(173g) In situ Growth of MOF Membranes Assisted By Electro-Deposition

Authors: 
Wei, Y., South China University of Technology
Wang, H., South China University of Technology
Metal–organic frameworks (MOFs) have great potential for use a membranes in separation processes because their pore size can be tuned and they have highly designable structures and adsorption properties.[1] The preparation of supported MOF membranes has attracted increasing attention in separation technology.[2] We develop a facile and efficient electro-deposition method to modify inexpensive porous stainless-steel nets for use as substrates in the in situ growth of metal–organic framework membranes, such as
ZIF-8, ZIF-67 and HKUST-1. Using this method, different metal precursors can be electro-deposited depending on the central metals required in the target metal–organic frameworks. The inorganic modifiers prepared by this approach are sufficiently reactive for the one-step growth of continuous metal–organic framework membrane.

We chose stainless-steel nets (SSNs) as the substrate as they are inexpensive
and easily welded. The preparation concept is shown schematically in Fig. 1. A metal oxide/hydroxide with a morphology exactly corresponding to the metal centres of the targeted MOFs is introduced onto the SSN via electro-deposition. For example, ZnO nanorods, Co(OH)2 nanosheets and Cu2O nanocubes can be electrodeposited onto substrates quickly and provide active sites for the crystallization of Zn–ZIF-8, Co–ZIF-67 and Cu–HKUST-1,
followed by in situ growth to form continues MOF membranes.

The metal precursors of ZnO nanorods, Co(OH)2 nanosheets and Cu2O nanocubes are electro-deposited onto SSN respectively as inorganic modifiers. As a representative, the microstructure images of ZnO nanorods are shown in Fig. 2a. These reactivity of these modifiers is excellent because electro-deposition is operated at low temperature and also some intrinsic defect exists. The following growth of three different MOF membranes can be finished in one step without any pre-treatment. The microstructure images of ZIF-8 membranes are shown in Fig. 2b, 2c. The pure phase is confirmed by XRD analysis (Fig 2d). This strategy is proved to be general and all the membranes are tested for gas separation performance (shown in Table 1).

An efficient electro-deposition strategy is proposed for the introduction of diverse metal clusters into inexpensive SSN substrates. These metal clusters universally act as inorganic modifiers for the subsequent facile in situ growth of the MOF
membranes. The fast and mild process of modification assisted by electro-deposition is promising for scaled-up production as well as low-cost manufacturing. The excellent reactivity of these metal oxide/hydroxide precursors arising from electro-deposition plays a vital part in the one-step in situ synthesis of various MOF membranes. The proposed electro-deposition-assisted strategy simplifies the procedure, exhibits excellent generality and can be applied to the preparation of different kinds of metal-centered MOF membranes.