Preparation Of Functionalized Multiwalled Carbon Nanotubes And Their Adsorption Performance On Furfurylamine

Furfurylamines have many applications as monomers in the synthesis of biopolymers and the preparation of pharmacologically active compounds.There are chemical and biological methods for the synthesis of furfuryl amine.The chemical method is usually based on the reductive amination of furfural over metal catalysts.It not only requires high temperature and high pressure reaction conditions,but also has high cost,many by-products and serious environmental pollution.In recent years,in order to solve the above problems,in 2017 and 2020,some scholars reported the biosynthesis of furfurylamine,which has the advantages of high efficiency,green and mild,but its separation and purification is an urgent problem at present.Based on adsorption separation,a series of synthesis strategies of monomer polymerization and acidification modification were established in this paper.Abundant carboxyl functional groups were introduced into MWNTs matrix,and the adsorption properties of MWNTs for furylamine were studied.(1)Preparation and adsorption properties of MWCNTs-AA-COOH.We designed and synthesized a series of carboxyl modified multi-walled carbon nanotubes(MWCNTs),including four modification strategies(acidification,grafting,acidification and grafting,grafting and acidification).In general,grafting and acidification were the best strategies.Firstly,the MWCNTs were utilized to carry out efficient free radical polymerization,and the adsorption capacity(Q_e)of MWCNTs on AA was up to 96.04mg/g.In order to obtain a higher adsorption capacity,the amount of initiator,monomer concentration,solvent type,temperature and reaction time were optimized during the docking process,and the adsorption capacity was increased to 133.16mg/g.On this basis,the Box-Behnken design experiment was carried out by Design-Expert,and the best experimental scheme was obtained.The adsorption capacity of MWCNTs-AA-COOH to furfurfuramine was 176.29 mg/g.TEM further proved that acidification caused damage to the grafted layer.MWCNTs-AA-COOH has 59.3%more Q_e than commercial materials.In addition,the adsorption behaviors of MWCNTs-AA(grafted material),MWCNTs-COOH(acidified material)and MWCNTs-AA-COOH(grafted and acidified material)were systematically studied.Langmuir equation can describe the adsorption process well,indicating that the adsorption process is internal heat and chemical adsorption process(Q_m=280.71mg/g).At the same time,the kinetic adsorption can be better fitted by Pseudo-second-order kinetic equation(Pseudo-second-order),which indicates that the adsorption rate of MWCNTs-AA-COOH is faster.After six cycles,the adsorption capacity only decreased by 6.8%,which indicated that the regeneration performance was good.Finally,the adsorption mechanism was analyzed according to FT-IR and X-Photoelectron spectroscopy(XPS)before and after adsorption,which showed that the adsorption mechanism was ion exchange.The above results show that MWCNTs-AA-COOH is a kind of efficient furosamine adsorption material.(2)Preparation and adsorption performance study of MWCNTs-AA-DVB-COOH.MWCNTs-AA-COOH has good adsorption performance,but this type of material is mainly linear polymerization reaction,and the utilization of the substrate modification sites is not sufficient.If a cross-linking agent is introduced,the polymerization reaction efficiency can be improved by constructing a reticulated polymer structure,and more matrix modification sites can be exposed for acidification modification,which is expected to obtain new materials with higher carboxyl loading.During the polymerization process,the amount of monomer,monomer type,cross-linker amount and reaction time were screened to obtain the superior material MWCNTs-AA-DVB with the adsorption capacity up to 140.67 mg/g.Further acidification on this basis yielded the material MWCNTs-AA-DVB-COOH with the adsorption capacity up to220.89 mg/g.MWCNTs-AA-DVB-COOH was 35.71,2.94,1.69,and 1.57 times higher than MWCNTs,MWCNTs-COOH,MWCNTs-AA,and MWCNTs-AA-DVB,respectively.Since the Langmuir model has a higher fitting coefficient compared with the Freundlich fit,the Langmuir model can better describe the adsorption process of MWCNTs-AA-DVB-COOH on furfurylamine.Meanwhile,the adsorption capacity showed an increasing trend with the increase of temperature,and the adsorption process was a heat absorption process.To investigate the kinetics of the adsorption process of furfurylamine by MWCNTs-AA-DVB-COOH,the correlation coefficient of Pseudo-second-order fitting was higher,and the adsorption processes all conformed to the quasi-second-order kinetic equation,and the adsorption rate of MWCNTs-AA-DVB-COOH was the fastest.The regeneration performance of the adsorbent was verified,and the adsorption capacity only decreased by 6.85%after six adsorption-desorption cycles,indicating that the adsorbent MWCNTs-AA-DVB-COOH had good regeneration performance.The carboxyl content of the material was precisely quantified,and the optimal material carboxyl content was 8.38 mmol/g,and the adsorption capacity was proportional to the content of carboxyl functional groups.Finally,the adsorption mechanism was analyzed based on the characterization of FT-IR and XPS before and after adsorption and the quantification of carboxyl groups,which revealed that the adsorption mechanism was ion-exchange interaction.