Photoactive Cationic Metal Halide Building Units
Metal halide crystalline materials (e.g. organolead halide perovskites) have promising optical properties, but are not frequently used in photocatalysis due to their moisture-sensitive nature. Our research focus on synthesis of cationic metal halide building units, including 0D clusters, 1D chains, 2D layers and 3D frameworks, by employing anionic structure-directing agents (Angew. Chem. Int. Ed. 2017, 14411; Angew. Chem. Int. Ed. 2019, 7818). The positively-charged inorganic connectivity renders high-coordinate bridging halide, which have a higher energy cost for hydrolysis process than corner halide. In addition, our anionic organic templating agents form coordinative bonding with metal centers, further enhancing their structural stability.
This class of cationic metal halide building units has intriguing optical characteristics, including tunable halide-dependent band gaps and excellent carrier diffusion properties. The vast majority exhibit large Stokes-shifted intrinsic broadband emission, probably arising from self-trapped excitons. The low-dimensional metal halide units have strong exciton confinement and populated self-trapped states with enhance photoluminescence quantum efficiency. Our recent focus is to develop cationic lead iodide layers in one-step-excitation solar water splitting, producing stoichiometric amounts of hydrogen and oxygen without the use of any sacrificial reagent (Nat. Catal. 2020, 1027–1033).
Metal-Organic Frameworks for Carbon Dioxide Conversion
Carbon dioxide (CO2), the anthropogenically emitted gas, has been recognized as the primary contributor to global warming. Metal-organic frameworks (MOFs) are potentially the ideal candidates for the next-generation CO2 capture and conversion materials, owing to ultrahigh surface area and versatile functionality. This project is to functionalize MOFs with organic moieties having strong interactions with CO2. Our recent focus is to use N-heterocyclic carbene as catalytic sites or stabilization ligands to introduce (photo)catalytic acitivity of CO2 reduction into MOFs (Angew. Chem. Int. Ed. 2019, 2844; Angew. Chem. Int. Ed. 2021, 17388-17393).