A comparative study for removal of different dyes over M/TiO2 (M = Cu, Ni, Co, Fe, Mn and Cr) photocatalysts under visible light irradiation

• Addition of dopants to TiO2 led to an increase in surface area except for Mn/ TiO2.
• Optical reflection edge shifted to visible light range with additives.
• Cu/TiO2 exhibited the highest activity under visible light for both of the dyes.

The purpose of this work is to design and develop a series of stable and effective TiO2 photocatalysts prepared by a modified precipitation method. In order to improve the photo response of the TiO2 to the visible region, the effect of addition of six successive transition metal elements of fourth period, namely chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu) was studied. Two different types of dyes, methyl orange (MO, azo dye) and methylene blue (MB, thiazine dye group), were used to investigate the influence of structure of dyes on the photocatalytic degradation rates. The results showed that loading titania with 0.3 wt.% of different transition metal elements was found to have significant influences on the crystallographic structure, physical properties and optical absorption properties of titania based catalysts, as well as catalytic activity during dye degradation reactions. The optical reflection edge was obviously shifted to the visible light range with the transition metal additives. The band gap energies of the doped TiO2 samples were considerably narrower than that of plain TiO2. The different activity levels of the catalysts for both dyes clearly show that the photocatalytic activity of samples strongly depended on the metal dopant used. Among all the catalysts, Cu/TiO2 sample exhibited the highest photocatalytic activity under visible light for both of the dyes owing to the low band gap energy and delayed electron-hole recombination.

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