Highly enhanced visible light water splitting of CdS by green to blue upconversion.

This paper reports a new class of visible light water splitting photocatalysts based on a triplet-triplet annihilation (TTA) upconversion (UC) process. The TTA-UC core composed of platinum-octaethyl-porphyrin (Pt(OEP)) and 9,10-diphenylanthracene (DPA) can upconvert low energy green light to high energy blue light with a high quantum yield. Using a silica nanocapsule (SNC), the quenching caused by oxygen can be avoided, even in aqueous solutions. The enhancement factor of the photocatalytic activity induced by the UC was estimated to be approximately 3, which indicates that the green to blue UC by the encapsulated Pt(OEP)/DPA can enhance the water splitting activity of CdS significantly. The reduced graphene oxide (rGO) attached to the CdS photocatalyst further enhances the water splitting activity via effective charge separation and suppressed recombination.