Theoretical and X-Ray Evidence of Electrostatic Phosphonium anti and gauche Effects.

Sulphur, not phosphorus, is the only known third-row element capable of experiencing an electrostatic gauche effect with fluorine. Some six-membered rings containing an endocyclic phosphorus atom and a ß-fluorine substituent that can interconvert to axial (gauche relative to phosphorus) and equatorial positions were then analysed. While phosphines do not establish an electrostatic attraction between fluorine and phosphorus, some oxidised forms exhibit surprising stability for the sterically disfavoured axial orientation. Because the nature of this behaviour was not obvious, since an intramolecular hydrogen bond can appear, a phosphonium derivative was further studied and its axial conformation was found to be highly stable. A preference for the gauche arrangement appears even for the acyclic and sterically hindered (2-fluoroethyl)triphenylphosphonium cation. On the other hand, (ethane-1,2-diyl)bis(phosphonium) cations are exclusively in anti conformation due to an (+/+)-electrostatic repulsion between the positively charged phosphonium groups.

Carbon/FexOy magnetic composites obtained from PET and red mud residues: paracetamol and dye oxidation.

Composite materials from PET and red mud (RM) wastes were used as catalysts for environmental application such as the wastewater treatment. The PET-RM catalysts were obtained by a mechanical mixture of the residues followed by thermal treatment under an N2 atmosphere (300°C/1 h). An additional activation of the composites with CO2 was investigated (at 800-900°C) to reduce the red mud basicity. The CO2 activation affected the composites surface area and reduced their carbon content. XRD revealed that the haematite (α-Fe2O3) and maghemite/magnetite are the main iron oxides present in the composites. Mössbauer characterization indicated the formation of reduced iron species (Fe2+), highly reactive, after the composites heat treatment. The materials were very active catalysts for methylene blue (MB) and paracetamol (PRC) removal from aqueous solution. The catalytic activity revealed to be dependent on the surface area and mainly of the presence of reduced iron species in the catalysts. The MB removal reached 97% for both PET-RM 800/2 h and PET-RM 800/5 h, after 1 h of reaction. In the case of PRC, the highest removal was also obtained for PET-RM 800/2 h and PET-RM 800/5 h, of ≈25% and 40%, respectively. The contaminants removal mechanism likely occurred through combined adsorption and Fenton-like oxidation processes.

Synthesis of glycerol carbonate over a 2D coordination polymer built with Nd3+ ions and organic ligands.

In this work, a two-dimensional coordination polymer was synthesized and the structure was determined by single-crystal X-ray diffraction. The crystal structure belongs to the space group Pna21 and was characterized by Raman and FT-infrared spectroscopy, powder X-ray diffraction and Brunauer-Emmett-Teller surface area analysis. Catalyst activities were evaluated through the synthesis of glycerol carbonate from glycerol and urea using a batch reactor. After the optimization of both reaction and reaction conditions, the activity results showed that the coordination polymer used as a heterogeneous catalyst has good values of conversions and selectivity for the manufacturing of glycerol carbonate in a fine-chemical process. The analysis of powder X-ray diffraction and spectroscopy for the coordination polymer employed, before and after the reaction, shows that some changes have taken place in the crystal structure during the process, in spite of a recovery at the end of the reaction. The advantages and limitations of the coordination polymer were discussed and compared with those of the previous heterogeneous catalysts in the literature.

Eco-friendly and biocompatible cross-linked carboxymethylcellulose hydrogels as adsorbents for the removal of organic dye pollutants for environmental applications.

In this study, new eco-friendly hydrogel adsorbents were synthesized based on carboxymethylcellulose (CMC, degree of substitution [DS] = 0.7) chemically cross-linked with citric acid (CA) using a green process in aqueous solution and applied for the adsorption of methylene blue (MB). Spectroscopic analyses demonstrated the mechanism of cross-linking through the reaction of hydroxyl functional groups from CMC with CA. These CMC hydrogels showed very distinct morphological features dependent on the extension of cross-linking and their nanomechanical properties were drastically increased by approximately 300% after cross-linking with 20% CA (e.g. elastic moduli from 80 ± 15 to 270 ± 50 MPa). Moreover, they were biocompatible using an in vitro cell viability assay in contact with human osteosarcoma-derived cells (SAOS) for 24 h. These CMC-based hydrogels exhibited adsorption efficiency above 90% (24 h) and maximum removal capacity of MB from 5 to 25 mg g-1 depending on the dye concentration (from 100 to 500 mg L-1), which was used as the model cationic organic pollutant. The adsorption of process of MB was well-fit to the pseudo-second-order kinetics model. The desorption of MB by immersion in KCl solution (3 mol L-1, 24 h) showed a typical recovery efficiency of over 60% with conceivable reuse of these CMC-based hydrogels. Conversely, CMC hydrogels repelled methyl orange dye used as model anionic pollutant, proving the mechanism of adsorption by the formation of charged polyelectrolyte/dye complexes.