Specific UV–vis absorbance changes of humic acid in the presence of clay particles during photocatalytic oxidation

Abstract

Photocatalytic oxidation of humic acid (HA) in the presence of clay particles (montmorillonite [Mt] or kaolinite [Kt]) followed using specific UV–vis parameters (SUVA₃₆₅, SUVA₂₈₀, SUVA₂₅₄, and SCoA) calculated by respective absorbance measurements through conversion to mass of carbon. Non-selective oxidative degradation of HA could be displayed by the observed changes in the UV–vis spectral features in accordance with the successful elimination of the dissolved organic carbon. It was previously reported that fractional UV–vis parameters (E₂₅₄/E₃₆₅, E₂₅₄/E₄₃₆, E₂₈₀/E₃₆₅, E₂₈₀/E₄₃₆, and E₃₆₅/E₄₃₆) could signify the removal of color forming groups in relation to the removal of UV absorbing centers revealing information on the different oxidation pathways through photocatalysis. Regarding the results attained in this study, with respect to the changes attained in the specific UV–vis parameters, it could be indicated that the photocatalytic oxidation mechanism was significantly different for HA in the presence of either Mt or Kt. No noteworthy variation could be detected for fractional UV–vis parameters under photocatalytic conditions for sole HA as well as for HA in the presence of either Mt or Kt. However, a significant correlative interaction was observed between the specific UV–vis parameters (SUVA₂₅₄ and SCoA) and the fractional UV–vis parameter (E₂₅₄/E₄₃₆) (r² > 0.80). Therefore, it could be concluded that E₃₆₅/E₄₃₆ parameter could be successfully used as a discriminative indicator parameter of the specific UV–vis parameters for the photocatalytic degradation of HA in the presence of either Mt or Kt.

Keywords:

• Photocatalytic oxidation
• Humic acid
• Specific and fractional UV–vis parameters
• Montmorillonite and kaolinite