Kinetic evaluation of photocatalytic degradation of food colorant E 131 VF by copper doped TiO2 nanophotocatalysts prepared at different calcination temperatures

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Abstract Pure TiO2 and copper doped TiO2 nanoparticles (Cu-TiO2, Cu/TiO2 molar ratio:​ 0.2-1.2%) were synthesized by a sol–gel method in the presence of various volumes of acetic acid (10–50 mL) in order to optimize the preparation conditions. The prepared samples were calcined at different temperatures (120–750 °C) to investigate the structural properties of TiO2 nanoparticles after calcination. Different techniques such as XRD, FTIR, Raman, UV–Vis DRS, nitrogen physisorption and SEM/EDX were used to characterize the structural and morphological properties of the prepared samples. XR diffraction results showed that TiO2 samples were synthesized in the presence of 40 mL and 50 mL acetic acid including pure anatase phase at calcination temperatures up to 600 °C; however, rutile phase was observed when they were annealed at 750 °C. In the XR diffraction patterns of Cu-TiO2 samples, no copper diffraction was found, while the EDX and DRS analyses proved the presence of copper in Cu-TiO2 samples. The average crystal size of TiO2 increased as the calcination temperature increased, but it was independent of the used acetic acid volume in the preparation process. The Raman spectra confirmed XR diffraction analysis results concerning the formation of pure anatase phase at calcination temperatures up to the 600 °C. The results of nitrogen physisorption, according to the BET model, confirmed that the higher calcination temperature was obviously favored for growth of particles and the agglomerate is related to the decline of specific surface area. The photocatalytic activity of the prepared samples was examined by photocatalytic removal of E 131 VF dye. The kinetics of dye removal fitted zero order and pseudo first order well in the presence of Cu-TiO2 and pure TiO2 respectively. TiO2 nanoparticles prepared in the presence of 10 ml and 50 mL acetic acid and calcined at 500 °C revealed the best catalytic activity. The rate constant of Cu-TiO2 samples decreased from 0.083 (a.u.) for 0 % Cu to 0.0044 (a.u.) for 1.2 % Cu due to the thickness of space charger layer. The obtained results confirmed the synthesis of high temperature stable anatase TiO2 photocatalysts that are promising candida for use in industrial wastewater treatment.