Enhancing the efficiency of direct conversion of ultra-low concentration CO2 in the atmosphere to CH4: Structural modulation of the photocatalytic Janus membrane's reactive layer through integration of membrane formation mechanisms based on thermodynamics and kinetics

Utilizing sunlight for the photocatalytic reduction of atmospheric carbon dioxide into valuable compounds or energy resources holds promise for sustainable energy applications and mitigating global warming by reducing atmospheric carbon dioxide concentrations. This study investigates Janus membranes capable of concurrently concentrating CO2 from ambient air and photocatalytically converting it to methane under simulated sunlight conditions. Through modulation of thermodynamic and kinetic parameters during membrane formation, adjustments to the pore structure of the Janus membrane are made to enhance CO2 conversion efficiency. Cloud point, viscosity, light transmittance, and dyeing experiments are employed to elucidate the factors influencing the formation of distinct pore structures within the membranes. Characterization techniques such as scanning electron microscopy, energy-dispersive X-ray spectroscopy, ultraviolet–visible spectroscopy, photoluminescence, gas permeation analyzer, and mechanical property assessments are utilized to analyze membrane properties. The photocatalytic reactive layer exhibiting a closed-pore structure effectively prolongs the residence time of CO2 within the reactive layer, resulting in an increased methane yield of 0.70 μmol gcat−1 h−1. Incorporating an optimal quantity of TiO2 (30 wt%) further enhances the methane yield to 1.17 μmol gcat−1 h−1. However, the methane yield of the Janus membrane exhibits a notable decline after prolonged continuous photocatalytic reactions, prompting a detailed examination of factors contributing to the membranes' poor long-term stability. This study introduces a novel approach to enhance the CO2 conversion efficiency of photocatalytic Janus membranes by regulating the pore structure of the reactive layer. The findings contribute to the advancement of high-performance Janus membranes, offering a promising avenue for future research and development endeavors.