Carboxymethylcellulose/Hydrotalcite Bionanocomposites as Paraben Sorbents.

In this work, we synthesized several bionanocomposites of hydrotalcites containing carboxymethylcellulose as interlayer anion (HT-CMC) to be used as sorbents for parabens, a family of emergent pollutants (specifically, for 4-methyl-, 4-propyl- and 4-benzylparaben). Bionanocomposites were obtained by ultrasound-assisted coprecipitation and characterized by X-ray diffraction analysis, fourier transform infrared and raman spectroscopies, elemental and thermogravimetric analysis, scanning and transmission electron microscopies and X-ray fluorescence. All materials proved to be efficient sorbents for parabens through a process conforming to a pseudo second-order kinetics. The experimental adsorption data fitted the Freundlich model very closely and were also highly correlated with the Temkin model. The effects of pH, adsorbate concentration, amount of sorbent and temperature on the adsorption process was evaluated, obtaining the best results for methylparaben adsorption at pH 7, 25 mg of adsorbent and 348 K. The sorbent, HT-CMC-3, showed the highest adsorption capacity (>70%) for methylparaben. Furthermore, a reusability study showed that the bionanocomposite is reusable after its regeneration with methanol. The sorbent still retained its adsorption capacity for up to 5 times with a little loss of efficiency (<5%).

Iridium-Complexed Dipyridyl-Pyridazine Organosilica as a Catalyst for Water Oxidation.

The heterogenization of metal-complex catalysts to be applied in water oxidation reactions is a currently growing field of great scientific impact for the development of energy conversion devices simulating the natural photosynthesis process. The attachment of IrCp*Cl complexes to the dipyridyl-pyridazine N-chelating sites on the surface of SBA-15 promotes the formation of metal bipyridine-like complexes, which can act as catalytic sites in the oxidation of water to dioxygen, the key half-reaction of artificial photosynthetic systems. The efficiency of the heterogeneous catalyst, Ir@NdppzSBA, in cerium(IV)-driven water oxidation was thoroughly evaluated, achieving high catalytic activity even at a long reaction time. The reusability and stability were also examined after three reaction cycles, with a slight loss of activity. A comparison with an analogous homogeneous iridium catalyst revealed the enhanced durability and performance of the heterogeneous system based on the Ir@NdppzSBA catalyst due to the stability of the SBA-15 structure as well as the isolated metal active sites. Thereby, this new versatile synthesis route for the preparation of water oxidation catalysts opens a new avenue for the construction of alternative heterogeneous catalytic systems with high surface area, ease of functionalization, and facile separation to improve the efficiency in the water oxidation reaction.

Luminescent Graphene-Based Materials via Europium Complexation on Dipyridylpyridazine-Functionalized Graphene Sheets.

Graphene-based materials exhibit outstanding physical properties and so are potentially applicable in a great variety of fields. Unlike their corresponding oxides, graphite and graphene are not prone to functionalization. Diels-Alder reactions are among the scarce reactions that they can occur without disrupting their conjugated sp2 systems. Herein, the reaction between graphite and 3,6-di(2-pyridyl)-1,2,4,5-tetrazine under different conditions affords several graphene-based materials consisting of dipyridylpyridazine-functionalized few-layer graphene, multilayer graphene and graphite, the sheets of which act as ligands for the grafting of a europium complex. These three materials show strong red emission under 365 nm UV radiation. Their emitting particles can be visualized by confocal microscopy. The rich coordination chemistry of dipyridylpyridazine ligands has potential novel properties for similarly functionalized graphene-based materials grafted with other metal complexes.

Coumarin Derivatives Solvent-Free Synthesis under Microwave Irradiation over Heterogeneous Solid Catalysts.

A suitable methodology of synthesis of coumarin derivatives by Pechmann reaction over heterogeneous solid acid catalysts in a free solvent media under microwave irradiation is described. Resorcinol, phenol and ethyl acetoacetate were selected as model reactants in the Pechmann condensation. The catalytic activity of several materials-Amberlyst-15, zeolite ß and sulfonic acid functionalized hybrid silica-in solvent-free microwave-assisted synthesis of the corresponding coumarin derivatives has been investigated in detail. 7-Hydroxy-4-methylcoumarin and 4-methylcoumarin were obtained in 97% and 43% yields, respectively, over Amberlyst-15. This was the most active catalyst in the Pechmann reaction under studied conditions.

Efficient Removal of Nonylphenol Isomers from Water by Use of Organo-Hydrotalcites.

The presence of potent organic endocrine-disrupting chemicals (EDCs) in natural aquifers can have adverse impacts on public health and the environment. 4-nonylphenol, one such EDC, can be efficiently removed from water by adsorption onto a clayey material. In this work, we created an effective sorbent for this purpose by using co-precipitation and subsequent ion-exchange to intercalate the organic anion deoxycholate into a Mg/Al hydrotalcite. Intercalating deoxycholate ions increased the organophilicity of the hydrotalcite surface. The solid was used to adsorb 4-nonylphenol at different pollutant concentrations and temperatures. The adsorption process was subjected to a kinetic study. Based on the results, the EDC was adsorbed by chemisorption. In addition, based on the equilibrium isotherms used for the process, the Freundlich model was the most accurate in reproducing the adsorption of 4-nonylphenol onto deoxycholate-intercalated hydrotalcite.

Copper-complexed dipyridyl-pyridazine functionalized periodic mesoporous organosilica as a heterogeneous catalyst for styrene epoxidation.

A new heterogeneous catalyst has been synthesized by immobilization of a copper complex on dipyridyl-pyridazine functionalized periodic mesoporous organosilica (dppz-vPMO). This ordered support was first prepared by a co-condensation reaction between vinyltriethoxysilane and 1,2-bis(trimethoxysilyl)ethane and further post-functionalized through a hetero Diels-Alder reaction with 3,6-di-2-pyridyl-1,2,4,5-tetrazine. Techniques such as XRD, N2 isotherms, TEM, 13C NMR, XPS and DRIFT, among others, were employed to characterize the surface functionalized materials. These results have proven the ordered mesostructure of the materials as well as the presence of novel nitrogen-chelating heterocyclic compounds on the pore surface after the post-modification process. Additionally, the successful anchoring of a copper complex on the dipyridyl-pyridazine (dppz) ligands has been confirmed. The resulting material was evaluated as a heterogeneous catalyst in the epoxidation of styrene using tert-butylhydroperoxide (TBHP) as an oxidant. Under the optimized reaction conditions, Cu@dppz-vPMO showed a high styrene conversion (86.0%) and a remarkable selectivity to styrene oxide (41.9%). Indeed, this catalyst provided excellent catalytic results in terms of stability, reaction rate, conversion and selectivity compared to other bipyridine-like copper catalysts.

Ru- and Ir-complex decorated periodic mesoporous organosilicas as sensitizers for artificial photosynthesis.

A versatile and facile strategy based on an inverse electron demand Diels-Alder reaction between 5-norbornen-2-yltriethoxysilane and a tetrazine derivative has been established for the synthesis of a new triethoxysilane precursor containing dipyridylpyridazine units. Such a precursor has been incorporated into the mesostructure of an ethylene-bridged periodic mesoporous organosilica (PMO) material through a one-pot synthesis via a co-condensation method. Upon attachment of Ru- and Ir-complexes to the pendant N-chelating heterocyclic ligands, the resulting decorated PMOs have acted as photosensitizers in artificial photosynthetic systems. The deposition of Pt on these PMOs has allowed us to obtain efficient photocatalytic materials for the hydrogen evolution reaction as a result of electron transfer from the light harvesting Ru- and Ir-complexes to the supported Pt nanoparticles through methyl viologen as an electron relay. They have exhibited total turnover number values of 573 and 846, respectively, under visible light irradiation. The role played by each component and the stability of the photocatalytic systems have been discussed. The present approach paves the way to the synthesis of different materials with coordination sites capable of forming surface complexes to be applied as sensitizers and catalysts.

Formation of stable nanolayers of meixnerite via a combined delamination-ion exchange process.

A combination of delamination and ion exchange allowed us to obtain new solids consisting of nanolayers of double hydroxides containing hydroxyl as charge balancing ion (i.e., meixnerite monolayers). The solids were prepared from Mg/Al HLCs containing dodecylbenzenesulphonate (DBS) anion in the interlayer region, using a procedure involving sonication and swelling of the interlayer region in the presence of 1-butanol as solvent. This treatment converts the initial, milky dispersion, into a translucent dispersion suggesting that the solid is completely exfoliated. Then, the translucent dispersion is treated with an NaOH solution in 1-butanol in order to exchange DBS- ions with OH- ions and simultaneously precipitate the DBS sodium salt while offsetting charge deficiencies in the solid layers. The exchange process results in no relamination of the structure, which allows a new material consisting of individual nanolayers of meixnerite to be prepared.

Oleate Epoxidation in a Confined Matrix of Hydrotalcite.

Oleate ion was intercalated into a hydrotalcite obtained using a conventional precipitation method and an alternative, novel method involving microwave-assisted ion exchange. The latter method gave a more crystalline hydrotalcite with better textural properties than the former. The spacing between layers in the hydrotalcites was used to epoxidize the double bond in oleate ion. X-ray diffraction patterns revealed that the layered structure of the hydrotalcites was not altered by the reaction. The epoxidation of oleate ion with m-chloroperbenzoic acid (mCPBA) was monitored using Raman spectroscopy. The results of this work testify to the high potential of hydrotalcites as molecular reactors for reactions in confined spaces.

Thiol-Functionalized Ethylene Periodic Mesoporous Organosilica as an Efficient Scavenger for Palladium: Confirming the Homogeneous Character of the Suzuki Reaction.

This work describes the synthesis of thiol-functionalized periodic mesoporous organosilicas (PMOs) prepared using the precursor 1-thiol-1,2-bis(triethoxysilyl)ethane, alone or mixed with 1,2-bis(triethoxysilyl)ethane. The thiol groups incorporated into the structure were found to be efficient for palladium binding. This has allowed these materials to be used as catalysts in the Suzuki cross-coupling reaction of bromobenzene and phenylboronic acid. Their performance has been compared to palladium-supported periodic mesoporous (organo)silicas and important differences have been observed between them. The use of different heterogeneity tests, such as hot filtration test and poisoning experiments, has provided a deep insight into the reaction mechanism and has confirmed that the reaction occurs in the homogeneous phase following a "release and catch" mechanism. Furthermore, the thiol-functionalized periodic mesoporous organosilica, synthesized using only 1-thiol-1,2-bis(triethoxysilyl)ethane as a precursor, has proven to be an efficient palladium scavenger.

Identification of pigments in the Annunciation sculptural group (Cordoba, Spain) by micro-Raman spectroscopy.

A highly flexible method based on micro-Raman spectroscopy was used to examine pigment traces on an Annunciation sculpture group dating from the late Middle Ages. The group comprises a statue of the Archangel Gabriel and another of the Virgin Mary. Both are currently housed in the Archaeological Museum of Cordoba, southern Spain. Information about the pigment palette used by the artists of the time to decorate religious limestone sculptures was for the first time obtained. The pigments found included vermilion (HgS), hematite (α-Fe2O3), azurite [Cu3(CO3)2(OH)2], cerussite (PbCO3) and anatase (TiO2). None was directly applied to the sculptures; rather, the limestone was coated with a primer containing calcium carbonate (possibly chalk or half-chalk). The polychromy on both sculptures, which was originally applied in the XV century and seriously damaged in the XVIII, had been treated with an ochre-coloured priming layer of gypsum to make it more uniform and optically similar to the underlying stone.

Fast ultrasound-assisted synthesis of highly crystalline MIL-88A particles and their application as ethylene adsorbents.

Highly crystalline MIL-88A particles have been successfully synthesized via fast ultrasound-assisted processes. The influence of the sonication generator and synthesis time on the structure, crystallinity, morphology and surface area of the materials were studied in detail. Under this modified ultrasonic method, X-ray diffraction patterns of MIL-88A particles showed highly crystalline structures in contrast to those reported in literature. Significant differences on surface areas and microporosity were appreciated under ultrasound conditions employed. Specific surface areas in the range between 179 and 359 m2 g-1 were obtained. That material synthesized under ultrasound batch conditions during 1 h had the highest surface area and microporous character. Different particle sizes and morphologies were obtained depending on the synthesis procedure. In general, probe sonicators led to smaller particle sizes. Moreover, a comparative study of the ethylene adsorption of the MIL-88A particles and several common MOFs in the ethylene adsorption was investigated. The results suggest that the modified ultrasound-assisted procedure for the synthesis of MIL-88A is effective to obtain highly crystalline particles, which are very efficient to adsorb ethylene molecules.

A Comparative Study of Particle Size Distribution of Graphene Nanosheets Synthesized by an Ultrasound-Assisted Method.

Graphene-based materials are highly interesting in virtue of their excellent chemical, physical and mechanical properties that make them extremely useful as privileged materials in different industrial applications. Sonochemical methods allow the production of low-defect graphene materials, which are preferred for certain uses. Graphene nanosheets (GNS) have been prepared by exfoliation of a commercial micrographite (MG) using an ultrasound probe. Both materials were characterized by common techniques such as X-ray diffraction (XRD), Transmission Electronic Microscopy (TEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). All of them revealed the formation of exfoliated graphene nanosheets with similar surface characteristics to the pristine graphite but with a decreased crystallite size and number of layers. An exhaustive study of the particle size distribution was carried out by different analytical techniques such as dynamic light scattering (DLS), nanoparticle tracking analysis (NTA) and asymmetric flow field flow fractionation (AF4). The results provided by these techniques have been compared. NTA and AF4 gave higher resolution than DLS. AF4 has shown to be a precise analytical technique for the separation of GNS of different sizes.

Spectroscopic analysis of corrosion products in a bronze cauldron from the Late Iberian Iron Age.

Selected bronze fragments unearthed at Cerro de la Cruz (Almedinilla, southern Spain) were analyzed to determine the chemical composition of the corrosion products formed on their surface. The fragments came from a large bronze cauldron used in an Iberian village that was devastated in the mid II century BCE - possibly around 141 BCE. The fragments were analyzed by using various instrumental techniques including electron scanning microscopy coupled to energy dispersive X-ray spectroscopy (SEM-EDS), X-ray fluorescence (XRF) spectroscopy, and also by X-ray diffraction (XRD) and micro-Raman spectroscopy. Based on the results, being buried for a long time caused the main elements in the alloy to mineralize and form stratified layers consisting of various mineral phases including cuprite (Cu2O), malachite [Cu2CO3(OH)2] and cassiterite (Sn2O). The fragments also contained chloride and trihydroxychloride compounds such as nantokite (CuCl) and atacamite [Cu2Cl(OH)3], respectively, which make conservation of archaeological objects troublesome. These results testify to a strong interaction of the alloy elements with soil components. Also, the results obtained suggest a Type I of corrosion structure. Using the SEM-EDS, XRD and XRF and micro-Raman spectroscopies allowed corrosion products in the fragments to be successfully characterized in microchemical and structural.

Microwave atmospheric pressure plasma jets for wastewater treatment: Degradation of methylene blue as a model dye.

The degradation of methylene blue in aqueous solution as a model dye using a non thermal microwave (2.45 GHz) plasma jet at atmospheric pressure has been investigated. Argon has been used as feed gas and aqueous solutions with different concentrations of the dye were treated using the effluent from plasma jet in a remote exposure. The removal efficiency increased as the dye concentration decreased from 250 to 5 ppm. Methylene blue degrades after different treatment times, depending on the experimental plasma conditions. Thus, kinetic constants up to 0.177 min-1 were obtained. The higher the Ar flow, the faster the degradation rate. Optical emission spectroscopy (OES) was used to gather information about the species present in the gas phase, specifically excited argon atoms. Argon excited species and hydrogen peroxide play an important role in the degradation of the dye. In fact, the conversion of methylene blue was directly related to the density of argon excited species in the gas phase and the concentration of hydrogen peroxide in the aqueous liquid phase. Values of energy yield at 50% dye conversion of 0.296 g/kWh were achieved. Also, the use of two plasma applicators in parallel has been proven to improve energy efficiency.

Heterogeneous Suzuki cross-coupling reactions over palladium/hydrotalcite catalysts.

The efficiency of various heterogeneous solids consisting of palladium supported on hydrotalcite as catalysts in the Suzuki cross-coupling reaction between bromobenzene and phenylboronic acid was studied. Based on the catalytic activity results, the reaction develops to an acceptable extent with 100% selectivity at moderate temperatures in the presence of some of the catalysts. The best results were provided by a catalyst consisting of an acetate-pyridine complex of Pd supported on hydrotalcite that gave high conversion values even after three reuses. The reactions conditions were very mild (a temperature of 55 degrees C and atmospheric pressure). In fact, the catalyst provided conversion and selectivity results surpassing those of existing heterogeneous phase catalysts and most homogeneous phase catalysts for the same purpose.

Raman microspectroscopic analysis of decorative pigments from the Roman villa of El Ruedo (Almedinilla, Spain).

In this work, we analysed the preparatory layer and paintings in the hypocaustum of the Roman villa of El Ruedo (Almedinilla, southern Spain). The specimens studied were from the III and IV centuries. Raman microscopy was for the first time used here to examine Roman pictures in the south of the Iberian peninsula. The results obtained allowed us to establish the chemical nature of the different pigments used by the Roman artists. All were applied over a preparatory layer consisting of limewash. The different colours used (black, white, red, yellow, green and blue) were obtained by using carbon, calcite, gypsum, hematite, goethite, green earth and Egyptian blue. Some exhibited various hues that were obtained by mixing the previous compounds. Worth special note is the incipient presence of blue pigments, which were rarely used in Roman Hispania owing to their scarcity and high price.

Preparation of Palladium-Supported Periodic Mesoporous Organosilicas and their Use as Catalysts in the Suzuki Cross-Coupling Reaction.

Three periodic mesoporous materials, i.e., two organosilicas with either ethylene or phenylene bridges and one silica, have been used as supports for Pd nanoparticles. All Pd-supported samples (1.0 wt%) were prepared by the incipient wetness method and subsequently reduced in an H2 stream at 200 °C. Both hydrogen chemisorption and temperature programmed reduction experiments revealed significant differences depending on the support. Pd2+ species were more reducible on the mesoporous organosilicas than on their silica counterpart. Also, remarkable differences on the particle morphology were observed by transmission electron microscopy. All Pd-supported samples were active in the Suzuki cross-coupling reaction between bromobenzene and phenylboronic acid.

Metal-Exchanged ß Zeolites as Catalysts for the Conversion of Acetone to Hydrocarbons.

Various metal-ß zeolites have been synthesized under similar ion-exchange conditions. During the exchange process, the nature and acid strength of the used cations modified the composition and textural properties as well as the Brönsted and Lewis acidity of the final materials. Zeolites exchanged with divalent cations showed a clear decrease of their surface Brönsted acidity and an increase of their Lewis acidity. All materials were active as catalysts for the transformation of acetone into hydrocarbons. Although the protonic zeolite was the most active in the acetone conversion (96.8% conversion), the metal-exchanged zeolites showed varied selectivities towards different products of the reaction. In particular, we found the Cu-ß to have a considerable selectivity towards the production of isobutene from acetone (over 31% yield compared to 7.5% of the protonic zeolite). We propose different reactions mechanisms in order to explain the final product distributions.

Study of organo-hybrid layered double hydroxides by medium and near infrared spectroscopy.

An Mg/Al layered double hydroxide (LDH) containing carbonate ion in its interlayer region was examined by medium infrared (MIR) and near infrared reflectance spectroscopy (NIRS). The MIR and NIR spectroscopy techniques was also used to study two organo-hybrid LDHs containing interlayer dodecylbenzenesulphonate (DBS) and dodecylsulphate (DS) ions, respectively. The NIR spectra for the latter solids were found to exhibit the overtone and combination bands for the hydroxyl groups in addition to those typical bands of the organic host functions.