Monitoring changes in the structure and properties of humic substances following ozonation using UV-Vis, FTIR and H-1 NMR techniques

作者：Rodriguez Francisco J^*; Schlenger Patrick; Garcia Valverde Maria

来源：Science of the Total Environment, 2016, 541: 623-637.

DOI：10.1016/j.scitotenv.2015.09.127

• Humic substances
• Ozonation
• UV-Vis
• FTIR
• H-1 NMR

The main objective of this work is to conduct a comprehensive structural characterization of humic substances using the following experimental techniques: FTIR, H-1 NMR and several UV-Vis parameters (Specific UV Absorbance at 254 nm or SUVA(254), SUVA(280), A(400), the absorbance ratios A(210/254), A(250/365), A(254/203), A(254/436), A(265/465), A(270/400), A(280/350), A(465/665), the Absorbance Slope Index (ASI), the spectral slopes S275-295, S350-400 and the slope ratio SR). These UV-Vis parameters have also been correlated with key properties of humic substances such as aromaticity, molecular weight (MW) and trihalomethane formation potential (THMFP). An additional objective of this work is also to evaluate the usefulness of these techniques to monitor structural changes in humic substances produced by the ozonation treatment. Four humic substances were studied in this work: three of them were provided by the International Humic Substances Society (Suwannee River Fulvic Acid Standard: SRFA, Suwannee River Humic Acid Standard: SRHA and Nordic Reservoir Fulvic Acid Reference: NLFA) and the other one was a terrestrial humic acid widely used as a surrogate for aquatic humic substances in various studies (Aldrich Humic Acid: AHA). The UV-Vis parameters showing the best correlations with aromaticity in this study were SUVA(254), SUVA(280), A(280)/A(350) ratio and A(250)/A(364) ratio. The best correlations with molecular weight were for SUVA(254), SUVA(280) and A(280)/A(350) ratio. Finally, in the case of the THMFP it was STHMFP-per mol HS the parameter showing good correlations with most of the UV-Vis parameters studied (especially with A(280)/A(350) ratio, A(265)/A(465) ratio and A(270)/A(400) ratio) whereas STHMFP-per mg C showed poor correlations in most cases. On the whole, the UV-Vis parameter showing the best results was A(280)/A(350) ratio as it showed excellent correlations for the three properties studied (aromaticity, MW and THMFP). A decrease in aromaticity following ozonation of humic substances can be readily monitored by H-1 NMR and FTIR; the latter technique also allows to monitor an increase in carboxylic acidity with ozone dosage. This organic matter originated following ozonation (more aliphatic in character and more polar) is expected to be recalcitrant to further oxidation. The terrestrial humic acid (AHA) showed some structural differences with the aquatic humic substances and its behavior upon ozonation also differed in some extent from that shown by them.

• 出版日期2016-1-15