Elsevier

Electrochemistry Communications

Volume 11, Issue 9, September 2009, Pages 1748-1751
Electrochemistry Communications

Photocatalytic activities of C–N-doped TiO2 nanotube array/carbon nanorod composite

https://doi.org/10.1016/j.elecom.2009.07.007Get rights and content

Abstract

A C–N-doped TiO2 nanotube (NT)/carbon nanorod composite is fabricated by chemical vapor deposition (CVD). Carbon nanorods are grown from the TiO2 NTs, and partly graphitized, while TiO2 is in the mixture of anatase and rutile. The C–N doping shifts the absorption edge of TiO2 NTs to the visible light region; the formed carbon nanorods promote the charge carrier transfer from the TiO2 surface to the electrolyte. Under the simulated solar light irradiation, the C–N-doped TiO2 NTs show higher photocatalytic activity in the degradation of methyl orange (MO) than the undoped TiO2 NTs.

Introduction

TiO2 NT arrays attract increasing research interests due to their high-oriented uniform NT architecture and the as-resulted excellent photocatalytic properties [1], [2] such as the rapid transfer of the photo-generated holes to the surrounding electrolyte and the extended electron lifetimes in the NTs [3]. However, the band gap of TiO2 is so wide (3.0–3.2 eV) [4] that only UV light can activate TiO2 to generate electrons/holes. Considerable efforts have been taken to increase the light-using efficiency in the visible region, involving dye sensitisation [5] and doping TiO2 with suitable species such as N, F, and C [6], [7], [8]. However, the trouble of doping is that the charge transfer properties would be destroyed since that the doping-introduced defect states can promote electron–hole recombination [1]. Efforts have been therefore devoted to increasing the interfacial electron-transfer rate to enhance quantum efficiencies for photocatalysis [9]. An available method is to form heterojunctions which can provide a potential driving force for the separation of photo-generated charge carriers, such as TiO2/carbon nanotube (CNT) nanocomposites [10], [11], [12]. It is suggested that the photo-generated charge carriers can transfer from TiO2 to the one-dimensional CNTs.

In this work, the C–N-doped TiO2 NT/carbon nanorod heterojunction composite was fabricated where the carbon nanorods were grown from the TiO2 NTs. The photoelectric performance of the as-prepared composite was studied. This composite is expected to absorb longer wavelength light than the undoped TiO2 due to the C–N doping, and with a fast charge transfer rate due to the carbon nanorods.

Section snippets

Experimental section

Titanium foil (99.8%, 0.127 mm thick) was purchased from Aldrich (Milwaukee, WI). Other reagents were of analytic grade. Twice-distilled water was used throughout our experiments.

The cleaned titanium ribbon was anodized at 15 V for 3 h in an electrolyte containing 0.1 M NaF and 0.5 M NaHSO4 at room temperature. Next, the as-anodized TiO2 NTs were annealed at 450 °C in air atmosphere for 3 h. To introduce the carbon and nitrogen dopants, the sintered samples were put in a graphite trough in which 5 mg

Results and discussions

Fig. 1A shows SEM images of the as-prepared TiO2 NTs (image 1) and the doped-TiO2 NTs (images 2–4). As shown in the Figure, in the carbon-doped TiO2 NTs carbon nanorods are grown from the TiO2 NTs, with a uniform distribution and each perpendicular standing on the substrate. The XRD spectra (Fig. 1B) show that all the samples consist of a rutile (2θ = 27.3°) and an anatase (2θ = 25.3°) phase besides the major titanium crystal. The rutile peaks of both C-doped and C–N-doped TiO2 NTs are more

Conclusions

In this work, the C–N-doped TiO2 NT/carbon nanorod heterojunction photocatalyst was fabricated and its photoelectric properties were investigated. With the C–N doping, an improved photocatalytic activity was observed. The average photocurrent density achieved on the C–N-doped TiO2 NTs/carbon nanorods is 3 times (1.24 mA at 0.2 V) that of the undoped TiO2 NTs, and the degradation rate of MO is 2 times that of the undoped TiO2 NTs. The enhanced photocatalytic activity is attributed to the C, N

Acknowledgments

This work was supported by National Basic Research Program of China, 2009CB421601, the Natural Science Foundation of Hunan Province, China, 08JJ3113, the National Science Foundation of China, 0878079, and the Innovation Project in Postgraduation Education for Excellent Doctors, 521218019.

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