This article focuses on the synthetic approach to the preparation of calcium carbonate–organic hybrid materials, which are obtained by self‐organization processes under mild conditions. In these processes, organic molecules such as functionalized polymers and aligned amphiphilic molecules on the surface play key roles in the crystallization of calcium carbonate, which results in the formation of hybrid materials. As well as being environmentally benign, the hybrid materials have controlled morphology and unique properties. Materials scientists have obtained the ideas for the design of such hybrid materials from biominerals such as shells, teeth, and bones.
Recent reports on the organic structure-directing agent (OSDA)-free synthesis of some zeolites with the aid of seed crystals have opened a new way to the robust and environmentally friendly production of industrially valuable zeolites. However, the details on the crystallization behavior as well as the role of the seeds have not been fully clarified yet. In this study, the crystallization process of zeolite beta in the OSDA-free, seed-embedded Na+−aluminosilicate gel system, which never yields beta in the absence of the seeds, is investigated in detail. The XRD and TEM studies of the solid aluminosilicate products in the course of the hydrothermal treatment suggest that the crystallization of zeolite beta proceeds on the outer surface of amorphous aluminosilicates. The Raman spectroscopy, solid-state 27Al and 23Na MAS NMR and high-energy XRD analyses of seeded and nonseeded amorphous materials just before crystallization reveal that the beta seeds induce no major changes in their structures, implying that the nucleation of beta does not occur directly from the amorphous phase. The intermediate addition of the seeds after prehydrothermal treatment of a nonseeded gel enhances the crystallization rate and results in the increased number of beta crystals with smaller size. It is elucidated that, during the hydrothermal treatment, the beta seeds embedded in the gel provide crystal growth surface after they are exposed and/or released to the liquid phase by partial dissolution of the amorphous aluminosilicates. These findings provide a promising approach to the designed syntheses of valuable zeolites in the completely OSDA-free system.
Sonogashira cross-coupling of bromophenylethenyl-terminated cubic, double four-ring, siloxane cages with di-/triethynyl compounds results in microporous poly(ethynylene aryleneethenylene silsesquioxane) networks, simply termed as polyorganosiloxane networks (PSNs). In comparison with porous organic polymers reported previously, these PSNs show relatively high surface area and comparable thermal stability. Their apparent BET specific surface areas vary in the range of 850-1040 m(2) g(-1) depending on the length and the connectable sites of the ethynyl compounds. Analyses of pore size distribution revealed bimodal micropores with relatively narrow distribution. The degree of cross-linking affects the degree of cleavage of the siloxane bonds, and this suggests that partial cleavage of the siloxane cages is mainly a result of cage distortion. Hydrogen adsorption was performed to evaluate potential of the PSNs as hydrogen storage media. Uptakes of up to 1.19 wt% at 77 K and 760 Torr and initial isosteric heats of adsorption as high as 8.0 kJ mol(-1) were observed. These materials have been obtained by a combination of structural, synthetic organic, and materials chemistry, which can exploited to synthesize porous hybrid materials with specifically designed structures and functions.
Gone fishing: Unidirectionally oriented CaCO3 crystalline films have been prepared on chitin matrices in the presence of calcification‐associated peptide (CAP‐1), which was isolated from the exoskeleton of the red swamp crayfish. The interactions of CAP‐1 with the matrix and the acidic nature of the peptide lead to a filmlike assembly of CaCO3 nanocrystals through transformation of amorphous calcium carbonate (see picture).
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