Electrochemical characterization of Z-scheme charge transfer in biomass-derived ZnO/carbon dots for efficient tetracycline degradation

Abstract

This study investigates the electrochemical properties of a zinc oxide/carbon dots (ZnO/CDs) nanocomposite synthesized via a hydrothermal route, where biomass-derived CDs enhance charge separation and extend visible-light absorption. X-ray photoelectron spectroscopy reveals strong interfacial interactions between ZnO and CDs, facilitating efficient charge transfer. The ZnO/CDs (1 : 2) nanocomposite demonstrated superior tetracycline degradation efficiency of 86.6% under visible light, significantly outperforming pristine ZnO and other composite ratios. To elucidate the enhanced charge carrier dynamics, a comprehensive electrochemical analysis was conducted. Electrochemical impedance spectroscopy showed a smaller semicircle diameter in the Nyquist plot, indicating a lower interfacial resistance, which suggests improved electron mobility. Cyclic voltammetry and transient photocurrent measurements further confirmed enhanced charge separation, while Mott–Schottky analysis verified a Z-scheme charge transfer mechanism, effectively suppressing electron–hole recombination. Reactive species trapping experiments identified ˙OH and O₂˙− radicals as the dominant active species responsible for photocatalytic degradation. The photocatalyst exhibited remarkable recyclability and reusability, maintaining 85% of its photocatalytic activity over five cycles, demonstrating its stability and practical applicability for wastewater remediation. This study underscores the pivotal role of biomass-derived CDs in modulating the electronic properties of ZnO, offering a sustainable and efficient strategy for environmental cleanup.