Diametrically opposite effect of Cu2+ on sulfamerazine and ciprofloxacin adsorption-photodegradation in g-C3N4/visible light system: behavior and mechanism study

Coexistence of heavy metals usually shows great impact on antibiotics removal. In this study, we firstly reported that Cu2+ shows diametrically opposite effect on adsorption-photodegradation of sulfamerazine (SMZ) and ciprofloxacin (CIP) in g-C3N4/visible light system. Cu2+ can greatly promote CIP adsorption, but showed negligible impact on its degradation, whereas, no obvious influence on SMZ adsorption was recorded, but strong inhibition to its photodegradation was observed. With help of several spectroscopy approaches and DFT calculation, functional mechanism of Cu2+ on the adsorption-photodegradation of SMZ and CIP was proposed. The main reasons for their different behaviors were found to be their distinct surface charge, spatial structure, electron distribution and complexation with Cu2+. Among them, effect of complexation played the most important role in depressing the reactivity of antibiotics during photodegradation. Aiming at retarding this inhibition, an effective approach with idea of complexation replacement was proposed. This study indicated that interactions between antibiotics and heavy metals are very specific, and an appropriate treatment scheme should be given based on systematic study targeting at the specific pollution system.

Automated summary

This study revealed the contrasting effects of Cu2+ on the adsorption and photodegradation of sulfamerazine (SMZ) and ciprofloxacin (CIP) in a g-C3N4/visible light system. The complexation effect of Cu2+ was found to play a key role in inhibiting the reactivity of antibiotics during photodegradation. A proposed approach of complexation replacement aims to mitigate this inhibition, highlighting the specificity of interactions between antibiotics and heavy metals.