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.