Humic Acid Extracts Leading to the Photochemical Bromination of Phenol in Aqueous Bromide Solutions: Influences of Aromatic Components, Polarity and Photochemical Activity

Dissolved organic matter (DOM) is considered to play an important role in the abiotic transformation of organobromine compounds in marine environment, for it produces reactive intermediates photochemically and is recognized as a significant source of reactive halogen species in seawater. However, due to the complex composition of DOM, the relationship between the natural properties of DOM and its ability to produce organobromine compounds is less understood. Here, humic acid (HA) was extracted and fractionated based on the polarity and hydrophobicity using silica gel, and the influences of different fractions (FA, FB and FC) on the photochemical bromination of phenol was investigated. The structural properties of HA fractions were characterized by UV-vis absorption, Fourier transform infrared spectroscopy and fluorescence spectroscopy, and the photochemical reactivity of HA fractions was assessed by probing triplet dissolved organic matter (3DOM*), singlet oxygen (1O2) and hydroxyl radical (•OH). The influences of HA fractions on the photo-bromination of phenol were investigated in aqueous bromide solutions under simulated solar light irradiation. FA and FB with more aromatic and polar contents enhanced the photo-bromination of phenol more than the weaker polar and aromatic FC. This could be attributed to the different composition and chemical properties of the three HAs’ fractions and their production ability of •OH and 3DOM*. Separating and investigating the components with different chemical properties in DOM is of great significance for the assessment of their environmental impacts on the geochemical cycle of organic halogen.

Theoretical Formulation of the Thermodynamic Properties of Ammonia-Water and Ammonia-Water-Lithium Bromide Solutions

System of Ammonia-Water-Lithium Bromide overcomes the disadvantage of Ammonia-Water absorption refrigeration system. Addition of lithium bromide reduces the formation of water vapour thus presents its entry into the condenser. A set of computational formulations of thermodynamic and Thermophysical properties of Ammonia-Water, Water-Lithium bromide and Ammonia-Water-Lithium Bromide solutions at different pressures and temperatures are presented in the paper. Obtained results are validated with the experimental data which were available in the literature. It is found to be in good agreement with those values of the literature..

Evidence of Radical Intermediate Generated in the Electrochemical Oxidation of Iodide

We present evidence of the generation of radical ion formation during the oxidation of iodide on a fluorine doped tin oxide (FTO) electrode in acetonitrile. The cyclic voltammograms for the oxidation of iodide and triiodide on FTO are significantly different as in the case of the oxidation of Pt electrode. These differences are assigned to kinetic differences on the FTO surface that require significant over potentials to drive the oxidation of iodide and triiodide. We propose that at the highly positive potentials the iodine radical intermediate, I·, becomes thermodynamically stable at FTO. The radical nature of the intermediate was verified by the formation of radicals of the usual traps of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and 2,2,5,5 tetramethyl-1-pyrroline N-oxide (TMPO) when these were added to an electrolyzed solution. Irradiation of an iodine solution causes the homolytic cleavage of I2 and yields the same radical intermediate with TMPO as in the electrolysis experiment. Similar results were obtained from the electrolysis of bromide solutions upon addition of TMPO. Short term electrolysis (< 1 h) gives triiodide as a final product while long-term electrolysis (> 17 h) yields additional byproducts. Byproducts were determined to be organoiodines by gas chromatography-mass spectrometry (GC-MS). Overall, our results are consistent with iodine atoms reacting with the electrolyte during electrolysis at the FTO electrode and with a sequential two-electron transfer process.