Ultrasonication-assisted synthesis of CN-TiO2 and its photocatalytic degradation of diclofenac under visible light irradiation

In this study, CN codoped TiO2 nanoparticles (CN-TiO2) were fabricated by solvothermal and low temperature calcination methods with the aid of ultrasonication. According to the number of ultrasonic treatments used in the preparation process, the samples were named NN, YN, NY and YY. The characteristics of transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible spectroscopy (UV-vis) were employed to analyse the effect of the ultrasonic treatment step in the synthetic process. The results showed that ultrasonication can increase the CN content in TiO2, reduce the band gap energy, and improve the catalytic performance of the CN-TiO2, and the effect of secondary ultrasound is particularly obvious. The YY obtained by two-step ultrasonication with the lowest band gap energy of 3.07 eV. The photocatalytic activity of the CN-TiO2 was evaluated using the degradation of diclofenac (DCF) under visible light irradiation (white LED strips with an emission wavelength of 450 nm). It was observed that the YY exhibited significantly superior DCF degradation activity. When using 0.4 g L-1 of YY, an excellent DCF degradation of 97% could be reached, which is 1.4 times that of NN (without ultrasonication). Moreover, YY had good visible light photocatalytic activity, and the degradation efficiency of YY for DCF under visible light was comparable to that of a xenon lamp. Therefore, ultrasonication played a critical role in the enhancement of photocatalytic activity during the synthesis of CN-TiO2.