Browsing by Author "Gounden, Asogan Nokan."

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Catalytic ozonation of hazardous halogenated compounds with mixed-metal oxides.
(2018) Gounden, Asogan Nokan.; Jonnalagadda, Sreekantha Babu.; Singh, Sooboo.
The study compares degradation of four hazardous halogenated pollutants, namely 2,3-DBP, 1,3-DCP, 2,4,6-TBP and 2,4-DCPA Acid in water, by ozonation alone and catalytic ozonation using Co and Ni loaded on Fe respectively by co-precipitation and a simple mixing method. The brominated pollutants showed a higher reactivity during ozonation than the chlorinated pollutants. In ozonation alone dehalogenation of each compound improved with an increase in the amount of hydroxide ions. TOC removal and DBP minimization was difficult to achieve in ozonation alone, however, in catalytic ozonation with Fe:Co (Co-ppt) and Fe:Ni (Co-ppt) significant improvements were noted. Fe:Ni (Co-ppt) catalyst material showed the best activity for conversion of the pollutants, TOC removal and DBP minimization in water during ozone treatment. BET and SEM data showed that the mixed metal oxides catalyst prepared by coprecipitation had better textural properties than the mixed metal oxide catalyst prepared by simple mixing, hence more superior catalytic activity for degradation of pollutants, TOC removal and DBP minimization, however, Fe:Co (Mixed) was the only catalyst material to effectively minimize bromate formation through lowering of solution pH. The chloride ion was found be refractory towards ozone, which is an added advantage during water treatment processes. NH3-TPD analysis and pZc values reveal that Fe alone has negligible acidic sites, whereas, Fe:Co (Co-ppt) and Fe:Ni (Co-ppt) have more acidic sites than Fe:Co (Mixed) and Fe:Ni (Mixed), hence improved decomposition of ozone to hydroxyl radicals on these active sites. The presence of 𝐻2𝑂2 showed an improvement in the debromination efficiency of 2,4,6- TBP. TOC data indicated that total mineralization of OBP’s occurred in the 𝑂3/𝐻2𝑂2 process, which was not achievable in ozonation alone. Only 10% 𝐻2𝑂2 was able to effectively lessen 𝐵𝑟𝑂3 − formation. In basic water both 2,4,6-TBP conversion and TOC removal decreased with an increase in 𝐶𝑂3 2−, hence minimizing 𝐵𝑟𝑂3 − formation.
Ozone initiated oxidation of organic pollutants, m-xylene and 2-chloroethanol.
(2010) Gounden, Asogan Nokan.; Jonnalagadda, Sreekantha Babu.
A variety of hazardous organic compounds are present in leachate from landfill sites that accept medical and industrial chemical waste. Most of these compounds find their way into nearby streams, rivers and dams, posing a threat to the ecosystem. In the present work two hazardous organic compounds, namely, m-xylene and 2-chloroethanol were chosen to react with ozone gas at different experimental conditions. The ozone initiated oxidation of m-xylene and 2-chloroethanol in solvent free conditions were investigated as a function of time. Gas chromatographic analysis of ozonated m-xylene, showed an increase in the conversion of substrate from about 1 % after 3 hours to about 14 % after 24 hours. Some of the ozonation products identified were formic acid, acetic acid, 3-methylbenzylalcohol, 3-methylbenzaldehyde and 3-methylbenzoic acid. The presence of acetic acid, ethyl acetate or acetone during ozonation significantly improved the percent conversion of m-xylene relative to similar products obtained under solvent free conditions. The presence of activated charcoal during ozonation of m-xylene showed marginal improvement in percent conversion compared to solvent free ozonation. The oxidation of 2-chloroethanol was followed by monitoring the consumption of the halogenated organic substrate which showed an increase in conversion from about 2 % after 3 hours to about 46 % after 12 hours. Ozonated products contained a mixture of acetaldehyde and acetic acid. It was also found that the ozonation of 2-chloroethanol yielded quantitative amounts of chloride ions. The percent conversion of 2-chloroethanol in the presence of acetic acid and ethyl acetate were higher than those under solvent free conditions. The use of activated charcoal during ozonolysis of 2-chloroethanol showed a significant increase in percent conversion of the substrate. Since 2-chloroethanol has a higher solubility in water than m-xylene the effects of solution pH, activated charcoal and hydrogen peroxide on ozone initiated reactions were studied. Solutions of 2-chloroethanol maintained at pH level 4 and 7 showed marginal changes in percent conversion compared to ozonation alone, however percent conversion improved significantly when the pH of the solution was increased to 10. The ozonation of 2-chloroethanol in the presence of 5 % hydrogen peroxide in water at pH levels 4 and 7 showed marginal changes in percent conversion compared to ozonation alone, however, percent conversion and product yields improved significantly, when the pH of the solution was increased to 10. Increasing the strength of the hydrogen peroxide in the reaction mixture from 5 % to 10 % had very little effect in the percent conversion of 2-chloroethanol and product formation. Based on the experimental findings the overall reaction mechanism for the reaction of both m-xylene and 2-chloroethanol with ozone is described.