Direct growth of cerium oxide nanorods on diverse substrates for superhydrophobicity and corrosion resistance
Graphical abstract
Introduction
Corrosion-resistive, superhydrophobic surfaces are of great interest in offshore applications such as heat exchangers, pipelines, power plants, and platform structures because of their resistance to salinity and the enhanced heat transfer performance with regard to drop-wise condensation [1], [2], [3], [4], [5]. Cerium oxide has anti-corrosion properties [6] and is intrinsically hydrophobic [7]. Specifically, cerium oxide has good corrosion resistive properties comparable to conventional chrome-based anti-corrosion coating [8], and its intrinsic hydrophobicity has been attributed to its inherent electronic structure [7]. Nanostructuring materials with intrinsic hydrophobicity can enhance their water repellent properties by increasing their surface roughness [9], and as such, nanostructured materials with intrinsic hydrophobicity are typically superhydrophobic without the help of hydrophobic modifiers of low surface energies [10]. Several synthesis methods for cerium oxide nanostructures such as chemical vapor deposition [11], electrodeposition [12], immersion [13], and hydrothermal [14], [15], [16], [17], [18], [19] and template methods [20] have been developed. However, there are few studies of direct growth of cerium oxide NRs on diverse substrates, despite their widespread potential applications. Here we report a facile, template-free hydrothermal method for direct growth of cerium oxide nanorods (NRs) on diverse substrates, including aluminum alloy, stainless steel, titanium, and silicon. This low-temperature hydrothermal method can be readily extended to large-scale processes. Directly grown cerium oxide NRs on the diverse substrates were not only crystalline, but also displayed superhydrophobic properties (i.e., contact angle of about 160.0 ± 1.0° and sliding angle of about 5.3 ± 0.6°) with no hydrophobic modifiers. Moreover, neutral salt spray tests and polarization measurements revealed that the grown cerium oxide NRs had good corrosion resistive properties in corrosive environments.
Section snippets
Direct growth of cerium oxide NRs on diverse substrates
Cerium oxide NRs were grown on diverse substrates using a hydrothermal method, as illustrated in Fig. 1. First, 0.1 M cerium nitrate hexahydrate (Ce(NO3)3·6H2O, Sigma Aldrich) and 1 M urea (CO(NH2)2, Sigma Aldrich) in deionized water were prepared in an autoclave. Second, the growth substrate was placed upside-down in the growth solution. Aluminum alloy (Al1050 and Al2024), stainless steel (SUS304), titanium (Ti, pure grade 2), and silicon (Si) substrates were used as the growth substrates in our
Scanning electron microscopy images of cerium oxide NRs
Scanning electron microscopy (SEM) images showed that cerium oxide NRs grew uniformly on aluminum alloy (Fig. 2a), stainless steel (Fig. 2b), titanium (Fig. 2c), and silicon (Fig. 2d) substrates. All cerium oxide NRs had similar morphologies, regardless of substrate type. Specifically, NRs grown on the diverse substrates had an average diameter of about 430 ± 140 nm and a length of about 2.12 ± 0.49 μm with an average growth rate of about 0.09 ± 0.02 μm/h.
X-ray photoelectron spectroscopy (XPS) analysis of cerium oxide NRs
Fig. 3 shows XPS measurements of as-grown NRs
Conclusion
We developed a facile, template-free, hydrothermal method for direct growth of cerium oxide NRs on diverse substrates such as aluminum alloy, stainless steel, titanium, and silicon. Cerium oxide NRs grew uniformly on the diverse substrates with similar morphologies, and the grown cerium oxide NRs consisted mainly of crystalline CeO2 NRs, which are intrinsically hydrophobic. All substrates modified with cerium oxide NRs showed superhydrophobicity (contact angle of about 160.0 ± 1.0° and sliding
Acknowledgement
This work is supported by the research fund of Hanyang University (HY-2012-000-0000-2272), Republic of Korea.
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