Optimized photocatalytic degradation of caffeic acid by sol–gel TiO₂

TiO₂ anatase powder was prepared by means of the sol–gel method with titanium(IV) butoxide as precursor. The formation of a tetragonal crystal structure of TiO₂ anatase at 500 °C was confirmed by X-ray powder diffraction. The characterization of the samples synthesized was complemented by scanning electron microscopy, diffuse reflectance infrared Fourier transform spectroscopy, nitrogen adsorption–desorption isotherms (Brunauer–Emmett–Teller) and diffuse reflectance spectroscopy. The photocatalytic activity of the TiO₂ anatase powder was evaluated in the degradation of caffeic acid in aqueous solution under ultraviolet radiation. A central composite circumscribed design was used to assess the weight of the experimental variables, pH and amount of catalyst in the percentage of caffeic acid degraded and the optimal conditions. The optimized conditions were found to be pH = 5.2 and a load of TiO₂ of 1.1 g L⁻¹. Under these conditions more than 90% of caffeic acid degradation was achieved after 30 min of lamp irradiation. At this time the mineralization reached was almost 60%.