Continuous-Flow Photosynthesis of Ultrahigh-Loading Single-Atom Catalysts via Expedited Ion Exchange

Photochemistry represents a paradigm shift toward sustainable materials synthesis, yet its sluggish kinetics compared to thermochemistry impose a stringent metal-loading limit in conventional photosynthesis of single-atom catalysts (SACs). Herein, we introduce an ion-exchange strategy to overcome the thermodynamic and kinetic barriers in SAC photodeposition. By incorporating potassium ions into polymeric carbon nitride (PCN), an ultrahigh density of transition-metal atoms (such as Cu) can be ion-exchanged and subsequently photodeposited as single atoms at up to 20 wt%. This is supported by molecular dynamics simulations, where the incorporation of potassium ions creates exchangeable anchoring sites and accelerates reaction kinetics. Further scaling up in a segmented-flow slurry photoreactor enables a productivity of Cu₁/PCN catalysts up to 8 g h^-1 for over 15 h, at a production cost of 32.1 USD/kg^-1 alongside reduced emissions relative to pyrolysis. The resulting Cu₁/PCN also delivers excellent activity in ligand-free C-O coupling for the production of a variety of fine chemicals. Our study paves the way for scalable production of ultrahigh-loading SACs in a translational continuous-flow photoreactor.