Catalytic Oxidation of Indigo Carmine in the Presence of Silver Nanoparticles: Application to Groundwater Analysis

The oxidation of indigo carmine by potassium hexacyanoferrate(III) is catalyzed by trace of silver nanoparticle (AgNP). The reaction is followed UV‐Vis absorption spectrophotometrically by measuring the change in the absorption spectra (λ_max 612 nm). The catalytic oxidation reaction is used for the quantification of indigo carmine. The calibration graph was linear in the concentration range 50 nM—1.8 μM of indigo carmine. The variables affecting the method have been optimized. The method is applied to the determination of indigo carmine in groundwater samples with the satisfactory results.     

Analysis of the conversion of indigo into indigo carmine dye using SERRS

In a novel application SERRS has been used, by employing a silver sol, to monitor and analyse the conversion of indigo into the indigo carmine dye.     

An Indigo Carmine‐Based Hybrid Nanocomposite with Supramolecular Control of Dye Aggregation and Photobehavior

Zn‐Al layered double hydroxides (LDHs) containing solely indigo carmine (IC) or 1‐hexanesulfonate (HS) anions, or a mixture of the two with different HS/IC molar ratios, were prepared by the direct synthesis method and characterized by various techniques. Hydrotalcite‐type phases were obtained with basal spacings of 17.6 Å for the LDH intercalated by IC (IC‐LDH) and 18.2–18.3 Å for the other materials containing HS. From the basal spacing for IC‐LDH and UV/Vis spectroscopic data, it is proposed that the dye molecules assemble within the interlayer galleries to form a J‐type stacking arrangement. A comprehensive electronic spectral and photophysical study was undertaken for IC in solution and all materials, aiming to obtain a detailed characterization of the host–guest and guest–guest interactions. In solution (the solvent surrounded “isolated” molecule), IC presents a fast excited state proton transfer with rate constants of ～1.2–1.4×10¹¹ s^?1, which is linked to the very efficient radiationless deactivation channel. In the solid state it is shown that incorporation of IC within the LDH decreases the level of aggregation, and that further addition of HS induces the appearance of isolated IC units within the LDH galleries. The indigo carmine‐based nanocomposites reported constitute a step forward in the design of hybrid materials with tunable properties.     

Voltammetric Determination of Indigo Carmine and Amaranth on a Silver-Based Mercury Film Electrode

Abstract

The voltammetric behavior of indigo carmine and amaranth on silver-based mercury film electrodes was studied. At pH 4, reduction current peaks were observed at potential ?0.11 V (indigo carmine) and ?0.24 V (amaranth), respectively. The system showed a linear response to both of the food colorants in a concentration range of 0 to 100 ng/ml. Detected at different reduction potentials, indigo carmine and amaranth could be determined separately without interfering with each other. This method demonstrated a better reproducibility and longer life time than the existing techniques.     

Comparative adsorption studies of indigo carmine dye on chitin and chitosan

The adsorption of indigo carmine dye onto chitin and chitosan from aqueous solutions was followed in a batch system. The ability of these materials to adsorb indigo carmine dye from aqueous solution was followed through a series of adsorption isotherms adjusted to a modified Langmuir equation. The maximum number of moles adsorbed was 1.24 +/- 0.16 x 10(-5) and 1.54 +/- 0.03 x 10(-4) mol g(-1) for chitin and chitosan, respectively. The same interactions were calorimetrically followed and the thermodynamic data showed exothermic enthalpic values of -40.12 +/- 3.52 and -29.25 +/- 1.93 kJ mol(-1) for chitin and chitosan, respectively. Gibbs free energies for the two adsorption processes of indigo carmine dye presented a positive value for chitin and a negative one for chitosan, reflecting that dye/surface interactions are thermodynamic favorable for chitosan and nonspontaneous for chitin at 298.15 K. The interaction processes were accompanied by an increase of entropy value for chitosan (90 +/- 6 J mol(-1)K(-1)) and a decrease for chitin (-145 +/- 13 J mol(-1)K(-1)). Thus, dye/chitosan interaction showed favorable enthalpic and entropic processes, reflecting thermodynamic stability of the formed complex, while dye/chitin interaction showed an exothermic enthalpic value and a highly nonfavorable entropic effect, resulting in a nonspontaneous thermodynamic system.     

X-ray structure of host-guest nanosized organotin supramolecular coordination polymer based on cobalt cyanide and quinoxaline as an efficient catalyst for treatment of waste water

New host-guest supramolecular coordination polymer catalyst ³_∞[Co(μ²CN)₅(CN)(μ²-Me₃Sn)₂(Me₃Sn)(H₂O)(qox)], SCP1 (qox = quinoxaline) has been synthesized and characterized by single crystal X-ray diffraction, FT-IR, UV/Visible and fluorescence spectra, thermal and elemental analyses. The tin atoms act as bridges connecting the Co (CN)₆ building blocks. The structure of SCP1 exhibits an unusual self-coordinated host-guest 3D network with qox as guest molecule. Also, the nanosized1^\ was prepared under ultrasonic irradiation while the morphological features of both were examined by TEM and SEM. SCP1 and nanosized1^\ are used as heterogeneous catalysts for removal of toxic dyes under UV and ultrasonic irradiation. The results show high effectively decolorized of indigo carmine dye (IC) without generation of any hazardous wastes or byproducts. The reaction is first order with respect to IC, while the factors affecting the rate constant of the degradation reaction are investigated. Mineralization of IC was investigated by IR and UV spectra. The trapping experiments were carried out to determine the role of active species used for degradation of the dye. The activation parameters of the reaction have been estimated and a possible mechanism of degradation was proposed and discussed in detail.     

Electrochemical Assessment of Indigo Carmine Dye in Lithium Metal Polymer Technology

Lithium metal batteries are inspiring renewed interest in the battery community because the most advanced designs of Li-ion batteries could be on the verge of reaching their theoretical specific energy density values. Among the investigated alternative technologies for electrochemical storage, the all-solid-state Li battery concept based on the implementation of dry solid polymer electrolytes appears as a mature technology not only to power full electric vehicles but also to provide solutions for stationary storage applications. With an effective marketing started in 2011, BlueSolutions keeps developing further the so-called lithium metal polymer batteries based on this technology. The present study reports the electrochemical performance of such Li metal batteries involving indigo carmine, a cheap and renewable electroactive non-soluble organic salt, at the positive electrode. Our results demonstrate that this active material was able to reversibly insert two Li at an average potential of ≈2.4 V vs. Li⁺/Li with however, a relatively poor stability upon cycling. Post-mortem analyses revealed the poisoning of the Li electrode by Na upon ion exchange reaction between the Na countercations of indigo carmine and the conducting salt. The use of thinner positive electrodes led to much better capacity retention while enabling the identification of two successive one-electron plateaus.     

Activation of H2O2 by methyltrioxorhenium(VII) inside β-cyclodextrin

The effect of β-cyclodextrin on the catalytic stability and reactivity of methylrhenium trioxide (MTO), CH₃ReO₃, which has been used for activation of hydrogen peroxide toward oxidation and epoxidation reactions, was studied using UV–Vis spectrophotometery. The stability and reactivity of the new catalytic system (MTO/β-CD) to activate H₂O₂ toward oxidation of indigo blue dye were investigated in basic media. Furthermore, effects of inclusion stoichiometry, temperature and concentrations of hydrogen peroxide on the stability and reactivity of the MTO/β-CD system were investigated. The formation of the inclusion complex between MTO and β-CD was confirmed experimentally using the changes in the UV–Vis absorption spectra. The results of this study demonstrate that the complexation process was better guaranteed when the amount of β-CD is higher than that of MTO, using a 1:2 molar ratio of MTO:β-CD enhances both the activity and stability of the catalyst. The results showed that the stability of the catalytic system was enhanced in presence of β-CD with maintaining good reactivity of the MTO even in the presence of high concentration of NaOH. The changes of thermodynamic activation parameters (ΔH^≠ and ΔS^≠) for the oxidation reaction of indigo with H₂O₂ catalyzed by MTO/β-CD system were determined on the basis of the experimental data.     

Electrospray ionization mass spectrometry monitoring of indigo carmine degradation by advanced oxidative processes

The degradation of the dye indigo carmine in aqueous solution induced by two oxidative processes (H(2)O(2)/iodide and O(3)) was investigated. The reactions were monitored by electrospray ionization mass spectrometry in the negative ion mode, ESI(-)-MS, and the intermediates and oxidation products characterized by ESI(-)-MS/MS. Both oxidative systems showed to be highly efficient in removing the color of the dye aqueous solutions. In the ESI(-)-MS of the indigo carmine solution treated with H(2)O(2) and H(2)O(2)/iodide, the presence of the ions of m/z 210 (indigo carmine in its anionic form, 1), 216, 226, 235, and 244 was noticeable. The anion of m/z 235 was proposed to be the unprecedented hydroperoxide intermediate 2 formed in solution via an electrophilic attack by hydroxyl and hydroperoxyl radicals of the exocyclic C=C bond of 1. This intermediate was suggested to be rapidly converted into the anionic forms of 2,3-dioxo-1H-indole-5-sulfonic acid (3, m/z 226), 2-amino-alpha-oxo-5-sulfo-benzeneacetic acid (4, m/z 244), and 2-amino-5-sulfo-benzoic acid (5, m/z 216). In the ESI(-)-MS of the indigo carmine solution treated with O(3), two main anions were detected: m/z 216 (5) and 244 (4). Both products were proposed to be produced via an unstable ozonide intermediate. Other anions in this ESI(-) mass spectrum were attributed to be [4 - H + Na](-) of m/z 266, [4 - H](2-) of m/z 121.5, and [5 - H](2-) of m/z 107.5. ESI-MS/MS data were consistent with the proposed structures for the anionic products 2-5.     

Photocatalytic Reduction of Nitro Compounds Using TiO2 Photocatalyst by UV and Vis Dye-sensitized Systems

Nitro‐aromatic compounds can be photocatalytically reduced into the corresponding amine‐aromatic compounds using TiO₂ as a photocatalyst in the UV/TiO₂/holes scavenger and Vis/TiO₂/dye‐sensitized systems. In the UV/TiO₂/holes scavenger system, reaction substrate alcohols such as methanol could be used as the holes scavengers, and in the Vis/TiO₂/dye‐sensitized system, substrate alcohols could be oxidized to the corresponding aldehydes with high selectivity. When methanol was used as the holes scavengers and the illumination time was 6 h, 87.2% of p‐nitrotoluene could be photocatalytically reduced into p‐toluidine. In the Vis/TiO₂/dye‐sensitized system, the effect of aromatic alcohols for the photocatalytic reduction of nitrobenzene was better than that of other alcohols. At the same time, aromatic alcohols can be easily oxidized, and the production efficiencies of the corresponding aldehydes were higher than those of other alcohols. The possible reaction mechanisms were also proposed.     

Adsorption Characteristics of Activated Carbon for the Reclamation of Eosin Y and Indigo Carmine Colored Effluents and New Isotherm Model

The adsorption response of eosin Y and indigo carmine acid dyes on activated carbon as a function of system temperature for a fixed concentration was investigated at various temperatures via adsorption isotherms and their thermodynamic quantities such as enthalpy, entropy, and Gibbs free energy changes. The adsorption data were exploited to develop a new adsorption isotherm. The new isotherm was developed with the spirit of solid–liquid phase equilibrium and regular solution theory. The proposed model has four adjustable constants and correlates adsorption isotherm in terms of the system temperature and melting temperature of the dye. The effect of pH on the removal of acid dyes was reported. The pH variation was observed to affect the adsorption efficiency. The removal of eosin Y and indigo carmine decreased from 99.4% to 82.6% and 92.38% to 79.48%, respectively, when the pH of the solution varied from 2 to 12. The thermodynamic analysis of the process reveals that the process of the removal of acid dyes is exothermic and spontaneous. Moreover, the kinetics parameters of the batch process are reported.     

Highly selective DNA biosensor based on the long-range electron transfer of indigo carmine through DNA duplex

We have developed a highly selective DNA biosensor. It was based on the long-range electron transfer (LRET) from the electroactive dye indigo carmine (IC) through the DNA duplex on a glassy carbon electrode. Voltammetric experiments showed that IC interacts with dsDNA through a typical intercalative mode with a relatively strong affinity of 2.3(±0.6)?×?10⁶?M^-1. If incubated with DNA in IC solution, no response was observed with the ssDNA-modified probe electrode. However, a pair of well-defined redox peak was observed with a DNA-hybridized electrode, proving the presence of LRET on the biosensor. The biosensor also can differentiate complementary sequences, non-complementary sequences, and even the mutated sequences with single-base mismatches at different sites.

Microdetermination of dissolved oxygen in water by a rapid spectrophotometric method

A spectrophotometric method utilizing the dye indigo carmine has been applied to the analysis of dissolved oxygen in water samples. Oxygen concentration has been determined by the decrease in absorbance at 410 mμ of reduced indigo carmine solutions oxidized by dissolved oxygen. A simple modification of the sample compartment of a Bausch and Lomb Spectronic 20 or 340 spectrophotometer allows rapid and accurate measurements to be made within 3 min. Dissolved oxygen in the ranges of 0 to 10% and 0 to 100% saturation can be analyzed without many of the interferences inherent in the standard Winkler method.     

Rapid kinetic determination of silver (I), using in-cuvette mixing and computerized data acquisition

 The determination of silver(I) based on its catalytic effect on the oxidation of indigo carmine with hexacyanoferrate(III) is described. The reaction is monitored spectrophotometrically by means of a home-made rapid system with computer data acquisition. The decrease in absorbance of indigo carmine at 612 nm, pH 6 and at a fixed concentration of hexacyanoferrate(III) and indigo carmine is proportional to the concentration of Ag(I). The acquired data based on the initial rate and fixed time are processed. Up to 100.0 μg/ml of silver are determined. The limit of detection and average relative standard deviation are 0.13 μg/ml and 1.9%, respectively. The effect of foreign ions on the determination of silver is also discussed. The proposed method is applied to the determination of Ag(I) in expired photographic film. Received: 17 June 1996 / Revised: 26 July 1996 / Accepted: 2 August 1996     

The Role of Interfacial Reactions in Determining Plasma–Liquid Chemistry

In this work, we investigate the production of highly oxidative species in solutions exposed to a self-pulsed corona discharge in air. We examine how the properties of the target solution (pH, conductivity) and the discharge power affect the discharge stability and the production of H₂O₂. Indigo carmine, a common organic dye, is used as an indicator of oxidative strength and in particular, hydroxyl radical (OH^·) production. The observed rate of indigo oxidation in contact with the discharge far exceeds that predicted from reactions based on concentrations of species measured in the bulk solution. The generation of H₂O₂ and the oxidation of indigo carmine indicate a high concentration of highly oxidizing species such as OH^· at the plasma–liquid interface. These results indicate that reactions at the air plasma–liquid interface play a dominant role in species oxidation during direct non-equilibrium atmospheric pressure plasma treatment.     

Influence of particle size on the photoactivity of Ti/TiO2 thin film electrodes,and enhanced photoelectrocatalytic degradation of indigo carmine dye

Photoanodes based on Ti/TiO₂ thin films were prepared by the sol–gel method, using either tetraisopropoxide (Ti(OPri)₄) or modified tetraisopropoxide, producing electrodes with different sized nanoparticle coatings, termed nanoporous (20 nm) or nanoparticulated (10 nm) electrodes. The anatase form dominated the composition of the nanoparticulated electrode, which presented a higher surface area, a flat band potential shift of ?160 mV and a 50% improvement in photoactivity, compared to the nanoporous electrode. 100% color removal, and 75% mineralization, of indigo carmine dye were achieved after 15 min of photoelectrocatalytic treatment using a nanoparticulated Ti/TiO₂ electrode operated at a current density of 0.4 mA cm^?2. Our findings indicate that the use of nanoparticulated electrodes, under UV irradiation and with controlled current density, is an efficient alternative for the removal of food dye contaminants during wastewater treatment.     

A STUDY ON VOLTAMMETRIC BEHAVIOR OF INDIGO CARMINE AND ITS MIXTURE WITH AMARANTH AT MERCURY FILM ELECTRODE ON SILVER SUBSTRATE

The voltammetric behavior of indigo carmine at mercury film electrode on a silver substrate (MFES) was studied in this paper. It was found that indigo carmine gave a sensitive reduction peak at a potential (Vp) of -0.11 V at pH 4.0 in aqueous solution. The MFES gave good reproducibility and life time. The peak currents (ip) depended lipearly on the concentrations of indigo carmine free 0 to 100 ng/ml.The Vp and Ip of indigo carmine at MFES were independent of the concentrations of amaranth at pH 4.0, the Vp of amaranth was -0.24 V at this pH. The differences of Vp between both colorants enabled to distinguish indigo carmine free amaranth.     

TiO2 nanotubes as recyclable catalyst for efficient photocatalytic degradation of indigo carmine dye

TiO₂ nanotubes have been synthesized in a hydrothermal system. The nanotubes were characterized by scanning electronic microscopy (SEM), FT-Raman spectroscopy and surface charge density by surface area analyzer. These nanocatalysts were applied to photocatalyse indigo carmine dye degradation. Photodegradation ability of TiO₂ nanotubes was compared to TiO₂ anatase photoactivity. Indigo carmine dye was completely degraded at 60 and 110 min of reaction catalysed by TiO₂ nanotubes and TiO₂ anatase, respectively. TiO₂ nanotubes presented high photodegradation activity at pH 2 and TiO₂ anatase at pH 4. TiO₂ nanotubes were easily recycled whereas the reuse of TiO₂ anatase was not effective. Nanotubes maintained 90% of activity after 10 catalytic cycles and TiO₂ anatase presented only 10% of its activity after 10 cycles.     

Voltammetric determination of alkaline phosphatase and horseradish peroxidase activity using 3-indoxyl phosphate as substrate Application to enzyme immunoassay

The use of 3-indoxyl phosphate (3-IP) as an electrochemical substrate for ELISAs with voltammetric detection was investigated. Indirect measurements of alkaline phosphatase (AP) and horseradish peroxidase (HRP) activity in solution were carried out. Picomolar levels of both enzymes can be detected, which enables the design of electrochemical immunoassays using this substrate. The enzymatic turnover of the substrate gives indigo blue, insoluble in aqueous solutions. This product is easily converted into its soluble parent compound, indigo carmine (IC), by addition of fuming sulphuric acid to the reaction media. IC shows a reversible voltammetric peak at the formal potential of −0.15 V (versus Ag pseudo-reference electrode) when a screen-printed carbon electrode (SPCE) is used. The peak current of this process constitutes the analytical signal. Using this approach an ELISA assay to quantify pneumolysin (PLY, a toxin related to respiratory infections) was carried out using AP or HRP as enzymatic label. Calibration plots obtained are reported. 3-IP is demonstrated to be the first suitable substrate for the two most common enzyme labels used in immunoassays.     

Semi-quantitative analysis of indigo carmine,using silver colloids,by surface enhanced resonance Raman spectroscopy (SERRS)

The application of surface enhanced resonance Raman spectroscopy (SERRS) to the semi-quantitative analysis of the dye, indigo carmine, has been examined using citrate-reduced silver colloids. Good linear correlations are observed for the dye band at 1580 cm(-1) in the concentration range 10(-7)-10(-5) and 10(-9)-10(-5) mol dm(-3), using laser exciting wavelengths of 514.5 [(R=0.9983)] and 632.8 nm [(R=0.9978)], respectively. At concentrations of dye above 10(-6) M the concentration dependence of the SERRS signals is non-linear due to the coverage of the surface of the colloidal particles by the dye being in excess of a full monolayer. At concentrations above 10(-6) M resonance Raman spectroscopy (RRS) can be employed for the quantitative analysis of the dye. An internal standard was used and a good linear correlation (R=0.997) was observed for the dependence of dye signal intensities at 1580 cm(-1) in the concentration range 10(-5)-10(-4) M using a laser exciting wavelength of 514.5 nm. The limits of detection of indigo carmine by SERRS (514.5 nm), SERRS (632.8 nm) and solution RRS (514.5 nm) are found to be 0.9, 1 and 38 ppm, respectively.