Efficient Catalytic Reduction of Hexavalent Chromium Using Palladium Nanoparticle-Immobilized Electrospun Polymer Nanofibers

We report a facile and economic approach to fabricating catalytic active palladium (Pd) nanoparticle (NP)immobilized electrospun polyethyleneimine (PEI)/polyvinyl alcohol (PVA) nanofibers for catalytic reduction of hexavalent chromium (Cr(VI)) to trivalent chromium (Cr(III)). In this study, PEI/PVA nanofibrous mats were first electrospun from homogeneous mixture solution of PEI and PVA, followed by cross-linking with glutaraldehyde 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 PEI/PVA nanofibers were characterized by different techniques. We show that the immobilization of Pd NPs does not significantly change the morphology of the PEI/PVA nanofibers; instead the mechanical durability of the fibers is significantly improved. The formed Pd NPs with a mean diameter of 2.6 nm 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.