Preparation Of Sodium Alginate Based Carbon Aerogels And Adsorption Of Tetracycline In Water

Tetracycline（TC）is widely used in medical treatment,animal husbandry and other fields as a class of antibiotics for the treatment of bacterial diseases,but excess tetracycline cannot be absorbed by organisms,resulting in its discharge into the water environment,causing water pollution.As a convenient,cheap and efficient method to remove antibiotics in water,adsorption method is widely used,but powdered adsorption materials are difficult to recover,which greatly limits their practical application.In this study,the advantages of efficient adsorption of porous carbon materials and the easy separation of aerogels are innovatively combined,and the preparation of functional carbon aerogels by nitrogen-manganese（N-Mn）co-doping and applied to the removal of tetracycline in water has certain theoretical and practical significance.In this paper,sodium alginate（SA）extracted from kelp and other organisms with abundant sources was used as the carbon source,and carbon aerogels with excellent adsorption performance were prepared and screened by adjusting the reaction parameters such as activation temperature,material ratio and oxidant concentration.Through a series of adsorption experiments,the kinetic behavior of functional carbon aerogel adsorption TC was studied.The adsorption kinetics model of TC in carbon aerogels was established,and the influence of temperature on its adsorption behavior was discussed.Based on the characterization and adsorption results of materials BET,SEM,FT-IR and XPS,the structure-activity relationship and adsorption mechanism of their structure and adsorption performance were elucidated.（1）With SA as the carbon source and K₂CO₃ as the activator,carbon aerogels with excellent pore structure and adsorption performance were prepared by the"crosslinking-lyophilization-high-temperature activation"process.By adjusting the activation temperature and doping ratio,the optimal material PC-800-0.7（activation temperature 800 degrees,SA:K₂CO₃=1:0.7）for TC adsorption was screened,and its adsorption capacity was 232.5 mg g^-1.The results of adsorption experiments showed that the adsorption of TC by PC-800-0.7conformed to the Langmuir isothermal model and quasi-secondary kinetic model,indicating that the adsorption process was mainly based on monolayer physical adsorption,accompanied by a certain degree of chemical adsorption.It mainly relies on pore filling,hydrogen bonding,electrostatic force,van der Waals force andπ-πinteraction.（2）In order to further improve the adsorption capacity of sodium alginate-based carbon aerogel,melamine was used as the N source and the pore structure was further optimized by N doping.By adjusting the N doping ratio,the optimal adsorption material PC_N-0.9（SA:K₂CO₃:melamine=1:0.7:0.9）was screened out,and the adsorption capacity was 302.0 mg g^-1,which increased by 29.9%compared with the non-nitrogen-doped material PC-800-0.7.The characterization results showed that N-doped carbon aerogel PC_N-0.9 had a better pore structure,and its pore volume and specific surface area increased by 106.6%and 150.7%,respectively,and was loaded with a large number of nitrogen-containing functional groups,among which pyridine nitrogen and pyrrole nitrogen were conducive to the surface of PC_N-0.9and TC molecules,effectively promoting the adsorption reaction.（3）Inspired by the research on metal-doped carbon materials,we innovatively proposed the idea of increasing the adsorption site on the surface of the material by oxidizing the metal Mn to improve the adsorption effect.On the basis of nitrogen doping modification,N-Mn co-doped carbon aerogel PCM-25(KMn O₄ solution concentration was 25 g L^-1)was prepared by controlling KMn O₄ concentration to screen the optimal oxidation conditions,with an adsorption capacity of 459.6 mg g^-1,which was 97.7%and 52.2%higher than that of non-doped and nitrogen-doped materials,respectively.The characterization results show that although the manganese-coated particles block the pore structure and reduce the specific surface area and pore volume by metal Mn oxidation loading nitrogen sodium alginate-based carbon aerogels,the multivalence Mn is loaded on the surface of PCM-25 in the form of agglomerated particles,which increases the adsorption site and improves the adsorption performance of the material.The research results provide basic data for the macroscopic design and surface functionalization modification of porous carbon,and provide a theoretical basis for the efficient removal of TC in water.