Understanding Nanopore Window Distortions in the Reversible Molecular Valve Zeolite RHO

Molecular valves are becoming popular for potential biomedical applications. However, little is known concerning their performance in energy and environmental areas. Zeolite RHO shows unique pore deformations upon changes in hydration, cation siting, cation type, or temperature-pressure conditions. By varying the level of distortion of double eight-rings, it is possible to control the adsorption properties, which confer a molecular valve behavior to this material. We have employed interatomic potentials-based simulations to obtain a detailed atomistic view of the structural distortion mechanisms of zeolite RHO, in contrast with the averaged and space group restricted information provided by diffraction studies. We have modeled four aluminosilicate structures, containing Li$^+$, Na$^+$, K$^+$, Ca$^{2+}$, and Sr$^{2+}$ cations. The distortions of the three different zeolite rings are coupled, and the six- and eight-membered rings are largely flexible. A large dependence on the polarizing power of the extra-framework cations and with the loading of water has been found for the minimum aperture of the eight-membered rings that control the nanovalve effect. The calculated energy barriers for moving the cations across the eight-membered rings are very high, which explains the experimentally observed slow kinetics of the phase transition as well as the appearance of metastable phases

Enhancement of the intrinsic fluorescence of ZIF-8 via post-synthetic cation exchange with Cd2+ and its incorporation into PDMS films for selective sulfide optical sensing

In this study, ZIF-8 MOF nanocrystals were synthesized and post-synthetically modified by applying different cation exchange strategies. Addition of cadmium nitrate in either methanol or DMF followed by either magnetic stirring or gentle heating led to the incorporation of a small amount of Cd (II) ions into the crystal structure in most cases, as clearly demonstrated by several characterization techniques including PXRD, SEM-EDS and FT-IR. This novel doped material exhibits a high fluorescence with the maximum emission wavelength at 444 nm upon excitation at 380 nm, which allows its use as an effective optical sensor. The sensing capability of the Cd-doped ZIF-8 material was demonstrated by its exposure to sulfide ions in aqueous solution. The fluorescence of the doped material was gradually quenched as the concentration of S2− was increased. Sensing devices based on mixed-matrix membranes (MMMs) were fabricated by using poly (dimethyl siloxane) (PDMS) as a hosting matrix for the Cd-doped ZIF-8 crystals, giving rise to fluorescent sensing films with fast and selective responses against a broad number of potential interferents

Selective sulfur dioxide adsorption on crystal defect sites on an isoreticular metal organic framework series

The widespread emissions of toxic gases from fossil fuel combustion represent major welfare risks. Here we report the improvement of the selective sulfur dioxide capture from flue gas emissions of isoreticular nickel pyrazolate metal organic frameworks through the sequential introduction of missing-linker defects and extra-framework barium cations. The results and feasibility of the defect pore engineering carried out are quantified through a combination of dynamic adsorption experiments, X-ray diffraction, electron microscopy and density functional theory calculations. The increased sulfur dioxide adsorption capacities and energies as well as the sulfur dioxide/carbon dioxide partition coefficients values of defective materials compared to original non-defective ones are related to the missing linkers enhanced pore accessibility and to the specificity of sulfur dioxide interactions with crystal defect sites. The selective sulfur dioxide adsorption on defects indicates the potential of fine-tuning the functional properties of metal organic frameworks through the deliberate creation of defects.We thank generous funding from the European Research Council through an ERC Starting Grant (ERC2011-StG-279520-RASPA), the Spanish Ministry of Economy (CTQ2013-48396-P, CTQ2014-53486-R, CTQ2015-70135-REDT) and FEDER and Marie Curie IIF-625939 (LMRA) funding from European Union and Andalucía Region (FQM-1851)

Modified natural zeolites for water disinfection using heterogeneous photo-Fenton at near neutral pH.

According to the World Health Organisation (WHO) [1], microbiologically contaminated water for for human consumption can transmit diarrheal diseases or acute respiratory infections, among others, causing 485,000 deaths from diarrhea each year. Therefore, water contaminated with pathogenic organisms (bacteria resistant to antibiotics, viruses, etc.) must be adequately treated for its safe use.Currently there are several types of treatments for water disinfection, and in recent years the interest of the scientific community in Advanced Oxidation Processes (POAs) has increased significantly [2]. Among all types of POAs, the heterogeneous photo-Fenton process has been used for the degradation of a large number of contaminants in water. Likewise, there are studies that demonstrate its efficacy for the inactivation of pathogens. Its effectiveness lies in the generation of hydroxyl radicals through the oxidation-reduction reactions that occur on the surface of a photocatalyst due to the action of UV-Vis light and the presence of an oxidising agent (hydrogen peroxide) capable of producing profound changes in the chemical structure of contaminants and irreversible damage to microorganisms.In this work, modified natural zeolites (NZ) were used as an efficient photocatalytic and low-cost support [3] for the inactivation of a model microorganism (E. coli). To do this, first, natural zeolite clinoptilolite from the Tasajeras site (Villa Clara) was was subjected to ion exchange with Fe2+, following an usual procedure [4]. Once the material was obtained, it was characterised by DRX, SEM and IR, to ensure that the synthesis had been carried out properly. Next, its efficiency was evaluated in an 850 mL jacketed glass reactor with constant agitation and illuminated with UV or visible light at a constant temperature of 25ºC and initial pH of 6.5. The tests were performed with an initial concentration of E. coli of 106 CFU/mL and adding H2O2 (10 mM) and modified zeolite2(0.85 gr) at the beginning. The reduction of bacterial concentration was then evaluated every 30 minutes through serial dilutions. Likewise, in addition to the photo-Fenton process, to understand the isolated effect of the different parameters of the process, radiation disinfection; radiation - H2O2; H2O2; modified zeolite; modified radiation-zeolite; H2O2 - modified zeolite (Fenton) and the viability of the cells and their recreation were evaluated. Finally, the ability of the used catalyst to be recovered and cyclically reused without losing its photocatalytic activity was evaluated

Chemical Engineering of Photoactivity in Heterometallic Titanium-Organic Frameworks by Metal Doping

[EN] We report a new family of titanium-organic frameworks that enlarges the limited number of crystalline, porous materials available for this metal. They are chemically robust and can be prepared as single crystals at multi-gram scale from multiple precursors. Their heterometallic structure enables engineering of their photoactivity by metal doping rather than by linker functionalization. Compared to other methodologies based on the post-synthetic metallation of MOFs, our approach is well-fitted for controlling the positioning of dopants at an atomic level to gain more precise control over the band-gap and electronic properties of the porous solid. Changes in the band-gap are also rationalized with computational modelling and experimentally confirmed by photocatalytic H-2 production.This work was supported by the EU (ERC Stg Chem-fs-MOF 714122) and Spanish MINECO (MDM-2015-0538, MAT2016-75586-C4-4-P & CTQ2017-83486-P). C.M.-G. and J.C.-G. thank the Spanish MINECO for a Ramon y Cajal Fellowship and FPI Scholarship (CTQ2014-59209-P), respectively. N.M.P. thanks the Junta de Andalucia for post-doctoral fellowship (P10-FQM-6050). BSC-RES and UG-Alhambra are acknowledged for the computational resources and F. Lloret for helpful discussions.Castells-Gil, J.; Padial, NM.; Almora-Barrios, N.; Albero-Sancho, J.; Ruiz-Salvador, AR.; Gonzalez-Platas, J.; García Gómez, H.... (2018). Chemical Engineering of Photoactivity in Heterometallic Titanium-Organic Frameworks by Metal Doping. Angewandte Chemie International Edition. 57(28):8453-8457. https://doi.org/10.1002/anie.201802089S845384575728Furukawa, H., Cordova, K. E., O’Keeffe, M., & Yaghi, O. M. (2013). The Chemistry and Applications of Metal-Organic Frameworks. Science, 341(6149), 1230444-1230444. doi:10.1126/science.1230444Adil, K., Belmabkhout, Y., Pillai, R. S., Cadiau, A., Bhatt, P. M., Assen, A. H., … Eddaoudi, M. (2017). 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Thermostructural Behaviour of Ni-Cr Materials: Modelling Bulk and Nanoparticle Systems

The thermostructural properties of Ni‐Cr materials, as bulk and nanoparticle (NP) systems, have been predicted with a newly developed interatomic potential, for Ni/Cr ratios from 100/0 to 60/40. The potential, which has been fitted using experimental data and further validated using Density Functional Theory (DFT), describes correctly the variation with temperature of the lattice parameters and the coefficient of thermal expansion, from 100 K to 1000 K. Using this potential, we have performed Molecular Dynamics (MD) simulations on bulk Ni‐Cr alloys of various compositions, for which no experimental data are available. Similarly, NPs with diameters of 3, 5, 7, 10 nm were studied. We found a very rapid convergence of NP properties with the size of the systems, showing already the 5 nm NPs a thermostructural behaviour similar to that the bulk. MD simulations of two 5 nm NPs show very little sintering and thermally‐induced damage, for temperatures between 300 K and 1000 K, suggesting that materials formed by agglomeration of Ni‐Cr NPs meet the thermostructural stability requirements for catalysis applications

Thermochemistry of strontium incorporation in aragonite from atomistic simulations

We have investigated the thermodynamics of mixing between aragonite (orthorhombic CaCO3) and strontianite (SrCO3). In agreement with experiment, our simulations predict that there is a miscibility gap between the two solids at ambient conditions. All SrxCa1−xCO3 solids with compositions 0.12 < x < 0.87 are metastable with respect to separation into a Ca-rich and a Sr-rich phase. The concentration of Sr in coral aragonites (x ∼ 0.01) lies in the miscibility region of the phase diagram, and therefore formation of separated Sr-rich phases in coral aragonites is not thermodynamically favorable. The miscibility gap disappears at around 380 K. The enthalpy of mixing, which is positive and nearly symmetric with respect to x = 0.5, is the dominant contribution to the excess free energy, while the vibrational and configurational entropic contributions are small and of opposite sign. We provide a detailed comparison of our simulation results with available experimental data

Unravelling the key factors in the chlorine-promoted epoxidation of ethylene over a silver-copper oxide nanocatalyst

Ethylene oxide is one of the most important raw materials in the chemical industry, with an annual production close to 35 million metric tons. Despite its importance, to date, no metal has been found that can compete with the original silver bulk material catalyst discovered in 1931. Recently, a few copper and copper–silver based nanostructures have demonstrated remarkable selectivity and activity, especially when coupled with an industrial chlorine promoter. The present work evaluates the mechanistic role of chlorine as an active promoter of the selective oxidation of ethylene to ethylene oxide in the presence of a silver–copper oxide hybrid nanocatalyst (AgCuO). Experimental kinetic studies combined with density functional theory (DFT) calculations provide insight into the influence that Ag/CuO-supported chlorine atoms have over the ethylene epoxidation reaction. Remarkably, the typically described indirect route via the formation of an oxametallacycle (OMC) is also accompanied by a direct route. Furthermore, the presence of chlorine seems to facilitate a more favorable adsorption energy for ethylene oxide (EO) than for acetaldehyde (AA), the main reaction by-product. As a result, complete oxidation of EO can be further prevented in the presence of this AgCuO hybrid heteronanostructure.We acknowledge financial support from the European Research Council ERC-Advanced Grant HECTOR (project number 267626) is gratefully acknowledged. The computations were performed on resources provided by the supercomputer “Caesaraugusta” (node of the Spanish Supercomputer Network) provided by BIFI (Universidad de Zaragoza). The TEM studies were conducted at the Laboratorio de Microscopias Avanzadas, Instituto de Nanociencia de Aragon, Universidad de Zaragoza, Spain. S.H. acknowledges funding from the Agencia Estatal de Investigación and the Ministerio de Ciencia, Innovación y Universidades, of Spain (PID2019-110430G B-C22), and from the EU FEDER Framework 2014-2020 and Consejería de Conocimiento, Investigación y Universidad of the Andalusian Government (FEDER-UPO-1265695).Peer reviewe