Fabrication of Ru-CoFe2O4/RGO hierarchical nanostructures for high-performance photoelectrodes to reduce hazards Cr(VI) into Cr(III) coupled with anodic oxidation of phenols.

Dual-functional photo (electro)catalysis (PEC) is a key strategy for removing coexisting heavy metals and phenolic compounds from wastewater treatment systems. To design a PEC cell, it is crucial to use chemically stable and cost-effective bifunctional photocatalysts. The present study shows that ruthenium metallic nanoparticles decorated with CoFe2O4/RGO (Ru-CoFe2O4/RGO) are effective bifunctional photoelectrodes for the reduction of Cr(VI) ions. Ru-CoFe2O4/RGO achieves a maximum Cr(VI) reduction rate of 99% at 30 min under visible light irradiation, which is much higher than previously reported catalysts. Moreover, PEC Cr(VI) reduction rate is also tuned by adding varying concentration of phenol. A mechanism for the concurrent removal of Cr(VI) and phenol has been revealed over a bifunctional Ru-CoFe2O4/RGO catalyst. A number of key conclusions emerged from this study, demonstrating the dual role of phenol during Cr(VI) reduction by PEC. Anodic oxidation of phenol produces the enormous H+ ion, which appears to be a key component of Cr(VI) reduction. Additionally, phenolic molecules serve as hole (h+) scavengers that reduce e-/h+ recombination, thus enhancing the reduction rate of Cr(VI). Therefore, the Ru-CoFe2O4/RGO photoelectrode exhibits a promising capability of reducing both heavy metals and phenolic compounds simultaneously in wastewater.