DES Assisted Synthesis Of Nitrogen-doped Magnetic Biochar For The Elimination Of Cr（Ⅵ） And Ibuprofen:Mechanism And Performance Insights

Agricultural and forestry waste biomass is often difficult to be effectively utilized,and the preparation of biochar by pyrolysis is a good utilization method.Deep eutectic solvent（DES）is a uniformly mixed solvent composed of a certain molar ratio of hydrogen bond acceptors and hydrogen bond donors,and which commonly used in the fields of metal electrodeposition,organic synthesis,separation and purification,and synthesis of functional materials.In this study,a low-cost and environmentally friendly biochar material was prepared using DES as a modifying agent and used to remediate Cr（Ⅵ）and ibuprofen（IBP）pollution in water bodies.The main research conclusions are as follows:（1）In this study,FeCl₃/urea-based DES and peanut shell（PS）were used as modifier and biomass raw material respectively to prepare nitrogen-doped magnetic biochar（NMBC）by one-step pyrolysis at 500^oC,and which was used to remove Cr（Ⅵ）.The experimental results shown that during the synthesis of NMBC,DES can not only be used as a source of heteroatoms for N and Fe doping,but also promote the pyrolysis of PS and the formation of pore structures at lower temperatures.The NMBC exhibited a distinct microporous structure.In addition,adsorption experiments showed that the removal process of Cr（Ⅵ）by NMBC was a spontaneous and endothermic multi-stage process dominated by chemisorption.Coexisting ions and cycling experiments confirmed the strong anti-interference performance and stability of NMBC.FTIR and XPS characterizations confirmed that oxygen-and nitrogen-containing groups as well as Fe ions were involved in the removal of Cr（Ⅵ）,and the removal mechanisms included pore filling,electrostatic attraction,cation bridges,ion exchange,reduction,and surface complexation.The method used in this experiment was simpler than the traditional mechanical grinding and impregnation methods,and the prepared NMBC has better removal effect of Cr（Ⅵ）.（2）By optimizing the preparation conditions of NMBC,the effect of preparation conditions on the performance of NMBC and its removal performance on IBP were explored.The characterization results shown that the increase of pyrolysis temperature was beneficial to the formation of pore structure.BET analysis indicated that the prepared samples showed obvious microporous and mesoporous characteristics,and the micropore size was mainly 1.3-1.6 nm.Meanwhile,high temperature can significantly enhance the species and content of iron species on the surface of the sample,and enhance its saturation magnetization.In addition,Boehm titration analysis indicated that the pyrolysis temperature and the amount of PS significantly affected the content of acidic groups（carboxyl group,lactone group,phenolic hydroxyl group and carbonyl group）and basic groups in NMBC,and the level of p H_pzc was closely related to the carbonyl group content.The adsorption experiments showed that the removal of IBP was a spontaneous and exothermic multi-stage process dominated by chemisorption.Coexisting ions and cycling experiments confirmed that NMBC_600-1.2has strong anti-interference performance and stability.The removal of IBP by NMBC_600-1.2 is the result of the combined action of various mechanisms mainly based on chemisorption,and the removal mechanism is mainly based on the hydrogen bonding of phenolic hydroxyl groups andπ-πinteractions.In addition,electrostatic interactions,pore filling and ion exchange also participate in the removal process.This study confirmed that the feasibility of DES-assisted preparation of NMBC and the synthesized NMBC were used to remove heavy metals and organics from water bodies.It provides a feasible method for the reuse of waste biomass and expands the application of DES in the synthesis of carbon functional materials.