Adsorption of Organic Molecules to van der Waals Materials: Comparison of Fluorographene and Fluorographite with Graphene and Graphite

Abstract

Understanding strength and nature of noncovalent binding to surfaces imposes significant challenge both for computations and experiments. We explored the adsorption of five small nonpolar organic molecules (acetone, acetonitrile, dichloromethane, ethanol, ethyl acetate) to fluorographene and fluorographite using inverse gas chromatography and theoretical calculations, providing new insights into the strength and nature of adsorption of small organic molecules on these surfaces. The measured adsorption enthalpies on fluorographite range from −7 to −13 kcal/mol and are by 1–2 kcal/mol lower than those measured on graphene/graphite, which indicates higher affinity of organic adsorbates to fluorographene than to graphene. The dispersion-corrected functionals performed well, and the nonlocal vdW DFT functionals (particularly optB86b-vdW) achieved the best agreement with the experimental data. Computations show that the adsorption enthalpies are controlled by the interaction energy, which is dominated by London dispersion forces (∼70%). The calculations also show that bonding to structural features, like edges and steps, as well as defects does not significantly increase the adsorption enthalpies, which explains a low sensitivity of measured adsorption enthalpies to coverage. The adopted Langmuir model for fitting experimental data enabled determination of adsorption entropies. The adsorption on the fluorographene/fluorographite surface resulted in an entropy loss equal to approximately 40% of the gas phase entropy.

Surface properties of MoS2 probed by inverse gas chromatography and their impact on electrocatalytic properties

“…1 ). 17 , 19 , 20 The surface energies measured at low coverage are a result of the intermixing of adsorption on high-energy sites and basal plane adsorption. 17 The amount of high-energy sites is rather low, which is indicated by only a slightly concave shape of the surface energy, particularly in comparison with analogical iGC measurements on graphite.…”

Studying physisorption processes and molecular friction of cycloparaphenylene molecules on graphene nano-sized flakes: role of π⋯π and CH⋯π interactions

“…The aromatic surface of graphene [19,20] makes it an ideal substrate for immobilization of these organic nanorings through CH• • • π and π • • • π noncovalent interactions. Graphene nano-sized flakes (or nanoislands on other substrates) are extremely useful models to study these highly local interactions in adsorption processes [21][22][23], as they can also be easily functionalized [24] and produced by STM experiments through mechanical contact between the tip and the surface or through electro-exfoliation [25]. Once a reasonable nano-sized graphene flake is selected one can choose the corresponding nanoring size to avoid pronounced edge effects.…”

Chemistry, properties, and applications of fluorographene

“…Concerning the surface properties of FG, recent studies by inverse gas chromatography revealed that GrF has a lower surface energy (of ∼80 mJ m −2 ) than graphite [35] . Additionally, the adsorption enthalpies of organic molecules are similar or even slightly lower to FG than to graphene [101] , [102] .…”