Study On Preparation,properties And Application Of Novel Nitrogen-containing Chelating Adsorption Fibers

In recent years,with the continuous growth of population and the accelerating industrialization process,a large number of heavy metal pollutants have been discharged into the environment.The pollutants in the form of industrial wastewater and urban domestic sewage have caused the destruction of the ecological functions of water body and,accordingly,have become the most serious problem with respect to water crisis.It is well known that to remove such pollutants,relying on the self-purification ability of water without any other treatments,is quite inefficient,so it is much necessary to develop and utilize the corresponding advanced technology for removing the metal pollutants and repairing the contaminated water.At present,there are various techniques for removing the metal pollutants including chemical precipitation,membrane-based separation,ion-exchange adsorption,and solvent extraction.Among them,the ion exchange adsorption technology is one of the important research areas.The adsorption materials have high adsorption capacity,velocity and other advantages.Consequently,the adsorption process needs lower energy consumption and produces less pollution,and is a cost-effective and widely used water treatment technology.The chelating fiber is a functional polymer material,with which a complex can be formed through coordinating the target metal ion.Compared with adsorbents such as conventional resins,it has distinct advantages in adsorption efficiency and adsorption amount.In this paper,four new nitrogen-containing chelating fibers were synthesizedusingpolypropylene-?g?-styrene-divinylbenzene?PP-St-DVB?,polyphenylene sulfide?PPS?and polyacrylonitrile?PAN?fibers as the basic skeletons.The PP-St-DVB fiber was brominated and azide to obtain a novel chelating fiber;The PPS fiber was modified by chloromethylation or bromination,then the azido group was introduced into the fiber to obtain two novel fibers;A novel tetrazolium chelating fiber was prepared by cycloaddition reaction between nitrile[3+2]and azido in PAN fiber.The conditions of preparing the adsorbent materials were discussed,the chemical structure as well as the thermal stability of the fibers was characterized.Also,the adsorption properties of four fibers for heavy metal ions Cd?II?,Hg?II?and Pb?II?were investigated.The full text is divided into five chapters,and the content summary is as follows:?1?A novel chelating fiber containing an azide group was prepared by a two-step reaction based on the PP-St-DVB fiber skeleton.Brominated fiber?PP-St-DVB-Br?was obtained by halogenation of PP-St-DVB fiber with bromine in Cl₂CH₂ solution.The brominated fiber undergoes a C-N Ullmann coupling reaction under copper catalysis,and the azide group is directly bonded to the benzene ring to obtain a chelating fiber?PP-St-DVB-TN?.The structure and properties of the fiber were characterized by FT-IR,EA,TGA,SEM and chemical titration,respectively.The adsorption isotherms,adsorption kinetics and reusing performance of the fibers were studied.The results showed that the azide content of the fiber was 2.11 mmol/g.The fiber has good adsorption capacity for Hg?II?and Pb?II?ions.The adsorption process for Hg?II?and Pb?II?accords with the Langmuir equation.The calculation of thermodynamic parameters indicates that the adsorption behavior is a spontaneous chemical adsorption process,which can reach equilibrium within 30 min.The kinetic adsorption process conforms to the quasi-second-order kinetic equation.The saturated adsorption amount was 408.9 mg/g for Hg?II?and 334.4 mg/g for Pb?II?.Five adsorption cycles showed that the fiber adsorption performance hardly changed after regeneration.?2?A novel PPS-based chelating fiber?PPS-CH₂-TN?was synthesized based on the nucleophilic substitution of chloromethyl with sodium azide on chloromethylated PPS fibers?CMPPS?.The structure and properties of the fiber were characterized.The highest azide content of the fiber was 3.20 mmol/g.The adsorption capacity of the fiber for Cd?II?was preliminarily studied and the effects of pH value and initial concentration of Cd?II?were systemically investigated.The results showed that the fiber could adsorb Cd?II?at pH 1.0-7.0,and the adsorption capacity was the strongest in weak acid environment,and the adsorption capacity of Cd?II?was 342.5 mg/g.More importantly,the adsorption equilibrium can be reached within 20 minutes indicating a fast adsorption when using the PPS-CH₂-TN fiber.?3?The pre-crosslinking reaction of PPS fiber was carried out by using nitrated4,4'-dichloromethylbiphenyl?BCMB?to improve the application stability of the fiber.A novel chelating fiber?PPS-Bc-TN?was obtained by grafting an azido group on the crosslinked PPS fiber by a two-step reaction.The bromination of the benzene ring in main chain of PPS fiber can be achieved by the reaction of liquid bromine,and sodium azide is coupled with the bromine on the benzene ring by C-N coupling.The highest azide content of the fiber was 2.45 mmol/g.The method avoids the complicated irradiation grafting process of ⁶⁰Co or other radiation devices.The adsorption of Hg?II?and Pb?II?on PPS-Bc-TN fiber was studied,and the adsorption isotherms and adsorption kinetics were described.The fiber can also be applied to achieve efficient adsorption of Hg?II?and Pb?II?in solution.The saturated adsorption amount was 406.7 mg/g for Hg?II?and 528.6 mg/g for Pb?II?.The fiber has potential applications in heavy metal wastewater treatments.The results of five adsorption cycles showed that the fiber's adsorption did not change much after regeneration.?4?A new method for chemically modification of grafted polyacrylonitrile?PAN?fibers with chelating groups was explored.The PAN fiber matrix has a large amount of-CN groups,in turn,has high reactivity.The nitrile group can undergo a[3+2]dipolar cycloaddition reaction with the azide.PAN fibers were pre-crosslinked with triethylenetetramine?TETA?.A novel PAN-based tetrazolium chelating fiber?PAN-Te-TTZ?was prepared by the crosslinked fiber?PAN-TETA?under the catalysis of CuI.The tetrazolium group content of the fiber was 7.90 mmol/g.It was found that the PAN fiber crosslinking process had a great effect on the[3+2]cycloaddition reaction.The adsorption behavior of the fiber on Hg?II?was preliminarily investigated.The adsorption capacity was the highest in the range of pH3.0-4.0,and the saturated adsorption capacity was 524.1 mg/g.The mechanism of the adsorbtion of Hg?II?by tetrazolium groups was discussed,which provided a theoretical basis and process reference for the practical application of PAN-Te-TTZ fibers in the treatment of mercury-containing wastewater.