The photocatalytic experiment for the reduction of CO2 was performed at ambient temperature (25 5 C) in a continuous gas flow reactor. The volume of the cylindrical reactor which was made of stainless steel and covered with quartz-glass was 300 ml (11 cm 4 cm). One sample dish containing 0.2 g of catalyst powder was placed in the middle of the reactor. A 300W commercial halogen lamp was used as the simulated solar-light source. The lamp was vertically placed outside the reactor above the sample dish. Two mini fans were fixed around the lamp to avoid the temperature rise of the ow system. The catalyst powder spread onto a glass disc, with a diameter of 7.5 cm. Initially nitrogen gas was purged inside the reactor to remove the air with other gases. Aer that CO2 was purged inside the reactor for another 1 hour and the ow rate was controlled at 4 sccm. CO2 was flowing through water to control the desired humidity level for the entire experiment. The halogen lamp was turned on aer one hour while adsorption and desorption of the gas and the photocatalyst reached the equilibrium. The concentration of methanol was continuously measured by a GCFID in the vapor phase. The detailed schematic drawing of the experimental setup is shown in Fig. S1