Designing heterogeneous MOF-on-MOF membrane with hierarchical pores for effective water treatment

Rationally regulating the separation pores is an effective way to achieve efficient separation membrane. However, the developed metal-organic framework (MOF) membranes for water treatment are all formed by one kind of MOF, which can only provide rigid pores, makes it difficult to achieve high flux and excellent rejection ratio simultaneity. Here, we proposed a facile strategy for the synthesis of heterogeneous MOF-on-MOF membrane with hierarchical pores, by site-specific grown ZIF-8 layer on UiO-66-NH 2 layer. Thus unique architecture of the obtained double-layered MOF membrane (UiO-66-NH 2 @ZIF-8) endows multidimensional separation pores: (i) the large pores of UiO-66-NH 2 can facilitate water transportation, (ii) the molecular-sieving pores of ZIF-8 can intercept dyes, (iii) UiO-66-NH 2 acting as active sites can promote the growth of ZIF-8. As a result, the optimized UiO-66-NH 2 @ZIF-8 membrane exhibits high flux (36.7 L m −2 h −1 bar −1 ) and excellent dye rejections (>97.0%). Through analysis and comparison, the regulated multi-type pores play an important role in membrane performance. Coupled with the facile membrane preparing method, this work can used as a potential approach of designing other advanced MOF membrane for water treatment. • A new heterogeneous MOF-on-MOF membrane with hierarchical pores was designed. • The layered MOF membrane (NH 2 -UiO-66@ZIF-8) endows multidimensional separation pores for separation. • The NH 2 -UiO-66@ZIF-8 membrane exhibits a high water flux of 36.7 L m −2 h −1 bar −1 with excellent rejections for dyes. • This strategy can be used as a potential approach of designing other advanced MOF membrane in various applications.