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 CeO 2 -ZrO 2 and CeO 2 -Al 2 O 3 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 CeO 2 -ZrO 2 (3.99 atomic %) than CeO 2 -Al 2 O 3 (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/CeO 2 -ZrO 2 displayed well-organized yarn textured particles with less than 5 nm size, which lacks in Au/CeO 2 -Al 2 O 3 . The reason for this less systematized and less Au embedding in the presence of alumina in CeO 2 -Al 2 O 3 was verified with the high-resolution XPS studies of both nanocomposites and an elevated binding energy due to the mobility of Au particles over CeO 2 -Al 2 O 3 was observed, while for Au/CeO 2 -ZrO 2 , a very small binding energy shift of gold states (Au 4f5/2 0.39; Au 4f7/2 0.17 eV) and the CeO 2 -ZrO 2 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/CeO 2 -ZrO 2 (4.2 eV) than Au/CeO 2 -Al 2 O 3 (4.94 eV) suggesting the elevated electron transfer from the conduction band of CeO 2 -ZrO 2 to Au interfaces. In addition, XRD and Raman studies of Au/CeO 2 -ZrO 2 showed a pronounced phase transformation of Ce 4+ to Ce 3+ in the presence of homovalent Zr 4+ ions with an increased structural disorder in CeO 2 promoting the localized surface plasmon resonance (LSPR) in the lattice of CeO 2 -ZrO 2 , which was less detected in Au/CeO 2 -Al 2 O 3 due to the interference of less-desired γ-Al 2 O 3 phases. These characteristics of Au/CeO 2 -ZrO 2 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.