The Influence of a Surface Treatment of Metallic Titanium on the Photocatalytic Properties of TiO2 Nanotubes Grown by Anodic Oxidation

Živa Marinko,Luka Suhadolnik,Janez Kovač,Miran Čeh,Zoran Samardžija

doi:10.3390/catal10070803

Živa Marinko, Luka Suhadolnik + Show 3 more

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https://doi.org/10.3390/catal10070803

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Abstract

Titanium dioxide (TiO2) nanotubes obtained by the anodic oxidation of titanium metal foils can be used for the photocatalytic degradation of organic pollutants. The aim of our study was to determine the influence of the titanium foil’s surface treatment on the final morphology of the TiO2 nanotubes and their photocatalytic activity. In our experiments, we used two different titanium foils that were electropolished or untreated prior to the anodic oxidation. The morphologies of the starting titanium foils and the resulting TiO2 nanotube layers were investigated and the photocatalytic activities measured by the decomposition of caffeine under UV irradiation. Our results showed that electropolishing of the starting foils produced a more uniform and smoother TiO2 nanotubes surface. In contrast, the TiO2 nanotube surfaces from untreated titanium foils mimic the initial surface roughness of the titanium foil. A comparison of the photocatalytic properties of the TiO2 nanotube layers obtained from the untreated and electropolished titanium foils showed that electropolishing does not necessarily improve the photocatalytic properties of the resulting TiO2 nanotube layer. It was found that the determining factors influencing the photocatalytic activity are the chemical impurities (Ti-nitride) on the surface of the titanium foils and the surface roughness of the TiO2 nanotube layer. The highest photocatalytic activity was achieved with the anodized untreated foil with the minimal presence of Ti-nitride and a relatively high roughness of the TiO2 nanotubes.

Highlights

TiO2 is a versatile, chemically inert, and low-cost photocatalyst that can decompose various organic pollutants with reactive oxygen species
Our results showed that electropolishing of the starting foils produced a more uniform and smoother TiO2 nanotubes surface
It was found that the determining factors influencing the photocatalytic activity are the chemical impurities (Ti-nitride) on the surface of the titanium foils and the surface roughness of the TiO2 nanotube layer

Summary

Introduction

TiO2 is a versatile, chemically inert, and low-cost photocatalyst that can decompose various organic pollutants with reactive oxygen species. The photocatalytic decomposition of the organic compounds starts with the absorption of photons with a suitable energy. It takes place in the presence of oxygen and consists of different chemical reactions, such as bond breakage and electron transfer/substitution. The photocatalysis process takes place primarily at structural defect sites [3] or on the facets of the TiO2 crystal with the highest surface energies [4,5,6]. The anodic oxidation process is the most straightforward method for synthesizing TiO2 nanotube arrays [12]

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