Glucose-assisted transformation of Ni-doped-ZnO@carbon to a Ni-doped-ZnO@void@SiO2 core–shell nanocomposite photocatalyst

Abstract

Carbon-coated nickel-doped-ZnO nanorods (Ni/ZnO@C NRs) are successfully prepared for the purpose of improving the visible-light photocatalytic performance of ZnO by expanding the absorption in the visible-light region and increasing the separation efficiency of photogenerated charges. The physicochemical properties of the catalysts were characterized using SEM, TEM, XRD, and Raman, FT-IR, UV-vis diffuse reflectance and PL spectra. The results indicated that nickel ions substituted for Zn²⁺ in the lattice of ZnO, whereas all the carbon was uniformly coated on the surface of the nanorod photocatalysts. Among the Ni/ZnO@C samples with different ion-doping levels and carbon coating content, the 1.0 mol% Ni/ZnO@C-3 sample possessing a carbon layer thickness of 3.8 nm exhibited a higher visible light activity and synergistic effects of the nickel and carbon, which were responsible for improving the photocatalytic activity. By using the hydrothermal carbon layer as a sacrificial template, nanovoid core–shell structured Ni/ZnO@void@SiO₂ was obtained through subsequent silica coating and calcination reactions. Its porous shell could adsorb dye molecules from the bulk solution and accumulate them in the void space where the Ni/ZnO core is more accessible than for the bare Ni/ZnO nanorods in bulk solution, meanwhile the nanovoid structure could also avoid shielding of the catalyst-active sites by the outer layer, which leads to a significant photocatalytic activity enhancement. In addition, antibacterial studies of Ni/ZnO@void@SiO₂ under sunlight irradiation were performed against Escherichia coli. This nanovoid photocatalyst exhibited high inhibition of the Gram-negative bacterial strain with co-action of the surface adsorption of the mesoporous SiO₂ and the strong oxidation abilities of the formed reactive oxygen species.