# Sum-Frequency Scattering Spectroscopy Reveals the Charging Mechanism and Surface Structure of hBN Nanoflakes in Solution

## TL;DR

This study uses advanced spectroscopy to understand how hBN nanoflakes interact with different solvents, revealing how their surface charge changes.

## Contribution

The paper introduces the use of sum-frequency scattering spectroscopy to uncover the charge reversal mechanism of hBN nanoflakes in solution.

## Key findings

- hBN nanoflakes are positively charged in ethanol and negatively charged in ethanol–water mixtures.
- Vibrational sum-frequency scattering spectroscopy detects charge transfer on both the nanoflake lattice and in the surrounding liquid.
- The charge reversal is explained by different partial charge distributions in ethanol and water.

## Abstract

A molecular understanding of the interactions between
two-dimensional
(2D) layered materials and liquids is crucial for nanofluidics, catalysis,
and solution-based 2D material processing. Among 2D materials, hexagonal
boron nitride (hBN) has a number of outstanding properties, but its
interactions with liquids remain poorly characterized. Here, we investigate
the interfacial structure of few-layer hBN nanoflakes suspensions
in ethanol and ethanol–water mixtures. Electrophoretic light
scattering suggests that the nanoflakes are effectively positively
charged in ethanol and negatively charged in an ethanol–water
mixture. Vibrational sum-frequency scattering spectroscopy reveals
the surface structural changes underlying this charge reversal. Signatures
of charge transfer of opposite direction are detected on both the
flake lattice and in the liquid. The different (partial) charge distributions
in ethanol and water explain the apparent charge reversal.