Effect of the structural integrity on the size and porosity of gold-implanted mixed-metal oxide nanocomposites: their influence on the photocatalytic degradation of thioanisole

Since the interfacial binding strength and structural integrity have a strong influence on the active sites of nanocomposites, this study focused on exploring the structural and electronic properties at the interface between the implanted metal ion and host support. For this, nanocomposites of gold embedded in CeO₂-ZrO₂ and CeO₂-Al₂O₃ matrices were fabricated, and their structural and morphological properties were investigated using ICP-OES, UV-vis, XRD, Raman, HRTEM, and high-resolution XPS studies and compared. From the results, it was found that the deposition of gold is highly favored over CeO₂-ZrO₂ (3.99 atomic %) than CeO₂-Al₂O₃ (1.21 atomic %); however, the same amount of gold was used for the synthesis of both nanocomposites, as befits it. The HRTEM images of Au/CeO₂-ZrO₂ displayed well-organized yarn textured particles with less than 5 nm size, which lacks in Au/CeO₂-Al₂O₃. The reason for this less systematized and less Au embedding in the presence of alumina in CeO₂-Al₂O₃ was verified with the high-resolution XPS studies of both nanocomposites and an elevated binding energy due to the mobility of Au particles over CeO₂-Al₂O₃ was observed, while for Au/CeO₂-ZrO₂, a very small binding energy shift of gold states (Au 4f5/2 0.39; Au 4f7/2 0.17 eV) and the CeO₂-ZrO₂ matrix that favored an increased intermolecular force between gold and the supporting host was observed. This agrees well with UV-vis electronic spectrum analysis, which revealed that the incorporation of gold nanoparticles narrowed the band gap more significantly in Au/CeO₂-ZrO₂ (4.2 eV) than Au/CeO₂-Al₂O₃ (4.94 eV) suggesting the elevated electron transfer from the conduction band of CeO₂-ZrO₂ to Au interfaces. In addition, XRD and Raman studies of Au/CeO₂-ZrO₂ showed a pronounced phase transformation of Ce⁴⁺ to Ce³⁺ in the presence of homovalent Zr⁴⁺ ions with an increased structural disorder in CeO₂ promoting the localized surface plasmon resonance (LSPR) in the lattice of CeO₂-ZrO₂, which was less detected in Au/CeO₂-Al₂O₃ due to the interference of less-desired γ-Al₂O₃ phases. These characteristics of Au/CeO₂-ZrO₂ ensured its performance as a promised photocatalyst for thioanisole degradation without using any harmful oxidants, and its stability towards different irradiation conditions, such as visible, ultraviolet, and solar light.