Abstract
In this paper, we emphasized the dual application of Cu-modified vertically aligned TiO2 nanotube arrays as photocatalyst and a relative humidity sensor. The TiO2 nanotube arrays were obtained by anodization of the titanium layer prepared using radio frequency magnetron sputtering (RFMS) and modified with different copper concentrations (0.5, 1, 1.5, and 2 M) by a wet-impregnation method. The sample modified with 2 M Cu(NO3)2 solution showed the highest efficiency for the NH3 photocatalytic degradation and the most pronounced humidity response in comparison to the other studied samples. In order to investigate the structure and impact of Cu modification, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) were used. The photocatalytic activity and the kinetic study of ammonia oxidation were studied in a mini-photocatalytic wind tunnel reactor (MWPT), while relative humidity sensing was examined by impedance spectroscopy (IS). Higher NH3 oxidation was a direct consequence of the increased generation of •OH radicals obtained by a more efficient photogenerated charge separation, which is correlated with the increase in the DC conductivity.
Highlights
Rapid population growth and technological advancements resulted in, among other things, an increase in anthropogenic pollution mostly related to industry, transport, and agriculture
From the top-view FEG-scanning electron microscopy (SEM) images (Figure 3), it can be observed that the photocatalyst samples prepared via radio frequency (RF) magnetron sputtering, followed by electrochemical anodization, exhibit a homogenous structure comprised of nanotube arrays with pore diameters of 100 nm
These findings corroborate those of a prior study [17], where we used a similar Cu-modification pathway to decorate TiO2 nanotubes immobilized on Ti foil
Summary
Rapid population growth and technological advancements resulted in, among other things, an increase in anthropogenic pollution mostly related to industry, transport, and agriculture. Nanostructuring TiO2 results in increased photo-induced reactions, light absorption, photogenerated carrier density, photo-reduction, and increased contact with the pollutant or the targeted gas in the case of sensing [6]. In both cases, photocatalysis and relative humidity sensing, TiO2 nanotube arrays (NT) have gained popularity [7,8] because of their large surface-to-volume ratio and shape. Photocatalysis and relative humidity sensing, TiO2 nanotube arrays (NT) have gained popularity [7,8] because of their large surface-to-volume ratio and shape This one-dimensional nano-architecture offers more direct pathways for charge transport along their elongated axis and higher possibilities to form surface electric fields that reduce charge carrier recombination, which enhances the sensitivity for light and gas exposure [9]. By controlling the anodization parameters [10,11], i.e., reaction duration, voltage, electrolyte temperature, electrolyte content and type, different
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