Sol gel synthesis of cobalt doped TiO2 and its dye sensitization for efficient pollutant removal

• Co-TiO2 nanoparticles were synthesized via sol-gel method in the presence of surfactant.
• Sensitization of Co-TiO2 were carried out using metal free phthalocyanine.
• Determination of the photocatalytic action of produced catalyst.
• Photocatalytic reduction of Cr(VI) ions.
• Photocatalytic degradation of methyl orange.

This study was concentrated on the synthesis of new cobalt doped (Co-TiO2) photocatalyst via sol-gel method in the presence of surfactant Triton X100 or Tween 20. Surfactant was used to obtain smaller particles and enhance the photocatalytic action of the catalyst. Co-TiO2 catalyst was further modified with a phthalocyanine for dye sensitization that facilitates electron transfer. A peripherally tetra 12-crown-4 substituted metal free phtalocyanine (Pc) derivative was first time synthesized and used as dye sensitizer employing same sol-gel method in the presence and absence of above surfactants (Pc/Co-TiO2). The as-synthesized photocatalysts were characterized by XRD, TGA, SEM, EDX, TEM, BET and UV–vis diffuse reflectance spectroscopy (DRS). The results revealed that the both cobalt and Pc had been successfully immobilized on the TiO2 nanoparticles and the nanocomposite had the anatase structure. Incorporation of Pc into TiO2 structure caused significant shift of absorption edge into visible range due to strong absorbance of Pc. Apart from this particle size of Pc immobilized TiO2 was dramatically decreased particularly in the presence of surfactant. The photocatalytic degradation of methyl orange (MO) dye solution (10 mg/L) and the photocatalytic reduction of Cr(VI) ions (10 mg/L) using Pc/Co-TiO2 (2 g/L) was investigated under UV light irradiation (λ=365 nm). Photocatalytic studies revealed that the Pc/Co-TiO2 prepared in the presence of Tween 20 has shown much higher photocatalytic activity than the other catalysts. After 150 min of irradiation, the photocatalytic activity of the catalysts follows the order: Pc/Co-TiO2-T20>Pc/Co-TiO2-TX100>Pc/Co-TiO2>Co-TiO2-T20>Co-TiO2-TX100>Co-TiO2. It was found that about 60.3% of the MO was removed and 71.3% of the Cr(VI) ions were reduced by Pc/Co-TiO2 after 150 min under 365 nm light irradiation.