,hard biochar has small specific surface area,few adsorption active sites,poor structural performance and weak adsorption capacity of pollutants.It is necessary to regulate its pore structure or change its surface properties by physical or chemical methods to enhance the adsorption capacity of pollutants.Therefore,the main work of this paper is to prepare almond shell carbon materials with high specific surface area by coating-CO₂ activation carbonization method using polymer compounds（phenolic resin,potassium humate,polyimide）as modifiers,and to adsorb methylene blue（MB）and metronidazole（MNZ）in water.It provides a scientific basis for the development of biochar water treatment adsorption materials and technologies.The main research contents and results are as follows:（1）Preparation and adsorption of phenolic resin derived carbon@hard carbonPhenolic resin derived carbon@hard carbon（PRC@HB）was prepared by coating-CO₂activation carbonization method with almond shell carbon as matrix and phenolic resin as coating modifier,which was used to adsorb and remove MB and MNZ.The adsorbent was characterized by scanning electron microscope（SEM）,X-ray diffractometer（XRD）,Raman spectrometer（Raman）,infrared spectrometer（FTIR）,N₂ adsorption and desorption device and contact angle meter.The results showed that when the mass fraction of phenolic resin was30%,the specific surface area of PRC@HB was the largest(346.39 m² g^-1),and the adsorption removal effect was the best.The removal rates of 10 mg L^-1 MB and MNZ were 94.21%and 97.44%,respectively.The isothermal adsorption process of MB on PRC@HB conformed to the Freundlich model,and the adsorption capacity reached 52.25 mg g^-1 at T=30℃.The adsorption process of MNZ on PRC@HB conforms to the Langmuir model,and the saturated adsorption capacity of single molecule is 47.87 mg g^-1 at T=30℃.In addition,it was also found that the adsorption process of MB on PRC@HB was a spontaneous endothermic process,and the adsorption mechanism was mainlyπ-πinteraction and electrostatic attraction.The adsorption process of MNZ by PRC@HB is a spontaneous exothermic process,withπ-πinteraction and hydrogen bonding as the main mechanisms.（2）Preparation and adsorption of potassium humate derived carbon@hard carbonPotassium humate-derived carbon@hard carbon（PHC@HB）was prepared by using potassium humate as coating modifier,and its adsorption and removal of MB and MNZ were investigated.The adsorbents were characterized by SEM,XRD,Raman,FTIR,N₂ adsorption-desorption device and contact angle tester.The results showed that when the mass fraction of potassium humate was 50%,the specific surface area was 498.94 m² g^-1.Compared with biochar without potassium humate,the adsorption rate of MB by PHC@HB increased from 22.40%to 96.91%,and the adsorption rate of MNZ increased from 12.90%to 92.42%.The isothermal adsorption process of MB and MNZ on PHC@HB conformed to the Langmuir model.At T=30℃,the saturated adsorption capacity of MB and MNZ was 84.67mg g^-1 and 112.87 mg g^-1,respectively.Thermodynamic data showed that the adsorption of MB and MNZ by PHC@HB was a spontaneous endothermic process.（3）Preparation and adsorption of polyimide-derived carbon@hard carbonPolyimide derived carbon@hard carbon（PIC@HB）was prepared by using polyimide as coating modifier.The structural properties of the adsorbent were investigated by various characterization techniques.The adsorption performance of PIC@HB was evaluated by using MB and MNZ as pollutant models,respectively.The results showed that the specific surface area reached 418.86 m² g^-1 and the total pore volume was 0.24 cm³ g^-1 when the mass fraction of polyimide was 60%.The removal rates of 100 mg L^-1 MB and MNZ by PIC@HB were 23.43%and 28.24%,respectively.Langmuir is more suitable to describe the adsorption process of MB and MNZ on PIC@HB surface.At T=40℃,the saturated adsorption capacities of MB and MNZ are 34.93 mg g^-1 and 33.29 mg g^-1,respectively.In addition,the adsorption of MB and MNZ by PIC@HB is a spontaneous endothermic process.The adsorption mechanism is physical adsorption and chemical adsorption,and the chemical adsorption is mainlyπ-πinteraction.