Functionalization And Dissolution Of Cellulose In Ionic Liquid For Adsorption

With the rapid development of modern industrial economy,the accompanying large-scale discharge of municipal and industrial wastewater has caused serious soil and water pollution in our country.Soil and water pollution is harmful to the growth and development of forest and other plants,and they will erode animals and humans through the food chain,causing great harm to the whole ecosystem.As a green and environmental friendly material,cellulose has many advantages,such as wide sources,excellent biocompatibility,renewability and environment friendly,and has received more and more attention from scientific researchers.In this dissertation,a series of cellulose-based materials were prepared and functionalized via introducing specific functional groups through various chemical modifications.In order to provide a reference for achieving the efficient utilization of cellulose,the as-prepared green adsorbents were used in the fields of wastewater treatment and heavy metal contaminated soil remediation.The results of this work were as follows:(1)Preparation and properties of carboxyl modified cellulose.The diethylenetriaminepentaacetic acid(DTPA)-modified cellulose adsorbent(DTMC)was prepared using N-[3-(trimethoxysllyl)propy]eth ylenediamine as a crosslinking reagent and used for the removal of Hg(?)ions from aqueous solution.Fourier Transform Infra-Red spectroscopy(FTIR)analysis showed the existence of-COOH and-NHCO-groups in DTMC.X-ray diffraction(XRD)confirmed the breaking of hydrogen bond among the cellulose hydroxyl groups.The scanning electron microscope(SEM)implied the rough surface in DTMC,indicating that DTPA are successfully attached to the surface of cellulose.The experimental and modeling results indicated that the adsorption process was better described by Langmuir isotherm model,and the maximum adsorption capacity reached as high as 476.2mg·g-1.The adsorption kinetics matched well with the pseudo-second-order kinetic model and mainly controlled by chemical adsorption.The thermodynamic analysis of adsorption showed that the adsorption was a spontaneous and endothermic process.Furthermore,the cellulose-based adsorbent had good regeneration performance,maintaining more than half of the initial adsorption capacity after seven adsorption-desorption cycles.(2)Preparation and properties of regenerated porous cellulose beads in ionic liquid.Modified porous cellulose beads(MCBs)with typical sizes ranging from 2 to 3 mm were successfully fabricated via acidic precipitation from the cellulose dissolved in 1-Butyl-3-methylimidazolium chloride([BMIM]Cl)ionic liquid,followed by surface-grafting with aminoguanidine hydrochloride using glutaric anhydride as a coupling agent.Modified cellulose powders(MCPs)(size ?m)were prepared by precipitating the solution of the cellulose which reacted with glutaric anhydride homogeneously in ionic liquid,followed by grafting with aminoguanidine hydrochloride.Batch adsorption experiments of MCBs and MCPs towards Hg(II)and Cu(?)were conducted under different conditions;and the results indicated that the pseudo-second-order kinetic model and the Langmuir isotherm model described the adsorption process well.The maximum adsorption capacities of MCBs towards Hg(?)and Cu(?)ions were 581.4 and 94.88 mg/g;whereas the maximum adsorption capacities of MCPs for Hg(?)and Cu(?)ions were 625 and 98.52 mg/g,respectively.The regeneration experiment indicated that MCBs maintained 79.4%adsorption capacity for Hg(?)and 70.5%adsorption capacity for Cu(?);whereas MCPs kept 78.7%adsorption capacity for Hg(?)and 67.5%adsorption capacity for Cu(?)after 10 recycles,demonstrating the good performance and recyclability of both adsorbents.(3)Preparation and properties of porous magnetic cellulose microspheres regenerated in ionic liquid.Porous magnetic cellulose/Fe3O4 beads(MCFBs),consisting of cellulose as matrix and ferrosoferric oxide,were successfully fabricated from microcrystalline cellulose dissolved in an ionic liquid and further modified with glutaric anhydride.FTIR structure analysis exhibited that the carboxyl groups were successfully introduced into MCFBs;XRD confirmed that Fe3O4 particles were well embedded in cellulose matrix;The saturation magnetization values of MCFBs was 9.34 emu/g,and MCFBs can be successfully separated from aqueous solution by applying an external magnetic field.The thermogravimetric analysis curve(TGA)showed that MCFBs had better thermal stability than cellulose.SEM and TEM images confirmed the spherical and porous structures of MCFBs.The adsorption behaviors indicated that the adsorption kinetics was preferably fitted to the pseudo-second-order kinetic model and mainly controlled by chemical adsorption;whereas the adsorption isotherms were well described by Langmuir model with the maximum adsorption capacity of 1186.8 and 151.8 mg/g for methylene blue(MB)and Rhodamine B(RhB),respectively.Regeneration experiments showed that the adsorption capacities on MCFBs retained 88.4%and 81.6%of the original adsorption capacities for MB and RhB after five reactive cycles.(4)Preparation and characterization of novel porous cellulose/chitosan composite microspheres.Zero-valent iron nanoparticles were successfully immobilized in porous cellulose/chitosan spheres with the size of approximately 2.5 mm,by using NaBH4 as a reducing agent and PEG-2000 as a dispersant to create nZVI/PCSs composite spheres.FTIR spectra proved the existence of amino groups and Fe-O groups in nZVI/PCSs;XRD confirmed that the Fe(0)took part in the adsorption of the Cd(?)ions;SEM images showed the porous structure of nZVI/PCSs,and nZVI particles were evenly distributed on the surface and inside the pores of PCSs after the loading.The reaction between nZVI/PCSs and Cd(?)was mainly responsible for the adsorption of nZVI towards Cd(?)ions,X-ray photoelectron spectroscopic(XPS)further revealed that Fe(0)and amino groups in nZVI/PCSs played crucial roles in the removal Cd(?)via the effects of precipitation or chelation.Through water and soil experiments,the adsorption performance of nZVI/PCSs on Cd(?)in aqueous solution and the solidification and stabilization effect of Cd(?)contaminated soil were investigated.The results from the experiments in aqueous solution and model fitting showed that the adsorption of Cd(?)induced by nZVI/PCSs was better described by Langmuir isotherm and the maximum adsorption capacity reached up to 110.3 mg/g.The soil remediation tests demonstrated that nZVI/PCSs could significantly enhance Cd immobilization,enabling the incorporation of most exchangeable Cd into Fe-Mn oxides and organic matter in contaminated soil after the remediation.