Electrospun core–sheath PAN@PPY nanofibers decorated with ZnO: photo-induced water decontamination enhanced by a semiconducting support

Abstract

We present here a photoactive system for water decontamination consisting of ZnO nanocrystals supported on a flexible mat of electrospun semiconducting nanofibers. The nanofibers have a core–sheath structure with a polyacrylonitrile (PAN) core and a sheath made of polypyrrole (PPY), a low band gap p-type semiconductor. Under UVA irradiation, the heterojunction formed between PPY and ZnO, an n-type semiconductor, promotes the separation of the charge carriers photogenerated at the interface. This decreases the charge recombination rate and increases the photocatalytic efficiency compared to a system where the same ZnO particles are supported on insulating bare PAN nanofibers. Based on photocatalytic tests and photoelectrochemical characterization, we find that the photoexcited electrons are preferentially collected on the PPY sheath and react with the dissolved oxygen while the holes in excess on the ZnO surface generate highly oxidizing radicals and degrade the persistent pollutants. The nanofiber production is scalable and sustainable, as the synthesis of the PPY sheath is carried out in water under ambient conditions. While previous studies immobilized photoactive metal oxide nanoparticles on insulating mats to help their collection after use, this is the first report showing that a flexible semiconducting supporting material can play an active role in the photocatalytic process and significantly enhance its efficiency. This approach paves the way for the design of new supported hybrid materials for photocatalytic applications.