Chloride-ion-directed synthesis of plate-like Cu2O mesocrystals for effective nitrogen fixation.

Abstract

Cuprous oxide (Cu2O) mesocrystals, which are composed of numerous nanocrystals with a common crystallographic orientation, are supposed to possess superior photocatalytic abilities than the normal constructions, but very few of them have been reported to date. In this work, plate-like Cu2O mesocrystals were successfully fabricated via a facile one-pot wet chemical strategy. Unlike the commonly used polymers or small molecules, chloride ions (Cl-) were employed as structure-directing agents and played the main role in the Cu2O mesocrystal formation. The formation mechanism was interpreted as follows: the presence of Cl- inhibited the formation of CuO and Cu by forming the intermediate product CuCl, which was further hydrolyzed to Cu2O nanocrystals. Cl- tended to adsorb on the (111) facets of the formed Cu2O nanocrystals and stabilize them. Then the Cu2O nanocrystals were aligned side by side through the unabsorbed side faces, leading to mutual nanocrystals orientation and crystallographic lock-in, facilitating the formation of plate-like Cu2O mesocrystals. The polymer, polyacrylamide (PAM), also promoted the mesocrystals formation by serving as a stabilizer and fixed the crystallographic orientation of the Cu2O nanocrystals during their orderly stacking process. The plate-like Cu2O mesocrystals showed a long decay time and pronounced performance toward the visible-light-driven photocatalytic reduction of N2 into NH3. This research may stimulate in-depth investigations into the exploration of new synthetic methods for the design and construction of novel mesocrystals.