Rational construction of MOF-on-MOF heterojunction with an array of flexible two-dimensional microsheets for efficient CO2 photoreduction

MOF-on-MOF composites are deemed promising candidates to accomplish synergistic CO2 capture and photoreduction thanks to their plentiful active sites, extended light response range, timely separation of photoexcited electron-hole pairs, and large CO2 adsorption capacities. Unfortunately, the controllable growth of the designed MOF-on-MOF heterostructure is challenging. Deficient interphase contact and the consequent mass transfer deprivation is one of the primary obstacles severely impairing the catalytic efficiency. Herein, the contact between two widely-employed MOFs of Ni-BDC and NH2-MIL-125 was significantly strengthened by exploiting a self-assembled array of Ni-BDC microsheets. In contrast to the spontaneously formed spheroidal aggregate, the loosely-packed array exhibits amplified accessible surfaces to interact with NH2-MIL-125, contributing to a radically improved interfacial built-in electric field and 7∼9 times rises in the product yields. Moreover, the preferably thin thickness of Ni-BDC microsheets prompts its macroscopic flexibility, permitting intensified deformation for enhanced interphase contact. Coupled with the additional contribution from its copious Lewis acid sites, the developed NH2-MIL-125@Ni-BDC array simultaneously converted CO2 into CO and CH4 at rates that cannot be matched by its isostructural Co counterpart with declined acidity and flexibility. This work innovatively reveals the immense importance of morphology tailoring and assembly tactic to interphase contact modulation and the upgrade of catalyst performances.