Doping transition metal in PdSeO₃ atomic layers by aqueous cation exchange: A new doping protocol for a new 2D photocatalyst

Elemental doping confined in atomically-thin 2D semiconductors offers a compelling strategy for constructing high performance photocatalysts. Although impressive progress has been achieved based on co-thermolysis method, the choices of dopants as well as semiconductor hosts are still quite limited to yield the elaborate photocatalyst with atomic-layer-confined doping defects, owing to the difficulty in balancing the reaction kinetics of different precursors. This study shows that the cation exchange reaction, which is dictated by the Pearson's hard and soft acids and bases (HSAB) theory and allowed to proceed at mild temperatures, can be developed into a conceptually new protocol for engineering elemental doping confined in semiconductor atomic layers. To this aim, the two atomic layers of a new type of 2D photocatalyst PdSeO₃ (PdSeO₃ 2ALs, 1.1 nm) are created by liquid exfoliation and exploited as a proof-of-concept prototype. It is demonstrated that the Mn(II) dopants with controlled concentrations can be incorporated into PdSeO₃ 2ALs via topological Mn²⁺-for-Pd²⁺ cation exchange performed in water/isopropanol solution at 30 °C. The resulting Mn-doped PdSeO₃ 2ALs present enhanced capacity for driving photocatalytic oxidation reactions in comparison with their undoped counterparts. The findings here suggest that the new route mediated by post synthetic cation exchange promises to give access to manifold 2D confined-doping photocatalysts, with little perturbations on the thickness, morphology, and crystal structure of the atomically-thin semiconductor hosts.