Modificação estrutural do Nb2O5 para aplicação em processos de remediação ambiental

Abstract

Brazil holds 98 % of the world’s niobium deposits, making it essential to add scientific and economic value to this material. This study investigated the modification of niobium pentoxide with other oxides, specifically vanadium pentoxide and tungsten trioxide, using the oxidative peroxide method followed by hydrothermal treatment, to enhance its photocatalytic and adsorptive properties for environmental remediation applications. The synthesized samples were characterized using X-ray diffraction (XRD), Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), N2 physisorption-desorption, and zeta potential analysis. The photocatalytic and adsorptive properties were evaluated through the photodegradation and adsorption of dyes Methylene Blue (MB) and Rhodamine B (RhB), the pharmaceutical Amiloride (AML), and the CO2 photoreduction process. For the vanadium-based modification, ammonium niobium oxalate (ANO) was used as a precursor. However, due to changes observed in the material over time, the experiments were conducted in two separate stages, using ANO from the 2017 and 2022 batches. In both cases, the analyses confirmed the doping of Nb2O5 with vanadium. Under the first condition (2017 batch), the doped sample exhibited excellent performance in the photodegradation of RhB and AML compared to isolated Nb2O5. In the CO2 photoreduction tests, the vanadium-modified sample favored CO formation over H2, suggesting that the modification enhanced CO2 adsorption on the material’s surface. Under the second condition (2022 batch), the modification improved the adsorptive properties of MB. Adsorption studies indicated that the primary adsorption mechanism was physisorption, and the sample maintained its efficiency over five consecutive cycles. For the modification of Nb2O5 with WO3, the optimal condition was achieved using ammonium niobium oxalate and tungstic acid, with a molar ratio of 80% WO3 to Nb2O5. The analyses confirmed the formation of a heterostructure. In the photodegradation tests, the heterostructure exhibited combined properties of both oxides, as bare Nb2O5 and WO3 were more effective in decolorizing MB and RhB, respectively. However, the heterojunction was capable of both adsorbing and photodegrading both dyes. The results indicate that modifying Nb2O5 with vanadium and tungsten compounds enhanced its photocatalytic and adsorptive properties, making these materials promising for environmental remediation applications.