Imidazolium Ionic Liquid Mediates Black Phosphorus Exfoliation while Preventing Phosphorene Decomposition

TL;DR

This study shows that the ionic liquid [EMIM][BF4] effectively exfoliates black phosphorene while preventing its decomposition, offering insights into solvent design for industrial phosphorene production.

Contribution

It reveals the molecular mechanisms by which [EMIM][BF4] facilitates phosphorene exfoliation and protection, highlighting the role of hydrophobic and electrostatic interactions.

Findings

[EMIM][BF4] is an excellent solvent for phosphorene exfoliation.

The ionic liquid prevents phosphorene decomposition by forming a protective layer.

Exfoliation requires external stimuli due to moderate thermodynamic favorability.

Abstract

Forthcoming applications in electronics and optoelectronics make phosphorene a subject of vigorous research efforts. Solvent-assisted exfoliation of phosphorene promises affordable delivery in industrial quantities for future applications. We demonstrate, using equilibrium, steered and umbrella sampling molecular dynamics, that the 1-ethyl-3- methylimidazolium tetrafluoroborate [EMIM][BF4] ionic liquid is an excellent solvent for phosphorene exfoliation. The presence of both hydrophobic and hydrophilic moieties, as well as substantial shear viscosity, allows [EMIM][BF4] simultaneously to facilitate separation of phosphorene sheets and to protect them from getting in direct contact with moisture and oxygen. The exfoliation thermodynamics is moderately unfavorable, indicating that an external stimulus is necessary. Unexpectedly, [EMIM][BF4] does not coordinates phosphorene by p-electron stacking with the imidazole ring. Instead, the solvation proceeds via hydrophobic side chains, while polar imidazole rings form an electrostatically stabilized protective layer. The simulations suggest that further efforts in solvent engineering for phosphorene exfoliation should concentrate on use of weakly coordinating ions and grafting groups that promote stronger dispersion interactions, and on elongation of nonpolar chains.