Effects of humic materials on photodegradation of chlorinated aromatic dye in surfactant solution

The photodegradation of hydrophobic dye in surfactant solution by ultraviolet in the presence of humic materials was investigated through the examination of decay quantum yields and a proposed reaction mechanism. Two different humic materials were used in this study for comparison, a well-defined Aldrich humic substance (Ha) and a soil extracted material (SEM) prepared using a surfactant-aided soil-washing process. Experimental results indicated that the low dose of humic substances mainly acted as a supplementary hydrogen source to improve the photodegradation rate, while at a high dose of humic substances, the characteristics of humic materials being a hydrogen source will be embedded by its amphoteric quenching property, thus retarding the reaction. The possible photodegradation mechanisms of the dye were proposed, and two models based on the dye's decay quantum yields were derived and found to successfully describe the reaction at both low- and high-humic concentrations, which verified and quantified the amphoteric characteristics of humic substances and made the process performance predictable. The results could be useful in quantifying the variation of photolytic rates and facilitating the reactor design for field applications.