Application of chemometric methods to resolve intermediates formed during photo- catalytic degradation of methyl orange and textile wastewater from Ethiopia

The efficiency of two catalysts (TiO2 and TiO2 supported on zeolite) for the photocatalytic degradation of methyl orange dye and wastewaters from Ethiopian textile industry was evaluated by chemometric methods from UV/Vis data of the reaction mixtures at different times. Multivariate curve resolution statistical analysis combined with an alternating least squares algorithm (MCR-ALS) proved to be an efficient method to resolve the different intermediates present during the photocatalytic degradation of the pollutants and to provide information about their evolution with time. Methyl orange photodegradation at pH = 3 showed different intermediate and concentration profiles than at pH = 6. The evolution of intermediates from textile wastewater photodegradation could also be resolved by this method. From the concentration profile or the reactants, a kinetic study was done. Results revealed that all the photodegradation reactions followed a first order kinetics. When TiO2 supported in Zeolite is used, reactions are in general slower, probably due to a mechanism of adsorption/desorption.               KEY WORDS: Chemometrics, Dye photodegradation, Wastewater, MCR-ALS, Methyl Orange Bull. Chem. Soc. Ethiop. 2017, 31(2), 223-232.DOI: http://dx.doi.org/10.4314/bcse.v31i2.4 

Organic aerosol formation photo-enhanced by the formation of secondary photosensitizers in aerosols

AIR+KAE:BNO:CGOSecondary organic aerosols (SOA), which are produced by the transformations of volatile organic compounds in the atmosphere, play a central role in air quality, public health, visibility and climate, but their formation and aging remain poorly characterized. This study evidences a new mechanism for SOA formation based on photosensitized particulate-phase chemistry. Experiments were performed with a horizontal aerosol flow reactor where the diameter growth of the particles was determined as a function of various parameters. In the absence of gas-phase oxidant, experiments in which ammonium sulfate seeds containing glyoxal were exposed to gas-phase limonene and UV light exhibited a photo-induced SOA growth. Further experiments showed that this growth was due to traces of imidazole-2-carboxaldehyde (IC) in the seeds, a condensation product of glyoxal acting as an efficient photosensitizer. Over a 19 min irradiation time, 50 nm seed particles containing this compound were observed to grow between 3.5 and 30 +/- 3% in the presence of either limonene, isoprene, alpha-pinene, beta-pinene, or toluene in concentrations between 1.8 and 352 ppmv. The other condensation products of glyoxal, imidazole (IM) and 2,2-bi1H-imidazole (BI), also acted as photosensitizer but with much less efficiency under the same conditions. In the atmosphere, glyoxal and potentially other gas precursors would thus produce efficient photosensitizers in aerosol and autophotocatalyze SOA growth

Application of chemometric methods to resolve intermediates formed during photo- catalytic degradation of methyl orange and textile wastewater from Ethiopia

The efficiency of two catalysts (TiO2 and TiO2 supported on zeolite) for the photocatalytic degradation of methyl orange dye and wastewaters from Ethiopian textile industry was evaluated by chemometric methods from UV/Vis data of the reaction mixtures at different times. Multivariate curve resolution statistical analysis combined with an alternating least squares algorithm (MCR-ALS) proved to be an efficient method to resolve the different intermediates present during the photocatalytic degradation of the pollutants and to provide information about their evolution with time. Methyl orange photodegradation at pH = 3 showed different intermediate and concentration profiles than at pH = 6. The evolution of intermediates from textile wastewater photodegradation could also be resolved by this method. From the concentration profile or the reactants, a kinetic study was done. Results revealed that all the photodegradation reactions followed a first order kinetics. When TiO2 supported in Zeolite is used, reactions are in general slower, probably due to a mechanism of adsorption/desorption

Secondary organic aerosol formation in the atmosphere by new aerosol-based photo-induced processes

AIR+KAE:MMO:CGO:BDA:BN

Secondary organic aerosol formation in the atmosphere by new aerosol-based photo-induced processes

AIR+KAE:MMO:CGO:BDA:BN

Glyoxal Induced Atmospheric Photosensitized Chemistry Leading to Organic Aerosol Growth

AIR+SRS:KAE:LTI:LFI:BNO:CGOIn recent years, it has been proposed that gas phase glyoxal could significantly contribute to ambient organic aerosol (OA) mass through multiphase chemistry. Of particular interest is the reaction between glyoxal and ammonium cations producing light-absorbing compounds such as imidazole derivatives. It was recently shown that imidazole-2-carboxaldehyde (IC) can act as a photosensitizer, initiating aerosol growth in the presence of gaseous volatile organic compounds. Given the potential importance of this new photosensitized growth pathway for ambient OA, the related reaction mechanism was investigated at a molecular level. Bulk and flow tube experiments were performed to identify major products of the reaction of limonene with the triplet state of IC by direct (+/-)ESI-HRMS and UPLC/(+/-)HESI-HRMS analysis. Detection of recombination products of IC with limonene or with itself, in bulk and flow tube experiments, showed that IC is able to initiate a radical chemistry in the aerosol phase under realistic irradiation conditions. Furthermore, highly oxygenated limonene reaction products were detected, clearly explaining the observed OA growth. The chemistry of peroxy radicals derived from limonene upon addition of oxygen explains the formation of such low-volatile compounds without any traditional gas phase oxidant

Heterogeneous photochemistry of imidazole-2-carboxaldehyde: HO₂ radical formation and aerosol growth

The multiphase chemistry of glyoxal is a source of secondary organic aerosol (SOA), including its light-absorbing product imidazole-2-carboxaldehyde (IC). IC is a photosensitizer that can contribute to additional aerosol ageing and growth when its excited triplet state oxidizes hydrocarbons (reactive uptake) via H-transfer chemistry. We have conducted a series of photochemical coated-wall flow tube (CWFT) experiments using films of IC and citric acid (CA), an organic proxy and H donor in the condensed phase. The formation rate of gas-phase HO₂ radicals (<i>P</i>_HO₂) was measured indirectly by converting gas-phase NO into NO₂. We report on experiments that relied on measurements of NO₂ formation, NO loss and HONO formation. <i>P</i>_HO₂ was found to be a linear function of (1) the [IC]  ×  [CA] concentration product and (2) the photon actinic flux. Additionally, (3) a more complex function of relative humidity (25 %  &lt;  RH  &lt;  63 %) and of (4) the O₂ ∕ N₂ ratio (15 %  &lt;  O₂ ∕ N₂  &lt;  56 %) was observed, most likely indicating competing effects of dilution, HO₂ mobility and losses in the film. The maximum <i>P</i>_HO₂ was observed at 25–55 % RH and at ambient O₂ ∕ N₂. The HO₂ radicals form in the condensed phase when excited IC triplet states are reduced by H transfer from a donor, CA in our system, and subsequently react with O₂ to regenerate IC, leading to a catalytic cycle. OH does not appear to be formed as a primary product but is produced from the reaction of NO with HO₂ in the gas phase. Further, seed aerosols containing IC and ammonium sulfate were exposed to gas-phase limonene and NO_<i>x</i> in aerosol flow tube experiments, confirming significant <i>P</i>_HO₂ from aerosol surfaces. Our results indicate a potentially relevant contribution of triplet state photochemistry for gas-phase HO₂ production, aerosol growth and ageing in the atmosphere