Chemical studies on the ozonation of synthetic glucose-glycine melanoidin as model color pollutant
2006
Belina, M.D.A., de Roxas, D.M.I., Guardian, M.G.E., del Rosario, E.J., Philippines Univ. Los Baños, College, Laguna (Philippines). Inst. of Chemistry
Synthetic melanoidin (a model color pollutant) was prepared by heating an aqueous solution of 1.0 M glucose, 1.0 M glycine and 0.5 M sodium carbonate at 121 degC for 3 hours. It was dialyzed against distilled water, eluted through a Sephadex G-75 column and then freeze-dried. The kinetics ozonation of the prepared melanoidin was studied in unbuffered and buffered solutions (pH 3.5, 5.0, 6.5, 7.0, 8.5 and 10). The reaction was found to obey first-order and half-order kinetics based on absorbance data at 475nm and 280nm, respectively. After two hours of ozonation, melanoidin decolorization was in the range 64-94%; decolorization was greater at lower pH values. Decolorization of the unbuffered melanoidin solution was 97.2%. Reduction in absorbance at 280nm generally increased from 31% to 51% as the pH was changed from 10 to 3.5; the value for unbuffered solution was 74.9%. Reduction of MW [molecular weight] was 78% and indicated melanoidin depolymerization. The UV-visible spectra of synthetic melanoidin after ozonation showed a decrease in absorbance at 230-280nm, a shift towards shorter wavelengths of the absorption peak at 300-400nm and decrease in absorbance in the visible region. The IR[infrared] spectra showed the presence of -OH, C=C and C=O groups in both unozonated and ozonated melanoidins. An increase in peak intensity corresponding to the C-O stretch was observed for the ozonated sample. The results showed that ozonation is effective in decolorizing melanoidin.
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