A series of imidazolium-based ionic liquids (ILs) were synthesised and used as single component and metal-free homogeneous catalysts to convert a renewable, inexpensive and non-toxic CO₂ feedstock into useful products. The cycloaddition of carbon dioxide to epoxides to produce cyclic carbonate was evaluated. A detailed investigation was carried out on a variety of factors that affected the reactivity and selectivity, such as the catalyst structures (nature of cation and anion). The effect of reaction parameters (temperature, reaction time, CO₂ uptake and catalyst amount) on the catalytic performance was also investigated in detail. High conversions and selectivities could be achieved under mild pressure condition (5 bar) using 1-n-butyl-3-methylimidazolium bromide. A synergetic effect of the acidic and basic sites as well as suitable hydrogen-bonding strength is considered crucial for the reaction to proceed smoothly. This protocol was found to be applicable to a disubstituted epoxide. Furthermore, the straightforward synthesis of cyclic carbonates by direct oxidative carboxylation from olefins was achieved using only 1-n-butyl-3-methylimidazolium bromide as a catalyst.

In the last few years, ionic liquids (ILs) have been the focus of extensive studies concerning the relationship between structure and properties and how this impacts their application. Despite a large number of studies, several topics remain controversial or not fully answered, such as: the existence of ion pairs, the concept of free volume and the effect of water and its implications in the modulation of ILs physicochemical properties. In this paper, we present a critical review of state-of-the-art literature regarding structure–property relationship of ILs, we re-examine analytical theories on the structure–property correlations and present new perspectives based on the existing data. The interrelation between transport properties (viscosity, diffusion, conductivity) of IL structure and free volume are analysed and discussed at a molecular level. In addition, we demonstrate how the analysis of microscopic features (particularly using NMR-derived data) can be used to explain and predict macroscopic properties, reaching new perspectives on the properties and application of ILs.

Direct air capture and integrated CO₂ conversion (DACC) technologies have emerged as promising approaches to mitigate the increasing concentration of carbon dioxide (CO₂) in the Earth's atmosphere. This Perspective provides a comprehensive overview of recent advancements in materials for capturing and converting atmospheric CO₂. It highlights the crucial role of materials in achieving efficient and selective CO₂ capture as well as catalysts for CO₂ conversion. The paper discusses the performance, limitations, and prospects of various materials in the context of sustainable CO₂ mitigation strategies. Furthermore, it explores the multiple roles DACC can play in stabilizing atmospheric CO₂.

Direct air capture and integrated conversion is a very attractive strategy to reduce CO₂ concentration in the atmosphere. However, the existing capturing processes are technologically challenging due to the costs of the processes and the low concentration of CO₂. The efficient valorization of the CO₂ captured could help overcome many techno-economic limitations. Here, we present a novel economical methodology for direct air capture and conversion that is able to efficiently convert CO₂ from the air into cyclic carbonates. The new approach employs commercially available basic ionic liquids, works without the need for sophisticated and expensive co-catalysts or sorbents and under mild reaction conditions. The CO₂ from atmospheric air was efficiently captured by IL solution (0.98 molCO₂/mol_IL) and, subsequently, completely converted into cyclic carbonates using epoxides or halohydrins potentially derived from biomass as substrates. A mechanism of conversion was evaluated, which helped to identify relevant reaction intermediates based on halohydrins, and consequently, a 100% selectivity was obtained using the new methodology.