Template synthesis of polyaniline/TiO₂ bilayer microtubes

Abstract

In this article, highly ordered PANI/TiO₂ bilayer microtubes were prepared with two-step method. Firstly, anodic aluminum oxide (AAO) membrane with regular channel structure was chosen as the template, the PANI microtubes were synthesized in the channels of template by in situ polymerization. Secondly, the TiO₂ microtubes were synthesized with sol–gel method in the channels of PANI microtubes. The structure and morphology of PANI/TiO₂ bilayer microtubes were characterized by SEM, energy dispersive spectroscopy (EDS), TEM, and UV–vis. The results showed that the bilayer microtubes were successfully synthesized in the microchannels of template, the diameter and length of microtubes were closed to the pore diameter and thickness of AAO template, respectively, the arrangement of bilayer microtubes was very regular and uniform, also, a bilayer structure was found. UV–vis spectra confirmed that the photocatalysis property of PANI/TiO₂ bilayer microtubes in sunlight was better than that of TiO₂ microtubes, due to the existence of sensitizer, PANI.

Introduction

One-dimensional nanostructure has potential applications in many fields, e.g. nanodevice, drug delivery, nanosensors and microelectronics, etc., due to its particular structure and properties. One-dimensional nanomaterials with regular arrangement can be synthesized in the template channels with sol–gel process [1], chemical polymerization [2], [3], [4] and electrochemical polymerization [5], [6], [7]. Many one-dimensional nanostructures, e.g. nanotubes and nanowires of SiC, GaN, MgO, GaAs, InAs, Au, Si, Ge were synthesized with template synthesis [8], [9], [10].

Polyaniline (PANI) as a typical conducting polymer has unique electrical, optical and photoelectric properties. It has large variety of applications in electronic, energy storage, chemical sensor, light-emitting diodes and corrosion-protecting paint, etc. Especially, one-dimensional PANI nanotubes or nanowires have received great attention due to their unique properties and potential applications in electrical nanodevices, drug delivery, etc. Martin et al. [11] synthesized PANI nanotubes with template method. They found that the conductivity of PANI nanotubes was several orders higher than that of the bulk sample prepared by conventional method. The increasing of conductivity is due to the alignment of PANI molecular chains induced by the order structure of template channels.

TiO₂ nanoparticles have unique electrical and optical properties as well as extensive applications in diverse areas [12]. And it is an effective photocatalyst. With TiO₂ as a catalyst in sunlight, the water can be decomposed into superoxidant ·OH radical, which can be used to decompose the poison inorganic and organic materials [13], [14], [15]. But there is a shortcoming that the forbidden band gap of TiO₂ is 3.2 eV, only UV light can be utilized, so its catalysis efficiency is low. One solution is using the dye with narrow forbidden band gap as sensitizer, so as to enhance the catalysis efficiency of TiO₂ [16]. PANI is one kind of conducting polymer and a dye with a forbidden band gap of 2.8 eV, so it is a good sensitizer of TiO₂. It is of great interest to synthesize PANI/TiO₂ nanocomposites in the template channels. Few papers on PANI/TiO₂ nanocomposites [17], [18], [19], [20], [21] and PANI/TiO₂ composite nanotubes [22] were reported. However, no paper on PANI/TiO₂ bilayer microtubes was published yet. In this article, Anodic Aluminum Oxide membrane with ordered pore structure was chosen as template, PANI/TiO₂ bilayer microtubes were synthesized based on template with two-step method, the structure and morphology of bilayer microtubes were characterized and the photocatalysis property of microtubes was studied.