Study On Preparation,Adsorption And Desorption Performance Of Modified Lignin-Based Adsorption Materials

Lignin is a natural polymer material,which has the advantages of wide sources,renewable,good biocompatibility and environmental friendliness,it was regarded as one of the most potential functional polymers by the majority of scientific researchers.Due to the complexity and resistance of its structure,it has not been fully utilized for a long time.How to make full use of the large amount of oxygen-containing groups on its surface through functional design,and how to realize its high net value utilization is still the focus of the current research.In this study,an aminated lignin adsorbent was prepared by modifying of alkali lignin with polyethylenimine(PEI).A modified lignin based aerogel reinforced with graphene oxide(GO)was prepared by one-step hydrothermal method and freeze drying method.The structure of the samples was characterized by Fourier Infrared Spectroscopy(FTIR),Thermogravimetric Analyzer(TGA),Scanning Electron Microscope(SEM),X-ray Photoelectron Spectroscopy(XPS),Fully Automatic Specific Surface Area(BET),etc.When they were utilized as adsorbents to remove methylene blue(MB)and Cr(VI)from wastewater,the effects of initial solution concentration,solution p H,adsorbent dosage,adsorption time,temperature,and synthesis ratio of different materials on the adsorption were discussed.The adsorption mechanism was explored by the kinetic and thermodynamic equations.And the specific results are as follows:(1)The modified lignin adsorbent(ALN)can be prepared by grafting PEI to the surface of lignin through Mannich reaction.Its adsorption of MB reached equilibrium within 360 min,and the equilibrium adsorption capacity was 58.17 mg/g.The adsorption of Cr(VI)reached equilibrium within 600 min,and the equilibrium adsorption capacity was 36.18 mg/g.The adsorption process of both satisfies the Langmuir isotherm adsorption model(R~2 is 0.9942,0.9754,respectively)and the pseudo-second-order kinetic equation(R~2 is 0.9983,0.9979,respectively).It shows that the adsorption process was mainly the chemical adsorption of the monolayer.(2)The modified lignin aerogel adsorption material(ALG)can be prepared by the combination of modified lignin,chitosan(CS)and graphene oxide under hydrothermal conditions.When synthesized according to the ratio of ALN:CS:GO=10:1:20,the material has the best adsorption capacity.At p H=10,the temperature is 45℃,its maximum adsorption capacity for MB can reach 951.22 mg/g.At p H=2,the temperature is 45℃,the best adsorption capacity for Cr(VI)is 180.04 mg/g.The adsorption process also conforms to the Langmuir isotherm adsorption model(R~2 is 0.9838,0.9850,respectively)and the pseudo-second-order kinetic equation(R~2 is 0.9999,0.9990,respectively),and the process is mainly monolayer chemical adsorption.(3)After three cycles of adsorption experiments,the adsorption performance of ALN adsorbent on MB and Cr(VI)decreased by 33.61%and 49.89%,respectively.After five cycles of adsorption experiments,the adsorption performance of ALG on MB and Cr(VI)decreased by 14.66%and 15.38%,respectively.Compared with ALN,ALG has better renewable performance.