Precious Metal Dioxide Nanosheets: Bridging the Gap between Solution Chemistry and Solid-State Two-Dimensional Materials.

Unraveling the atomic structures of chemically exfoliated precious metal dioxide (PMD) nanosheets is the key to understanding their diverse properties and realizing their potential in applications like catalysis. Using pair distribution function (PDF) analysis, we have solved the structures of platinate and iridate nanosheets, revealing they both adopt a T-MoS-type crystal structure. This discovery not only establishes a crucial structural analogy to well-understood transition metal dichalcogenides (TMDs) but, more importantly, allows us to explain the origins of their distinct properties. Our calculations based on these structures correctly predict that the platinate nanosheet is a yellow semiconductor, while the iridate nanosheet is a blue semimetal. Having established this powerful structure-property relationship, we further probed the unique chemical nature of these materials. We found that the structural polymorphism (T- vs T'-type) is governed by intrinsic elemental characteristics, rather than simple redox states as explored by in situ experiments. Instead of large-scale distortions, these nanosheets exhibit subtle short-range order (SRO) in their metal atom positions. This work provides a robust methodology for PMD research and highlights that chemically imparted features like SRO are key to designing the next generation of 2D materials.