Synthesis of Er3+:Al2O3-doped and rutile-dominant TiO2 composite with increased responsive wavelength range and enhanced photocatalytic performance under visible light irradiation

• Long wavelength visible light to UV and short wavelength upconversion by Er3+:Al2O3.
• Higher photoactivity of rutile due to extra short-wavelength visible light adsorption.
• Er3+:Al2O3/TiO2-SAC possessed high photocatalytic capability under visible light.
• RSM model is significant and predicts well for the actual experimental values.
• Photocatalytic degradation followed the Langmiur–Hinshelwood kinetics.

Much more attentions were paid to the anatase TiO2 than rutile due to its higher photoactivety with a larger band gap. However, it is usually ignored that the relative narrow band gap of rutile TiO2 benefits to the increasing in the responsive wavelength range. In this work, spherical activated carbon-supported Er3+:Al2O3-doped rutile TiO2 (Er3+:Al2O3/TiO2-SAC) was synthesized by a sol–gel method using tetrabutyl titanate as titanium precursor, and erbium nitrate and aluminum nitrate as dopant sources. Long-wavelength visible light from a light-emitting diode source was upconverted to ultraviolet light and short-wavelength visible light by Er3+ dopant, which could then be absorbed by the synthesized photocatalyst that contained rutile TiO2. This resulted in higher photocatalytic activity of samples with rutile than those with anatase. A response surface methodology based on the central composite design model was used to determine the optimum synthesis conditions: Er concentration, 0.07 mol‱; Al concentration, 0.08 mol%; and calcination temperature, 700 °C. The catalyst achieved a 90.0% removal efficiency for methyl orange (MO) with a reaction rate of 18.98 × 10−3 min−1 at an initial MO concentration of 500 mg L−1 in 2 h under visible-light irradiation.

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