CO2 Adsorption-desorption Isotherms Research Articles

From fundamental materials chemistry to sensing applications: Unravelling the water adsorption mechanism of a luminescent optical fibre sensor membrane

This work provides insight into the correlation between the luminescent response of a water-vapour optical fibre sensor and the textural properties of its lanthanide-doped silica coating. To this end, a library of 16 silica xerogels derived from combinations between 2 lanthanide dopants (EuIII, TbIII) and 8 antenna ligands was synthesised and characterised by photoluminescence spectroscopy and N2 and CO2 adsorption-desorption isotherms, among others. Based on the best luminescent response and most-suited porous texture, the material doped with TbIII and 2,2′-(4-(2-Ethoxyethoxy)pyridine-2,6-diyl)bis(4,5-dihydrooxazole) was selected to construct the probe. A film of this material was affixed to a commercial silica fibre by dip-coating and the resulting sensor was tested in a climatic chamber with relative humidity ranging from 20 to 90% to obtain normalised time-response and calibration curves at three temperatures. The response was linear up to certain water-vapour concentrations, beyond which abruptly changed to polynomial, acting against the sensor resolution. The adsorption mechanism was elucidated by comparing the isosteric enthalpies of adsorption calculated from the sensor calibration curves to those determined from the monolith water-vapour isotherms, revealing that capillary condensation in the membrane mesopores was the key phenomenon leading to the response deviating from linearity.

Microwave-Assisted Synthesis of Zeolite A from Metakaolinite for CO2 Adsorption.

The global demand for energy and industrial growth has generated an exponential use of fossil fuels in recent years. It is well known that carbon dioxide (CO2) is mainly produced, but not only from fuels, which has a negative impact on the environment, such as the increasing emission of greenhouse gases. Thus, thinking about reducing this problem, this study analyzes microwave irradiation as an alternative to conventional heating to optimize zeolite A synthesis conditions for CO2 capture. Synthesis reaction parameters such as different temperatures (60-150 °C) and different time durations (1-6 h) were evaluated. The CO2 adsorption capacity was evaluated by CO2 adsorption-desorption isotherms at 25 °C and atmospheric pressure. The results showed that the synthesis of zeolite A by microwave irradiation was successfully obtained from natural kaolinite (via metakaolinization), reducing both temperature and time. Adsorption isotherms show that the most promising adsorbent for CO2 capture is a zeolite synthesized at 100 °C for 4 h, which reached an adsorption capacity of 2.2 mmol/g.

Delineating the effects of pore structure and N-doping on CO2 adsorption using coco peat derived carbon

The CO2 adsorption capacity of carbon materials depends on their structural properties and chemical nature of the functionalization of carbon networks. In this work, amorphous carbon materials are derived from coco peat by activation using KOH and melamine. These are studied to determine the relative influence of pore size distribution and N-doping effect on CO2 adsorption capacity at 298 K and 1 bar. Melamine is used as a pore-directing template and N-doping agent in the preparation of ultra-microporous carbons. The surface areas and ultra-micropore volumes of carbon materials are estimated by NLDFT method based on CO2 adsorption-desorption isotherms at 273 K which vary from 753 m2 g−1 to 1702 m2 g−1 and from 0.13 cm3 g−1 to 0.33 cm3 g−1, respectively. Contrary to many theoretical and experimental studies where N-doping in carbon is reported to have a positive impact on CO2 adsorption, the present study does not indicate any beneficial effect of nitrogen content in biomass-derived carbon while the pore size distribution has a profound effect on CO2 adsorption. A direct correlation has been observed between ultra-micropore (< 0.7 nm) volume and the CO2 adsorption capacity. This study demonstrates that pore size distribution can be tuned in coco peat-derived carbons to achieve maximum CO2 adsorption capacity of 4.8 mmol g−1 at 298 K and 1 bar. It is, therefore, possible to utilize biomass materials to generate carbons with suitable pore size distribution and pore volume for CO2 capture effectively at room temperature.

Kaolinite-based zeolites synthesis and their application in CO2 capture processes

In light of the urgent need of reducing the atmospheric CO2 emissions, the use of low-cost adsorbents, that exhibit a high affinity and CO2 adsorption capacity, is a promising method from the economic and environmental point of view to separate CO2 from the flue gas emitted from large sources of emissions like power-fueled plants. Clay minerals are low-cost raw materials with high availability all over planet and great versatility in the fields of adsorption and catalysis processes. The present study pretends to elucidate the link between the reaction conditions during the synthesis of the zeolite from kaolinite and its CO2 adsorption capacity. For that purpose, the type A zeolite was synthesized via hydrothermal process in alkaline solution using metakaolinite as a starting material. The metakaolinite was obtained by calcination of kaolinite at 600 °C and some parameters such as temperature and synthesis time were modified to optimize the synthesis aiming for a high CO2 adsorption capacity adsorbent. Synthesized materials were characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), N2 adsorption–desorption at −196 °C and CO2 adsorption at 0 °C (up to 10 bars) isotherms and Nuclear Magnetic Resonance of solids (NMR). In addition, the adsorption capacity of CO2 was evaluated by means of CO2 adsorption–desorption isotherms at 25 °C up to atmospheric pressure. The obtained results indicated that synthesized zeolite 4A can be successfully prepared from natural kaolinite (via metakaolinization) at 100 °C for 48 h under alkaline conditions, showing chemical and physical properties similar to that of the commercial 4A zeolite.

Sorption mechanisms of diethyl phthalate by nutshell biochar derived at different pyrolysis temperature

The sorption properties of diethyl phthalate (DEP) by four series of biochar samples produced from apricot shell, coconut shell, peanut shell and walnut shell at 300–800 ℃ were investigated. The morphology, physical structure and chemical composition of biochar were characterized by SEM, N2 and CO2 adsorption-desorption isotherms, elemental analysis, 13C NMR, FTIR and TGA, showing that with the increase of pyrolysis temperature, the yield and polarity of biochar decreased, while the aromaticity increased. All the sorption isotherms were fitted by Freundlich model and exhibited highly nonlinear with n ranging from 0.16 to 0.55. Compared with higher-temperature biochar (HBCs, 500–700 ℃), the lower-temperature biochar (LBCs, ≤ 400 ℃) had stronger sorption intensity in each series due to specific interaction (e.g. hydrogen bonding) between the polar functional groups in LBCs (ASBs, WSBs and PSBs) and DEP molecules. Differently, the sorption interactions between HBCs and DEP were mainly driven by the surface adsorption at the energy sites and the 800 ℃-derived biochars with high specific surface area (415.13–454.17 m2/g) were the strongest in the same series. Peanut shell derived-biochar with higher Koc (Ce=0.1Sw) values of 358–3670 L/kg had excellent sorption performance, suggesting its promising potential for remediation of DEP in the environment. CapsuleThe underlying sorption mechanisms of diethyl phthalate (DEP) by four series of nutshell biochar derived at different pyrolysis temperature (300–800 ℃) were investigated.

Fluorous Metal–Organic Frameworks with Unique Cage-in-Cage Structures Featuring Fluorophilic Pore Surfaces for Efficient C 2 H 2 /CO 2 Separation

Fluorous Metal–Organic Frameworks with Unique Cage-in-Cage Structures Featuring Fluorophilic Pore Surfaces for Efficient C ₂ H ₂ /CO ₂ Separation

Comprehensive Analysis of Hierarchical Porous Carbons Using a Dual-Shape 2D-NLDFT Model with an Adjustable Slit-Cylinder Pore Shape Boundary.

A thorough characterization of the textural properties of hierarchical porous carbons (HPCs) is of utmost importance as it provides information that aids in the selection of a suitable material for a given application and in understanding the phenomena observed once the material becomes part of a system. Gas adsorption-desorption isotherms coupled with the application of density functional theory (DFT) models to these isotherms are common tools for the textural characterization of HPCs, for which pore shape is an essential factor for the determination of pore size distributions (PSDs). By analyzing the experimental adsorption data of a series of CO2-activated HPCs with a progressive development of porosity, it is shown that artifacts are found in the derived PSDs when a slit-cylinder pore shape boundary is fixed at 2 nm, which is the case for the original dual-shape nonlocal DFT (2D-NLDFT-HS) and hybrid quenched solid DFT (QSDFT) models. This study presents a new dual-shape 2D-NLDFT-HS (DS-HS) model that, combined with the 2D-NLDFT-HS model for CO2, provides the possibility of analyzing simultaneously N2 and CO2 adsorption-desorption isotherms and adjusting at the same time the limits for the assumed slit and cylindrical pore shapes. Using the DS-HS approach and adjusting the slit-cylinder boundary at 3 nm allowed eliminating PSDs artifacts. The interactive adjustment of the slit-cylindrical pore shape boundary of the DS-HS model represents a major advantage of this approach allowing for a comprehensive analysis of the adsorption data and a more accurate description of the textural properties of HPC materials.

Imparting Superhydrophobicity to Porphyrinic Coordination Frameworks Using Organotin

Imparting Superhydrophobicity to Porphyrinic Coordination Frameworks Using Organotin

Application of Octadecylamine-Based Adsorbent on Carbon Dioxide Capture

Porous surface of silica gel (SG) have been modified with alkyl fatty amine compounds (octadecylamine, ODA) via wet impregnation process. The ODA-based adsorbents were physically characterized by XRD. The presence of crystalline peaks on ODA/SG diffractograms were ascertained the well-dispersion of ODA on the SG surface. XRD analysis displayed the increasing intensity of crystalline ODA with higher percent amine loaded and shifting of the several crystalline peaks of ODA verified the interaction of SG600-ODA. Capacity of CO2 capture by prepared solid adsorbents were evaluated using CO2 adsorption-desorption isotherms. This study shows that increasing percentage of ODA were improved the amount of CO2 uptake by following this trend: 35ODA/SG &gt; 25ODA/SG &gt; 15ODA/SG &gt; SG &gt; 5ODA/SG. However, promotion of 5 wt.% ODA unabled to enhance the capacity of CO2 captured due to pore blockage and reduction in SG pore surface, thus hindered the physisorption between CO2 and SG.

Study of the Active Carbon from Used Coffee Grounds as the Active Material for a High-Temperature Stable Supercapacitor with Ionic-Liquid Electrolyte.

This study reveals a simple approach to recycle wasted coffee grounds into highly valuable carbon material with superior electrochemical performance. Activated carbon prepared from wasted coffee grounds has been formed via hydrothermal acidic hydrolysis followed by a KOH chemical activation at 800 . To understand the electrochemical properties of the sample, a set of characterization tools has been utilized: N2 and CO2 adsorption–desorption isotherms, thermal gravimetric analysis, Fourier transform infrared spectroscopy, Raman spectroscopy and scanning electron microscopy. The specific surface area obtained from a Brunner–Emmett–Teller (BET) analysis reached . Prepared sample (designated as ACG-800KOH) was tested as electrode material in an electric double layer capacitor (EDLC) device with ionic liquid PYR13-TFSI as an electrolyte. The EDLC test was conducted at temperatures ranging from 20 to 120 . The specific material capacitance reached 178 measured at 20 and 50 A and was in the range 182 to 285 at the 20 to 120 temperature range.

Extension of BET theory to CO2 adsorption isotherms for ultra-microporosity of covalent organic polymers

Usually, nitrogen and argon adsorption–desorption isotherms are used at their respective boiling points for the determination of specific surface area via the BET theory of microporous materials. However, for ultra-micropores, where nitrogen and argon cannot access at cryogenic temperatures, the CO2 adsorption–desorption isotherms have been considered as alternative options for the determination of specific surface area by extending BET theory, but the surface area determined by using CO2 adsorption–desorption isotherms is not significant due to strong CO2-CO2 interactions. In this study, the microporous covalent organic polymers are subjected to nitrogen and CO2 adsorption–desorption isotherms and the results showed that a clear linear region is available in isotherms, which confirms the presence of ultra-micropores. The surface area determined by the CO2 adsorption–desorption isotherms is higher than the surface area determined by N2 adsorption–desorption isotherms. These results indicate that the microporous covalent organic polymers contain ultra-micropores where only CO2 can reach, while nitrogen and argon cannot access at cryogenic conditions because their kinetic diameter is larger than CO2.

Green synthesis of a magnetic β-cyclodextrin polymer for rapid removal of organic micro-pollutants and heavy metals from dyeing wastewater

Adsorption is one of the most preferred techniques in the advanced treatment of dyeing wastewater. Magnetic porous materials with good adsorption performance, excellent reusability, and a green synthesis route are highly desirable adsorbents in commerce. In this study, we synthesized a magnetic β-cyclodextrin polymer (MNP-CM-CDP) containing many macro- and ultramicropores in aqueous phase. CO2 adsorption-desorption isotherms and a dye adsorption method provided Langmuir specific surface areas for the MNP-CM-CDP of 114.4 m2 g−1 and 153 m2 g−1, respectively. Model pollutants (BPA, MB, BO2, RhB, Cr(III), Pb(II), Zn(II), and Cu(II)) were rapidly and efficiently removed from the aqueous solution by the MNP-CM-CDP. In addition, the polymer could be easily separated from the solution under an external magnetic field. The adsorption of the contaminants was dependent on pH, while the effects of ionic strength and humic acid were slight in the concentration range studied. The polymer could be easily regenerated at room temperature and retained good adsorption performance. Moreover, the MNP-CM-CDP showed good feasibility for the removal of pollutants from actual dyeing wastewater samples.

Facile preparation of cross-linked polyimide aerogels with carboxylic functionalization for CO2 capture

In this study, highly cross-linked and completely imidized polyimide aerogels containing carboxyl groups were successfully synthesized using a mild sol-gel method at room temperature from 3,5-diaminobenzoic (DABA) and biphenyl-3,3′,4,4′-tetracarboxylic (BPDA) and cross-linked with 1,3,5-triaminophenoxybenzene. The densities of the obtained polyimide aerogels are between 0.116 and 0.386g/cm3, the specific surface areas range from 173 to 461m2/g, and the porosities are as high as 97%. The CO2 adsorption-desorption isotherms are reversible, and the CO2 uptakes at 25°C and 1bar are as high as 21.10cm3/g, which are comparable to those of previously reported microporous organic polymers. The high CO2 adsorptions are attributed to the abundance of electron-rich heteroatoms in the polyimide networks and to the presence of carboxyl groups, a type of CO2-philic group. The facile preparation and high CO2 adsorptive capacity indicate that polyimide aerogels may be ideal candidates for capturing CO2.

Photochemical reactivity of apical oxygen in KSr2Nb5O15 materials for environmental remediation under UV irradiation

The photocatalytic activity of a series of novel KSr2Nb5O15 materials was studied using the photooxidation of methylene blue as model reaction. The influence of the calcination time upon the crystalline structure and photoactivity was verified. Characterization was performed by XRD, SEM, FTIR, UV–Vis/DR, Helium picnometry, and N2 and CO2 adsorption-desorption isotherms. The diffraction line profile and the refinement of the structural parameters of KSr2Nb5O15 were obtained from the XRD patterns by the Rietveld method. Data showed that samples were photoactive under UV irradiation, regardless the synthesis conditions. However, the calcination time had a clear influence upon the photocatalytic activity of the samples, being more efficient towards the degradation of the dye those obtained at a lower calcination time. Indeed, the sample calcined for 4h showed up to 4 times higher photocatalytic activity than commercial TiO2. Additionally, a correlation between the photocatalytic activity and the displacement of the Nb ion from the central position in the [NbO6] octahedron was found. It is suggested that this fact causes an important polarization of the niobate structure. The apical oxygen in these samples is very reactive and can lead to the formation of superoxoradical anions (O2-) showing that KSr2Nb5O15 can be potentially used in photocatalytic reactions under UV irradiation.

Preparation and characterization of chemically activated carbon materials for CO2capture

Activated carbon (AC) has attracted considerable interest because of its low cost, availability, facile tunability, and thermal stability. In this work, chemically activated carbon materials were prepared with different amounts of KOH (i.e., AC/KOH ratios of 1:1, 1:2, 1:3, and 1:4). The specific surface area and micropore volume were analyzed via N2 adsorption- desorption isotherms at 77 K. The CO2 adsorption capacity was investigated by CO2 adsorption-desorption isotherms at 298 K and 1 bar. The indoor CO2 capture capacities of the samples were examined in a manufactured chamber at the laboratory scale. The K2-AC sample exhibited a large specific surface area (1507 m2/g) and high total pore volume (0.670 cm3/g) and micropore volume (0.580 cm3/g). The prepared KOH-AC samples exhibited a high CO2 capture capacity of 144.5 mg/g (at an AC/KOH ratio of 1:2). Therefore, we proved that the CO2 capture capacity is significantly affected by chemical activation.

Silica-coated multi-walled carbon nanotubes impregnated with polyethyleneimine for carbon dioxide capture under the flue gas condition

In this study, silica-coated multi-walled carbon nanotubes impregnated with polyethyleneimine (PEI) were prepared via a two-step process: (i) hydrolysis of tetraethylorthosilicate onto multi-walled carbon nanotubes, and (ii) impregnation of PEI. The adsorption properties of CO2 were investigated using CO2 adsorption–desorption isotherms at 298K and thermogravimetric analysis under the flue gas condition (15% CO2/85% N2). The results obtained in this study indicate that CO2 adsorption increases after impregnation of PEI. The increase in CO2 capture was attributed to the affinity between CO2 and the amine groups. CO2 adsorption–desorption experiments, which were repeated five times, also showed that the prepared adsorbents have excellent regeneration properties.

Synthesis of nitrogen-doped carbon with three-dimensional mesostructures for CO2 capture

The objective of this research was to develop a new CO2 sorbent, three-dimensional nitrogen-doped mesoporous carbon (KIT-6-CN). KIT-6-CN was synthesized by nano-replication using carbon tetrachloride and ethylenediamine as precursors, and KIT-6 with cubic Ia3d symmetry as a hard template. The new CO2 sorbent has a relatively high BET surface area of 587 m2/g, a high pore volume of 0.91 cm3/g, and the mesostructures with pore diameters centered at 1.7 and 6.3 nm. The transmission electron microscopy of the KIT-6-CN shows that after removal of silica by NaOH, KIT-6-CN possesses three-dimensional mesoporous structure. CO2 adsorption–desorption isotherms indicate that this nitrogen-doped material has relatively high CO2 capture capacities of 2.11 mmol/g at 25 °C and 3.09 mmol/g at 0 °C, which are superior to those of the pure carbon material (KIT-6-C) with analogous mesostructures. Cyclic CO2 sorption–desorption tests demonstrated the stability of the sorbent. Thus, the new sorbent can potentially be a good candidate for CO2 capture.

Synthesis and characterization of novel hyperbranched poly(imide silsesquioxane) membranes

AbstractA new family of hyperbranched polymers with chemical bonds between the hyperbranched polyimide and polysilsesquioxane network was synthesized by the reaction of an amine‐terminated aromatic hyperbranched polyimide with 3‐glycidoxypropyl trimethoxysilane, followed by hydrolysis and polycondensation in the presence of an acid catalyst. The hyperbranched poly(imide silsesquioxane) membranes were fabricated by the casting the aforementioned polymer solution onto a NaCl optical flat, which was followed by heating at 80 °C for 24 h. The membranes were characterized by Fourier transform infrared, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy, N2 adsorption and desorption, and CO2 adsorption and desorption. The presence of covalent bonds between the hyperbranched polyimide and polysilsesquioxane segments had a significant effect on the properties of the membranes. N2 adsorption–desorption isotherms for these membranes showed surface areas of 6–16 m2/g, whereas CO2 adsorption–desorption isotherms showed much higher surface areas in the range of 106–127 m2/g. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3736–3743, 2003