Photocatalytic elimination of bisphenol A under visible light using Ni-doped TiO2 synthesized by microwave assisted sol-gel method

In this work, heterogeneous photocatalysis under visible light was applied as treatment to degrade bisphenol A (BPA) using Ni-TiO2 catalysts with different Ni contents (0.5 and 1.0 wt%). The materials were synthesized by rapid microwave assisted sol-gel process (MW). For comparison, 1.0% Ni-TiO2 by conventional sol-gel method (CM) was prepared. Semiconductors were characterized by various analytical techniques. Diffuse reflectance spectroscopy studies indicated a red shift in the band gap absorption to the visible region when nickel was incorporated while results from powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses showed the substitution of sites of Ti4+ ions by Ni2+ ions into the crystal lattice of anatase TiO2. The best results in BPA degradation were obtained at solution pH 9 in the follow order 1.0% Ni-TiO2 MW > 0.5% Ni-TiO2 MW > 1.0% Ni-TiO2 CM > TiO2 MW. This behavior was explained by the lower band gap (Eg) value, smaller crystallite size and the inhibition in recombination of the electron/hole pairs, caused by nickel incorporation. Using 1.0% Ni-TiO2 MW as catalyst, complete BPA degradation, and 77% mineralization were achieved in 210 min. The toxicity of the final solution was also evaluated by means of the marine bacteria Vibrio fischeri.