Global warming is caused by anthropogenic carbon dioxide (CO2) emissions in the atmosphere, and different options have been proposed to mitigate CO2 emissions, where CO2 separation plays an important role. To develop cost-effective technologies for CO2 separation, immobilizing ionic liquids (ILs) into porous materials demonstrates potential. Different ILs are strategically immobilized into different porous materials like MOFs, activated carbons, pops, and silica, resulting in IL-porous composites with the functional properties of the pristine porous materials and the peculiar physicochemical of the immobilized ILs. These progressive developments reveal novel opportunities in separation science.In this review, we discuss the functionalization of ILs for CO2 separation. We also highlight several porous materials, such as MOFs, carbon nanotubes, zeolites, carbonaceous materials, and graphene. Finally, we demonstrate the development of hybrid ionic materials composed of ILs and porous materials, especially MOFs, to provide a perspective on the potential of ILs/porous material composites for CO2 separation. The most significant opportunities and challenges in ILs/porous materials as well as their synthesis methods, characterization techniques, applications, and future possibilities are thoroughly explored to develop a roadmap for CO2 separation. Considering future developments in this field, the design and development of these innovative hybrid materials and their potential to replace conventional materials are also carefully evaluated.

Electrochemical oxidation of lignin for the production of high-value aromatic aldehydes, while co-generating hydrogen, represents a promising strategy to achieve dual benefits. However, the selective electrochemical cleavage of the nonpolar and robust C–C bonds in lignin presents tremendous challenges. Here, FeNi@C derived from metal–organic frameworks (MOFs) is designed for the high-selectivity electrochemical oxidation of the lignin model compound veratrylglycerol-β-guaiacyl ether (VG) to achieve C–C bond cleavage, resulting in the production of veratraldehyde (VAld). Moreover, a trace amount of an ionic liquid (IL) additive is incorporated into the electrolyte to further optimize the selectivity for VAld. In an anion exchange membrane (AEM) single cell, the FeNi@C anode, under the synergistic catalytic effect of BmpyrroCl, demonstrates a remarkable conversion efficiency of up to 89.8% for VG, with the yield and selectivity of VAld reaching 63.9% and 70.1%, respectively. Notably, this approach demonstrates exceptional performance in lignin upgrading, achieving an aromatic aldehyde yield of 23.5 wt%, with VAld showing a yield and selectivity of 7.3 wt% and 31.1%, respectively, highlighting its significant practical potential. In situ electron spin resonance (ESR) analysis and density functional theory (DFT) calculations reveal that the exceptional selectivity of FeNi@C for VAld is attributed to the ability of Fe to serve as an electronic conversion switch, regulating the valence state of Ni. Specifically, it enhances the formation of highly active Ni3+δ at 1.4 V, fostering C–C bond dissociation while mitigating the continuous oxidation of Ni3+δ to higher valence states, thereby inhibiting the undesired conversion of VAld to veratric acid (VAc). The Gaussian calculation results indicate that the strong hydrogen bond between the ILs and Cα–OH promotes the preactivation of VG, thus exerting a synergistic catalytic effect on FeNi@C.

CO2/CH4 separation is crucial for biogas upgrading. In this study, the bamboo-derived activated carbons (BACs) were prepared with different ratios of potassium hydroxide (KOH)/bamboo charcoal (BC), and the hybrid sorbents of aqueous BACs were developed for CO2/CH4 separation. Both the gas solubility and sorption rate were measured, and Henry’s constant and liquid-side mass-transfer coefficient as well as the CO2/CH4 selectivity were calculated. Meanwhile, the comprehensive performances of aqueous BACs were evaluated using a novel index, and the cost of biogas upgrading using the aqueous BACs was estimated and compared to the commercialized technology. The results proved the effectiveness of aqueous BACs, and the comprehensive performance of 7.0 wt% aqueous BAC with the KOH/BC mass ratio of 2:1 was 4.2 times than that of H2O, having the potential to decrease the average CO2/CH4 separation cost by 65.0% compared to the commercialized technology.

Single-atom catalysts (SACs), known for their high atomic utilization efficiency, are highly attractive for electrochemical CO2 conversion. Nevertheless, it is struggling to use a single active site to overcome the linear scaling relationship among intermediates. Herein, an isolated diatomic Ni-Mn dual-sites catalyst was anchored on nitrogenated carbon, which exhibits remarkable electrocatalytic performance towards CO2 reduction. The catalyst achieves CO Faradaic efficiency (FECO) over 90 % within the potential range of −0.6 to −1.4 V vs. reversible hydrogen electrode (RHE), and a nearly 100 % FECO at a current density of 325 mA cm−2 in the flow cell. The Ni-Mn-NC also exhibits long-term stability, maintaining FECO above 96 % for over 14 h. The density functional theory (DFT) studies further reveal that the synergistic effect of adjacent Ni-Mn centers effectively reduces the reaction barriers for the formation of *COOH and thus accelerates the reduction of CO2.

The imperative need to mitigate CO₂ emissions has become increasingly critical due to their severe impact on environmental sustainability and public health. Among the emerging carbon capture technologies, deep eutectic solvent (DES)-based technologies have attracted significant attention owing to their facile synthesis and superior CO₂ capture capacity. However, their widespread industrial deployment has been hindered by challenges associated with high viscosity and cost. To address these limitations, this study adopts novel a approach that synergistically integrates cosolvent addition and immobilization to develop a slurry with enhanced CO₂ capture efficiency. Specifically, an aqueous DES solution was formulated using imidazolium chloride-ethylenediamine ([ImCl][EDA]) in a 1:6 molar ratio with water as the cosolvent, followed by the immobilization of DES onto mesoporous silica to form a composite slurry. CO₂ capture experiments revealed a high sorption capacity of 28.34 wt% at 22 °C and 1 bar, along with rapid sorption and desorption rates of 1.39 and 0.30 mol CO₂/(kg sorbent·min) within the first 2 min. Furthermore, the slurry exhibited excellent cyclic stability, maintaining a 98 % recovery rate. The significant improvements in CO₂ capture capacity, desorption kinetics, and thermal stability underscore the potential of this hybrid system for scalable industrial applications in carbon capture and utilization.

Deep eutectic solvents (DESs) have recently gained attention due to their tailorable properties and versatile applications in several fields, including green chemistry, pharmaceuticals, and energy storage. Their tunable properties can be enhanced by mixing DESs with cosolvents such as ethanol, acetonitrile, and water. DESs are structurally complex, and molecular modeling techniques, including quantum mechanical calculations and molecular dynamics simulations, play a crucial role in understanding their intricate behavior when mixed with cosolvents. While the most studied cosolvent is water, in some applications, even a small content of water is considered a contaminant, for example, when the processes of interest require dry conditions. Only quite recently have modeling studies begun to focus on DES mixed with cosolvents other than water. This tutorial provides the first comprehensive overview of these studies. It highlights how modern molecular modeling increases our understanding of their structural organization, transport properties, phase behavior, and thermodynamic properties. Additionally, case studies and recent developments in the field are discussed along with the challenges and future directions in molecular modeling of DES in cosolvent mixtures. Overall, this review offers valuable insights into the molecular-level understanding of DES-cosolvent systems and their implications for designing novel solvent mixtures with tailored properties for various applications. 

The urgency of mitigating CO2 emissions has become increasingly critical due to their detrimental effects on environmental sustainability and human health. Among emerging solutions, deep eutectic solvents (DESs) have garnered attention for their high CO2 capture capacities. However, widespread application of DESs has been constrained by their inherent high viscosity and cost. To overcome these limitations, this study further explores the novel strategy, where cosolvent addition and immobilization are combined to develop a non-aqueous slurry for CO2 capture with high efficiency. Here, [MEACl][EDA] with (1:5) molar ratio is mixed with ethylene glycol (EG) to form a non-aqueous DES solution, and the DES is further immobilized into the mesoporous silica to form a composite and then mixed with the DES-EG solution to make a slurry. The CO2 capture tests demonstrated 15 wt.% capture capacity at 22 °C and 1 bar, and efficient sorption and desorption rates (0.34 and 0.38 mol CO2/(kg sorbent·min) within the initial 2 min). The slurry also exhibited promising cyclic performance with 96.4 % recovery together with minimal solvent loss of 0.97 % and almost intact structure after 120 hr of heating at 110 °C. The improved capture capacity and kinetics, especially for desorption, as well as enhanced thermal stability of the non-aqueous system highlight its potential for industrial applications.

The development of generalized engineering equations of the heat-transfer performance in enhanced geometries for different slurries is crucial for practical applications but difficult owing to the complex rheological properties. In the present study, a method of computational-fluid-dynamics-data-driven machine learning was proposed to establish generalized engineering equations in a novel twisted geometry for multiple slurries with a single substrate. The applicability of the equations for a mixed slurry was determined by comparing the predictions and computational fluid dynamics simulations. It was found that the established equations considering the key parameter–effective shear rate show a high accuracy with an average relative deviation of 17.3 % for single-substrate slurries with the scope of viscosities and flow behavior index ranging from 0.057-93.96 Pa·s and 0.257–0.579, respectively. Moreover, the generalized engineering equations show an average relative deviation of 12.4 % in prediction for the mixed slurry possessing the temperature- and shearing-sensitive rheological behavior. The generalized engineering equations quantitatively reveal the positive effect of non-Newtonian behavior on the heat-transfer enhancement of THT for different slurries. Based on this mechanism, a mixed slurry is recommend with energy-conservation of 60.00 GW·h/year for a full-scale biogas plant.

Confinement effect is an effective method to enhance carbon dioxide (CO₂) solubility. In this study, a hybrid sorbent of 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Hmim][NTf₂])/mesoporous titanium dioxide (M-TiO₂)/water (H₂O) was developed, and its confinement effect was regulated by changing the pore structure of M-TiO₂. CO₂ solubility in the hybrid sorbent was measured experimentally, and the thermodynamic properties including Henry's constant and desorption enthalpy were calculated. Furthermore, the confinement effect in the hybrid sorbent was quantified. Additionally, the hybrid sorbent was recycled with a multi-cycle experiment. The results showed that M-TiO₂ calcined at 773.2 K (MT500) could lead to an efficient confinement effect. CO₂ solubility in the hybrid sorbent increased by 49.8% compared to that of H₂O when the mass fraction of [Hmim][NTf₂]/MT500 was 5.0% (mass), where the contribution of confinement effect on Gibbs free energy occupied 5.2%.

N-methyldiethanolamine (MDEA) is a commercial amine with the deficiency of slow CO2 absorption rate. In this study, four amino-functionalized ionic liquids (AFILs), i.e., tetraethylenepentamine dimethylimidazole, pentaethylenehexamine dimethylimidazole ([TMTD][2-MI]), tetraethylenepentamine piperazine, and pentaethylenehexamine piperazine, are synthesized to promote CO2 absorption rate in aqueous MDEA. The result shown that CO2 absorption rate in 20 wt% aqueous MDEA-10 wt% [TMTD][2-MI] was 10.7 times than that of 30 wt% aqueous MDEA, demonstrating the highest CO2 absorption rate intensification in aqueous MDEA reported so far. Furthermore, the mechanism underlying the intensified CO2 absorption rate was elucidated through pH measurement and nuclear magnetic resonance. The comprehensive ability of CO2 absorption and deprotonation of [TMTD][2-MI] was the dominant factor for the excellent CO2 absorption rate intensification.