Optimization of Solar Photocatalytic Degradation of Chloroxylenol Using TiO 2 , Er 3+ /TiO 2 , and Ni 2+ /TiO 2 via the Taguchi Orthogonal Array Technique

摘要

In this study, the optical properties of a TiO 2 photocatalyst were enhanced with various impregnations of Er 3+ and Ni 2+ separately, using the impregnation method as photocatalysts for the direct solar photolysis degradation of chloroxylenol. The synthesized Er 3+ /TiO 2 and Ni 2+ /TiO 2 catalysts were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), metal mapping, and ultraviolet visible (UV–Vis) spectroscopy. The results showed that the Er 3+ /TiO 2 and Ni 2+ /TiO 2 nano-particles have the same structures of TiO 2 nano-particles with little difference in particle size. The Er 3+ and Ni 2+ ions were well-distributed on the TiO 2 surface, and it was found that the maximum band gap decreased from 3.13 eV for intrinsic TiO 2 to 2.63 eV at 1.8 wt % Er 3+ /TiO 2 and to 2.47 eV at 0.6 wt % for Ni 2+ /TiO 2 . The initial concentration of chloroxylenol, catalyst loading, and pH of the solution are the most important factors affecting the solar photocatalytic degradation efficiency that were optimized using Design Expert software (version 6.0.10, Minneapolis, MN, USA, 2003). The results showed that the optimal conditions for chloroxylenol degradation include a pH of 4, TiO 2 loading at 3 g/L, and a chloroxylenol concentration of 50 mg/L. These conditions resulted in a degradation efficiency of 90.40% after 60 min of direct solar irradiation, wherein the solar energy recorded during a clear sunny day is 1000 W/m 2 . However, some experiments were conducted on a semi-cloudy day to cover all weather stated and to study the degradation kinetics. During semi-cloudy day experiments, using Er 3+ /TiO 2 and Ni 2+ /TiO 2 with a solar irradiation activity of 600 W/m 2 for a 60 min exposure at optimal conditions increased the degradation efficiency from 68.28% for intrinsic TiO 2 to 82.38% for Er 3+ /TiO 2 and 80.70% for Ni 2+ /TiO 2 .