Specifics of the formation of J-aggregates of cyanine dyes in solutions of AOT/water/hexane reverse micelles

The behavior of a cyanine dye (3,3′-di-(gamma-sulfopropyl)-4,5,4′,5′-dibenzo-9-ethylthiacarbocyanine betaine pyridinium salt) was studied in AOT/water/hexane reverse micelles over a wide range of W at various concentrations of the dye, AOT, and reverse micelles. The processes occurring during the formation of the AOT/water/hexane micellar solution were studied in detail. It has been shown that, before the formation of the stable microemulsion, the dye aggregation processes occur by virtue of the interaction of the dye with the AOT anion. The amount of J-aggregates is proportional to the logarithm of the ratio of the amount of AOT molecules to the amount of dye molecules. The time behavior of J-aggregates after the formation of a micellar structure depends on the concentration of reverse micelles, thereby indicating an important role of intermicellar exchange.     

Adsorption and desorption studies of a water soluble dye, Quinoline Yellow, using waste materials

Bottom ash, a power plant waste, and de-oiled soya, an agricultural waste material, were employed for the removal and recovery of Quinoline Yellow, a water-soluble dye. Characterization of adsorbent materials was made by their infrared and differential thermal analysis curves. Along with batch adsorption studies, which involve effect of pH, adsorbate concentration, sieve size, adsorbent dosage, contact time, temperature, etc., kinetic studies and column operations were also made to remove the dye from wastewater. On the basis of kinetic studies, specific rate constants involved in the processes were calculated and first-order adsorption kinetics was observed in both the cases. The paper also incorporates Langmuir and Freundlich adsorption isotherm models, which are used to calculate thermodynamic parameters and also to suggest a plausible mechanism of the ongoing adsorption processes. Fixed bed columns were prepared for both the adsorbents and bulk removal of the dye was achieved by eluting aqueous solution of the dye and saturation factor for both columns were evaluated. Dilute NaOH solution was then percolated through the exhausted columns to recover the adsorbed dye.     

Electrochemical degradation of acid green dye in aqueous wastewater dyestuff solutions using a lead oxide coated titanium electrode

A modified electrode, which can be used as an anode for electrocatalytic oxidation processes of dyestuff in aqueous solutions, was fabricated by the electrodeposition of a lead oxide layer on a titanium substrate. The modified electrode was used for the electrochemical degradation of an acid green dye. The results of the electrocatalytic oxidation process of the dyestuff solutions were expressed in terms of the remaining dye concentration and chemical oxygen demand (COD) values. The different operating conditions of the treatment process were studied. The optimum operating conditions for the dye and modified electrode were determined, where good results for complete removal of the dye and COD were achieved. The optimum conditions were applied to the treatment of a sulfur black dye in true wastewater solutions.     

Factors controlling charge recombination under dark and light conditions in dye sensitised solar cells

A simple and powerful approach for assessing the recombination losses in dye sensitised solar cells (DSSCs) across the current voltage curve (j-V) as a function of TiO(2) electron concentration (n) is demonstrated. The total flux of electrons recombining with iodine species in the electrolyte and oxidised dye molecules can be thought of as a recombination current density, defined as j(rec) = j(inj)-j where j(inj) is the current of electrons injected from optically excited dye states and j is the current density collected at cell voltage (V). The electron concentration at any given operating conditions is determined by charge extraction. This allows comparison of factors influencing electron recombination rates at matched n. We show that j(rec) is typically 2-3 times higher under 1 sun equivalent illumination (j(inj) > 0) relative to dark (j(inj) = 0) conditions. This difference was increased by increasing light intensity, electrolyte iodine concentration and electrolyte solvent viscosity. The difference was reduced by increasing the electrolyte iodide concentration and increasing the temperature. These results allowed us to verify a numerical model of complete operational cells (Barnes et al., Phys. Chem. Chem. Phys., DOI: 10.1039/c0cp01554g) and to relate the differences in j(rec) to physical processes in the devices. The difference between j(rec) in the light and dark can be explained by two factors: (1) an increase in the concentration of electron acceptor species (I(3)(-) and/or I(2)) when current is flowing under illumination relative to dark conditions where the current is flowing in the opposite direction, and (2) a non-trivial contribution from electron recombination to oxidised dye molecules under light conditions. More generally, the technique helps to assign the observed relationship between the components, processing and performance of DSSCs to more fundamental physical processes.     

Kinetics and mechanism of azo dye destruction in advanced oxidation processes

The kinetics and mechanism of dye destruction in advanced oxidation processes is discussed on the example of Apollofix Red (Ar-28) radiolysis in aqueous solution. When the reactive intermediate reacts with the color bearing part of the molecule causing with nearly 100% efficiency destruction of the conjugation, the dose dependence, or time dependence of color disappearance is linear. In this case, spectrophotometry can be used to follow-up dye decomposition. Linear dependence was observed when hydrated electrons or hydrogen atoms reacted with the dye. In hydroxyl radical reactions some colored products form with spectra similar to those of the starting dye molecules. For that reason, spectrophotometry gives false result about the intact dye molecule concentration. Analysis by the HPLC reveals logarithmic time dependence in agreement with a theoretical model developed.     

CuNPs as an activator of K2S2O8 for the decolorization of diazo dye in aqueous solution

Degradation of trypan blue (TB) by persulfate/CuNPs system was investigated as a function of TB concentration, persulfate concentration, CuNPs concentration, pH, and reaction temperature in aqueous solution. The rate of the decolorization and destruction of aromatic ring were studied spectrophotometrically. The dye mineralization was performed with potassium dichromate for the determination of chemical oxygen demand (COD) in solution. The blue color reaction mixture became red-chocolate, purple, light blue to dark blue as a function of time. The CuNPs acted as an activator of K₂S₂O₈ and generates various reactive oxygen and/or sulphur species. Decolorization of dye starts due to the cleavage of azo bond by the generated radical species. The role of sulfate radicals (SO₄^?-), and hydroxyl radicals (HO^?) were established by using different radical scavengers. Degradation and mineralization of dye follows first-order kinetics. These results can support the design of remediation processes and also assist in predict their fate in environment.     

Influence of electrolytes on the association processes of dissimilar dyes

The influence of an electroyte on the association processes of dissimilar dye molecules has been investigated. It has been established that the degree of heterogeneous association depends on the concentration of LiCl. The bonding energy of the molecules in a complex has been determined from temperature measurements of the luminescence-spectroscopic characteristics of multipcomponent dye solutions.Translated from Teoreticheskaya i Éksperimental/naya Khimiya, Vol. 26, No. 5, pp. 600–605, September–October, 1990.     

Modeling of the dynamic adsorption of an anionic dye through ion-exchange membrane adsorber

The present study examines the dynamic adsorption through ion-exchange membrane adsorbers. The model used in the study includes convection, axial dispersion with simultaneous adsorption and desorption of the solute in the membrane. Adsorption and desorption processes give the Langmuir isotherm for the equilibrium. The mathematical model makes use of dimensionless parameters in terms of characteristic times for the different mechanisms that take place during the process (convection, dispersion, adsorption and desorption characteristic times). The model has five independent dimensionless parameters. Three of these parameters are related to the equilibrium isotherm and the other two are related to the dynamic process. Equilibrium and dynamic experiments were carried out in order to fit their respective parameters. In order to examine the suitability of the model to describe real processes, the adsorption of an anionic dye (Orange-G) through the ion-exchange membrane adsorber was investigated as a function of dye and KCl concentration, obtaining strong correlation between fitted and experimental breakthrough curves. The results show the relative importance of axial dispersion, adsorption and desorption as a function of operational variables.     

Influence of cation on charge recombination in dye-sensitized TiO2 electrodes

The reaction of a dye cation recombining with an electron in TiO(2), in the presence of Li(+), Ca(2+), and TBA(+) cations, was studied with laser-induced transient absorption measurements. The active cations, Li(+) and Ca(2+), shorten the dye cation lifetime on sensitized TiO(2) but not ZnO electrodes. By combining the absorbance measurements of the dye cation with simultaneous measurements of the current transient, the contribution of the recombination reaction to the current is identified. Furthermore, classical porous electrode theory is used to quantify the behavior of the heterogeneous electrode, and in doing so, the processes contributing to photoinduced current are identified as Helmholtz layer charging, porous electrode charging, recombination reactions, and surface diffusion of the active cations. The rate of charge recombination is proportional to the concentration of initially deposited active cations. The effect of water on the recombination rate and the current is also observed.     

Thiacarbocyanine as ligand in dye‐affinity chromatography for protein purification. II. dynamic binding capacity using lysozyme as a model

A constant development of dye‐affinity chromatography to replace more traditional techniques is verified, with the aim of increasing specificity in the purification of biomolecules. The establishment of a new dye‐affinity chromatographic support imposes their complete characterization, namely with relation to the binding capacity for proteins, in order to evaluate its applicability on global purification processes. Following previous studies, the adsorption of lysozyme onto a thiacarbocyanine dye immobilized on beaded cellulose was investigated. The effect of different parameters, such as temperature, ionic strength, pH, protein concentration and flow rate, on the dynamic binding capacity of the support to retain lysozyme was also studied. Increasing the temperature and the lysozyme concentration had a positive effect on the dynamic binding capacity (DBC), whereas increasing the ionic strength and the flow rate resulted in the opposite. It was also discovered that the pH used had an important impact on the lysozyme binding onto the immobilized dye. The maximum DBC value obtained for lysozyme was 8.6 mg/mL, which was achieved at 30°C and pH 9 with a protein concentration of 0.5 mg/mL and a flow rate of 0.05 mL/min. The dissociation constant (K_d) obtained was 2.61 ± 0.36 × 10^–5 m , proving the affinity interaction between the thiacarbocyanine dye ligand and the lysozyme. Copyright © 2009 John Wiley & Sons, Ltd.     

Removal of Reactive Yellow 84 from aqueous solutions by adsorption onto hydroxyapatite

The adsorption of a reactive dye, Reactive Yellow 84, from aqueous solution onto synthesized hydroxyapatite was investigated. The experiments were carried out to investigate the factors that influence the dye uptake by the adsorbent, such as the contact time under agitation, absorbent dosage, initial dye concentration, temperature and pH of dye solution. The experimental results show that the amount of dye adsorbed increases with an increase in the amount of hydroxyapatite. The maximum adsorption occurred at the pH value of 5. The equilibrium uptake was increased with an increase in the initial dye concentration in solution. The experimental isotherm data were analyzed using Langmuir isotherm equation. The maximum monolayer adsorption capacity was 50.25 mg/g. The adsorption has a low temperature dependency and was endothermic in nature with an enthalpy of adsorption of 2.17 kJ mol⁻¹.     

Drying dissipative patterns of dyes in ethyl alcohol on a cover glass

Drying dissipative structural patterns formed in the course of drying ethyl alcohol solutions of rhodamine 6G, uranine, 7-hydroxy coumarin, and 7-amino-4-(trifluoro methyl)-coumarin are studied on a cover glass. The macroscopic broad ring patterns form for all the solutions examined, which supported importance of the convectional flow of ethyl alcohol and dye solutes. Dried area increases as dye concentration increases above the critical dye concentration. Microscopic fine patterns including street-like, needle-like, and flower-like crystal structures are formed in the solidification processes. Change in the functional side group moieties of the dyes gives the strong effect on the microscopic drying patterns; even the main chemical structures are same. Kinetic aspect of the drying patterns is studied.     

Visualizing transport processes at liquid-liquid interfaces--the application of laser-induced fluorescence

Modeling of liquid-liquid extraction processes involves the concentration of the extracted component directly at the interface. Currently, only very few and specialized methods are available for the direct measurement of these concentrations. Therefore a new, fluorescence-based measurement system with a high spatial resolution and a broad application spectrum was developed and tested. The detection principle is based on the use of fluorescent dyes excited by an argon ion laser. The intensity of the emitted light is dependent on the concentration of the extracted component in the very near surroundings of the dye. This intensity distribution is reproduced by an optical, microscope-based system onto a highly sensitive camera with a spatial resolution of 1 mum. This distribution is converted into a concentration profile at the interface using a calibration function and digital image processing routines. Measurements were performed in a commonly used stirred two-phase reactor modified to meet the requirements of an optical measurement system. It was shown that the concentration profiles at moving and nonmoving interfaces could be visualized with a resolution of 1 mum. The profiles formed at the interface differ significantly according to the kinetic of the used extraction system and the flow profiles in the reactor and can be used for further modeling of the extraction processes.     

Low-temperature synthesis of nanoparticle-assembled, transparent, and low-crystallized hydroxyapatite blocks

The mesoporous carbon CMK-3 adsorbent was prepared, characterized, and used for the removal of anionic methyl orange dye from aqueous solution. Adsorption experiments were carried out as batch studies at different contact time, pH, initial dye concentration, and salt concentration. The dye adsorption equilibrium was rapidly attained after 60 min of contact time. Removal of dye in acidic solutions was better than in basic solutions. The adsorption of dye increased with increasing initial dye concentration and salt concentration. The equilibrium data were analyzed by the Langmuir and Freundlich models, which revealed that Langmuir model was more suitable to describe the methyl orange adsorption than Freundlich model. Experimental data were analyzed using pseudo-first-order and pseudo-second-order kinetic models. It was found that kinetics followed a pseudo-second-order equation. Thermodynamic study showed that the adsorption was a spontaneous and exothermic process.     

Concentration-dependent energy transfer studies in ternary dye mixture of Stilbene-420, Coumarin-540 and Nile Blue

The energy transfer studies in the case of ternary dye mixture [Stilbene-420 (donor)+Coumarin-540 (intermediator)+Nile Blue (acceptor)] have been done and discussed through optical gain characteristics at various acceptor concentrations under nitrogen laser excitation. The concentration of the other two dyes were kept constant. It is observed that the concentration of the acceptor dye plays a very critical role in energy transfer dye laser (ETDL) as small change in its concentration varies the intensity of the laser output in the red region by large amount. Also, the highest laser output in the red region is obtained when the concentration of the acceptor dye is slightly higher than that of the intermediator dye. The present studies are helpful in deciding the optimum concentration of the acceptor dye to be used in ternary dye mixture for maximum gain and tuning range. The ternary dye mixture under study provides an ETDL tuning range up to 700 nm.     

A New method of determining the extent of binding of an ionic dye to a polyelectrolyte in solution

A method of determining the free dye concentration in a dye/polyelectrolyte solution is described. The method utilizes the tendency of cationic dyes to adsorb to a cellulose dialysis membrane, and the nature of the membrane binding is studied by spectrophotometric methods. The binding of the cationic dye toluidine blue to the polyanion sodium carboxymethylcellulose in solution is used as an example. The proposed technique gives reliable estimates of free dye concentration over a wide range of polyanion and dye concentrations, both in the presence and absence of added simple electrolyte. The method possesses inherent advantages over estimates of free dye concentration obtained by absorption spectrophotometry and is more versatile than fluorimetry.     

A Mechanochromic Luminescent Dye Exhibiting On/Off Switching by Crystalline–Amorphous Transitions

A mechanochromic luminescent dye based on a simple aminomaleimide skeleton was readily synthesized in a one‐pot process. It exhibited an on/off mechanochromic luminescent switching property dependent on external stimuli, unlike a traditional mechanochromic color change. The green emission was turned on by grinding in a mortar and turned off by heating or treatment with dichloromethane. In the crystalline state, two molecules were stacked by cofacial π–π interactions, which caused concentration self‐quenching. The crystalline‐to‐amorphous transition induced by grinding removed cofacial π–π stacking, which led to intensive emission. Crystallizing processes recovered the cofacial π–π stacking, resulting in elimination of the emission. Theoretical calculations and X‐ray diffraction analyses revealed that the dye molecule was distorted in the crystalline state; thus even a mechanical stimulus caused the crystalline‐to‐amorphous transition.     

Unburned carbon as a low-cost adsorbent for treatment of methylene blue-containing wastewater

Fly ash, natural zeolite, and unburned carbon separated from fly ash have been employed as low-cost adsorbents for dye adsorption in methylene blue-containing wastewater. It is found that the unburned carbon exhibits a much higher adsorption capacity than raw fly ash and natural zeolite. The adsorption capacities of fly ash, natural zeolite, and unburned carbon for methylene blue are 2 x 10(-5), 5 x 10(-5), and 2.5 x 10(-4) mol/g, respectively. Investigation also indicates that adsorption is influenced by initial dye concentration, particle size, dye solution pH, and adsorption temperature. Adsorption on unburned carbon increases with the initial dye concentration, solution pH, and temperature, but reduces with the increasing particle size. Kinetic studies show that adsorption of methylene blue on fly ash, natural zeolite, and unburned carbon can be best described by the pseudo-second-order adsorption model and that adsorption is a two-step diffusion process. The apparent activation energies for methylene blue adsorption on unburned carbon in the first and second diffusion processes are 12.4 and 39.3 kJ/mol, respectively.     

Molecular control of recombination dynamics in dye sensitised nanocrystalline TiO2 films

Modification of the structure of a porphyrin dye shows a significant change in the rate of charge recombination between injected electrons in the TiO2 and the oxidized dye anchored to it following optical excitation, offering an insight into fundamental understanding of processes occurring at the dye/semiconductor interface.     

Removal of Pararosaniline Hydrochloride Dye (Basic Red 9) from Aqueous Solution by Electrocoagulation: Experimental,Kinetics, and Modeling

In this work, the removal of pararosaniline hydrochloride (Basic red 9) dye from aqueous solutions by electrocoagulation was investigated. The effect of parameters such as current density, initial pH, electrolysis time, inter-electrode distance, initial dye concentration and salt concentration on dye removal efficiency were investigated. The experimental results showed that 99% dye removal was observed after 30 minutes of electrolysis for an initial dye concentration of 100 mg/L, current density of 111.1 A/m² and initial pH of 7.0. It was observed that an increase in current density, time of operation and decrease in inter-electrode distance improved the dye removal efficiency. The optimum pH range for highest dye removal was 5.0–10.25. It was also observed that increase in salt concentration in the solution reduces the specific electrical energy consumption. The kinetic study inferred that the dye removal primarily follows a first order reaction. Finally, phenomenological models were proposed to illustrate the dependence of dye removal rate constant and specific electrical energy consumption on current density, inter-electrode distance, initial dye concentration and salt concentration.