Influence of structural and surface properties of Nb2O5 pellets on methylene blue adsorption and adsorbent reuse capacity

Abstract

Abstract This study aimed to describe the preparation of Nb2O5 pellets by uniaxial pressing, to investigate the influence of heat treatment at different temperatures (800, 900, and 1000 °C) on the physical, surface, microstructural, and adsorptive properties of the materials, and to assess their potential as reusable adsorbents for methylene blue removal. Specimens treated at 800 °C contained a mixture of monoclinic and hexagonal phases, with a predominance of monoclinic structures. By contrast, heat treatment at 900 °C and above resulted in complete conversion to the monoclinic phase. The surface of Nb2O5 particles contained basic groups, possibly oxygen ions (O-). Experimental investigations showed that methylene blue adsorption followed second-order kinetics, suggesting chemical diffusion as the dominant process. Maximum adsorption occurred at pH 6.0. Pellets remained intact after the adsorption test. A study was carried out to determine the reusability of pellets over five adsorption cycles in methylene blue solutions at different concentrations. The maximum adsorbed concentration was 10.4 mg.L-1. The adsorption capacity of Nb2O5 specimens gradually decreased from 56% in the first cycle to 25% in the fifth cycle. Despite this reduction in removal efficiency, Nb2O5 pellets showed promise as reusable adsorbents in heterogeneous processes because of their high potential adsorption capacity and easy separation from the reaction medium.

Keywords

• adsorption
• methylene blue
• niobium pentoxide
• reuse