RESUMEN
The success and continued expansion of research on metal-oxo clusters owe largely to their structural richness and wide range of functions. However, while most of them known to date are negatively charged polyoxometalates, there is only a handful of cationic ones, much less functional ones. Here, we show an all-inorganic hydroxyiodide [H10.7Sb32.1O44][H2.1Sb2.1I8O6][Sb0.76I6]2·25H2O (HSbOI), forming a face-centered cubic structure with cationic Sb32O44 clusters and two types of anionic clusters in its interstitial spaces. Although it is submicrometer in size, electron diffraction tomography of HSbOI allowed the construction of the initial structural model, followed by powder Rietveld refinement to reach the final structure. The cationic cluster is characterized by the presence of acidic protons on its surface due to substantial Sb3+ deficiencies, which enables HSbOI to serve as an excellent solid acid catalyst. These results open up a frontier for the exploration and functionalization of cationic metal-oxo clusters containing heavy main group elements.
RESUMEN
Considerable efforts have been devoted to developing oxygen evolution reaction (OER) catalysts based on transition metal oxides. Polyoxometalates (POMs) can be regarded as model compounds of transition metal oxides, and cobalt-containing POMs (Co-POMs) have received significant interest as candidates. Nanocomposites based on Co-POMs have been reported to show high OER activities due to synergistic effects among the components; however, the role of each component is unclear due to its complex structure. Herein, we utilize porous ionic crystals (PICs) based on Co-POMs, which enable a composition-structure-function relationship to be established to understand the origin of the synergistic catalysis. Specifically, a Keggin-type POM [α-CoW12O40]6- and a Cr complex [Cr3O(OOCCH2CN)6(H2O)3]+ are implemented as PIC building blocks for the OER under nonbasic conditions. The potentially OER-active but highly soluble [α-CoW12O40]6- was successfully anchored in the crystalline PIC matrix via Coulomb interactions and hydrogen bonding induced by polar cyano groups of the Cr complex. The PIC exhibits efficient and sustained OER catalytic activity, while each building block is inactive. The Tafel slope of the linear sweep voltammetry curve and the relatively large kinetic isotope effect value suggest that elementary steps closely related to the OER rate involve single-electron and proton transfer reactions. Electrochemical and spectroscopic studies clearly show that the synergistic catalysis originates from the charge transfer from the Cr complex to [α-CoW12O40]6-; the increased electron density of [α-CoW12O40]6- may increase its basicity and accelerate proton abstraction as well as enhance electron transfer to stabilize the reaction intermediates adsorbed on [α-CoW12O40]6-.
RESUMEN
The introduction of pyridinic nitrogen (pyri-N) into carbon-based electrocatalysts for the oxygen reduction reaction is considered to create new active sites. Herein, the role of pyri-N in such catalysts was investigated from a mechanistic viewpoint using carbon black (CB)-supported pyri-N-containing molecules as model catalysts; the highest activity was observed for 1,10-phenanthroline/CB. X-ray photoemission spectroscopy showed that in acidic electrolytes, both pyri-N atoms of 1,10-phenanthroline could be protonated to form pyridinium ions (pyri-NH+ ). In O2 -saturated electrolytes, one of the pyri-NH+ species was reduced to pyri-NH upon the application of a potential; no such reduction was observed in N2 -saturated electrolytes. This behavior was ascribed to electrochemical reduction of pyri-NH+ occurring simultaneously with the thermal adsorption of O2 , as supported by DFT calculations. According to these calculations, the coupled reduction was promoted by hydrophobic environments.
RESUMEN
Eleven isostructural mesoporous ionic crystals (meso-PICs) are synthesized. The initial activities of the Barbier-Grignard reaction, which is a typical C-C bond formation reaction, catalyzed by the meso-PICs are dependent on the acid dissociation constant of the aqua ions of Mn+ and the types of polyoxometalates, which construct the meso-PICs.
RESUMEN
Amorphous high-surface-area aluminum hydroxide-bicarbonates were synthesized starting from AlCl3, base, and bicarbonate in water. Composites with a chemical formulas of [Al13O4(µ-OH)24(H2O)6.5(OH)5.5](HCO3)1.5 (I-NaOH) and [Al13O4(µ-OH)24(H2O)6(OH)6](HCO3) (I-NH3) were obtained by the use of NaOH/NaHCO3 and NH3/NH4HCO3 as base/bicarbonate, respectively. The surface area of the composites was highly dependent on the pH level of the synthetic solution, and composites with high surface areas (ca. 200 m2 g-1) were obtained around pH 7-8. Pore-size distributions determined from the N2 adsorption isotherms showed that I-NH3 and I-NaOH possess mainly large (pore radius rp > 3 nm) and small (rp < 3 nm) pores, respectively, despite similar surface areas. While SEM images showed that both I-NH3 and I-NaOH were aggregates of nanoparticles, the particles were more fused in I-NaOH, which is in line with the existence of small pores and the use of a stronger base (NaOH), which would facilitate the dehydration condensation reaction. The composites were applied as adsorbents to remove methyl orange (MO) from water. The time course of MO adsorption was readily fitted with a pseudo-second-order model, and over 90% MO removal was attained within 10 min with I-NH3, while I-NaOH showed much less MO removal (26%). The MO adsorption isotherm of I-NH3 was reproduced with a Langmuir model with an adsorption capacity of 154 mg g-1. Notably, the aluminum hydroxide-bicarbonates could not absorb methylene blue, which is a cationic dye, while anions (MO and PO43-) were readily absorbed. Solid-state 27Al MAS NMR spectra showed that the concentration of 5-coordinated aluminum species, which may serve as guest binding sites, was higher for I-NH3. These results show that electrostatic interaction between anionic MO and coordinatively unsaturated 5-coordinated cationic aluminum species and the large external surface area of I-NH3 contribute to the highly efficient MO adsorption.
RESUMEN
Polycondensation via Pd-catalyzed cross-dehydrogenative-coupling reaction of 2,2',3,3',5,5',6,6'-octafluorobiphenyl with thiophene analogues was studied. The synthetic protocol, in which employment of prefunctionalized starting monomers was fully avoided, allowed straightforward access to an alternating π-conjugated polymer. The addition of K2CO3 to the catalytic system promotes the cross-coupling reaction and suppresses the undesired homocoupling reaction, producing the corresponding donor-acceptor type π-conjugated polymers with minor homocoupling defects. The reaction also proceeded using O2 as the terminal oxidant, resulting in lower loading of the Ag oxidant. The obtained polymer was evaluated as an emitting material for an organic light-emitting diode.
RESUMEN
Artificial reconstruction of fibre-shaped cellular constructs could greatly contribute to tissue assembly in vitro. Here we show that, by using a microfluidic device with double-coaxial laminar flow, metre-long core-shell hydrogel microfibres encapsulating ECM proteins and differentiated cells or somatic stem cells can be fabricated, and that the microfibres reconstitute intrinsic morphologies and functions of living tissues. We also show that these functional fibres can be assembled, by weaving and reeling, into macroscopic cellular structures with various spatial patterns. Moreover, fibres encapsulating primary pancreatic islet cells and transplanted through a microcatheter into the subrenal capsular space of diabetic mice normalized blood glucose concentrations for about two weeks. These microfibres may find use as templates for the reconstruction of fibre-shaped functional tissues that mimic muscle fibres, blood vessels or nerve networks in vivo.
