Preparation of polyaniline-modified TiO2 nanoparticles and their photocatalytic activity under visible light illumination

doi:10.1016/j.apcatb.2007.12.022

Applied Catalysis B: Environmental

Volume 81, Issues 3–4, 24 June 2008, Pages 267-273

https://doi.org/10.1016/j.apcatb.2007.12.022 Get rights and content

Abstract

Titanium dioxide nanoparticles were modified by polyaniline (PANI) using ‘in situ’ chemical oxidative polymerization method in hydrochloric acid solutions. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared spectra (FT-IR), X-ray photoelectron spectroscopy spectrum (XPS) and UV–vis spectra were carried out to characterize the composites with different PANI contents. The photocatalytic degradation of phenol was chosen as a model reaction to evaluate the photocatalytic activities of the modified catalysts. Results show that TiO₂ nanoparticles are deposited by PANI to mitigate TiO₂ particles agglomeration. The modification does not alter the crystalline structure of the TiO₂ nanoparticles according to the X-ray diffraction patterns. UV–vis spectra reveal that PANI-modified TiO₂ composites show stronger absorption than neat TiO₂ under the whole range of visible light. The resulting PANI-modified TiO₂ composites exhibit significantly higher photocatalytic activity than that of neat TiO₂ on degradation of phenol aqueous solution under visible light irradiation (λ ≥ 400 nm). An optimum of the synergetic effect is found for an initial molar ratio of aniline to TiO₂ equal to 1/100.

Introduction

Photocatalytic degradation is an efficient and economical method to decompose organic pollutions into less dangerous matter. As a photocatalyst, TiO₂ has the advantages of high chemical stability, high photocatalytic activity to oxidize pollutants in air and water, relative low-price and nontoxicity [1]. However, the wide band gap of TiO₂ (3.2 eV) only allows it to absorb the ultraviolet light (<387 nm) that occupies only a small fraction (3–5%) of the solar photons, which limits its wide use. It is of paramount importance to improve the photocatalytic efficiency of TiO₂ by shifting its optical response from the UV to the visible range without the decrease of photocatalytic activity. In recent years, several groups have reported investigations to convert TiO₂ absorption from the ultraviolet to the visible region by doping TiO₂ with transition metals such as Cr, Mn, Fe, V, etc. [2], [3], [4], [5], [6]. Recently, doping TiO₂ with nonmetal atoms has received much attention. For example, the doping of nitrogen [7], [8], [9], carbon [10], [11], [12], [13], sulfur and iodine [14], [15] in TiO₂ can lower its band gap and shift its optical response to the visible light region. In addition, a variety of dyes can be used to photosensitize TiO₂ particles by absorbing visible light photons and inject electrons to conduction band (CB) of TiO₂, so as to improve the efficiency of visible light [16], [17].

At present, attention is paid to conducting polymers, which are used as photosensitizers to modify TiO₂ nanoparticles [18]. Conducting polymers have already been widely used in photovoltaic devices such as solar cells, light-emitting diodes and corrosion-protecting paint. Although there are plenty of conducting polymers, little work has been done on using conducting polymer to modify TiO₂ to degrade organic pollutions. As a typical conducting polymer, polyaniline (PANI) has unique electrical, optical and photoelectric properties. And most importantly, it is cheaper than other conducting polymers. Recently, Li reported hybrid composites of conductive polyaniline and nanocrystalline TiO₂, which were prepared by self-assembling and graft polymerization [19]. Compared with neat TiO₂ nanoparticles, the nanocomposites showed better photocatalytic activity in photodegradation of methyl orange under sunlight. Zhang has got polyaniline-anatase TiO₂ nanocomposites powders and investigated their solid-phase photocatalytic degradation [20].

In the present study, a series of polyaniline-TiO₂ nanocomposite powders with different PANI/TiO₂ ratios were prepared by ‘in situ’ chemical oxidative polymerization of aniline. In addition, their photocatalytic degradation of phenol was investigated. Results indicate that the introduction of PANI to TiO₂ nanoparticles can enhance the photocatalytic efficiency of TiO₂ under visible light irradiation.

Section snippets

Reagents and materials

Phenol, aniline, ammonium peroxydisulfate and hydrochloric acid were obtained from Tianjin Chemical Reagents Company. All these reagents were of AR grades and used without further purification with the exception of aniline that had been distilled before used.

Nanoparticulate TiO₂, which was mostly anatase, with an average particle size of ca.15 nm and BET specific surface area of ca.70 m²/g, was prepared by sol–gel hydrolysis and condensation of ethanol solutions of tetrabutyl titanate (Ti(OC₄H₉)₄

TEM images

The nanoparticles of neat TiO₂ and polyaniline-modified TiO₂ are clearly displayed on their images in Fig. 1. From the TEM images, we find that PANI-modified TiO₂ does not change the size of neat TiO₂ significantly, as shown in Fig. 1(a) and (b). The sizes of both modified and neat TiO₂ are monodisperse about 10–20 nm. Moreover, the crystal lattice line can be clearly found in the TEM images. The aggregations of both kinds of particles are caused by high surface energy; however, the

Conclusion

PANI-modified TiO₂ composites were prepared by ‘in situ’ chemical oxidative polymerization of aniline in the TiO₂ suspension. As a photosensitizer to TiO₂, PANI can improve the photocatalytic efficiency of nano-TiO₂ catalyst. The degradation of phenol in an aqueous solution under visible light was carried out to evaluate the photocatalytic activity. It is found that PANI-modified TiO₂ shows significantly higher photocatalytic activity than neat TiO₂ under visible light illumination. The

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Preparation of polyaniline-modified TiO2 nanoparticles and their photocatalytic activity under visible light illumination

Abstract

Introduction

Section snippets

Reagents and materials

TEM images

Conclusion

Chem. Phys. Lett.

Appl. Catal. B: Environ.

Appl. Catal. B: Environ.

Appl. Catal. B: Environ.

Catal. Commun.

Catal. Today

Sci. Tech. Adv. Mater.

Appl. Catal. B: Environ.

Appl. Catal. B: Environ.

J. Mol. Catal. A: Chem.

Appl. Catal. B: Environ.

Int. J. Hydrogen Energy

Chem. Phys. Lett.

J. Photochem. Photobio. A: Chem.

Preparation of polyaniline-modified TiO₂ nanoparticles and their photocatalytic activity under visible light illumination