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 (3DBC*) are poorly understood. Here, the photolytic kinetics of sulfadiazine and carbamazepine induced by 3DBC* involving Cu2+ was explored. The presence of Cu2+ reduced the 3DBC*-induced photodegradation rate of sulfadiazine; whereas for carbamazepine, Cu2+ enhanced 3DBC*-induced photodegradation. Cu(II)-DBC complex was formed due to the decreasing fluorescence intensities of DBC in the presence of Cu2+. Cu2+ complexation caused the decrease of 3DBC* steady-state concentrations, which markedly reduced 3DBC*-induced photodegradation rate of sulfadiazine due to its high triplet reactivity. Kinetic model showed that 3DBC* quenching rate by Cu2+ was 7.98 × 109 M−1 s−1. Cu2+ complexation can also enhance the electron transfer ability, thereby producing more ∙OH in Cu(II)-DBC complex, which explains the promoting effect of Cu2+ complexation on carbamazepine photodegradation in view of its low triplet reaction rate. These indicate that 3DBC* reactivity differences of organic micropollutants may explain their photodegradation kinetics differences in DBC system with/without Cu2+, which was supported by the linearized relationship between the photodegradation rate ratios of ten micropollutants with/without Cu2+ and their triplet reaction activity.