Ultrasound-assisted synthesis of rGO supported NiO-TiO₂nanocomposite: An efficient superior sonophotocatalyst under diffused sunlight

Photocatalytic water treatment is the key to resolve alarming ill effects of water pollution. However, inefficient charge carrier separation, inappropriate position of the top valence band and/or the bottom conduction band, and effective finite light absorption are three paramount issues related to the high-efficiency photocatalytic water treatment. To surpass these limitations, the addition of reduced graphene oxide (rGO) has been proposed as one of the key strategies. Here, we present an easy, low cost and ascendable preparation of rGO supported NiO-TiO2 nanocomposite as a photocatalyst using wet impregnation method with ultrasound-assistance. The structure, morphology and optical properties of the prepared catalysts are studied through PL (Photoluminescence), UV-DRS (Ultraviolet-visible diffuse reflectance spectroscopy), XPS (X-ray photoelectron spectroscopy), XRD (X-ray diffraction), SEM (Scanning electron microscopy), TEM (Transmission electron microscopy), TRPL (Time resolved photoluminescence) and BET (Brunauer-Emmett-Teller). Methyl orange pollutant is degraded sonophotocatalytically to evaluate the activity of rGO supported NiO-TiO2 under the diffused sunlight irradiation. A promisingly high photocatalytic dye degradation percentage of 99% in 100 min is achieved. This achievement was possible under diffused sunlight irradiation on NiO-TiO2 impregnated with 4 wt% of rGO. Addition of NiO helped to enhance the catalytic activity from UV-region to visible region. In addition, the incorporation of rGO helped to inhibit the electron-hole pair recombination thereby increasing the catalytic activity. Furthermore, the catalyst showed an effective sonophotocatalytic activity with high stability even after being used repeatedly for five times under similar degradation processes.