Enhanced photoelectrocatalytic degradation of tetracycline using a bifacial electrode of nickel-polyethylene glycol-PbO2//Ti//TiO2-Ag2O

A bifacial electrode of nickel-polyethylene glycol-PbO2//Ti//TiO2-Ag2O was prepared for the photoelectrocatalytic degradation of tetracycline. The side of nickel-polyethylene glycol-PbO2 was fabricated by electrodepositing PbO2 in an acid solution containing both nickel ions (Ni) and polyethylene glycol (PEG). The Ag2O modification on TiO2 nanotube arrays (TiO2-Ag2O) was completed by the method of successive ionic layer adsorption and reaction. The physicochemical properties of the bifacial electrode were characterized in terms of morphology, crystal structure, elemental composition, optical absorption, and electrochemical behavior. With tetracycline as the model pollutant, the degradation performance of different approaches, i.e. photocatalysis (PC), electrically assisted photocatalysis (EPC), electrocatalysis (EC) and photoelectrocatalysis (PEC), were investigated. Additionally, the operating conditions including pH, electrolyte concentration, initial tetracycline concentration, and current intensity were optimized. The characterization results showed that, by co-modification with Ni and PEG, PbO2 grains became fine, and the grain size was reduced from approximately 5 μm to less than 1 μm. Moreover, the surface of Ni-PEG-PbO2 was more compact. The deposition of Ag2O enhanced the light absorption of the composite TiO2-Ag2O in the visible light region. The degrading experiments revealed that the tetracycline removal rate by PEC was the best, and 1.3, 4.4, and 13.1 times as high as those by EC, EPC, and PC, respectively. The enhanced photoelectrocatalytic degradation of tetracycline by PEC should mainly benefit from the design of the bifacial electrode. This was because both the light-facing side and the back side of the electrode could simultaneously perform their own functions effectively.