Ultrathin Single‐crystalline MgO (111) Nanosheets

Synthesizing high-quality two-dimensional nanomaterials of non-layered metal oxide is a grand challenge, especially when long range single-crystallinity and clean high-energy surfaces are required. Here, we report the synthesis of single-crystalline MgO(111) nanosheets via a two-step process involving the formation of ultrathin Mg(OH) 2  nanosheets as precursor and their selective topotactic conversion upon heating under dynamic vacuum. The defect-rich surface displays terminal -OH groups, 3-coordinated O 2-  sites, low-coordinated Mg 2+  sites as well as single electrons trapped at oxygen vacancies, that render MgO nanosheets highly reactive as evidenced by the activation of CO molecules at low temperatures and pressures, with formation of strongly adsorbed red-shifted CO and coupling of CO molecules into C 2 species.