Synthesis of TiO2/copper-based oxide photocatalytic composites from copper smelting flotation slag for photocatalytic H2 evolution

Pure TiO 2 and its composites can be used for hydrogen production by a two-step photocatalytic reduction: photocatalytic reduction of Pt (IV) and subsequent H 2 evolution. Here, photocatalysts were synthesized from copper smelting flotation slags from Uzbekistan for hydrogen production. The crystallinity of the two main phases of the slag, CuFe 2 O 4 and Fe 3 O 4 , was increased by calcinating the slag (Cal900Air5h). Subsequently, the Cal900Air5h was composited with TiO 2 by in-situ hydrothermal reaction (TiO 2 -5 %Cal900Air5h_HT). The TiO 2 -5 %Cal900Air5h_HT catalyzed the production of a significant amount of H 2 , 2.6 times more than pure TiO 2 . Moreover, the most interesting result is that the TiO 2 -5 %Cal900Air5h_HT showed H 2 -generating activity not only higher than pure TiO 2 and physically mixed composite (TiO 2 -5 %Cal900Air5h_PM), but also higher than the reagent-based hydrothermally fabricated TiO 2 composite (TiO 2 -5 %CuFe 2 O 4 , Fe 3 O 4 , CuO_HT). This suggested other amorphous phases including Si, Ca, and Al in Cal900Air5h, which are insulators by themselves, might contribute in an indirect way to the photocatalytic reactions. A possible mechanism of the photocatalytic H 2 evolution is as follows: The band structure determined using various techniques indicated that a Type II heterojunction formed mainly between TiO 2 and CuFe 2 O 4 and less between TiO 2 and CuO in the calcined material. Therefore, when the composite was exposed to light, electrons were excited in both phases of TiO 2 and CuFe 2 O 4 (slightly CuO) in the calcined slag, and then the excited electrons were transferred from CuFe 2 O 4 and CuO to TiO 2 through the heterojunction. The electrons were accumulated on the TiO 2 side, and the photocatalytic reduction of H 2 O molecules into H 2 on the surfaces of Pt (0) nanoparticles serving as a cocatalyst. This study uniquely explored the recycling of copper slag as an econtomical and sustainable photocatalyst for hydrogen evolution to achieve carbon neutrality. • Cu smelting slag was pretreated by calcination to enhance its crystallinity. • Calcined product included CuFe 2 O 4 and Fe 3 O 4 as well as CuO as crystal phases. • TiO 2 was crystalized in the presence of the calcined product of Cu smelting slag. • Photocatalytic H 2 yield rate on the composite was 1.5 times greater than TiO 2 . • Heterojunction was evidenced by XPS, RDB-PAS, and KPFM study for the composite.