The role of crystalline Nb2O5 nanoparticles for enhanced dye adsorption and photodegradation

Niobium pentoxide (Nb2O5) nanoparticles have attracted attention in recent years due to their enhanced adsorption and photocatalysis properties against emerging contaminants. The photocatalytic properties of niobium pentoxide are directly related to defects and non-stoichiometric phases in its structure. This work presents the synthesis of Nb2O5 nanoparticles using the Pechini method and precursor decomposition techniques. X-ray diffraction (XRD) showed the presence of niobium pentoxide crystallized in TT, T, H, and the non-stoichiometric Nb12O29 phases. The samples calcined at 500 degrees C showed a specific surface area (SSA) between 55 and 65 m(2) g(-1), acting as a good adsorbent and photocatalyst to degrade crystal violet (CV). The contaminant adsorption process was studied and optimized using zeta-potential analysis, showing a negatively charged surface at pH > 2, with optimal adsorption at pH = 10. The adsorption study showed the best fit for the adsorption isotherm proposed by Liu and also the possibility of reusing Nb2O5. The photodegradation of crystal violet dye using Nb2O5 as catalyst showed synergetic properties, in which samples with higher SSA and crystallization in the TT-phase decolored the solution in 2 h 30 min. However, the mixture of H-Nb2O5 and Nb12O29 also showed good adsorption properties and decolored the CV pollutant in 2 h 30 min, demonstrating that adsorption and photodegradation mechanisms strongly depend on the crystalline phase of the niobium pentoxide.