Precise engineering single-atom catalysts (SACs) with optimal hierarchical structures and favorable local chemical environment 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 O3 mass transfer by 3.2-fold and directs O3 adsorption from a conventional “end-on” to a bidental “side-on” configuration. The enhanced inter-orbital electronic interactions lower the O3 activation barrier and form highly oxidizing surface-confined O3 (*O3). 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-SAC-doped carbon microspheres. 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.
