Advanced Materials for NH3 Capture: Interaction Sites and Transport Pathways.

Ammonia (NH3) is a carbon-free, hydrogen-rich chemical related to global food safety, clean energy, and environmental protection. As an essential technology for meeting the requirements raised by such issues, NH3 capture has been intensively explored by researchers in both fundamental and applied fields. The four typical methods used are (1) solvent absorption by ionic liquids and their derivatives, (2) adsorption by porous solids, (3) ab-adsorption by porous liquids, and (4) membrane separation. Rooted in the development of advanced materials for NH3 capture, we conducted a coherent review of the design of different materials, mainly in the past 5 years, their interactions with NH3 molecules and construction of transport pathways, as well as the structure-property relationship, with specific examples discussed. Finally, the challenges in current research and future worthwhile directions for NH3 capture materials are proposed.

Upcycling poly(succinates) with amines to N-substituted succinimides over succinimide anion-based ionic liquids.

The chemical transformation of waste polymers into value-added chemicals is of significance for circular economy and sustainable development. Herein, we report upcycling poly(succinates) (PSS) with amines into N-substituted succinimides over succinimide anion-based ionic liquids (ILs, e.g, 1,8-diazabicyclo[5.4.0]undec-7-ene succinimide, [HDBU][Suc]). Assisted with H2O, [HDBU][Suc]) showed the best performance, which could achieve complete transformation of a series of PSS into succinimide derivatives and corresponding diols under mild and metal-free conditions. Mechanism investigation indicates that the cation-anion confined hydrogen-bonding interactions among IL, H2O, ester group, and amino/amide groups, strengthens nucleophilicity of the N atoms in amino/amide groups, and improves electrophilicity of carbonyl C atom in ester group. The attack of the amino/amide N atom on carbonyl C of ester group results in cleavage of carbonyl C-O bond in polyester and formation of amide group. This strategy is also effective for aminolysis of poly(trimethylene glutarate) to glutarimides, and poly(1,4-butylene adipate) to caprolactone diimides.

Polyimide/Ionic Liquids Hybrid Membranes with NH3-Philic Channels for Ammonia-Based CO2 Separation Processes.

An efficient separation technology involving ammonia (NH3) and carbon dioxide (CO2) is of great importance for achieving low-carbon economy, environmental protection, and resource utilization. However, directly separating NH3 and CO2 for ammonia-based CO2 capture processes is still a great challenge. Herein, we propose a new strategy for selective separation of NH3 and CO2 by functional hybrid membranes that integrate polyimide (PI) and ionic liquids (ILs). The incorporated protic IL [Bim][NTf2] is confined in the interchain segment of PI, which decreases the fractional free volume and narrows the gas transport channel, benefiting the high separation selectivity of hybrid membranes. At the same time, the confined IL also provides high NH3 affinity for transport channels, promoting NH3 selective and fast transport owing to strong hydrogen bonding interaction between [Bim][NTf2] and NH3 molecules. Thus, the optimal hybrid membrane exhibits an ultrahigh NH3/CO2 ideal selectivity of up to 159 at 30 °C without sacrificing permeability, which is 60 times higher than that of the neat PI membrane and superior to the state-of-the art reported values. Moreover, the introduction of [Bim][NTf2] also reduces the permeation active energy of NH3 and reverses the hybrid membrane toward "NH3 affinity", as understood by studying the effect of temperature. Also, NH3 molecules are much easier to transport at high temperature, showing great application potential in direct NH3/CO2 separation. Overall, this work provides a promising ultraselective membrane material for ammonia-based CO2 capture processes.

Effective Absorption of Dichloromethane Using Carboxyl-Functionalized Ionic Liquids.

Dichloromethane (DCM) is recognized as a very harmful air pollutant because of its strong volatility and difficulty to degrade. Ionic liquids (ILs) are considered as potential solvents for absorbing DCM, while it is still a challenge to develop ILs with high absorption performances. In this study, four carboxyl-functionalized ILs-trioctylmethylammonium acetate [N1888][Ac], trioctylmethylammonium formate [N1888][FA], trioctylmethylammonium glycinate [N1888][Gly], and trihexyl(tetradecyl)phosphonium glycinate [P66614][Gly]-were synthesized for DCM capture. The absorption capacity follows the order of [P66614][Gly] > [N1888][Gly] > [N1888][FA] > [N1888][Ac], and [P66614][Gly] showed the best absorption capacity, 130 mg DCM/g IL at 313.15 K and a DCM concentration of 6.1%, which was two times higher than the reported ILs [Beim][EtSO4] and [Emim][Ac]. Moreover, the vapor-liquid equilibrium (VLE) of the DCM + IL binary system was experimentally measured. The NRTL (non-random two-liquid) model was developed to predict the VLE data, and a relative root mean square deviation (rRMSD) of 0.8467 was obtained. The absorption mechanism was explored via FT-IR spectra, 1H-NMR, and quantum chemistry calculations. It showed a nonpolar affinity between the cation and the DCM, while the interaction between the anion and the DCM was a hydrogen bond. Based on the results of the study of the interaction energy, it was found that the hydrogen bond between the anion and the DCM had the greatest influence on the absorption process.

Copper Recovery from Industrial Bimetallic Composite Ionic Liquids by Direct Electrodeposition and the Effect of Temperature and Ultrasound.

Critical processing protocols of industrial bimetallic composite ionic liquid (IL) are necessary to assure good mass transfer rates for process optimization and efficient metal recovery. Here, the effects of different conditions on the electrochemical behavior and copper recovery from the industrial bimetallic composite IL are crucial for effective resource utilization. Cyclic voltammetry (CV) shows that the reduction of Cu(I) to Cu(0) during the cathodic reduction region is the irreversible diffusion-controlled process, and the diffusion coefficient increased with temperature which indicated that increasing temperature could promote the diffusion and mass transfer. During electrodeposition, metallic copper is obtained exclusively on the cathode, while CuCl2 accumulates exclusively on the anode. Scanning electron microscopy shows that the micron-size electrodeposits become larger and significantly rougher with increasing temperature and ultrasonic frequency, illustrating that these factors hasten the nucleation and crystallization rates at high overpotentials. The efficiency of copper recovery is greatly improved by employing high temperature and ultrasonic cavitation, and the highest values correspond to r = 76.9% at 80 °C and r = 63.6% at 40 kHz. The study lays the foundation for efficient and rapid recovery of copper from spent ILs.

Biodegradable functional chitosan membrane for enhancement of artemisinin purification.

Artemisinin is mainly derived from Artemisia annua L. Since the leaves composition is complex, artemisinin purification faces great challenges. In this work, functional chitosan membranes were fabricated by a one-step hydrolysis method through grafting long-chain alkyl group on the surface of chitosan to increase its hydrophobicity. The as-prepared membranes were used to adsorb wax oil (i.e., the impurity components) in Artemisia annua L. and to avoid co-precipitation of wax oil along with artemisinin using the crystallization technique for purification. Octyl-trimethoxysilane modified chitosan membrane (FCM-C8) showed excellent capability to intensify this purification process. The product purity could reach more than 98 % using one crystallization step under the optimal conditions, and in this case, adsorption capacity of FCM-C8 for wax oil was 478.9 mg/g. In addition, the adsorption kinetics and mechanism of wax oil on FCM-C8 were studied. The membrane can simultaneously adsorb multiple components in wax oil through interactions like electrostatic forces, hydrogen bondings.

A Mn-N3 single-atom catalyst embedded in graphitic carbon nitride for efficient CO2 electroreduction.

Developing effective catalysts based on earth abundant elements is critical for CO2 electroreduction. However, simultaneously achieving a high Faradaic efficiency (FE) and high current density of CO (jCO) remains a challenge. Herein, we prepare a Mn single-atom catalyst (SAC) with a Mn-N3 site embedded in graphitic carbon nitride. The prepared catalyst exhibits a 98.8% CO FE with a jCO of 14.0 mA cm-2 at a low overpotential of 0.44 V in aqueous electrolyte, outperforming all reported Mn SACs. Moreover, a higher jCO of 29.7 mA cm-2 is obtained in an ionic liquid electrolyte at 0.62 V overpotential. In situ X-ray absorption spectra and density functional theory calculations demonstrate that the remarkable performance of the catalyst is attributed to the Mn-N3 site, which facilitates the formation of the key intermediate COOH* through a lowered free energy barrier.

Aromatic Ester-Functionalized Ionic Liquid for Highly Efficient CO2 Electrochemical Reduction to Oxalic Acid.

Electrochemical reduction of CO2 into valuable chemicals is a significant route to utilize CO2 resources. Among various electroreduction products, oxalic acid (H2 C2 O4 ) is an important chemical for pharmaceuticals, rare earth extraction, and metal processing. Here, an aprotic aromatic ester-functionalized ionic liquid (IL), 4-(methoxycarbonyl) phenol tetraethylammonium ([TEA][4-MF-PhO]), was designed as an electrolyte for CO2 electroreduction into oxalic acid. It exhibited a large oxalic acid partial current density of 9.03 mA cm-2 with a faradaic efficiency (FE) of 86 % at -2.6 V (vs. Ag/Ag+ ), and the oxalic acid formation rate was as high as 168.4 µmol cm-2 h-1 , which is the highest reported value to date. Moreover, the results of density functional theory calculations demonstrated that CO2 was efficiently activated to a -COOH intermediate by bis-active sites of the aromatic ester anion via the formation of a [4-MF-PhO-COOH]- adduct, which finally dimerized into oxalic acid.

Screening Deep Eutectic Solvents for CO2 Capture With COSMO-RS.

In this work, 502 experimental data for CO2 solubilities and 132 for Henry's constants of CO2 in DESs were comprehensively summarized from literatures and used for further verification and development of COSMO-RS. Large systematic deviations of 62. 2, 59.6, 63.0, and 59.1% for the logarithmic CO2 solubilities in the DESs (1:2, 1:3, 1:4, 1:5), respectively, were observed for the prediction with the original COSMO-RS, while the predicted Henry's constants of CO2 in the DESs (1:1.5, 1:2, 1:3, 1:4, 1:5) at temperatures ranging of 293.15-333.15 K are more accurate than the predicted CO2 solubility with the original COSMO-RS. To improve the performance of COSMO-RS, 502 data points of CO2 solubility in the DESs (1:2, 1:3, 1:4, 1:5) were used for correcting COSMO-RS with a temperature-pressure dependent parameter, and the CO2 solubility in the DES (1:6) was predicted to further verify the performance of the corrected model. The results indicate that the corrected COSMO-RS can significantly improve the model performance with the ARDs decreasing down to 6.5, 4.8, 6.5, and 4.5% for the DESs (1:2, 1:3, 1:4, and 1:5), respectively, and the corrected COSMO-RS with the universal parameters can be used to predict the CO2 solubility in DESs with different mole ratios, for example, for the DES (1:6), the corrected COSMO-RS significantly improves the prediction with an ARD of 10.3% that is much lower than 78.2% provided by the original COSMO-RS. Additionally, the result from COSMO-RS shows that the σ-profiles can reflect the strength of molecular interactions between an HBA (or HBD) and CO2, determining the CO2 solubility, and the dominant interactions for CO2 capture in DESs are the H-bond and Van der Waals force, followed by the misfit based on the analysis of the predicted excess enthalpies.

Highly Selective Oxygen/Nitrogen Separation Membrane Engineered Using a Porphyrin-Based Oxygen Carrier.

Air separation is very important from the viewpoint of the economic and environmental advantages. In this work, defect-free facilitated transport membranes based on poly(amide-12-b-ethylene oxide) (Pebax-2533) and tetra(p-methoxylphenyl)porphyrin cobalt chloride (T(p-OCH3)PPCoCl) were fabricated in systematically varied compositions for O2/N2 separation. T(p-OCH3)PPCoCl was introduced as carriers that selectively and reversibly interacted with O2 and facilitated O2 transport in the membrane. The T(p-OCH3)PPCoCl had good compatibility with the Pebax-2533 via the hydrogen bond interaction and formed a uniform and thin selective layer on the substrate. The O2 separation performance of the thin film composite (TFC) membranes was improved by adding a small amount of the T(p-OCH3)PPCoCl and decreasing the feed pressure. At the pressure of 0.035 MPa, the O2 permeability and O2/N2 selectivity of the 0.6 wt % T(p-OCH3)PPCoCl/Pebax-2533 was more than 3.5 times that of the Pebax-2533 TFC membrane, which reached the 2008 Robeson upper bound. It provides a candidate membrane material for O2/N2 efficient separation in moderate conditions.

Insights into Carbon Dioxide Electroreduction in Ionic Liquids: Carbon Dioxide Activation and Selectivity Tailored by Ionic Microhabitat.

Electroreduction of carbon dioxide (CO2 ) into high value-added products is a potential solution to a reduction in CO2 levels and its utilization. One major challenge is the lack of an efficient system that can highly selectively reduce CO2 into desirable products with low energy consumption. Ionic liquids (ILs) have been used as electrolytes for the electroreduction of CO2 , and it has been proven that the CO2 -cation complex results in a low-energy pathway. In this work, an ionic microhabitat (IMH) has been built for CO2 electroreduction, and a novel anion-functionalized IL, 1-butyl-3-methylimidazolium 1,2,4triazolide ([Bmim][124Triz]), has been designed as the reaction medium. The results showed that the IMH played a key role in enhancing the performance of CO2 electroreduction, especially in dominating the product selectivity, which is recognized to be a great challenge in an electroreduction process. New insights into the role of the IMH in higher CO2 solubility, bending linear CO2 by forming the [124Triz]-CO2- adduct, and transferring activated CO2 into the cathode surface easily were revealed. The Faradaic efficiency for formic acid is as high as 95.2 %, with a current density reaching 24.5 mA cm-2 . This work provides a promising way for the design of robust and highly efficient ILs for CO2 electroreduction.

Ionic-Liquid-Based CO2 Capture Systems: Structure, Interaction and Process.

The inherent structure tunability, good affinity with CO2, and nonvolatility of ionic liquids (ILs) drive their exploration and exploitation in CO2 separation field, and has attracted remarkable interest from both industries and academia. The aim of this Review is to give a detailed overview on the recent advances on IL-based materials, including pure ILs, IL-based solvents, and IL-based membranes for CO2 capture and separation from the viewpoint of molecule to engineering. The effects of anions, cations and functional groups on CO2 solubility and selectivity of ILs, as well as the studies on degradability of ILs are reviewed, and the recent developments on functionalized ILs, IL-based solvents, and IL-based membranes are also discussed. CO2 separation mechanism with IL-based solvents and IL-based membranes are explained by combining molecular simulation and experimental characterization. Taking into consideration of the applications and industrialization, the recent achievements and developments on the transport properties of IL fluids and the process design of IL-based processes are highlighted. Finally, the future research challenges and perspectives of the commercialization of CO2 capture and separation with IL-based materials are posed.

Imidazole tailored deep eutectic solvents for CO2 capture enhanced by hydrogen bonds.

Deep eutectic solvents (DESs) have emerged as promising alternative candidates for CO2 capture in recent years. In this work, several novel DESs were firstly prepared to enhance CO2 absorption. Structural and physical properties of DESs were investigated, as well as their absorption performance of CO2. A distinct depression in the melting point up to 80 K of DESs was observed compared with that of BMIMCl. The observed red shifts of the C2H group in an imidazolium ring and its chemical shifts downfield in NMR spectra are indicative of a hydrogen bond interaction between BMIMCl and MEA. In particular, CO2 uptake in MEA : ILs (4 : 1) at room temperature and atmospheric pressure is up to 21.4 wt%, which is higher than that of 30 wt% MEA (13%). A hydrogen bond related mechanism was proposed in which ILs act as a medium to improve CO2 uptake through hydrogen bonds. Finally, the firstly reported overall heat of CO2 absorption is slightly higher than that of 30 wt% MEA, implying that the hydrogen bonds of DESs contribute to the overall heat of CO2 absorption. This study reveals that the heat of CO2 absorption can be tailored by the proper molar ratio of MEA and ILs.

New models for predicting thermophysical properties of ionic liquid mixtures.

Potential applications of ILs require the knowledge of the physicochemical properties of ionic liquid (IL) mixtures. In this work, a series of semi-empirical models were developed to predict the density, surface tension, heat capacity and thermal conductivity of IL mixtures. Each semi-empirical model only contains one new characteristic parameter, which can be determined using one experimental data point. In addition, as another effective tool, artificial neural network (ANN) models were also established. The two kinds of models were verified by a total of 2304 experimental data points for binary mixtures of ILs and molecular compounds. The overall average absolute deviations (AARDs) of both the semi-empirical and ANN models are less than 2%. Compared to previously reported models, these new semi-empirical models require fewer adjustable parameters and can be applied in a wider range of applications.

[Comparison on concentrations and quality of dissolved organic matter in throughfall and stemflow in a secondary forest of Castanopsis carlesii and Cunninghamia lanceolata plantation].

In this paper, monthly variation of dissolved organic matter (DOM) concentrations as well as humification and aromaticity indices in throughfall and stemflow from secondary broadleaved Castanopsis carlesii (BF) forest and Cunninghamia lanceolata plantation (CP) were measured. The DOC concentrations in throughfall were significantly higher with greater variation in BF than in CP. The concentrations of DOC in throughfall were averagely 7.2 and 3.2 times of those in rainfall in BF and CP forests, respectively. The DOC concentrations of stemflow in CP were averagely 2.5 times as much as those in BF, and the DOC concentrations in stemflow tended to be greater in dry season than in rain season for the two forests. A significantly negative relationship was' found between the DOC concentrations in stemflow and the amounts of stemflow for both BF and CP. Moreover, the humification and aromaticity indices of DOM in throughfall in BF was significantly greater than in CP. In contrast, the humification and aromaticity indices of DOM from stemflow of CP were significantly greater than those of BF. This result indicated that the structure of DOM from throughfall was more complex in BF than in CP, and the structure of DOM from stemflow was vice versa. These results indicated that DOM in stemflow and throughfall showed significant variations in quantity and quality between BF and CP and may greatly impact the accumulation of soil organic carbon.