Visible-Light-Responsive Sillen-Structured Mixed-Cationic CdBiO2Br Nanosheets: Layer Structure Design Promoting Charge Separation and Oxygen Activation Reactions

Exploration for new layered-structured materials is of significance in multiple fields, e.g., catalysis, energy storage, and conversion, etc. In this work, we develop a visible-light-responsive Sillen-structured mixed-cationic layered catalyst CdBiO2Br based on the typical Sillen-structured BiOBr, and first propose layer structure design as a novel tactic for promoting charge separation and oxygen activation reactions. Differing from BiOBr characterized by [Bi2O2](2+) layer and interleaved Br- double slabs, the crystal structure of CdBiO2Br comprises the [CdBiO2](+) layer and interbedded single Br- slice, rendering a narrowed interlayer spacing from 8.11 to 6.23 angstrom. The largely reduced interlayer distance drastically shortens the diffusion paths of photogenerated electrons (e(-)) and holes (h(+)) in CdBiO2Br, allowing favorable migration of carriers from bulk to the surface of the catalysts. Profiting from this structural advantage, CdBiO2Br presents a superior visible-light driven oxygen activation ability in evolution of superoxide radicals (O-center dot(2)-) and hydroxyl radicals ((OH)-O-center dot), with a production rate of similar to 2.4 and 14.1 times that of BiOBr, respectively. DFT calculations unearth that CdBiO2Br has smaller effective masses for both e(-) and h(+) than BiOBr, and meanwhile bears a significant difference in the respective mobility of e(-) and h(+), indicative of efficient mobility and separation of carrier charge. In particular, the h(+) effective mass of CdBiO2Br is merely one-third of that in BiOBr, corresponding well to the far higher (OH)-O-center dot generation rate of CdBiO2Br. Our work not only exposes a visible-light-active layered material for environmental chemistry/biochemistry applications but also discloses the huge potential of crystal structure manipulation in governing the charge transport behavior and photo(electro)chemical properties.