57 research outputs found
Guest Molecule-Responsive Functional Calcium Phosphonate Frameworks for Tuned Proton Conductivity
We report the synthesis, structural characterization, and functionality of an open-framework hybrid that combines Ca2+ ions and the rigid polyfunctional ligand 5-(dihydroxyphosphoryl) isophthalic acid (PiPhtA). Ca-PiPhtA-I is obtained by slow crystallization at ambient conditions from acidic (pHâ3) aqueous solutions. It possesses a high water content (both Ca coordinated and in the lattice), and importantly, it exhibits water-filled 1D channels. At 75 °C, Ca-PiPhtA-I is partially dehydrated and exhibits a crystalline diffraction pattern that can be indexed in a monoclinic cell with parameters close to the pristine phase. Rietveld refinement was carried out for the sample heated at 75 °C, Ca-PiPhtA-II, using synchrotron powder X-ray diffraction data.All connectivity modes of the âparentâ Ca-PiPhtA-I framework are retained in Ca-PiPhtA-II. Upon Ca-PiPhtA-I exposure to ammonia vapors (28% aqueous NH3) a new derivative is obtained (Ca-PiPhtA-NH3) containing 7 NH3 and 16 H2O molecules according to elemental and thermal analyses. Ca-PiPhtA-NH3 exhibits a complex X-ray diffraction pattern with peaks at 15.3 and 13.0 Ă
that suggest partial breaking and transformation of the parent pillared structure. Although detailed structural identification of Ca-PiPhtA-NH3 was not possible, due in part to nonequilibrium adsorption conditions and the lack of crystallinity, FT-IR spectra and DTA-TG analysis indicate profound structural changes compared to the pristine Ca-PiPhtA-I. At 98% RH and T = 24 °C, proton conductivity, Ï, for Ca PiPhtA-I is 5.7 Ă10â4 S·cmâ1. It increases to 1.3 Ă 10â3 S·cmâ1 upon activation by preheating the sample at 40 °C for 2 h followed by water equilibration at room temperature under controlled conditions. Ca-PiPhtA-NH3 exhibits the highest proton conductivity, 6.6 Ă 10â3 S·cmâ1, measured at 98% RH and T = 24 °C. Ea for proton transfer in the above-mentioned frameworks range between 0.23 and 0.4 eV, typical of a Grothuss mechanism of proton conduction.Proyecto nacional MAT2010-1517
Towards an interactive, processâbased approach to understanding range shifts: developmental and environmental dependencies matter
Control of Crystalline Proton-Conducting Pathways by Water-Induced Transformations of Hydrogen-Bonding Networks in a MetalâOrganic Framework
Electroreduction of Carbon Dioxide to Hydrocarbons Using Bimetallic CuâPd Catalysts with Different Mixing Patterns
Electrochemical conversion
of CO<sub>2</sub> holds promise for
utilization of CO<sub>2</sub> as a carbon feedstock and for storage
of intermittent renewable energy. Presently Cu is the only metallic
electrocatalyst known to reduce CO<sub>2</sub> to appreciable amounts
of hydrocarbons, but often a wide range of products such as CO, HCOO<sup>â</sup>, and H<sub>2</sub> are formed as well. Better catalysts
that exhibit high activity and especially high selectivity for specific
products are needed. Here a range of bimetallic CuâPd catalysts
with ordered, disordered, and phase-separated atomic arrangements
(Cu<sub>at</sub>:Pd<sub>at</sub> = 1:1), as well as two additional
disordered arrangements (Cu3Pd and CuPd3 with Cu<sub>at</sub>:Pd<sub>at</sub> = 3:1 and 1:3), are studied to determine key factors needed
to achieve high selectivity for C1 or C2 chemicals in CO<sub>2</sub> reduction. When compared with the disordered and phase-separated
CuPd catalysts, the ordered CuPd catalyst exhibits the highest selectivity
for C1 products (>80%). The phase-separated CuPd and Cu3Pd achieve
higher selectivity (>60%) for C2 chemicals than CuPd3 and ordered
CuPd, which suggests that the probability of dimerization of C1 intermediates
is higher on surfaces with neighboring Cu atoms. Based on surface
valence band spectra, geometric effects rather than electronic effects
seem to be key in determining the selectivity of bimetallic CuâPd
catalysts. These results imply that selectivities to different products
can be tuned by geometric arrangements. This insight may benefit the
design of catalytic surfaces that further improve activity and selectivity
for CO<sub>2</sub> reduction
Isomaltodextrin strengthens model starch gels and moderately promotes starch retrogradation
Design and Synthesis of Hydroxide IonâConductive MetalâOrganic Frameworks Based on Salt Inclusion
Direct Observation of Two Types of Proton Conduction Tunnels Coexisting in a New Porous IndiumâOrganic Framework
Enhancing Proton Conduction in a MetalâOrganic Framework by Isomorphous Ligand Replacement
Imparting High Proton Conductivity to a MetalâOrganic Framework Material by Controlled Acid Impregnation
- âŠ