Molecular Sieving Properties of Nanoporous Mixed-Linker ZIF-62: Associated Structural Changes upon Gas Adsorption Application

The evaluation of the flexibility in zeolitic imidazolate frameworks (ZIFs) has been very useful to understand their performance in gas adsorption and separation applications. Here, we have evaluated the adsorption properties of a nanoporous mixed-linker ZIF-62 using a combination of gas adsorption measurements, grand canonical Monte Carlo simulations, and synchrotron X-ray powder diffraction under operando conditions. While adsorption studies in nanoporous ZIF-62 at 77 K and atmospheric pressure predict a large O2/N2 separation ability, computational studies anticipate that the observed differences must be attributed to kinetic restrictions of N2 to access the internal porosity at cryogenic temperatures. Interestingly, upon a small increase in the adsorption temperature (90 K vs 77 K), both N2 and O2 are able to access the inner porous structure through the promotion of a phase transition (ca. 3.8% volume expansion) upon gas adsorption. This narrow phase (np) to expanded phase (ep) structural transition in ZIF-62 is completely suppressed above 150 K. Based on the excellent molecular sieve properties of nanoporous ZIF-62 for O2/N2 at cryogenic temperatures, we extended our study to the adsorption of linear and branched hydrocarbons. This study predicts the preferential adsorption of alkanes over alkenes in ZIF-62 for small hydrocarbons (C2), while in the case of C3 hydrocarbons and above, the adsorption process is mainly defined by kinetic restrictions.J.S.-A. acknowledges financial support from the MINECO (Projects MAT2016-80285-p and PID2019-108453GB-C21). The authors acknowledge ALBA for providing beamtime (Project No. 2019023264). Computational work was supported by the Cambridge High-Performance Computing Service, the Cambridge Service for Data-Driven Discovery (CSD3)

Controlling the Adsorption and Release of Ocular Drugs in Metal–Organic Frameworks: Effect of Polar Functional Groups

A series of UiO-66 materials with different functional groups (−H, −NH2, and −NO2) have been evaluated for the adsorption and release of a common ocular drug such as brimonidine tartrate. UiO-66 samples were synthesized under solvothermal conditions and activated by solvent exchange with ethanol. Experimental results suggest that the incorporation of surface functionalities gives rise to the development of structural defects (missing linker defects) but without altering the basic topology of the UiO-66 framework. These defects improve the adsorption performance of the parent metal–organic framework (MOF), while the bulkier functionalities infer slower release kinetics, with the associated benefits for prolonged delivery of brimonidine. Among the evaluated MOFs, defective UiO-66-NO2 can be proposed as the most promising candidate due to the combination of a larger brimonidine volumetric uptake (680 mg/cm3), a prolonged delivery (period of up to 25 days), a small particle size, and a larger instability. Contrariwise, at high concentrations UiO-66-NO2 has higher toxicity toward human retinal pigment epithelium cells (ARPE-19) compared to the pure and NH2-functionalized UiO-66.Authors would like to acknowledge financial support from the Ministerio de Ciencia e Innovación (Project PID2019-108453GB-C21), H2020 (Project MSCA-RISE-2016/NanoMed) and Conselleria de Innovación, Universidades, Ciencia y Sociedad Digital (Project CIPROM/2021/022)

New insights into the breathing phenomenon in ZIF-4

Structural changes in ZIFs upon adsorption remain a paradigm due to the sensitivity of the adsorption mechanism to the nature of the organic ligands and gas probe molecules. Synchrotron X-ray diffraction under operando conditions clearly demonstrates for the first time that ZIF-4 exhibits a structural reorientation from a narrow-pore (np) to a new expanded-pore (ep) structure upon N2 adsorption, while it does not do so for CO2 adsorption. The existence of an expanded-pore structure of ZIF-4 has also been predicted by molecular simulations. In simulations the expanded structure was stabilized by entropy at high temperatures and by strong adsorption of N2 at low temperatures. These results are in perfect agreement with manometric adsorption measurements for N2 at 77 K that show the threshold pressure for breathing at ∼30 kPa. Inelastic neutron scattering (INS) measurements show that CO2 is also able to promote structural changes but, in this specific case, only at cryogenic temperatures (5 K).The authors would like to acknowledge financial support from the MINECO (MAT2016-80285-p), Generalitat Valenciana (PROMETEOII/2014/004), H2020 (MSCA-RISE-2016/NanoMed Project), Spanish ALBA synchrotron (Projects AV-2017021985 and IH-2018012591) and Oak Ridge beam time availability (Project IPTS-20843.1). JSA and JGL acknowledge financial support from UA (ACIE17-15) to cover all the expenses for INS measurements at Oak Ridge. JGL acknowledges GV (GRISOLIAP/2016/089) for the research contract

Metal–Organic Frameworks as Drug Delivery Platforms for Ocular Therapeutics

Metal–organic frameworks (MOFs) have been evaluated as potential nanocarriers for intraocular incorporation of brimonidine tartrate to treat chronic glaucoma. Experimental results show that UiO-67 and MIL-100 (Fe) exhibit the highest loading capacity with values up to 50–60 wt %, whereas the performance is quite limited for MOFs with narrow cavities (below 0.8 nm, for example, UiO-66 and HKUST-1). The large loading capacity in UiO-67 is accompanied by an irreversible structural amorphization in aqueous and physiological media that promotes extended release kinetics above 12 days. Compared to the traditional drawbacks associated with the sudden release of the commercial drugs (e.g., ALPHAGAN), these results anticipate UiO-67 as a potential nanocarrier for drug delivery in intraocular therapeutics. These promising results are further supported by cytotoxicity tests using retinal photoreceptor cells (661W). Toxicity of these structures (including the metal nodes and organic ligands) for retinal cells is rather low for all samples evaluated, except for HKUST-1.Authors would like to acknowledge the financial support from MINECO (MAT2016-80285-p), GV (PROMETEOII/2014/004), and H2020 (MSCA-RISE-2016/NanoMed Project). J.G.-L. acknowledges GV (GRISOLIAP/2016/089) for the research contract. N.C. acknowledges the financial support from MINECO (MINECO-FEDER-BFU2015-67139-R), ISCIII (RETICS-FEDER RD16/0008/0016), and GV (Prometeo 2016/158). I.O.-L. acknowledges Ministerio de Educación, Spain (FPU 14/03166)

Large versatililty of metal-organic frameworks (MOFs) in gas/liquid adsorption processes

La tesis Doctoral está dividida en dos grandes bloques: el primero relacionado con el estudio estructural y de flexibilidad de distintos "Zeolític imidazolate fremewroks (ZIFs) utilizando distintas técnicas de caracterización de alta resolución y, además, simulación molecular; así como el efecto en la adsorción de distintas moléculas en fase gas. El segundo bloque hace referencia al estudio de MOFs en aplicaciones biomédicas, en específico en el estudio de adsorción y liberación en fase líquida de fármacos para el tratamiento del glaucoma

MOF-Based Polymeric Nanocomposite Films as Potential Materials for Drug Delivery Devices in Ocular Therapeutics

Novel MOF-based polymer nanocomposite films were successfully prepared using Zr-based UiO-67 as a metal–organic framework (MOF) and polyurethane (PU) as a polymeric matrix. Synchrotron X-ray powder diffraction (SXRPD) analysis confirms the improved stability of the UiO-67 embedded nanocrystals, and scanning electron microscopy images confirm their homogeneous distribution (average crystal size ∼100–200 nm) within the 50 μm thick film. Accessibility to the inner porous structure of the embedded MOFs was completely suppressed for N2 at cryogenic temperatures. However, ethylene adsorption measurements at 25 °C confirm that at least 45% of the MOF crystals are fully accessible for gas-phase adsorption of nonpolar molecules. Although this partial blockage limits the adsorption performance of the embedded MOFs for ocular drugs (e.g., brimonidine tartrate) compared to the pure MOF, an almost 60-fold improvement in the adsorption capacity was observed for the PU matrix after incorporation of the UiO-67 nanocrystals. The UiO-67@PU nanocomposite exhibits a prolonged release of brimonidine (up to 14 days were quantified). Finally, the combined use of SXRPD, thermogravimetric analysis (TGA), and Fourier transform infrared (FTIR) analyses confirmed the presence of the drug in the nanocomposite film, the stability of the MOF framework and the drug upon loading, and the presence of brimonidine in an amorphous phase once adsorbed. These results open the gate toward the application of these polymeric nanocomposite films for drug delivery in ocular therapeutics, either as a component of a contact lens, in the composition of lacrimal stoppers (e.g., punctal plugs), or in subtenon inserts.The authors would like to acknowledge financial support from MINECO (MAT2016-80285-p), Spanish ALBA Synchrotron (Project 2020014008), and H2020 (MSCA-RISE-2016/NanoMed Project). B.E.S. thanks the Minas Gerais Research Foundation (FAPEMIG CNPJ n21.949.888/0001-83) for a DPhil scholarship award. J.-C.T. thanks the EPSRC (Grant No. EP/N014960/1) and ERC Consolidator Grant (PROMOFS under the grant agreement 771575) for funding

Oxidative dehydrogenation of ethylbenzene over CMK-1 and CMK-3 carbon replicas with various mesopore architectures

Nanoreplication strategy was used for the synthesis of mesoporous ordered carbon materials with various pore architectures and surface compositions. Two different silica templates (regular MCM-48 and hexagonal SBA-15) were filled with a carbon precursor – poly(furfuryl alcohol) or sucrose – by the precipitation polycondensation or incipient wetness impregnation, respectively. Furthermore, the resulting carbon precursor/silica composites were carbonized at various temperatures from the range of 650–1050 °C. It was shown that the carbon precursor and method of its deposition strongly influenced structural and textural parameters of the final carbon material determined by XRD, low-temperature N2 adsorption and TEM. The specific surface area of the sucrose-based CMK-3 was ca. 45% higher than the poly(furfuryl alcohol)-derived replicas. On the other hand, this effect was not observed for CMK-1 replicas. The carbonization temperatures tuned up the content of C=O moieties on the surface of carbon replica calculated based on temperature-programmed desorption (TPD) profiles. Obviously, the concentration of C=O functionalities was correlated to the catalytic activity in the oxidative dehydrogenation of ethylbenzene (EB) to styrene. Nevertheless, the CMK-1 replicas were more sensitive to the C=O concentration in terms of EB conversion. Hence, we discussed carefully the role of the pore geometry in the catalytic performance of the studied carbon materials. For the CMK-1 and CMK-3 carbon replicas with comparable chemical and textural properties, but different pore structure, the initial EB conversion varied considerably, reaching 34.2% and 21.6%, respectively, at 350 °C and EB/O2 ratio = 1.0.This work was supported by the Polish National Science Centre (grant no. 2013/09/B/ST5/03419), MINECO (Project MAT2016-80285-p) and Generalitat Valenciana (PROMETEOII/2014/004). The research was carried out with the equipment purchased thanks to the financial support of the European Regional Development Fund in the framework of the Polish Innovation Economy Operational Program (contract no. POIG.02.01.00-12-023/08). Sebastian Jarczewski received funds from the Polish National Science Centre in the form of a doctoral scholarship (grant no. 2016/20/T/ST5/00256)

On the catalytic role of superficial VOx species and coke deposited on mesoporous MgO replica in oxidative dehydrogenation of ethylbenzene

Mesoporous MgO was synthesized by the nanoreplication method using CMK-3 carbon as a hard template and magnesium nitrate as a metal oxide precursor. The produced support was modified with different amounts of ammonium metavanadate solution. Various distributions of V-containing species on the MgO surface were found by XRD, low-temperature adsorption of N2, TEM, XPS and UV–vis-DR spectroscopy. At low V loadings isolated VO4 dominated. Increasing V content resulted in clustering of VO4 species and the formation of Mg3V2O8 crystallites. As found in temperature-programmed reduction (H2-TPR), the latter phase was clearly harder in reduction by H2 compared to highly dispersed VO4 forms. The developed materials appeared to be very active catalysts of oxidative dehydrogenation of ethylbenzene (ODH). The optimal catalytic performance was observed for the sample containing 10 wt% of vanadium. The initial ethylbenzene conversion of 63.6% at selectivity to styrene of 86.9% was achieved at temperature as low as 500 °C. A notable influence of carbonaceous deposit formed during the ODH reaction on the catalytic activity was discussed, including presentation of both coexisting superficial reaction mechanisms. A reasonable regeneration procedure to recover lost activity was developed.This work was supported by the Polish National Science Centre (grant no. 2013/09/B/ST5/03419). The research was carried out with the equipment purchased thanks to the financial support of the European Regional Development Fund in the framework of the Polish Innovation Economy Operational Program (contract no. POIG.02.01.00-12-023/08). S.J. received a doctoral scholarship from the Polish National Science Centre (grant no. 2016/20/T/ST5/00256). J.S.A. acknowledges financial support by MINECO (Project MAT2016-80285-p), H2020 (MSCA-RISE-2016/NanoMed Project), and GV (PROMETEOII/2014/004)

Layered double hydroxides as base catalysts for the synthesis of dimethyl carbonate

In this work, we have prepared two series of layered double hydroxides (LDHs) based on three different divalent cations (Zn2+, Ni2+ and Mg2+), that were ion-exchanged by a trivalent cation (Al3+). The charge was balanced with interlayer anions, either silicate or carbonate. Thus, we have synthetized six different samples and we have studied their physicochemical properties by a wide range of techniques, in order to elucidate their properties. Finally, we have used the prepared materials as catalysts in the transesterification of ethylene carbonate with methanol to produce dimethyl carbonate and ethylene glycol. We have found that materials containing Ni as divalent cation present better catalytic activity due to their basic properties, whereas catalysts containing silicate as interlayer anion yield better selectivity, since they have a lower amount of acid sites.The authors acknowledge financial support from the MINECO projects MAT-2013-45008-P, MAT2016-81732-ERC. EVRF gratefully acknowledge support from MINECO for his Ramón y Cajal grant (RyC-2012-11427) and University of Alicante for the project GRE-13-31. Generalitat Valenciana is acknowledges for support (PROMETEOII/2014/004). JGL Fellowship for National Master Studies 2014 of the National Council of Science and Technology (CONACYT), Mexico

Sustainable routes for acetic acid production: Traditional processes vs a low-carbon, biogas-based strategy

The conversion of biogas, mainly formed of CO2 and CH4, into high-value platform chemicals is increasing attention in a context of low-carbon societies. In this new paradigm, acetic acid (AA) is deemed as an interesting product for the chemical industry. Herein we present a fresh overview of the current manufacturing approaches, compared to poten- tial low-carbon alternatives. The use of biogas as primary feedstock to produce acetic acid is an auspicious alternative, representing a step-ahead on carbon-neutral industrial processes. Within the spirit of a circular economy, we propose and analyse a new BIO-strategy with two noteworthy pathways to potentially lower the environmental impact. The generation of syngas via dry reforming (DRM) combined with CO2 utilisation offers a way to produce acetic acid in a two-step approach (BIO-Indirect route), replacing the conventional, petroleum-derived steam reforming process. The most recent advances on catalyst design and technology are discussed. On the other hand, the BIO-Direct route offers a ground-breaking, atom-efficient way to directly generate acetic acid from biogas. Nevertheless, due to thermo- dynamic restrictions, the use of plasma technology is needed to directly produce acetic acid. This very promising ap- proach is still in an early stage. Particularly, progress in catalyst design is mandatory to enable low-carbon routes for acetic acid production.Ministerio de Ciencia e Innovación y Agencia Estatal de Investigación, de España. MCIN/AEI - PID2019- 08502RJ-I00, IJC2019-040560-I y RYC2018-024387-IComisión Europea - H2020-MSCA-RISE-2020 BIOALL/10100805