| Due to the fast industrial and agricultural development and accelerated urbanization process,although people's living standard is rising,the resulted water contamination is becoming a more and more serious environmental problem.As the typical pollutants in water,organic dyes,pesticides or heavy metal ions could cause a serious threat to the ecosystem and human health.Among the many physical and chemical methods for the removal of typical pollutants in wastewater,adsorption method has become a common technology in water purification field,owing to its advantages of convenient operation,simple design and low cost.As the key in the adsorption method,the performance of adsorbent plays a decisive role.Various types of adsorbents have been studied and developed constantly.The results have shown that reducing the dimension size of the adsorbent could increase the adsorption sites and then improve the adsorption capacity.Electrospinning could fabricate one-dimensional nano/micron scale fibers,which could achieve the purpose of reducing material dimensions.The one-dimensional micro/nano fibers prepared by electrospinning technique show high porosity,easy preparation,easy modification,and recoverability,which makes them as suitable adsorbents in wastewater treatment.Among the many electrospun fiber adsorbents,electrospun organic polymer fibers have advantages of good film forming,easy separation and wide varieties,rendering them being better choices for electrospun fiber adsorbents.In order to further improve the adsorption performance of traditional electrospun polymer fiber adsorbents,modification is an effective way and it is also the current research hotspot.Herein,on the basis of above introduction,this thesis focuses on the preparation of modified electrospun organic polymer fiber adsorbents and investigating their adsorption performance toward typical pollutants in water.Through choosing different materials and modification ways,a series of high-performance electrospun fiber adsorbents were prepared and studied the adsorption toward organic dyes,organic pesticide or heavy metal ions in detail,which aims at the preparation of high efficiency,cheap,recycled water treatment absorbents and contributes to the development of a new type of adsorbents.The detailed contents are shown as follows:1.Blending electrospinning is a simple and direct way to obtain modified electrospun polymer fiber,and choosing effective modified materials is important.b-Cyclodextrin has special toroid-shaped molecular structure(hydrophobic internal cavity and hydrophilic external surface)and it can form noncovalent host–guest inclusion complexes with a variety of dye molecules,making it a good dye adsorbent material.b-Cyclodextrin modified electrospun polymer fibers were prepared by blending electrospinning,cross-linking agent citric acid was also added into the electrospinning system and in-site thermal cross-linking was conducted to make b-cyclodextrin based fibers insoluble in water and possible for the adsorption of dye methylene blue(MB).These preparation processes could solve the problem that water-soluble b-cyclodextrin materials couldn't be used as adsorbents in aqueous phase directly.(1)b-Cyclodextrin/sericin/poly(vinyl alcohol)composite fiber adsorbent(PVA-SS-CD)was firstly fabricated by blending electrospinning using water as the electrospinning solvent.After the following thermal cross-linking,the insoluble fraction of PVA-SS-CD was above 95%.The adsorption process toward MB by PVA-SS-CD fitted well with the pseudo-second-order model and Langmuir isotherm model.The calculated maximum adsorption capacity was 187.97 mg/g at 20 oC and the removal efficiency even remained above 92% after five adsorption-desorption cycles.(2)To improve the content of b-cyclodextrin in the composite fibers,N,N-dimethylformamide was used as the electrospinning solvent to prepare b-cyclodextrin/poly(acrylic acid)composite fiber adsorbent through blending electrospinning;the mass fraction of b-cyclodextrin in the composite fiber can be as high as 71.43%.The obtained maximum adsorption capacity toward MB by cross-linked b-cyclodextrin/poly(acrylic acid)composite fiber adsorbent was 826.45 mg/g.In addition,due to the existence of polyacrylic acid and citric acid,there were rich carboxyl groups on the surface of the composite fiber adsorbent,making it separate the methylene blue/methyl orange mixture solution by static adsorption and dynamic filtration;the separation efficiencies are both over 99%.2.To make the modified materials distribute onto the surface of electrospun fibers and contact with adsorbate more adequately,we combined electrospinning with hydrothermal carbonization method to prepare flexible hydrothermal carbon coating modified electrospun polyacrylonitrile(PAN)fibers and the as-prepared fiber adsorbents were employed for the adsorption of herbicide from agricultural wastewater.(1)Carboxyl group-rich hydrothermal carbon coated PAN fibers were firstly fabricated.Glucose was used as the hydrothermal carbon source and cross-linking reaction by ethanediamine was necessary to improve the stability of the electrospun PAN fibers for hydrothermal process.Carbon coated PAN fibers were activated by Na OH solution;and then carboxyl group-rich hydrothermal carbon coated PAN fiber adsorbent(AC-PAN)was obtained.AC-PAN was used to adsorb cationic herbicide paraquat.The adsorption process obeyed with the pseudo-second-order model and Langmuir isotherm model.The calculated maximum adsorption capacity was 437.64 mg/g and the removal efficiency even remained above 83% after five adsorption-desorption cycles.(2)In order to enrich the type of adsorbed pollutants,amino-rich hydrothermal carbon coated electrospun PAN fiber adsorbent(PAN@NC)was prepared by adding diethylenetriamine into the hydrothermal reaction solution.Diethylenetriamine in the hydrothermal reaction was not only the amino source but also the cross-linking agent for PAN fibers.The adsorption performance toward 2,4-dichlorophenoxyacetic acid by PAN@NC was investigated.The adsorption process fitted better with the pseudo-second-order model and Langmuir isotherm model.The maximum adsorption capacity was 164.47 mg/g and the removal efficiency even remained above 93% after five adsorption-desorption cycles.3.In order to obtain tighter surface modification,graft modified electrospun PAN fiber adsorbents were fabricated though chemical bond connection and the obtained fiber adsorbents were used for the adsorption of heavy metal ions.(1)Phosphate,amine dual groups grafted electrospun PAN fiber adsorbents(PN-PAN)were prepared through cross-linking,amination and phosphorylation;and the adsorption ability of PN-PAN toward Pb2+,Cu2+,Ag+ and Cd2+ was studied.Kinetics of adsorption was found to follow pseudo-second-order rate equation.The adsorption isotherms of PN-PAN toward Pb2+,Cu2+,and Ag+ were fitted better with Freundlich isotherm and the adsorption of Cd2+ was fitted better with Langmuir isotherm.By comparison,the adsorption capacities by phosphate,amine dual groups grafted electrospun PAN fibers toward Pb2+,Cu2+,and Ag+ were higher than only amine groups grafted electrospun PAN fibers.After three adsorption-desorption cycles,the removal efficiencies for all the metal ions even remained above 80%.(2)We prepared a novel branched polyethylenimine(b PEI)grafted electrospun polyacrylonitrile(PAN)fiber adsorbent(b PEI-EPAN)by a facile refluxing approach and studied its adsorption performance toward Cr(VI).The adsorption process obeyed with the pseudo-second-order model and Langmuir isotherm model.The calculated maximum adsorption capacity was 637.46 mg/g and the removal efficiency even remained above 90% after five adsorption-desorption cycles.Moreover,the residual Cr(VI)concentration could be decreased to below 0.05 mg/L(Cr(VI)concentration:10 mg/L or 20 mg/L,adsorbent dosage: 2 mg/m L).The b PEI-EPAN membrane could decrease the residual Cr(VI)in the filtrate to below 0.05 mg/L from over 50 m L of solution at a high flux of 731.7 L·m-2·h-1. |
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