Black TiO2 Thin Films Production Using Hollow Cathode Hydrogen Plasma Treatment: Synthesis, Material Characteristics and Photocatalytic Activity

Armstrong Godoy Junior,André Pereira,Argemiro Da Silva Sobrinho,Mariana Fraga,Walter Miyakawa,Gilberto Petraconi,Marcos Massi,Rodrigo Pessoa,Heberton Wender,Marcilene Gomes,Douglas Leite,Adailton Nogueira

doi:10.3390/catal10030282

Abstract

Black TiO2 materials have been quite widely explored due to their large solar absorption and superior photocatalytic activity. In this paper, the blackening process of titanium dioxide (TiO2) thin film using the hollow cathode hydrogen plasma (HCHP) technique is reported. First, pristine anatase TiO2 films were grown by magnetron sputtering onto silicon and cover glass substrates and then annealed at 450 °C for 2 h. Then, the as-grown TiO2 films were treated with HCHP for 15 min. The physical, chemical and morphological properties of the films were analyzed by profilometry, X-ray diffraction (XRD), UV-Vis spectrophotometry, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) techniques. Electrical and photocatalytic measurements were performed by four-point probe and methylene blue UV degradation assays, respectively. The results showed that the black TiO2 film is highly absorbent in the UV-visible region, has low electrical resistance and greater surface area compared to the non-treated TiO2 film. These properties of black TiO2 film, as well as its performance as a photocatalytic agent, were investigated, indicating the superior quality of this material in thin film form and the promising potential of the HCHP treatment to produce hydrogenated TiO2 in short process time.

Highlights

Over the centuries, due to the unreasonable use of the planet’s resources and the reduction of water resources, the increased need for renewable energy sources and food production are currently considered as urgent problems to be solved, facts that have motivated countless studies focused on the Catalysts 2020, 10, 282; doi:10.3390/catal10030282 www.mdpi.com/journal/catalystsCatalysts 2020, 10, 282 synthesis and modification of materials with direct application to mitigate these problems [1,2,3]
Several approaches, such as the incorporation of metallic or non-metallic dopants into TiO2 -based materials, have been explored to increase the absorption rate of this material as much as possible in the entire range of the solar spectrum [7,8,9]. This approach is still a matter of much discussion, as dopants can attract holes, behaving as recombination centers that affect the efficiency of photoinduced processes [10]
For the case of the black TiO2 surface, Figure 1b shows that it is made up of densely packed agglomerates of particles ranging in size from 40 to 50 nm

Summary

Introduction

Due to the unreasonable use of the planet’s resources and the reduction of water resources, the increased need for renewable energy sources and food production are currently considered as urgent problems to be solved, facts that have motivated countless studies focused on the Catalysts 2020, 10, 282; doi:10.3390/catal10030282 www.mdpi.com/journal/catalystsCatalysts 2020, 10, 282 synthesis and modification of materials with direct application to mitigate these problems [1,2,3]. TiO2 has a wide bandgap on the order of 3.2 eV, which limits its photocatalytic activity only to the narrow light-response range of the ultraviolet (UV), i.e., only a small amount of solar radiation reaching the Earth’s surface is harnessed [6]. Several approaches, such as the incorporation of metallic or non-metallic dopants into TiO2 -based materials, have been explored to increase the absorption rate of this material as much as possible in the entire range of the solar spectrum [7,8,9]. Heterojunctions by coupling two semiconductors are a method that has been studied to improve the photocatalytic activities [11,12]

Methods

Results

Conclusion