Multi-Photonic behavior of Nb2O5 and its correlation with synthetic methods

The performance of niobium pentoxide (Nb2O5) as photoanodes in dye-sensitized solar cells (DSSCs) and as catalysts in the photocatalytic degradation of Rhodamine B (RhB) was investigated. Four samples of Nb2O5 (Nb2O5_SG, Nb2O5_CR, Nb2O5_PP, and Nb2O5_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 Nb2O5 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 Nb2O5 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 Nb2O5_CR to 1.64 mA.cm−2 for Nb2O5_SG. The same trend was observed for the photocatalytic degradation of RhB, where the smaller and dispersed particles of Nb2O5_CR and Nb2O5_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.