Crystallization of calcium carbonate, typically, progresses sequentially via metastable phases. Amorphous CaCO 3 (ACC) generally forms initially, both in vitro and in vivo, and is the precursor of the predominant anhydrous polymorphs (calcite, aragonite, and vaterite). [1][2][3][4][5][6][7][8][9][10][11][12][13] A new picture of the crystallization of calcium carbonate is emerging, which involves transformations of clusters to ACC and eventually to crystalline polymorphs. [14,15] This stepwise manner has implications for the understanding of biomineralization [16] and of crystallization. ACCs that contain additives display order over atomic length scales that are related to crystalline polymorphs; [1][2][3] ACC synthesized at high supersaturation levels without additives, [17][18][19][20] on the other hand, show no distinct short-range order. [21,22] Herein, we analyze proto-crystalline features of two amorphous intermediates, ACCI and ACCII, [15] and discuss their relevance for crystallization of CaCO 3 . We rationalize the identification of ACCI with pc-ACC (proto-calcite ACC) and ACCII with pv-ACC (proto-vaterite ACC), respectively. These ACCs were precipitated from metastable solutions of calcium carbonate at different pH values by destabilization in excess ethanol.TEM (Figure 1) reveals the ACCs as spherical particles with a diameter of approximately 20 nm. Small-angle X-ray scattering (SAXS) data support this characteristic size

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 CO2 than did amine-modified MCM-48. By in situ FTIR spectroscopy, we showed that the amine groups reacted with CO2 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 CO2 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 CO2 under dry conditions. Significant amounts of physisorbed, linear CO2 were detected at relatively high partial pressures of CO2, such that they could adsorb only after the reactive amine groups were consumed.

The uptake of carbon dioxide and nitrogen gas by zeolite NaKA was studied. A very high ideal CO(2)-over-N(2) selectivity and a high CO(2) capacity were observed at an optimal K(+) content of 17 at.%. NaKA is a very promising adsorbent for CO(2) separation from water-free flue gases.

In aquatic ecosystems, microplastics are a relatively new anthropogenic substrate that can readily be colonized by biofilm-forming organisms. To examine the effects of substrate type on microbial community assembly, we exposed ambient Baltic bacterioplankton to plastic substrates commonly found in marine environments (polyethylene, polypropylene and polystyrene) as well as native (cellulose) and inert (glass beads) particles for 2 weeks under controlled conditions. The source microbial communities and those of the biofilms were analyzed by Illumina sequencing of the 16S rRNA gene libraries. All biofilm communities displayed lower diversity and evenness compared with the source community, suggesting substrate-driven selection. Moreover, the plastics-associated communities were distinctly different from those on the non-plastic substrates. Whereas plastics hosted greater than twofold higher abundance of Burkholderiales, the non-plastic substrates had a significantly higher proportion of Actinobacteria and Cytophagia. Variation in the community structure, but not the cell abundance, across the treatments was strongly linked to the substrate hydrophobicity. Thus, microplastics host distinct bacterial communities, at least during early successional stages.

Adsorption-mediated CO(2) separation can reduce the cost of carbon capture and storage. The reduction in cost requires adsorbents with high capacities for CO(2) sorption and high CO(2)-over-N(2) selectivity. Amine-modified sorbents are promising candidates for carbon capture. To investigate the details of CO(2) adsorption in such materials, we studied mesocaged (cubic, Pm3n 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 CO(2) in the materials. We present direct molecular evidence for physisorption using FTIR spectroscopy in mesoporous silica sorbents modified with propylamines. Physisorption reduced the CO(2)-over-N(2) selectivity in amine-rich sorbents. Samples with homogeneous coatings showed typical CO(2) adsorption trends and large quantities of IR-observable physisorbed CO(2). The uptake of CO(2) 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 CO(2) 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 CO(2) 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 CO(2) 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.

Porosity and chirality are two of the most important properties for materials in the chemical and pharmaceutical industry. Inorganic microporous materials such as zeolites have been widely used in ion-exchange, selective sorption/separation and catalytic processes. The pore size and shape in zeolites play important roles for specific applications. Chiral inorganic microporous materials are particularly desirable with respect to their possible use in enantioselective sorption, separation and catalysis. At present, among the 179 zeolite framework types reported, only three exhibit chiral frameworks. Synthesizing enantiopure, porous tetrahedral framework structures represents a great challenge for chemists. Here, we report the silicogermanates SU-32 (polymorph A), SU-15 (polymorph B) (SU, Stockholm University) and a hypothetical polymorph C, all built by different stacking of a novel building layer. Whereas polymorphs B and C are achiral, each crystal of polymorph A exhibits only one hand and has an intrinsically chiral zeolite structure. SU-15 and SU-32 are thermally stable on calcination.

Crystallization of calcium carbonate, typically, progresses sequentially via metastable phases. Amorphous CaCO 3 (ACC) generally forms initially, both in vitro and in vivo, and is the precursor of the predominant anhydrous polymorphs (calcite, aragonite, and vaterite). [1][2][3][4][5][6][7][8][9][10][11][12][13] A new picture of the crystallization of calcium carbonate is emerging, which involves transformations of clusters to ACC and eventually to crystalline polymorphs. [14,15] This stepwise manner has implications for the understanding of biomineralization [16] and of crystallization. ACCs that contain additives display order over atomic length scales that are related to crystalline polymorphs; [1][2][3] ACC synthesized at high supersaturation levels without additives, [17][18][19][20] on the other hand, show no distinct short-range order. [21,22] Herein, we analyze proto-crystalline features of two amorphous intermediates, ACCI and ACCII, [15] and discuss their relevance for crystallization of CaCO 3 . We rationalize the identification of ACCI with pc-ACC (proto-calcite ACC) and ACCII with pv-ACC (proto-vaterite ACC), respectively. These ACCs were precipitated from metastable solutions of calcium carbonate at different pH values by destabilization in excess ethanol. TEM (Figure 1) reveals the ACCs as spherical particles with a diameter of approximately 20 nm. Small-angle X-ray scattering (SAXS) data support this characteristic size Figure 1. TEM images of pc-ACC and pv-ACC at various magnifications. Insets in (b) and (e) are selective area electron diffraction (SAED) patterns obtained from an area slightly larger than the particular image sections, SAED scale bars: 5 nm À1 . SAED patterns are shown as negatives to make weak features clear. Arrows in (f) indicate nanostructural features.

The synthesis of carbonaceous materials with a high surface density of amino functions for CO(2) sorption and sequestration is reported. The amino-rich carbonaceous materials are characterized by elemental analysis, N(2) sorption, scanning and transmission electron microscopy, zeta potential, TGA and FTIR measurements. A detailed discussion on the use of these materials in CO(2) capture is provided. The materials show significant sorption capabilities for CO(2) (4.3 mmol g(-1)at -20 degrees C and 1 bar). Furthermore, they show a high apparent selectivity for CO(2) over N(2) at both low and high temperatures.