Fig. 2

Photocatalytic CO2 conversion experiments. a Amounts of CH4 (black), CO (red), and H2 (blue) production, and b amounts of CH4 production under CO2 saturation (black) and N2 bubbling (red) conditions using the ZnO-Cu2O catalysts as a function of the irradiation time. The reaction conditions (a, b) were catalyst amount 19 mg, pH = 7.4, and λ > 200 nm. The error bars were obtained from three independent experiments