Smart Mn⁷⁺ Sensing via Quenching on Dual Fluorescence of Eu³⁺ Complex-Modified TiO₂ Nanoparticles

In this work, titania (TiO₂) nanoparticles modified by Eu(TTA)₃Phen complexes (ETP) were prepared by a simple solvothermal method developing a fluorescence Mn⁷⁺ pollutant sensing system. The characterization results indicate that the ETP cause structural deformation and redshifts of the UV-visible light absorptions of host TiO₂ nanoparticles. The ETP also reduce the crystallinity and crystallite size of TiO₂ nanoparticles. Compared with TiO₂ nanoparticles modified with Eu³⁺ (TiO₂-Eu³⁺), TiO₂ nanoparticles modified with ETP (TiO₂-ETP) exhibit significantly stronger photoluminescence under the excitation of 394 nm. Under UV excitation, TiO₂-ETP nanoparticles showed blue and red emission corresponding to TiO₂ and Eu³⁺. In addition, as the concentration of ETP in TiO₂ nanoparticles increases, the PL intensity at 612 nm also increases. When ETP-modified TiO₂ nanoparticles are added to an aqueous solution containing Mn⁷⁺, the fluorescence intensity of both TiO₂ and ETP decreases. The evolution of the fluorescence intensity ratio (I₁/I₂) of TiO₂ and ETP is linearly related to the concentration of Mn⁷⁺. The sensitivity of fluorescence intensity to Mn⁷⁺ concentration enables the design of dual fluorescence ratio solid particle sensors. The method proposed here is simple, accurate, efficient, and not affected by the environmental conditions.