Facet-dependent photocatalytic hydrogen production of metal–organic framework NH2-MIL-125(Ti)

Abstract

Facet-dependent catalytic activity of hard materials such as metals and metal oxides is well recognized in previous works. However, it has rarely been established for metal–organic frameworks (MOFs), possibly because the soft crystals of MOFs are conceptually different from the hard solids. In this work, the surface structure of the MOF NH₂-MIL-125(Ti) has been investigated by density functional theory (DFT) calculations for the first time. These calculations predict that the {110} facet has a surface energy of 1.18 J m⁻², which is superior to those of the {001}, {100} and {111} facets. This difference can be attributed to the larger percentage of exposed metal clusters, which can act as active sites in catalysis. Thus, we have devised and successfully obtained a series of nanoscaled NH₂-MIL-125(Ti) MOFs with controlled facets both experimentally and theoretically. The sample containing the {110} facet exhibits the highest photocatalytic hydrogen production activity and apparent quantum yield, which are approximately three times those of the sample with a dominant {111} facet.