Indigo Carmine in a Food Dye: Spectroscopic Characterization and Determining Its Micro-Concentration through the Clock Reaction

Indigo carmine is a commonly used industrial blue dye. To determine its concentration in a commercially available food dye composed of a mixture of indigo carmine and D-glucose, this paper characterizes it through (ATR, KBr) FTIR micro-Raman as well as UV/Vis and clock: Briggs-Rauscher (BR) oscillatory reaction methods. The indigo carmine was detected in the bulk food dye only by applying micro-Raman spectroscopy, indicating a low percentage of the indigo carmine present. This research provides an improvement in the deviations from the experimental Raman spectrum as calculated by the B97D/cc-pVTZ level of theory one, resulting in a better geometrical optimization of the indigo carmine molecule compared to data within the literature. The analytical curves used to determine indigo carmine concentrations (and quantities) in an aqueous solution of food dye were applied by means of UV/Vis and BR methods. BR yielded significantly better analytical parameters: 100 times lower LOD and LOQ compared to commonly used UV/Vis. The remarkable sensitivity of the BR reaction towards indigo carmine suggests that not only does indigo carmine react in an oscillatory reaction but also its decomposition products, meaning that the multiple oxidation reactions have an important role in the BR's indigo carmine mechanism. The novelty of this research is the investigation of indigo carmine using a clock BR reaction, opening new possibilities to determine indigo carmine in other complex samples (pharmaceutical, food, etc.).

Rapid Selective Circumneutral Degradation of Phenolic Pollutants Using Peroxymonosulfate-Iodide Metal-Free Oxidation: Role of Iodine Atoms

The development of environmentally friendly, oxidation-selective advanced oxidation processes (AOPs) for water decontamination is important for resource recovery, carbon dioxide abatement, and cost savings. In this study, we developed an innovative AOP using a combination of peroxymonosulfate (PMS) and iodide ions (I^-) for the selective removal of phenolic pollutants from aqueous solutions. The results showed that nearly 100% degradation of phenol, bisphenol A, and hydroquinone was achieved after reaction for 4 min in the presence of 65 μM PMS and 50 μM I^-. PMS-I^- oxidation had a wide effective pH range, with the best performance achieved under circumneutral conditions. The ratio between [PMS] and [I^-] influenced the degradation, and the optimal ratio was approximately 1.00 for the degradation of the phenols. Neither sulfate nor hydroxyl radicals were found to be the active species in PMS-I^- oxidation. Instead, we found evidence that iodide atoms were the dominant oxidants. In addition, both Cl^- and Br^- also promoted the degradation of phenol in PMS solution. The results of this work may promote the application of reactive halogen species in water treatment.

Critical factors in sonochemical degradation of fumaric acid

The effects of critical factors such as Henry's Law constant, atmospheric OH rate constant, initial concentration, H2O2, FeSO4 and tert-butanol on the sonochemical degradation of fumaric acid have been investigated. The pseudo first-order rate constant for the sonochemical degradation of 1mM fumaric acid is much lower than those for chloroform and phenol degradation, and is related to solute concentration at the bubble/water interface and reactivity towards hydroxyl radicals. Furthermore, fumaric acid is preferentially oxidized at the lower initial concentration. It is unreactive to H2O2 under agitation at room temperature. However, the degradation rate of fumaric acid increases with the addition of H2O2 under sonication. 0.1 mM of fumaric acid suppresses H2O2 formation thanks to water sonolysis, while degradation behavior is also dramatically affected by the addition of an oxidative catalyst (FeSO4) or radical scavenger (tert-butanol), indicating that the degradation of fumaric acid is caused by hydroxyl radicals generated during the collapse of high-energy cavities.