Transformation of tetracycline by multipurpose Fe-Mn-Cu nano-composite oxide: Dual-synergies and dual-mechanisms.

The interaction between tetracycline (TTC) and mixed metallic oxides remains unclear, and even complexation usually is ignored. This study firstly distinguished the triple functions of adsorption, transformation and complexation in presence of Fe-Mn-Cu nano-composite metallic oxide (FMC) on TTC. Rapid adsorption and faint complexation initiated the transformation that dominated the entire reactions at 180 min, which completed TTC removal (up to 99.04%) synergistically within 48 h. Environmental factors (dosage, pH and coexisting ions) had small influence on TTC removal, which primarily depended on the stable transformation characteristics of FMC. Kinetic models incorporating pseudo-second-order kinetics and transformation reaction kinetics demonstrated that the surface sites of FMC promoted electron transfer process through chemical adsorption and electrostatic attraction. ProtoFit program coupled with characterization methods concluded that Cu-OH was the main reaction site of FMC where the protonated surface favored to generate·O. Meanwhile, three metal ions developed simultaneous mediated transformation reactions on TTC in liquid phase, and·O induced the production of·OH. The transformed products were subjected to toxicity assessment, which had lost antimicrobial properties toward Escherichia coli. Insights gained from this study can refine the dual mechanisms of multipurpose FMC in solid and liquid phases underlying TTC transformation.