Catalytically active (Pd) nanoparticles supported by electrospun PIM-1: Influence of the sorption capacity of the polymer tested in the reduction of some aromatic nitro compounds

Abstract

Microfibers of the first so-called polymer of intrinsic microporosity (PIM-1) were prepared by electrospinning 10 wt.% PIM-1 in tetrachloroethane and used as immobilized supports for catalytic reactions. Solutions with varied concentrations of palladium diacetate (PdAc2) were coated on electrospun PIM-1 to show that PIM-1 is a superior catalyst supporting material with a high surface per weight ratio. Palladium (Pd) nanoparticles (NPs) were produced via the reduction of the PdAc2 with ethanol followed by subsequent thermal treatment for durably fixing the NPs on the fibers. A comparison of the catalytic activity of PIM-1 supported PdNPs was made with that of similarly produced electrospun nanofibers of polyacrylonitrile (PAN) and polyimide (6FDA-6FpDA) with catalytic PdNPs. The morphology of the electrospun fibers and the distribution of the Pd nanoparticles on the outer surface of the fibers were determined by scanning electron microscopy (SEM). Transmission electron microscopy (TEM) analysis of the cross section of the fibers showed the distribution of PdNPs across the fiber with a slight excess on the outer surface of the fibers. The nanoparticles (NPs) supported by the electrospun polymers catalyzed the reduction of different aromatic nitro compounds to their corresponding amino derivatives. The kinetics of the reduction reactions were monitored by ultraviolet-visible (UV-Vis) spectroscopy. Results showed that the PdNPs supported by electrospun PIM-1 fiber possessed high activity in the reduction reaction with an only slight dependence on the fiber diameter in the case of p-nitrophenol, while in the case of the dinitro compounds the dependence of the kinetics on the fiber diameter was more pronounced. The catalytic tests on two dinitro compounds proved the higher sorption of PIM-1 for p-nitrophenol is responsible for the higher catalytic activity of PIM-1 based catalytic nanofiber mats. These results clearly show that the catalytic activity of the PIM-1 fiber mats is higher compared to the fiber mats from PAN or 6FDA-6FpDA in the case of small reactants, which is mainly due to the fact that the PdNPs are also formed within the microporous PIM-1 fibers, while this is not the case for the other more dense fibers, where the catalytic particles are located only on the outer surface.