Theoretical insights into CO2/N2 selectivity of the porous ionic liquids constructed by ion-dipole interactions

Porous liquids: a novel porous medium for efficient carbon dioxide capture

Porous liquids (PLs) are the combination of porous solid material and flowing liquid, which provides alternative options to solve difficulties in the development of porous solids. With the booming development of PLs since 2015, plenty of syntheses and applications have been reported with a specific focus on gas adsorption. Given the lack of a comprehensive review, this paper reviews the application of PLs in CO2 capture. To start with, ground-breaking case studies are reviewed to help understand the progress of PLs research. Then, as a major part of this paper, studies of PLs for CO2 capture are reviewed separately. Moreover, five basic properties of porous liquids, including stability, viscosity, selectivity, porosity, capacity, and the influencing factors are systemically reviewed respectively. Furthermore, gas storage and release mechanisms in PLs are briefly outlined, and potential processing methods of PLs used for CO2 capture are discussed.

Impact of Vertex Functionalization on Flexibility of Porous Organic Cages

Efficient carbon capture requires engineered porous systems that selectively capture CO2 and have low energy regeneration pathways. Porous liquids (PLs), solvent-based systems containing permanent porosity through the incorporation of a porous host, increase the CO2 adsorption capacity. A proposed mechanism of PL regeneration is the application of isostatic pressure in which the dissolved nanoporous host is compressed to alter the stability of gases in the internal pore. This regeneration mechanism relies on the flexibility of the porous host, which can be evaluated through molecular simulations. Here, the flexibility of porous organic cages (POCs) as representative porous hosts was evaluated, during which pore windows decreased by 10-40% at 6 GPa. POCs with sterically smaller functional groups, such as the 1,2-ethane in the CC1 POC resulted in greater imine cage flexibility relative to those with sterically larger functional groups, such as the cyclohexane in the CC3 POC that protected the imine cage from the application of pressure. Structural changes in the POC also caused CO2 adsorption to be thermodynamically unfavorable beginning at ∼2.2 GPa in the CC1 POC, ∼1.1 GPa in the CC3 POC, and ∼1.0 GPa in the CC13 POC, indicating that the CO2 would be expelled from the POC at or above these pressures. Energy barriers for CO2 desorption from inside the POC varied based on the geometry of the pore window and all the POCs had at least one pore window with a sufficiently low energy barrier to allow for CO2 desorption under ambient temperatures. The results identified that flexibility of the CC1, CC3, or CC13 POCs under compression can result in the expulsion of captured gas molecules.

Constructing protic porous ionic liquids via one-step coupling neutralization reaction for extraction-adsorption coupled desulfurization

Porous ionic liquids (PILs) offer a distinctive combination of liquid-like fluidity and solid porosity, making them well-suited for various applications including separation, catalysis, and energy storage. Nevertheless, the design limitations and complex synthesis processes have hindered the development of PILs. Here, the one-step coupling neutralization reaction (OCNR) method has been first proposed for the controllable synthesis of functionalized protic porous ionic liquids (PPILs). Specifically, three types of PPILs have been synthesized based on tuning the position of the corona amino functional groups. The results indicate the crucial role of protic ion pairs in the formation of pure liquid PPILs with low viscosity. The extraction efficiency has obviously increased after introducing the porous materials from 38.5% to 51.9%. The results showed PPILs play good extraction-adsorption coupled desulfurization (EADS) performance. The density functional theory (DFT) results show that both the protic ion pairs and the porous structure have significant roles in EADS, with the former offering CH···π interactions, while the latter provides hydrogen bonding (CH···O) interactions. Ultimately, the strategy simplifies the synthesis process, providing a new idea for the directional design of low-viscosity PILs with specific functions.

Group IIIA Single-Metal Atoms Anchored on Hexagonal Boron Nitride for Selective Adsorption Desulfurization via S-M Bonds

Single-atom adsorbents (SAAs) featuring maximized atom utilization and uniform isolated adsorption sites have aroused extensive research interest in recent years as a novel class of adsorption materials research. Nevertheless, it is still challenging to gain a fundamental understanding of the complicated behaviors of SAAs for adsorbing thiophenic compounds (THs). Herein, this work systematically investigated the mechanisms of adsorption desulfurization (ADS) over a single group IIIA metal atom (Ga, In, and Tl) anchored on hexagonal boron nitride nanosheets (BNNSs) via density functional theory (DFT) calculations. First, all the possible doping sites have been considered and their stabilities have been evaluated by the doped energy. DFT calculations reveal that metal atoms prefer to substitute B atoms on BNNSs rather than N atoms. Additionally, SAAs all exhibit considerably enhanced adsorption capacity for THs primarily by the sulfur-metal (S-M) bond with π-π interactions maintained. Among them, In-atom-based SAAs would be adequate to provide the highest adsorption energy (In_cen_B, -40.1 kcal mol^-1). Furthermore, from the perspective of adsorption energy, the SAAs show superior selectivity to THs than aromatic compounds due to the newly formed S-M bond. We hope that our work will manifest the design and application of SAAs in the field of ADS and shed light on a new strategy for fabricating SAAs based on BNNSs.

Ag Atom Anchored on Defective Hexagonal Boron Nitride Nanosheets As Single Atom Adsorbents for Enhanced Adsorptive Desulfurization via S-Ag Bonds

Single atom adsorbents (SAAs) are a novel class of materials that have great potential in various fields, especially in the field of adsorptive desulfurization. However, it is still challenging to gain a fundamental understanding of the complicated behaviors on SAAs for adsorbing thiophenic compounds, such as 1-Benzothiophene (BT), Dibenzothiophene (DBT), and 4,6-Dimethyldibenzothiophene (4,6-DMDBT). Herein, we investigated the mechanisms of adsorptive desulfurization over a single Ag atom supported on defective hexagonal boron nitride nanosheets via density functional theory calculations. The Ag atom can be anchored onto three typical sites on the pristine h-BN, including the monoatomic defect vacancy (B-vacancy and N-vacancy) and the boron-nitrogen diatomic defect vacancy (B-N-divacancy). These three Ag-doped hexagonal boron nitride nanosheets all exhibit enhanced adsorption capacity for thiophenic compounds primarily by the S-Ag bond with π-π interaction maintaining. Furthermore, from the perspective of interaction energy, all three SAAs show a high selectivity to 4,6-DMDBT with the strong interaction energy (-33.9 kcal mol^-1, -29.1 kcal mol^-1, and -39.2 kcal mol^-1, respectively). Notably, a little charge transfer demonstrated that the dominant driving force of such S-Ag bond is electrostatic interaction rather than coordination effect. These findings may shed light on the principles for modeling and designing high-performance and selective SAAs for adsorptive desulfurization.

Porous Liquids: Computational Design for Targeted Gas Adsorption

In this Perspective, we present the unique gas adsorption capabilities of porous liquids (PLs) and the value of complex computational methods in the design of PL compositions. Traditionally, liquids only contain transient pore space between molecules that limit long-term gas capture. However, PLs are stable fluids that that contain permanent porosity due to the combination of a rigid porous host structure and a solvent. PLs exhibit remarkable adsorption and separation properties, including increased solubility and selectivity. The unique gas adsorption properties of PLs are based on their structure, which exhibits multiple gas binding sites in the pore and on the cage surface, varying binding mechanisms including hydrogen-bonding and π-π interactions, and selective diffusion in the solvent. Tunable PL compositions will require fundamental investigations of competitive gas binding mechanisms, thermal effects on binding site stability, and the role of nanoconfinement on gas and solvent diffusion that can be accelerated through molecular modeling. With these new insights PLs promise to be an exceptional material class with tunable properties for targeted gas adsorption.

Extensively amino-functionalized graphene captures carbon dioxide

Amino-functionalized graphene demonstrates certain potential to fix carbon dioxide.