Preparação de nanocompósitos de hexaniobato com nanopartículas de Au com alta estabilidade e eficiência fotocatalítica para produção de hidrogênio

Abstract

Photocatalysis is one of the topics of great scientific and technological interest today because it potentially allows the sustainable use of solar radiation. Considering that lamellar niobates are materials with the potential to act as photocatalysts and that Brazil holds 98% of the world's niobium reserves, the present work presents a strategy of modification of potassium hexaniobate with gold nanoparticles in order to improve the its photocatalytic performance and obtain a nanocomposite with high stability in a simple and ecological way. K4Nb6O17 was synthesized from the solid-state reaction of niobium pentoxide with potassium carbonate and exfoliated with a solution of tetrabutylammonium hydroxide. Gold nanoparticles coated with polyethyleneimine, at concentrations of 1% and 2% m/m (Nb6O17-Au1% and Nb6O17-Au2%), were adsorbed in the interlamellar region of the exfoliated hexaniobate (Nb6O17-esf). The synthesized materials had their structures characterized by X-ray diffractometry and Raman scattering spectroscopy, and their morphology analyzed by scanning and transmission electron microscopy. X-ray excited photoelectron spectroscopy data showed that the nanoparticles are strongly adsorbed to hexaniobate and cause a change in the electron density of their surface atoms. By excitation in the band gap region of hexaniobate, electrons were efficiently transferred to the gold nanoparticles as shown by electron paramagnetic resonance spectroscopy. The photocatalytic performances of the nanocomposites were evaluated for hydrogen evolution from aqueous methanol solutions. H2 evolution rates of up to 294  20 mol h-1 g-1 were observed for Nb6O17-Au2%, with an apparent quantum yield of 1.1 . Such performance is comparable with hexaniobates modified with Au nanoparticles obtained by photodeposition and lower than that observed for the oxide modified with Pt. However, the new nanocomposite stands out in terms of stability under a long period of irradiation, being three times more stable. Through transmission electron microscopy images and inductively coupled plasma atomic emission spectroscopy measurements, it was observed that the use of polyethyleneimine-coated nanoparticles prevented the agglomeration and leaching of the metal, thus enabling the development of a more robust photocatalyst.