Abstract
The adsorption of water on solid surfaces is a scientific evergreen which again recently prompted considerable attention in the materials, nano-, and surface science communities, respectively, due to conflicting evidence presented in the most highly regarded scientific journals. This mini review is a brief and personal perspective of the current literature (and our own data) about water adsorption for two examples, namely graphene and silicatene, which are both two-dimensional (2D) crystals. Silicatene, an inorganic companion of graphene, is intriguing as it presents us with the possibility to synthesize a 2D analog to zeolites by doping this crystalline silicon film. The wettability by water and whether or not support effects of epitaxial 2D crystals are present is of concern. Regarding applications: some 2D crystals appear promising for the hydrogen evolution reaction, i.e., hydrogen generation from water; a functionalization of graphene (by oxygen/water) to graphene oxide may be interesting for metal-free catalysis; the latest highlight in this field appears to be “icephobicity”, an application related to the hydrophobicity of surfaces.
Highlights
The perhaps obvious question may be: how can we enhance the reactivity? can a metal-free catalyst be build based on a graphene functionalization, for example, as graphene oxide? Ideally, graphene would directly provide reactive oxygen/oxygenates for surface reactions
There is no real controversial discussion about water adsorption on silicatene in the literature, but in the few works available on the subject [16,17,18] it was apparently a priori assumed that 2D silica behaves like bulk silica and must be hydrophobic. This is somewhat astonishingly since firstly, for amorphous bulk silica surfaces, hydrophilic interactions are known for quite some time [21]
Contact angle measurements with water do not work at ultra-high vacuum (UHV), but standard temperature ramping techniques (TDS-thermal desorption spectroscopy) can be applied to characterize fairly directly wetting properties of surfaces at clean conditions
Summary
Due to quasi mass production of graphene, applications in catalysis are potentially achievable. From a fundamental perspective, the overarching question may be: do graphene’s widely praised unique electronic properties make it useful as a (heterogeneous) catalytic material? The permeability which affects chemistry and surface science applications is certainly related to graphene’s unique electronic properties. The example shows that graphene’s well-known unique electronic properties can make it useful in heterogeneous catalysis. The second even more obvious example is small-molecule gas sensors. Graphene can be advantageous as a component of small-molecule gas sensors. In the light of these two briefly described examples, one may respond with “yes” to the question “does graphene’s unique electronic structure make it a catalytically useful material?” it makes sense to study the basic surface science properties of graphene such as water adsorption in regard of heterogeneous catalysis
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