In a glass photoreactor, 5 mg TiO2 was suspended in 1 mL of the aqueous enzyme pretreated PET solution before or after TPA precipitation (see above) followed by 2 mL of MeCN. A known amount (25 or 50 nmol) of the molecular catalyst CotpyP (from a freshly prepared 2 mM solution in H2O; 0.0125 mL for 25 nmol or 0.025 mL for 50 nmol CotpyP) was added while stirring. The photoreactor (~3 mL solution) was capped with a rubber septum and purged with CO2 containing 2% CH4 as an internal gas chromatography standard for 15 min, followed by stirring for 15 min in the dark. The photoreactor (kept at 25 ºC and stirred at 600 rpm) was then irradiated with simulated solar irradiation (AM 1.5G, 100 mW cm -2 ) equipped with a water filter to remove infrared radiation. The photocatalytic process was monitored periodically by sampling the headspace (typically after 24 and 48 h) by GC to monitor H2 and CO formation. Products in the solution (formate) was detected by 1 H NMR spectroscopy in D2O (1:1 v:v photocatalysis solution:D2O). Control exclusion experiments were performed by omitting components of the photocatalytic system (TiO2, CotpyP, light, CO2) at a time. For the photocatalytic control experiments in the absence of CO2, the photoreactor was purged with N2 containing 2% CH4 as an internal standard (15 min). Reference experiments directly using the electron donor were performed by using aqueous stock solutions containing 60 mM EG or 60 mM EG + TPA as the aqueous phase. The turnover numbers (TON) were calculated based on CotpyP assuming that all cobalt sites are active catalytic sites.