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@NH_(2)-UiO-66@Cu_(2)O heterojunction was designed and synthesized by integration of electron collector Pd and hole collector Cu_(2)O inside and outside of a photoactive metal-organic framework(MOF)NH_(2)-UiO-66,respectively.The obtained Pd@NH_(2)-UiO-66@Cu_(2)O 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/NH_(2)-UiO-66@Cu_(2)O,Pd@NH_(2)-UiO-66,and Pd/NH_(2)-UiO-66,Pd@NH_(2)-UiO-66@Cu_(2)O exhibits the highest photocatalytic activity.More importantly,Pd@NH_(2)-UiO-66@Cu_(2)O shows a conversion rate of benzylamine up to 99%either by oxidation under aerobic conditions or by strong adsorption of H atom(Hads)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.

Plasmon-enhanced photocatalytic oxidative coupling of amines in the air using a delicate Ag nanowire@NH_(2)-UiO-66 core-shell nanostructures

MOF-based core-shell structures with high surface area, abundant active sites, and broad absorption bands are viable alternatives to traditional single-component photocatalysts. In this report, we describe the design and construction of delicate Ag nanowires@NH_(2)-UiO-66 with a core-shell structure for use as photocatalysts in imine synthesis under light. The optimized composites exhibited 80% imine production, which was higher than both MOF and Ag NWs. The significant improvement in photocatalytic activity under light may be attributed to the plasmonic effect of silver nanowires and their core-shell structure, which promotes the separation of electron-hole pairs. Moreover, the photocatalytic activity of the core-shell nanostructure may provide valuable insight into the design and construction of MOF-based composite photocatalysts for oxidative coupling of amines.

Electronic interaction and oxygen vacancy engineering of g-C_(3)N_(4)/α-Bi_(2)O_(3) Zscheme heterojunction for enhanced photocatalytic aerobic oxidative homo-/hetero-coupling of amines to imines in aqueous phase

Photocatalytic oxidation coupling of amines represents a green and cost-effective method for the synthesis of highly value-added imines under visible light irradiation.However,the catalytic efficiency was severely limited by poor visible light response and easy recombination of photogenerated charge carriers.Herein,we report a g-CgN_(4)/α-Bi_(2)O_(3)Z-scheme heterojunction via electrostatic self-assembly of g-C_(3)N_(4)nanosheets and oxygen-va-cancy-rich aα-Bi_(2)O_(3)microsphere for visible-light driven oxidative coupling of amines to imines in H_(2)0 as green solvent at room temperature.Amines with diverse functional groups were efficiently converted into the corre-sponding imines in good to excellent yields.Impressively,this photocatalytic protocol is applicable for the challenging hetero-coupling of two structurally different amines to construct complicated asymmetric imines,which is the first report of photocatalytic hetero-coupling of amines to imines to our knowledge.Furthermore,the Z-scheme heterojunction also demonstrated high stability and could be readily separated and reused without obvious decay in activity and selectivity.Comprehensive characterizations and control experiments reveal the construction of Z-scheme heterojunction with intimate interface between g-CgN4 and a-Bi_(2)O_(3)greatly boosts the transfer and separation of photogenerated charge carries and enhances the redox capability.Meanwhile,the surface oxygen vacancies in a-Biz_(2)O_(3)also benefits the separation of photogenerated charge carriers and acti-vation of reactants.These jointly contributed to an enhanced photocatalytic performance for oxidative coupling of amines to imines.

Insights into the synergistic promotion of spin polarization over C_(3)N_(5.4) for enhancing cooperative hydrogen evolution and benzylamine oxidation coupling

Polymers are usually restricted on the high exciton binding energies and sluggish electron transfer because of the low dielectric constants.Regulating spin-polarized electrons is regarded as an attractive strategy,but often confined to the d-orbital elements.Here,the nonmetal P and N elements co-mediated the spin polarization of carbon nitrides(PCN)have been elaborately designed.The optimized PCN-3 shows an outstanding hydrogen production(22.2 mmol·g^(-1)·h^(-1))coupled with selective benzylamine oxidation without using any solvent and cocatalysts,which is 200 times of original C_(3)N_(4)and superior to the photocatalysts has been reported to date.Experimental and theoretical results verified that the spin-orbital coupling of N 2p and P 2p remarkably increased the parallel spin states of charge and reduced the formation of singlet excitons to accelerate exciton dissociation in carbon nitride.In addition,charge separation and surface catalysis can be significantly enhanced by the electron spin polarization of carbon nitride with the parallel arrangement,huge built-in electric field and disturbed electronic structure.Our finding deepens the insight into the charge separation and exciton dissociation in spin polarization,and offers new tactics to develop high-efficiency catalysts.

Defect-rich ultrathin poly-heptazine-imide-framework nanosheets with alkali-ion doping for photocatalytic solar hydrogen and selective benzylamine oxidation

Polymeric carbon nitride(CN)as a metal-free photocatalyst holds great promise to produce high-value chemicals and H_(2) fuel utilizing clean solar energy.However,the wider deployment of pristine CN is critically hampered by the poor charge carrier transport and high recombination.Herein,we develop a facile salt template-assisted interfacial polymerization strategy that insitu introduces alkali ions(Na+,K+)and nitrogen defects in CN(denoted as v-CN-KNa)to simultaneously promote charge separation and transportation and steer photoexcited holes and electrons to their oxidation and reduction sites.The photocatalyst exhibits an impressive photocatalytic H_(2) evolution rate of 8641.5μmol·g^(−1)·h^(−1)(33-fold higher than pristine CN)and also works readily in real seawater(10752.0μmol·g^(−1)·h^(−1))with a high apparent quantum efficiency up to 18.5%at 420 nm.In addition,we further demonstrate that the v-CN-KNa can simultaneously produce H_(2) and N-benzylidenebenzylamine without using any other sacrificial reagent.In situ characterizations and DFT calculations reveal that the alkali ions notably promote charge transport,while the nitrogen defects generate abundant edge active sites,which further contribute to efficient electron excitation to trigger photoredox reactions.

Palladium-catalyzed amination of chloro-substituted 5-nitropyrimidines with amines

A concise and efficient approach was developed for the synthesis of mono-substituted and di-substituted pyrimidines products via palladium-catalyzed amination of chloro-substituted 5-nitropyrimidines and amines. This synthetic methodology can produce various di-substituted pyrimidines in high yields with good functional group tolerance, and provide a complementary tool for the syntheses of important intermediates of nucleosides and purines with bioactivities.