Quantification of microporosity in fruit by MRI at various magnetic fields: comparison with X-ray microtomography

Microstructure determines the mechanical and transport properties of fruit tissues. One important characteristic of the microstructure is the relative volume fraction of gas-filled intercellular spaces, i.e., the tissue microporosity. Quantification of this microporosity is fundamental for investigating the relationship between gas transfer and various disorders in fruit.     

Adsorption and structural properties of soft-templated mesoporous carbons obtained by carbonization at different temperatures and KOH activation

Two series of phenolic resin-based mesoporous carbons were prepared by soft-templating strategy, which involves the formation of thermosetting carbon precursor by polymerization of phloroglucinol and formaldehyde in hydrophilic mesodomains of a thermally decomposable triblock copolymer used as a soft-template. It was shown that the volumes of mesopores and micropores in the resulting carbons can be tuned by varying carbonization temperature of phenolic resins in the range from 400 to 1000 °C followed by the post-synthesis KOH activation at 700 °C. The highly microporous carbons were obtained by KOH activation of phenolic resins pyrolyzed at lower temperature (∼500 °C), while high temperature KOH activation (∼800 °C) afforded microporous carbons with preserved mesoporosity.     

Self-Accelerating Diels–Alder Reaction for Preparing Polymers of Intrinsic Microporosity

It is a formidable challenge in polycondensation to simultaneously construct multiple covalent bonds to prepare double-stranded polymers of intrinsic microporosity (PIMs) with fused multicyclic linkages. To the best of our knowledge, this is the first study to develop a self-accelerating Diels–Alder reaction for successfully preparing double-stranded PIMs with fused multicyclic backbone structures. A self-accelerating Diels–Alder reaction was developed based on the [4+2] cycloaddition of sym-dibenzo-1,5-cyclooctadiene-3,7-diyne (DIBOD) and ortho-quinone compounds. In this reaction, the cycloaddition of ortho-quinone with the first alkyne of DIBOD activates the second alkyne, which reacts with ortho-quinone at a rate constant 192 times larger than that of the original alkyne. Using this self-accelerating reaction to polymerize DIBOD and spirocyclic/cyclic difunctional ortho-quinone monomers, a novel stoichiometric imbalance-promoted step-growth polymerization method was developed to prepare PIMs. The resultant PIMs possess intrinsic ultramicropores with pore sizes between 0.45 to 0.7 nm, high specific surface areas above 646 m² g⁻¹, and good H₂ separation performance.     

Theoretical analysis of the adsorption of metal ions to the surface of melanin particles

We have re-examined the problem of the interaction of melanins with metal ions. Metal ions are normal constituents of the pigment, but in some cases they can be related to pathologies, mainly at the level of the skin (Cu²⁺ and Fe³⁺) and of the central nervous system (Fe²⁺ and Mn²⁺). Our approach has been based on the mechanisms of adsorption on the particle surface, by the use of theoretical adsorption isotherms and kinetic models. Although this analysis doesn’t give detailed information on the specific sites involved, it is useful to better characterize the surface behaviour of the colloidal melanin. The results obtained demonstrate that the affinity of melanin for metal ions is very high, comparable to the most efficient materials employed in decontamination and recovery techniques. Moreover, our results demonstrate that three-parameters models, such as Langmuir-Freundlich, Redlich-Peterson and Tóth equations, fit the experimental data with great accuracy and that the adsorption follows pseudo-second-order kinetics.     

Synthesis of Microporous Transition Metal Oxide Molecular Sieves with Bifunctional Templating Molecules

Systematic tuning of the micropore size in microporous transition metal oxide molecular sieves can be achieved by varying the length of the hydrocarbon chain of the diamine molecules used as templating agents. The large bifunctional molecules self-assemble with much smaller cross-sectional micellar dimensions than their monofunctional counterparts. The resulting family of porous materials offers exciting new flexibility in designing molecular sieves targeted for size selectivity and chemical functionality.     

Towards a Rational Synthesis of Large-Pore Zeolite-Type Materials?

A range of novel structures , such as the metalloaluminosilicate UCSB-8 (depicted schematically), are accessible by synthetic strategies that could provide the basis for the rational design of other large-pore zeolites and zeolite-type materials. The combination of experimental approaches with computational methods, for example host–guest shape analysis, may provide further breakthroughs in this field.     

A Robust (10,3)-a Network Containing Chiral Micropores in the AgI Coordination Polymer of a Bridging Ligand that Provides Three Bidentate Metal-Binding Sites

Framework integrity is retained when water molecules replace the nitromethane molecules in the coordination polymer [Ag(hat)ClO₄]⋅2 CH₃NO₂ (see picture for structure), which are arranged in a helical fashion within the chiral micropores of the three-dimensional [Ag(hat)⁺]_n network with a (10,3)-a topology. Remarkably, this is also the case after subsequent displacement of the water by nitromethane molecules. hat=1,4,5,8,9,12-hexaazatriphenylene.     

PAN基活性炭纤维的氮吸附研究

用相同原料不同活化方法制备聚丙烯腈基活性炭纤维,并对其进行了氮吸附研究.结 果表明,由不同活化方法所制备的活性炭纤维的孔结构存在较大差异,并对随着活化程度的 改变其孔结构的发展进行了研究.结果表明,通过简单的改变活化方法即可以制得不同孔隙占 主导地位的炭质吸附剂;也揭示出,不同的活化方法其活化机理有所差别.     

Preparation and characterization of microporous SiO2-ZrO2 pillared montmorillonite

SiO₂-ZrO₂ pillared montmorillonite (SZM) was prepared by the reaction of Na-montmorillonite with colloidal silica-zirconia particles which were prepared by depositing zirconium hydroxy cations on silica particles. By pillaring with the colloidal particles, the basal spacing of montmorillonite was expanded to ca. 45 Å and the calcined SZM samples showed large specific surface areas up to 320 m²/g at 400 °C. In spite of large interlayer separation, adsorption results indicated the presence of micropores generated between the colloidal particles. The microporous structure was maintained at least up to 600 °C and exhibited specific shape selectivity for the adsorption of large organic molecules, especially between toluene and mesitylene. According to the temperature-programmed-desorption (TPD) spectra of ammonia, the calcined SZM showed weakly acidic sites.     

Effect of synthetic conditions on the structures of silver(I)-hexamethylenetetramine coordination polymers: crystal structures of two three-dimensional frameworks featuring new topological motifs

Two novel coordination complexes, [Ag₃(μ₄-hmt)₂(μ-ssa)(H₂O)](NO₃)·3H₂O 1, and [Ag₈(μ₃-hmt)₂(μ₄-hmt)₂(μ-pma)₂(μ-H₂O)₃]·18H₂O 2 (hmt=hexamethylenetetramine, ssa=sulfosalicylate and pma=1,2,4,5-benzenetetracarboxylate), have been prepared and structurally characterized. Crystal data: 1 C₁₉H₃₃Ag₃N₉O₁₃S, orthorhombic, Pna2₁, a=20.483(7) Å, b=21.890(1) Å, c=6.493(2) Å, V=2911.3(13) Å³, Z=4; 2 C₄₄H₉₄Ag₈N₁₆O₃₇, monoclinic, C2/c, a=32.099(10) Å, b=12.916(3) Å, c=21.431(8) Å, β=126.74(1)°, V=7120(4) Å³, Z=4. Both complexes exhibit unprecedented and different topological motifs of Ag-hmt networks. Complex 1 is a novel three-dimensional cationic network with two types of channels, in which the larger one is the largest one in Ag-hmt networks; while 2 is a three-dimensional network with cylindrical channels, consisting of mixed μ₃- and μ₄-hmt ligands. The results demonstrate that under different synthetic conditions, such as the presence of multiple small counter anions or different pH values, different Ag-hmt linkages may be formed to generate new three-dimensional networks.