Nanochanneling and Local Crystallization Engineering Accelerate Multiphase Single‐Atom Catalysis for Rapid Water Decontamination

Abstract Precise engineering of single‐atom catalysts (SACs) with optimal hierarchical structures and favorable local chemical environments remains a significant challenge to cater for multiphase heterogeneous processes. Here, we develop a universal strategy for synthesizing channel‐digging microspherical SACs that markedly enhance gas–liquid–solid mass transfer and fine‐tune the thermodynamics of catalytic ozonation. By catalytically graphitizing carbon microspheres and selectively etching amorphous carbon domains via mild combustion, we fabricate cross‐linked hierarchical graphitic nanochannels confining transition metal (e.g., Co, Cr, Mn, Fe, Ni) single atoms (TMCSs‐Air). This nanoenvironment engineering increases interfacial ozone (O 3 ) mass transfer by 3.2‐fold and directs O 3 adsorption from a conventional “end‐on” to a bidental “side‐on” configuration. The enhanced inter‐orbital electronic interactions lower the O 3 activation barrier and form highly oxidizing surface‐confined O 3 (*O 3 ). Consequently, the CoCSs‐Air catalyst achieves a 3.6‐fold higher ozone utilization efficiency and a 4.2‐fold greater turnover frequency (TOF = 1580 min −1 ) compared with pristine Co‐doped carbon microspheres (CoCSs). Technical and economic evaluations further confirm the feasibility of TMCSs‐Air nanoreactors in treating real‐world petrochemical wastewater, highlighting its broader potential in overcoming gas diffusion barriers and tuning reaction pathways for multiphase heterogeneous catalysis.