Synthesis of visible light responsive iodine-doped mesoporous TiO2 by using biological renewable lignin as template for degradation of toxic organic pollutants

The visible light responsive I-doped mesoporous TiO2 (I/TiO2-T) catalysts were synthesized by facile hydrolysis method with lignin as a template. The resulting I/TiO2-T catalysts synthesized from different amounts of I as a dopant and lignin as a template were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis diffuse spectroscopy (DRS), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL), and electrochemical impedance spectroscopy (EIS). The photocatalytic activities of the resulting catalysts were investigated by the degradation of p-chlorophenol under artificial visible light irradiation. The results showed that the lignin-templated TiO2 with a suitable amount of I-doping (I/TiO2-T) had higher catalytic activity than the catalyst prepared form I-doped TiO2 without lignin template (I/TiO2). Complete degradation of p-chlorophenol was achieved by I/TiO2-T with suitable amount of I-doping at 60 min. However, 95.7, 10.7, and 5.5% of the p-chlorophenol was degraded with I/TiO2, TiO2-T, and P25 catalysts, respectively, under 140 min visible light irradiation. The enhanced catalytic activities of the samples with template and I-doping may be due to the small grain size and high specific surface area of the catalysts. The band gap and the electrical properties of TiO2 also could be adjusted with I-doping. The I-doped TiO2 with the extrinsic I5+-to-Ti4+ and the iodine-to-oxygen donor defects could be excited by visible irradiation for efficient pollutants degradation. A possible photocatalytic mechanism for the degradation of the pollutants with I/TiO2-T under visible light irradiation was also proposed.