Enhancive and inhibitory effects of copper complexation on triplet dissolved black carbon-sensitized photodegradation of organic micropollutants.

Excited-triplet dissolved black carbon (DBC) was deemed as a significant reactive intermediate in the phototransformation of environmental micropollutants, but the impacts of concomitant metal ions on photochemical behavior of excited-triplet DBC (DBC*) are poorly understood. Here, the photolytic kinetics of sulfadiazine and carbamazepine induced by DBC* involving Cu was explored. The presence of Cu reduced the DBC*-induced photodegradation rate of sulfadiazine; whereas for carbamazepine, Cu enhanced DBC*-induced photodegradation. Cu(II)-DBC complex was formed due to the decreasing fluorescence intensities of DBC in the presence of Cu. Cu complexation caused the decrease of DBC* steady-state concentrations, which markedly reduced DBC*-induced photodegradation rate of sulfadiazine due to its high triplet reactivity. Kinetic model showed that DBC* quenching rate by Cu was 7.98 × 10 M s. Cu complexation can also enhance the electron transfer ability, thereby producing more ∙OH in Cu(II)-DBC complex, which explains the promoting effect of Cu complexation on carbamazepine photodegradation in view of its low triplet reaction rate. These indicate that DBC* reactivity differences of organic micropollutants may explain their photodegradation kinetics differences in DBC system with/without Cu, which was supported by the linearized relationship between the photodegradation rate ratios of ten micropollutants with/without Cu and their triplet reaction activity.