Metal–organic frameworks embedded in a liposome facilitate overall photocatalytic water splitting

Metal–organic frameworks (MOFs) have been studied extensively in the hydrogen evolution reaction (HER) and the water oxidation reaction (WOR) with sacrificial reagents, but overall photocatalytic water splitting using MOFs has remained challenging, principally because of the fast recombination of photo-generated electrons and holes. Here we have integrated HER- and WOR-MOF nanosheets into liposomal structures for separation of the generated charges. The HER-MOF nanosheets comprise light-harvesting Zn–porphyrin and catalytic Pt–porphyrin moieties, and are functionalized with hydrophobic groups to facilitate their incorporation into the hydrophobic lipid bilayer of the liposome. The WOR-MOF flakes consist of [Ru(2,2′-bipyridine)3]2+-based photosensitizers and Ir–bipyridine catalytic centres, and are localized in the hydrophilic interior of the liposome. This liposome–MOF assembly achieves overall photocatalytic water splitting with an apparent quantum yield of (1.5 ± 1)% as a result of ultrafast electron transport from the antennae (Zn–porphyrin and [Ru(2,2′-bipyridine)3]2+) to the reaction centres (Pt–porphyrin and Ir–bipyridine) in the MOFs and efficient charge separation in the lipid bilayers. Some metal–organic frameworks (MOFs) can promote photocatalytic hydrogen evolution and others can facilitate water oxidation, but it is difficult to combine them into a single system. Now, by confining MOFs that can promote each half-reaction within the hydrophobic and hydrophilic regions of a liposome to avoid the fast recombination of photo-generated charges, evidence for water splitting has been obtained.