Photocatalyst Cr-doped titanium oxide nanoparticles: Fabrication, characterization, and investigation of the effect of doping on methyl orange dye degradation

The Cr/TiO2 nanoparticles were synthesized via sol–gel technique by using tetraisopropylorthotitanate (TIPOT) and chromium nitrate (Cr(NO3)3·9H2O) as precursors. The framework substitution of Cr into TiO2 nanoparticles was evaluated by X-ray diffraction (XRD), scanning electron microscopy equipped with energy dispersive X-ray microanalysis (SEM-EDX), transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR) techniques. XRD results showed that pure TiO2 and Cr/TiO2 nanoparticles own anatase phase with some rutile phase. SEM and TEM images confirmed the successful doping of Cr3+ ions into TiO2 structure. The result of photocatalytic degradation of methyl orange (MO) demonstrated that appropriate Cr3+ doping can greatly enhance photocatalytic activity of TiO2, which was attributed to the "red-shift" in ultraviolet–visible light (UV–vis) absorption spectra of TiO2 nanoparticles while doped with Cr3+ ions and also to the improved transfer efficiency of photogenerated electrons and holes caused by incorporation of Cr3+ ions. The optimal Cr3+ concentration to obtain the highest photocatalytic activity was 5% mol. The relatively high photocatalytic activity of Cr/TiO2 nanoparticles, suggests that it may have a promising future for water and wastewater purifications.