Visible-Light-Driven Photocatalytic Degradation of Tetracycline Using Heterostructure Cu2O−TiO2 Nanotubes, Kinetics, and Toxicity Evaluation of Degraded Products on Cell Lines

Abstract

This study first reports on the tetracycline photodegradation with thesynthesizedheterostructuredtitaniumoxidenanotubescoupledwithcuprous oxide photocatalyst. The large surface area andmore active sites onTiO2 nanotubes with a reduced band gap (coupling of Cu2O) provide faster photodegradation of tetracycline under visible light conditions. Cytotoxicity experiments performed on theRAW264.7 (mousemacro phage) andTHP-1 (humanmono cytes)cell lines of tetracycline and the photodegradedproductsof tetracyclineaswellasquenchingexperiments werealsoperformed.Theeffectsof different parameters likepH, photocatalyst loadingconcentration, cuprousoxide concentration, and tetracycline load on the photodegradation rate were investigated.Withanenhancedsurfaceareaof nanotubes anda reducedband gap of 2.58 eV, 1.5 g/L concentration of 10%C-TAC showed the highest efficiencyofvisible-light-drivenphotodegradation(∼100%photodegradationrate in60min)of tetracyclineatpH5,7, and9.Thephotodegradationefficiencyisnotdepleteduptofiveconsecutivebatchcycles. Quenchingexperiments confirmed that superoxide radicals andhydroxyl radicals are themost involved reactive species in the photodegradationoftetracycline,whilevalancebandelectronsaretheleastinvolvedreactivespecies.Thecytotoxicitypercentageof tetracyclineanditsdegradedproductsonRAW264.7(−0.932)aswellasTHP-1(-0.931)showedanegativecorrelationwiththe degradationpercentagewith a p-value of 0.01. The toxicity-free effluent of photodegradation suggests the applicationof the synthesizedphotocatalyst inwastewater treatment.