LAUSR

Significance In the bulk phase, hydroxyl radical from the one-electron transfer and high-valent iron-oxo species from the O-atom transfer compete to be the reactive intermediates in the Fenton and related reactions. In the confined space at a nanoscale, however, the behavior of the Fenton reaction is elusive. Herein, we report an unprecedented singlet oxygen mediated Fenton’s reaction occurred inside carbon nanotube with inner diameter of ∼7 nm, showing exotic catalytic activities, unforeseen adsorption-dependent selectivity, and pH stability for the oxidation of organic compounds. Our results suggest the use of Fenton’s reaction in more scenarios than ever explored. For several decades, the iron-based Fenton-like catalysis has been believed to be mediated by hydroxyl radicals or high-valent iron-oxo species, while only sporadic evidence supported the generation of singlet oxygen (1O2) in the Haber–Weiss cycle. Herein, we report an unprecedented singlet oxygen mediated Fenton-like process catalyzed by ∼2-nm Fe2O3 nanoparticles distributed inside multiwalled carbon nanotubes with inner diameter of ∼7 nm. Unlike the traditional Fenton-like processes, this delicately designed system was shown to selectively oxidize the organic dyes that could be adsorbed with oxidation rates linearly proportional to the adsorption affinity. It also exhibited remarkably higher degradation activity (22.5 times faster) toward a model pollutant methylene blue than its nonconfined analog. Strikingly, the unforeseen stability at pH value up to 9.0 greatly expands the use of Fenton-like catalysts in alkaline conditions. This work represents a fundamental breakthrough toward the design and understanding of the Fenton-like system under nanoconfinement, might cause implications in other fields, especially in biological systems.