Chloride-ion-directed synthesis of plate-like Cu 2 O mesocrystals for effective nitrogen fixation.

Cuprous oxide (Cu 2 O) 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 Cu 2 O 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 Cu 2 O 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 Cu 2 O nanocrystals. Cl - tended to adsorb on the (111) facets of the formed Cu 2 O nanocrystals and stabilize them. Then the Cu 2 O 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 Cu 2 O mesocrystals. The polymer, polyacrylamide (PAM), also promoted the mesocrystals formation by serving as a stabilizer and fixed the crystallographic orientation of the Cu 2 O nanocrystals during their orderly stacking process. The plate-like Cu 2 O mesocrystals showed a long decay time and pronounced performance toward the visible-light-driven photocatalytic reduction of N 2 into NH 3 . This research may stimulate in-depth investigations into the exploration of new synthetic methods for the design and construction of novel mesocrystals.