CO₂ capture and conversion using Deep eutectic Solvents: Recent progress and outlooks

Carbon dioxide (CO₂) emissions are threatening the continuous development of human civilization, requiring effective measures to combat this serious environmental problem. Recently, deep eutectic solvents (DESs) have emerged as a promising tool for CO₂ capture and conversion due to their sustainable properties, high solubility for CO₂, low toxicity, and environmental friendliness. Accordingly, this review article provides a comprehensive analysis of recent progress and development of the application of DESs for CO₂ capture and conversion. Although there are some existing reviews on CO₂ capture and conversion using ionic liquids, comprehensive reviews dedicated to CO₂ capture and conversion using DESs are relatively scarce in the literature, highlighting the novelty of this article. This article briefly covers the synthesis of DESs from components like choline chloride and urea, exhibiting tunable physicochemical properties, making them suitable for various industrial applications. The characterizations of DESs cover critical parameters like density, viscosity, surface tension, and thermal stability. This review article also investigates the mechanisms of CO₂ absorption by DESs, emphasizing both physical absorption and chemical interactions. Operational parameters such as temperature, pressure, and water content significantly impact DES performance in CO₂ capture, with higher temperatures potentially reduce solubility, while increased pressures enhance absorption capacity. The article also highlights DESs potential in CO₂ conversion through catalytic, thermal, and electrochemical methods, showcasing their advantages over traditional ionic liquids. Compared to ionic liquids, DESs are safer for industrial use because they are less flammable, less toxic, and more environmentally friendly. The catalytic conversion of CO₂ into value-added products such as methanol and formic acid, highlights DESs role in creating a circular carbon economy. The article critically discusses the challenges and future outlooks for DESs-based CO₂ capture and conversion technologies, emphasizing the need for enhanced stability, reduced viscosity, and improved regeneration processes. It also highlights the necessity for ongoing research to enhance the Technology Readiness Level (TRL) of CO₂ mitigation using DESs, integrating environmental and social matters into economic evaluations, and developing standardized preparation and purification methods. Analyzing DES properties and operational conditions could assist in optimizing their industrial performance, fostering sustainable practices, and significantly contributing to climate change mitigation efforts. This article further highlights the need for continued research to expand the understanding and application of DESs, transforming CO₂ from a waste product into a valuable resource, thereby supporting international climate goals and promoting environmental sustainability.