Synthesis and characterization of double heterojunction-graphene nano-hybrids for photocatalytic applications

Nanoparticles of double heterojunction n-CuO-p-NiO-n-ZnO system and its nano-hybrids with reduced graphene oxide (rGO) were synthesized by simple and easily adoptable co-precipitation method. The prepared n-CuO-p-NiO-n-ZnO nanoparticles and their hybrids with rGO were characterized by various characterization techniques. Structural, optical and morphological characterization was done by X-rays diffraction (XRD), Fourier Transform Infrared (FTIR), UV–Visible spectroscopy etc. It was found that the developed hetero-structure is composed by p-NiO as cubic, n-CuO as monoclinic and n-ZnO as hexagonal crystal structure. Formation of heterojunction is confirmed by current-voltage (I-V) measurement. The optical bandgap energy of heterojunction was around 1.6 eV which made this system active in both UV and Visible light region. Photocatalytic degradation efficiency was examined using methylene blue and it showed prominent enhancement as compared to pure metal oxides. This excellent efficiency was attributed due to efficient charge carrier separation which leads to inhibit recombination rate at photocatalyst interface. Moreover, photocatalytic activity was increased meaningfully up to 70% by graphene based n-CuO-p-NiO-n-ZnO. This excellent increment in activity was due to large surface area offered by graphene which caused adsorption of dye molecules and helped in transfer of electrons to metal conduction band.