In Situ Generation and Activation of H2O2 by Metal-Free Catalysts for Efficient Gas Phase NO Removal

A metal-free PEI/Nv-C 3 N 4 photocatalyst enables efficient gas-phase NO oxidation via an in situ photo-self-Fenton process. • Nitrogen vacancies and PEI cooperatively regulate interfacial electronic structure, O 2 activation, and proton-coupled electron transfer. • PEI functionalization switches ROS evolution from a ·O 2 ⁻ pathway to an H 2 O 2 /·OH-dominated oxidation pathway. • PEI/Nv-C 3 N 4 achieves 85% NO removal, 98.4% nitrate selectivity, and stable operation over 800   min under visible light. Photo-Fenton processes are highly effective for pollutant degradation, yet their application to gas-phase NO oxidation remains limited by metal leaching, external H 2 O 2 addition, and inefficient oxidant utilization. Herein, we develop a metal-free photocatalyst based on polyethyleneimine-functionalized nitrogen-vacancy-rich graphitic carbon nitride (PEI/N v -C 3 N 4 ) for efficient NO oxidation via an in situ photo-self-Fenton process under visible light irradiation. Nitrogen vacancies serve as the primary sites for O 2 adsorption and activation, while PEI functionalization reconstructs the interfacial electronic structure by introducing defect-molecule coupled mid-gap states and a proton-rich microenvironment. This molecular-defect synergy alters the oxygen reduction pathway from a conventional one-electron route toward a selective two-electron process (O 2 → ⁎OOH → H 2 O 2 ), followed by efficient in situ H 2 O 2 activation into ·OH radicals. Simultaneously, PEI enhances NO adsorption and stabilizes NO-derived intermediates, facilitating their complete oxidation into nitrate. As a result, PEI/N v -C 3 N 4 achieves 85% NO removal efficiency, 98.4% nitrate selectivity, and stable operation over 800   min without introducing metal components. Combined experimental and theoretical analyses reveal a mechanistic transition from a ·O 2 - -dominated pathway to an H 2 O 2 /·OH-mediated photo-self-Fenton process. This work provides a general molecular-defect co-engineering strategy for regulating ROS evolution in metal-free photocatalytic systems toward sustainable air purification. Download: Download high-res image (170KB) Download: Download full-size image This research shows an in situ generation and activation pathway of H 2 O 2 enabled by metal-free catalysts, enhancing the efficient removal of gas phase NO via photo-self-Fenton reaction.