Single-atom site catalysts (SACs) with high atom utilization efficiencies exhibit unexpected properties, making them ideal candidate catalysts for numerous reactions. Herein, we report a chemical-waste-vapor-assisted (CWVA) strategy for the synthesis of a catalyst with single atom Fe on semi-hollow N-doped carbon (SA-Fe/SHNC). Benefitting from its atomic Fe sites, the prepared catalyst exhibited a 103-fold higher activity (0.827 vs. 0.008 mol_PCB-209·mol_M⁻¹·h⁻¹) and much longer time-stability (more than 50 vs. 0.5 h) than benchmarked Fe₃O₄ nanoparticles toward decachlorobiphenyl (PCB-209) degradation. Experiments and density functional theory calculations revealed that the highly active isolated Fe sites are responsible for the activity of Fe-SAC/SHNC. In addition, the CWVA method was shown to be applicable for synthesizing other single atoms on various structured supports, thereby providing new opportunities for the design of various structured SACs for different applications.