Active site microenvironment engineering in M–N–C single-atom nanozymes: from precision regulation to mechanistic insights

This review focuses on the active site microenvironment engineering of metal-nitrogen-carbon single-atom nanozymes (M-N-C SANs), a frontier subfield of nanozymes renowned for their exceptional catalytic activity, selectivity, and cycling stability due to the synergistic effects of highly dispersed metal single atoms and carbon-based carriers, making them a core research focus in the nanozyme field. This paper systematically reviews the regulatory mechanisms and catalytic principles governing the active site microenvironment of M-N-C nanozymes. Focusing on three core components (carbon carrier defects, metal coordination environments, and surface functional groups), this paper elucidates the structural characteristics, action mechanisms, and targeted regulation strategies for each element. By integrating advanced characterization techniques such as <i>in situ</i> X-ray absorption fine structure (XAFS) and transmission electron microscopy (TEM) with density functional theory (DFT) calculations, the structure-electronic-catalytic performance relationship within the microenvironment is elucidated, revealing the intrinsic logic of microenvironmental regulation in optimizing catalytic pathways. Current research still faces challenges such as the difficulty of precise microenvironment regulation, insufficient understanding of dynamic catalytic mechanisms, and unclear multi-factor synergistic mechanisms. Future efforts should focus on innovative precision control technologies, high spatiotemporal resolution characterization techniques, multi-factor synergistic regulation systems, and interdisciplinary integration. This will propel M-N-C nanozymes from empirical regulation to precision design, providing theoretical foundations and technical references for their large-scale applications in biomedicine, environmental remediation, and energy conversion.