Research On The Preparation And Modification Of Biochar For Dye Removal Effect And Mechanism

In response to the increasing dye wastewater caused by the rapid development of the textile and printing&dyeing industries,which has caused increasingly serious water pollution,and continued threats to the environment and human health.Biochar prepared from agricultural and forestry waste buckwheat husks and pine needles was selected as the treatment material,which have been found eco-friendly,economically viable and high-performance removal efficiency.In addition,the biochar has been modified to improve the adsorption performance,and the adsorption and removal performance of methylene blue and ponceau 4R,two typical cationic and anionic dye pollutants,has been studied in depth,in order to provide a new way and method for the effective treatment of dye wastewater.Firstly,buckwheat hulls and pine needles,which are relatively less studied in the field of biochar,are used to prepare biochar.The buckwheat husk biochar was prepared by the pre-carbonization method,and the adsorption performance of HNO₃ impregnation modification and KOH activation modification on MB and P4R were compared,in order to explore the best modification method which could further improve its adsorption effect.Then,BET test,EDS element analysis,scanning electron microscope SEM observation,XRD test,FTIR analysis and vibrating sample magnetometer and other instruments and methods have been used to characterize the materials.Finally,the adsorption effect of these two biochar on the above two dyes was studied experimentally,and the microscopic mechanism and kinetics of the adsorption process were analyzed.Meanwhile,the adsorption effect and reusability of these two biochar on other dyes were investigated.Research indicates:（1）.The optimal carbonization temperature of buckwheat husk biochar is 500℃and it was impregnated with HNO₃ and activated with KOH,the specific surface area,pore structure and adsorption effect of activated biochar with KOH are better than those of modified biochar with HNO₃,the activated biochar with KOH is named QBC.The carbon content of QBC is 91.78%,the specific surface area is 2229.7564 m²·g^-1,and it has a total pore volume of 1.14 cm³·g^-1,which is significantly higher than that of unmodified biochar,it means QBC is porous and has well-developed pore structure.The surface of the material contains-OH,-C-H,-N-H,and the degree of graphitization is higher than that of unmodified biochar;（2）.The experimental values of the maximum adsorption capacity of QBC on MB and P4R were 1108.55 mg·g^-1 and 603.75 mg·g^-1,respectively.When the dosage of QBC is 0.010g and0.015g,the removal rate and adsorption capacity of MB and P4R can be maintained at aa relatively high level.The lower p H is conducive to the adsorption of P4R,and the higher p H is conducive to the adsorption of MB.As time and initial concentration increase,the adsorption capacity of MB and P4R increases.With the increase of temperature,MB adsorption capacity increases,while P4R adsorption capacity decreases;（3）.Adsorption thermodynamics study shows that the adsorption of MB by QBC is a high-temperature spontaneous adsorption process,while the adsorption of P4R is a low-temperature spontaneous adsorption process.The adsorption process of QBC for MB and P4R can be well described by the Freundlich adsorption model,which belongs to multilayer adsorption.According to the adsorption kinetics study,the adsorption process of the two dyes are all in line with the quasi-second-order kinetic model,meanwhile,there is an intra-particle diffusion process,but it is not a rate-controlling step,which means the adsorption is affected by various adsorption mechanisms.Besides,QBC has a good adsorption effect on many other dyes,and has a certain recycling capacity under the condition of unactivated thermal regeneration;（4）.The pine needles were immersed in 8mol·L^-1 KOH for 12h and dried,then activated at800℃and loaded with Fe₃O₄ to prepare MBC.The carbon content of MBC is 55.62%,and Fe accounts for 27.86%.The material is loose and porous,and it has a developed pore structure,the specific surface area is 785.75 m2·g^-1 and the total pore volume is 0.59cm3·g^-1.SEM shows that the surface is loaded with Fe₃O₄ particles,and the specific saturation magnetization is15.9ome·g^-1,make it easy to be separated.The surface contains functional groups such as-OH,-C-H,-N-H,and C-O.The crystal structure is more orderly after loading Fe₃O₄,and there are diffraction peaks related to Fe₃O₄;（5）.The experimental values of the maximum adsorption capacity of MBC on MB and P4R were 465.6mg·g^-1 and 336.6mg·g^-1,respectively.When the dosage of MBC is 0.010g and0.015g,the removal rate and adsorption capacity of MB and P4R can be maintained at a high level.The lower p H is conducive to the adsorption of P4R,and the higher the p H is conducive to the adsorption of MB.As time and initial concentration increase,the adsorption capacity of both dyes increases.With the increase of temperature,the adsorption capacity of methylene blue increases,while the adsorption capacity of carmine decreases;（6）.The adsorption thermodynamics study shows that the adsorption of MB by MBC is a high-temperature spontaneous adsorption process,and the adsorption of P4R is a low-temperature spontaneous adsorption process.The adsorption process of MBC for MB can be well described by the Langmuir adsorption model,which is a single-layer adsorption,and the Freundlich adsorption model can well describe the adsorption process of MBC for P4R,which is a multi-layer adsorption.Both of the two dyes adsorption process are all in line with the quasi-second-order kinetic model,meanwhile there is an intra-particle diffusion process,but it is not a rate-controlling step,which means the adsorption process is affected by various adsorption mechanisms.MBC has an acceptable adsorption effect on other types of dyes,and has a certain recycling capacity when thermal regeneration is not activated.