An UVC probe (Oriel instrument, Goldilux model
70239) was attached on the outer wall of the quartz
reactor, and the energy flux (W/cm2) was indicated
by a lumen meter (Oriel instrument, Goldilux model
70235) connected to the probe. The photon flux was
obtained by dividing the energy flux by the energy of
a photon with a wavelength of 254 nm. The energy
flux was first measured for the reactor filled with
water only. The energy flux was then measured for
the reactor containing the catalyst and CO2 during
the reaction. The difference between those energy
fluxes was the photo energy absorbed in photoreduction.