In this work, niobium pentoxide (Nb 2 O 5 ) nanoparticles of varying sizes and morphology were synthesized using the controlled precipitation method. Ammonium niobate oxylate hydrate (NH 4 )H 2 [NbO(C 2 O 4 ) 3 ] · 3 H 2 O was used as a niobium precursor and distilled water or acetic acid was used as solvent. The obtained solids were characterized using Fourier transform infrared and Raman spectroscopies, X-ray diffraction and transmission electron microscopy. The as-synthesized solid

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... e was amorphous, but after heat treatment between 500°C and 600°C, the T-Nb 2 O 5 phase was obtained. The size of the primary particles of the niobium pentoxide was nanometric (<100 nm), with agglomerate size of >500 nm, when water was used as a solvent for synthesis. Considering the nature of the process, a possible reaction mechanism of the precursor with the water and NH 4 OH was proposed, which explains the formation of the solid within an aqueous solution. Considering one potential use of Nb 2 O 5 synthesized in this work, the photo-degradation action of the particles on the organic molecule methylene blue was tested. The sample synthesized in acetic acid at pH ∼9.0 and heat treated at 600°C showed the highest photo-degradation capacity, with a degradation of ∼60% of the dye for 60 minutes.