Reduced graphene oxide-MoO3 composites via microwave-assisted synthesis for dual-functional photocatalysis of organic dyes and heavy metal cation under simulated sunlight irradiation

Background: When organic dyes or heavy metal cations are present in wastewaters, it is often necessary to add sacrificial molecules so that catalysts can effectively remove these pollutants. However, when organic dyes and heavy metal cations coexist, the composite removal rate of both contaminants by a few specific catalysts is higher, and no sacrificial molecules are needed. Methods: Herein, molybdenum trioxide (MoO3)-reduced graphene oxide (rGO) composites were synthesized using a two-step microwave hydrothermal method. The samples were characterized with X-ray diffraction, scanning electron microscopy (SEM), Raman spectroscopy, ultraviolet -visible spectroscopy, X-ray photoelectron spectroscopy, and energy -dispersive X-ray microanalysis. The photocatalytic degradation/reduction ability of the catalysts was evaluated under irradiation from a 300-W Xe lamp. Significant findings: In the presence of H2O2, MoO3-rGO exhibited good degradation efficiency for rhodamine B (RhB) dye. Cr(VI) reduction over MoO3-rGO occurred more favorably in an acidic environment (pH = 2). Moreover, when RhB and Cr(VI) coexisted, the composite removal rate of both contaminants was higher, and no sacrificial molecules were needed. The dual synergistic removal of RhB and Cr(VI) occurred through the combination of the photosensitized and photocatalysis mechanisms accompanied by rGO-mediated charge transfer.