The performance of niobium pentoxide (Nb 2 O 5 ) as photoanodes in dye-sensitized solar cells (DSSCs) and as catalysts in the photocatalytic degradation of Rhodamine B (RhB) was investigated. Four samples of Nb 2 O 5 (Nb 2 O 5 _SG, Nb 2 O 5 _CR, Nb 2 O 5 _PP, and Nb 2 O 5 _MA) were synthesized by four different methods, respectively, entailing the sol-gel, combustion, polymeric precursors, and a microwave-assisted hydrothermal reaction. In all these samples, the orthorhombic phase of Nb 2 O 5 was obtained, which resulted in different shapes and assemblies, which is very relevant because the surface area, shape, and size distribution of the nanoparticles significantly contribute to the optical process. The bandgap remained constant at 3.0 eV for all the samples, even for the sample prepared by the combustion method. An additional phase, which is related to local distortions, was revealed by Raman spectroscopy within the vibration range of 688-260 cm -1 . DSSCs using photoanodes with smaller and more dispersed Nb 2 O 5 particles showed better results than those with inhomogeneities. For comparison, DSSCs were assembled using two different counter electrodes, platinum and graphite. The DSSC with platinum showed better photovoltaic results, mainly with photocurrents from 1.17 mA.cm -2 for Nb 2 O 5 _CR to 1.64 mA.cm -2 for Nb 2 O 5 _SG. The same trend was observed for the photocatalytic degradation of RhB, where the smaller and dispersed particles of Nb 2 O 5 _CR and Nb 2 O 5 _SG exhibited the best performance and, respectively, degraded approximately 75% and 61% of the RhB dye over 180 min. Therefore, the results of this study established a correlation between the synthesis methods and photonic behavior.
Microwave-assisted hydrothermal synthesis of aluminum (Al)-doped TiO 2 (ALT) and niobium (Nb)-doped TiO 2 (NBT) nanoparticles were carried out. Investigations were performed to examine the crystallinity, vibrational modes, surface morphology, and composition using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS), respectively. The XRD study indicated the higher crystallinity of the ALT particles compared to the Al and Nb-doped TiO 2 (ALNBT) particles, and only the presence of the anatase phase was observed in all samples. As a result of doping, the Raman mode at ∼147 cm −1 is found to be shifted toward a higher wavenumber for both samples. SEM analysis showed the spherical morphology of ALT and NBT nanoparticles. The elemental composition peaks of Al, titanium, Nb, and oxygen were noticed by EDS measurements. Furthermore, both prepared nanoparticles were used as photocatalytic materials. The Nb and Al-doped samples showed an improvement in the photocatalysis response in relation to the pure TiO 2 sample, in which Al-doped sample was able to decolorize 100% of rhodamine B in 75 min of analysis.
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