Elsevier

Catalysis Communications

Volume 61, 10 February 2015, Pages 107-111
Catalysis Communications

Short communication
Design of TiO2 nanorods and nanotubes doped with lanthanum and comparative kinetic study in the photodegradation of formic acid

https://doi.org/10.1016/j.catcom.2014.12.020Get rights and content

Highlights

  • Evaluation of anisotropic TiO2 materials in the photodegradation of formic acid

  • Lanthanum slows down the growth of the anatase crystalline domains.

  • Lanthanum favors the formation of surface oxygen vacancies.

  • Lanthanum increases the life-time of photo-generated electron–hole pairs.

Abstract

Lanthanum doped 1D-TiO2 nanomaterials (nanorods and nanotubes) with tuned structural and textural properties have been evaluated in the photocatalytic degradation of formic acid (FA) under UV conditions. La-doped nanorods and nanotubes calcined at 973 K show interesting photocatalytic properties with respect to La-free nanomaterials. The presence of La inhibits TiO2 crystallite growth and increases the lifetime of photo-generated electron–hole pairs.

Introduction

In the last decades, titanium dioxide was considered as the most interesting semiconductor for photocatalytic applications [1]. Among the different polymorphs of TiO2, anatase was found to be the most active phase in photocatalytic processes. According to Yu et al. [2], the presence of hydroxyl groups and high specific surface area is the key parameters to obtain a highly active photocatalyst. Thermal post-treatment improves particle crystallinity and slows down the recombination of photo-induced charges [3]. On the other hand, this treatment can also induce the growth of crystalline domains, the decrease of the specific surface area and, ultimately, the rutile growth nucleation which led to a loss of the intrinsic photocatalytic activity. Both constructive and destructive contributions explain the optimal treatment temperature of about 400 °C for the best photocatalytic performance as reported for most TiO2 samples [4]. Moreover, the transition temperature of the anatase–rutile transformation decreases with the nanoparticle size which makes the stabilization of a pure anatase phase difficult [5]. Hence, many researchers reported doped TiO2 nanomaterials using metals and nonmetallic elements [5], [6], [7] or also using rare earth elements [8], [9], [10], [11], [12], [13], [14]. From all these studies, one can conclude that high surface area and reduced TiO2 crystallite size are obviously the main factors for photocatalytic behavior enhancement [8], [9], [10], [11]. Among the different rare earth elements, lanthanum, characterized by an electronic configuration [Xe] 5d1 6 s2, might be useful for photocatalytic processes through an increase of the electron–hole lifetime. Moreover, the discovery of different anisotropic TiO2 nanostructures with controlled morphology such as nanorods, nanowires and nanotubes was found very interesting in many fields and especially in photocatalysis [1], [15]. However, rare earth element doping was not extensively investigated for anisotropic 1D TiO2 nanomaterials.

Therefore, the aim of this work was to study the effect of lanthanum-doping on TiO2 of controlled morphology like nanorods and nanotubes. Several parameters were herein highlighted like the post-thermal treatment and the morphology of TiO2 used as starting material. Structural, textural and morphological properties were first evaluated while photocatalytic activity was investigated for the degradation of formic acid in aqueous media.

Section snippets

Photocatalyst preparation

TiO2 nanorods (NRs) and nanotubes (NTs) were elaborated via an alkaline hydrothermal method using TiO2 P25 as described by Turki et al. [15]. 3.0 g of TiO2 powder (P25) was first dispersed under stirring into 90 mL of 11.25 M NaOH aqueous solution before being placed into a 150 mL Teflon-lined autoclave at 403 K (heating rate: 2 °C/min) for 20 h. The resulting precipitate was recovered by filtration and washed with distilled water and a 1 M HCl solution. For nanorods, the procedure was essentially

Structural evaluation and photocatalytic properties of La-doped TiO2 nanorods

The textural and structural properties of the different TiO2 nanorods doped or not by La after post-thermal treatments between 673 K and 973 K are summarized in Table 1. Doping TiO2 NR by lanthanum is accompanied by the creation of inter- and intragranular porosity leading to high specific surface area (Table 1). The BET surface areas of La-NRs are higher than NRs whatever the temperature of calcination. Moreover, increasing the temperature of the thermal treatment from 673 to 973 K led to a

Conclusions

Throughout this work, the effect of lanthanum introduced into TiO2 nanomaterials with controlled morphologies (nanorods and nanotubes) has been investigated. Main results reveal that 1 wt.% La inhibits nanoparticle aggregation, slows down the growth of the anatase crystalline domains and therefore retards the transformation of anatase into rutile. The post-thermal treatments (773–973 K) of non-doped TiO2 nanomaterials yield to less photoactive catalysts than for their La-containing equivalents.

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