Effects of Iron Species on Low Temperature CO2 Electrolyzers.

Electrochemical energy conversion devices are considered key in reducing CO2 emissions and significant efforts are being applied to accelerate device development. Unlike other technologies, low temperature electrolyzers have the ability to directly convert CO2 into a range of value-added chemicals. To make them commercially viable, however, device efficiency and durability must be increased. Although their design is similar to more mature water electrolyzers and fuel cells, new cell concepts and components are needed. Due to the complexity of the system, singular component optimization is common. As a result, the component interplay is often overlooked. The influence of Fe-species clearly shows that the cell must be considered holistically during optimization, to avoid future issues due to component interference or cross-contamination. Fe-impurities are ubiquitous, and their influence on single components is well-researched. The activity of non-noble anodes has been increased through the deliberate addition of iron. At the same time, however, Fe-species accelerate cathode and membrane degradation. Here, we interpret literature on single components to gain an understanding of how Fe-species influence low temperature CO2 electrolyzers holistically. The role of Fe-species serves to highlight the need for considerations regarding component interplay in general.

Amorphous Calcium Phosphates: Solvent-Controlled Growth and Stabilization through the Epoxide Route.

Calcium phosphates stand among the most promising nanobiomaterials in key biomedical applications, such as bone repairment, signalling or drug/gene delivery. Their intrinsic properties as crystalline structure, composition, particle shape and size define their successful use. Among these compounds, metastable amorphous calcium phosphate (ACP) is currently gaining particular attention due to its inherently high reactivity in solution, which is crucial in bone development mechanisms. However, the preparation of this highly desired (bio)material with control over its shape, size and phase purity remains as a synthetic challenge. In this work, the epoxide route was adapted for the synthesis of pure and stable ACP colloids. By using biocompatible solvents, such as ethylene glycol and/or glycerine, it was possible to avoid the natural tendency of ACP to maturate into more stable and crystalline apatites. Moreover, this procedure offers size control, ranging from small nanoparticles (60 nm) to micrometric spheroids (>500 nm). The eventual fractalization of the internal mesostructured can be tuned, by simply adjusting the composition of the ethylene glycol:glycerine solvent mixture. These findings introduce the use of green solvents as a new tool to control crystallinity and/or particle size in the synthesis of nanomaterials, avoiding the use of capping agents and preserving the natural chemical reactivity of the pristine surface.

The Missing Link in the Magnetism of Hybrid Cobalt Layered Hydroxides: The Odd-Even Effect of the Organic Spacer.

A dramatic change in the magnetic behaviour, which solely depends on the parity of the organic linker molecules, has been found in a family of layered CoII hydroxides covalently functionalized with dicarboxylic molecules. These layered hybrid materials have been synthesized at room temperature using a one-pot procedure through the epoxide route. While hybrids connected by odd alkyl chains exhibit coercive fields (Hc ) below ca. 3500 Oe and show spontaneous magnetization at temperatures (TM ) below 20 K, hybrids functionalized with even alkyl chains behave as hard magnets with Hc >5500 Oe and display a TM higher than 55 K. This intriguing behaviour was studied by density functional theory with the incorporation of a Hubbard term (DFT+U) calculations, unveiling the structural subtleties underlying this observation. Indeed, the different molecular orientation exhibited by the even/odd alkyl chains, and the orientation of the covalently linked carboxylic groups modify the intensity of the magnetic coupling of both octahedral and tetrahedral in-plane sublattices, thus strongly affecting the magnetic properties of the hybrid. These findings offer an outstanding level of tuning in the molecular design of hybrid magnetic materials based on layered hydroxides.

Unveiling the Occurrence of Co(III) in NiCo Layered Electroactive Hydroxides: The Role of Distorted Environments.

Co- and Ni-based layered hydroxides constitute a unique class of two-dimensional inorganic materials with exceptional chemical diversity, physicochemical properties and outstanding performance as supercapacitors and overall water splitting catalysts. Recently, the occurrence of Co(III) in these phases has been proposed as a key factor that enhance their electrochemical performance. However, the origin of this centers and control over its contents remains as an open question. We employed the Epoxide Route to synthesize a whole set of α-NiCo layered hydroxides. The PXRD and XAS characterization alert about the occurrence of Co(III) as a consequence of the increment in the Ni content. DFT+U simulation suggest that the shortening of the Co-O distance promotes a structural distortion in the Co environments, resulting in a double degeneration in the octahedral Co 3d orbitals. Hence, a strong modification of the electronic properties leaves the system prone to oxidation, by the appearance of Co localized electronic states on the Fermi level. This work combines a microscopic interpretation supported by a multiscale crystallochemical analysis, regarding the so-called synergistic redox behavior of Co and Ni, offering fundamental tools for the controllable design of highly efficient electroactive materials. To the best of our knowledge, this is the first computational-experimental investigation of the electronic and structural details of α-NiCo hydroxides, laying the foundation for the fine tuning of electronic properties in layered hydroxides.

Mild Homogeneous Synthesis of Gold Nanoparticles through the Epoxide Route: Kinetics, Mechanisms, and Related One-Pot Composites.

A new one-pot homogeneous methodology at room temperature to obtain Au nanoparticles (AuNP) on the basis of the epoxide route is presented. The proposed method takes advantage of the homogenous generation of OH- moieties driven by epoxide ring-opening, mediated by chloride nucleophilic attack. Once reached alkaline conditions, the reducing medium allows the quantitative formation of AuNP under well-defined kinetic control. A stabilizing agent, such as polyvinylpyrrolidone (PVP) or cetyltrimethylammonium chloride (CTAC), is required to maintain the AuNP stable. Meanwhile their presence dramatically affects the reduction kinetics and pathway, as demonstrated by the evolution of the UV/Vis spectra, small-angle X-ray scattering (SAXS) patterns, and pH value along the reaction. In the presence of PVP nanogold spheroids are obtained following a similar reduction mechanism as that observed for control experiments in the absence of PVP. However, if CTAC is employed a stable complex with AuIII is formed, leading to a different reaction pathway and resulting in ellipsoidal-like shaped AuNP. Moreover, the proposed methodology allows stabilize the growing AuNP, by coupling their formation with nonalkoxidic sol-gel reactions, leading to nanocomposite gels with embedded metallic nanoparticles. The epoxide route thus offers a versatile scenario for the one-pot preparation of new metal nanoparticles-inorganic/hybrid matrices nanocomposites with valuable optical properties.

Halide-Mediated Modification of Magnetism and Electronic Structure of α-Co(II) Hydroxides: Synthesis, Characterization, and DFT+U Simulations.

The present study introduces a comprehensive exploration in terms of physicochemical characterization and calculations based on density functional theory with Hubbard's correction (DFT+U) of the whole family of α-Co(II) hydroxyhalide (F, Cl, Br, I). These samples were synthesized at room temperature by employing a one-pot approach based on the epoxide route. A thorough characterization (powder X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis/mass spectroscopy, and magnetic and conductivity measurements) corroborated by simulation is presented that analyzes the structural, magnetic, and electronic aspects. Beyond the inherent tendency of intercalated anions to modify the interlayer distance, the halide's nature has a marked effect on several aspects. Such as the modulation of the CoOh to CoTd ratio, as well as the inherent tendency towards dehydration and irreversible decomposition. Whereas the magnetic behavior is strongly correlated with the CoTd amount reflected in the presence of glassy behavior with high magnetic disorder, the electrical properties depend mainly on the nature of the halide. The computed electronic structures suggest that the CoTd molar fraction exerts a minor effect on the inherent conductivity of the phases. However, the band gap of the solid turns out to be significantly dependent on the nature of the incorporated halide, governed by ligand to metal charge transfer, which minimizes the gap as the anionic radius becomes larger. Conductivity measurements of pressed pellets confirm this trend. To the best of our knowledge, this is the first report on the magnetic and electrical properties of α-Co(II) hydroxyhalides validated with in silico descriptions, opening the gate for the rational design of layered hydroxylated phases with tunable electrical, optical, and magnetic properties.

On Demand One-Pot Mild Preparation of Layered Double Hydroxides and Their Hybrid Forms: Advances through the Epoxide Route.

Epoxide ring opening driven alkalinization process was explored with the aim of preparing layered double hydroxide (LDH) phases on demand, at room temperature. Employing iodide as nucleophilic agent, the precipitation reaction can be driven under much lower halide concentrations. This scenario favors the selective intercalation of concomitant bulky oxo anions as nitrate or perchlorate in the LDH products, allowing for the one-pot synthesis of an LDH able to delaminate in formamide. Even large dicarboxylic acids, - O2 C-(CH2 )n -CO2 - , with n up to 8, can be quantitively intercalated within the growing LDH phase, providing a versatile one-pot route for hybrid LDHs as well. Under the mild conditions employed, governed by a continuous pH rise from a starting acid condition, a MII to M*III ratio of 2 prevails, independently from the overall cationic composition. However, after moderate hydrothermal aging LDH phases bearing a cationic ratio higher than 2 could result. The solubility of a given chloride-containing MII 2 M*III LDH can be approximated as a linear combination of the solubility of the pure hydroxylated phases of the constitutive cations, M(OH)2 and M* (OH)3 .

Biopolymeric pellets of polyvinyl alcohol and alginate for the encapsulation of Ib-M6 peptide and its antimicrobial activity against E. coli.

The encapsulation of Ib-M6 antibacterial peptide in pellets of polyvinyl alcohol (PVA) and polyvinyl alcohol-alginate (PVA-Alg) matrices was carried out in order to explore its controlled release and activity against Escherichia coli K-12. The pellets were obtained by combined ice segregation induced self-assembly (ISISA) and freezing-thawing methods and their microstructure was studied by scanning electron microscopy. Bromothymol blue was used as a model compound to study the transport mechanisms and release from pellets. The results show that there is a significant effect of the total concentration of PVA precursor solutions, the mass ratio of PVA of different molecular weights and the addition of alginate on the microstructure and transport properties of pellets. The antibacterial activity of Ib-M6 against Escherichia coli K-12 was not affected by the encapsulation in PVA pellets. However, the release of Ib-M6 from PVA-Alg pellets was not possible, probably due to the electrostatic interaction of positively charged Ib-M6 and negatively alginate structure. Nonetheless, the controlled release of Ib-M6 from polymeric matrices can be fitting by modifying parameters such as the concentration and type of polymer precursors.

Interplay of Coordination Environment and Magnetic Behavior of Layered Co(II) Hydroxichlorides: A DFT+U Study.

In this work we present a systematic computational study of the structural and magnetic properties of a layered family of Co(II) hydroxichlorides, obeying to the general formula Co(OH)2- xCl x(H2O) y. This solid contains both octahedral and tetrahedral cobalt ions, displaying a complex magnetic order arising from the particular coupling between the two kinds of metallic centers. Here, supercells representing concentrations of 12, 20, and 40% of tetrahedral sites were modeled consistently with the compositions reported experimentally. Our simulations show that the two types of cobalt ions tend to couple antiferromagnetically, giving rise to a net magnetic moment slightly out of the plane of the layers. The band gap reaches its minimum value of 1.4 eV for the most diluted fraction of tetrahedral Co(II) sites, going up to 2.2 eV when the content is 40%. Moreover, our results suggest that the presence of interlayer water stabilizes the material and at the same time strongly modifies the electronic environment of tetrahedral Co(II), leading to a further drop of the band gap. To our knowledge, this is the first theoretical investigation of this material.

Highly Structured Polyvinyl Alcohol Porous Carriers: Tuning Inherent Stability and Release Kinetics in Water.

Polyvinyl alcohol (PVA) porous carriers were prepared by means of ice templating of aqueous solutions containing of 90 kD and/or 16 kD PVA. The carriers were loaded with traces of a colored probe (methyl orange) to screen their release properties, once immersed in water. The carriers prepared from solutions containing 90 kD and 16 kD PVA resulted in intimate polymer mixtures, exhibiting physical properties that stand in between those of the bare 90 kD or 16 kD PVA end members. The freezing protocols employed were adapted to prepare carriers textured in the form of either monolithic scaffolds (directional constant freezing rate) or millimetric pellets (flash-freeze). Monolithic carriers remain stable in aqueous solution, and the probe release is governed by a swelling-diffusion mechanism. The kinetics of probe release can be tuned from minutes to hours by either increasing the total PVA content or the 90 kD-to-16 kD PVA ratio in the parent solution. In contrast, pellets (millimetric carriers) immersed in water release the probe on the scale of minutes, irrespective of the PVA content or composition. However, the PVA content and the 90 kD-to-16 kD PVA ratio dramatically affect the stability of the carriers. Depending on the formulation, these small carriers can develop swelling, erosion, or eventually massive dissolution.

Extremely efficient crystallization of HKUST-1 and Keggin-loaded related phases through the epoxide route.

Highly crystalline HKUST-1 and COK-16-like phases were obtained based on a mild in situ alkalinization one-pot epoxide driven method. A slurry composed of finely ground trimesic acid, H3BTC, dispersed in a CuCl2 aqueous solution quantitatively developed well crystallized HKUST-1 after the addition of propylene oxide. The use of solid H3BTC ensures a low concentration of free linker, favoring crystalline growth over the precipitation of amorphous or metastable impurities. An extreme space-time yield of 2.1 × 105 kg m-3 day-1 was reached, with no linker excess and minimum use of solvent. The method was equally efficient in the achievement of pure NENU/COK-16 phases, containing [PW12O40]3-, [PMo12O40]3- and [SiMo12O40]4- polyoxometalates.

CeIV -GdIII Mixed Oxides as Hosts for ErIII -Based Upconversion Phosphors.

A family of ErIII and ErIII -YbIII based nanophosphors, hosted in monophasic oxidic CeIV -GdIII binary solid solutions, was prepared. The samples were formulated with a constant ErIII content as the activator, with the eventual addition of YbIII as a sensitizer. The amorphous Ce0.94-x Gdx Er0.06 (OH)CO3 ⋅H2 O and Ce0.94-x Gdx Er0.05 Yb0.01 (OH)CO3 ⋅H2 O precursors were prepared by following the urea method to obtain monodispersed spheres of tunable size ranging from 30 to 450 nm. After being decomposed at 1273 K under an atmosphere of air, the precursors of 200 nm in diameter evolved into monophasic polycrystalline particles preserving the parent shape and size. The role of the composition of the binary matrices in the emission properties was evaluated for two different excitation wavelengths (976 nm and 780 nm) based on the upconversion (UC) emission spectra and their dependence on the incident power. The yield of the UC process is discussed in the framework of established and novel alternative mechanisms. The number of vacancies and mainly the symmetry of the ErIII environment play major roles in the deactivation pathways of the UC emission mechanisms. However, the colours obtained by employing bare CeIV or GdIII hosts are preserved in the related monophasic CeIV -rich or GdIII -rich binary hosts.

Rich stochastic dynamics of co-doped Er:Yb fluorescence upconversion nanoparticles in the presence of thermal, non-conservative, harmonic and optical forces.

The stochastic dynamics of individual co-doped Er:Yb upconversion nanoparticles (UCNP) were investigated from experiments and simulations. The UCNP were characterized by high-resolution scanning electron microscopy, dynamic light scattering, and zeta potential measurements. Single UCNP measurements were performed by fluorescence upconversion micro-spectroscopy and optical trapping. The mean-square displacement (MSD) from single UCNP exhibited a time-dependent diffusion coefficient which was compared with Brownian dynamics simulations of a viscoelastic model of harmonically bound spheres. Experimental time-dependent two-dimensional trajectories of individual UCNP revealed correlated two-dimensional nanoparticle motion. The measurements were compared with stochastic trajectories calculated in the presence of a non-conservative rotational force field. Overall, the complex interplay of UCNP adhesion, thermal fluctuations and optical forces led to a rich stochastic behavior of these nanoparticles.

The magnetic structure of ß-cobalt hydroxide and the effect of spin-orientation.

Synchrotron X-ray and neutron diffraction experiments at various temperatures, down to 3 K, along with ab initio calculations, are carried out to elucidate the magnetic order of layered ß-cobalt-hydroxide. This combination of techniques allows for the unambiguous assignment of the magnetic structure of this material. Our results confirm that below the Néel temperature high-spin cobalt centers are ferromagnetically coupled within a layer, and antiferromagnetically coupled across layers (magnetic propagation vector k = (0,0,½)), in agreement with the indirect interpretation based on magnetic susceptibility measurements. A paramagnetic/antiferromagnetic transition is observed at around 15 K. Moreover, the thermal expansion behavior along the c-lattice direction, perpendicular to the layers, shows an inflection slightly above this temperature, at around 30 K. The neutron diffraction patterns and the non-collinear DFT+U calculations indicate that the magnetization forms an angle of about 35° with the cobalt planes. In particular, for an isolated ferromagnetic layer, the electronic structure calculations reveal sharp cusps on the potential energy surface when the spins point parallel or perpendicular to the planes, suggesting that the ferromagnetic superexchange mechanism is strongly sensitive to the orientation of the magnetic moment.

Microorganism mediated biosynthesis of metal chalcogenides; a powerful tool to transform toxic effluents into functional nanomaterials.

Cadmium contained in soil and water can be taken up by certain crops and aquatic organisms and accumulate in the food-chain, thus removal of Cd from mining or industrial effluents - i.e. Ni-Cd batteries, electroplating, pigments, fertilizers - becomes mandatory for human health. In parallel, there is an increased interest in the production of luminescent Q-dots for applications in bioimaging, sensors and electronic devices, even the present synthesis methods are economic and environmentally costly. An alternative green pathway for producing Metal chalcogenides (MC: CdS, CdSe, CdTe) nanocrystals is based on the metabolic activity of living organisms. Intracellular and extracellular biosynthesis of can be achieved within a biomimetic approach feeding living organisms with Cd precursors providing new routes for combining bioremediation with green routes for producing MC nanoparticles. In this mini-review we present the state-of-the-art of biosynthesis of MC nanoparticles with a critical discussion of parameters involved and protocols. Few existing examples of scaling-up are also discussed. A modular reactor based on microorganisms entrapped in biocompatible mineral matrices - already proven for bioremediation of dissolved dyes - is proposed for combining both Cd-depletion and MC nanoparticle's production.

Ca(ii) and Ce(iii) homogeneous alginate hydrogels from the parent alginic acid precursor: a structural study.

Alginate hydrogels are suitable for the encapsulation of biomolecules and microorganisms for the building of bioactive materials. Several alternatives to the conventional alginate formulation are being studied for a broad range of biotechnological applications; among them the crosslinking of alginate by lanthanide cations, Ln(iii), envisages expanded biomedical applications. The performance of these functional materials is highly related to the microstructure of the alginate matrix, which in turn is affected by the conditions of synthesis. In particular, when a diffusing gradient of the crosslinking cation is involved, microstructure inhomogeneities are expected at the macroscopic level. Here we discuss the subtle differences in the microstructure, as assessed by SAXS (Small Angle X-ray Scattering), established in the direction of the gradient of diffusion of Ca(ii) or Ce(iii).

Feasibility of using a translucid inorganic hydrogel to build a biosensor using immobilized algal cells.

Anthropic activities generate contaminants, as pesticides and other pollutants, in the aquatic environment which present a real threat to ecosystems and human health. Thus, monitoring tools become essential for water managers to detect these chemicals before the occurrence of adverse effects. In this aim, algal cell biosensors, based on photosystem II activity measurement, have been designed for several years in previous studies. In this work, we study a new immobilization technique of algal cells in the aim of improving the performance of these biosensors. Immobilization was here achieved by encapsulation in a hybrid alginate/silica translucid hydrogel. The feasibility of this process was here assessed, and the biosensor designed was tested on the detection of chemicals in urban rainwaters.

Silica@proton-alginate microreactors: a versatile platform for cell encapsulation.

As an alternative approach to the well known Ca(ii)-alginate encapsulation process within silica hydrogels, proton-driven alginate gelation was investigated in order to establish its capacity as a culture carrier, both isolated and embedded in an inorganic matrix. Control over the velocity of the proton-gelation front allows the formation of a hydrogel shell while the core remains liquid, allowing bacteria and microalgae to survive the strongly acidic encapsulation process. Once inside the inorganic host, synthesized by a sol-gel process, the capsules spontaneously redissolve without the aid of external complexing agents. The entrapped cells survive the two-step process to a significant extent; culture's growth restores the initial cell count in less than two weeks. Biosynthesis of Au nanoparticles mediated by the entrapped microalgae illustrates the preservation of the biosynthetic abilities supported by this platform.

Hierarchical bioglass scaffolds: introducing the "milky way" for templated bioceramics.

Free standing hierarchical bioglass scaffolds were prepared by the ISISA (ice-segregation-induced self-assembly) method. Commercial low-cost precursors such as Ludox® HS-40 and cow milk were employed as the source of SiO2 and biominerals (Ca(ii), P(v), Na(i) and K(i)), respectively. Then, in a single macroscopic piece, three levels of porosity coexist due to the simultaneous templating effect of ice (macropores), milk (50-200 nm mesopores) and the voids left between preformed Ludox® nano building blocks (2-5 nm mesopores). These low cost and green biological nanotemplates, coupled with the ISISA texturing method, allows the preparation of free standing bioglass monoliths, with hierarchical porosity. The effect of the main preparative variables on the final texture is explored; in vitro biomineralization revealed a well-distributed hydroxyapatite-like nanoparticulated layer within 24 h of exposure to a simulated body fluid.

Halide exchange on Mg(II)-Al(III) layered double hydroxides: exploring affinities and electrostatic predictive models.

The crystalline chloride form of layered double hydroxide (LDH) with the formula Mg0.75Al0.25(OH)2Cl0.25·mH2O was gradually exchanged with F(-), Br(-), or I(-) up to a total displacement of Cl(-). For the three anions, both the exchange isotherms as well as the structural changes were inspected along the whole range of chloride displacement. The bulkier Br(-) and I(-) followed an ideal exchange behavior isotherm while F(-) denoted strong deviations from the ideal regime as well as phase segregation. The exchange constants recorded herein were contrasted with bibliographic data belonging to an analogous LDH host, revealing a strong linear free energy correlation. Higher Al(III) to Mg(II) ratios, or layer charge densities, favor a stronger selectivity for smaller halides. For both hosts, the exchange free energy was satisfactorily described in terms of strictly electrostatic-based models.