| Water resources shortage and pollution have been common problems currently. Among the number of polluting species at issue, heavy metal ions and organic dyes are of special concern because of their high toxicity for human and animals’health. Affinity membrane separation technology has been widely used in environmental remediation application due to its high performance of affinity chromatography and membrane technology, such as high selectivity, high efficiency, and no pollution and so on.This work mainly focuses on the removal of heavy metal ions and anionic dyes, and detection of trace heavy metal ions in aqueous solution. Fitstly, cross-linked electrospun poly(ethyleneimine)(PEI) nanofibrous membranes doped with PVA were fabricated by wet-electrospinning in a one-step method instead of the conventional electrospinning and subsequent crosslinking method and the PEI/PVA nanofibrous membranes were applied to metal ions adsorption from an aqueous solution; Secondly, micro-nano structure nanofibrous affinity membranes of poly(ether sulfones)(PES) blended with a functional polymer PEI were fabricated by electrospinning technique followed by solvent etching in crosslinking solution, and this novel micro-nano structure PEI/PES nanofibrous membrane was utilized as an adsorbent for anionic dyes and heavy metal ions from aqueous solutions; the concentrations of the heavy metal ions solutions treated by two kinds of nanofibrous affinity membranes should be detected whether it meet the demand of environmental protection. So, a novel nanofibrous affinity membrane sensor was fabricated from a fluorescence molecule doped PES solutions and its sensing properties to Cu2+were investaged systematically.1. PEI and PVA were chosen as functional affinity polymer and fiber-forming agent, respectively. Crosslinked PEI nanofibrous affinity membranes for effective removing heavy metal ions were fabricated via wet-electrospinning from its aqueous solution. The coagulating bath for wet-electrospinning was composed of the crosslinking agent glutaraldehyde (GA) and N,N-dimethylformamide (DMF) as a non-solvent. This wet-electrospinning method provided a new approach for fabricating the crosslinked nanofibers from the polymers, in which sticky phenomenon could occur at the process of the electrospinning. When the PEI/PVA weight ratio was90/10, the PVA doped PEI nanofibrous membranes with ideal morphology was obtained. The nanofibers had an average diameter of650nm and the surface of the nanofibers was very smooth. The Langmuir equation gave a better fit to the experimental data than the Freundlich equation, and the maximum absorption capacities (from Langmuir isotherm data) for Cu(II), Cd(II) and Pb(II) were70.92mg/g,121.95mg/g and94.34mg/g, respectively. The PEI nanofibrous affinity membrane adsorbed with heavy metal ions could be regenerated successfully in EDTA aqueous solution without significantly affecting its adsorption efficiency, it was found that the desorption efficiency reached about95.6%after the third cycles. The Cu(II) and Cd(II) adsorption data were about1.31and2.27times higher than the reported values of PEI/PVA cast membrane.2. PEI/PES nanofibers were fabricated by electrospinning and PES was an excellent candidate for the matrix due to its good electrospinnability. In order to obtain PEI/PES nanofibrous membrane with high PEI content and finer fiber diameter, the blend ratio of1/1.4(w/w) and the total polymer concentration of30wt%were chosen in the electrospinning process. From the SEM images, it was found that the average diameter of the nanofibers was300nm and in addition most joints of PEI/PES nanofibers were stuck together, indicating that liquid PEI with high viscocity was concentrated at the fiber surface. The nanofibrous PEI/PES membranes were crosslinked in a mixture of acetone and water with glutaraldehyde (crosslinking agent, GA), and the micro-nano structural surface of the nanofibrous membranes was created by solvent etching due to the solvation between PEI and the solvent water in the crosslinking solution during the crosslinking process. The influence of the component of the crosslinking bath on the mophology of the resulting PEI/PES nanofibers was investigated. It was found that the relatively uniform micro-nano spherules grew on the surface of the nanofibers when the content of water in crosslinking solution was more than20wt%, and the diameters of the spherules were in the range of50-250nm. From the data of BET results and Cu2+adsorption performance, it was found that when the water content in crosslinking solution was30%, the resulting PEI/PES nanofibrous membrane has the maximum specific surface area, which was7.27m2/g.3. Adsorption performance of the micro-nano structure PEI/PES nanofibrous membrane for anionic dyes or heavy metal ions from aqueous solutions was investigated. A series of adsorption experiments were carried out to investigate the influence of membrane dosage, initial solution pH value, contact time, initial solution concentration and adsorption temperature on the adsorption performance. The experimental results showed that the removal of the anionic dyes and metal ions on this PEI/PES nanofibrous membrane was a pH-dependent process with the maximum adsorption capacity at the initial solution pH of1for anionic dyes and5-7for metal ions, respectively. The adsorption equilibrium data were all fitted well to the Langmuir isotherm equation, with a maximum adsorption capacity values of1000mg/g,344.83mg/g,454.44mg/g,94.34mg/g,161.29mg/g and357.14mg/g for Sunset Yellow FCF, Fast Green FCF, Amaranth, Pb(II), Cu(II) and Cd(II), respectively. The kinetic study indicated that the adsorption of metal ions and anionic dyes could be well fitted by the pseudo-second-order model and intraparticle diffusion model, suggesting intra-particle diffusion process as the rate-limiting step of the adsorption process. Thermodynamic parameters such as free energy, enthalpy and entropy of adsorption of anionic dyes and metal ions were also evaluated and the results showed that the adsorption was a spontaneous physical adsorption process. In addition, the adsorption process of heavy metal ions was exothermic; however, the adsorption process of anionic dyes was endothermic. This micro-nano structure PEI/PES nanofibrous membrane could be regenerated successfully in0.05M NaOH and0.05M EDTA aqueous solution used for removal of anionic dyes and heavy metal ions, respectively.4. The concentrations of the heavy metal ions solutions treated by two kinds of nanofibrous affinity membranes should be detected whether it meet the demand of environmental protection. Firstly, a fluorescence molecule, rhodamine hydrazone salicylaldehyde Schiff base, was synthesized as the sensing material and its chemical structure was obtained. It was found that the ion-recognition was based on the Cu+induced spirolactam ring "close-open" switch of the fluorescence molecule, with their advantages of significant absorption and fluorescence enhancement and the detection limit was1×10-6M. Secondly, the fluorescence molecule was blended with PES solution and electrospun to prepare a novel nanofibrous membrane sensor. It was found that this novel nanofirous membrane sensor showed high selectivity and sensitivity for Cu2+. In addition, the sensitivity of the fluorescence probe on the nanofibrous membrane sensor was much higher than that in the aqueous solution and the detection limit of the nanofibrous membrane sensor was1×10-8M. The complex mechanism between rhodamine hydrazone salicylaldehyde Schiff base and Cu2+was investigated by Job method, and it was found the nonlinear fitting of the titration curve assumed a1:1stoichiometry for the Cu-complex. |
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