Researchers at the Xinjiang Technical Institute of Physics and Chemistry (XTIPC) of the Chinese Academy of Sciences (CAS) have developed a core-shell confined iron-based single-atom catalyst that combines high Fenton-like catalytic activity with structural stability, enabling nearly complete removal of 2,4-dichlorophenol (2,4-DCP) within 20 minutes under mildly acidic conditions.

Iron‑based single‑atom catalysts (Fe‑SACs) hold great promise for heterogeneous Fenton‑like water remediation, yet their practical deployment is severely hampered by the intrinsic activity‑stability trade‑off. Under harsh acidic oxidative environments, isolated Fe atoms tend to leach from carbon supports and trigger rapid deactivation. Rational modulation of local coordination environments to reconcile high catalytic activity and structural robustness remains a critical challenge for designing advanced single‑atom Fenton catalysts.

In a recent study published in the Journal of Catalysis, Profs. YANG Liping and YIN Jiao's team at the Research Center for Energy and Chemical Engineering at XTIPC carried out comparative structure‑performance investigations between Fe‑N₄ and Fe‑N₄O₂ single‑atom moieties.

Taking mesoporous MCM‑41 as a confined support and o‑phenylenediamine as ligand, polymerizable monomer and nitrogen source, the group fabricated a core‑shell confined Fe‑N₄ single‑atom catalyst denoted SiO₂@Fe‑N‑C via an in‑situ polymerization‑pyrolysis route.

Comprehensive characterizations including XRD, HAADF‑STEM, XPS and synchrotron‑based X‑ray absorption spectroscopy (XAS) validate atomic dispersion of Fe species within nitrogen‑doped carbon shells, well‑defined symmetric Fe‑N₄ coordination configuration, and well‑preserved ordered mesoporous framework originating from MCM‑41.

The as‑synthesized SiO₂@Fe‑N‑C delivers outstanding Fenton‑like catalytic performance. Under mildly‑acidic conditions, nearly complete removal of 2,4‑dichlorophenol (2,4‑DCP) is achieved within 20 minutes with an apparent rate constant of 0.70 min^-1 and a mineralization efficiency of 62%.

The catalyst maintains over 95% pollutant‑removal efficiency across ten successive cycling tests with negligible iron leaching. EPR and radical‑quenching experiments verify that ·OH serves as the dominant reactive oxygen species assisted by ¹O₂. The degradation proceeds through sequential dechlorination, hydroxylation and ring‑opening pathways towards final mineralization.

Combining density functional theory (DFT) calculations with post-reaction XPS measurements, the researchers uncovered a "strong adsorption-low perturbation" mechanism. Compared with asymmetric Fe‑N₄O₂ sites, symmetric Fe‑N₄ centers enable favorable reactant adsorption originating from enhanced orbital hybridization, while only ~0.01 e^- charge transfer occurs during catalysis to retain structural integrity of active sites. This feature successfully decouples the conventional activity‑stability trade‑off in Fenton‑like catalysis.

According to the researchers, the findings establish a clear link between coordination symmetry and catalytic performance, providing fundamental design principles for developing highly efficient and durable Fe-based single-atom Fenton-like catalysts.

The study was carried out by interdisciplinary teams at XTIPC. WANG Xiaoyan of XTIPC is the first author, while YANG and YIN are co-corresponding authors.

This research was financially supported by the Key Research and Development Program of Xinjiang Uygur Autonomous Region, the Xinjiang Tianshan Talent Training Program, and the Youth Innovation Promotion Association of the CAS.

Fabrication of core‑shell confined SiO₂@Fe‑N‑C catalyst and Fe‑N₄‑driven Fenton‑like degradation of 2,4‑DCP toward high activity and long‑term cycling stability. (Image by Prof. YIN Jiao's group)