Transformation of hydrogen titanate nanoribbons to TiO2 nanoribbons and the influence of the transformation strategies on the photocatalytic performance.

Melita Rutar,Srečo D Škapin,Romana Cerc Korošec,Carla Bittencourt,Aleš Mrzel,Matej Pregelj,Polona Umek,Andrijana Sever Škapin,Nejc Rozman

doi:10.3762/bjnano.6.86

Abstract

The influence of the reaction conditions during the transformation of hydrogen titanate nanoribbons to TiO2 nanoribbons on the phase composition, the morphology, the appearance of the nanoribbon surfaces and their optical properties was investigated. The transformations were performed (i) through a heat treatment in oxidative and reductive atmospheres in the temperature range of 400–650 °C, (ii) through a hydrothermal treatment in neutral and basic environments at 160 °C, and (iii) through a microwave-assisted hydrothermal treatment in a neutral environment at 200 °C. Scanning electron microscopy investigations showed that the hydrothermal processing significantly affected the nanoribbon surfaces, which became rougher, while the transformations based on calcination in either oxidative or reductive atmospheres had no effect on the morphology or on the surface appearance of the nanoribbons. The transformations performed in the reductive atmosphere, an NH3(g)/Ar(g) flow, and in the ammonia solution led to nitrogen doping. The nitrogen content increased with an increasing calcination temperature, as was determined by X-ray photoelectron spectroscopy. According to electron paramagnetic resonance measurements the calcination in the reductive atmosphere also resulted in a partial reduction of Ti4+ to Ti3+. The photocatalytic performance of the derived TiO2 NRs was estimated on the basis of the photocatalytic oxidation of isopropanol. After calcinating in air, the photocatalytic performance of the investigated TiO2 NRs increased with an increased content of anatase. In contrast, the photocatalytic performance of the N-doped TiO2 NRs showed no dependence on the calcination temperature. An additional comparison showed that the N-doping significantly suppressed the photocatalytic performance of the TiO2 NRs, i.e., by 3 to almost 10 times, in comparison with the TiO2 NRs derived by calcination in air. On the other hand, the photocatalytic performance of the hydrothermally derived TiO2 NRs was additionally improved by a subsequent heat treatment in air.

Highlights

Titanium dioxide (TiO2) is a technologically important material due to its remarkable combination of properties, its chemical stability and nontoxicity [1,2]
The chemical analysis, performed by using energy dispersive X-ray spectrometry (EDX), showed that the sodium content in the hydrogen titanate nanoribbons (HTiNRs) is below 0.1 wt %
The TEM images (Figure S5, Supporting Information File 1), on the other hand, show that porous structure of the nanoribbons is not reduced at higher calcination temperatures, as in the case with the TiO2 nanoribbons [12] (NR) calcined in air (Figure 4)

Summary

Introduction

Titanium dioxide (TiO2) is a technologically important material due to its remarkable combination of properties, its chemical stability and nontoxicity [1,2]. A direct comparison of the XRD patterns of the samples calcined in air (Figure 1) and in the NH3(g)/Ar(g) flow (Figure 2) at the same temperatures gives the impression that the transformation rate from TiO2-B to anatase is slower in the reductive atmosphere than in static air.

Results

Conclusion