Preparação e avaliação fotocatalítica de hexaniobatos lamelares e seus filmes finos obtidos por Layer-by-Layer

Abstract

As the technological development and population growth continuously increases, energy consumption is becoming higher over the years. In this aspect, photocatalysis attracts great interest due to its potential to harvest and convert solar energy. In a national scenario, layered niobates are interesting materials to act as photocatalysts, since Brazil accounts for 98% of the world’s niobium reserves. In this work application of K4Nb6O17 as a photocatalyst both, in powder form and immobilized as thin films, was investigated. K4Nb6O17 was prepared by the solid state reaction between Nb2O5 and K2CO3 and then it was exfoliated in tetrabutylammonium hydroxide solution. The exfoliated niobate was modified with platinum using two different precursors, H2PtCl6 and [Pt(NH3)4]Cl2, and it was also combined with gold nanoparticles. The samples were characterized by different techniques and the photocatalytic performance was evaluated for methylene blue and methanol oxidation and for H2 production. In the dye photodegradation, the unmodified exfoliated niobate exhibited the highest photonic efficieny (ξ = 2.1%). In contrast, for the methanol photodegradation and H2 evolution, the modified samples presented higher photocatalytic performance than the exfoliated niobate. For H2 evolution, photonic efficiencies close to 0.2% were obtained for samples modified by Pt and Au. For methanol photodegradation, the Pt-niobate composites exhibited photonic efficiencies close to 4.0% and the Au-niobate 7.0%. The assembly of thin films can favor the application as photocatalysts due to ease of recovering, smaller losses and reduced material agglomeration. The bare niobate and the Pt-niobate films were assembled by the Layer-by-Layer (LbL) technique because of its easiness and versatility. The films were characterized towards their morphology, photocatalytic and photoelectrochemical properties. For methylene blue photodegradation, both films resulted in similar photonic efficiencies (ξ = 0.1%). In contrast, for the H2 photocatalytic production, the presence of Pt in the films resulted in a photonic efficiency twice higher (ξ = 1.2%) than the bare niobate film (ξ = 0.6%). The increase in the bilayers number caused a linear increase of the H2 evolution rate, indicating that the material immobilization did not lead to the active sites losses.