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

Abstract

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 × 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.