Ag/AgCl coated polyacrylonitrile nanofiber membranes: Synthesis and photocatalytic properties

Abstract

A membrane based photocatalyst consisting of Ag/AgCl coated PAN nanofibers was synthesized in large quantities by electrospinning technique combining electroless plating method and subsequent in situ oxidation strategy. Electrospinning was firstly used to fabricate PAN/AgNO₃ composite nanofibers. After reduction, Ag nanoparticles dispersed along the nanofibers act as seeds in the following metal electroless plating step for the growth of continuous Ag shell. Then an in situ oxidation reaction between Ag shells and FeCl₃ solution was carried on to prepare Ag/AgCl coated PAN nanofiber membranes. The as-prepared materials exhibited excellent photocatalytic activity under visible-light, long-term stability, flexibility, as well as easy separation from the liquid. The present work can open a new and effective route for preparing high-performance membrane based photocatalysts for practical application.

Introduction

Growing concerns over the threat of chemical warfare agents and exposure to toxic industrial chemicals have drawn much attention to the challenge of developing new harmless treatment methods for the toxic organic materials. Photocatalytic degradation of harmful organic pollutants in water using semiconductor materials is one of the most widely studied methods [1], [2], [3]. However, semiconductor materials as photocatalysts present several major problems when used in the form of powder slurries: (a) the complicated separation or filtration steps, (b) the problematic use in continuous flow systems, and (c) the particles aggregation or loss, especially at high concentrations [4]. To overcome these drawbacks, considerable efforts have been oriented towards the photocatalysts immobilization on solid supports as bound particles or thin solid films in recent years [5], [6], [7]. However, in the case of such membranes, the exposed area for photocatalytic activity is much lower than that of the highly dispersed slurry’s surface resulting in a decreased photocatalytic performance of the thin film compared with the slurry solution [8]. A proficient solution to enhance the photocatalytic reaction rate is to immobilize much more efficient semiconductor photocatalysts in the form of films. To date, modified TiO₂ has attracted considerable research interests in this field [9], [10], [11], [12]. Despite some success, the degradation efficiency of film based photocatalysts needs further improvement to meet academic and commercial demands.

Recently, by taking the advantages of plasmon resonance of silver nanoparticles, silver/silver halide, a novel and highly efficient visible-light photocatalyst, has been synthesized by Huang and co-workers [13]. Hitherto, various silver/silver halide photocatalysts have been investigated [13], [14], [15]. However, these reports were all focused on powder based silver/silver halide, which has the tendency to agglomerate into larger particles. This created an obstacle for practical applications during the complicated solid–liquid separation process as the damages caused by the intrinsic brittleness of the inorganic structures.

Electrospun polymer nanofiber membranes have attracted increasing attention to serve as photocatalysts supports due to the three-dimensional open structure, large specific surface area, and flexibility in operation. These properties make them quite suitable for loading photocatalysts [16], [17]. Thus in the present work, we combined electrospinning technique with subsequent electroless plating method and in situ oxidation strategy [15] and fabricated a novel photocatalyst: Ag/AgCl coated polyacrylonitrile (PAN) nanofiber membranes. Our products exhibit a high surface area and with the flexibility of PAN nanofibers and the high efficient visible-light photocatalytic ability of the Ag/AgCl nanoshells.