Facile cascade-anchored synthesis of ultrahigh metal loading single-atom for significantly improved Fenton-like catalysis

It is important to break the low metal loading limited by stringent conditions and reveal the catalytic behavior of single-atom catalysts (SACs) governed by individual and interacting sites. Here, a facile and universal synthesis strategy was employed to achieve the highest loading of transition metals (Fe 41.31wt%, Mn 35.13wt%), rare-earth metals (La 28.62wt%), and noble metals (Ag 27.04wt%) to date. Systematic investigation confirms that the powerful ligand-chelation between oxalic acid and metal ions, as well as the simultaneously generated entangled polymer networks are crucial for achieving high-loading SACs. High single-atoms density induced site-intensive effects and site-to-site interactions, which regulated the local electron density of the catalyst, altered the electronic structure of metal, and shifted the valence state toward the metal. As a demonstration, the activation of peroxymonosulfate (PMS) for sulfamethoxazole degradation showed a significant dependence on catalyst site density, with the rate constant at least 1-2 orders of magnitude higher than that of most current SACs. The higher metal loading increased the potential jumps in Fenton-like reaction, promoted the electron transfer and reduced the energy barrier of the rate-determining step in 1O2 generation. This material also showed promising prospect for real wastewater treatment due to its high decontamination efficiency and application stability. The cascade-anchoring synthesis strategy, which can maximize the atomically dispersed metal loadings and simultaneously enhance the reactivity, is universally applicable. It is anticipated that it will take SACs a step closer to practical applications.