Harvesting the photoexcited holes on a photocatalytic proton reduction metal-organic framework
The highly porous titanium based metal-organic framework NH2-MIL-125(Ti) has recently attracted significant attention in the field of photocatalysis as a promising material for H+ reduction. This work reveals charge transfer upon visible light illumination from this MOF to two different charge acceptors, as alternative to sacrificial electron donors. Charge transfer is demonstrated through a combined spectroscopic study between this MOF and: 1) 2-(1H-Pyrazol-3-yl)phenol, a molecule that functionally mimics the tyrosine-hystidine pair, resposable to shuttle the holes to the oxygen evolving centre in natural photosynthesis, and 2)TEMPO, a well known and stable radical. Charge transfer of the holes from the MOF to these occluded molecules takes place on the time scale of picoseconds. This work suggests that, by coupling a stable and recyclable charge acceptor to the photogenerated holes, the charges can be utilised for oxidation reactions and, thus, link the reduction to the oxidation reactions in water splitting.