Photochemical reduction of Cr(vi) compounds by amino acid Schiff base copper complexes with a hydroxyl group and titanium oxide composites in aqueous solutions

Abstract

Synthesis of Cu(II) complexes with condensation products of 2,4-dihydroxybenzaldehyde and four amino acids (L-alanine, L-valine, L-phenylalanine, and glycine) is reported. Their physicochemical properties are compared to each other and a previously studied Schiff base Cu(II) complex, the product of condensation of salicylaldehyde and L-aspartic acid. The complexes were characterized by means of electrochemical, spectroscopic, and X-ray diffraction techniques. (TD-) DFT calculations were used for the assignment of transitions in UV-Vis spectra. Photocatalytic activity for reduction from Cr(VI) to Cr(III) was studied under UV to visible light irradiation in methanol or water as sole complexes or hybrid systems with TiO₂. For the first time among the analogous systems, in aqueous solutions, the complexes with TiO₂ reduced Cr(VI) to Cr(III) efficiently. The Cr(VI) reduction ratio with the CuVDB–TiO₂ system reached 91%.