| Summary: | In order to improve TiO2 activity under visible light while exploiting the highly concentrated Cu in electroplating wastewater, doping of Cu from the wastewater into TiO2 has been addressed. Bare TiO2 and Cu-doped TiO2 were synthesized using the sol–gel method with different initial doping amounts of Cu. The prepared photocatalysts were characterized through X-ray diffractometer, Fourier-transform infrared spectrometer, scanning electron microscope, transmission electron microscope, and UV–Vis specular reflectance spectrometer. Photocatalytic activity of the samples under visible light was evaluated through methylene blue degradation. The results show that Cu from wastewater has been successfully doped into TiO2, introducing a narrower band gap energy and higher photocatalytic activity under visible light than bare TiO2. This study shows that the initial doping amount of Cu influenced the properties and photocatalytic activity of doped TiO2. The 6 mg/g Cu-doped TiO2 sample exhibits the most significant narrowing of band gap energy (2.878 eV) and the highest photocatalytic activity (93.30% of dye degradation). Moreover, the Cu-doped photocatalyst could be reused up to five photodegradation cycles with no significant activity decrease. Graphical abstract: [Figure not available: see fulltext.].
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