Surface wettability of titania thin films with increasing Nb content

Abstract

TiO 2 and TiO 2 /Nb amorphous thin films were grown on glass substrates by a sol-gel technique (spin coating). Films' surface composition, structure, and morphology were derived from x-ray photoelectron spectroscopy, x-ray diffraction, and atomic force microscopy data. The investigated films showed a smooth surface (roughness values below 5 nm). A separate surface wettability investigation showed that by increasing the Nb amount in pristine titania films results in a decrease of contact angle (CA) values from 40 to nearly 0 , thus, indicating a super-hydrophilic conversion under UV illumination. This conversion rate is greatly enhanced by increasing the Nb content, the surface super-hydrophilic behavior occurring after a couple of minutes in the TiO 2 /Nb samples, but after 4 h in the pristine titania specimen. The current results are discussed in terms of the optical band gap shift towards higher energies, by increasing the Nb content in the films, a process explained based on small polaron hopping model. V

Nb-doped TiO2 thin films as photocatalytic materials

“…Cross-sectional images were also acquired to obtain the thickness of the films. The obtained values confirm the previous results determined by ellipsometry, 12 that the films are very thin, with thickness under 100 nm. *Author for correspondence (dianam@uaic.ro)…”

“…Some of the properties of these films were already discussed in our previous work. 12,13 Results show that all the films are amorphous and they are very smooth, with roughness values under 5 nm. The films are slightly overoxidized and the ratio Ti/Nb derived from XPS was found to decrease from 11.4 to 0.46 with the increase of the dopant concentration.…”

“…It was observed that Nb-doped films could be photoactivated with UV radiation of higher energy, as Nb percentage increases, which contradicts some results in the literature, 15 while they are in good agreement with others. 16 The explanation made from a polaronic point of view was given in Mardare et al 12 The Nbdoped films present excellent hydrophilic properties under UV irradiation, comparing with the undoped one. 12 It has been already shown that Mo-doped titania films with higher hydrophilic performances are also good photocatalysts, confirming the idea that investigating the hydrophilic properties constitutes a much simpler way to obtain information on their photocatalytic activity.…”

“…10 The sol-gel method, more precisely spin coating (the method used to obtain undoped and Nb-doped films discussed in this paper), provides a number of advantages such as easy to use, relatively low cost of technology and materials, precise control of the composition in the obtained films, adhesion to the substrate, etc. 11 While previous studies dealt with the hydrophilic properties of similar samples, which proved to be excellent for the Nb-doped films compared with the undoped one, 12 in this study it was investigated how doping influences their oxidation power and they also show good photocatalytic performances.…”

Efeito do teor de nióbio na molhabilidade de filmes TiO2:Nb

“…2 e na Tabela II. É relatado na literatura que filmes de TiO 2 puros, obtidos por outros métodos como deposição reativa por sputtering quando ativados por radiação UV, podem atingir valores de ângulo de contato tão baixos quanto 10° para filmes com rugosidade da ordem de 10-20 nm [10,20,21], ou seja, com rugosidade maior que os valores encontrados neste trabalho (Ra ~3-6 nm). Portanto, filmes de TiO 2 :Nb, obtidos por oxidação de filmes de Ti-Nb metálico, apresentaram menor rugosidade (na ordem de nanômetros) e valores de ângulo de contato um pouco maiores do que em filmes de TiO 2 puros, quando ativados por luz UV.…”