Enhanced Piezo-Phototronic Effect in Carbon Nitride Nanosheets via Oxidative Exfoliation for High-Efficiency Piezo-Photocatalysis

Abstract

The application of piezo-photocatalysis in wastewater treatment by harnessing solar and mechanical energy simultaneously offers a promising strategy for sustainable pollutant degradation. Nevertheless, integrating robust piezoelectric and semiconducting properties effectively within a single-component catalyst to achieve an optimal synergy remains challenging due to their inherent tradeoff. To tackle this limitation, a series of graphitic carbon nitride (g-C3N4) nanosheets with a controlled degree of exfoliation has been fabricated through a facile oxidative exfoliation strategy in this work. The exfoliated nanosheets demonstrate substantial improvements in both piezoelectricity (36 pm·V⁻¹) and semiconducting properties, significantly enhancing their piezo-photocatalytic performance for organic pollutants degradation. Combined experimental and theoretical analysis reveals that the oxidative exfoliation process not only enables the easy domain deformation feature of the nanosheets, but also introduces surface polar functional groups, thus accelerating the polarization and piezoelectric response. Meanwhile, the charge carrier migration pathway to surface-active sites has been largely shortened, benefiting from the nanosheet structure. Consequently, the optimized material E500-CN (g-C3N4 exfoliated at 500 °C) demonstrates superior piezo-photocatalytic degradation performance, achieving a degradation rate of 97% within 20 min and a first-order kinetic rate constant of 0.152 min⁻¹, which is 5.1-fold faster than that of B-CN. Mechanism study highlights the critical role of the enhanced piezo-phototronic effect, where the vibration-induced in-plane piezopotential effectively manipulates the separation and transportation of photogenerated electron-holes. This study offers a feasible design strategy for efficient 2D piezo-photocatalysts in water remediation, enabling a sustainable water treatment approach.