The effect of photocatalytic oxidation on molecular size distribution profiles of humic acid

Abstract

The influence of photocatalytic degradation on molecular size fractionation (0.45 μm filtered, 100 kDa, 30 kDa and 3 kDa) of humic acid as a model compound of natural organic matter was investigated. The results were evaluated using UV-vis parameters, dissolved organic carbon (DOC) and excitation emission matrix (EEM) fluorescence spectral features. EEM fluorescence signatures displayed an irradiation period dependent transformation of humic-like fluorophores to fulvic-like fluorophores in accordance with the photocatalytic mineralization of HA. Molecular size distribution profiles expressed the formation of lower molecular size (<3 kDa) fractions through oxidative degradation of humic acid of higher molecular size fractions (100 kDa and 30 kDa fractions). The fluorescence-derived index (fluorescence intensity (FI), represented by the ratio of the emission intensity at λ_emis = 450 nm to that at λ_emis = 500 nm, following the excitation at λ_exc = 370 nm) was also investigated. The use of EEM features has proven to be a useful tool for monitoring the effect of photocatalytic degradation on the structure and molecular size distribution profile of HA.