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