Abstract
Confined and interstitial water has a key role in several chemical, physical and biological processes. It is remarkable that many aspects of water behavior in this regime (e.g., chemical reactivity) remain obscure and unaddressed. In particular for gold surfaces, results from simulations indicated that the first wetting layer would present hydrophilic behavior in contrast to the overall hydrophobic character of the bulk water on this surface. In the present work we investigate the properties of confined water on Au 〈111〉 nanochannels. Our findings, based on a large set of morphological, structural and spectroscopic experimental data and ab initio computer simulations, strongly support the hypothesis of hydrophilicity of the first wetting layer of the Au 〈111〉 surface. A unique oxidation process was also observed in the nanochannels driven by confined water. Our findings indicated that the oxidation product is Au(OH)3. Therefore, the Au surface reactivity against confined water needs to be considered for nanoscopic applications such as, e.g., catalysis in fine chemicals, pharmaceuticals, and the food industry green processes.
Highlights
Con ned and interfacial water is very important in chemical, physical, and biological processes
Typical 2D Atomic force microscopy (AFM) microscopy images before and a er patterning for the 600 nm Au layer sample are presented in the Electronic supplementary information (ESI).† We checked the DLC-coated cantilever pro le by Scanning Electron Microscopy (SEM) and we notice that the DLC lm remained intact a er the patterning process
The relative intensities of water bands probed by Fourier-transform infrared spectroscopy (FTIR) as function of nanochannels depth (Fig. 4) and the assignment of the tiny Raman bands (Fig. 5) presented strong pieces of evidence concerning the hydrophilicity of Au h111i
Summary
Con ned and interfacial water is very important in chemical, physical, and biological processes. It is relevant to probe how geometric con nements and surface interactions affect the properties of bulk water as well as the substrates containing it.[1,2] In this sense, a large number of investigations have been performed to study the structure and dynamics of water in diverse systems such as biological environments,[3] nanoporous silica matrices,[4,5] vermiculites,[6] molecular sieves,[7] and organic coatings.[8]. Xia et al.[10] investigated the corrosion characteristics of micro- and nano-particles of Cu in distilled water by measuring the absorbance and structure of corrosion products using X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) They concluded that corrosion products of micro-particles increase slowly with increasing immersion time. Liu et al.[11] investigated the de-
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