This supplementary material provides additional information and data supporting the study on ultrathin covalent organic framework (COF) nanosheets for enhanced photocatalytic water oxidation. The supplementary text includes computational calculations of the CoTPP-Bpy structure using Materials Studio and VASP, detailing the optimization of atomic positions, energy, and the simulation of photocatalytic reactions. The calculations involved determining the energy of proton-electron pairs, free energy of species, and the charge difference in intermediates. The TOF (turnover frequency) for CoTPP-CoBpy₃ was calculated as 373 h⁻¹ based on the amount of loaded cobalt determined by ICP-OES. The supplementary figures include digital photographs, simulated structures, XRD patterns, BET surface area, FTIR spectra, NMR patterns, ICP-OES spectra, XPS spectra, AFM images, Cryo-TEM images, UV-vis absorbance spectra, PL emission spectra, fs-TA spectra, kinetic traces, UPS spectra, GC signals, FT-IR spectra, and XPS spectra before and after reaction. These figures provide detailed characterization of the CoTPP-CoBpy₃ and CoTPP-Bpy materials, including their dispersibility, solubility, and structural properties. The supplementary movie includes a contact angle measurement. The references list a wide range of literature related to photocatalytic water oxidation, covalent organic frameworks, and related materials. The supplementary material highlights the performance of CoTPP-CoBpy₃ in photocatalytic water oxidation, demonstrating its high efficiency and stability, and provides a comprehensive set of data and figures to support the study's findings.This supplementary material provides additional information and data supporting the study on ultrathin covalent organic framework (COF) nanosheets for enhanced photocatalytic water oxidation. The supplementary text includes computational calculations of the CoTPP-Bpy structure using Materials Studio and VASP, detailing the optimization of atomic positions, energy, and the simulation of photocatalytic reactions. The calculations involved determining the energy of proton-electron pairs, free energy of species, and the charge difference in intermediates. The TOF (turnover frequency) for CoTPP-CoBpy₃ was calculated as 373 h⁻¹ based on the amount of loaded cobalt determined by ICP-OES. The supplementary figures include digital photographs, simulated structures, XRD patterns, BET surface area, FTIR spectra, NMR patterns, ICP-OES spectra, XPS spectra, AFM images, Cryo-TEM images, UV-vis absorbance spectra, PL emission spectra, fs-TA spectra, kinetic traces, UPS spectra, GC signals, FT-IR spectra, and XPS spectra before and after reaction. These figures provide detailed characterization of the CoTPP-CoBpy₃ and CoTPP-Bpy materials, including their dispersibility, solubility, and structural properties. The supplementary movie includes a contact angle measurement. The references list a wide range of literature related to photocatalytic water oxidation, covalent organic frameworks, and related materials. The supplementary material highlights the performance of CoTPP-CoBpy₃ in photocatalytic water oxidation, demonstrating its high efficiency and stability, and provides a comprehensive set of data and figures to support the study's findings.