Preparation Of Peanut Shell-Based Biochar And Its Adsorption Performance Towards Methylene Blue

Peanut shell is a kind of biomass waste with wide source,low cost,environmental protection and renewable energy.Biochar derived from carbonized peanut shell has shown a significant potential in the adsorption treatment of pollutants.However,biochar prepared by traditional methods from peanut shell often possesses the disadvantages of uneven pore structure,low content and unreasonable distribution of surface oxygen-containing functional groups,which leaded to its poor adsorption properties towards pollutants.In this study,a series of modified biochar derived from peanut shell was prepared using different methods such as K₂CO₃activation,nitrogen doping,and co-precipitation,then they were used to the adsorption of MB in a simulated wastewater.The apparent morphology,functional groups and pore structure characteristics of these biochar were characterized by modern analytical instruments such as scanning electron microscopy（SEM）,Fourier transform infrared spectrometer（FT-IR）,physical adsorption instrument（BET）,X-ray diffractometer（XRD）and X-ray photoelectron spectrometer（XPS）,etc.Potassium carbonate modified peanut shell-based biochar（KBC）were firstly prepared by low-temperature pre-carbonization and K₂CO₃activation using peanut shell was used as a carbon precursor.The results showed that after K₂CO₃activation modification,the oxygen-containing functional groups such as hydroxyl and carboxyl on the surface of biochar increased,and the specific surface area increased to 1460.92m²·g^-1,which is dominated with micropore.The adsorption capacity of KBC towards MB is related to its pore size and surface functional groups.At a calcination temperature of 600℃,activation time of 1.5 h,heating rate of 3℃/min,activation temperature of 750℃,and an impregnation ratio of 1:1.5,KBC showed the best adsorption performance towards MB,with a maximum adsorption capacity of 398.2mg/g.To enhance the adsorption capacity of biochar towards MB,a nitrogen-doped biochar（NBC）was prepared by a nitrogen doping strategy combined with high-temperature pyrolysis using melamine as the main nitrogen source.SEM analysis showed that the pore structure of NBC was more uniform than that of KBC.BET analysis indicated that the specific surface area of NBC is obvious larger than that of KBC,which reaches 2062.31 m²·g^-1.FT-IR and XPS analysis showed that NBC had abundant nitrogen-containing functional groups.The NBC prepared under the activation temperature of 800℃,and the mass ratio of peanut shell to melamine was2:1,and NBC prepared had the best adsorption effect on MB,and the adsorption capacity reached 480.5 mg/g.To improve the recyclability of peanut shell-based biochar,NBC is magnetized by a co-chemical precipitation method.By changing the mixed salt solution concentration of Fe³⁺and Fe²⁺and adjusting its p H value result in the precipitation of iron hydroxides in the pore structure of biochar,then the biochar was dried at 70℃to convert the iron hydroxides into iron oxide.Finally,the magnetic biochar loaded with magnetic particles（M/NBC）was prepared.Compared with NBC,M/NBC possesses smaller pores size,and higher porosity and specific surface area.The FT-IR spectrum of M/NBC showed the Fe-O characteristic peak belonging to Fe₃O₄at 563 cm^-1,which confirmed the addition of Fe and iron-containing functional groups.M/NBC had a superparamagnetism characteristic,with a magnetization intensity of 1 emu?g^-1.Under the optimal conditions,M/NBC had a maximum adsorption capacity of 610.5mg/g towards MB and was easy to recycle.The studies of adsorption kinetics and adsorption isotherms found that the adsorption process of KBC,NBC and M/NBC towards MB followed the Langmuir isotherm model and a pseudo-second-order kinetic equation,indicating chemical adsorption is the crucial step to determine adsorption rate.This work identified the effects of the modification methods on adsorption performance of biochar towards MB,and elucidated their adsorption kinetics and adsorption mechanism,which provide a theoretical basis and technical support for the preparation of high-performance biochar and the development of pollutant removal technology in wastewater.