CO2 Affinity Research Articles

Reticular Synthesis of Hydrogen‐Bonded Organic Frameworks and Their Derivatives via Mechanochemistry

AbstractRational synthesis of hydrogen‐bonded organic frameworks (HOFs) with predicted structure has been a long‐term challenge. Herein, by using the efficient, simple, low‐cost, and scalable mechanosynthesis, we demonstrate that reticular chemistry is applicable to HOF assemblies based on building blocks with different geometry, connectivity, and functionality. The obtained crystalline HOFs show uniform nano‐sized morphology, which is challenging or unachievable for conventional solution‐based methods. Furthermore, the one‐pot mechanosynthesis generated a series of Pd@HOF composites with noticeably different CO oxidation activities. In situ DRIFTS studies indicate that the most efficient composite, counterintuitively, shows the weakest CO affinity to Pd sites while the strongest CO affinity to HOF matrix, revealing the vital role of porous matrix to the catalytic performance. This work paves a new avenue for rational synthesis of HOF and HOF‐based composites for broad application potential.

Solubilities and Transport Properties of CO2, Oxalic Acid, and Formic Acid in Mixed Solvents Composed of Deep Eutectic Solvents, Methanol, and Propylene Carbonate.

Recently, deep eutectic solvents (DES) have been considered as possible electrolytes for the electrochemical reduction of CO2 to value-added products such as formic and oxalic acids. The applicability of pure DES as electrolytes is hindered by high viscosities. Mixtures of DES with organic solvents can be a promising way of designing superior electrolytes by exploiting the advantages of each solvent type. In this study, densities, viscosities, diffusivities, and ionic conductivities of mixed solvents comprising DES (i.e., reline and ethaline), methanol, and propylene carbonate were computed using molecular simulations. To provide a quantitative assessment of the affinity and mass transport of CO2 and oxalic and formic acids in the mixed solvents, the solubilities and self-diffusivities of these solutes were also computed. Our results show that the addition of DES to the organic solvents enhances the solubilities of oxalic and formic acids, while the solubility of CO2 in the ethaline-containing mixtures are in the same order of magnitude with the respective pure organic components. A monotonic increase in the densities and viscosities of the mixed solvents is observed as the mole fraction of DES in the mixture increases, with the exception of the density of ethaline-propylene carbonate which shows the opposite behavior due to the high viscosity of the pure organic component. The self-diffusivities of all species in the mixtures significantly decrease as the mole fraction of DES approaches unity. Similarly, the self-diffusivities of the dissolved CO2 and the oxalic and formic acids also decrease by at least 1 order of magnitude as the composition of the mixture shifts from the pure organic component to pure DES. The computed ionic conductivities of all mixed solvents show a maximum value for mole fractions of DES in the range from 0.2 to 0.6 and decrease as more DES is added to the mixtures. Since for most mixtures studied here no prior experimental measurements exist, our findings can serve as a first data set based on which further investigation of DES-containing electrolyte solutions can be performed for the electrochemical reduction of CO2 to useful chemicals.

Does the composition in PtGe clusters play any role in fighting CO poisoning?

The high catalytic activity of Pt is accompanied by a high affinity for CO, making it extremely susceptible to poisoning. Such CO poisoning limits the use of proton exchange membrane fuel cells. In this work, using global minima search techniques and exhaustive electronic structure characterization, the dopant concentration is pinpointed as a crucial factor to improve the CO tolerance of Pt catalysts. By investigating the PtGe nanoclusters of different sizes and compositions, we found that, for those clusters with roughly the same amount of Pt and Ge, the binding to CO is weakened significantly. The uniqueness of the PtGe equimolar clusters is traced down to the electronic effects. The strong covalency and electrostatic stabilization arising from the advantageous Pt-Ge mixing make the equimolar clusters highly resistant toward CO poisoning and therefore more durable. Importantly, the novel catalysts not only are more resistant to deactivation but also remain catalytically active toward hydrogen oxidation. Representative clusters are additionally deposited on graphene with a pentagon-octagon-pentagon (5-8-5) reconstructed divacancy. The remarkable results of free-standing clusters hold true for surface mounted clusters, in which the interaction with CO is dramatically weakened for those compounds with a Pt:Ge ratio of 1:1. Our results demonstrate that Ge can be a promising alloying agent to mitigate the deactivation of Pt and that the dopant concentration is a critical factor in the design of advanced catalysts.

Enhancing the leaching performance of molybdenite and Co-white alloy simultaneously: A structure conversion process

Molybdenite (MoS2), driven by its unique sandwich structure, is chemical inert and hydrophobic leading to a high refractory sulfide ore, and Co-white alloy, due to its grinding and corrosion resistance, is a refractory product (mainly containing Co, Fe, Cu and Si) for use in traditional hydro-metallurgical processing. In this work, a novel, two-step process was proposed to enhance the leaching performance of both molybdenite and Co-white alloy. First, prior to leaching and based on the sulfur affinity of Co, Fe and Cu, molybdenite and Co-white alloy were converted into ternary sulphides (MxMo6S8) with high leaching activity. Second, a leaching process was carried out in an autoclave with oxygen as the oxidant. Compared to molybdenite and Co-white alloy, the leaching performance of the ternary sulfides was greatly improved under moderate conditions. During the leaching of ternary sulfides, the sulfur is partially converted to elemental sulfur, which is unlike the acid leaching process of molybdenite where sulfur is oxidized to sulfuric acid. Factors affecting the decomposition of ternary sulfide were also studied in detail under moderate conditions. The optimal leaching conditions were found to be a temperature of 120 °C, a sulfuric acid concentration of 1 mol/L, a duration of 150 min, and an oxygen partial pressure of 0.95 MPa. The oxidation efficiency of molybdenum reached 99%, the elemental sulfur yield was 55%, and the leaching efficiencies of cobalt and copper were both greater than 99%.

Proton conduction-assisted direct CO2 methanation using Ni/CaO/Y-doped BaZrO3 proton conductor

This study investigates the conversion of captured CO2 to CH4 with Ni and CaO supported on 10 mol% Y-doped BaZrO3 (BZY10) proton-conducting oxides. The on-site treatment of CO2 to cut back CO2 emission has been demonstrated, further transforming it into an energy carrier. This report describes direct CO2 methanation using Ni materials in O2– and H2O-containing gases at the carbonation step. Ni and CaO supported on BZY10 were used to capture CO2 in simulated flue gas containing O2 or H2O and convert it into CH4 at the same temperature (380–450 °C). High reducibility of Ni and high methanation reactivity were observed. Through the FTIR spectra observation, it was found out that transformation of bicarbonate to formate was facile due to proton-conducting property of the BZY10 support, i.e., hydrogen spillover, compared to BaZrO3-supported materials., It is hypothesized that the hydroxyl ions at the interface of CaO and BZY10 intervene in the carbonation and methanation steps. Also, carbonation accelerates the kinetic and diffusion-controlled regions with a high affinity for CO2. In the methanation step, the adsorbed CO2 enables the hydrogen species to produce CH4.

Calcium Poly(Heptazine Imide): A Covalent Heptazine Framework for Selective CO2 Adsorption.

Potassium poly(heptazine imide) (KPHI) has recently garnered attention as a crystalline carbon nitride framework with considerable photoelectrochemical activity. Here, we report a Ca2+-complexed analogue of PHI: calcium poly(heptazine imide) (CaPHI). Despite similar polymer backbone, CaPHI and KPHI exhibit markedly different crystal structures. Spectroscopic, crystallographic, and physisorptive characterization reveal that Ca2+ acts as a structure-directing agent to transform melon-based carbon nitride to crystalline CaPHI with ordered pore channels, extended visible light absorption, and altered band structure as compared to KPHI. Upon acid washing, protons replace Ca2+ atoms in CaPHI to yield H+/CaPHI and enhance porosity without disrupting crystal structure. Further, these proton-exchanged PHI frameworks exhibit large adsorption affinity for CO2 and exceptional performance for selective carbon capture from dilute streams. Compared to a state-of-the-art metal organic framework, UTSA-16, H+/CaPHI exhibits more than twice the selectivity (∼300 vs ∼120) and working capacity (∼1.2 mmol g-1 vs ∼0.5 mmol g-1) for a feed of 4% CO2 (1 bar, 30 °C).

Exploring the potential energy surface of nCO2 (n = 1–5) capture by imidazole-and fluorine-based ionic liquids: A DFT study

One of the reasons for global warming is the rising of greenhouse gasses causing the planet's temperature to increase; among these gases, CO2 accounts for 80%. For this reason, it is essential to contemplate environmentally sustainable alternatives for CO2 capture and storage, such as the use of ionic liquids (ILs), which represent an excellent option due to their high affinity for CO2. This theoretical study considered ILs based on imidazole ([bmim]+ and [emim]+) and fluorinated ([TFSI]- and [PF6]-) dimers, thorough exploration of the potential energy surfaces of nCO2[bmim]+[PF6]−, nCO2[emim]+[TFSI]−, nCO2[bmim]+[PF6]− and nCO2[emim]+[TFSI]− molecular clusters, n = 1–5, by using a stochastic SnippetKick searching algorithm. Followed by the optimisation of the molecular cluster geometries using Density Functional Theory (DFT) calculations to describe the effect of physisorption of up to five CO2 in ILs. It was revealed an aggregation of CO2 molecules between the imidazole ring and the anion, mainly surrounding [TFSI]- or [PF6]-, in the form of an orbital in putative global minimum-energy structures, which allows a higher CO2 physisorption. Finally, a detailed analysis of the thermodynamic properties and intermolecular interactions between ILs and CO2 molecules was performed with different approximations of the electron density scalars. Overall, this confirms the use of the ILs studied to capture CO2 efficiently.

Precise regulation of CO2 packing pattern in s-block metal doped single-layer covalent organic frameworks for high-performance CO2 capture and separation

The development of high-performance CO2 capture and separation adsorbents is critical to alleviate the deteriorating environmental issues. Herein, six s-block metal doped single-layer polymeric tetraoxa[8]circulene (SBM-TOCs, SBM = Li, Na, K, Be, Mg, and Ca) were introduced as potential CO2 capture and separation adsorbents via precise regulation of CO2 packing patterns. Structural analyses showed that Li-TOC, Na-TOC, K-TOC, and Ca-TOC were screened with high cohesive energies ranging from 7.02 to 7.08 eV/atom and moderate formation energies ranging from –2.92 to –1.41 eV, guaranteeing their structural stabilities for CO2 capture and separation. Electronic structure analyses confirmed the large charge transfer and strong covalent bonding characters between the SBMs and direct-connected O atoms, thus constructing a favorable gas adsorption environment. Li-TOC exhibited an ultrahigh CO2 adsorption capacity of 10.78 mmol/g at 298 K and 1.0 bar, which was superior to previously reported Li-doped adsorbents. At 298 K and 1.0 bar, the selectivity of CO2 over N2/CH4 in Li-TOC reached up to ∼ 516 and ∼ 821, respectively. Polarity regulation analyses showed that SBMs had a more positive effect on the framework affinity for CO2 than N2/CH4 via both coulomb and van der Waals interactions. Space regulation analyses showed that strong interactions between the electropositive SBMs and the electronegative O atoms of CO2 facilitated vertical CO2 configurations and compact distributions, thereby rendering a multilayer CO2 adsorption and enhancing the CO2 adsorption capacity. Results of this work highlighted SBM-TOCs as ultrahigh-performance adsorbents for CO2 capture and separation over N2/CH4, and demonstrated that the precise regulation of CO2 packing pattern was an effective strategy to achieve high-performance gas capture and separation.

Synthesis of dual-functionalized APTES-Bentonite/PVDF mixed-matrix membranes for the efficient separation of CO2/CH4 and CO2/N2

In response to global climate change, most countries have set carbon reduction targets. Mixed matrix membranes (MMMs), which combine the characteristics of inorganic nanofillers and organic matrices, have received wide attentions because of their good permeability and selective performance for the separation of CO2 from industrial waste gases. However, the poor dispersion, compatibility and interfacial defects often lead to poor gas separation performance. In this paper, according to the dissolution-diffusion and Lewis acid-base theories, inorganic filler of amino-functionalized Bentonite (APTES-Bentonite) with -NH2 was firstly synthesized to improve the affinity of CO2. Then, the dual-functionalized MMMs of APTES-Bentonite/PVDF (A-B/P MMMs) was prepared and adopted for the separation of CO2/CH4 and CO2/N2, showing the increase of 87.76% and 75.31% compared to the pristine PVDF membrane, respectively. These excellent performances were attributed to the synergistic effect of APTES-Bentonite with -NH2 groups and PVDF with -F groups, which provide a dual-functional transport pathway for CO2 molecules due to the interactions of host-guest. Overall, the customized A-B/P MMMs offer superior CO2 separation performance, which provides some valuable references for large-scale CO2 capture studies.

Post-modification of metal-organic framework for improved CO2 photoreduction efficiency

Utilizing metal-organic frameworks (MOFs) to design photocatalysts for CO2 reduction catalysts is an excellent idea but currently restricted by the relatively low activity. Enhancing CO2 affinity and tuning the oxidation state of metal clusters in MOFs might be a solution to improve the catalytic performance. Herein, the Cl-bridge atoms in the metal clusters of a cobalt MOF were easily exchanged with OH−, which simultaneously oxidized a portion of Co(II) to Co(III) and resulted in a much enhanced photocatalytic activity for CO2 reduction. In contrast, the original framework does not exhibit such superior activity. Comprehensive characterizations on their physicochemical properties revealed that the introduction of hydroxyl group not only greatly increases the CO2 affinity but also alters the oxidation state of metal clusters, resulting in significantly improved photocatalytic activities for CO2 reduction. This work provides important insight into the design of efficient photocatalysts.

Hydrogen bond donor functionalized poly(ionic liquids)@MIL-101 for the CO2 capture and improving the catalytic CO2 conversion with epoxide

Hydrogen bond donor functionalized poly(ionic liquids) were incorporated into MIL-101 framework for synthesis of composites PIL-R@MIL-101 (R = COOH, OH, NH2). The effect of different hydrogen bond donors on CO2-epoxide cycloaddition reaction was discussed through XPS, NH3-TPD characterizations. Thereinto, PIL-COOH@MIL-101 showed efficient catalytic performance in the cycloaddition reaction of CO2 and epichlorohydrin, 92.7% substrate conversion was obtained under 70 °C, 1.0 MPa, cocatalyst- and solvent-free conditions for 2.5 h. The improved activity was benefited from the synergistic effects of Lewis acidic Cr centers, carboxyl group, and nucleophilic Br-, together with the high surface area (1178 m2/g), and good CO2 affinity. In addition, PIL-COOH@MIL-101 also showed facile recovery method by easy centrifugation and good recycling stability. Considering the good CO2 affinity, excellent catalytic performance in CO2 cycloaddition reaction, better thermal and recycling stabilities, the facilely prepared functionalized poly(ionic liquid)@MIL-101 composite would exhibit promising application prospect in CO2 capture and conversion.

Self-supported membranes fabricated by a polymer‒hydrogen bonded network with a rigidified MOF framework

Mixed matrix membranes (MMMs) combine the advantages of porous fillers and polymer membranes, endowing them with potential applications in gas separation. Due to their high porosity and defined pore sizes, metal‒organic frameworks (MOFs) have been extensively investigated as MMM fillers. However, the frameworks of many MOFs are flexible, which may limit selectivity. Here, hydrogen bonding between polyimide (PI) and flexible MIL-53(Al) with large pore size (M53-L) is utilized to rigidify the framework in a series of PI/M53-L MMMs. The high pore volume and large pore size of rigid M53-L increased the affinity of CO2 with hydroxy groups, leading to higher separation performance than the pure PI membrane. The separation performance of PI/M53-L MMMs exceeds the Robeson 2008 upper bounds for both CO2/N2 and CO2/CH4. We propose a method of utilizing hydrogen bonds to rigidify flexible MOF frameworks to prepare self-supported MMMs, providing a strategy for the application of flexible MOFs in gas separation.

An MOF-tailored hierarchical porous microenvironment for CO2 as an efficient filler for mixed matrix membranes

Mixed matrix membranes (MMMs) for separating CO2/CH4 mixture were prepared through incorporating Cu@Al(bpydc) into a Pebax polymer in which Cu@Al(bpydc) synthesized through a competitive coordination method achieved a controllable micro/mesopores structure and abundant functional sites for CO2. The hierarchical pores of Cu@Al(bpydc) provided multidimensional diffusion channels in the Pebax matrix, which increased the diffusion of CO2. In addition, the abundant chemical groups, such as the polar group COO– and nitrogen Lewis basic groups, created a microenvironment with multiple CO2 affinity sites in the membrane, increasing the selectivity of CO2. A MMM loaded with 5 wt% Cu@Al(bpydc) exhibited excellent CO2 separating property under wet mixed-gas test conditions. In particular, the CO2 permeability and selectivity of the MMMs were increased by 92.90% and 27.10% respectively, compared with those of pure Pebax, showing exceptional potential for the separation and capture of CO2 from biological natural gas.

Adsorption equilibria and kinetics of CO2, CH4, CO, N2, and H2 on KOH-treated activated carbon pellets up to 1000 kPa

• Adsorption behaviors of CO 2 , CH 4 , CO, N 2 , and H 2 on KOH-treated ACs were studied. • KOH-treated ACs showed improved adsorption capacities, but reduced adsorption rates. • Affinity for CO increased on KACi, in the presence of intercalated K chemicals. • KACi showed higher capacity and selectivity than CAC and KACa based on volume. • Adsorption rate of KACi was faster for CO 2 , CH 4 , and N 2 and slower for CO than KACa. Activated carbon (AC) is critical for bulk separation to produce high-purity H 2 . Coal-based AC pellets (CAC) were modified through KOH activation (KACa) or impregnation (KACi) via bulk preparation. The adsorptive behaviors of CO 2 , CH 4 , CO, N 2 , and H 2 , which are components of various H 2 mixtures, were investigated at 293.15–323.15 K and up to 1000 kPa. The experimental data and model parameters are tabulated for applications by related researchers. The experimental isotherms fitted well to the Sips and dual-site Langmuir models. The improved textural properties of KACa resulted in higher adsorption capacity based on the adsorbent mass. However, based on volume-based evaluation, KACi showed higher adsorption capacities for CO 2 , CO, and CH 4 at low pressures, with capacities almost equivalent to those of KACa at high pressures, despite the deterioration of textural properties due to K impregnation. Furthermore, more favorable isotherms on KACi resulted in higher selectivities toward various H 2 mixtures. From the non-isothermal kinetic model, CO 2 and CH 4 showed a lower adsorption rates than CO and N 2 due to higher heats of adsorption. Compared to those of KACa, the adsorption rates of KACi were faster for CO 2 , CH 4 , and N 2 and slower for CO, but within the same order of magnitude. KACa was found to be more affected by pre-adsorbed molecules than KACi. KACa and KACi exhibited enhanced performances with excellent cyclic stabilities and batch preparation consistencies. Considering its selectivity and adsorption rate, KACi can be used for improving the efficiencies of adsorptive processes for H 2 production.

Enhanced CO2-capture performance of polyimide-based mixed matrix membranes by incorporating ZnO@MOF nanocomposites

Mixed matrix membranes (MMMs) have received numerous interests as promising membrane configurations for dealing with the energy-intensive gas separation processes. In this study, MMMs were fabricated by incorporating novel ZnO@MOF nanocomposites (ZnO@ZnBDC) into Matrimid (PI) matrix. The physico-chemical properties and microstructures of ZnO@ZnBDC nanocomposites and ZnO@ZnBDC/PI MMMs were characterized. The CO2/CH4 separation performance of MMMs was evaluated and analyzed according to the solution-diffusion mechanism. ZnBDC in the nanocomposites increased CO2 permeability by providing mass transfer pathways with low resistance in the MMMs, while ZnO increased the CO2/CH4 selectivity via high CO2 affinity. Owing to the synergistic effect of the nanocomposites, MMMs with 0.75 wt% ZnO@ZnBDC showed CO2 permeability of 11.5 Barrer and CO2/CH4 selectivity of 39.5, which increased by 67% and 33%, respectively, by comparing with control PI membrane.

Mechanical property alterations across coal matrix due to water-CO2 treatments: A micro-to-nano scale experimental study

CO2 sequestration in geological coal formations is a promising pathway to store a huge amount of CO2 due to a strong CO2 affinity on coal. It has been reported that CO2 sorption can cause a strength reduction of coals. However, the mechanism-based understandings of CO2-coal interactions induced alterations are still challenging in micro-to-nano scale. We conducted the combined grid-based nanoindentation tests and FESEM-EDS analyses to understand and quantify the mechanical property variations and distributions of coals in micro- or nano-scale due to its mineral and structural variations. We also quantified the mechanical property alterations induced by gaseous CO2, ScCO2, and ScCO2-water mixture treatments at different treating durations. The combined results from the FESEM-EDS and XRD confirmed that the heterogeneity of two tested coal is prevailing at micro-to-nano scale and the corresponding mechanical properties are composition- and microstructure-dependent. The mechanical properties of coals can be altered by gaseous CO2, ScCO2, and ScCO2-water mixture treatments primarily due to the organic carbon-CO2 interactions and water hydration effects in wetted coals, or potentially due to the dissolution and precipitation of minerals occurred in fluid environment typically under the ScCO2-water treatment condition.

Tuning N-doping thermal-process enables biomass-carbon surface modification for potential separation effect of CO2/CH4/N2

• The optimal N-doping temperature of 600 ℃ for biomass activated carbon was validated. • The detailed comparative studies of two types of activated carbon were conducted. • The thermal stability of N-doping activated carbon was improved from 403 ℃ to 541 ℃. • The adsorption ability of the optimized sample for CO 2 was drastically enhanced. • The N-doping activated carbon afford great potential for separation of CO 2 /CH 4 /N 2 . Gas-adsorption-Sieving especially for CO 2 /CH 4 /N 2 became attractive in flue-gas separation, natural-gas energy upgrading, and gas-layer-methane recovery. Herein, a detailed study on the potential adsorption separation effect of CO 2 /CH 4 /N 2 using two kinds of synthesized temperature-tuning N-doping biomass activated carbon (BCx and GCx) derived from banana peel and grapefruit peel was explored. A comprehensive comparison of the structural properties and surface character of N-doping carbon was conducted through various characterizations, revealing that two N-doping AC both afford a better doping effect and higher post-implanted surface skeleton N species at 600 °C. Impressively, CO 2 adsorption capacity of optimal GC600 and BC600 at 0 °C/25 °C and 1 bar reaches 5.09/3.05 mmol g −1 and 3.04/3.57 mmol g −1 , respectively, which have exceeded most reported AC adsorbents. Especially, BC600 affords appreciable N and O component proportion, which renders better surface affinity for CO 2 adsorption at 25 °C. While GC600 endows better CO 2 adsorption at 0 °C by right of the highest occupation fraction of pore-volume-selected corresponding to specific pore-size of 1.2 nm and post-implanted beneficial surface N species. The tentative linear fitting among CO 2 adsorption performance with surface N species state and structural properties validates their comprehensive influence on CO 2 adsorption. Through the rational correlation of the adsorption of pure components, the adsorption selectivity to the binary mixture of CO 2 /N 2 (15/85), CO 2 /CH 4 (10/90), and CH 4 /N 2 (30/70) is predicted for optimized GC600 and BC600 through Ideal Adsorbed Solution Theory(IAST), which reaches 22.84/3.46/5.84 and 17.45/3.66/3.98, respectively and reveals obvious improvements compared to original biomass-carbon and traditional AC adsorbents. Most importantly, the optimal adsorbent afford extremely low-level adsorption heat for CO 2 , thereby rendering the good reversibility and reusability during 7 cycles at room temperature without any extra thermal process.

Free-Standing Nanometer-Thick Covalent Organic Framework Films for Separating CO2 and N2

Covalent organic frameworks (COF) have been gathering much attention because the shapes, sizes, and chemical functions of their nanostructured pores can be arbitrarily controlled by designing the organic precursors. We fabricated cm-sized free-standing COF films with the thickness of 50–100 nm by an alternating vacuum deposition polymerization method. Precise adjustment of the stoichiometry by digitally controlled deposition was essential for producing the robust free-standing COF films. High-resolution electron microscopy revealed 3 nm pore structures, which correspond to the atomic structure of the COF. Small angle X-ray diffraction shows the existence of a similar periodicity. The CO2/N2 gas phase separation properties were evaluated from 103–105 Pa, and the parameters for each molecular permeation were determined. Based on the detailed analysis, it was found that the selectivity comes from the greater sorption affinity of CO2 to the COF compared to N2, which is consistent with the quantum chemical calculation. Since the vapor phase method can be used to coat various shaped templates, our method provides a new option for fabrication of neat COF membranes with various structures and their applications for the separation membrane.

Homogeneous sub-nanophase network tailoring of dual organosilica membrane for enhancing CO2 gas separation

Dual organosilica membranes were synthesized to investigate the effects of differing molar ratios of bis (triethoxysilyl) ethane (BTESE)/glycidyl Polyhedral oligomeric silsesquioxane (glycidyl POSS) on the membrane performance. The reaction mechanism behind CO2 capture using the organosilica membranes under ambient conditions was also investigated. A facile in-situ framework synthesis approach was introduced for the copolymerization reaction of dual organosilica. BTESE has a smaller molecular size than that of glycidyl POSS, and the Si–C–C–Si linkage is the main structure contributing to its high CO2 affinity. Additionally, the dimensional and mechanical stability were maintained at high doping levels owing to the inclusion of glycidyl POSS. Consequently, the free volume of the resulting hybrid networks increased owing to the cage structure and high cross-link density, which was attributed to the coexistence of epoxy ring-opening polymerization and condensation polymerization. The characterization and permeation tests revealed that the 1B0.5P gel with the best copolymerization effect exhibits a high CO2 permeance of 5.74 × 10−8 mol m−2 s−1 Pa−1 at 25 °C and ideal selectivity values of 11.61, 37.55 and 63.67 for CO2/H2, CO2/CH4 and CO2/N2, respectively. Moreover, a new analytical technique was proposed to investigate the surface microstructure of organosilica membranes for the first time using optical microscopy.

Enhanced CO2 capture kinetics by using macroporous carbonized natural fibers impregnated with an ionic liquid

In this research a new hybrid material was prepared to improve the kinetics and CO2 sorption capacity of an ionic liquid supported on the macroporous structure of carbonized agave bagasse fibers, which are low-cost renewable materials. The ionic liquid was 1-butyl-3-methylimidazolium acetate that has high affinity for CO2. The CO2 capture was assessed in a dynamic mode at atmospheric pressure by monitoring the weight change of the fibers in a thermogravimetric analyzer when passing a CO2 gas stream. The CO2 capture was evaluated on carbonized fibers (CF), acid washed carbonized fibers (CFw) and carbonized fibers impregnated with ionic liquid (IL) using a mass ratio that ranges from 1:10−3 to 1:1 (wt CFw: wt IL). The BET surface area of CF was 75 m2/g that decreased after the acid wash to 2 m2/g. However, after impregnation with IL, the surface area was maintained at 2 m2/g when using the lowest impregnation ratio (1:10−3). The impregnated sample with a mass ratio of 1:10−3 (CFwIL1:10−3) exhibited the highest sorption capacity (1.29 mmol CO2/g evaluated at 50 min of CO2 exposure) and sorption rate of 0.02 mmol CO2/min*g. These values were superior to those obtained by the IL (0.77 mmol CO2/g and 0.012 mmol CO2/min*g), which showed the synergy between the IL and the support in the CO2 capture. Finally, the cycles of CO2 capture (25 °C, 50 min) and thermal desorption (80 °C, 50 min, under nitrogen atmosphere) reported that the IL captured up to 1.07 mmol CO2/g but released only 41.5%, in contrast the impregnated carbon fibers (CFwIL1:10−3) captured 1.13 mmol CO2/g and released 91%. The rapid CO2 sorption-desorption processes and high reversibility of the impregnated carbon fibers suggest that this material could be used in CO2 concentrators.