Dielectric Properties and Spectral Characteristics of Photocatalytic Constant of TiO2 Nanoparticles Doped with Cobalt.

Valentin G Bessergenev,João P Lourenço,Ana Maria Botelho Do Rego,Martin Hantusch,Eberhard Burkel,Adwaa Ahmed,Maria Conceição Mateus,José F Mariano

doi:10.3390/nano11102519

Abstract

Dielectric properties and spectral dependence of the photocatalytic constant of Co doped P25 Degussa powder were studied. Doping of TiO2 matrix with cobalt was achieved by precipitation method using of Tris(diethylditiocarbamate)Co(III) precursor (CoDtc–Co[(C2H5)2NCS2]3). Five different Co contents with nominal Co/Ti atomic ratios of 0.005, 0.01, 0.02, 0.05 and 0.10 were chosen. Along with TiO2:Co samples, a few samples of nanopowders prepared by Sol-Gel method were also studied. As it follows from XPS and NMR studies, there is a concentration limit (TiO2:0.1Co) where cobalt atoms can be uniformly distributed across the TiO2 matrix before metallic clusters start to form. It was also shown that CoTiO3 phases are formed during annealing at high temperatures. From the temperature dependence of the dielectric constant it can be concluded that the relaxation processes still take place even at temperatures below 400 °C and that oxygen defect Ti–O octahedron reorientation take place at higher temperatures. The spectral dependency of the photocatalytic constant reveals the presence of some electronic states inside the energy gap of TiO2 for all nanopowdered samples.

Highlights

In according with the XRD data the Co–doped TiO2 powders shows the formation of the anatase and rutile phases at 550 ◦ C without any indication of the presence of metallic dopants within the sensitivity of XRD method
It is necessary to mention, that by XPS method some small amount of metallic Co was detected. This probably indicates the limit of Co dissolution in the TiO2 matrix
As shown earlier from studies of magnetic properties of Co doped TiO2 samples [10], saturated magnetic moment indicates the presence of different oxidation states of cobalt that depend of the content of this element

Summary

Introduction

As it was shown [1,2,3,4], additional features of titanium dioxide, that is widely used as photocatalyst and has potential applications in photovoltaic and spintronic devices, can be achieved by its doping with 3d-transition metals. Due to high dielectric constant titanium dioxide can be used as an isolator component in electronic devices [5], or can be combined with organic–inorganic composites [6,7]. Additional energy states of 3d transition metal are formed inside the original TiO2 band gap, effectively reducing band gap [8]. Doping TiO2 with 3d metals occurs normally by heterovalent substitution. Several possible oxidation states e.g., Co2+ , Co3+ and Co4+

Methods

Results

Discussion

Conclusion