Fe3O4/Co3O4–TiO2 S-scheme photocatalyst for degradation of organic pollutants and H2 production under natural sunlight

Sunlight responsible mono- and co-doped TiO2 nanoparticles (Con+ and Fen+) were prepared via sol–gel technique. The X-ray diffraction (XRD) results showed no phase change of TiO2 was observed after the addition of Con+ and Fen+ ions. Diffuse reflectance spectra (DRS) results showed a significant red-shift of the absorption edge after doping TiO2 by Con and Fen+ and the band gap energy reduced sharply from 3.10 to 1.72 eV. X-ray photoelectron spectroscopy (XPS) results emphasized the existence of multivalent states of Co2+, Co3+, Fe2+ and Fe3+. The results of ultraviolet photoelectron spectroscopy (UPS), work function, electron spin resonance (ESR) illustrated the Fe3O4/Co3O4–TiO2 formed of ternary heterojunctions. The photocatalytic performance of the prepared photocatalysts was determined for photodegradation of tetracycline (TC) and phenol (Pl) and production of hydrogen. The results illustrated the existence of multivalent states of Fe and Co ions (Co2+, Co3+, Fe2+ and Fe3+) together improved the solar light absorption, inhibited the recombination of photogenerated charges and consequently enhanced the photocatalytic efficiency of TiO2 compared with mono-doped TiO2 (Co3O4/TiO2 and Fe3O4/TiO2). The sample with 5%Fe3O4/Co3O4–TiO2 showed the highest photoactivity. The mineralization (TOC), photodegradation mechanism and reusability of prepared photocatalysts were also studied. The Fe3O4/Co3O4–TiO2 nanoparticles showed high photoactivity and stability and can be adopted as a promising materials for different environmental and H2 production applications.