Cobalt and titanium co-doped zinc ferrite film photoanode with boosted interfacial photoelectrocatalytic activity for efficient degradation of tetracycline via the covalency competition in the Zn-O-Fe backbone

Abstract

• The co-doping of Co and Ti in the ZFO leads to its lattice expansion. • LB-CoTiZFO film shows higher PEC activities than LB-ZFO film in TC degradation. • Surface rearrangement occurs in the LB-CoTiZFO film under the PEC circumstances. • Fe-O bond breakage caused by the covalency competition leads to boosted PEC activity. For efficient removal of the residual tetracycline (TC) in the aquatic environment, a novel cobalt (Co) and titanium (Ti) co-doped zinc ferrite (CoTiZFO) film was prepared via the Langmuir-Blodgett (LB) method in this study. With the co-doping of Co and Ti, the interfacial photoelectrocatalytic (PEC) activities for degradation of TC by the LB-assembled CoTiZFO (LB-CoTiZFO) films were significantly improved. As the applied voltage was 0.6 V in a two-electrode system, the five-layered LB-CoTiZFO (LB-CoTiZFO-5) films exhibited the optimal TC degradation rate and mineralization rate, which were accordingly 92.85% ± 1.45% and 81.92% ± 0.26%. In the same case, the kinetic rate constant ( k ) for PEC degradation of TC by the LB-CoTiZFO-5 films is equivalent to 3.3-fold of that by the films without the co-doping of Co and Ti. Under the PEC circumstances, the Co 3+ and Ti 4+ in the LB-CoTiZFO-5 film would be reduced to Co 2+ and Ti 3+ , while the Fe 2+ was oxidized to Fe 3+ , which results in the surface rearrangement of the LB-CoTiZFO-5 film. In addition, the Density Functional Theory (DFT) calculation results manifest the covalency competition in the Zn-O-Fe backbone can lead to the Fe-O bond breakage, the bare Fe metals with unpaired valence electrons will diffuse to the Helmholtz layer and serve as active sites, which endows the LB-CoTiZFO-5 films with boosted interfacial PEC activities. Therefore, the LB-CoTiZFO-5 film photoanode shows great prospective in efficient PEC degradation of TC.