Electrospun Palladium Nanoparticle-immobilized&Thymine Grafting Nanofibrous Mats:Preparation And Enviromental Remediation Applications

Electrospinning has been considered as one of the powerful methods to generate polymer nano fibers with diameter ranging from tens of nanometers to several micrometers. Through this facile and low-cost strategy, various polymeric nanofibers and nanostructured materials with a high aspect ratio and specific surface area have been fabricated for different applications including environmental remediation.In this thesis, we employed water stable electrospun PVA/PEI nanofibrous mat as template, immobilized palladium (Pd) nanoparticles (NPs) into the fibers through in situ reduction, and systematically investigated the ability of this inorganic/inorganic composite nanofibrous material in the catalytic removal of hexavalent chromium (Cr(VI)) in aqueous solution, as well as their reusability. In addition, we grafted thymine molecules onto polyethyleneimine (PEI), then mixed with Poly(vinyl alcohol)(PVA) solution to form homogeneous mixture, followed by electrospinning to generate thymine grafted PVA/PEI-T nanofibers. This thymine moiety-functionalized nanofibrous material was used to selectively absorb mercury ions in aqueous solution. Generally, our work consists of the following two parts:First, we introduce a facile and economic approach to fabricating catalytic active Pd NP-immobilized electrospun PVA/PE1nanofibers for catalytic reduction of Cr(VI) to trivalent chromium (Cr(Ⅲ)). In this study, PVA/PEI nanofibrous mats were first electrospun from homogeneous mixture solution of PEI and PVA, followed by cross-linking with glutaraldehyde (GA) vapor to render the fibers with good water stability. The nanofibrous mats were then alternatively soaked in potassium tetrachloropallidate (K2PdCl4) and sodium borohydride solution, and the PdCl42-anions complexed with the free amine groups of PEI were able to be reduced to form zero-valent Pd NPs. The formed Pd NP-containing PVA/PEI nanofibers were characterized by different techniques. We show that the immobilization of Pd NPs does not significantly change the morphology of the PVA/PEI nanofibers; instead the mechanical durability of the fibers is significantly improved. The formed Pd NPs with a mean diameter of2.6nm are quite uniformly distributed within the fibers with a small portion of particles having a denser distribution at the outer surface of the fibers. The catalytic activity and reusability of the fabricated Pd NP-containing fibrous mats were evaluated by transformation of Cr(Ⅵ) to Cr(Ⅲ) in aqueous solution in the presence of a reducing agent. Our results reveal that the Pd NP-containing nanofibrous mats display an excellent catalytic activity and reusability for the reduction of Cr(Ⅵ) to Cr(Ⅲ). The facile approach to fabricating metal NP-immobilized polymer nanofibers with a high surface area to volume ratio, enhanced mechanical durability, and uniform NP distribution may be extended to prepare different NP-immobilized fibrous systems for various applications in catalysis, sensing, environmental sciences, and biomedicine.On the other part of our work, thymine groups were first grafted on PEI via conjugating amine groups of PEI and carboxyl groups of thymine-1-acetic acid. The formed PEI-T was then mixed with PVA solution for electrospinning to generate electrospun PVA/PEI-T nanofibrous mats. SEM.1H NMR, FTIR were used to characterized PEI-T and PVA/PEI-T nanofibers. We show that thymine-1-acetic acid have reacted with amine groups of PEI, which means, thymine groups have grafted on PEI chain successfully, which is indicated by the arising of several signal peaks in’H NMR spectrum, while the absorption peaks of acylamino in FTIR spectrum also confirm this. SEM images of PVA/PEI-T nanofbrous mat show that, compared with PVA/PEI nanofibers. the diameter of grafted fibers slightly increase, even so they have maintained the well fibrous structure. FTIR spectrum reveals that the electrospun PVA/PEI-T nanofibers still reserve considerable quantity of thymine groups, which are favorable for the following specific absorption experiment. The absorption ability and reusability of electrospun PVA/PEI-T nanofibrous mats were evaluated by separating hazardous mercury (Ⅱ) ion in aqueous solution. We show that the thymine grafted nanofibrous mats display a remarkable activity and reusability for the absorption of Hg2+, and this activity enhances with the increasing of thymine quantity. In addition, competitive absorption experiment reveals that electrospun PVA/PEI-T nanofibrous mats have excellent selectivity towards Hg2+. This newly developed thymine functionalized sorbent holds a great promise in the separation of Hg2+in laboratory and industrial wastes.