Engineering Modification And Application Of Chitin-Derived Biochar

With the improvement of the economic level,shrimp and crab have become one of common foods in our daily life.While most of the inedible shrimp shells are discarded,only a small amount is recycled.Chitin,one of the main components of shrimp shells,is a natural alkaline polysaccharide that is widely used in biomedicine,agriculture,microelectronics,the environment,and the chemical industry.Due to the high nitrogen content in its own structure or chemical composition,chitin is an ideal raw material for the preparation of nitrogen-rich biochar.The pristine biochar BCs were prepared at different pyrolysis temperatures（350-650℃）to investigate the effects of pyrolysis parameters on the structural properties of biochar.The pristine biochar BCs were prepared based on hydrochloric acid pickling and modified by ball milling to optimize the structural properties of MBCs.The adsorption performance of pristine biochar has been poor for anionic pollutants due to its physicochemical properties.Ball-milled biochar（BMBC and Mg/Al-BC）was prepared by ball milling treatment to adsorb typical anionic pollutant arsenate and explore the changes in adsorption performance.Zero-valent iron is widely used for environmental remediation because of its high reactivity.However,zero-valent iron is very easy to focus on,and reducing the effective contact area with pollutants will reduce the adsorption efficiency.Biochar composites loaded with zero-valent iron can not only solve the problem of zero-valent iron focusing but also improve their adsorption performance.Therefore,this paper focuses on optimizing the structural properties of biochar,preparing a series of chitin-based biochar,and investigating the performance of adsorption of methylene blue and arsenate.The main research contents and results are as follows:（1）All biochar samples were characterized by SEM,BET,FT-IR,XRD,XPS,TG,and element analysis.Surface area,pore volume,and other surface functional groups were significantly improved after acidizing and ball-milling.The adsorption capacities for MB were MBC350>MBC500>MBC650>BC350>BC650>BC500,and the equilibrium adsorption capacities were 575.01 mg/g,506.52 mg/g,424.59 mg/g,113.31mg/g,93.53 mg/g and 86.25 mg/g,respectively.The excellent adsorption performance of MBCs for MB was ascribed to Lewis acid-base interaction,π-πinteraction,electrostatic interaction,and van der Waals,and the quinone group and pyridinic-N on the surface of the MBCs are identified as the major active sites.（2）Mg/Al hydroxides-modified biochar composite（Mg/Al-BC）was directly prepared using ball milling technology to effectively adsorb As（Ⅴ）,and nitrogen-rich biochar was obtained through pyrolysis using shrimp shells as precursors.Several characterization technologies including FTIR,BET,XRD,SEM,TG,XPS,and element analysis were used to analyze the adsorbent.The physicochemical characteristics of ball-milled biochar improved significantly compared with pristine biochar.The arsenic adsorption kinetics and isothermal models,the effects of p H,temperature,and co-existing anions were tested in batches.As（Ⅴ）adsorption capacities were Mg/Al-BC>BMBC>BC,their maximum adsorption capacities correspond to 24.49,6.52,and 0.49mg/g.The arsenic adsorbed onto Mg/Al-BC was dependent on p H and coexisting anions.Ion exchange,electrostatic interaction,precipitation,and surface complexation were possibly the governing adsorption mechanism.Protonation of pyridinic-N/quinone groups in biochar contributed to the electrostatic effect between arsenic anion and quaternary ammonium cation.（3）The magnetic composites of shrimp shell biochar loaded with zero-valent iron were prepared in one step by pyrolysis of FeCl₃-impregnated shrimp shell biomass under high temperature and anaerobic environment,which can efficiently remove As（Ⅴ）from the water environment.The physicochemical properties of the shrimp shell biochar were analyzed by characterization techniques such as XRD,FTIR,SEM,BET,XPS,and elemental analysis.The adsorption capacity of As（Ⅴ）was BC-ZVIc>BC-ZVIb>BC-ZVIa>BC,and the corresponding adsorption equilibrium capacities were119.7,40.13,33.01,and 27.04 mg/g.The adsorption behavior of shrimp shell biochar in solutions was also analyzed,fitted well by pseudo-second-order kinetic model,indicating that the adsorption process was controlled by multiple mechanisms.FTIR and XPS characterization of BC-ZVIc after adsorption of As（Ⅴ）were carried out to analyze the adsorption mechanism.The adsorption mechanisms include electrostatic gravitational interaction,complexation of Fe with As（Ⅴ）,and co-precipitation.