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.