Visible light induced degradation of perfluorooctanoic acid using iodine deficient bismuth oxyiodide photocatalyst.

A bismuth oxyiodide photocatalyst having coexistent iodine deficient phases viz. Bi4O5I2 and Bi5O7I was prepared by using a solvothermal method followed by calcination process. This has been used for the degradation of model perfluoroalkyl acids such as perfluorooctanoic acid at low concentrations (1 ppm) under simulated solar light irradiation. 94% PFOA degradation with a rate constant of 1.7 h-1 and 65% defluorination of PFOA have been achieved following 2 h of photocatalysis. The degradation of PFOA happened by the parallel direct redox reactions with high energy photoexcited electrons at the conduction band, electrons in iodine vacancies and superoxide radicals. The degradation intermediates were analyzed by electrospray ionization-mass spectrometry in the negative mode. The catalyst was converted to a more iodine deficient Bi5O7I phase during photocatalysis following creation of iodine vacancies, some of which were compensated by the fluoride ions released from degraded PFOA.

Decomposition of antibiotic ornidazole by gamma irradiation in aqueous solution: kinetics and its removal mechanism.

An efficient gamma radiolytic decomposition of one of the extensively used pharmaceutical ornidazole (ORZ) was explored under different experimental conditions by varying initial concentrations, solution pHs, and doses and concentrations of inorganic ([Formula: see text]) and organic (t-BuOH) additives. The results showed that low ORZ concentrations could be efficiently decomposed using gamma irradiation. The decomposition was followed by pseudo first-order reaction kinetics with rate constant values of 2.34, 1.48, 1.11, and 0.80 kGy-1 for the following initial concentrations: 25, 50, 75, and 100 mg L-1 with their corresponding (G(-ORZ)) values of 1.004, 1.683, 2.237, and 2.273, respectively. Decomposition rate of ORZ was remarkably improved under acidic condition when compared to neutral or alkaline medium. It was also observed that the decomposition was primarily caused by the reaction of ORZ with radiolytically generated reactive HO• radicals. The addition of H2O2 had a synergistic effect on the decomposition and mineralization extent of ORZ. However, the removal of total organic carbon (TOC) was not as effective as the decomposition of ORZ. Finally, the quantum chemical calculations were employed to optimize the geometry structure of ORZ and liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) was used to identify the decomposition intermediates. On the basis of Gaussian calculations and analysis of LC-QTOF-MS, it can be inferred that ORZ radiolytic decomposition was mainly attributed to oxidative HO• radicals and the direct cleavage of ORZ molecules. Possible pathways for ORZ decomposition using gamma irradiation in aqueous medium were proposed.

Assessment of reaction intermediates of gamma radiation-induced degradation of ofloxacin in aqueous solution.

Gamma radiolytic degradation of an antibiotic, ofloxacin (OFX) was investigated under different experimental conditions. The parameters such as initial OFX concentration, solution pH, absorbed dose and the concentrations of inorganic (CO32-) and organic (t-BuOH) additives were optimized to achieve the efficient degradation of OFX. The degradation dose constant values of OFX were calculated as 2.364, 1.159, 0.776 and 0.618 kGy-1 for the initial OFX concentrations of 0.05, 0.1, 0.15 and 0.2 mM with their corresponding (G (-OFX)) values of 0.481, 0.684, 1.755 and 1.971, respectively. Degradation rate of OFX was significantly increased with increase in the absorbed dose and decrease in the initial OFX concentration under acidic condition when compared to neutral or alkaline condition. Reaction of OFX in the presence of CO32- and t-BuOH showed that the degradation was primarily caused by the reaction of OFX with radiolytically generated reactive hydroxyl radicals. Mineralization extent of OFX was determined in terms of percentage reduction in total organic carbon (TOC) and results revealed that the addition of H2O2 enhanced the mineralization of OFX from 29% to 36.1% with H2O2 dose of 0.5 mM at an absorbed dose of 3.0 kGy. Based on the LC-QTOF-MS analysis, gamma radiolytic degradation intermediates/products of OFX were identified and the possible degradation pathways of OFX were proposed. Cytotoxicity study of the irradiated OFX solutions showed that gamma radiation has potential to detoxify OFX.

Efficient degradation of butylparaben by gamma radiolysis.

Gamma radiolysis and ozonolysis are two competitive advanced oxidation processes for degradation of organic pollutants present in the ground water. In this paper, the gamma radiolytic degradation of an emerging organic pollutant Butylparaben (BP) in aqueous solution has been investigated for the first time at different absorbed doses. The effect of the absorbed dose rate in the degradation and mineralization of BP has been investigated. About 65% mineralization of BP was observed at absorbed dose of 70kGy and dose rate of 0.7kGyh-1. Interestingly, turbidity appeared in the solution during radiolysis at doses higher than 2kGy, which disappeared again at very higher dose (~90kGy) making the solution again transparent. At lower dose rate of 0.175kGyh-1 the turbidity was appeared at much lower dose about 1kGy. However, the dose rate showed no effect in the dose of the disappearance of the turbidity. The hydrophobic fragments insoluble in water were generated during the initial stage of gamma radiolysis and those were completely mineralized to CO2 and H2O by direct absorption of gamma radiation. About 90kGy dose was required to achieve ~90% mineralization of BP. On the contrary, maximum 50% mineralization was achieved after 5h of ozonation at the O3 flow rate of 0.5Lmin-1 at pH 7.5 and it remained even constant upon prolonged ozonation. The oxygen-equivalent-chemical-oxidation-capacity (OCC) was used as the parameter to compare the % mineralization efficiencies of the two oxidative processes studied here and the gamma radiolysis was found to be more efficient between those processes. The phytotoxicity of the treated BP solution to agricultural seeds showed that the radiolytically generated fragments were less toxic compared to ozonolytically generated fragments. Thus gamma radiolysis is effective for reducing the organic burden and the toxicity of water polluted with emerging pollutants like BP.