Green Decorated of Au/TiO₂ Nanocomposites as Superior Photocatalyst in Methylene Blue Dye Degradation Under Sodium Light Irradiation

We describe the green synthesis of Au/TiO₂ nanocomposites and its photocatalytic application towards the methylene blue (MB) dye degradation. Au/TiO₂ nanocomposites were green synthesis using Pilea melastomoides leaf (PML) and Tamarindus indica L. fruit (TIF) extract. The UV–visible spectroscopy exhibits an absorption peak of Au colloids at 531 nm wavelength. The reflectance properties of Au/TiO₂ nanocomposites to confirm a bandgap at 400–600 nm with the value of 2.9 eV. The morphological images show the spherical-like structure of Au/TiO₂ nanocomposite with an average particle size distribution of 5–10 nm. The Au/TiO₂ nanocomposite exhibits excellent degradation efficiency for methylene blue (MB) dye under sodium light irradiation of 92.5% for 60 min reaction time. The electron transfer mechanism might explain the still debatable MB dye degradation mechanism in the present case. The photogenerated electrons transfer to the conduction band (CB) of TiO₂ from the CB of Au under UV light exposure. This results in the creation of defect levels of Au in TiO₂, lowering the CB of TiO₂. These results suggest the Au/TiO₂ nanocomposites were the superior photocatalyst for MB wastewater treatment.