Activation of persulfate ions by QDs-sized Z-scheme TiO_2−x/Cu₃Mo₂O₉ photocatalysts in visible-light detoxification of organic contaminants

As known, colored TiO_2−x is a promising material in the photocatalytic detoxification of water pollutants. Herein, brown TiO_2−x was combined with Cu₃Mo₂O₉ nanoparticles to fabricate quantum dot-sized photocatalysts through hydrothermal method preceded calcination at 350 °C. The optical, electrochemical, textural, structural, and morphological features of the prepared photocatalysts were explored via various techniques. The photocatalytic ability of the materials was studied in the presence of persulfate ions (PS) upon visible light to remove different pollutants. After adding PS, the TiO_2−x/Cu₃Mo₂O₉ (1%)/PS system represented an efficient performance for the degradation of tetracycline (TC), cephalexin (CFX), fuchsine (FS), and methyl orange (MO). The rate constants of TC oxidation in the TiO_2−x/Cu₃Mo₂O₉ (1%)/PS system were respectively 333, 245, 198, 190, 95.2, 92.9, 77.9, and 2.03 times higher than the TiO₂, PS, TiO₂/PS, Cu₃Mo₂O₉, Cu₃Mo₂O₉/PS, TiO_2−x, TiO_2−x/PS, and TiO_2−x/Cu₃Mo₂O₉ (1%) systems. So, the synergistic effect of PS and heterogeneous photocatalysis was confirmed by the TiO_2−x/Cu₃Mo₂O₉ (1%) material in the removal reactions. The quenching tests demonstrated that the ^•O₂ ⁻, h⁺, ^•OH, and ^•SO₄ ⁻ are key reactive species. Finally, a Z-scheme mechanism was suggested for the degradation reactions by TiO_2−x/Cu₃Mo₂O₉ /PS system.