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

Abstract

Carbon dioxide (CO<inf>2</inf>) photoreduction is a promising alternative to carbon capture, utilization, and storage (CCUS) technologies. It relies on photocatalysts to convert CO<inf>2</inf> 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 CO<inf>2</inf> 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 CO<inf>2</inf> photoreduction. TEOA performed the best, producing methanol, ethanol, isopropanol, acetone, and n-butanol with an impressive total carbon consumption (TCC) of 7890 μmol g<inf>cat</inf>⁻¹. Alkanolamines exhibited a dual function as a sacrificial agent (SCR) and a CO<inf>2</inf>-capturing substance for photoreduction. TEOA was an excellent SCR and captured CO<inf>2</inf> loosely via base-catalyzed hydration, promoting the subsequent release of CO<inf>2</inf> for photoreduction. A study on medium pH revealed a decreased photoreduction rate at increased pH due to a strong bond between CO<inf>2</inf> and the alkali solution, which reduces the reaction rate.