Composition Effect on the Formation of Oxide Phases by Thermal Decomposition of CuNiM(III) Layered Double Hydroxides with M(III) = Al, Fe.

The thermal decomposition processes of coprecipitated Cu-Ni-Al and Cu-Ni-Fe hydroxides and the formation of the mixed oxide phases were followed by thermogravimetry and derivative thermogravimetry analysis (TG - DTG) and in situ X-ray diffraction (XRD) in a temperature range from 25 to 800 °C. The as-prepared samples exhibited layered double hydroxide (LDH) with a rhombohedral structure for the Ni-richer Al- and Fe-bearing LDHs and a monoclinic structure for the CuAl LDH. Direct precipitation of CuO was also observed for the Cu-richest Fe-bearing samples. After the collapse of the LDHs, dehydration, dehydroxylation, and decarbonation occurred with an overlapping of these events to an extent, depending on the structure and composition, being more pronounced for the Fe-bearing rhombohedral LDHs and the monoclinic LDH. The Fe-bearing amorphous phases showed higher reactivity than the Al-bearing ones toward the crystallization of the mixed oxide phases. This reactivity was improved as the amount of embedded divalent cations increased. Moreover, the influence of copper was effective at a lower content than that of nickel.

Editorial on Special Issues "Aerogels" and "Aerogels 2018".

Aerogels can be defined as ultralight materials with a 3D porous structure, similar to their parent wet gels, where the solvent has been replaced by a gas without a collapse of the gel structure, thanks to the drying process used (supercritical CO2 drying, freeze drying, etc.). (...).

Sodium and acidic alginate foams with hierarchical porosity: Preparation, characterization and efficiency as a dye adsorbent.

A novel approach for the preparation of sodium alginate foams by ice-templating, followed by freeze-drying was described. Important effects of the preparation parameters on the macroporous structure of the final materials could be evidenced. A functionalization procedure for the preparation of acidified macro/meso-porous foams with high surface area was optimized and the efficiency of one alginic acid foam was demonstrated for the adsorption of a basic dye (methylene blue) from aqueous solution. The comparison of the maximum monolayer adsorption capacity of this adsorbent with the values already reported for other biosorbents clearly identified alginic acid foams as competitive sorbents for the removal of methylene blue from aqueous solutions.

Boronic acid-modified alginate enables direct formation of injectable, self-healing and multistimuli-responsive hydrogels.

One-step functionalization of alginate with boronic acid groups allowed spontaneous formation of biocompatible hydrogels under basic conditions without additional complementary molecules or crosslinking agents. The dynamic nature of boronate ester bonds formed with vicinal diols present on alginate pyranose rings provided remarkable self-healing, injectable and multi-stimuli responsive properties to the material.

Keratin Protein-Catalyzed Nitroaldol (Henry) Reaction and Comparison with Other Biopolymers.

Here we describe a preliminary investigation on the ability of natural keratin to catalyze the nitroaldol (Henry) reaction between aldehydes and nitroalkanes. Both aromatic and heteroaromatic aldehydes bearing strong or moderate electron-withdrawing groups were converted into the corresponding ß-nitroalcohol products in both DMSO and in water in the presence of tetrabutylammonium bromide (TBAB) as a phase transfer catalyst. Negligible background reactions (i.e., negative control experiment in the absence of keratin protein) were observed in these solvent systems. Aromatic aldehydes bearing electron-donating groups and aliphatic aldehydes showed poor or no conversion, respectively. In general, the reactions in water/TBAB required twice the amount of time than in DMSO to achieve similar conversions. Moreover, comparison of the kinetics of the keratin-mediated nitroaldol (Henry) reaction with other biopolymers revealed slower rates for the former and the possibility of fine-tuning the kinetics by appropriate selection of the biopolymer and solvent.

Hydrocarbon adsorption in the flexible metal organic frameworks MIL-53(Al, Cr).

A general study of the adsorption of n-alkanes in the flexible metal organic framework (MOF) MIL-53 is presented. The roles of the length of the alkyl chain (n = 1-9), the nature of the metal (Al, Cr), and temperature were investigated. The shape of the adsorption curves is driven by the alkyl chain length of the n-alkanes. While traditional type-I isotherms are observed for short alkanes (n = 1, 2), adsorbates with longer chains induce clear substeps in the isotherm curves whose positions depend on the chain length. Such substeps are due to a breathing phenomenon, as proven by ex situ X-ray diffraction analysis. They strongly depend on the amount of adsorbate in the pores and on the nature of the metal (Al, Cr), which, for a given alkane, leads to a strong change in the substep positions despite the similar characteristics of the two metals. The adsorption kinetics are highly sensitive to small variations in temperature. Their detailed analysis in different regions of the isotherms shows in some cases the existence of distinct diffusion regimes and/or conformations within the flexible phases.

A macrothermodynamic approach to the limit of reversible capillary condensation.

The threshold of reversible capillary condensation is a well-defined thermodynamic property, as evidenced by corresponding states treatment of literature and experimental data on the lowest closure point of the hysteresis loop in capillary condensation-evaporation cycles for several adsorbates. The nonhysteretical filling of small mesopores presents the properties of a first-order phase transition, confirming that the limit of condensation reversibility does not coincide with the pore critical point. The enthalpy of reversible capillary condensation can be calculated by a Clausius-Clapeyron approach and is consistently larger than the condensation heat in unconfined conditions. Calorimetric data on the capillary condensation of tert-butyl alcohol in MCM-41 silica confirm a 20% increase of condensation heat in small mesopores. This enthalpic advantage makes easier the overcoming of the adhesion forces by the capillary forces and justifies the disappearing of the hysteresis loop.

New evidence of confinement effects in mesoporous materials and the definition of confined Pitzer acentric factors.

In the present work, the corresponding states principle is proposed as a new approach to clarify the comparison between adsorption-desorption isotherms obtained on porous solids. The applicability of this principle at the capillary critical point in adsorption-desorption isotherms is demonstrated. Deviations of the Clausius-Clapeyron curves in reduced coordinates are interpreted in terms of polarizability, and those are perfectly correlated using analogous Pitzer acentric factors in confined environments. New acentric factors are proposed to take confinement effects in mesoporous materials into account. Enthalpic excesses during capillary condensation could be predicted, and those are supported by calorimetric experiments.