The impact of Au nanoparticles and lanthanide-doped NaYF4 on the photocatalytic activity of titania photocatalyst

Highlights: • Composites were formed from TiO₂, lanthanide doped NaYF₄ and Au nanoparticles. • Hexagonal NaYF₄ and anatase TiO₂ were detected. • The gold nanoparticles were proved to be present by using TEM and DRS. • The samples had better photocatalytic activity in visible light then in UV light. Composite systems were prepared by doping NaYF₄ (NYF) with lanthanide cations (Yb³⁺, Er³⁺, Tm³⁺), TiO₂, and gold nanoparticles to exploit the light conversion properties of NYF and its possible impact on the photocatalytic activity of the composites. The composites were synthesized via solvothermal crystallization and the obtained structures were anatase TiO₂, hexagonal NYF, and gold nanoparticles of 5–7 nm. The presence of NYF enhanced the photoactivity of TiO₂ towards Rhodamine B degradation under UV irradiation, while it decreased its performance under visible light. The presence of Au was beneficial when visible light was applied for the degradation experiments. The reason behind the enhanced activity was the fluorescence of NYF at 400 nm that was the most intense for the composites that did not contain gold. The NYF-based samples also showed signs of up-conversion when 900 nm was the excitation light source, highlighting the potential of this material for photocatalytic applications that utilize the full (UV–IR) light spectrum.