Abstract: Floating photocatalysis can mitigate the catalyst-recovery, light-utilization and mass-transfer limitations of conventional suspended photocatalysts. However, current floating configurations often rely on passive immobilization without addressing the critical issue of bulk carrier recombination. Here, an S-scheme all-organic graphitic carbon nitride (g-C₃N₄)/covalent organic framework (iCOF) heterojunction was constructed in situ and immobilized on an annealed melamine sponge (AMS) substrate for visible-light-driven tetracycline (TC) degradation coupled with hydrogen evolution. The optimized composite (CNCF50) achieved 99.8% removal of TC within 60 min, yielding an apparent rate constant of 0.062 min^-1, and a hydrogen evolution rate of 16.5 mmol g^-1 h^-1. When deployed as a macroscopic floating catalyst, the CNCF50/AMS system maintained a hydrogen evolution rate of 12.6 mmol g^-1 h^-1 and a TC removal efficiency of 80.3%. Mechanistic studies using electron paramagnetic resonance (EPR), trapping experiments, photoelectrochemical characterization, and femtosecond transient absorption (fs-TA) spectroscopy indicate that the S-scheme interface modifies the relaxation pathways of photogenerated charge carriers, thereby promoting their efficient separation and interfacial transfer. This work demonstrates the integration of pollutant oxidation and solar fuel production through molecular-scale charge regulation and macroscopic-scale interface engineering.

Key words: Floating photocatalysts, Tetracycline degradation, Photocatalytic hydrogen evolution, g-C₃N₄/iCOF heterojunction, S-scheme charge transfer