Lanthanide Metal-Doped Ca Aluminate Nanoflakes with Enhanced Photocatalytic Activity

Abstract

Background: Ca aluminate (CaAlO) is an important aluminate material that shows promising applications in optics, catalysts, photoelectrons, semiconductors, and biological materials. The band gap of the CaAlO nanoflakes is as large as 3.87 eV, limiting the application of the CaAlO nanoflakes. Thus, it is essential to research efficient methods for improving the photocatalytic performance of the CaAlO nanoflakes. The improvement of gentian violet degradation can be further enhanced by lanthanide metal doping. Methods: Lanthanide metal (La or Pr)-doped CaAlO nanoflakes were prepared using a simple method. Lanthanide metal-doped CaAlO nanoflakes were analyzed by electron microscopy, X-ray diffraction, photoelectron spectra, solid diffusion reflectance, and photoluminescence spectra. Results: La or Pr was incorporated into the CaAlO nanoflakes with orthorhombic Ca5Al6O14 phase. La dopant with the content of 8wt.% existed in the form of hexagonal La0.9Al11.7O19. Pr dopant induced the phase transformation from the orthorhombic Ca5Al6O14 phase to the cubic Ca3Al2O6 phase. The size of the doped nanoflakes reduced from 2 μm to 500 nm with increasing the content of lanthanide metal dopants. The band gap of the lanthanide metal-doped CaAlO nanoflakes decreased from 3.74 eV to 2.98 eV, decreasing the La dopant from 8 wt.% to 2 wt.%, 3.62 eV to 3.34 eV and improving Pr dopant from 2 wt.% to 8 wt.%. About 20 mL of 10 mgL-1 gentian violet was entirely removed using 2 wt.%-La-doped CaAlO nanoflakes under irradiation for 30 min, and 8wt.%-Prdoped CaAlO nanoflakes under irradiation for 50 min, respectively. 2wt.%-La-doped CaAlO nanoflakes exhibited the highest photocatalytic degradation reaction rate constant (0.115 min-1), which was 3.6 times as high as that of the CaAlO nanoflakes. The major reaction active substances involved in the photo-degradation were hydroxyl radicals and holes. Conclusion: Photocatalytic activity of the CaAlO nanoflakes towards gentian violet can be greatly enhanced by lanthanide metals owing to the harvest light absorption, reduced band gap, and recombination ability of photo-generated electron-hole pairs. other: The present work provides a good strategy for enhancing the photocatalytic activity of the CaAlO nanoflakes.