One-pot synthesis of ZnO–Ag and ZnO–Co nanohybrid materials for photocatalytic applications

ZnO–Ag and ZnO–Co nanohybrid materials with different Ag and Co contents were successfully prepared through a simple one-pot method at room temperature in the absence of surfactants. This synthesis route is effective and environmentally friendly and can produce spherical nanoparticles with sizes between 7 and 20 nm. The nanohybrid materials were characterized by UV–vis spectroscopy, fluorescence spectroscopy, scanning electron microscopy–energy-dispersive X-ray analysis, X-ray diffraction, Fourier transform IR spectroscopy, and high-resolution transmission electron microscopy. Their photocatalytic activity was evidenced by discoloration of the synthetic diazo dye Bismarck brown Y; ZnO–Ag nanohybrid materials had greater efficiency for decolorization of the dye compared with ZnO–Co, ZnO, and TiO₂. The enhanced photocatalytic activity of the ZnO–Ag nanohybrid material is due to three important aspects: (1) the oxygen vacancies present on the ZnO surface, (2) the efficient absorption of visible light due to the interaction of the semiconductor and the surface plasmon resonance of Ag, and (3) the effective separation of charges due to the formation of the Schottky barrier between ZnO and Ag, where Ag acts as an electron trap, and thereby reduces recombination. When the ZnO–Co nanohybrid is used, the addition of Co introduces intermediate energy levels between the valence and conduction bands on the semiconductor surface, which results in a recombination that reduces the photocatalytic activity, making the azo dye decolorization less efficient.