Preparation Of Lignin-based Adsorbents And Study On Their Adsorption Properties For Dyes And Heavy Metal Ions

The use of renewable biomass resources instead of traditional fossil resources is one of the hot spots in contemporary chemical research.Lignin as reserves on earth after cellulose,the second largest biomass resources,its structure contains rich active functional groups,absorbs some dye molecules and the heavy metal ions,biomass resource utilization and environmental protection play an irreplaceable role,is more than 95%of the lignin treated as waste combustion use,can not achieve high resource utilization.In this paper,lignin was used as raw material to prepare modified lignin-based adsorbents with good adsorption and removal ability for dyes and heavy metal ions.The chemical structure and adsorption performance of the prepared lignin-based adsorbents were studied in detail,which further widened the application channels of lignin.The thesis is mainly divided into the following two parts.（1）To prepare magnetic lignin-based adsorbent and explore its adsorption mechanism.Using lignin as raw material,an improved co-precipitation synthesis method was adopted.First,lignin was modified on the surface of magnetic Fe3O4nanoparticles,and then the magnetic lignin-based adsorbent was obtained by high temperature carbonization.The average particle size of magnetic lignin particles was5.42um,and the saturation magnetization was about 51.3 emu/g.The specific surface area is 42.1 m²/g,the average pore diameter is 12.3 nm,belongs to the mesoporous structure.The experiment of adsorption of methyl orange by magnetic lignin-based adsorbent shows that the adsorption process conforms to Langmuir adsorption model and quasi-second order adsorption dynamic model,which belongs to chemical adsorption.The whole adsorption process belongs to entropy reduction and spontaneous process.The maximum adsorption capacity of magnetic lignin-based adsorbent on methyl orange is 85mg/g,and the magnetic lignin-based adsorbent can be recycled by soaking 95%ethanol.（2）Preparation of amine lignin adsorbent and explore its adsorption mechanism.The effect of different experimental conditions on the nitrogen content of amine lignin was investigated.The maximum nitrogen content of the product was 7.93%.The average molecular weight（MW）and number average molecular weight（Mn）of amine lignin were 4354 and 1162,respectively.The adsorption experiments showed that the adsorption rate of amine lignin for Pb²⁺was very fast,and the adsorption saturation point could be reached at about 60min.The adsorption process was consistent with the Langmuir adsorption isothermal model and the pseudo-second-order adsorption kinetics model.The maximum adsorption capacity of amine lignin for Pb²⁺was 69.3mg/g.The preparation of amine lignin from lignin has the advantages of high adsorption efficiency and environmental protection,which can be used to treat heavy metal ion wastewater.