Study on the UV Protection and Photocatalytic Activity of Cu²⁺ and Fe³⁺ Doped TiO₂ Nanoparticles

Titanium dioxide (TiO₂) is a safe inorganic sunscreen that provides broad-spectrum ultraviolet (UV) protection. It is usually mixed with organic materials or directly applied to the protected area. However, the photocatalytic activity of TiO₂ can decompose organic substances upon UV light exposure, causing negative effects. To further extend the UV protection wavelength range of TiO₂ and reduce its photocatalytic activity, copper/iron sulfate was added to titanium tetraisopropoxide (as TiO₂ precursor) in isopropanol in the presence of hydrochloric acid (as catalyst), yielding Cu²⁺/Fe³⁺-doped TiO₂ nanoparticles. X-ray diffraction analysis revealed the anatase crystal phase in doped TiO₂ nanoparticles annealed at 100 and 400 °C, whereas annealing at 700 °C resulted in rutile phase formation. Doped TiO₂ nanoparticles annealed at 100 °C exhibited an average particle size of approximately 10 nm, and the particle size distribution remained below 100 nm even when annealed at 700 °C, suggesting that Cu²⁺/Fe³⁺ inhibited the condensation and crystallization of TiO₂. UV-Visible spectrophotometry analysis confirmed that Cu²⁺/Fe³⁺ doping effectively reduced UV light transmittance and enhanced visible light blocking, achieving broad-spectrum light protection. Moreover, by adjusting the weight percentage of Cu²⁺ or Fe³⁺, doped TiO₂ nanoparticles annealed at 100 °C, 400 °C, or 700 °C demonstrated reduced photocatalytic activity, offering a considerable advantage for sunscreen applications containing organic materials.