Isotopic labelling experiments with EG in 13 CO2 purged- C-carbonate buffer (obtained after TPA removal and pH-readjustment; Experimental Section for details) revealed the presence of both CO and CO after the photocatalytic experiments (Figure ). This further corroborates the fact that TiO2|CotpyP is successful in reducing both the externallypurged and in-situ generated CO2, in addition to other side reactions producing CO. The overall yield of CO is therefore, a contribution from these individual processes.