Iron phosphate mediated magnetite synthesis:a bioinspired approach

The biomineralization of intracellular magnetite in magnetotactic bacteria (MTB) is an area of active investigation. Previous work has provided evidence that magnetite biomineralization begins with the formation of an amorphous phosphate-rich ferric hydroxide precursor phase followed by the eventual formation of magnetite within specialized vesicles (magnetosomes) through redox chemical reactions. Although important progress has been made in elucidating the different steps and possible precursor phases involved in the biomineralization process, many questions still remain. Here, we present a novelin vitromethod to form magnetite directly from a mixed valence iron phosphate precursor, without the involvement of other known iron hydroxide precursors such as ferrihydrite. Our results corroborate the idea that phosphate containing phases likely play an iron storage role during magnetite biomineralization. Further, our results help elucidate the influence of phosphate ions on iron chemistry in groundwater and wastewater treatment.</p

A tunable azine covalent organic framework platform for visible light-induced hydrogen generation

Hydrogen evolution from photocatalytic reduction of water holds promise as a sustainable source of carbon-free energy. Covalent organic frameworks (COFs) present an interesting new class of photoactive materials, which combine three key features relevant to the photocatalytic process, namely crystallinity, porosity and tunability. Here we synthesize a series of water-and photostable 2D azine-linked COFs from hydrazine and triphenylarene aldehydes with varying number of nitrogen atoms. The electronic and steric variations in the precursors are transferred to the resulting frameworks, thus leading to a progressively enhanced light-induced hydrogen evolution with increasing nitrogen content in the frameworks. Our results demonstrate that by the rational design of COFs on a molecular level, it is possible to precisely adjust their structural and optoelectronic properties, thus resulting in enhanced photocatalytic activities. This is expected to spur further interest in these photofunctional frameworks where rational supramolecular engineering may lead to new material applications

Molecular Insights into Carbon Dioxide Sorption in Hydrazone-Based Covalent Organic Frameworks with Tertiary Amine Moieties

Tailorable sorption properties at the molecular level are key for efficient carbon capture and storage and a hallmark of covalent organic frameworks (COFs). Although amine functional groups are known to facilitate CO2 uptake, atomistic insights into CO2 sorption by COFs modified with amine-bearing functional groups are scarce. Herein, we present a detailed study of the interactions of carbon dioxide and water with two isostructural hydrazone-linked COFs with different polarities based on the 2,5-diethoxyterephthalohydrazide linker. Varying amounts of tertiary amines were introduced in the COF backbones by means of a copolymerization approach using 2,5-bis(2-(dimethylamino)ethoxy)terephthalohydrazide in different amounts ranging from 25 to 100% substitution of the original DETH linker. The interactions of the frameworks with CO2 and H2O were comprehensively studied by means of sorption analysis, solid-state NMR spectroscopy, and quantum-chemical calculations. We show that the addition of the tertiary amine linker increases the overall CO2 sorption capacity normalized by the surface area and of the heat of adsorption, whereas surface areas and pore size diameters decrease. The formation of ammonium bicarbonate species in the COF pores is shown to occur, revealing the contributing role of water for CO2 uptake by amine-modified porous frameworks

Fabrication of chitosan-flax composites with differing molecular weights and its effect on mechanical properties

An aqueous fabrication method is investigated for a composite reinforced with chitosan and flax fibers. The composite is characterized structurally, mechanically and chemically. A strong influence of molecular weight (MW) is identified on the composite properties. A strong fiber-matrix interface, which is associated with porosity and effective fiber impregnation, is achieved by applying low molecular weight (LMW) solution followed by casting using LMW or medium molecular weight (MMW) solution. Porosity is analyzed using μ-CT analysis. Increasing porosity with increasing molecular weight results in a decline of the tensile and flexural properties of the composites. The chitosan-flax composites have a low density compared to synthetic and natural fiber composites, which is a competitive advantage as a replacement material for particle board or plyboard in suspended ceilings, furniture compartments, sports or leisure equipment. A multiscale simulation is carried out to compute the directional effective elastic properties and predicts a potential 21% improvement of the tensile modulus if the process is optimized. This work shows the potential of chitosan-flax composites as a sustainable green material with an aqueous fabrication procedure and useful mechanical properties

A hydrazone-based covalent organic framework for photocatalytic hydrogen production

Covalent organic frameworks (COFs) have recently emerged as a new generation of porous polymers combining molecular functionality with the robustness and structural definition of crystalline solids. Drawing on the recent development of tailor-made semiconducting COFs, we report here on a new COF capable of visible-light driven hydrogen generation in the presence of Pt as a proton reduction catalyst (PRC). The COF is based on hydrazone-linked functionalized triazine and phenyl building blocks and adopts a layered structure with a honeycomb-type lattice featuring mesopores of 3.8 nm and the highest surface area among all hydrazone-based COFs reported to date. When illuminated with visible light, the Pt-doped COF continuously produces hydrogen from water without signs of degradation. With their precise molecular organization and modular structure combined with high porosity, photoactive COFs represent well-defined model systems to study and adjust the molecular entities central to the photocatalytic process

A tunable azine covalent organic framework platform for visible light-induced hydrogen generation

Hydrogen evolution from photocatalytic reduction of water holds promise as a sustainable source of carbon-free energy. Covalent organic frameworks (COFs) present an interesting new class of photoactive materials, which combine three key features relevant to the photocatalytic process, namely crystallinity, porosity and tunability. Here we synthesize a series of water-and photostable 2D azine-linked COFs from hydrazine and triphenylarene aldehydes with varying number of nitrogen atoms. The electronic and steric variations in the precursors are transferred to the resulting frameworks, thus leading to a progressively enhanced light-induced hydrogen evolution with increasing nitrogen content in the frameworks. Our results demonstrate that by the rational design of COFs on a molecular level, it is possible to precisely adjust their structural and optoelectronic properties, thus resulting in enhanced photocatalytic activities. This is expected to spur further interest in these photofunctional frameworks where rational supramolecular engineering may lead to new material applications

Nitrogen-Rich Covalent Triazine Frameworks as High-Performance Platforms for Selective Carbon Capture and Storage

The search for new efficient physisorbents for gas capture and storage is the objective of numerous ongoing researches in the realm of functional framework materials. Here we present the CO2 and H-2 uptake capacities of nitrogen rich covalent triazine frameworks (CTFs) based on lutidine, pyrimidine, bipyridine, and phenyl units, showing superior gas uptakes and extremely high CO2 selectivities toward N-2. The CO2 uptake of a bipyridine-CTF synthesized at 600 degrees C (5.58 mmol g(-1), 273 K) is the highest reported for all CTFs so far and the second highest for all porous organic polymers (POPs). Moreover, the CO2 selectivity toward N-2 of a nitrogen-rich pyrimidine-based CTF synthesized at 500 degrees C (Henry: 189, IAST: 502) is the highest reported for all POPs, and the H-2 uptake of CTF1 synthesized at 600 degrees C at 1 bar (2.12 wt %, 77 K) is the highest found for all CTFs to date as well. With the wide range of sorption data at hand, we carve out general trends in the gas uptake behavior within the CTF family and nitrogen-containing porous polymers in general, revealing the dominant role of the micropore volume for maximum CO2 uptake, while we find that the nitrogen content is a secondary effect weakly enhancing the CO2 uptake. The latter, however, was identified as the main contributor to the high CO2/N-2 selectivities found for the CTFs. Furthermore, ambient water vapor sorption has been tested for CTFs for the first time, confirming the highly hydrophilic nature of CTFs with high nitrogen content

Iron phosphate mediated magnetite synthesis: a bioinspired approach

The biomineralization of intracellular magnetite in magnetotactic bacteria (MTB) is an area of active investigation. Previous work has provided evidence that magnetite biomineralization begins with the formation of an amorphous phosphate-rich ferric hydroxide precursor phase followed by the eventual formation of magnetite within specialized vesicles (magnetosomes) through redox chemical reactions. Although important progress has been made in elucidating the different steps and possible precursor phases involved in the biomineralization process, many questions still remain. Here, we present a novelin vitromethod to form magnetite directly from a mixed valence iron phosphate precursor, without the involvement of other known iron hydroxide precursors such as ferrihydrite. Our results corroborate the idea that phosphate containing phases likely play an iron storage role during magnetite biomineralization. Further, our results help elucidate the influence of phosphate ions on iron chemistry in groundwater and wastewater treatment