| Recently, environmental pollution, especially the wastewater containing metalions which is harmful to human body and animals, has been one of the seriousproblems for China in the development of modern industry. China is the country ofwater shortage, and the problem will be aggregated if we couldn’t control and treat thewastewater containing metal ions which was generated and discharged from industrialand agricultural production. Meanwhile, most of the metals are the necessary rawmaterials for many industries and agriculture. With the increasing consumption ofmetal and shortage of mineral resource, how to improve the recyclability and recoveryof the metal ions from the discharged effluents has been one of the popular researchtopics. Affinity membrane has been widely used as adsorption material for therecovery and removal of heavy metal ions, noble metals, rare metal ions, etc, whichcontains high selectivity, high rate, high efficiency, low energy consumption, easyoperation, non-secondary pollution, and so on.In this study, nanofibrous affinity membrane with hierarchical structures utilizedin the removal and recovery of heavy metal ions and rare earth metal ions has beeninvestigated. Firstly, a novel mussel-inspired composite nanofibrous affinitymembranes were prepared by the functional cortex of polydopamine (PDA) adheredonto the electrospun polysulfone (PSF)/polyacrylonitrile (PAN) nanofibers. Thereinto,a kind of micro-phase separation occurred due to the two incompatible polymers withPSF/PAN mass ratio of1:1, which resulted in the construction of heterogeneousstructure on the surface of PSF/PAN nanofibers. The PDA composite nanofibrousaffinity membrane with rough surface contains high specific surface area, which couldbe applied to the removal and recovery of rare earth metal ion of La3+in aqueoussolution. Secondly, highly porous PAN nanofibrous membranes were successfully fabricated by wet-electrospinning technique from PAN and poly(vinyl pyrrolidone)(PVP) blended solution using hot water bath as extractor, and then aminated withdiethylene triamine (DETA). The obtained aminated PAN (APAN) nanofibrousmembrane showed unique micro/nano structures and possessed extra high aminationrate, BET surface area and excellent mechanical property resulting in highly efficientrecovery of heavy metal ions of Pb2+, Cu2+, Cd2+from aqueous solution. Finally,micro-nano structured p-sulfonatocalixarene complex membranes prepared byelectrostatic adsorbing anionic p-sulfonatocalixarene onto the cationic nanofibrousmats with micro-nano structure were utilized as an affinity membrane for the selectiveadsorption of Lanthanum (III) ions in mixed metal cations aqueous solution.1. PSF blended with PAN was dissolved in dimethyl acetamide (DMAc) withmagnetic stirrer in water bath to form homogeneous solution for electrospinning, andthe heterogeneous structures on the surface of PSF/PAN composite nanofibers wasformed due to the micro-phase separation occurred during the process ofelectrospinning. The dopamine composite nanofibrous affinity membrane wasprepared by PDA adhered on the surface of PSF/PAN nanofibers via theself-polymerization of dopamine and forming a functional cortex. The PSF/PANnanofiber with the roughest surface and the highest BET surface area was obtained atthe concentration of20%(wt/wt) with mass ratio of1:1, which resulted in theas-prepared PDA composite nanofibrous membrane with roughest surface at thedopamine solution of1g/L and the soaking time of7h. The results of adsorptionisotherm and the adsorption dynamic demonstrated that the adsorption of La3+ontodopamine composite nanofibrous affinity membrane was fit well to the Langmuirequation and the pseudo-second-order model. The maximum equilibrium uptakecapacity of La(III) on PDA membrane was59.5mg/g (0.43mmol/g). The PDAcomposite nanofibrous affinity membrane could be desorbed in0.01M H3PO4aqueous solution and then regenerated in0.1M ammonia aqueous solution. After4cycles of adsorption-desorption, the regeneration rate and the desorption rate wasabove85%,98%, respectively. In this study, the PDA composite nanofibrous affinitymembrane biomaterial via dopamine adhered onto electrospun nanofibers and formedheterogeneous structure was subjected to the adsorption and recovery of rare earthmetal ion La3+in aqueous solution, which has the instructive function on theconstruction of novel nanofibrous affinity membrane used in the adsorption orremoval of rare earth metal ions such as La3+and the development of dopamineapplication field. 2. The porous PAN nanofibers with micro/nano structures were fabricated bywet-electrospinning technique from PAN and poly(vinyl pyrrolidone)(PVP) blendedsolution using hot water bath for PVP removal, where the leaching of PVP and poreformation occurred simultaneously during the electrospinning process. The porousPAN nanofibers with throughout pores and micro/nano structural protuberances wasobtained at the PAN/PVP mass ratio of1:2.5and the temperature of PVP leachingwater bath at85oC. Then, the precursor was aminated with DETA to obtainmicro/nano structure APAN nanofibrous membrane. The APAN nanofibrousmembrane with the highest amination rate, excellent morphology and mechanicalproperty was obtained at the amination temperature of90oC for2h. The micro/nanostructure APAN nanofibrous membrane showed highly efficient recovery of heavymetal ions such as Pb(II), Cu(II) and Cd(II). The FESEM images showed that theobtained porous PAN nanofibers were uniform in size (the average diameter was310±32nm) and contained many pores and micro/nano structures with different size onthe surface of nanofibers. The special micro/nano structure ensured APAN nanofibermembranes large specific surface areas. In addition, it should be noted that theresultant APAN nanofibrous membrane originated from the precursors fabricated bythe in-situ pore-forming method was flexible and could be curved, and its tensilestrength was1.5times and the elongation at break was about2.5times of those of themembrane fabricated by ex-situ pore-forming method (two steps: first electrospinningfollowed by PVP leaching), respectively. The BET surface area of porous PANnanofibrous membrane and micro/nano structure APAN nanofibrous membrane was183.1m2/g and29.1m2/g, respectively. The obtained micro/nano structure APANnanofibrous membrane possessed ultra-high extraction capacity to heavy metal ions ofPb2+, Cu2+and Cd2+owing to the super high content of amine group and BET surfacearea. The crystals of basic lead (II) carbonate (Pb3(CO3)2(OH)2) and brochantite(Cu4SO4(OH)6) was observed growth on the surface of micro/nano structural APANnanofibers after immersed in the aqueous solution containing Pb2+, Cu2+, respectively.Meanwhile, there was no crystal observed on the surface of APAN nanofibers for Cd2+.The results of SEM images, XRD, FTIR and XPS revealed that the crystal growthincreased with the increase of extraction time and there was coordination between theaffinity membrane and the heavy metal ions, and then the complex was hydrolyzedinto crystal compounds. The micro/nano structure APAN nanofibrous membrane afterPb2+, Cu2+and Cd2+extraction could be regenerated in1M HCl aqueous solution, andthe extraction rate was still above95.5%,91.5%and86.4%, respectively, after6 cycles of extraction-regeneration. The maximum extraction capacity was1519.98mg/g (7.34mmol/g),324.21mg/g (5.11mmol/g) and308.52mg/g (2.74mmol/g),respectively. Comparison with the results reported from literatures, the recoverycapacity of the as-prepared micro/nano structural APAN nanofibrous membrane wasthe highest for Pb2+among all the adsorption materials,3times for Cu2+adsorptiononto the APAN nanofibrous membrane, and which was higher than other adsorptionmaterials containing amino group for Cd2+. The residual concentration of Pb2+, Cu2+and Cd2+after extraction by micro/nano structural APAN nanofibrous membrane waslower than the liminal value of the instrument ICP-AES, which was0.02ppm,0.01ppm and0.01ppm, respectively. It was the first time that the hexagonal flak shapecrystals of basic lead (II) carbonate and3D crystal nanoflower of branchite wereobserved growth onto APAN nanofibers. The growth of crystals on micro/nanostructural APAN nanofiber resulted from the ultra high surface area and amino groupcontent, which was the critical factor to increase the recovery amount of Pb2+andCu2+. The obtained results were useful to improve the recovery amount of metal ionsboth in theory and application, and it can be used in large scale production.3. The micro-nano structure p-sulfonatocalix[n]arenes (n=4,6,8)(named ascalix4, calix6and calix8in abbreviation, respectively) complex membranes preparedby electrostatic adsorbing anionic calix4, calix6and calix8onto the cationicnanofibrous mats with micro-nano structure at pH of5.0, named as calix[n]-APAN(n=4,6,8) respectively, were utilized as an affinity membrane for the selectiveadsorption of Lanthanum (III) ions. The adsorption quantity ofp-sulfonatocalix[n]arenes (n=4,6,8) onto micro/nano structural APAN nanofibrousmembrane was in the order of calix8> calix6> calix4due to the differentconformation of the three compounds. In the single La3+solution system with pH of5.0, the maximum adsorption capacity of calix8-APAN was155.12mg/g which wasthe highest amount reported in literature except for active carbon. The adsorptionbehaviour at equilibrium was fit well to the Langmuir isotherm equation and thepseudo-second-order model. The as-prepared nanofibrous calix8-APAN complexmembranes were subject to selective adsorption of La (III) ions in aqueous solutionand showed very high adsorption selectivity toward La3+from other metal ions suchas Fe3+, Al3+, Cu2+, Ca2+, Mg2+and K+and the selective coefficient SLa/Mwas in therange of129~1144, where the SLa/Cuwas the lowest and the SLa/Kwas the highest. Theadsorption amount was almost same as La3+for other Lanthanide metal ions such asCe3+, Nd3+, Eu3+, Er3+, Pr3+, and so on, and the selective coefficient SLa/Mwas in the range of1.3~2.2. The resultant membranes adsorbed with La (III) ions could bedesorbed and regenerated in0.01M H3PO4aqueous solution successfully withoutsignificantly affecting their adsorption capacity and the desorption rate was above85%after4cycles of adsorption-desorption. The results of FTIR and XPS showedthat the p-sulfonatocalix[n]arenes (n=4,6,8) was adsorbed onto micro/nanostructural APAN nanofibrous membrane via electrostatic interaction and themechanism of La3+adsorption onto the calix8-APAN composite nanofibrous affinitymembrane formed coordination between La3+ions and the phenolic hydroxyl groupson the calixarene. The results obtained in this study can be used in thepreconcentration, recovery and separation of rare earth metal ions in the industry field,such as wastewater treatment and mineral metallurgical. |
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