Redox Potentials Of Dyes Research Articles

Redox Behaviour and Redox Potentials of Dyes in Aqueous Buffers and Protic Ionic Liquids.

Organic dyes hold promise as inexpensive electrochemically-active building blocks for new renewable energy technologies such as redox-flow batteries and dye-sensitised solar cells, especially if they display high oxidation and/or low reduction potentials in cheap, non-flammable solvents such as water or protic ionic liquids. Systematic computational and experimental characterisation of a representative selection of acidic and basic dyes in buffered aqueous solutions and propylammonium formate confirm that quinoid-type mechanisms impart electrochemical reversibility for the majority of systems investigated, including quinones, fused tricyclic heteroaromatics, indigo carmine and some aromatic nitrogenous species. Conversely, systems that generate longlived radical intermediates - arylmethanes, hydroquinones at high pH, azocyclic systems - tend to display irreversible electrochemistry, likely undergoing ring-opening, dimerisation and/or disproportionation reactions.

Rational design of visible-light-driven Pd-loaded α/β-Bi2O3 nanorods with exceptional cationic and anionic dye degradation properties

Here, we report a simple sono-chemical method to fabricate Pd-loaded α/β-Bi2O3 nanorods with exceptional methylene blue (MB), brilliant green (BG) and acid red 1 (AR) dye degradation properties. The unique nanorods morphology was accomplished by treating of bismuth complexes with sodium hydroxide at room temperature. Palladium was introduced by UV-photo-deposition method from palladium (II) chloride source. The successful substitution of Bi3+ by Pd2+ in bulk of Pd-loaded α/β-Bi2O3 was confirmed by X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). The surface presence of α-, β-Bi2O3, PdO and metallic Pd0 was confirmed by X-ray photoelectron spectroscopy (XPS). The rational design and fabrication approach is based on matching of (1) valence band (VB) and conduction band (CB) of as-prepared catalyst with redox potentials of dyes, (2) VB and CB with reactive oxygen species (ROS), and (3) redox potentials of dyes with ROS. By using the approach of rational design the material is able to degrade cationic MB (90.8%), BG (83.3%) and anionic AR (83.2%) dyes within 20 min under LED light irradiation (100 mW/cm2), as well as to degrade mixtures of cationic/anionic MB-AR and BG-AR dyes. Further optimization of dye degradation parameters, such as initial concentration of dye, amount of catalyst, and solution pH was carried out. A mechanism of dye degradation was proposed based on ROS scavenging experiments and mapping out of semiconductor band structures with redox potentials of dyes and ROS. Pd-loaded α/β-Bi2O3 catalyst has potential applications in wastewater treatment, water splitting and healthcare industries.

Ag/Ag2O/BiNbO4 structure for simultaneous photocatalytic degradation of mixed cationic and anionic dyes

In principle, n-type and p-type semiconductors are respectively responsible for photo-catalytic degradation of cationic dyes (e.g., methylene blue) and anionic dyes (e.g., acid red 1), governed by photoelectrons in the former and photo-holes in the later system. Hence, we present a new strategy: design and fabrication of photocatalytic structures to match the redox potentials of mixed basic/acidic dyes as well as the reactive oxygen species (ROS). For the first time Ag/Ag2O/BiNbO4 structure is (1) designed to match the redox potentials of basic/acidic dyes as well as ROS, (2) fabricated using photoreduction to control the Ag/Ag2O/BiNbO4 interfaces, and (3) able to simultaneously degrade 84% methylene blue dye (MB) in 240 min and 88% acid red 1 (AR) in 25 min under LED light irradiation, corresponding to 7 wt% Ag loading. To the best of our knowledge, this is the first photocatalytic degradation study on mixed basic and acidic dyes using a single catalyst. We also tested the new redox potential matching strategy in mixed basic dyes (MB and rhodamine B (RhB)). As expected our experimental results reproduced well our model predictions: in particular, results support our proposed hydroxyl radical (OH) mechanism, which is initiated by photo-holes. Therefore, this new design strategy, which consists of matching band structures of the photocatalyst with redox potentials of dyes and ROS, has immediate implications to general photocatalytic applications beyond dye degradation and water-splitting.

Benzo[1,2,5]thiadiazole dyes: Spectral and electrochemical properties and their relation to the photovoltaic characteristics of the dye-sensitized solar cells

Important aspects of dye-sensitized solar cells (DSSCs) fabrication based on dyes including benzothiadiazole unit were investigated. Two absorption peaks of the dyes covering the 330–551 nm region and possessing moderate band energy gap (1.83–2.16 eV) were found to be important to demonstrate high photovoltaic efficiency (η > 8) in metal free iodide/iodine electrolyte composed DSSCs. Furthermore, the dye energy band gap determined from optical spectra decreases with the increase of DSSCs short circuit photocurrent density, which in turn linearly increases the photovoltaic efficiency of DSSCs. While the RedOx potentials of dyes are less functionally related to the photovoltaic properties of the DSSCs, their appropriate values (0.67 ≤ Eox ≤ 1.1 V and −1.75 ≤ Ered ≤ −0.91 V) can be important for efficient DSSCs. Fabrication details increasing photovoltaic efficiency of the devices based on dyes with benzothiadiazole unit were found. The relationships obtained in the work can be used for preliminary prognosis whether a newly synthesized dye is a promising metal-free sensitizer for DSSCs or not.

352 - Redox processes during photodynamic damage of DNA III. Redox mechanism of photosensitization and radical reaction

Sensitized photoreactions are frequently characterized by electron transfer processes. In this work electron transfer processes were observed and confirmed for two more photochemical reactions. 1. The fluorescence quenching of dyes by deoxyribonucleic acids (DNA) was identified as a reversible electron transfer from DNA bases in the ground state to sensitizer dyes in the first excited singlet state. The excited state potentials have been obtained by combination of electrochemical and spectroscopic data. The electron-donating properties of nucleic acid bases increase in the order: Gua > Ade > Thy > Cyt. Quenching preferentially occurs by Gua. 2. Irreversible photodynamic degradation of DNA by visible light in the presence of a sensitizer dye can be described by a redox mechanism where the oxidized sensitizer radical is an important intermediate. The photodynamic efficiency of the dye-DNA system can be predicted from the linear free energy relationship between the redox potentials of dyes and nucleic acid bases.