Preparation And Characterization Of Chitosan Supported Magnetic Biochars And Its Adsorption Properties Research

Biochar is typically obtained through the pyrolysis of biomass under oxygen-limited conditions.Biochar has received extensive attention due to simple preparation methods and the wide range of raw materials.Biochar is used to remove heavy metals and organic pollutants.In the study,chitosan/magnetic biochar（CMLB）with different loading rates was prepared by using loofah and by-products as precursor materials of biochar.CMLB was analyzed though X Ray diffraction（XRD）,Fourier Transform Infrared（FTIR）,Scanning Electron MiCroscopy（SEM）,X Ray Photoelectron Spectroscopy（XRS）,specific surface area and pore size analysis methods.The impact of various adsorption conditions were carried out,such as pH,contact time,solution concentration and temperature.The interaction mechanism between functional groups and heavy metals were also studied.The use of chitosan combined with magnetic biochar（CMLB）was prepared.The results showed that a layer of dense iron trichloride particles appeared on the surface of CMLB,which may beγ-Fe₂O₃.Theγ-Fe₂O₃ particles had the uniformity and consistency.After MLB is loaded with chitosan,the specific surface area is 104.91m²/g（40wt%-CMLB）.The drop of sample surface and pore volume were deeased as chitosan loading increases.Adsorption results showed 40%-CMLB had high Cr（Ⅵ）and Cu（Ⅱ）adsorption capacity of32.4 mg/g and 54.68 mg/g,respectively,reaching 86%of chitosan adsorption capacity.The initial solution pH 3.0±0.1 was used for Cr（Ⅵ）adsorption by CMLB.The initial solution pH5.8±0.1 was selected for further Cu（Ⅱ）adsorption experiments.These datas indicate that the pseudo-second-order model is more suitable for explaining the behavior of Cr（Ⅵ）and Cu（Ⅱ）adsorption on CMLB.The fitting adsorption capacity is closer to the equilibrium adsorption capacity.Freundlich isotherm model was more appropriate than Langmuir model to depict the adsorption behavior of CMLB towards Cr（Ⅵ）and Cu（Ⅱ）.Though results of magnetic separation experiments showed that the saturation magnetization（Ms）of the CMLB compsite was 15.6 emu/g,which can be separated from the aqueous phase.After the third cycle,Cr（Ⅵ）and Cu（Ⅱ）adsorption by CMLB was 24.34 mg/g and 42.6 mg/g,respectively.The interaction mechanisms of removal of Cr（Ⅵ）and Cu（Ⅱ）include three key steps:（1）physical adsorption,where Cr（Ⅵ）and Cu（Ⅱ）were adsorbed and completely reduced by porous material;（2）ion exchange&surface complexation,where Cr（Ⅵ）and Cu（Ⅱ）were adsorbed onto active sites of CMLB sample;（3）precipitation,where Cr（Ⅵ）and Cu（Ⅱ）were adsorbed by combination with exchangeable cations.