Visible-Light-Driven Photocatalytic H2 Production Using Composites of Co-Al Layered Double Hydroxides and Graphene Derivatives.

The direct conversion of solar energy into chemical energy represents an enormous challenge for current science. One of the commonly proposed photocatalytic systems is composed of a photosensitizer (PS) and a catalyst, together with a sacrificial electron donor (ED) when only the reduction of protons to H2 is addressed. Layered double hydroxides (LDH) have emerged as effective catalysts. Herein, two Co-Al LDH and their composites with graphene oxide (GO) or graphene quantum dots (GQD) have been prepared by coprecipitation and urea hydrolysis, which determined their structure and so their catalytic performance, giving H2 productions between 1409 and 8643 µmol g-1 using a ruthenium complex as PS and triethanolamine as ED at 450 nm. The influence of different factors, including the integration of both components, on their catalytic behavior, has been studied. The proper arrangement between the particles of both components seems to be the determining factor for achieving a synergistic interaction between LDH and GO or GQD. The novel Co-Al LDH composite with intercalated GQD achieved an outstanding catalytic efficiency (8643 µmol H2 g-1) and exhibited excellent reusability after 3 reaction cycles, thus representing an optimal integration between graphene materials and Co-Al LDH for visible light driven H2 photocatalytic production.

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%).

Bioprotection of Olive Trees Against Verticillium Wilt by Pomegranate and Carob Extracts.

Bioprotection using plant extracts is an environmentally friendly strategy in crop protection. Effective control of Verticillium wilt of olive (Olea europaea; VWO), caused by Verticillium dahliae, has proven challenging due to the ineffectiveness of chemicals, which makes it necessary to search for new control tools. Thus, the aim of this study was to evaluate the effect of pomegranate (Punica granatum) and carob (Ceratonia siliqua) extracts against VWO. Extracts derived from pomegranate peels and carob pods and leaves were obtained using ethanol, methanol, or ethyl acetate as solvents. A targeted analysis of their metabolite composition was performed using QTRAP Ultra High-Performance Liquid Chromatography with Mass Spectrometry (QTRAP UHPLC‒MS). Remarkably, gallic acid was detected in all extracts at a high concentration. The effect of the extracts on the mycelial growth and on the germination of conidia and microsclerotia of V. dahliae was evaluated by in vitro sensitivity tests at various doses: 0 (control), 3, 30, 300 and 3,000 mg of extract/liter. Extracts obtained with ethanol or methanol significantly reduced the viability of V. dahliae structures when applied at the highest dose, while those obtained with ethyl acetate were ineffective across all doses. The most effective extracts, as determined in vitro, were then evaluated against the disease in olive plants. Potted plants of cv. Picual were treated by spraying (foliar application) or irrigation (root application) of extracts at 3,000 mg of extract/liter, followed by inoculation with V. dahliae. The results indicated that foliar applications were ineffective, while root treatments with pomegranate peel or carob leaf extracts were more effective in reducing disease severity, regardless of solvent, compared to that of the untreated control.

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.

Luminescent thermometer based on Eu3+ /Tb3+ -organic-functionalized mesoporous silica.

In this work we investigate a mesoporous silica (MS) decorated with dipyridyl-pyridazine (dppz) ligands and further grafted with a mixture of Eu3+ /Tb3+ ions (28.45%:71.55%), which was investigated as a potential thermometer in the 10-360 K temperature range. The MS material was prepared employing a hetero Diels-Alder reaction: 3,6-di(2-pyridyl)-1,2,4,5-tetrazine was reacted with the double bonds of vinyl-silica (vSilica) followed by an oxidation procedure. We explore using the dppz-vSilica material to obtain visible emitting luminescent materials and for obtaining a luminescent thermometer when grafted with Eu3+ /Tb3+ ions. For the dppz-vSilica@Eu,Tb material absolute sensitivity Sa of 0.011 K-1 (210 K) and relative sensitivity Sr of 1.32 %K-1 (260 K) were calculated showing good sensing capability of the material. Upon temperature change from 10 K to 360 K the emission color of the material changed gradually from yellow to red.

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.

Periodic Mesoporous Organosilicas: from simple to complex bridges; a comprehensive overview of functions, morphologies and applications.

Periodic Mesoporous Organosilicas (PMOs) were developed in 1999 and are basically ordered templated mesoporous organosilicas, prepared by the combination of a surfactant as template and a silsesquioxane as the organosilica precursor. They were one of the first examples of the so-called "hybrid" organic/inorganic materials. In the years that followed, an amazing variety of functional groups, morphologies and applications has been developed. Some of these high-end applications, like low-k buffer layers in microelectronics, chiral catalysts, chromatographic supports, selective adsorbents and light-harvesting devices, have clearly shown their potential. In this review, we will give a comprehensive overview of all these different functionalities and applications that have been created for Periodic Mesoporous Organosilicas.

Modified surfatron device to improve microwave-plasma-assisted generation of RONS and methylene blue degradation in water.

Microwave-induced plasmas generated at atmospheric pressure are very attractive for a great variety of applications since they have a relatively high electron density and can generate large amounts of reactive species. Argon plasmas can be sustained inside dielectric tubes but are radially contracted and exhibit filamentation effects when the diameter of the tube is not narrow enough (over 1.5 mm). In this work, we describe a new approach for creating microwave (2.45 GHz) plasmas under atmospheric pressure conditions by using a surfatron device and power from 10 W. This modified design of the reactor enables the sustenance of non-filamented argon plasmas. These new plasmas have a higher gas temperature and electron density than the plasma generated in the original surfatron configuration. The new design also allows for the maintenance of plasmas with relatively high proportions of water, resulting in the generation of larger quantities of excited hydroxyl radicals (·OH*). Thus, this novel configuration extends the applicability of microwave-induced plasmas by enabling operation under new conditions. Finally, the degradation of methylene blue (MB) in aqueous solutions has been assessed under different initial dye concentrations and argon flow conditions. The new plasma produces a substantial increase in hydrogen peroxide and nitrate concentrations in water and leads to a noteworthy enhancement in MB degradation efficiency. The introduction of water into the plasma produces a minor additional improvement.

Manipulating the Coordination Structure of Molecular Cobalt Sites in Periodic Mesoporous Organosilica for CO2 Photoreduction.

Photocatalytic CO2 reduction, including reaction rate, product selectivity, and longevity, is highly sensitive to the coordination structure of the catalytic active sites, and the precise design of the active site remains a challenge in heterogeneous catalysts. Herein, we report on the modulation of the coordination structure of MN x -type active sites (M = Co or Ni; x = 4 or 5) anchored on a periodic mesoporous organosilica (PMO) support to improve photocatalytic CO2 reduction. The PMO was functionalized with pendant 3,6-di(2'-pyridyl)pyridazine (dppz) groups to allow immobilization of molecular Co and Ni complexes with polypyridine ligands. A comparative analysis of CO2 photoreduction in the presence of an organic photosensitizer (4CzIPN, 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene) and a conventional [Ru(bpy)3]Cl2 sensitizer revealed strong influence of the coordination environment on the catalytic performance. CoN5-PMO demonstrated a superior CO2 photoreduction activity than the other materials and displayed a cobalt-based turnover number (TONCO) of 92 for CO evolution at ∼75% selectivity after 3 h irradiation in the presence of 4CzIPN. The hybrid CoN5-PMO catalyst exhibited better activity than its homogeneous [CoN5] counterpart, indicating that the heterogenization promotes the formation of isolated active sites with improved longevity and faster catalytic rate.

Solar driven CO2 reduction with a molecularly engineered periodic mesoporous organosilica containing cobalt phthalocyanine.

A molecular cobalt phthalocyanine (CoPc) catalyst has been integrated in an ethylene-bridged periodic mesoporous organosilica (PMO) to fabricate a hybrid material, CoPc-PMO, that catalyses CO2 reduction to CO in a photocatalytic system using [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine) as a photosensitizer and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) as an electron donor. CoPc-PMO displays a Co-based turnover number (TONCO) of >6000 for CO evolution with >70% CO-selectivity after 4 h irradiation with UV-filtered simulated solar light, and a quantum yield of 1.95% at 467 nm towards CO. This system demonstrates a benchmark TONCO for immobilised CoPc-based catalysts towards visible light-driven CO2 reduction.

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.

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.

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.

Synthesis of BiOI/Mordenite Composites for Photocatalytic Treatment of Organic Pollutants Present in Agro-Industrial Wastewater.

Recently, bismuth oxyiodide (BiOI) is an attractive semiconductor to use in heterogeneous photocatalysis processes. Unfortunately, BiOI individually shows limited photocatalytic efficiency, instability, and a quick recombination of electron/holes. Considering the practical application of this semiconductor, some studies show that synthetic zeolites provide good support for this photocatalyst. This support material permits a better photocatalytic efficiency because it prevents the quick recombination of photogenerated pairs. However, the optimal conditions (time and temperature) to obtain composites (BiOI/ synthetic zeolite) with high photocatalytic efficiency using a coprecipitation-solvothermal growth method have not yet been reported. In this study, a response surface methodology (RSM) based on a central composite design (CCD) was applied to optimize the synthesis conditions of BiOI/mordenite composites. For this purpose, eleven BiOI/mordenite composites were synthesized using a combined coprecipitation-solvothermal method under different time and temperature conditions. The photocatalytic activities of the synthesized composites were evaluated after 20 min of photocatalytic oxidation of caffeic acid, a typical organic pollutant found in agro-industrial wastewater. Moreover, BiOI/mordenite composites with the highest and lowest photocatalytic activity were physically and chemically characterized using nitrogen adsorption isotherms, scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and diffuse reflectance spectroscopy (DRS). The optimal synthesis conditions prove to be 187 °C and 9 h. In addition, the changes applied to the experimental conditions led to surface property modifications that influenced the photocatalytic degradation efficiency of the BiOI/mordenite composite toward caffeic acid photodegradation.

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.

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.

Temperature dependent NIR emitting lanthanide-PMO/silica hybrid materials.

Two materials - a mesoporous silica (MS) and a periodic mesoporous organosilica (PMO) functionalized with dipyridyl-pyridazine (dppz) units were grafted with near-infrared (NIR) emitting lanthanide (Nd3+, Er3+, Yb3+) complexes in an attempt to obtain hybrid NIR emitting materials. The parent materials: dppz-vSilica and dppz-ePMO were prepared by a hetero Diels-Alder reaction between 3,6-di(2-pyridyl)-1,2,4,5-tetrazine (dptz) and the double bonds of either ethenylene-bridged PMO (ePMO) or vinyl-silica (vSilica) and subsequent oxidation. The dppz-vSilica is reported here for the first time. The prepared lanthanide-PMO/silica hybrid materials were studied in depth for their luminescence properties at room temperature and chosen Nd3+ and Yb3+ samples also at low temperature (as low as 10 K). We show that both the dppz-vSilica and dppz-ePMO materials can be used as "platforms" for obtaining porous materials showing NIR luminescence. To obtain NIR emission these materials can be excited either in the UV or Vis region (into the π→π* transitions of the ligands or directly into the f-f transitions of the Ln3+ ions). More interestingly, when functionalized with Nd3+ or Yb3+ß-diketonate complexes these materials showed interesting luminescence properties over a wide temperature range (10-360 K). The Yb3+ materials were investigated for their potential use as ratiometric temperature sensors.

Thiol-ethylene bridged PMO: A high capacity regenerable mercury adsorbent via intrapore mercury thiolate crystal formation.

Highly ordered thiol-ethylene bridged Periodic Mesoporous Organosilicas were synthesized directly from a homemade thiol-functionalized bis-silane precursor. These high surface area materials contain up to 4.3mmol/g sulfur functions in the walls and can adsorb up to 1183mg/g mercury ions. Raman spectroscopy reveals the existence of thiol and disulfide moieties. These groups have been evaluated by a combination of Raman spectroscopy, Ellman's reagent and elemental analysis. The adsorption of mercury ions was evidenced by different techniques, including Raman, XPS and porosimetry, which indicate that thiol groups are highly accessible to mercury. Scanning transmission electron microscopy combined with EDX showed an even homogenous distribution of the sulfur atoms throughout the structure, and have revealed for the first time that a fraction of the adsorbed mercury is forming thiolate nanocrystals in the pores. The adsorbent is highly selective for mercury and can be regenerated and reused multiple times, maintaining its structure and functionalities and showing only a marginal loss of adsorption capacity after several runs.

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.