21 , after the reaction was carried out for 70 min, A 253 / A 203 decreased from the initial 0.66 to 0.32, indicating that the stability of the functional groups such as carboxyl and carbonyl groups within the aromatic structure of HA decreased, resulting in a decreasing trend in the content of the substituted aromatic ring structure within the HA molecule; A 465 / A 665 decreased from 5.73 to 3.33, which is a further evidence of the disruption of the aromaticity in HA.
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Degradation of humic acid by UV/PMS: process comparison, influencing factors, and degradation mechanism.
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