Study On The Adsorption And Degradation Performance Of Modified Lignin-based Porous Carbon For Heavy Metals And Polycyclic Aromatic Hydrocarbons

Heavy metals and polycyclic aromatic hydrocarbons（PAHs）are two types of pollutants that are ubiquitous in the environment,which are carcinogenic,teratogenic and mutagenic.They not only destroy the balance of the ecosystem,but also enter the human body through the food chain,causing serious harm to human health.Therefore,it is urgent to explore economical,safe,and efficient environmental pollutant treatment technologies to remove heavy metals and polycyclic aromatic hydrocarbon.In this paper,a series of functional porous carbon materials were prepared and modified using lignin extracted from papermaking black liquor as a precursor.The adsorption method and advanced oxidation technology were used to achieve the removal of heavy metals Cd（Ⅱ）,1-naphthol and naphthalene.The relationship between the morphology,structure and performance of the material was discussed,and the optimal reaction conditions for adsorption and degradation were determined.At the same time,the reaction mechanism for the material to adsorb heavy metal ions and catalytically degrade organic pollutants was proposed.The main content included the following three aspects:（1）Three-dimensional magnetic nitrogen-doped porous carbon modified by EDTA（N-MPC-EDTA）was successfully prepared by two-step method with lignin as the precursor,and was used for the removal of Cd（Ⅱ）.The 3D adsorbents were characterized by SEM,TEM,BET,XRD,XPS and the performance of the materials was tested by the batch adsorption method.The results showed that the material presented a three-dimensional network porous structure and had excellent adsorption performance for Cd（Ⅱ）.Under the condition of pH=6,the equilibrium adsorption capacity of Cd（Ⅱ）was 43.68 mg·L^-1 and the adsorption equilibrium was quickly reached within 45 min.A possible adsorption mechanism was proposed,in which the chelation of EDTA as well as the electrostatic attraction of hydroxyl,carboxyl and nitrogen-containing functional groups dominated the adsorption of Cd（Ⅱ）.The adsorption kinetics and isotherm data fitted well with the pseudo-second-order kinetic model and Freundlich model,respectively.After four adsorption and desorption experiments,N-MPC-EDTA still had a good adsorption capacity for Cd（Ⅱ）.This work provided a new type of material for the adsorption of heavy metal ions in the environment,and had a good application prospect in wastewater treatment.（2）A novel iron nanoparticles encapsulated within nitrogen and sulfur co-doped magnetic porous carbon（Fe-N-S-MPC）was proposed by one-pot pyrolysis strategy to activate PMS to degrade 1-naphthol using low-cost lignin as precursors.The Fe-N-S-MPC was characterized for structure and properties by SEM,TEM,FT-IR and XPS.The obtained materials had the morphology of iron nanoparticles encapsulated within nitrogen and sulfur co-doped magnetic porous carbon with rich functional groups and large specific surface area,which made the materials have a good catalytic property.It was proved that the doping of nitrogen and sulfur was pivotal for improving the catalytic performance.The radical quenching experiment confirmed that sulfate radical（SO₄.^-）and hydroxyl radical（OH.）were two major reactive oxygen groups.The reaction had phenomenon of the free radicals upsurge in the early stage and the shortage in the later stage.Therefore,a mathematical model was put forward to represent the two-stage reaction kinetics.By adding oxidants in batches,the degradation effect could reach nearly 100%within 30 min.This work provided a new type of catalytic material by the high-value utilization of waste for the degradation of organic pollutants.（3）Using lignin as precursor,a novel three-dimensional flower-like nitrogen-doped Fe-Cu bimetallic nanoparticle composite（FeCu-N-PC）was prepared by direct pyrolysis for catalytic degradation of naphthalene in the presence of PMS.Under the conditions of 20 mg.L^-1naphthalene,0.1 g.L^-1 FeCu-N-PC,0.4 g.L^-1 PMS and pH=3,the FeCu-N-PC catalyst degraded 93.2%of the naphthalene within 60 min.Through SEM,TEM,FT-IR and XPS characterization,we proposed the unique structure and composition of FeCu-N-PC.The porous flower-like carbon matrix not only facilitated the rapid diffusion of the reactants to the internal bimetallic nanoparticles,but also provided a specific adsorption effect to enrich the naphthalene molecules from the solution,increasing the probability of contact between naphthalene and free radicals,and further improving reaction efficiency.The quenching reaction proved that the non-radical pathway（involving ¹O₂）was considered to be the main catalytic reaction,and the free radical pathway（involving SO₄.^-and OH.）played a secondary role.In addition,with its high magnetization performance,FeCu-N-PC can be magnetically recovered and after four degradation cycles,80%of naphthalene was still degraded.This work provided a theoretical basis for the development of green,high-efficiency,and environmentally friendly technologies for the treatment of environmental pollutants.