Synthesis And Fabrication Of Functional Fibers And Their Sorption Behaviors And Mechanisms Of Predominant Perfluoroalkyl Acids

Perfluoroalkyl acids?PFAAs?as one of the most important part of Perfluorinated compounds?PFCs?have drawn great attention for their widely production and consumption.Because of the high-energy carbon-fluorine?C-F?bonds,PFAAs exhibits good chemical stability,persistence,bioaccumulation,and long-range transportation.So PFAAs could be found ubiquitously in the environment on a global scale.Therefore,investigations into the effective removal of PFAAs are urgently needed.Sorption treatments are widely applied because it provides an effective and economical approach to remove pollutants from water.Various types of sorbents have been reported to be effective for PFAAs removal.However,these sorbents that generally exist in the form of nano-powders or particles are difficult to recycle from water.Secondary contamination after sorption and their nanotoxicity may cause health and environmental risks once they are released into the water environment.They usually possess slow sorption,low sorption capacity.Moreover,the research in the dynamic mode has not started yet.The objective of this study is to realize effective removal of PFAAs and expend the application of functional fibers in the field of water pollution control.The detailed contents are described as follows:?1?Chitosan?CS?fibrous membranes grafted with?-cyclodextrin??-CD?were obtained by thermally induced phase separation?TIPS?.The overall appearance,internal structure,chemical composition of this functional fibers?CCFM?were evaluated.Sorption of Perfluorohexane sulfonate?PFHxS?,Perfluorobutane sulfonate?PFBS?and Perfluorobutanoic acid?PFBA?on CCFM was explored.It was found that the specific surface areas and the effective sorption sites would be affected by the ratio of CS/?-CD.Sorption capacities of PFHxS,PFBS and PFBA decreased as the steric effects from the excessive epichlorohydrin?EPI?concentration.Sorption kinetics was fitted with pseudo-second-order model and sorption isotherm was well fitted with Freundlich model.Sorption equilibrium coefficient decreased in the order PFHx S,PFBS and PFBA,indicating that the higher sorption energy for PFHxS.Furthermore,the sorption capacities of three contaminants were affected by solution pH and temperature.The positive value of?H⁰ indicates that the sorption process was endothermic.The CCFM show good reusability over five sorption-desorption cycles with mixture?ethanol solution of 0.05 mol/L NaOH?.?2?Polyacrylonitrile fibers?PANFs?-derived functional fibers?GTPANFs?were successfully prepared,and the preparation conditions were optimized using response surface methodology?RSM?.T_{-polyamine reaction},V_-GTA and T_{-quaterisation reaction} were the major factors affecting the strongly basic exchange capacity of GTPANFs.By numerical optimization,the GTPANFs were used to remove perfluorooctane sulfonate?PFOS?and perfluorooctanoate?PFOA?from aqueous solution.The GTPANFs exhibited the maximum adsorbed amount of2.78 mmol/g for PFOS and 2.49 mmol/g for PFOA,much higher than some conventional adsorbents.Solution pH in a wide range of 2-10 had little effect on their sorption process,and high sorption capacities were also achieved in the presence of coexisting anion.The uptake mechanisms including electrostatic and hydrophobic interactions besides anion exchange were involved in the sorption.Additionally,the GTPANFs have shown excellent performance of regeneration with the mixture of CH₃OH and 1%NaCl.?3?PANFs-derived activated carbon fibers?PACFs?were successfully prepared by one step carbonation-activation,and used to sorption perfluorooctane sulfonate?PFOS?and perfluorooctanoate?PFOA?.High specific surface areas?SSAs?and micro/mesoporous structure of PACFs were obtained by optimizing the preparation conditions of the PANFs-based pre-oxidized fibers?PANOFs?/KOH ratio and activation temperature.The as-prepared PACFs exhibited flexibility and endless forms,and the sorption capacities of 1.52 mmol/g for PFOS and 0.73 mmol/g for PFOA,much higher than the commercially available coal-based powder activated carbon?PAC?and granular activated carbon?GAC?,which was also indicated by the site energy distributions.The Intra-particle diffusion and Boyd's film-diffusion models were also used to verify the liquid film diffusion controlled the rate of sorption in the first stage slightly,and intra-particle diffusion was the main rate-controlling steps subsequently.It was assumed that the multilayer sorption may probably occur through electrostatic attraction and hydrophobic interaction,and form some micelles and hemi-micelles formation on the ACFs surface.The PACFs shown good reusability in five times sorption-desorption cycle studies.Finally,the function mechanism of PFOS were studied with DFT-B3LYP method.?4?Sorption of PFOS,PFOA and PFBS on PACFs by electrochemical polarization assistance were investigated.It was found that the adsorbates are electrochemically stable.Conventional three-dimensional electrodes quartz unit cell was employed in electrosorption experiments.The sorption kinetics of PFOS,PFOA and PFBS under electrochemical polarization assistance were well fitted with pseudo-second-order model.Compared with sorption of PFOS,PFOA and PFBS on PACFs,v₀ increased 59-fold,32.5-fold and 40-fold,q_e increased 1.28-fold,2.44-fold and 2.68-fold.k₂,q_e and E were interrelated.Considering of zeta potential of PACFs,the zero charge of PACFs electrode and N₂ sorption-desorption analysis of PACFs electrode before and after electrochemical polarization,electrochemical polarization can effectively enhance the v₀ and q_e due to the enhancement of electrostatic attraction and sorption sites.The sorption capacities of PFOS,PFOA and PFBS were also affected by C-F chain,electrolyte concentration and solution pH.Besides,a durable and convenient electrosorption device with PACFs electrodes were used to investigate the electrosorption performance of voltage,influent concentration,solution pH and HRT?Hydraulic Retention Time?for PFOS and PFOA in continuous flow mode,which could offer reference basis for practical application.