UV–visible light photocatalytic properties of NaYF ₄ :(Gd, Si)/TiO ₂ composites

In this study, a new novel composite photocatalyst of NaYF ₄ :(Gd, Si)/TiO ₂ phosphor has been synthesized by two step method of solution combustion and sol-gel. The photocatalyst powders were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), UV–vis spectroscopy and photoluminescence (PL) spectroscopy. Raman spectroscopy confirmed the anatase TiO ₂ phase which remarkably increased with existence of yttrium silicate compounds between 800 cm ⁻¹ and 900 cm ⁻¹ . Double-addition of Gd ³⁺ -Si ⁴⁺ ions in NaYF ₄ host introduced sub-energy band levels with intense absorption in the ultraviolet (UV) light region. Photocatalytic activity was examined by exposing methylene blue (MB) solutions mixed with photocatalyst powders to 254 nm UV-C fluorescent lamp and 200 W visible lights. The UV and visible photocatalytic reactivity of the NaYF ₄ :(Gd, 1% Si)/TiO ₂ phosphor composites showed enhanced MB degradation efficiency. The coating of NaYF ₄ :(Gd, 1% Si) phosphor with TiO ₂ nanoparticles creates energy band bending at the phosphor/TiO ₂ interfaces. Thus, these composites exhibited enhanced absorption of UV/visible light and the separation of electron and hole pairs for efficient photocatalysis.