Ultrathin two-dimensional (2D) metal oxyhalides show excellent photocatalytic properties due to their unique electronic and interfacial structures. A novel top-down wet-chemistry desalination approach was developed to remove the alkali-halide salt layer from the precursor Pb<sub>0.6</sub>Bi<sub>1.4</sub>Cs<sub>0.6</sub>O<sub>2</sub>Cl<sub>2</sub>, creating the 2D bimetallic oxyhalide Pb<sub>0.6</sub>Bi<sub>1.4</sub>O<sub>2</sub>Cl<sub>1.4</sub>. This new material's increased surface area, bimetallic active sites, and faster carrier dynamics significantly enhance atmospheric CO<sub>2</sub> reduction efficiency, surpassing its parent material and other bismuth-based oxyhalide photocatalysts. This desalination strategy offers a new approach for designing ultrathin 2D catalysts for environmental and energy applications.
