Photoelectrochemical Study of Novel Solar Light N-P Heterojunction Photocatalyst Including Molybdates Decorated on RGO Nanosheets for Dye Degradation of Wastewater

Different types of metal molybdates were decorated into the reduced graphene oxide (RGO) nanosheets via a straightforward approach. RGO/NiMoO4 nanocomposite showed the best activity for the photodegradation of dye under visible light irradiation. To evaluate the photocatalytic performance of RGO/NiMoO4, the effect of various parameters was evaluated and the role of every involved species was explained in detail. Results showed that more than 95% dye photodegradation was obtained at dye concentration 5 ppm, pH 3 and catalyst loading of 1 g/L as optimum conditions. The superior photocatalytic activity of RGO/NiMoO4 can be ascribed to the efficient light harvesting, lowest electron–hole recombination, easy and remarkable electron-transferring properties, and suitable electronic properties of RGO sheets. Mott–Schottky plots showed different flat band potential and donor density for different kinds of photocatalysts and effect of pH on n- or p-type behavior of heterojunction. RGO/NiMoO4 was selected because of more negative Efb, and also there are no significant differences in Efb at pH 3 and 7. The Nyquist and Bode plots of the samples showed an efficient separation of the photo-generated electrons and holes, lifetime and confirmed the existence of small surface resistance for prepared photocatalysts. Lifetime for RGO/NiMoO4 was 125.89 ms at pH 3 compared with 13.2, 19.22, 6.22 19.22 and 5.94 ms for RGO/CoMoO4, RGO/CuMoO4, RGO/FeMoO4, NiMoO4 and RGO, respectively. Utilization of different scavengers in the trapping experiment showed that the (1O2) and h+ are the major involved species in the photocatalytic system. Reusability and stability tests showed that the catalyst could be reused four times. To figure out the successful synthesis of RGO/NiMoO4 nanocomposite, XRD, FT-IR, DRS, XPS, ICP-OES, FESEM, and EDS mapping characterization techniques were employed.