| Abstrakt: |
CeO2 nanoparticles are synthesized at different reaction times, different reaction temperatures, and different pH of the starting precursor solution. Metal (Ni2+, Cd2+, and Nb5+) doped CeO2 nanoparticles are prepared with different concentrations of dopant ions by maintaining the reaction time at 24 hrs, reaction temperature at 180 °C, and pH of the starting precursor solution at 12. The physical properties of the prepared samples are studied by powder X-ray diffraction analysis (PXRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) specific surface area analysis, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, UV–visible spectroscopy (UV–vis), and photoluminescence (PL) analysis. The photocatalytic activity of the prepared samples is studied by methylene blue (MB) degradation under sunlight irradiation. The effect of reaction time, reaction temperature, pH of the starting solution, and dopant ions concentration on the physical properties and photocatalytic activity of CeO2 nanoparticles are analyzed. All the synthesized samples are found to have a cubic fluorite structure. The crystallite size and lattice parameter of undoped CeO2 nanoparticles increase with the reaction time, reaction temperature, and pH of the precursor solution used for the synthesis and decrease with the dopant ions concentration. All of the samples have spherical morphology, as seen by SEM pictures. With increasing reaction time, reaction temperature, precursor solution pH, and dopant concentration, the particle size drops, and the specific surface area increases. However, for Nb5+ ions doped CeO2 nanoparticles, a decrease in the specific surface area with doping is observed which may be due to the formation of the fergusonite (CeNbO4) phase at higher doping levels. FTIR analysis confirms the presence of Ce–O-Ce or Ce–O-M stretching vibrations in the samples. The bandgap energy of Ni2+ doped samples increase from 3.57 to 3.85 eV and that of Cd2+ doped samples increases from 3.55 to 4.03 eV when the dopant concentration is increased from 5 to 15 M%. The observed increase in the bandgap energy of the Ni2+ and Cd2+ doped CeO2 samples could be due to the decrease in the particle size. The bandgap energy of Nb5+ ions doped CeO2 nanoparticles decreases with an increase in dopant concentration which could be ascribed to the increased formation of the Fergusonite phase at a higher doping level. A shift in the F2g peak position towards lower wavenumbers and a reduction of peak intensity with increased doping is observed in the Raman spectra confirming the enhancement of oxygen vacancies with an increase in dopant concentration. The PL studies show that the CeO2 nanoparticles and Ni2+, Cd2+, and Nb5+ ions doped CeO2 nanoparticles exhibit luminescence in the violet-blue-green wavelength region. The PL emission intensity of the doped samples decreases as the dopant concentration increases. The undoped CeO2 nanoparticles prepared at higher reaction time, higher reaction temperature and higher pH (= 12) of the precursor solution exhibit higher photocatalytic activity. In the case of doped CeO2 samples, the MB degradation efficiency of Ni2+ ions doped CeO2 NPs is found to be comparatively higher than that of undoped and Cd2+ and Nb5+ doped CeO2 NPs. 15 M% Ni2+ doped CeO2 NPs exhibited smaller particle size, higher specific surface area of 49.7m2/g and a higher MB degradation efficiency of 81.9% within 1 hr. [ABSTRACT FROM AUTHOR] |
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