Guido Viscardi

Determination of banned Sudan dyes in food samples by molecularly imprinted solid phase extraction-high performance liquid chromatography.

A method for molecularly imprinted SPE of banned Sudan azo-dyes from food samples was investigated. The molecularly imprinted polymer was obtained by suspension polymerization using 1-(4-chlorophenyl)azonaphthalen-2-ol as the mimic template. The molecular recognition properties of imprinted beads were evaluated for use as a SPE sorbent, in order to develop a selective extraction protocol for the Sudan class of dyes. The optimized extraction protocol resulted in a reliable molecularly imprinted SPE (MISPE) method suitable for HPLC analysis. It was selective for the main analyte, Sudan I, and the related azo-dyes Sudan II, III, IV, Sudan Red B, and Sudan Red 7B, while the permitted azo-dyes Allura Red AC, Neococcin, and Sunset Yellow FCF were not extracted. The method was tested for Sudan I, II, III, and IV in five different food samples (hot chilli pepper, hot chilli tomato sauce, sausage, tomato sauce, and hard boiled egg yolk) at three concentration levels (15, 100, and 300 microg/g). It demonstrated itself to be insensitive to the presence of different complex matrices, precise, accurate, and with good recovery rates (85-101%). The LOD and LOQ were satisfactory for most analytical determinations.

Approaching truly sustainable solar cells by the use of water and cellulose derivatives

Aqueous dye-sensitized solar cells (DSSCs) are emerging as the first truly safe, cheap and eco-friendly photovoltaic technology, at the same time overcoming the well-known instability upon moisture/water contamination typical of many solar cells. While many aqueous DSSCs recently proposed still contain little amounts of organic solvents or petroleum-derived polymeric matrices, here we propose the first 100% hydrogel electrolyte, consisting of carboxymethylcellulose as a green jellifying agent, water and iodide/triiodide redox mediator. Electrochemical and photoelectrochemical properties of the resulting electrolytes and solar cells are thoroughly investigated, with a special focus on the long-term stability of the aqueous devices under different operating and aging conditions. The obtained promising efficiencies and stabilities, combined with a metal-free sensitizer, lead here to sustainable, stable, transparent and building-integrable solar cells, without suffering from any safety and/or toxicity issues.

Enhancing the efficiency of a dye sensitized solar cell due to the energy transfer between CdSe quantum dots and a designed squaraine dye

The power conversion efficiency of a dye-sensitized solar cell with tailored squaraine dye enhanced by 47%, due to Forster resonance energy transfer from CdSe quantum dots to the squaraine dye. The incident photons to collection efficiency of electrons indicate panchromatic response from the visible to the near-infrared spectrum.

Reactivity and effects of cyclodextrins in textile dyeing

Abstract Four- to 10-fold improvement of colour uniformity and minor changes of colour yield have been found upon dyeing Nylon 66 and microfiber Nylon 6 fabrics in the presence of cyclodextrin compared to dyeing without it. 1 H NMR data supported the role of cyclodextrin as dye complexing agent. Product quality, however, was also dependent on fabric nature, since for conventional Nylon 6, color uniformity was not improved by the presence of cyclodextrin systems.

Synthesis and properties of cationic surfactants with tuned hydrophylicity

A series of pyridinium-based cationic surfactants has been synthesised and their amphiphilic properties have been studied by conductivity and surface tension measurements. The modification of the substitution pattern on the pyridinium ring by hydrophobic moieties (methyl vs. hydrogen and presence or not of condensed benzene ring) gave the opportunity to investigate structure-activity relationships. Characterization by conductivity and surface tension measurements shed light on the behaviour at the air/water interface and in the micellar environment. In particular, the tendency to form ion pairs at very low concentration was evidenced for all the surfactants substituted on the ring, but not for the simple pyridinium ones. The formation of ion pairs affects both the conductivity and the surface tension plots, showing that a series of steps is involved during the adsorption to the air/water surface. An attempt was made to qualify the single steps in the adsorption at the surface layer. Those steps were attributed to different chemical species (free surfactant ions or ion pairs) and to different arrangements of the surfactant. This work also represents a contribution of investigation at very low surfactant concentrations and high surface tension values.

Microwave-Assisted Synthesis of Near-Infrared Fluorescent Indole-Based Squaraines

A microwave-assisted method for the preparation of a wide color range of 2,3,3-trimethylindolenine-based squaraines and their intermediates is described. This practical approach allows the rapid preparation of both symmetrical and nonsymmetrical squaraine dyes, reducing reaction time from days to minutes with more than 2-fold improvement in product yields when compared to conventional methods.

Near-infrared sensitization in dye-sensitized solar cells

Dye-sensitized solar cells (DSCs) are a low cost and colorful promising alternative to standard silicon photovoltaic cells. Though many of the highest efficiencies have been associated with sensitizers absorbing only in the visible portion of the solar radiation, there is a growing interest for NIR sensitization. This paper reviews the efforts made so far to find sensitizers able to absorb efficiently in the far-red NIR region of solar light. Panchromatic sensitizers as well as dyes absorbing mainly in the 650-920 nm region have been considered.

A Simple Synthetic Route to Obtain Pure Trans‐Ruthenium(II) Complexes for Dye‐Sensitized Solar Cell Applications

We report a facile synthetic route to obtain functionalized quaterpyridine ligand and its trans-dithiocyanato ruthenium complex, based on a microwave-assisted procedure. The ruthenium complex has been purified using a silica chromatographic column by protecting carboxylic acid groups as iso-butyl ester, which are subsequently hydrolyzed. The highly pure complex exhibits panchromatic response throughout the visible region. DFT/time-dependent DFT calculations have been performed on the ruthenium complex in solution and adsorbed onto TiO2 to analyze relative electronic and optical properties. The ruthenium complex endowed with the functionalized quaterpyridine ligand was used as a sensitizer in dye-sensitized solar cell yielding a short-circuit photocurrent density of more than 19 mA cm(-2) with a broad incident photon to current conversion efficiency spectra ranging from 400 to 900 nm, exceeding 80 % at 700 nm.

Synthesis and photophysical characterization of highly luminescent complexes of Ru(II) containing 4,4′-di-(p-carboxyphenyl)-2,2′-bipyridine

Abstract The synthesis and photophysical characterization of several complexes of Ru(II) containing 4,4′-di(carboxyphenyl)-2,2′-bipyridine (DCPB) and related bipyridine ligands are reported. In all complexes studied the lowest excited state is associated with Ru→DCPB charge transfer (CT) transition. The introduction of phenyl groups between the peripheral carboxyl group and the bipyridine framework caused a red-shifted, more intense absorption but the excited state properties (luminescence and transient absorption) remain nearly the same. The acid-base properties in the ground and excited state are different. With respect to 4,4′-carboxy-2,2′-bipyridine (dcbpy) derivative, the ground state pKa of Ru(DCPB)3 increases by about 2.5 pH units and a further extremely small increase in the pKa is observed upon visible light excitation. The results suggest that the charge density is largely localized in the diimine unit and does not carry through the phenyl group. This could account for inefficient sensitization (⩽8% monochromatic photon-to-current conversion efficiency) obtained on TiO2 electrodes. Possible implication of the present results on the design of photosensitizers is also discussed.

Aqueous micellar solutions of some N-alkylnicotinamide and N-alkylpyridinium halide surfactants: Apparent and partial molar enthalpies

In order to acquire thermodynamic data for aqueous solutions of functionalized surfactants, and to study the effect of the amidic group in the polar head and of the counterion, the enthalpies of dilution at 25°C of N-alkylnieotinamide chlorides (alkyl chain length 7, 9 or 10 carbon atoms), N-alkylpyridinium chlorides (alkyl chain length 8, 10 or 12 carbon atoms), N-octylpyridinium bromide and N-decylpyridinium bromide have been measured by means of an LKB 2107 flow microcalorimeter. From the experimental data, apparent and partial molar relative enthalpies as a function of the molality of the surfactant have been derived. The amidic group in the nicotinamide compounds greatly enhances the hydrophobicity relative to the pyridinium compounds. For cationic surfactants with the same alkyl chain, the trends of the molar enthalpies vs. concentration can be explained in terms of charge localization on the polar head. For the compounds under investigation, enthalpic data are not able to show phase transitions in the micellar region, but they confirm the role of the counterion in the energetics of micellar solution. The thermodynamic functions of micellization have been evaluated on the basis of the pseudo-phase transition model by graphical extrapolation.