Encapsulating conducting polypyrrole into electrospun TiO2 nanofibers: a new kind of nanoreactor for in situ loading Pd nanocatalysts towards p-nitrophenol hydrogenation

This work describes the encapsulation of conducting polypyrrole (PPy) into electrospun TiO2 nanofibers to form PPy/TiO2 nanocomposites using V2O5 as an oxidant and sacrificial template via a simple vapor phase polymerization approach. The PPy/TiO2 nanocomposites could be used as nanoreactors for loading Pd nanocatalysts towards the catalytic reduction of p-nitrophenol by sodium borohydride (NaBH4) at ambient conditions. The Pd nanocrystals synthesized through the in situ reduction by the PPy/TiO2 matrix have a small size of only about 2.0 nm. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible-near infrared spectroscopy (UV-vis-NIR) and thermo-gravimetric analysis (TGA) results demonstrated that PPy/TiO2 and PPy/TiO2/Pd composite nanofibers were successfully synthesized. Pd nanoparticles supported on the PPy/TiO2 composite nanofibers exhibited good catalytic activity when they worked as catalysts for the reduction of p-nitrophenol. The apparent kinetic rate constant (K-app) was calculated to be about 12.2 x 10(-3) s(-1). The protective PPy/TiO2 composite nanofibers render the Pd nanoparticles stable against poisoning by the product of the reaction, enabling the composite nanocatalysts to be recyclable when used over multiple cycles.