Heteroepitaxial MOF-on-MOF photocatalyst for solar-driven water splitting

Assembly of different Metal-Organic Frameworks (MOFs) into hybrid MOF-on-MOF heterostructures has been established as a promising approach to develop unique synergistic performances for a variety of applications. Here we report the synthesis of MOF-on-MOF heterostructures by the epitaxial growth of MIL-88B(Fe) onto UiO-66(Zr)-NH2 nanoparticles. The face-selective design and appropriate energy band structure alignment of the selected MOF constituents have permitted its application as active heterogeneous photocatalyst for solar-driven water splitting. The composite achieves apparent quantum yields for photocatalytic overall water splitting at 400 and 450 of about 0.9 %, values that compare much favourably with previous analogous reports. Understanding of this high activity has been gained by spectroscopic and electrochemical characterization together with STEM-EDX and HRTEM-EDX measurements. This study exemplifies the possibility of developing MOF-on-MOF heterostructures with outstanding activity towards photocatalytic water splitting under solar light.