Cristina Pozo-Gonzalo

Metal organic framework based catalysts for CO2 conversion

Metal organic frameworks (MOFs) are hybrid crystalline materials, exhibiting high specific surface areas, controllable pore sizes and surface chemistry. These properties have made MOFs attractive for a wide range of applications including gas separation, gas storage, sensing, drug delivery and catalysis. This review focuses on recent progress in the application of MOF materials as catalysts for CO2 conversion through chemical fixation, photocatalysis and electrocatalysis. In particular, this review discusses the co-relationship between the physicochemical properties of MOF materials including their catalytic performance as well as their stability and recyclability under different reaction conditions, relevant to CO2 conversion. Current modification techniques for improving MOF performance are highlighted along with the recent understanding of their electronic properties. The limitations of MOF based catalysts are also discussed and potential routes for improvement are suggested.

Redox chemistry of the superoxide ion in a phosphonium-based ionic liquid in the presence of water

Stable electrogenerated superoxide ion has been observed for the first time in a phosphonium-based ionic liquid in the presence of water, leading to a chemically reversible O2/O2(•-) redox couple instead of the disproportionation reaction that is usually observed. It appears that the cation solvates the superoxide anion, stabilizing it against the disproportionation reaction. The electrogeneration is studied at various levels of water or other diluents including toluene to explore the limits of stability of the superoxide ion under these conditions.

Innovative materials and applications based on poly(3,4-ethylenedioxythiophene) and ionic liquids

The combination of ionic liquids (ILs) and conducting polymers is a topic of current interest due to the significant advances observed in applications such as optoelectronics, actuators and energy storage. Among conducting polymers, poly(3,4-ethylenedioxythiophene) (PEDOT) has emerged as the most promising due to its high chemical stability, high conductivity and high transparency. The unique characteristics of ionic liquids like ionic conductivity, solvent and ordering capabilities, thermal stability and low melting point (often below room temperature) can complement the characteristics of PEDOT and so favour the development of advanced materials and applications. This article features recent research progress in the design of innovative materials based on PEDOT modified or functionalized with ionic liquids. Recent applications of these materials in different fields are finally summarized.

Synthesis of 2‐(Selenophen‐2‐yl)pyrroles and Their Electropolymerization to Electrochromic Nanofilms

Bridging pyrrole and selenophene chemistries: Molecular assemblies have been developed that allow scrutiny of the electronic communication between pyrrole and selenophene nuclei. Divergent syntheses of 2-(selenophen-2-yl)pyrroles and their N-vinyl derivatives from available 2-acylselenophenes and acetylenes in a one-pot procedure have been devised (see scheme), which provide access to these exotic heterocyclic ensembles.The divergent syntheses of 2-(selenophen-2-yl)pyrroles and their N-vinyl derivatives from available 2-acylselenophenes and acetylenes in a one-pot procedure make these exotic heterocyclic ensembles accessible. Now we face a potentially vast area for exploration with a great diversity of far-reaching consequences including conducting electrochromic polymers with repeating of pyrrole and selenophene units (emerging rivalry for polypyrroles and polyselenophenes), the synthesis of functionalized pyrrole-selenophene assembles for advanced materials, biochemistry and medicine, exciting models for theory of polymer conductivity.

Tailoring the fibre-to-matrix interface using click chemistry on carbon fibre surfaces

A convenient and effective strategy to control the surface chemistry of carbon fibres is presented, comprising electro-chemical reduction of aryl diazonium salts onto the surface, followed by ‘click chemistry’ to tether the desired surface characteristic of choice. The power of this approach was demonstrated by engineering a small-molecule interface between carbon fibre and an epoxy matrix improving interfacial shear strength by up to 220%, relative to unmodified control fibres. The techniques used in this work do not impede the fibre performance in tensile strength or Youngs modulus. This work provides a platform upon which any carbon fibre-to-resin interface can be easily and rapidly designed and implemented.

Novel dithiolene complexes incorporating conjugated electroactive ligands

A series of new metal (M) dithiolene complexes bearing terthiophene (3, 12, M = Ni; 4, M = Pd; 5, 6, M = Au) and 2,5-bis(para-methoxyphenyl)thiophene units (14, M = Ni; 15, 16, M = Au; 17, M = Pd) have been synthesised in 38-99% yield. The electrochemical properties of the materials have been characterised by cyclic voltammetry and UV-vis spectroelectrochemistry. The nickel complexes possess low oxidation potentials (-0.12 to -0.25 V vs Ag/AgCl) due to the electron-rich dithiolene centres and all complexes display ligand-based redox activity. The terthiophene derivatives have been polymerised by electrochemical oxidation to give stable films with, in the case of poly(3), broad absorption characteristics. Charge transfer materials have been isolated from 14 and 16 with conductivities in the range 9 x 10(-6) to 7 x 10(-8) S cm(-1).

Supramolecular ionic networks with superior thermal and transport properties based on novel delocalized di-anionic compounds

Supramolecular ionic networks based on highly delocalized dianions having (trifluoromethane-sulfonyl)imide, (propylsulfonyl)methanide and (cyano-propylsulfonyl)imide groups were developed and their physical properties were examined in detail. Most of the synthesized compounds were semi-crystalline possessing Tm values close to 100 °C; however, amorphous networks were also obtained using aromatic asymmetric dianions. Rheological measurements in temperature sweep tests at a constant frequency confirmed two different behaviors: a fast melting close to the Tm for semi-crystalline materials and a thermoreversible network for liquid transition for the amorphous supramolecular ionic networks. It was found that the amorphous ionic networks showed significantly higher ionic conductivity (10−3 S cm−1 at 100 °C) than the crystalline ionic networks (10−6 S cm−1) and previously reported amorphous citrate ionic networks (10−5 S cm−1). The supramolecular ionic networks containing hydrophobic (trifluoromethanesulfonyl)imide groups demonstrated improved water stability and higher thermal stability than the previously synthesized carboxylate ones. Noticeably, the obtained amorphous supramolecular ionic networks combine not only high ionic conductivity and thermal stability, but also self-healing properties into the same material.

Aggregation of a dibenzo[b,def]chrysene based organic photovoltaic material in solution.

Detailed electrochemical studies have been undertaken on molecular aggregation of the organic semiconductor 7,14-bis((triisopropylsilyl)-ethynyl)dibenzo[b,def]chrysene (TIPS-DBC), which is used as an electron donor material in organic solar cells. Intermolecular association of neutral TIPS-DBC molecules was established by using (1)H NMR spectroscopy as well as by the pronounced dependence of the color of TIPS-DBC solutions on concentration. Diffusion limited current data provided by near steady-state voltammetry also reveal aggregation. Furthermore, variation of concentration produces large changes in shapes of transient DC and Fourier transformed AC (FTAC) voltammograms for oxidation of TIPS-DBC in dichloromethane. Subtle effects of molecular aggregation on the reduction of TIPS-DBC are also revealed by the highly sensitive FTAC voltammetric method. Simulations of FTAC voltammetric data provide estimates of the kinetic and thermodynamic parameters associated with oxidation and reduction of TIPS-DBC. Significantly, aggregation of TIPS-DBC facilitates both one-electron oxidation and reduction by shifting the reversible potentials to less and more positive values, respectively. EPR spectroscopy is used to establish the identity of one-electron oxidized and reduced forms of TIPS-DBC. Implications of molecular aggregation on the HOMO energy level in solution are considered with respect to efficiency of organic photovoltaic devices utilizing TIPS-DBC as an electron donor material.

Inorganic nanoparticles/metal organic framework hybrid membrane reactors for efficient photocatalytic conversion of CO2

Photocatalytic conversion of carbon dioxide (CO2) to useful products has potential to address the adverse environmental impact of global warming. However, most photocatalysts used to date exhibit limited catalytic performance, due to poor CO2 adsorption capacity, inability to efficiently generate photoexcited electrons, and/or poor transfer of the photogenerated electrons to CO2 molecules adsorbed on the catalyst surface. The integration of inorganic semiconductor nanoparticles across metal organic framework (MOF) materials has potential to yield new hybrid materials, combining the high CO2 adsorption capacity of MOF and the ability of the semiconductor nanoparticles to generate photoexcited electrons. Herein, controlled encapsulation of TiO2 and Cu-TiO2 nanoparticles within zeolitic imidazolate framework (ZIF-8) membranes was successfully accomplished, using rapid thermal deposition (RTD), and their photocatalytic efficiency toward CO2 conversion was investigated under UV irradiation. Methanol and carbon monoxide (CO) were found to be the only products of the CO2 reduction, with yields strongly dependent upon the content and composition of the dopant semiconductor particles. CuTiO2 nanoparticle doped membranes exhibited the best photocatalytic performance, with 7 μg of the semiconductor nanoparticle enhancing CO yield of the pristine ZIF-8 membrane by 233%, and methanol yield by 70%. This work opens new routes for the fabrication of hybrid membranes containing inorganic nanoparticles and MOFs, with potential application not only in catalysis but also in electrochemical, separation, and sensing applications.

Assessment of permethylated transition-metal sandwich complexes as internal reference redox systems in ionic liquids

This work reports the voltammetric behaviour of decamethylcobaltocenium, DmCc(+), in different ionic liquids for the first time. Its redox potential was studied relative to that of decamethylferrocene, DmFc, and it is shown that the difference in the mid-point potential between these two permethylated transition-metal sandwich complexes is independent of the ionic liquid composition. A variable difference in mid-point potential, in contrast, was observed for ferrocene and cobaltocenium relative to that of DmFc in similar ionic liquids. In addition, different limitations in the application of DmFc(0/+) and DmCc(+/0) couples as internal reference redox systems in ILs are discussed. From these, the observed spontaneous reaction between DmFc and oxygen leads to important implications toward the establishment of particular conditions for DmFc applications.