Photocatalytic experiments. In a typical experiment, to TiO2 (P25, 5 mg) was added 2 mL of MeCN and 1 mL of the solution obtained from cellulase pre-treatment in a glass photoreactor (7.74 mL total volume) equipped with a magnetic stir bar. 50 nmol of CotpyP (from a freshly prepared 2 mM solution in H2O; 0.025 mL) was added, and the photoreactor (3 mL solution with 4.74 mL headspace) was capped with a rubber septum and purged with CO2 (100 vol% or 20 vol% balanced with N2) controlled by mass flow controllers for 15 min at 15 mL min -1 , followed by stirring for 15 min in the dark. The photoreactor (kept at 25 °C and stirred at 600 rpm) was then irradiated with a calibrated solar light simulator (Newport Oriel, 100 mW cm -2 ) equipped with an air mass 1.5 global (AM 1.5G) filter and a water filter to remove infrared radiation. The photocatalytic process was monitored by analysing the headspace after 6 and 24 h by gas chromatography to monitor H2 and CO formation. Formate in the solution (diluted in H2O (1:9 v:v photocatalysis solution:H2O)) were analysed at the end of the photocatalytic studies (after 24 h) by ion chromatography.