Effects of alkanolamines on photocatalytic reduction of carbon dioxide to liquid fuels using a copper-doped dititanate/graphene photocatalyst†

Carbon dioxide (CO₂) photoreduction is a promising alternative to carbon capture, utilization, and storage (CCUS) technologies. It relies on photocatalysts to convert CO₂ to high-value products. The copper-doped dititanate nanosheets/graphene oxide composite (CTGN) is a heterostructure of two 2-dimensional nanomaterials: nanosheets and graphene oxide (GO), exhibiting outstanding photoactivity. It was demonstrated to assist in CO₂ photoreduction, yielding fuel products such as methanol, ethanol, and isopropanol. In this study, we used CTGN as a photocatalyst model to investigate the effects of alkanolamines, including monoethanolamine (MEOA), diethanolamine (DEOA), and triethanolamine (TEOA), in facilitating CO₂ photoreduction. TEOA performed the best, producing methanol, ethanol, isopropanol, acetone, and n-butanol with an impressive total carbon consumption (TCC) of 7890 μmol g_cat⁻¹. Alkanolamines exhibited a dual function as a sacrificial agent (SCR) and a CO₂-capturing substance for photoreduction. TEOA was an excellent SCR and captured CO₂ loosely via base-catalyzed hydration, promoting the subsequent release of CO₂ for photoreduction. A study on medium pH revealed a decreased photoreduction rate at increased pH due to a strong bond between CO₂ and the alkali solution, which reduces the reaction rate.