MOF-on-MOF hybrids: Synthesis and applications

Metal-organic frameworks (MOFs) are a promising class of porous crystalline materials with diverse applications, the properties of which are dependent on their structures including both compositions and architectures. The intensive research of MOFs has led to an emerging family of MOF-on-MOF hybrid materials constructed by the conjugation of two or more MOFs units. The advances in the field of MOFs have been summarized in numerous excellent reviews on single MOFs, MOFs-based composites via conjugation with non-MOF materials and their derivates. However, there is a lack of dedicated review on MOF-on-MOF hybrids. Within this context, herein we provide a timely and comprehensive summary on the achievements of MOF-on-MOF hybrids. An introduction of the synthetic strategy/formation mechanism is firstly presented to explain the interaction between host and guest MOFs. Then, the structural diversity in MOF-on-MOF systems is discussed in detail to demonstrate how MOF-on-MOF hybrid systems enable advances in various applications. Finally, challenges and future directions of MOF-on-MOF development are described as our own perspectives.