# Advanced oxidation processes at water/hydrophobic interfaces: energy-fluctuation mechanism and electron utilization quantification

## TL;DR

This study explores how energy fluctuations at water/hydrophobic interfaces drive chemical reactions, offering a sustainable method for water purification.

## Contribution

The paper introduces a quantifiable method to assess electron utilization in contact-electro-catalysis at macroscopic interfaces.

## Key findings

- Flexoelectric effects at the interface generate a polarization field strong enough to separate electrons from water molecules.
- A press-and-release device estimates triboelectric electron utilization at approximately 44.8%.
- The study extends advanced oxidation processes to macroscopic interfaces without high energy input.

## Abstract

The fundamental driving force and mechanism of water/hydrophobic interface chemistry remain debated. Contact-electro-catalysis (CEC), which converts mechanical energy into extensive interfacial charge separation in water, has introduced a new perspective. However, the introduction of ultrasonication has prompted a renewed scrutiny of its reaction mechanisms. At the same time, those studies have no quantification assessment due to the calculation difficulty of energy-to-electron conversion. Here, we investigate radical-mediated advanced oxidation processes (AOPs), at a macroscopic water/hydrophobic interface without violent energy input. Theoretical analysis reveals that the flexoelectric response of interfacial water creates a local polarization field that is strong enough to separate electrons from H2O or OH−. These interfacial energy fluctuations are thus proposed as the primary origin of the reaction driving force. Furthermore, by leveraging a quantifiable press-and-release device, we establish a methodological framework for evaluating the triboelectric electron utilization ratio in CEC, yielding a first estimation of ∼44.8%. This work provides new insights into both interfacial AOPs and contact electrification at water/hydrophobic interfaces. This breakthrough offers a new and sustainable strategy for low-energy water purification and pollutant degradation, and also provides a basis for future precise quantification of electron utilization efficiency.

AOPs, traditionally limited to microscopic interfaces, are extended to a macroscopic water/hydrophobic interface without intense energy input. Flexoelectricity couples interfacial energy fluctuations with the energy required for charge transfer.