Ordered arrays of N-doped mesoporous titania spheres with high visible light photocatalytic activity

doi:10.1016/j.matlet.2013.05.076

Materials Letters

Volume 106, 1 September 2013, Pages 421-424

https://doi.org/10.1016/j.matlet.2013.05.076 Get rights and content

Highlights

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Ordered arrays of N-doped mesoporous TiO₂ spheres were prepared.
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A dual-templating synthesis approach was employed.
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The TiO₂ spheres showed enhanced visible light photocatalytic activity.

Abstract

A preparation of three-dimensionally ordered arrays of N-doped mesoporous TiO₂ spheres by a dual-templating synthesis approach employing a combination of both polymer inverse opal templating (hard-templating) and surfactant templating (soft-templating) techniques was developed in this work. The N-doped mesoporous TiO₂ spheres were composed of nanocrystalline anatase titania and exhibited well-defined mesoporous structure. The ordered arrays of N-doped mesoporous TiO₂ spheres showed enhanced visible light photocatalytic activity, which could be attributed to the N doping effect, abundant ordered mesopores and unique opal structure. Such obtained TiO₂ sphere arrays may be promising for practical applications in the fields of environmental purification, water photoelectrolysis and dye-sensitized solar cells.

Introduction

Ordered mesoporous TiO₂ materials with a crystalline framework, high specific surface area and tailored pore structure are of much interest for numerous studies [1], [2]. Three-dimensionally (3D) ordered arrays of mesoporous TiO₂ spheres, which act as photonic crystals, show enhanced light harvesting efficiency for photocatalytic applications because of the slow photon effect and multiple scattering relating to their unique opal photonic crystal structure [3], [4]. However, only relying on physical approaches through structural and morphological modifications is difficult to improve the visible light photocatalytic activity significantly because the wide band gap (3.2 eV) confines the spectral response of TiO₂ to ultraviolet light, seriously limiting the efficient use of sunlight. In recent years, big efforts for chemical modifications have been made in order to narrow the band gap of TiO₂ so as to shift its optical response from the UV to the visible spectral range, including non-metal doping, metal doping, dye sensitization, and semiconductor coupling [5], [6]. Non-metal doping is one of the typical chemical modifications to enhance the visible light photocatalytic activity of oxide effectively [7], [8]. Among various non-metallic doping elements, the nitrogen doping has been proved to be a simple and effective way to increase the visible light absorption [9], [10]. Most recently, Zang et al. [6] investigated the N doping in cuprous oxide films by radical oxidation of Cu films at low temperature, and N doping efficiently widened the band gap of cuprous oxide films.

In our previous work, we reported the synthesis of 3D ordered arrays of mesoporous TiO₂ spheres by a combination of two-step templating approaches [11]. So far, there have been a lot of studies on the preparation of N-doped TiO₂ materials [12], [13]. However, ordered arrays of N-doped mesoporous titania spheres were rarely reported. In this paper, we reported for the first time the fabrication of 3D ordered arrays of N-doped mesoporous titania spheres. Because of their unique opal structure, abundant ordered mesopores and nitrogen doping effect, in this work, the prepared sample of N-doped mesoporous TiO₂ sphere arrays showed high photocatalytic activity under visible light for the degradation of Rhodamine B (RhB).

Section snippets

Experimental

The highly ordered opal templates composed of 290 nm silica spheres were synthesized by the methods previously described [14]. A silica opal piece was immersed in methyl methacrylate (MMA) monomer with 1 wt% benzoylperoxide (BPO) as an initiator. After polymerization, a 10 wt% HF solution was used to remove silica opal spheres in order to obtain a freestanding PMMA inverse opal. The titania precursor solution contained 5.68 g titanium tetraisopropoxide (TTIP), 4.8 g concentrated HCl (37 wt%), 2.32 g

Results and discussion

Fig. 1A demonstrates the SEM image of the silica opal monolith consisting of highly ordered close-packed silica spheres with 290 nm diameter. Fig. 1B shows the SEM image of the PMMA uniform porous structure produced from the silica opal template that is the inverse of the original opal. Ordered arrays of N-doped mesoporous titania spheres (Fig. 1C,D) have the same spherical shape and ordered close-packed structure as in the initial silica opal, but the size of the mesoporous TiO₂ spheres is ca.

Conclusions

We here demonstrated a dual-templating preparation of 3D ordered arrays of N-doped mesoporous titania spheres by using PMMA inverse opal and triblock copolymer Pluronic P123 as templates. The N-doped mesoporous TiO₂ spheres show an ordered mesoporous structure and are of good anatase crystallinity. Owing to the N doping effect, abundant ordered mesopores and unique opal structure, our N-doped mesoporous TiO₂ spheres by this method showed high photocatalytic activity under visible light for

Acknowledgments

The authors gratefully acknowledge financial support from the National Natural Science Foundation of China (51172014 and 20971012), and the National 973 Program of China (2009CB219903).

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Ordered arrays of N-doped mesoporous titania spheres with high visible light photocatalytic activity

Highlights

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusions

Acknowledgments

Appl Catal B

Mater Lett

Mater Res Bull

Mater Lett

J Hazardous Mater

Appl Catal A

J Mater Chem

Adv Mater

J Phys Chem B