Alternative synthesis of nitrogen and carbon co-doped TiO2 for removing fluoroquinolone antibiotics in water under visible light

Abstract

Nitrogen and carbon co-doped TiO2 nano-catalysts (NCD-TiO2) with visible light activity were prepared using a sol-gel approach involving less chemicals and were evaluated for photocatalytic destruction of two fluoroquinolone antibiotics (ciprofloxacin (CIP) and levofloxacin (LEV)). Nitric acid was used as the reagent of esterification for water formation and the nitrogen precursor, while surfactant Tween 80 was applied as the structure directing agent and the carbon precursor. The synthesis parameters of NCD-TiO2 nanoparticles, including the calcination temperature and nitric acid content, were optimized and the obtained catalysts were characterized by X-ray diffraction (XRD), Raman, porosimetry analysis, high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse-reflectance spectrum (UV–vis DRS), photoluminescence (PL), and electron spin resonance (ESR) analysis. NCD-TiO2 prepared with the highest amount of HNO3 and calcined at 430 °C (NCD200-430) showed the highest photocatalytic activity under visible light, which was essentially attributed to the larger surface area and the higher content of dopants. The photogenerated holes, instead of hydroxyl radical, and partially superoxide radical were confirmed as the effective oxidation species for CIP and LEV destruction in this work. The high efficiency of NCD-TiO2 under visible light demonstrates the great application potential of such photocatalysts in water treatment for the removal of antibiotics contaminants.