A study on photocatalytic Janus membrane reactor for direct conversion of low concentration carbon dioxide in air to methane: Effects of combination of two-dimensional carbon nanosheets

Large CO2 emissions cause the greenhouse effect, which threatens human survival. Directly converting CO2 in the air into energy and valuable resources is the most effective way to address the greenhouse effect. Currently, the main problem with CO2 conversion is the poor conversion efficiency owing to low CO2 concentrations in the air. In this study, a Janus membrane with the functions of concentrating CO2 (gas separation layer) and photocatalytic reaction (photocatalytic reaction layer) was fabricated. The Janus membrane directly converted extremely low concentrations of CO2 in the air into CH4. Amine-functionalized graphene oxide was added to regulate the CO2 conversion efficiency and the structure of the gas separation layer. Graphene was added to the photocatalytic reaction layer to suppress electron-hole recombination and increase the probability of excited electrons colliding with CO2. The experimental results showed that the modification of the gas separation layer or the photocatalytic reaction layer effectively increased the CH4 yield of the Janus membrane. By maintaining a balance between the selectivity and permeability coefficients of the gas separation layer, the highest methane yield (8.9 ppm) was obtained. The CH4 yield of the Janus membrane was further improved (8.9 ppm to 11.1 ppm) by modifying the photocatalytic reaction layer with graphene. This study proposes a feasible method for improving the efficiency of the Janus membrane for converting low-concentration CO2 in air to CH4.