Enhancement of visible-light-driven oxidative amine coupling under aerobic and anaerobic conditions by photocatalyst with spatial separation of photoinduced charge carriers

Spatial separation of oxidation/reduction cocatalyst is an effective means to improve the efficiency of charge separation in photocatalytic reaction systems. Herein, a yolk-shell Pd@NH2-UiO-66@Cu2O heterojunction was designed and synthesized by integration of electron collector Pd and hole collector Cu2O inside and outside of a photoactive metal-organic framework (MOF) NH2-UiO-66, respectively. The obtained Pd@NH2-UiO-66@Cu2O heterojunction effectively inhibits the electron and hole recombination through the photo-induced electrons and holes flow inward and outward of the composite, and promotes the reduction and oxidation abilities for the oxidative coupling of benzylamine to imines. Compared with Pd/NH2-UiO-66@Cu2O, Pd@NH2-UiO-66, and Pd/NH2-UiO-66, Pd@NH2-UiO-66@Cu2O exhibits the highest photocatalytic activity. More importantly, Pd@NH2-UiO-66@Cu2O shows a conversion rate of benzylamine up to 99% either by oxidation under aerobic conditions or by strong adsorption of H atom (H-ads) under anaerobic conditions. In addition, the catalyst shows good stability and can be recycled at least ten times. This work provides useful guidance on construction of MOFs-based composites with spatially separated photoinduced charge carriers to realize efficient oxidation coupling of benzylamine in both aerobic and anaerobic conditions.

Automated summary

This study successfully achieved spatial separation of photoinduced charge carriers through the design and synthesis of a special heterojunction, leading to improved efficiency of the catalytic reaction. The obtained material exhibited high activity in oxidative coupling reaction and achieved high conversion rates under both aerobic and anaerobic conditions.