Study On The Performance And Mechanism Of Methylene Blue Adsorption By Bismuth-based Biochar With High Carbon Content

Bismuth-based biochar has attracted extensive attention in the treatment of methylene blue dye wastewater due to its rich source,easy preparation and high activity.At present,the research on bismuth-based biochar mainly focuses on the influence of reaction conditions and bismuth loading on the adsorption capacity of bismuth-based biochar for methylene blue.There are few reports on the influence of biochar carrier properties on the adsorption capacity of bismuth-based biochar.Therefore,from the perspective of carbon content of biochar,this paper discussed its effect on the adsorption of methylene blue by bismuth-based biochar.Bismuth-based biochar with high carbon content was prepared by loading bismuth oxide to adsorb methylene blue,and its adsorption mechanism was clarified.The main conclusions are as follows:（1）Three kinds of biochar with different carbon contents,beech wood biochar（WBC,carbon content is 82.4%）,corn biochar（CBC,carbon content is 60.86%）and bamboo biochar（BBC,carbon content is 63.95%）,were used as carriers,and bismuth oxide（Bi₂O₃）was loaded on the surface to prepare bismuth-based biochar with different carbon contents,respectively.The adsorption and removal rates of MB were ranked as follows:bismuth-based beech wood biochar（Bi@WBC）>bismuth-based bamboo biochar（Bi@BBC）>bismuth-based corn biochar（Bi@CBC）.（2）Characterization by SEM,Fourier transform infrared spectroscopy,X diffraction spectroscopy and specific surface and porosity analyzer as well as correlation analysis showed that the higher the carbon content of the biochar carrier,the larger the specific surface area and pore capacity,which is more favorable for the loading of Bi₂O₃ and thus enhance the adsorption performance on MB.（3）The preparation conditions of Bi@WBC were optimized,and the single-factor experiments showed that the optimal impregnation mass ratio of Bi³⁺to biochar was 0.1:1,the optimal heating rate was 10℃/min,and the optimal pyrolysis temperature was 400℃.The response surface method was used to optimize the preparation conditions of Bi@WBC with the pyrolysis temperature of 468℃,the pyrolysis rate of 10℃/min and the impregnation mass ratio of Bi³⁺:C=0.1:1,and the adsorption rate of the prepared Bi@WBC biochar could reach 94%for100 m L and 100 mg/L MB.（4）Bi@WBC prepared under the optimum conditions has the highest adsorption rate for MB at neutral or alkaline p H.In addition,the adsorption capacity and adsorption rate of MB on Bi@WBC increased with increasing temperature.Finally,Bi@WBC has good adsorption performance for cationic dyes.（5）In the adsorption kinetics experiment,the adsorption process of MB on Bi@WBC can be simulated by pseudo-second-order kinetics,Elovich and Bangham kinetics models,indicating that the adsorption process of MB on Bi@WBC is chemical adsorption,and there is a significant pore diffusion control adsorption process.Langmuir model was more suitable to simulate the adsorption process of MB on Bi@WBC,indicating that the adsorption process was monolayer adsorption.The maximum adsorption capacity was 259 mg/g at 298 K.（6）The characterization of the samples before and after the adsorption of MB by Bi@WBC showed that the adsorption mechanism of MB by Bi@WBC included electrostatic adsorption and chemisorption.By Raman spectroscopy,Bi@WBC has more graphite carbon structure.Through the analysis of the degradation products of MB adsorption by Bi@WBC,it was speculated that there might be two possible pathways for MB degradation by Bi@WBC adsorption:one is the generation of a large number of intermediate products after MB demethylation,which are mineralized into small molecular weight organic compounds after a series of degradation reactions;the other possible pathway is the attack of O in Bi-O functional group with OH^-generated on the surface of biochar to generate polyhydroxy compounds from MB.