Photoluminescence And Visible-Light Photocatalysis Of Ni²⁺, Co²⁺-Doped ZnO/ZnAl₂O₄ Composite Films Preparated Via Hydrotalcite-Like Precursors

Zinc oxide (ZnO), a semiconductor with a wide direct band gap, is well recognized as a multifunctional material in various applications. Particularly, doped ZnO has attracted more attention because of their excellent optical and electrical properties and their potential application in optoelectronic devices. Ni2+, Co2+ -doped ZnO/ZnAl2O4 composite films were prepared using hydrotalcite-like as precursors by slurry coating/sintering technique and their component, structure, morphology, were characterized by XRD, SEM-EDS, HTEM, Raman, TPR, XPS. In addition, the photoluminescence and photocatalytic activity of the resulting films were investigated by UV-vis and PL spectra. The details are as follows:(1) Ni2+ -modifled ZnO/ZnAl2O4 composite films were obtained by thermal-decomposition of Ni/Zn/Al-CO3-LDHs precursors with different Ni contents at 900℃. The result shows that Ni2+ is incorporated into ZnO and ZnAl2O4 lattice matrix, when Ni content is less than or equal to 4.3 mol%. From UV-vis spectra, it can be found that Ni2+ has two types of coordination geometries in tetrahedral and octahedral sites, but has a clear preference for octahedral coordination. SEM-EDS shows that composite films deposited on Si are homogeneous and well-dispered. The band edge emission and red emission are enhanced due to the incorporation of Ni2+. Moreover, when Ni content reaches up to 4.3 mol%, it can be observed two new emission bands (591 nm and 618 nm) attributable to d-electron transition in Ni2+(2) Co2+- modified ZnO/ZnAl2O4 composites were obtained by sintering Co/Zn/Al-CO3-LDHs precursors at different temperatures and Co/Zn/Al molar ratios. The effects of microstructure on the visible light photocatalytic performance of the composites were investigated by adjusting preparation parameters, such as initial ratio and sintering temperature. Furthermore, the influence of agglomeration state of the Co2+ doped ZnO/ZnAl2O4 composites, such as powders and films, on the the visible light photocatalytic activity. The resuts show that Co2+ doped ZnO/ZnAl2O4 with Co/Zn/Al of 0.05:3:1 sintered at 600℃has the best photocatalytic activity under visible-light, and the degradation percentage of methylene blue reaches 86.4%.