Comparative study of degradation mechanism of antibiotics pollutants in seawater via mesoporous TiO2 composite catalyst excited by weak visible light
To explore the mechanism of degradation and performance improvement for pollutants in seawater by multiphase photocatalysis,the degradation of ofloxacin(OFX)and tetracycline(TC)under weak visible light excitation in fresh water,simulated seawater,and real seawater was first carried out.The differences in the photodegradation process of OFX and TC in seawater were comparatively studied.Then,adsorption layer nanoreactor synthesis was used to deposit Ag nanoparticles on the surface of mesoporous TiO2 to enhance the performance of the photocatalyst.Finally,photocatalytic floating spheres were prepared using Ag-deposited mesoporous TiO2 as the active component.The photodegradation experiments in three water systems showed that salt ions in seawater had inhibitory effects on the degradation process of OFX and TC,but the difference in molecular structure between TC and OFX resulted in a more significant inhibitory effect on the photodegradation for OFX.Density functional theory(DFT)calculations and intermediate product analysis had found that the atoms attacked by photo-generated hole h+and free radicals in OFX molecules were different.The edge atom was most susceptible to electrophilic reagent h+attack,and salt ion enrichment seriously hindered the attack of photo-generated hole h+on this atom.The removal rate for OFX by mesoporous TiO2 catalysts in seawater would not exceed 10%However,degraded OFX could be mineralized,and the intermediate products showed lower toxicity in a short time.After the deposition of Ag on the surface of mesoporous TiO2,the photogenerated electron transfer and plasma resonance effects would both enhance the separation rate of photogenerated holes and electrons,thereby enhancing the degradation performance for OFX of the catalysts.The removal rate of the catalyst for low concentration OFX(1 mg∙L-1)in seawater was close to 90%.Using Ag deposited mesoporous TiO2 catalyst as the active component,the removal rate of OFX by the filled floating spheres exceeded 90%(20 h)under weak visible light excitation.
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