CaF₂-Based Near-Infrared Photocatalyst Using the Multifunctional CaTiO₃ Precursors as the Calcium Source

Multistage formation of fluoride upconversion agents from the related-semiconductor precursors provides a promising route for the fabrication of near-infrared (NIR) photocatalysts with high photocatalytic activities. Herein, the cotton templated CaTiO3 "semiconduction" precursors (C-CaTiO3) were used to synthesize the NIR photocatalyst of Er3+/Tm3+/Yb3+-(CaTiO3/CaF2/TiO2) (C-ETYCCT), and the functions of the Ca2+ source for CaF2 and the heterostructure formations were displayed by C-CaTiO3. The generated CaF2 acted as the host material for the lanthanide ions, and the heterostructures were constructed among anatase, rutile, and the remaining CaTiO3. The induced oxygen vacancies and Ti3+ ions enabled the samples to utilize most of the upconversion luminescence for photocatalysis. The NIR driven degradation rate of methyl orange (MO) over C-ETYCCT reached 52.34%, which was 1.6 and 2.5 times higher than those of Er3+/Tm3+/Yb3+-(CaTiO3/TiO2) (C-ETYCT) and Er3+/Tm3+/Yb3+-(CaTiO3/CaF2) (C-ETYCC), respectively. The degradation rates of MO and salicylic acid over C-ETYCCT with UV-vis-NIR light irradiation were also much higher than those of other samples, which were mainly results of the contributions of its high upconversion luminescence and the efficient electron-hole pair separation.