Clara Comuzzi

The solid-state rearrangement of the Wells-Dawson K6P2W18O62·10H2O to a stable Keggin-type heteropolyanion phase: a catalyst for the selective oxidation of isobutane to isobutene

The thermal and structural stability of the Wells-Dawson-type heteropoly compound K6P2W18O62·10H2O was examined by FT-IR spectroscopy, X-ray powder diffraction, thermogravimetric analysis and HRTEM. It was found that calcination at temperatures higher than 850 K led to the formation of a Keggin-type compound “K3PW12O40”, containing small amounts of an additional phase originated from the high-temperature interaction between potassium phosphate (K3PO4 formed during the decomposition of the K6P2W18O62·10H2O) and the Keggin-type compound itself. The Keggin-type product showed a higher activity in the selective oxidative dehydrogenation of isobutane to isobutene compared to both the Wells-Dawson precursor and to pure, authentic K3PW12O40. This higher activity can be tentatively attributed to the presence of an amorphous layer of unknown stoichiometry at the surface of the thermally rearranged Wells-Dawson compound.

Lanthanide(III) complex formation with diethylenetriamine in anhydrous N,N-dimethylformamide

Abstract The formation of diethylenetriamine (dien) complexes of the lanthanide(III) ions has been studied in N,N-dimethylformamide (dmf) containing 0.1 mol dm−3 tetraethylammoniumtrifluoromethanesulfonate as constant ionic medium at 298 K. The stability constants have been obtained by potentiometry using the method of competitive reactions, silver(I) being the auxiliary central ion. The thermodynamic investigations have therefore been extended also to this metal ion. The data concerning lanthanide(III) complexation are well explained in terms of formation of two successive mononuclear complexes which are enthalpy stabilized, entropy changes being unfavourable. Dien coordinates with all N atoms both in ML and ML2 lanthanide(III) complexes; with silver(I), tridentation is achieved only when the first mononuclear complex is formed. The trends in enthalpy and entropy values of the lanthanide(III) complexes are discussed taking into account the presence of multiple solvation equilibria which involve the bare ions and the complexes in solution. Comparison with similar data previously obtained in dimethylsulfoxide (dmso) both for the lanthanide(III)- and silver(I)-dien systems, shows the remarkable influence of the solvent on the thermodynamics of complex formation.

Oxygenation reaction of Co(trien)2+ complex in dimethylsulfoxide and the aerobic oxidation of 2,6-di-tert-butylphenol catalyzed by Co(II)–amine complexes

Abstract The kinetics and the thermodynamics of the oxygenation reaction of Co(trien)2+ complex (trien=1,4,7,10-tetraazadecane) have been studied in dimethylsulfoxide (dmso) at 298 K and in a medium adjusted to 0.1 mol dm−3 with Et4NClO4 by means of UV–Vis spectrophotometric technique. The reaction mechanism is consistent with the fast formation of an initial CoL–O2 species, followed by a rate determining step which gives the final (CoL)2O2 adduct. The results are compared with similar data in water and discussed considering the effects of ligand/solvent substitution. The catalytic activity of Co(trien)2+ as well as that of other diamine complexes, CoL2 (L=ethylenediamine (en), N,N′-dimethylethylenediamine) has also been tested towards the aerobic oxidation of 2,6-di-tert-butylphenol in mild conditions and the results are discussed in term of both catalytic ability and selectivity.

Salt-assisted thermal desorption of mercury from contaminated dredging sludge

In this study, we tested a new procedure for the decontamination of mercury-polluted dredging sludge (Marano-Grado Lagoon, northeastern Italy) based on cationic exchange associated with thermal desorption at a low temperature. Four mercury-polluted sludge slurries were treated using thermal desorption at 393 K for 2h. Three different salts, NaCl (sodium chloride), (CH(3))(4)NCl (tetramethylammonium chloride) and (C(4)H(9))(4)NCl (tetrabutylammonium chloride) were used as exchangers. The selected salts have a monovalent cationic part that progressively increases in molecular weight. The results show that the association of cationic exchange with thermal treatment leads to a significant improvement in the removal of mercury from the contaminated material at a low temperature compared to samples that were not treated with salt. The highest levels of decontamination were attained were obtained when the slurries, which had mercury pollution ranging from 20 to 200 ppm, were treated with a 15% solution of (C(4)H(9))(4)NCl. The efficiency of the removal at 393 K (from 24% up to 60%) depended on the nature of the sample. When the samples were treated at a similar temperature without the salt, no remediation of mercury was detected. Our results show that the thermal decontamination temperature can be significantly lowered by this remediation approach, which is the first example based on cationic exchange of the pollutant with an appropriate salt.

Thermal stability and catalytic properties of the Wells-Dawson K6P2W18O62·10H2O heteropoly compound in the oxidative dehydrogenation of isobutane to isobutene

The thermal stability of the Wells-Dawson heteropoly compound K6P2W18O62·10H2 was examined under both reducing and oxidizing conditions, and its structural and morphological evolution was characterized by several complementary solid state techniques. It is shown that the primary structure of this compound remains intact up to 770 K, while at higher temperature structural changes and rearrangements are observed. These modifications depend considerably on the treatment conditions and catalyst composition. Under oxidizing conditions the Wells-Dawson compound rearranges with formation of a mixed phase containing the Keggin-type unit K3PW12O40 and the hexatungstate K2W6O19. Furthermore, the catalytic activity in the oxidation of isobutane is affected considerably by these changes. The best catalytic performance was shown by the rearranged Wells-Dawson compound.

The photodynamic inactivation of Staphylococcus aureus in water using visible light with a new expanded porphyrin.

In this work, the results of the application of organic expanded porphyrins in the disinfection of water by the photodynamic inactivation (PDI) technique are presented. The photoinactivation properties of a novel, expanded porphyrin, namely 20-(4-carboxyphenyl)-2,13-dimethyl-3,12-diethyl-(22π) pentaphyrin (PCCox), were tested in the disinfection of water using Staphylococcus aureus as a Gram-positive bacteria model. The data showed that PCCox was effective against S. aureus bacteria at nanomolar concentrations. The variation with irradiation time and concentration was studied using both a multi-LED monochromatic light (λ = 470 nm) and an incandescent light bulb with a wide emission spectrum. A PCCox dosage of 5 μM was sufficient to achieve a 99.997% abatement of S. aureus within 1 h of 40 W/m(2) irradiation with monochromatic light (λ = 470 nm), whereas under the same conditions using irradiation with white light, the abatement was 99.9997%.

Affinity of lanthanide(III) ions for oxygen- and mixed oxygen-nitrogen-donor ligands in dimethylsulfoxide: a thermodynamic and spectroscopic investigation

Abstract The interactions of lanthanide(III) ions with the following oxygen- and mixed oxygen–nitrogen-donor ligands: 2-methoxyethylamine ( L1 ), 2-aminoethanol ( L2 ), 2-methoxyethylether ( L3 ), di(ethyleneglycol) ( L4 ), 2,2′-oxydiethylamine ( L5 ) and 1,5-diaminopentane ( L6 ) have been investigated in dimethylsulfoxide (DMSO) at 298 K and I =0.1 mol dm −3 (Et 4 NClO 4 ). Calorimetric and 1 H NMR results show that L1 – L4 and L6 are not able to complex Ln(III) ions. L5 is shown to be able to bind heavier Ln(III) ions (LnHoLu). Potentiometric and calorimetric measurements have been carried out to obtain the Ln(III)– L5 thermodynamic parameters of complexation. All the complexes are formed in exothermic reactions being the entropy terms generally negative or slightly positive. Comparison between the complexing abilities of L1 and L5 shows that at least two CH 2 CH 2 NH 2 side-arms added to an ether function are needed to promote effective interaction between an ether O atom and Ln(III) ions in the high coordinating solvent DMSO. The results are discussed in terms of different donor properties and solvation of NR and O groups towards metal ions. A comparison with data previously obtained in DMSO for the complex formation of Ln(III) with the purely N donor diethylenetriamine (dien) is made.

Complexation of thorium(IV) by tris((2,3-dihydroxybenzylamino)ethyl)amine—a new strong chelating agent

Abstract The interaction of thorium(IV) with tris((2,3-dihydroxybenzylamino)ethyl)amine (TRENCAT) has been investigated by means of potentiometric measurements in an aqueous solution of 0.1 mol dm −3 sodium perchlorate at 25°C. The formation of a chelate structure, as well as of protonated compounds has been observed. The values of the formation constants of these complexes are reported.

Phototreatment of Water by Organic Photosensitizers and Comparison with Inorganic Semiconductors

Phototreatment of water is drawing the attention of many as a promising alternative to replace methods like chlorination, ozonization, and other oxidation processes, used in current disinfection methods limiting harmful side-products and by-products that can cause damage to the fauna and flora. Porphyrins, phthalocyanines, and other related organic dyes are well known for their use in photodynamic therapy (PDT). These photosensitizers cause cell death by generating reactive oxygen species (ROS) especially singlet oxygen in the presence of light. Such molecules are also being explored for photodynamically treating microbial infections, killing of unwanted pathogens in the environment, and oxidation of chemical pollutants. The process of photosensitisation (phototreatment) can be applied for obtaining clean, microbe-free water, thus exploiting the versatile properties of photosensitizers. This review collects the various attempts carried out for phototreatment of water using organic photosensitizers. For comparison, some reports of semiconductors (especially TiO2) used in photocatalytic treatment of water are also mentioned.

22π-Electrons [1.1.1.1.1] pentaphyrin as a new photosensitizing agent for water disinfection: experimental and theoretical characterization

In view of their promising photosensitizing features, expanded porphyrins are gaining wide attention for their potential use both in photodynamic therapy of cancer and as likely photoactivated agent for water disinfection. Herein, we report a joint experimental and theoretical investigation on the 20-(4′-carboxyphenyl)-2,13-dimethyl-3,12-diethyl-[22] pentaphyrin complex 4. The synthesis, NMR, UV–Vis and mass characterization of the new compound together with a detailed theoretical investigation of the photophysical properties, are presented. In particular, type I and type II photoreactions have been explored by means of DFT and its TDDFT formulation characterizing the electronic absorption spectra, providing singlet–triplet energy gap, vertical ionization potential and electron affinity. Results show that title compound is able to generate the cytotoxic singlet oxygen species supporting the application of the proposed molecule as a photoactivated agent for water disinfection.