Iron-Doped Carbon Nanotubes Facilitate ZnO Interfacial Charge Accumulation for Selective Singlet Oxygen Generation in Piezo-Photocatalytic Microplastics Upcycling

Abstract

Efficient catalytic upcycling of microplastics (MPs) remains challenging due to uncontrolled reactive oxygen species (ROS) evolution pathways and the reliance on predepolymerization of MPs prior to catalytic conversion. Here, we demonstrate that interfacial band engineering in an iron-doped carbon nanotube (CNFe)-mediated zinc oxide/carbon nitride (ZnO/DCN-Cg, ZCN) heterojunction enables selective ROS steering toward a dominant nonradical pathway. The ZCNCNFe nanocomposite, featuring N–Zn bonding, C–O–Zn coordination, and C–C conjugation, provides a structurally integrated platform that dynamically regulates interfacial charge transfer during peroxymonosulfate activation, resulting in singlet oxygen (1O2) as the dominant ROS with a high yield (67.71 μmol/L). Notably, real-world HDPE MPs (∼700 mg), directly extracted from commercial facial cleansers via a novel dual-density separation method, were selectively oxidized into oxygenated intermediates (e.g., carboxylic acids and esters) without any predepolymerization, rather than being fully mineralized (∼39.2 wt % weight loss, TOC = 14.06 mg/L), accompanied by pronounced surface erosion and fragmentation under piezo-photocatalysis. The introduction of CNFe triggers Fermi-level realignment to accelerate interfacial charge flux toward ZnO adsorption sites, promoting peroxo bond polarization and cleavage, driving the self-disproportionation of HSO5– to generate 1O2. This study establishes a charge-transfer-regulated framework for steering ROS pathways in piezo-photocatalytic systems, challenging conventional radical-dominated approaches for microplastics upcycling.