Surface Multifunctional Sites Design on the Nh2-Mil-125(Ti) Nanosheets for Visible-Light Photocatalytic Synthesis of N-Benzylidene Benzylamine

Abstract

The two-dimensional (2D) Metal Organic Framework (MOF) of NH 2 -MIL-125(Ti) nanosheets with oxygen vacancies were prepared to construct a multifunctional photocatalyst via surface modification of Pd nanoparticles (Pd/MTNs). The obtained photocatalyst showed the highly efficiency for precisely transformation of benzylamine to N-benzylidene benzylamine under visible light irradiation and 1atm air atmosphere at room temperature. With the assistance of theoretical mathematical model, the MTNs loaded 0.5% wt Pd completed the transformation for benzylamine (>99%) to N-Benzylidene benzylamine (99%). AFM, XPS and UV-vis DRS experiments indicated that the open 2D structure of MTNs would contribute to the generation of surface oxygen vacancies (OV) sites and abundant Ti metal sites with underfilling electrons 3d orbit, enhancing the light absorption. In-situ FTIR revealed that these exposed Ti atoms would act as the discriminating sites to specifically adsorb the benzylamine molecules forming chemical coordination bonds -C-N∙∙∙Ti- on interface, polarizing and activating -C-N-bonds in benzylamine. Additionally, series of in-situ EPR and experimental results elucidated that the surface OV sites would act as the functional sites to capture the O 2 molecules from air. Furthermore, surface Pd sites would as a active sites to accelerate the photo-generated electrons transfer from inside to interface, inducing the activation of adsorbed O 2 molecules to ∙O 2 - . Based on these cooperating function sites in MTNs, a possible catalytic mechanism was discussed in a molecular scale.

Keywords: Two-dimensional metal-organic frameworks, NH2-MIL-125(Ti) nanosheets, Visible light photocatalysis, Selective surface coordination, benzylamine