Defective Black TiO2: Effects of Annealing Atmospheres and Urea Addition on the Properties and Photocatalytic Activities.

Xu Zhang,Guoyan Zou,Li Zhou,Guifa Chen,Min Cai,Naxin Cui

doi:10.3390/nano11102648

Xu Zhang, Guoyan Zou + Show 4 more

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https://doi.org/10.3390/nano11102648

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Abstract

A series of black TiO2 with and without the addition of urea were successfully prepared using a simple one-step synthetic method by calcination under different atmospheres (vacuum, He, or N2). The physicochemical, optical, and light-induced charge transfer properties of the as-prepared samples were characterized by various techniques. It was found that a vacuum atmosphere was more beneficial for the formation of oxygen vacancies (OVs) than the inert gases (He and N2) and the addition of urea-inhibited OVs formation. The samples annealed in the vacuum condition exhibited better visible-light adsorption abilities, narrower bandgaps, higher photo-induced charge separation efficiency, and lower recombination rates. Hydroxyl radicals (·OH) were the dominant oxidative species in the samples annealed under a vacuum. Finally, the samples annealed under vacuum conditions displayed higher photocatalytic activity for methylene blue (MB) degradation than the samples annealed under He or N2. Based on the above, this study provides new insights into the effects of annealing atmospheres and urea addition on the properties of black TiO2.

Highlights

Titanium dioxide (TiO2 ) is the most widely investigated photocatalyst for use in solar-driven environmental purification
The results show that vacuum condition was more beneficial for oxygen vacancies (OVs) formation than the inert gases (He and N2 ) and that urea addition inhibited OVs formation
A series of black TiO2 with or without urea addition were synthesized by calcination under different atmospheres

Summary

Introduction

Titanium dioxide (TiO2 ) is the most widely investigated photocatalyst for use in solar-driven environmental purification. Conventional white TiO2 has poor visible-light absorption and rapid electron-hole recombination, resulting in unsatisfactory photocatalytic activity in solar-driven reactions [1]. Many efforts have been expended to harvest visible photons and improve the photocatalytic activities of TiO2 -based materials. Chen et al firstly reported that hydrogenation was used to produce black TiO2 to improve visible light absorption and photocatalytic activity without chemical doping [4]. TiO2 has triggered an explosion in interest for many environmental applications, due to its absorption of both visible and near-infrared solar light without the need for the addition of dopants to alter its properties. The synthesis methods of black TiO2 include hydrogenation, chemical reduction, electrochemical reduction, laser ablation (in liquid), and oxidation approaches [5]. Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations

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