An afford to enhance TiO₂ activity under visible light as well as to utilize the iron rusty waste, has been conducted by doping Fe from the waste into TiO₂. The doping was performed by sol-gel method of titania tetra isopropoxide with Fe³⁺ ions dissolved from the iron rust waste. In the doping, the concentration of Fe³⁺ was varied giving various mole ratios of TiO₂:Fe. The doped TiO₂ photocatalysts were characterized using FTIR, XRD, SRUV, and SEM-EDX instruments. The photocatalytic activity of the doped TiO₂ was evaluated by photodegradation of Congo red under visible light. The effect of some parameters that govern the photodegradation process such as the amount of Fe dopant, reaction time, photocatalyst mass, solution pH, and initial concentration of dye was also studied. The characterization results reveal that Fe³⁺ ions from the rusty waste have been doped into TiO₂ which can remarkably narrow the band gap energy (Eg), shifting into the visible zone. In accordance, the activity of TiO₂ under visible light in the dye photodegradation is considerably enhanced. The Eg decreasing and actively improving the doped TiO₂ are controlled by the amount of Fe dopant, and the most effective Eg decreasing is shown by TiO₂–Fe (1:0.8), but the highest activity is observed for TiO₂–Fe (1:0.4). It is also found that the highest photodegradation of Congo red 5 mg/L in 50 mL of the solution over TiO₂–Fe (1:0.4) under visible light, that is about 99%, can be reached by applying 60 mg of the photocatalyst mass, in 60 min, and solution pH 5. It is implied that the rusty waste can be utilized to prepare the visible responsive photocatalyst that can be used for preventing dye pollution.

The photocatalysis process over N-doped TiO₂ under visible light is examined for Pb(II) removal. The doping TiO₂ with N element was conducted by simple hydrothermal technique and using urea as the N source. The doped photocatalysts were characterized by DRUVS, XRD, FTIR and SEM-EDX instruments. Photocatalysis of Pb(II) through a batch experiment was performed for evaluation of the doped TiO₂ activity under visible light, with applying various fractions of N-doped, photocatalyst mass, irradiation time, and solution pH. The research results attributed that N doping has been successfully performed, which shifted TiO₂ absorption into visible region, allowing it to be active under visible irradiation. The photocatalytic removal of Pb(II) proceeded through photo-oxidation to form PbO₂. Doping N into TiO₂ noticeably enhanced the photo-catalytic oxidation of Pb(II) under visible light irradiation. The highest photocatalytic oxidation of 15 mg/L Pb(II) in 25 mL of the solution could be reached by employing TiO₂ doped with 10%w of N content 15 mg, 30 min of time and at pH 8. The doped-photocatalyst that was three times repeatedly used demonstrated significant activity. The most effective process of Pb(II) photo-oxidation under beneficial condition, producing less toxic and handleable PbO₂ and good repeatable photocatalyst, suggest a feasible method for Pb(II) remediation on an industrial scale.

The C,N co-doped TiO₂ photocatalyst was prepared by interacting the chicken egg white having various weights (1, 2, and 4g) with 1g of TiO₂ in an autoclave through the hydrothermal process at 150°C. The C,N co-doped TiO₂ photocatalysts were characterized using Fourier transform infrared (FTIR), X-ray diffraction (XRD), specular reflectance UV/visible (SRUV/Vis), and transmission electron microscope (TEM) instruments. The photocatalytic activity of the co-doped TiO₂ was evaluated by monitoring the photo-decolorization of Congo red dye under visible light through a batch experiment. The characterization results assigned that the C and N atoms from the chicken egg white have been successfully co-doped into TiO₂ through interstitial and substitutional combination, which could notably narrow their band gap energy entering into the visible region. In line with the gap narrowing, the co-doping C,N into TiO₂ could remarkably improve the photocatalytic activity under visible light in the dye photo-decolorization. The enhancement of the photocatalyst activity of TiO₂-C,N was controlled by the weight of the egg white introduced, and 2g of the egg white resulted in the highest activity. Further, the best dye photo-decolorization, which was about 98, of 10mg/L Congo red dye in 100mL of the solution under visible irradiation could be reached by applying TiO₂-C,N prepared from 2g of the egg white, within 45min, at pH 7, and 50mg of the photocatalyst mass.