Tio2@lipophilic porphyrin composites: New insights into tuning the photoreduction of cr(vi) to cr(iii) in aqueous phase

Metal-free and Cu(II)-lipophilic porphyrins [H2Pp and Cu(II)Pp] loaded on titanium dioxide in the anatase phase (TiO2) were prepared and used as a heterogeneous catalyst for the photoreduction of Cr(VI) to Cr(III) in aqueous suspensions under UV–Vis light irradiation. TiO2 impregnated with copper(II) porphyrin [TiO2@Cu(II)Pp] was the most effective in photocatalyst reduction of toxic chromate Cr(VI) to non-toxic chromium Cr(III). We further evaluated an experimental design with the scope of fast optimization of the process conditions related to the use of TiO2 or TiO2-porphyrin based photocatalysts. A full factorial design as a chemometric tool was successfully employed for screening the affecting factors involved in photoconversion catalysis, with the modification of TiO2 both with porphyrin H2Pp and Cu(II)Pp. The studied experimental factors were the catalyst amount, the concentration of Cr(VI) ions, and the pH of the medium. The performed multivariate approach was successfully used for fast fitting and better evaluation of significant factors affecting the experimental responses, with the advantage of reducing the number of available experiments. Thus, the stability of the optimized TiO2 embedded Cu(II)Pp was investigated, confirming the high reproducibility and suitability for environmental purposes.