FACILE HYDROTHERMAL SYNTHESIS OF NIOBIUM PENTOXIDE SEMICONDUCTOR AND THEIR APPLICATION IN THE PHOTODEGRADATION OF DYES AND REDUCTION OF FREE FAT ACIDS IN WASTE OIL

We report a facile hydrothermal method for the synthesis of niobium pentoxide (Nb₂O₅) under two different temperatures, 120 °C (Nb₂O₅-120) and 150 °C (Nb₂O₅-150). The obtained materials were characterized by structural, optical and morphological techniques. Also, the photocatalytic properties of the Nb₂O₅ samples were evaluated in two reactions under ultraviolet (UVC) irradiation: degradation of methylene blue (MB) and indigo carmine (IC) dyes; and esterification of free fatty acids (FFA) present in waste cooking oil (WCO). The Nb₂O₅ was formed at different temperatures of synthesis, and the increase in temperature did not cause significant changes in the structural and optical characteristics, but resulted in an increased surface area of the synthesized materials. Both synthesized materials showed excellent efficiency for dye photodegradation. The sample Nb₂O₅-150 presented the best performance for the MB photodegradation, with almost 85% of the removal efficiency. In this case, the adsorption of MB molecules on the surface of the material was high due to the favorable electrostatic interaction and also because of its high surface area. For the IC photodegradation, the adsorption was insignificant, and both samples presented approximately 100% of the removal efficiency. These materials were also promising for the reduction of free fat acids in waste oil by photoesterification.

Keywords:
Nb₂O₅; hydrothermal method; photodegradation; photoesterification; UVC irradiation