This paper deals with a systematic study on the co-doping N,S on TiO2 photocatalyst to improve its activity under visible light on the removal of Pb(II) from the aqueous media. The co-doping TiO2 by N,S atoms was conducted in an autoclave by one-step hydrothermal of TiO2 mixed with nitric and sulfuric acids as the sources of N and S, respectively. The mole ratio of TiO2:nitric acid:sulfuric acid was varied as 1:1:0.5, 1:1:1, and 1:1:1.5 to find the best ratio toward the activity. The co-doped photocatalysts obtained were characterized by specular reflectance UV/Vis (SRUV), X-ray diffraction (XRD), and fourier transform infrared (FTIR) instruments. A batch experiment was carried out for oxidation of Pb(II), driven by a combination of visible light and TiO2-N,S photocatalyst. The research results attribute that co-doping N,S into TiO2 has remarkably narrowed the gap in the TiO2 structure, emerging in the visible region. It was also proven that the co-doped in TiO2 can considerably enhance its activity in the removal of Pb(II) under visible light, and the highest activity was owned by TiO2-N,S (1:1:1). Furthermore, the most effective removal of Pb(II) 10 mg/L (98%) could be reached by employing 500 mg L-1 of the TiO2-N,S (1:1:1) dose, 45 min of the time, and the solution pH at 7. The Pb(II) removed is due to the photo-oxidation induced by OH radicals to form the handleable PbO2.
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.
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