Chemisorption of Hydroxide on 2D Materials from DFT Calculations: Graphene versus Hexagonal Boron Nitride

Abstract

Recent nanofluidic measurements revealed strongly different surface charge measurements for boron-nitride and graphitic nanotubes when in contact with saline and alkaline water. 1,2 These observations contrast with the similar reactivity of a graphene layer and its boron nitride counterpart, using Density Functional Theory (DFT) framework, for intact and dissociative adsorption of gaseous water molecules. Here, we investigate, by DFT in implicit water, single and multiple adsorption of anionic hydroxide on single layers. A differential adsorption strength is found in vacuum for the first ionic adsorption on the two materials -chemisorbed on BN while physisorbed on graphene. The effect of implicit solvation reduces all adsorption values resulting in a favorable (non-favorable) adsorption on BN (graphene). We also calculate a pK a ≃ 6 for BN in water, in good agreement with experiments. Comparatively, the unfavorable results for graphene in water echoes the weaker surface charge measurements, but points to an alternative scenario.The successful isolation of single-layer graphene sheet3 has led to tremendous progress in the discovery of new 2D materials including boron nitride, silicene and transition metal dichalcogenides to cite a few. In particular hexagonal boron nitride monolayers share the planar honeycomb structure of graphene, with boron and nitrogen atoms alternating in the vortices of the honeycomb structure. Despite of their similar crystallographic structure, the electronic structure of BN and graphene nano sheets are drastically different : semimetallic for graphene and insulating for BN. Until recently both pristine layered materials were assumed to present inherently low chemical reactivity. However recent experimental works showed that covalent chemical fonctionalization could be achieved under drastic reactive conditions, either via reduction4,5 or reaction with oxidative reagents (H 2 O 2 ,6 oxygen radical7) or via fluorination8 Furthermore recent nanofluidic experiments have altered the long-standing picture of the chemical inertness of BN nanotubes by showing a large negative surface charge when the BN materials is in contact with aqueous saline solutions. In contrast, similar experimental investigations based on nanofluidic investigations showed that carbon nanotubes2 and planar graphitic surfaces9 exhibit smaller and even minute surface charge. The magnitude of the maximum charging -ranging from 0.1 C / m 2 for C to 1 C/m 2 for BN depending on the solution pH -rules out point defects as the sole origin of the measured surface charging. These experimental results therefore call for two challenging questions: (i) what are the potential chemical species present in basic and saline solutions that could adhere on the surface and strongly charge the pristine nanotubes ? (ii) how can we explain the different charging behavior of graphene and BN ideal nanotubes ? Europe PMC Funders GroupA recent DFT study has investigated the dissociation barrier of a water molecule in contact with pristine ...

Ultrahigh Ionic Exclusion through Carbon Nanomembranes

“…This implies two membrane properties: First, the limited passage of ions is controlled by an efficient size exclusion mechanism. Second, the membrane can effectively block the penetration of Cl − ions, which might be related to a negative charged surface originated from the adsorption of anionic species such as hydroxide on the membrane surface . Figure d compares the impedance of a sealed Si chip, a CNM, and an open aperture.…”

“…Second, the membrane can effectively block the penetration of Cl − ions, which might be related to a negative charged surface originated from the adsorption of anionic species such as hydroxide on the membrane surface. [19] Figure 2d compares the impedance of a sealed Si chip, a CNM, and an open aperture. One clearly observes the exceedingly high resistance of the CNM even in HCl which has the smallest hydration radius.…”

Functional MXene Materials: Progress of Their Applications

“…It is clear that graphene, in the past several years, has dominated the research field of 2D materials as the most promising 2D material . For instance, graphene oxide, as well as its derivatives, have potential applications in organic dyes and in the adsorption of heavy metal ions and arsenate ions.…”

“…[22,23] It is cleart hat graphene, in the past several years, has dominated the research field of 2D materials as the most promising 2D material. [24][25][26] For instance, graphene oxide,a sw ell as its derivatives, have potentiala pplicationsi no rganic dyes and in the adsorption of heavy metal ions and arsenate ions. Nevertheless, practical applications of graphene are limited by its simple chemistry,a si tc omprises only ac arbon network.…”

Hydrogenated boron nitride monolayer functionalization: A density functional theory study

“…Several theoretical studies have been reported on the twodimensional hexagonal boron nitride (2D h-BN) functionalization using different materials such as H [24], C [25], metals [26,27], functional groups [28][29][30] and organic molecules [17,[31][32][33][34]. In particular we are interested in the functionalization of hydrogenated 2D h-BN by a surface radical reaction that have been previously explored in hydrogenated Si(1 1 1) and (0 0 1) surfaces both experimentally and theoretically [35][36][37][38][39][40][41] in other hydrogenated 2D materials [42][43][44][45].…”