Nature Catalysis, Published online: 17 June 2026; doi:10.1038/s41929-026-01555-2 Heterogeneous and homogeneous photocatalysts offer different strengths and weaknesses. Here, continuous-flow photocatalytic oxidation reactions are performed using covalent organic framework nanofluids that heterogenize molecular units to combine the advantages of catalyst efficiency, light utilization and easy separation.