CO2 Isotherms Research Articles

Carbon materials derived from cyano-based IL@ZIF-8 composites for CO2 sorption separation systems

The sorption capacity and selectivity of pre- and post-carbonized cyano-based metal-organic framework (MOF) composite materials (cyano-based IL@ZIF-8) were investigated for the first time. The influence of the ionic liquid (IL) loading and number of cyano groups in the IL anion on a materials gas sorption separation performance was studied. Sorption-desorption equilibrium isotherms of CO2, CH4, and N2 were measured at 303 K in the ZIF-8, cyano-based IL@ZIF-8 composites and their derived carbon materials. The IL loading did not significantly affect the gas uptake of the carbon materials, while for the composites its main contribution was on the increase of the selectivity. The number of cyano groups in the anion played a key role in the sorption capacity and selectivity performance as it directly affects the N content and textural properties. The carbon material obtained from ZIF-8 (C_ZIF-8) precursor showed the best sorption capacity for all gases, just being surpassed by the C_15%[C6MIM][B(CN)4]@ZIF-8 carbon up to 1 bar. In terms of selectivity performance, carbons based on [C6MIM][B(CN)4]@ZIF-8 composites revealed to be equally or more selective than C_ZIF-8, increasing up to 65% between 0 and 1 bar depending on the mixture. The composites produced and their respective carbons demonstrated a promising application as sorbents for post-combustion CO2 separation systems.

Breakthrough analysis for parameter estimation of CO2 adsorption on pelletized flexible metal–organic framework

Pellets of elastic layer-structured metal–organic framework-11 (ELM-11), one of the flexible metal–organic frameworks (MOFs), were prepared by mixing ELM-11 powder with a cellulose binder, and the CO2 adsorption behavior of ELM-11 pellets in a fixed-bed adsorber was analyzed to estimate equilibrium and kinetic parameters. Adsorption breakthrough tests were performed under various conditions for the simulated flue gas (20 % CO2–80 % N2) of a blast furnace gas in addition to CO2 isotherm measurements. Experimental CO2 adsorption isotherms on ELM-11 followed a weighted dual-site Langmuir equilibrium model well. The breakthrough analysis results by numerical calculation using the equilibrium model suggested that the gate-opening pressure of ELM-11 shifted to a lower pressure through repeated breakthrough tests. The CO2 adsorption kinetics on ELM-11 pellets agreed well with the linear-driving-force model. Furthermore, CO2 adsorption behavior under various conditions was described well by a mathematical model using a constant value of the mass transfer coefficient under the condition of this study, which was validated against additional experimental data. In addition, it was found that the mass transfer becomes slow under certain conditions that the driving force of the phase transition of ELM-11 is smaller than a threshold, where the amount of CO2 adsorbed on the breakthrough tests did not reach the equilibrium capacity of CO2, which may because the rate-limiting step may be dependent on the CO2 partial pressure and temperature.

In silico engineering of ion-exchanged zeolites for high-performance carbon capture in PSA processes

In this article we employ a multiscale computational framework to design zeolites with competitive performance in post-combustion carbon capture. The efficiency of CO2 capture from flue gas critically depends on the adsorption properties of the adsorbent material. In recent studies, the search for the best performing materials has been predominantly confined to Metal-Organic Frameworks (MOFs), due to the wide diversity in their adsorption characteristics. Inspired by MOFs and their properties, we sought to produce a similar variety in the CO2 isotherms of zeolites. To this end, we modified the properties of the well-known LTA zeolite by varying the Si:Al ratio and the cation composition. Using molecular simulations, we show that these in silico engineered zeolites exhibit a wide range of isotherms for carbon capture. Pressure Swing Adsorption (PSA) simulations using the modified Skarstrom cycle show that structures with the Si:Al ratio ranging from 2.2 to 3.9 can meet the standard requirement of 90 % purity at 90 % recovery for CO2. This performance can be further improved by modifying the cation composition via moderate ion-exchange of Na+ with K+ ions. Several designed structures exhibit performance that is comparable to or even better than the current industrial benchmark, Zeolite l3X, therefore offering interesting alternatives to MOFs as adsorbents for carbon capture in PSA.

Estimation of CO2 Separation Performances through CHA-Type Zeolite Membranes Using Molecular Simulation.

Chabazite (CHA)-type zeolite membranes are a potential material for CO2 separations because of their small pore aperture, large pore volume, and low aluminum content. In this study, the permeation and separation properties were evaluated using a molecular simulation technique with a focus on improving the CO2 separation performance. The adsorption isotherms of CO2 and CH4 on CHA-type zeolite with Si/Al = 18.2 were predicted by grand canonical Monte Carlo, and the diffusivities in zeolite micropores were simulated by molecular dynamics. The CO2 separation performance of the CHA-type zeolite membrane was estimated by a Maxwell-Stefan equation, accounting for mass transfer through the support tube. The results indicated that the permeances of CO2 and CH4 were influenced mainly by the porosity of the support, with the CO2 permeance reduced due to preferential adsorption with increasing pressure drop. In contrast, it was important for estimation of the CH4 permeance to predict the amounts of adsorbed CH4. Using molecular simulation and the Maxwell-Stefan equation is shown to be a useful technique for estimating the permeation properties of zeolite membranes, although some problems such as predicting accurate adsorption terms remain.

Facile synthesis of sulfonated poly(phenyl-alkane)s for proton exchange membrane fuel cells

Sulfonated poly (phenyl-alkane)s with all-carbon backbones exhibit excellent chemical stability; however, their applications in proton exchange membranes are limited. Herein, we report a facile synthesis of three sulfonated poly (phenyl-alkane)s SP1–SP3 via efficient acid-catalyzed Friedel−Crafts polycondensations of commercially available 2,3,4,5,6-pentafluorobenzaldehyde with three aromatic monomers, followed by mild and efficient nucleophilic substitution of para-aryl-F with sodium 4-oxybenzenesulfonate. In the characterization of the three polymers, the single-component adsorption–desorption isotherms of N2 and CO2 confirmed their intrinsic ultramicroporosity. For the SP3 membrane, small-angle X-ray scattering and atomic force microscopy measurements revealed that larger ionic clusters and smaller hydrophobic assembly domains led to better ionic channel connectivity. These features and the observed high ion exchange capacity and narrowly distributed ultramicropores synergistically determined its high conductivity. Moreover, the SP3 membrane exhibited excellent oxidative stability and good mechanical properties, enabling the successful application in H2/air proton exchange membrane fuel cells.

The potential of direct air capture using adsorbents in cold climates.

Global warming threatens the entire planet, and solutions such as direct air capture (DAC) can be used to meet net-zero goals and go beyond. This study investigates using DAC in a 5-step temperature vacuum swing adsorption (TVSA) cycle with adsorbents' Li-X and Na-X, readily available industrial zeolites, to capture and concentrate CO2 from air in cold climates. From this study, we report that Na-X in cold conditions has the highest known CO2 adsorption capacity in air of 2.54mmol/g. This combined with Na-X's low CO2 heat of adsorption, and fast uptake-rate in comparison to other benchmark materials, allowed for Na-X operating in cold conditions to have the lowest reported DAC operating energy of 1.1 MWh/tonCO2. These findings from this study show the promise of this process in cold climates of Canada, Alaska, Greenland, and Antarctica to be part of the solution to global warming.

Efficient separation of CO2 from methane at high pressures by modified microporous titanosilicates; design and breakthrough studies

In this work, type-4 titanosilicate (TS-4) having a micro-pore size of 3–4 Å, was synthesized from inexpensive source materials, such as commercial silicon dioxide, with the template-free hydrothermal method. The XRD analysis confirmed formation of the TS-4 crystalline phase. Then, strontium cation modification was performed using SrCl2 solution to adjust the pore structure and increase the basicity of the surface to improve CO2 selectivity versus methane. In this study, the adsorption isotherms of methane and CO2 were measured in the range of 0 to 50 bars, at two different temperatures of 298 K and 308 K, then the ideal selectivities of CO2/CH4 were calculated at different pressures. The ideal CO2/CH4 selectivity was determined at 19.04 and 38.49 for TS-4 and Sr-TS-4, respectively, at the pressure of 50 bar and the temperature of 298 K. The isosteric heat of adsorption of CO2 was calculated by Van’t Hoff equation as −29.63 kJ/mol and −26.22 kJ/mol, respectively. Low CO2 heat of adsorption of Sr-TS-4 and high selectivity of CO2/CH4 at high pressures, against zeolites, offer Sr-TS-4 as an economic and efficient adsorbent for cyclic adsorption processes. To study the dynamic selectivity of CO2/CH4, dynamic adsorption experiments were conducted at the temperature of 298 K, pressures of 7 and 15 bars, flow rates of 10 and 20 Nml/min in a bed of 2.7 gr adsorbent, with the inlet molar fraction of 5–95 % CO2-CH4 mixture. Comparison of the breakthrough curves indicated that Sr-TS-4 had a longer breakpoint and a larger used ratio of the length at any feed flow rate. The maximum relative dynamic selectivity of CO2/CH4 at 15 bar, by the Sr-TS-4, was obtained 95.29 at CO2 breakpoint of 40 min, whereas maximum relative dynamic selectivity, by the TS-4, was obtained 63.54 at CO2 breakpoint of 30 min. It is concluded that Sr-TS-4 would be an efficient adsorbent for separation of CO2 from natural gas in commercial scales at high pressures with high methane recovery.

A Better Understanding of the SBA-15 Pores Filling through Textural Changes in CMK-3 Carbon Synthesis and Its CO2:CH4 Adsorption Selectivity

This text reports the morphological and textural behavior of the synthesis stages of a CMK-3 carbon type using a silicon matrix of the SBA-15 type calcined at 823 K as a template. During the synthesis, three intermediate materials were obtained because of (i) the addition of sucrose to the SBA-15 template (CCMK3-1st), (ii) the addition of sucrose to the CCMK3-1st material (CCMK3-2nd), and (iii) the carbonization by pyrolysis of the by-product CCMK3-2nd (CCMK3-F). The texture of the above materials was found by analyzing the N2 adsorption isotherms, applying the classical adsorption theories to obtain the BET-specific surface and the meso- and micropore distributions by the BJH and Dubinin–Astakhov (DA) methods, respectively, in addition to the non-localized density functional theory (NLDFT). Similarly, with high resolution, the samples were analyzed morphologically by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Finally, the adsorption isotherms of CO2 and CH4 of the CMK-3 sample were obtained at six different temperatures in the interval of 243 to 303 K to evaluate the behavior of the isosteric enthalpy of adsorption (qst) and its CO2:CH4 ideal selectivity. The final CMK-3 carbon presented two families of micro- and mesopores of 1.5 and 3.2 nm, nanopipe diameters of 3.5 nm, and a specific surface area of 1350 m2/g. It also presented values of 6.0 and 2.4 mmol/g adsorbed CO2 and CH4 at 243 K, respectively, and strong intermolecular interactions, with qst values higher than 22 kJ/mol reflected in high selectivity values for an ideal mixture of CO2:CH4 (30:70%).

De novo syntheses of multi-linker Zn- and Co-based ZIFs with application in CO2 fixation

Zeolitic Imidazolate Frameworks (ZIFs) and ZIF derivatives can catalyze the fixation of CO2 with epoxide substrates. Herein, we report a De Novo (direct mixing) synthesis method to produce nano-sized Zn- and Co-based Multi-Linker ZIFs (termed as ML-ZIFs) with polar 2-mercaptoimidazolate (SHIm) and non-polar 2-methylimidazolate (mIm) linkers, characterized by PXRD, TGA, TEM, 1H NMR, N2 and CO2 isotherms. All the ML-ZIFs have sodalite (SOD) topologies with permanent porosity and thermal stability of up to 250 °C. Both Zn- and Co-based ML-ZIFs were efficient in the fixation of CO2 with epichlorohydrin (ECH) and propylene-oxide (PrO) substrates without co-catalyst, showing improved catalytic activity over their single-linker counterparts (ZIF-8 and ZIF-67). ML-ZIF 5Co (with Co metal center and Co(mIm)1.68(SHIm)0.32 composition) showed a maximum Turn-Over Frequency (TOF) of 893 and 787 h−1 for CO2 fixation with PrO and ECH, respectively.

CO2 capture using in-situ polymerized amines into pore-expanded-SBA-15: Performance evaluation, kinetics, and adsorption isotherms

Over the last decades, carbon dioxide capture has attracted lots of attention and different solution have been proposed, yet the global CO2 concentration is still increasing along with its environmental impacts. Covalently tethered amines were in-situ polymerized into mesoporous silica support, namely PE-SBA-15, for the reversible temperature swing CO2 adsorption. The in-situ polymerization approach shows high loadings of amines in comparison to the grafting technique which was confirmed via thermal decomposition and CHN elemental analysis. The covalent tethering of amines, evidenced by the characteristic absorption peaks via FTIR, resulted in good thermal stability of the sorbent and constant CO2 uptake during multicycle operation. Porosimetry analysis, pore volume and BET surface area, showed a noticeable decrease upon the functionalization of support indicating that most of the pores of the support are occupied by the amines. CO2 capture of the sorbent at different concentrations and temperatures, from 400 ppm for the direct air CO2 capture to 15 % CO2 for coal-powered plants showed good performance. A reduction in CO2 uptake was noticed upon the decrease in adsorption temperature with an optimum temperature of 25 °C. Adsorption kinetics were found to be best represented by a pseudo-second order model with significant adsorption rates. Dry adsorption isotherms of CO2 and N2 were studied at different temperatures and the CO2 isotherms were found to follow Langmuir dual site (LDS) model with a very high selectivity towards CO2. This study shows that in-situ polymerization is a key route for mitigating the continuous increase in atmospheric CO2 concentration.

Selective CO2/CH4 Separation by Fixed-Bed Technology Using Encapsulated Ionic Liquids

The performance of encapsulated ionic liquid (ENIL) sorbents has been experimentally evaluated in CO2/CH4 separation by means of gravimetric and fixed-bed measurements. Six ionic liquids (ILs) with CO2 chemical absorption ([Emim][Acetate], [Bmim][Acetate], [P66614][CNPyr], [Bmim][GLY], [Bmim][MET], and [Bmim][PRO]) were selected for the selective separation of CO2 from CH4. ENIL materials were prepared by encapsulation of these ILs in synthesized carbon submicrocapsules, achieving a ∼70% in mass of IL. Fixed-bed experiments of CO2 capture were carried out to evaluate the CO2/CH4 separation performance of prepared ENIL materials at different CO2 partial pressures and 303 K. Both thermodynamics and kinetics of CO2 sorption were analyzed. The experimental CO2 and CH4 isotherms in ENIL materials obtained from fixed-bed experiments were successfully compared to those obtained by reliable gravimetric tests and fitted to the Langmuir–Freundlich equilibrium model. In addition, experimental CO2 breakthrough curves were well-described by the linear driving force and Yoon and Nelson kinetic models, providing sorption rate constants. ENIL sorbents show high CO2 uptake capacity, comparable to conventional adsorbents, but with drastically higher selectivity, in concordance with the negligible CH4 solubility in ILs at the used operating conditions, with acetate-based ENIL materials being the best sorbents in thermodynamic terms. The obtained kinetic parameters revealed that the CO2 chemical sorption with ENIL materials overcomes the IL mass transfer limitations. The sorption rates are faster than those obtained with ENIL using IL physical absorbents and seem to be controlled by the reaction kinetics. The [P66614][CNPyrr]-based ENIL is found to be the most promising material, combining favorable kinetic and thermodynamic considerations for future development of CO2/CH4 separation using fixed-bed technology.

Influence of chain length on structural properties of carbon molecular sieving membranes and their effects on CO[formula omitted], CH[formula omitted] and N[formula omitted] adsorption: A molecular simulation study

Carbon molecular sieving membranes (CMSM) derived from 6FDA/BPDA-DAM polymer precursors (6F-CMSM) show excellent adsorption and selectivity towards CO2. Using molecular dynamics (MD) simulations, we investigate how the length of individual carbon chains determines the morphologies emerging from the same monomers. Smaller chains produce densely packed structures, whereas longer chains arrange in layers, creating larger voids comprising both micropores and ultra-micropores. The pure gas adsorption isotherms of CO2, CH4, and N2 inside various 6F-CMSM morphologies, obtained from MD, provide theoretical insights into most feasible structures formed in experiments, thereby providing an estimate of the corresponding 6F-CMSM density. Using grand canonical Monte Carlo simulations, we observe that high isosteric heats of adsorption for CO2 leads to enhanced adsorption capacity and high sorption selectivity from binary mixtures of these gases. Studying the asphericity of carbon chains, we report the existence of an optimum chain length of highest curvature, leading to low density, high porosity, and high CO2 adsorption capacities that compare well with available experimental data, without compromising sorption selectivity of 6F-CMSM. This work provides a theoretical basis of how slight modifications of the physical arrangements of chemical components lead to significant changes in porosity and gas adsorption capacities of molecular sieving membranes.

Design of highly microporous activated carbons based on walnut shell biomass for H2 and CO2 storage

Low-cost walnut shell-based carbons with high microporosity were prepared by simple one-step carbonization with chemical activation using KOH, exhibiting the promising potential to be a very good CO2 and H2 adsorbent. The physicochemical properties of the obtained carbons were characterized by N2 and CO2 adsorption isotherms, X-ray powder diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and elemental analysis. The activated carbon AC-800 was characterized by a highly developed specific surface area of 1868 cm2/g and a high micropore content of 0.94 cm3/g. It highly exhibited CO2 uptake in 1 bar was up to 9.54, 5.17, 4.33 mmol/g for 0, 25 and 40 °C, respectively. In addition, the H2 storage capacity was 3.15 mmol/g at 40 bars. Significantly, confirmed an exceptionally high dependency of CO2 and H2 uptake vs micropores structure of activated carbon. AC-800 also shows good selectivity for CO2/N2 and fast adsorption kinetics that be easily regenerated with superior cyclic stability after multiple cycles The experimental isotherm data of activated carbon produced from walnut shells were analyzed using Langmuir, Freundlich, Temkin, Sips, and Toth isotherm equations. The fitting details showed that the multitemperature Toth equation is a powerful tool to mathematically represent CO2 and H2 isotherms on activated carbon. The easy way of preparation and high capture abilities endow this kind of activated carbon attractive as a promising adsorbent for CO2 and H2 storage.

Fabrication and application of novel core–shell MIL-101(Cr)@UiO-66(Zr) nanocrystals for highly selective separation of H2S and CO2

Removal of H2S and CO2 is essential in diverse industrial applications such as natural gas treatment for avoiding their corrosion, toxicity, and environmental damages. To improve selective separation of H2S and CO2 at ambient temperature, we designed novel core–shell-structure MOFs based on a porous MIL-101(Cr) as seeds and a less porous UiO-66(Zr) shell. MU-4 and MU-8 nanocrystals, with different shell growth times, were synthesized and characterized by different techniques. The adsorption isotherms of H2S, CO2, CH4, and N2 on individual and hybrid samples were measured, using a volumetric method in a wide pressure region and at different temperatures. MU nanocrystals exhibited high adsorption capacity for both H2S (20.62 mmol g−1 at 15 bar) and CO2 (17.21 mmol g−1 at 35 bar), elevated up to 84.4 % and 121.8 % compared to pristine UiO-66(Zr). Most importantly, ideal adsorbed solution theory (IAST) showed that adsorption selectivity of H2S/CH4, H2S/N2, CO2/CH4, and CO2/N2 was significantly improved up to 7.8 %, 47.0 %, 32.1 % and 59.9 % at highest pressure compared to pristine MIL-101(Cr). Besides additional open metal sites, this high separation efficiency was ascribed to the size exclusion separation due to optimized pores diameter of MU nanocrystals. According to impressive preferential gas adsorption along with excellent cyclic adsorption–desorption performance and thermal stability, MU nanocrystals can broaden the horizon of H2S and CO2 capture and separation.

Gas-Phase Simulated Moving Bed for Methane/Nitrogen Separation Using a Commercial Activated Carbon

This work focuses on designing and developing a simulated moving bed (SMB) process for the separation of methane and nitrogen mixtures, using a commercial activated carbon (BPL) as the adsorbent material and two potential desorbent gases: argon and carbon dioxide. As such, the material performance was evaluated by measuring the adsorption equilibrium data and the dynamic behavior of single and multicomponent adsorption through fixed-bed experiments. The pure component isotherms of N2, CH4, Ar, and CO2 were measured at 303, 323, and 343 K in a pressure range of 0–2.5 bar using a volumetric apparatus, with CO2 exhibiting the highest affinity to the stationary phase and Ar the lowest. The data was regressed against the dual-site Langmuir (DSL) model. Single, binary, and ternary breakthrough curves were also assessed, allowing the validation of the proposed mathematical model. Two SMB cycles were employed to separate an equimolar CH4/N2 mixture using each desorbent gas to evaluate the impact of the desorbent strength in the process. The respective separation regions were drawn. Both cycles were capable of producing a high-purity methane stream (96.2 and 97.4% for the Ar and CO2 experiment, respectively) with high recovery (>92%). When argon is used as the desorbent gas, the extract product stream is obtained with productivity of 14.1 kg·m–3ads·h–1.

Temperature Effects in Flexible Adsorption Processes for Amorphous Microporous Polymers.

A collection of atomistic molecular simulations is reported that illustrate the impact of adsorption temperature on species uptake and adsorbate-induced structural rearrangement for amorphous polymers of intrinsic microporosity. Temperature-sensitive structural rearrangement is evaluated by contrasting two methods: standard grand canonical Monte Carlo simulations using a rigid framework approximation and a combined Monte Carlo/molecular dynamics approach that fully incorporates framework flexibility. We report single-component gas phase adsorption isotherms for CH4, C2H4, C2H6, C3H6, C3H8, and CO2 across a temperature range of 250-400 K for models of an archetypal polymer of intrinsic microporosity, PIM-1. A quadratic model is presented that captures two main mechanisms of temperature-dependent adsorption-induced deformation of PIM-1 up to a relative swelling of 1.15: thermal expansion and an increased propensity to swell as a function of species uptake. Two case studies are reported that highlight the critical role of operating temperature in industrial storage and separation applications. The first study focuses on methane storage and delivery applications using a pressure-temperature swing adsorption application (PTSA). We demonstrate that larger working capacities are accompanied by increased volumetric strain between adsorption-desorption steps. The second case study considers PIM-1 as an adsorbent to separate an exemplar ternary syngas mixture at operating temperatures ranging 300-550 K. A temperature threshold of ∼400 K is identified, beyond which adsorption-induced PIM-1 swelling is negligible and the solubility selectivity-loading curve transitions to exhibiting a nearly linear relationship.

Elucidating the role of adsorption during artificial photosynthesis: H2O and CO2 adsorption isotherms over TiO2 reveal thermal effects under UV illumination.

Adsorption measurements of CO2 and H2O over TiO2 surfaces in dark and under illumination were carried out to reveal the ensuing bottlenecks of the initial steps of the artificial photosynthesis reaction. When the adsorption isotherms of both CO2 and H2O were measured under illumination, the results were comparable to isotherms measured at higher temperatures in dark. This evidence is interpreted as the presence of hot spots, due to charge carrier recombination reactions. Differential heat of adsorption measurements revealed that H2O adsorption on TiO2 is stronger, and with a higher coverage than that of CO2. Dissociation of water is an energetically uphill reaction, and the local hot spots due to charge carrier recombination in indirect bandgap semiconductors can enhance the reaction probability. At higher temperatures, higher reaction probabilities are expected and estimated by a thermodynamic analysis for water splitting reaction. The potential role of these hot spots during natural and artificial photosynthetic reactions is discussed.

Boosting Electrocatalytic CO 2 Reduction with Conjugated Bimetallic Co/Zn Polyphthalocyanine Frameworks

Boosting Electrocatalytic CO ₂ Reduction with Conjugated Bimetallic Co/Zn Polyphthalocyanine Frameworks

Assessment of density functional approximations for N2 and CO2 physisorption on benzene and graphene.

Experimental isotherms of N2 and CO2 on carbon‐based porous materials and models of the physisorption of gases on surfaces are used to obtain the pore size distribution (PSD). An accurate modelization of the physisorption of N2 and CO2 on the surface of carbon‐based porous materials is important to obtain accurate N2 and CO2 storage capacities and reliable PSDs. Physisorption depends on the dispersion interactions. High precision ab initio methods, such as CCSD(T), consider accurately the dispersion interactions, but they are computationally expensive. Double hybrid, hybrid and DFT‐based methods are much less expensive. In the case of graphene, there are experimental data of the adsorption of N2 and CO2 on graphite that can be used to build the Steele interaction potential of these gases on graphene. The goal is to find out hybrid and/or DFT methods that are as accurate as the CCSD(T) on benzene and as accurate as the experimental results on graphene. Calculations of the interaction energy curves of N2 and CO2 on benzene and graphene have been carried out using the CCSD(T) method and several double hybrid, hybrid, and DFT methods that consider the dispersion interactions. The energy curves on benzene have been compared to the CCSD(T) and the energy curves on graphene have been compared with the Steele energy curves. The comparisons indicate that double hybrids with dispersion corrections and ωB97 based DFT methods are accurate enough for benzene. For graphene, only the PBE‐XDM functional has a good agreement with the Steele energy curves.

A silk-like hydrogen-bonded organic framework functionalized membrane with intrinsic catalytic activity for nonmetallic reduction of 4-nitrophenol

Investigating the hydrogen-bonded organic frameworks (HOFs) with intrinsic functions has been a great challenge for the development of HOF materials. In this paper, an efficient way of obtaining a HOF with intrinsic catalytic activity is presented. A microporous HOF-PyTTA was self-assembled by using 4,4′,4′',4′''-(pyrene-1,3,6,8-tetrayl) tetraaniline (PyTTA) as an organic monomer. The monomer has a pyrene ring with a conjugated structure, which is conducive to the construction of large-area π-π interactions, therefore improving the stability of the HOF structure. The amino-functional group of the monomer serves as the active site which enables the HOF-PyTTA, which acts as a non-metallic catalyst to catalyze the conversion of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The permanent pore structure of the HOF-PyTTA was confirmed by X-ray single-crystal diffraction and CO2 isotherm adsorption experiments. To broaden the application of HOF-PyTTA, we propose growing HOF-PyTTA on the filter membranes of diverse materials and making a catalytic column by filling the HOF-PyTTA/glass fiber membrane into the syringe. After pouring the mixture of 4-NP and NaBH4 into the catalytic column, 4-NP was converted into 4-AP with a high rate of conversion. This work develops a simple, robust, and flexible HOF with intrinsic catalytic reduction activity for 4-NP, and broadens the application of HOF for functional modification and catalytic application.