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 synergistic performances for a variety of applications. Here, we explore the performance of a MOF-on-MOF heterostructure by 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 an active heterogeneous photocatalyst for solar-driven water splitting. The composite achieves apparent quantum yields for photocatalytic overall water splitting at 400 and 450 nm of about 0.9%, values that compare much favorably with previous analogous reports. Understanding of this high activity has been gained by spectroscopic and electrochemical characterization together with scanning transmission and transmission electron microscopy (STEM, TEM) measurements. This study exemplifies the possibility of developing a MOF-on-MOF heterostructure that operates under a Z-scheme mechanism and exhibits outstanding activity toward photocatalytic water splitting under solar light.