Phase-dependent photocatalytic activity of Nb2O5 nanomaterials for rhodamine B degradation: The role of surface chemistry and crystal structure

Abstract

Niobium oxides are promising materials for catalytic applications due to their unique structural versatility and surface chemistry. Nb2O5 nanomaterials were synthesized via a solvothermal method at 150 °C using niobium oxalate as a precursor. A comprehensive characterization of the material was performed using electron microscopy, X-ray diffraction, and Raman spectroscopy. The as-prepared nanoparticles primarily crystallized in a mixture of the TT-Nb2O5 phase (TT from the German Tief-Tief, meaning “low-low”) and niobic acid, while subsequent thermal treatment at 900 and 1100 °C induced a phase transformation to T-Nb2O5 and H-Nb2O5, respectively (T from the German Tief, meaning “low”, and H from Hoch, meaning “high”). The as-prepared samples consist of micro-coils composed of interconnected nanometer-scale fibers, whereas the morphology changes into rods when they are treated at 1100 °C. The photocatalytic performance of the nanoparticles was evaluated by comparing the as-prepared and thermally treated samples. The as-prepared nanoparticles exhibited the highest photocatalytic activity under visible illumination, achieving 100% degradation after 180 min. More interestingly, the treatment of the as-prepared material with H2O2 modified the surface species formed on the Nb2O5, altering the photocatalytic behavior under various illumination conditions. This sample showed the highest photocatalytic activity under UV illumination, reaching 100% degradation after 75 min. On the other hand, the calcined samples are practically inactive, attributed to the loss of active catalytic sites during thermal treatment and phase transformation.