Equilibrium and Kinetic Aspects in the Sensitization of Monolayer Transparent TiO2 Thin Films with Porphyrin Dyes for DSSC Applications

Free base, Cu(II) and Zn(II) complexes of the 2,7,12,17-tetrapropionic acid of 3,8,13,18-tetramethyl-21H,23H porphyrin (CPI) in solution and bounded to transparent monolayer TiO2nanoparticle films were studied to determine their adsorption on TiO2surface, to measure the adsorption kinetics and isotherms, and to use the results obtained to optimize the preparation of DSSC photovoltaic cells. Adsorption studies were carried out on monolayer transparent TiO2films of a known thickness. Langmuir and Frendlich adsorption constants of CPI-dyes on TiO2monolayer surface have been calculated as a function of the equilibrium concentrations in the solutions. The amount of these adsorbed dyes showed the accordance with Langmuir isotherm. Kinetic data on the adsorption of dyes showed significantly better fits to pseudo-first-order model and the evaluated rate constants linearly increased with the grow of initial dye concentrations. The stoichiometry of the adsorption of CPI-dyes into TiO2and the influence of presence of coadsorbent (chenodeoxycholic acid) have been established. The DSSC obtained in the similar conditions showed that the best efficiency can be obtained in the absence of coadsorbent with short and established immersion times

Polypyridyl Ru( ii )-derivatized polypropylacrylate polymer with a terminal water oxidation catalyst. Application of reversible addition–fragmentation chain transfer polymerization

A Ru(II) polypyridyl-derivatized polypropylacrylate end-capped with a water-oxidation-catalyst (WOC) has been synthesized by using reversible addition–fragmentation chain transfer polymerization (RAFT) followed by click reaction and end-group functionalization. In cyclic voltammograms in propylene carbonate, chromophore oxidation occurs at 1.27 V vs. NHE and the RuIII/II wave for the catalyst at 0.84 V vs. NHE. Upon excitation of the Ru(II) chromophore, excited-state energy migration occurs by site-to-site, –RuII*– → –RuII–, energy transfer hopping along the polymer chain, in part, reaching the terminal catalyst site where –RuII*– → –RuII–OH2 2+ energy transfer is favored by ΔGen = −2100 cm−1. Added MV2+ as an electron transfer acceptor oxidizes the –RuII*– excited state on the polymer to Ru(III), –RuII*– + MV2+ → –RuIII– + MV+ , and ultimately, the catalyst, by site-to-site electron transfer hopping and oxidation, -RuIII-← e-RuII - OH2 2+. Oxidation is followed by relatively slow, diffusional back electron transfer from MV•+ to Ru(III) sites on the polymer chain. The mixed chromophore-catalyst polymer is a water oxidation catalyst with potential for enhanced light harvesting and water oxidation

Visible photoelectrochemical water splitting into H 2 and O 2 in a dye-sensitized photoelectrosynthesis cell

Mesoporous SnO2/TiO2 core/shell nanostructured electrodes derivatized with a surface-bound Ru(II) polypyridyl-based chromophore–catalyst assembly are used for water splitting into H2 and O2 with visible light in a dye-sensitized photoelectrosynthesis cell. Photocurrents with a small applied bias are among the highest reported. Stabilization of the assembly on the surface of the TiO2 shell by using atomic layer deposition to deposit overlayers of Al2O3 or TiO2 results in long-term water splitting even in a phosphate buffer at pH 7

Kinetic model for astaxanthin aggregation in water-methanol mixtures

The aggregation of astaxanthin in hydrated methanol was kinetically studied in the temperature range from 10 ◦C to 50◦C, at different astaxanthin concentrations and solvent composition. A kinetic model for the formation and transformation of astaxanthin aggregated has been proposed. Spectrophotometric studies showed that monomeric astaxanthin decayed to H-aggregates that after-wards formed J-aggregates when water content was 50% and the temperature lower than 20 ◦C; at higher temperatures, very stable J-aggregates were formed directly. Monomer formed very stable H-aggregates when the water content was greater than 60%; in these conditions H-aggregates decayed into J-aggregates only when the temperature was at least 50 ◦C. Through these findings it was possible to establish that the aggregation reactions took place through a two steps consecutive reaction with first order kinetic constants and that the values of these depended on the solvent composition and temperature

Kinetic and photochemical behaviour of Zn(II)-Coproporphyrin-I complex : a spectrophotometric and fluorimetric study. Evidence of sitting atop complex formation

The kinetic of the reaction of coproporphyrin-I with Zn(II) was spectrophotometrically studied with different metal counter-ions and in the temperature range 25-40°C. The rate constant values depended on counter-ions of Zn(II) and on temperature. The influence of Uv-Vis light on Zn(II)-coproporphyrin-I complex was monitored. The photo-reaction showed a first order kinetic with respect to Zn(II)-coproporphyrin-I complex concentrations with metal liberation and bleaching of solution. The complex was studied and characterized also by fluorescence measurements

Aggregation behavior of a tetracarboxylic porphyrin in aqueous solution.

The aggregation of 3,8,13,18-tetramethyl-21H,23H-porphine-2,7,2,17-tetrapropionic acid (Coproporphyrin-I) has been investigated by UV–vis spectroscopy in aqueous solutions. The aggregation occurred by total neutralization of propionic groups and can be induced by alkaline salts, hydrogen peroxide or acidification. The hydrogen peroxide effect is investigated in the presence of different concentrations and it has been observed that only high concentrations favour the formation of H-aggregates. The dimerization constants in the several experimental conditions are reported. The H-dimers of Coproporphyrin-I in particular experimental conditions formed highly aggregate species depending on the pH. The kinetic of aggregation has been studied at different pHs and the results have showed that the log of kinetic constants kP were linearly dependent on the pH. The morphology of these aggregates, investigated by SEM spectroscopy, showed that the solvent polarity influenced their structures

Spectral and Kinetic Investigation on Oxidation and Reduction of Water Soluble Porphyrin-Manganese(III) Complex.

In this work the oxidation and reduction reactions of MnIII–Coproporphyrin-I (MnIII-CPI) have been studied and four forms of manganese–CPI complexes have been characterized. This complex was observed to be highly reactive (at basic pH) towards Mn(II), hypochlorite, hydrogen peroxide and oxone, forming [MnIV(O)CPI(OH)] that was unstable and, after a short time, formed again [MnIIICPI(OH)2]. With an excess of NaClO, a further oxidation of the complex [MnIV(O)CPI(OH)], provoked a significant spectral change for the [MnV(O)CPI(OH)] formation that showed, in the time, a partial polymerization.[MnIIICPI(OH)2] was reduced by sodium dithionite to form the very unstable complex of [MnIICPI(OH)] that successively degraded with Mn(II) release