Renewable Chitosan Modified Biochar For Pb(Ⅱ) Adsorption

Modified biochar and its application in environmental pollution remediation have attracted more and more researchers’attention.In this paper,the recyclable chitosan modified biochar（CBC）was prepared by pyrolysis,KOH activation and nitridat ion.The kinetics,thermodynamics and adsorption mechanism of Pb（II）were studied.The influence of relevant boundary conditions on the adsorption process was studied,and the recycling,performance stability of CBC and its feasibility as a reactive fil er for permeable react ive wall were confirmed.First,the activated bamboo biochar is prepared,and the bamboo is carbonized at different temperatures,and then mixed with KOH for activation at different temperatures to obtain the activated carbon with the best physical pore structure.Through elemental analysis,FT-IR,BET and SEM,it was found that the carbonization temperature of 500°C,the activated alkali carbon ratio of 1:4,and the activation temperature of 800°C are the best preparation condit ions.It is found that the aerobic functional groups in the carbonization process will continue to follow When the temperature is increased and removed,the KOH activation can affect the physical structure of the bamboo charcoal,and increase the pore volume and specific surface area.Secondly,biochar is modified by nitriding method,and a saturated chitosan acetic acid solution is arranged,glutaraldehyde is added to the activated bamboo charcoal,and the modified biochar material CBC is prepared by cross-linking of the aldehyde group.After modification,the elemental analysis and FT-IR results showed that the C/N ratio of the bamboo charcoal decreased by 11.9 times.After the modification,the surface of the biochar showed a large number of amine,hydroxyl and C-O functional groups.These functional groups are excellent heavy metal combinations.And it was confirmed by thermogravimetric weight loss curve that about 20%of chitosan was successfully loaded on activated biochar.Finally,Pb（II）static adsorption kinetics experiment,adsorption thermodynamics experiment and CBC regeneration adsorption experiment were carried out to investigate the adsorption capacity of the CBC.The fitting model was used to calculate the experiment and XRD,SEM and other characterization methods to verify Pb（II）Adsorption mechanism.Among them,the fitting of CBC to the adsorption isotherm of Pb（II）is more consistent with the Langmuir isotherm adsorption model,indicat ing that the adsorption of monolayers is dominant,and the adsorption kinetics of Pb（II）is more in line with the pseudo-second-order kinetics model.Chemical adsorption is dominant.XRD characterization also proves that the amine functional group of modified biochar can chelate with lead and form lead complex on CBC surface.Therefore,CBC adsorption of Pb（II）is a chemisorption process.The adsorption thermodynamics calculation proves that?H⁰ is positive and?G⁰ is negat ive,indicating that the adsorption process of heavy metal Pb（II）by chitosan modified biochar is a spontaneous endothermic process.At the same time,the CBC after saturated adsorp tion was placed in EDTA-Na₂ solution for heavy metal desorption,and then used for adsorption of Pb（II）.After five cycles of experiments,it was found that adsorption only decreased by20%,and the FT-IR analysis showed that the amine group which adsorbed on the surface of the cycle did not undergo large attenuation,which proved that CBC has the characterist ics of strong stability and recyclability.