Efficient Photoreduction of Hexavalent Chromium Using the Reduced Graphene Oxide-Sm2MoO6-TiO2 Catalyst under Visible Light Illumination.

Abstract

In past years, the presence of toxic heavy metal ions in water and soil has caused major health problems. The ternary type semiconductor material, reduced graphene oxide (rGO)–Sm2MoO6–TiO2, has been investigated as a photocatalyst for the reduction of soluble chromium(VI) into (III) for the first time. The as-synthesized rGO–Sm2MoO6–TiO2 catalyst was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy, X-ray photoelectron spectroscopy, FT-Raman, Fourier transform infrared, and optical spectroscopy. The maximum Cr(VI) reduction of 96% was achieved within 70 min under visible light illumination. The powder XRD analysis confirmed the formation of anatase TiO2. Field-emission SEM images depicted well-dispersed rGO sheets, and TiO2 and Sm2MoO6 particles are randomly distributed onto rGO. The reduction of Cr(VI) by rGO–Sm2MoO6–TiO2 was considerably greater than the reduction by Sm2MoO6, TiO2, Sm2MoO6–rGO, TiO2–rGO, and Sm2MoO6–TiO2. Sm2MoO6 acts as an effective cocatalyst to TiO2 to enhance the separation of photo-generated electron–holes. Even after six consecutive cycles, the photoreduction of Cr(VI) was more than 85%, which reveals that the excellent reusability performance of the catalyst for practical applications. The photogenerated electron plays an important role in the reduction of Cr(VI) into nontoxic Cr(III), and the synergistic effect of rGO greatly improved the separation of h+ and e– pairs.