Breaking planar confinement: Tailoring the curvature of nanoconfined catalysts to activate PMS for efficient ¹O₂ generation

Although single-atom catalysts (SACs) have been widely applied in Fenton and Fenton-like processes, the role of curvature effects on their catalytic activity and reaction mechanisms remains poorly understood. Herein, PCN-FeSA were synthesized by anchoring Fe single atoms onto hollow porous carbon nanospheres with well-controlled curvature to activate peroxymonosulfate (PMS). Among them, PCN-FeSA1, characterized by the smallest particle size and thus the highest curvature, exhibited the largest specific surface area and superior electrochemical performance, resulting in the highest PMS activation efficiency and enabling complete degradation of ciprofloxacin (CIP) within 10 min. Mechanistic analysis revealed that increasing curvature shifted the Fe d-band center closer to the Fermi level. This electronic structure modulation reduced the adsorption energy of PMS and facilitated interfacial charge transfer, thereby improving oxidant utilization efficiency. Notably, the curvature effect regulated the transformation of dominant reactive oxygen species. Singlet oxygen (¹O₂) was identified as the primary species in high-curvature systems, whereas high-valent metal-oxo species dominated in control systems. Moreover, the PCN-FeSA1/PMS system exhibited high stability, excellent resistance to interference, and superior environmental safety. Overall, this work elucidates the pivotal role of curvature effects in Fenton-like reactions and provides a new strategy for designing highly efficient catalysts for environmental remediation.