Highly Stable CsPbBr ₃ Nanocrystals for Photocatalytic Reduction of CO ₂ : Ionic Liquid as a Surface Passivation Ligand and Reaction Precursor

All inorganic metal halide perovskites (MHPs) have been regarded as a new type of promising photocatalyst for the reduction of CO 2 . However, due to their strong ionicity and the labile surface ligands, there is still much room for improvement of the stability and efficiency of MHP photocatalysts. Here, we propose a new strategy simultaneously using ionic liquid (IL) as a surface passivation ligand and a precursor to mediate the growth and then stabilize CsPbBr 3 MHPs for the photocatalytic reduction of CO 2 . First, the TEM and XRD results show that the prepared CsPbBr 3 has a cubic morphology with the monoclinic phase when the IL of 1-octyl-3-methylimidazolium bromide ([Omim]Br) is used as the surface ligand. When the molar ratio of [Omim]Br to Pb(CH 3 COO) 2 is optimized to 2, the photoluminescence quantum yield of the prepared CsPbBr 3 can reach as high as 90.93%, suggesting the effective reduction of surface defects by the IL ligand. Importantly, the CsPbBr 3 nanocrystals show high stability under the ambient stimuli of light, heat, and humidity. The subsequent FT-IR and XPS characterizations indicate that the presence of [Omim]Br on the surface of CsPbBr 3 increases the Br-rich state, which accounts for the excellent optical property and stability of the CsPbBr 3 nanocrystals. Finally, with the assistance of IL as the activator of CO 2, the CsPbBr 3 photocatalysts provide a high evolution rate of 24.56 and 6.66 μmol g –1 h –1 for CO and CH 4, respectively. Multifunctional ILs as passivation ligands, reaction precursors, and CO 2 activators provide an efficient pathway to fabricate stable metal halide perovskites for photocatalytic CO 2 conversion.