Figure shows the final experimental setup prior to degassing and irradiation, with the photocatalyst dispersion placed in the photoreactor, closed with the NS14 cap for oxygen measurement and the light source set-up (following the power measurement). Degassing is then achieved by sparging argon through the photocatalyst dispersion. This is done by threading a 1.5 mm PTFE tube through a NS14 rubber septum, which is placed on the valve of the Schlenk flask (see Figure ). A needle is also pierced through the NS14 septum, creating an outlet for gas to escape during degassing. The PTFE tube is then threaded further through the valve down into the dispersion. Afterwards, argon is carefully sparged through the dispersion. The progress of degassing can be followed by measuring the gas phase O2 concentration. Argon sparging should be continued until the O2 concentration reaches a steady-state close to 0 vol% O2, which typically takes 15 -30 min. At this point, the PTFE tube can be pulled back out of the Schlenk flask (while continuing the argon flow). Once the PTFE tube has left the valve (but remains in the area between the valve and the septum), the valve can be closed.