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Ternary supertetrahedral chalcogenolate clusters were interlinked with bipyridines into a microporous semiconducting framework with properties qualitatively different from those of the original clusters. Both the framework and the clusters were effective photocatalysts, and rapidly degraded the dye rhodamine B., AuthorCount:4

A method to form ordered mesoporous silica based on the use of folate supramolecular templates has been developed. Evidence based on in situ small-angle X-ray scattering (SAXS), electron microscopy, infrared spectroscopy, and in situ conductivity measurements are used to investigate the organic inorganic interactions and synthesis mechanism. The behavior of folate molecules in solution differs distinctively from that of surfactants commonly used for the preparation of ordered mesoporous silica phases, notably with the absence of a critical micellar concentration. In situ SAXS studies reveal fluctuations in X-ray scattering intensities consistent with the condensation of the silica precursor surrounding the folate template and the growth of the silica mesostructure in the initial stages. High-angle X-ray diffraction shows that the folate template is well-ordered within the pores even after a few minutes of synthesis. Direct structural data for the self-assembly of folates into chiral tetramers within the pores of mesoporous silica provide evidence for the in register stacking of folate tetramers, resulting in a chiral surface of rotated tetramers, with a rotation angle of 30 degrees. Additionally, the self-assembled folates within pores were capable of adsorbing a considerable amount of CO2 gas through the cavity space of the tetramers. The study demonstrates the validity of using a naturally occurring template to produce relevant and functional mesoporous materials., AuthorCount:6;Funding agencies:Swedish Research Council 2009-4716; Swedish Energy Agency; Spanish Ministry of Sport and Education JC2009-00141

In general, the post-combustion capture of CO2 is costly; however, swing adsorption processes can reduce these costs under certain conditions. This review highlights the issues related to adsorption-based processes for the capture of CO2 from flue gas. In particular, we consider studies that investigate CO2 adsorbents for vacuum swing or temperature swing adsorption processes. Zeolites, carbon molecular sieves, metal organic frameworks, microporous polymers, and amine-modified sorbents are relevant for such processes. The large-volume gas flows in the gas flue stacks of power plants limit the possibilities of using regular swing adsorption processes, whose cycles are relatively slow. The structuring of CO2 adsorbents is crucial for the rapid swing cycles needed to capture CO2 at large point sources. We review the literature on such structured CO2 adsorbents. Impurities may impact the function of the sorbents, and could affect the overall thermodynamics of power plants, when combined with carbon capture and storage. The heat integration of the adsorption-driven processes with the power plant is crucial in ensuring the economy of the capture of CO2, and impacts the design of both the adsorbents and the processes. The development of adsorbents with high capacity, high selectivity, rapid uptake, easy recycling, and suitable thermal and mechanical properties is a challenging task. These tasks call for interdisciplinary studies addressing this delicate optimization process, including integration with the overall thermodynamics of power plants., AuthorCount:4

Porous tablets of crystalline calcium carbonate were formed upon sintering of a precursor powder of amorphous calcium carbonate (ACC) under compressive stress (20 MPa) at relatively low temperatures (120-400 degrees C), induced by pulsed direct currents. Infrared spectroscopy ascertained the amorphous nature of the precursor powders. At temperatures of 120-350 degrees C and rates of temperature increase of 20-100 degrees C min(-1), the nanoparticles of ACC transformed into crystallites of mainly aragonite, which is generally difficult to achieve using wet-chemicals under kinetic control. The amorphous precursor particles (similar to 10 nm) transformed into crystallites (similar to 30-50 nm) during sintering. Consistently, the specific surface areas of 140-160 m(2) g(-1) for the precursor particles were reduced to 10-20 m(2) g(-1) for the porous tablets. The porous network within the tablets consisted of fused aragonite and vaterite particles in a ratio of similar to 80 : 20. The fraction of aragonite to vaterite was invariant to the temperature and rate of temperature change used. The particle size increased only to a small amount on an increased rate of temperature change. At temperatures above 400 degrees C, porous tablets of calcite formed. The later transformation was under thermodynamic control, and led to a minor reduction of the specific surface area. The size of the crystallites remained small and the transformation to calcite appeared to be a solid-state transformation. Porous, template-and binder-free tablets of calcium carbonate could find applications in for example, biology or water treatment., AuthorCount:5

Classical molecular dynamics and Grand Canonical Monte Carlo simulations are carried out for sorbates (CO2 and N-2) in zeolite NaKA using a universal type ab initio force field. By combining the results of these simulations, we reproduce the CO2 uptake as a function of the K+ content in the zeolite NaKA as measured experimentally by Liu et al.(1) The experiment yielded an exceptionally high CO2-over-N-2 selectivity of >200 at a specific K+/(K+ + Na+) ratio of 17 atom %. This high selectivity could be attributed to the nonlinear uptake dependency of the K+/(K+ + Na+) ratio measured for both CO2 and N-2. Additionally, our simulations show a strong coupling between the self-diffusion of CO2 and the site-to-site jumping rate of the extra-framework cations. These results show that this nonlinear uptake dependency of CO2 is the result of molecular sieving. Following this, our simulations conclude that contributions must be taken into account when modeling the uptake of this and similar materials both thermodynamic and kinetic with the same functionalities., AuthorCount:3

Cationic surfactants of the quaternary ammonium bromide type C(16)TABr, C(14)TABr, C(12)TABr, and C(10)TABr were adsorbed from aqueous solutions onto three different types of activated carbons and compared with the adsorption of the anionic surfactant sodium dodecyl benzene sulfonate. The concentrations of both cationic and anionic surfactants in aqueous solutions were determined by UV spectroscopy. In the case of anionic surfactants, a linear dependence of UV absorbance on the surfactant concentration at 200 nm can be related to the benzene fragment of the molecule. The UV sensitivity of C(n)TABr solutions is controlled by the hydration of bromide counterions, the electron dense nature of bromine, and a charge-transfer-to-solvent phenomenon. Changes in the textural properties of the activated carbons after adsorption of surfactants were studied by N-2 adsorption and mercury intrusion porosimetry, and could be correlated to surface characteristics and adsorptive capacity. The mechanism of adsorption was found to be complex, but the porous structure of the carbon exerted a critical role and the cationic surfactants were adsorbed step-by-step. At low surfactant concentrations, adsorption occurred in micropores. We conclude that surfactants are adsorbed as individual molecules. Adsorption from more concentrated solutions occurs in meso- and macropores, and resembles surfactant adsorption on flat carbon surfaces. The carbons display somewhat different tendencies to adsorb C(n)TABr. Activated carbons with small pores of 0.56-0.77 nm appear to be most effective for surfactant removal. A negative electrostatic potential on the interface of the carbons appears to enhance the adsorption of cationic surfactants, as would be expected. Controlling the electrostatic potential and pore size distribution of the activated carbons would be beneficial in the application of activated carbons for removal of surfactants from wastewater., AuthorCount:3;Funding agencies:Swedish Institute;Swedish Energy Agency

We report on a new series of isoreticular frameworks based on zinc and 2-substituted imidazolate-4-amide-5-imidate (IFP-14, IFP=imidazolate framework Potsdam) that form one-dimensional, microporous hexagonal channels. Varying R in the 2-substitued linker (R=Me (IFP-1), Cl (IFP-2), Br (IFP-3), Et (IFP-4)) allowed the channel diameter (4.01.7 angstrom), the polarisability and functionality of the channel walls to be tuned. Frameworks IFP-2, IFP-3 and IFP-4 are isostructural to previously reported IFP-1. The structures of IFP-2 and IFP-3 were solved by X-ray crystallographic analyses. The structure of IFP-4 was determined by a combination of PXRD and structure modelling and was confirmed by IR spectroscopy and 1H MAS and 13C CP-MAS NMR spectroscopy. All IFPs showed high thermal stability (345400?degrees C); IFP-1 and IFP-4 were stable in boiling water for 7 d. A detailed porosity analysis was performed on the basis of adsorption measurements by using various gases. The potential of the materials to undergo specific interactions with CO2 was investigated by measuring the isosteric heats of adsorption. The capacity to adsorb CH4 (at 298 K), CO2 (at 298 K) and H2 (at 77 K) at high pressure were also investigated. In situ IR spectroscopy showed that CO2 is physisorbed on IFP-14 under dry conditions and that both CO2 and H2O are physisorbed on IFP-1 under moist conditions., AuthorCount:18

Adsorption-driven separation of CO2 from flue gas has the potential to cut the cost for carbon capture and storage. Among the porous physisorbents, metal-organic frameworks (MOFs) are a class of promising candidates for gas separation and storage owing to their extraordinarily high specific surface areas and pore volumes, and predesigned pore structures. Here, we report three interpenetrated MOFs composed of Zn4O clusters and rigid dicarboxylate anions, namely SUMOF-n (SU StockholmUniversity; n = 2, 3, 4). All the interpenetrated MOFs possess small pores of two different types and high pore volumes. SUMOF-2 had a structure similar to interpenetrated MOF-5, but with an extra-framework cation present in one of the two types of pores. SUMOF-3 was an interpenetrated version of IRMOF-8 while SUMOF-4 crystallized with mixed linkers, biphenyl-4,4'-dicarboxylic acid and benzene-1,4-dicarboxylic acid. Among the three SUMOFs, SUMOF-4 had the largest specific surface area (1612 m(2) g(-1)) and pore volume. Single component adsorption of CO2 and N-2 was determined at 273 K. We showed that the interpenetrated SUMOF-2 adsorbedmore CO2 than non-interpenetrated MOF-5 under 273 K and 1 bar. This may be explained by the increased electric field gradients due to the interpenetration in the MOF. The uptake of CO2 for SUMOF-2 and SUMOF-4 was significant at somewhat higher pressure. Their CO2 isotherms were close to linear, which could be beneficial for separation of CO2 via pressure swing adsorption from biogas or natural gas. On the other hand, SUMOF-3 adsorbed most CO2 at pressures relevant for CO2 capture from flue gas., AuthorCount:6

The adhesive properties of gastroliths from a freshwater crayfish (Cherax quadricarinatus) were quantified by colloidal probe atomic force microscopy (AFM) between heavily demineralized gastrolith microparticles and gastrolith substrates of different composition. Combined AFM and transmission electron microscopy studies demonstrated that the sequential detachment and large adhesion energies that characterise the adhesive behaviour of a native gastrolith substrate are dominated by sacrificial bonds between chitin fibres and between chitin fibres and CaCO3. The sacrificial bonds were shown to be strongly related to the gastrolith proteins and when the majority of these proteins were removed by ethylenediaminetetraacetic acid (EDTA), the sequential detachment disappeared and the adhesive energy was reduced by more than two orders of magnitude., AuthorCount:9

Silicoaluminophosphates (SAPO-17, SAPO-35, SAPO-56 and SAPO-RHO) synthesised via hydrothermal means are tested for their abilities to adsorb carbon dioxide. These 8-ring microporous phosphates show high capacities to adsorb CO2. SAPO-RHO has a high uptake of CO2 and a very low uptake of N-2 due to its narrow pore window aperture at 273 K. Its significant uptake of N-2 at 77 K is rationalised by a temperature induced shrinkage effect. SAPO-56 has a slightly higher CO2 capacity (5.42 mmol/g, 273 K, 101 kPa) and is less water sensitive than zeolite 13X. Cyclic adsorption and in situ infrared spectroscopy (IR) reveal that SAPOs retain 95% of their original CO2 capacity after six cycles and that adsorption occurs via physisorption. The calculated heat of adsorption for CO2 (at 0.2-0.7 mmol/g loading) on SAPO-56 and SAPO-RHO lies in the physisorption range (similar to 35 kJ/mol). SAPOs, in particular SAPO-56 and SAPO-RHO, possess many desirable properties and are potentially good adsorbents for CO2 capture in swing adsorption processes., AuthorCount:4

Mechanically strong monoliths of zeolite NaKA with a hierarchy of pores displayed very high CO2-over-N-2 selectivity. The zeolite monoliths were produced by pulsed current processing (PCP) without the use of added binders and with a preserved microporous crystal structure. Adsorption isotherms of CO2 and N-2 were determined and used to predict the co-adsorption of CO2 and N-2 using ideal adsorbed solution theory (IAST). The IAST predictions showed that monolithic adsorbents of NaKA could reach an extraordinarily high CO2-over-N-2 selectivity in a binary mixture with a composition similar to flue gas (15 mol% CO2 and 85 mol% N2 at 25 degrees C and 101 kPa). Structured NaKA monoliths with a K+ content of 9.9 at% combined a CO2-over-N-2 selectivity of >1100 with a high CO2 adsorption capacity (4 mmol g(-1)) and a fast adsorption kinetics (on the order of one minute). Estimates of a figure of merit (F) based on IAST CO2-over-N-2 selectivity, and time-dependent CO2 uptake capacity, suggest that PCP-produced structured NaKA with a K+ content of 9.9 at% offers a performance far superior to 13X adsorbents, in particular at short cycle times., AuthorCount:4

We studied equilibrium adsorption and uptake kinetics and identified molecular species that formed during sorption of carbon dioxide on amine-modified silica. Bicontinuous silicas (AMS-6 and MCM-48) were postsynthetically modified with (3-aminopropyl)triethoxysilane or (3-aminopropyl)methyldiethoxysilane, and amine-modified AMS-6 adsorbed more CO(2) than did amine-modified MCM-48. By in situ FTIR spectroscopy, we showed that the amine groups reacted with CO(2) and formed ammonium carbamate ion pairs as well as carbamic acids under both dry and moist conditions. The carbamic acid was stabilized by hydrogen bonds, and ammonium carbamate ion pairs formed preferably on sorbents with high densities of amine groups. Under dry conditions, silylpropylcarbamate formed, slowly, by condensing carbamic acid and silanol groups. The ratio of ammonium carbamate ion pairs to silylpropylcarbamate was higher for samples with high amine contents than samples with low amine contents. Bicarbonates or carbonates did not form under dry or moist conditions. The uptake of CO(2) was enhanced in the presence of water, which was rationalized by the observed release of additional amine groups under these conditions and related formation of ammonium carbamate ion pairs. Distinct evidence for a fourth and irreversibly formed moiety was observed under sorption of CO(2) under dry conditions. Significant amounts of physisorbed, linear CO(2) were detected at relatively high partial pressures of CO(2), such that they could adsorb only after the reactive amine groups were consumed., authorCount :7

Wilkinson’s catalyst [RhCl(PPh3)3] was heterogenized on common silica by the use of a grafting/anchoring technique. The immobilized catalyst showed high activity and selectivity in transfer hydrogenation reactions of a range of carbonyl compounds in 2-propanol. Reactions carried out in 2-propanol at reflux afforded the corresponding alcohols in high yields in short reaction times. The heterogeneous feature ofthe catalyst allows for easy recovery and efficient reuse in the same reaction up to 5 times without any detectible loss of catalytic activity., authorCount :5

The pressure-swing adsorption method for carbon dioxide capture would ideally be facilitated by adsorbents with a high capacity and a high selectivity for CO(2). Several aluminophosphates with 8-ring window apertures (AlPO(4)-17, AlPO(4)-18, AlPO(4)-53, and AlPO(4)-25) were synthesized by hydrothermal crystallization, calcined, and their CO(2) uptake and CO(2)/N(2) selectivity were studied. CO(2) and N(2) uptake was determined for pressures up to 101 kPa at 273 and 293 K. Langmuir and Toth adsorption models were used to describe the adsorption isotherms. The CO(2) and N(2) uptakes strongly indicated that the squeezed 8-ring windows of certain aluminophosphates can sieve CO(2) from a CO(2) and N(2) gas mixture. Both AlPO(4)-53 and AlPO(4)-25 exhibited a remarkably higher uptake of CO(2) compared to N(2). The hydrophilicity of the AlPO(4) materials was investigated by means of water adsorption, and the results showed that all of the tested aluminophosphates were less water sensitive than a benchmark zeolite (13X). In particular, AlPO(4)-53 and AlPO(4)-25 showed a very low degree of water uptake with up to 20-30% relative humidity. Determination of cyclic adsorption and desorption confirmed the relatively hydrophobic nature of the aluminophosphates, which render them less energy costly for the regeneration of adsorbents., authorCount :4

By changing the temperature, pH, stirring rate, or time for calcium carbonate crystallization, complex shapes of aggregated calcium carbonates formed. Such shapes have earlier been ascribed to specific interactions with specialized additives. Without polymeric additives, aggregates of vaterite transformed more rapidly into calcite aggregates under slow than under fast stirring. With an anionic polyelectrolyte added, vaterite was stabilized. Larger polycrystalline aggregates of vaterite formed under rapid than under slow stirring, indicative of a particle mediated growth of aggregates controlled by convective currents. The size of the underlying nanoparticles was temperature dependent, with grain sizes of similar to 20 to 50 nm at 20 degrees C and similar to 350 nm at 90 degrees C. The small differences in free energy between the anhydrous polymorphs of calcium carbonate made both kinetic and equilibrium dependencies important.

Mesoporous silica particles (Davisil) were functionalized with aminopropyltriethoxysilane (APTES) in a fractional factorial design with 19 different synthesis and uptake experiments. The number of amino groups and the uptake of CO(2) were optimized in a 2(V)(5-1) design. Most important to functionalizationwas the amount of water present during synthesis, the reaction time, and pretreating the silica with a mineral acid; certain two-way interactions were shown to be statistically significant as well. Modifications performed at 110 or 80 degrees C showed no significant differences concerning amine content or uptake of CO(2). Properly choosing center points for the discrete variables is problematic and is somewhat related to the lack of fit with respect to CO(2) uptake; the regression was good. Solid-state (29)Si NMR showed that the APTES was mainly fully condensed. Specific surface areas did not correlate with the number of n-propylamine groups on the silica, which is indicative of differential levels of heterogeneity in the coverage of propylamines. The uptake of CO(2) and N(2) was measured from -20 to 70 degrees C and from 0 to 1 bar and parametrized by the Freundlich isotherm. Amine-modified silica adsorbed significant amounts of CO(2), especially at the low partial pressure, which is important for CO(2) capture from flue gas. At such pressures, samples with a high density of amine (4 amines/nm(2)) showed a much higher uptake of CO(2) than did those with densities of similar to 2-3 amines/nm(2), reflecting differential tendencies to form propylammonium-propylcarbamate ion pairs; these require close proximity among amine groups to form. Water affected the uptake of carbon dioxide in different ways. Certain samples took up more moist CO(2) gas than dry CO(2), and others took up less moist CO(2) than dry CO(2), which is indicative of differential tendencies toward water adsorption. We conclude that experimental design is a time-efficient approach to the functionalizat, 3

By changing the temperature, pH, stirring rate, or time for calcium carbonate crystallization, complex shapes of aggregated calcium carbonates formed. Such shapes have earlier been ascribed to specific interactions with specialized additives. Without polymeric additives, aggregates of vaterite transformed more rapidly into calcite aggregates under slow than under fast stirring. With an anionic polyelectrolyte added, vaterite was stabilized. Larger polycrystalline aggregates of vaterite formed under rapid than under slow stirring, indicative of a particle mediated growth of aggregates controlled by convective currents. The size of the underlying nanoparticles was temperature dependent, with grain sizes of similar to 20 to 50 nm at 20 degrees C and similar to 350 nm at 90 degrees C. The small differences in free energy between the anhydrous polymorphs of calcium carbonate made both kinetic and equilibrium dependencies important.

We studied equilibrium adsorption and uptake kinetics and identified molecular species that formed during sorption of carbon dioxide on amine-modified silica. Bicontinuous silicas (AMS-6 and MCM-48) were postsynthetically modified with (3-aminopropyl)triethoxysilane or (3-aminopropyl)methyldiethoxysilane, and amine-modified AMS-6 adsorbed more CO(2) than did amine-modified MCM-48. By in situ FTIR spectroscopy, we showed that the amine groups reacted with CO(2) and formed ammonium carbamate ion pairs as well as carbamic acids under both dry and moist conditions. The carbamic acid was stabilized by hydrogen bonds, and ammonium carbamate ion pairs formed preferably on sorbents with high densities of amine groups. Under dry conditions, silylpropylcarbamate formed, slowly, by condensing carbamic acid and silanol groups. The ratio of ammonium carbamate ion pairs to silylpropylcarbamate was higher for samples with high amine contents than samples with low amine contents. Bicarbonates or carbonates did not form under dry or moist conditions. The uptake of CO(2) was enhanced in the presence of water, which was rationalized by the observed release of additional amine groups under these conditions and related formation of ammonium carbamate ion pairs. Distinct evidence for a fourth and irreversibly formed moiety was observed under sorption of CO(2) under dry conditions. Significant amounts of physisorbed, linear CO(2) were detected at relatively high partial pressures of CO(2), such that they could adsorb only after the reactive amine groups were consumed., authorCount :7

By changing the temperature, pH, stirring rate, or time for calcium carbonate crystallization, complex shapes of aggregated calcium carbonates formed. Such shapes have earlier been ascribed to specific interactions with specialized additives. Without polymeric additives, aggregates of vaterite transformed more rapidly into calcite aggregates under slow than under fast stirring. With an anionic polyelectrolyte added, vaterite was stabilized. Larger polycrystalline aggregates of vaterite formed under rapid than under slow stirring, indicative of a particle mediated growth of aggregates controlled by convective currents. The size of the underlying nanoparticles was temperature dependent, with grain sizes of similar to 20 to 50 nm at 20 degrees C and similar to 350 nm at 90 degrees C. The small differences in free energy between the anhydrous polymorphs of calcium carbonate made both kinetic and equilibrium dependencies important.

We studied equilibrium adsorption and uptake kinetics and identified molecular species that formed during sorption of carbon dioxide on amine-modified silica. Bicontinuous silicas (AMS-6 and MCM-48) were postsynthetically modified with (3-aminopropyl)triethoxysilane or (3-aminopropyl)methyldiethoxysilane, and amine-modified AMS-6 adsorbed more CO(2) than did amine-modified MCM-48. By in situ FTIR spectroscopy, we showed that the amine groups reacted with CO(2) and formed ammonium carbamate ion pairs as well as carbamic acids under both dry and moist conditions. The carbamic acid was stabilized by hydrogen bonds, and ammonium carbamate ion pairs formed preferably on sorbents with high densities of amine groups. Under dry conditions, silylpropylcarbamate formed, slowly, by condensing carbamic acid and silanol groups. The ratio of ammonium carbamate ion pairs to silylpropylcarbamate was higher for samples with high amine contents than samples with low amine contents. Bicarbonates or carbonates did not form under dry or moist conditions. The uptake of CO(2) was enhanced in the presence of water, which was rationalized by the observed release of additional amine groups under these conditions and related formation of ammonium carbamate ion pairs. Distinct evidence for a fourth and irreversibly formed moiety was observed under sorption of CO(2) under dry conditions. Significant amounts of physisorbed, linear CO(2) were detected at relatively high partial pressures of CO(2), such that they could adsorb only after the reactive amine groups were consumed., authorCount :7

By changing the temperature, pH, stirring rate, or time for calcium carbonate crystallization, complex shapes of aggregated calcium carbonates formed. Such shapes have earlier been ascribed to specific interactions with specialized additives. Without polymeric additives, aggregates of vaterite transformed more rapidly into calcite aggregates under slow than under fast stirring. With an anionic polyelectrolyte added, vaterite was stabilized. Larger polycrystalline aggregates of vaterite formed under rapid than under slow stirring, indicative of a particle mediated growth of aggregates controlled by convective currents. The size of the underlying nanoparticles was temperature dependent, with grain sizes of similar to 20 to 50 nm at 20 degrees C and similar to 350 nm at 90 degrees C. The small differences in free energy between the anhydrous polymorphs of calcium carbonate made both kinetic and equilibrium dependencies important.

We studied equilibrium adsorption and uptake kinetics and identified molecular species that formed during sorption of carbon dioxide on amine-modified silica. Bicontinuous silicas (AMS-6 and MCM-48) were postsynthetically modified with (3-aminopropyl)triethoxysilane or (3-aminopropyl)methyldiethoxysilane, and amine-modified AMS-6 adsorbed more CO(2) than did amine-modified MCM-48. By in situ FTIR spectroscopy, we showed that the amine groups reacted with CO(2) and formed ammonium carbamate ion pairs as well as carbamic acids under both dry and moist conditions. The carbamic acid was stabilized by hydrogen bonds, and ammonium carbamate ion pairs formed preferably on sorbents with high densities of amine groups. Under dry conditions, silylpropylcarbamate formed, slowly, by condensing carbamic acid and silanol groups. The ratio of ammonium carbamate ion pairs to silylpropylcarbamate was higher for samples with high amine contents than samples with low amine contents. Bicarbonates or carbonates did not form under dry or moist conditions. The uptake of CO(2) was enhanced in the presence of water, which was rationalized by the observed release of additional amine groups under these conditions and related formation of ammonium carbamate ion pairs. Distinct evidence for a fourth and irreversibly formed moiety was observed under sorption of CO(2) under dry conditions. Significant amounts of physisorbed, linear CO(2) were detected at relatively high partial pressures of CO(2), such that they could adsorb only after the reactive amine groups were consumed., authorCount :7

Predictions of future climate change have triggered a search for ways to reduce the release of greenhouse gases into the atmosphere. Carbon capture and storage (CCS) assists this goal by reducing carbon dioxide emissions, and CO2 adsorbents in particular can reduce the costs of CO2 capture. Here, we review the nanoscale sorbent materials that have been developed and the theoretical basis for their function in CO2 separation, particularly from N2-rich flue gases.

The uptake of carbon dioxide and nitrogen gas by zeolite NaKA was studied. A very high ideal CO2-over-N2 selectivity and a high CO2 capacity were observed at an optimal K+ content of 17 at.%. NaKA is a very promising adsorbent for CO2 separation from water-free flue gases.

The synthesis of carbonaceous materials with a high surface density of amino functions for CO2 sorption and sequestration is reported. The amino-rich carbonaceous materials are characterized by elemental analysis, N2 sorption, scanning and transmission electron microscopy, zeta potential, TGA and FTIR measurements. A detailed discussion on the use of these materials in CO2 capture is provided. The materials show significant sorption capabilities for CO2 (4.3 mmol g−1at −20 °C and 1 bar). Furthermore, they show a high apparent selectivity for CO2 over N2 at both low and high temperatures.

The fine structural details of mesoporous materials possessing Pmn symmetry prepared with varying amphiphilic surfactants under acid and alkaline conditions are investigated using electron crystallography and sorption studies. The structural data derived is used to understand the parameters that govern the formation of cavity–windows and to propose synthetic strategies in order to control independently the size of the cavities and cavity–windows. Results support that whilst attainment of Pmn cubic packing is due to the overall surfactant geometry, the formation of cavity–windows is associated with the hydration layer formed at the interphase between the surfactant and the silica wall. The charge density at the micelle surface may be tailored using two strategies: (i) using dicationic gemini surfactants at low pHs resulting in an increase in the hydration layer; or (ii) by using co-structure directing agents such as organoalkoxysilanes which reduce the hydration layer surrounding the micelles. The latter leads to the formation of higher cavity sizes and may be useful for tuning fine structural details of mesoporous materials when considering their use in important applications such as gas separation.

Adsorption-mediated CO2 separation can reduce the cost of carbon capture and storage. The reduction in cost requires adsorbents with high capacities for CO2 sorption and high CO2-over-N2 selectivity. Amine-modified sorbents are promising candidates for carbon capture. To investigate the details of CO2 adsorption in such materials, we studied mesocaged (cubic, Pm3̅n symmetry) silica adsorbents with tethered propylamines using Fourier transform infrared (FTIR) spectroscopy and volumetric uptake experiments. The degree of heterogeneity in these coatings was varied by either cosynthesizing or postsynthetically introducing the propylamine modification. In situ FTIR spectroscopy revealed the presence of both physisorbed and chemisorbed CO2 in the materials. We present direct molecular evidence for physisorption using FTIR spectroscopy in mesoporous silica sorbents modified with propylamines. Physisorption reduced the CO2-over-N2 selectivity in amine-rich sorbents. Samples with homogeneous coatings showed typical CO2 adsorption trends and large quantities of IR-observable physisorbed CO2. The uptake of CO2 in mesocaged materials with heterogeneous propylamine coatings was higher at high temperatures than at low temperatures. At higher temperatures and low pressures, the postsynthetically modified materials adsorbed more CO2 than did the extracted ones, even though the surface area after modification was clearly reduced and the coverage of primary amine groups was lower. The principal mode of CO2 uptake in postsynthetically modified mesoporous silica was chemisorption. The chemisorbed moieties were present mainly as carbamate−ammonium ion pairs, resulting from the quantitative transformation of primary amine groups during CO2 adsorption as established by NIR spectroscopy. The heterogeneity in the coatings promoted the formation of these ion pairs. The average propylamine−propylamine distance must be small to allow the formation of carbamate−propylammonium ion pairs.