Synthesis and characterization of pure and Al-substituted akaganeites and evaluation of their performance to adsorb As(V)

Abstract

Several samples of pure and Al-substituted akaganeites with somatoid (SOM), rod-like (ROD) and nano-crystals (NANO) morphologies were synthesized and fully characterized. The specific surface areas and the total pore volume varied in the trend SOM < ROD < NANO, and both values were enlarged by the Al-substitution. All samples were mesoporous solids with pore and modal size range following the trend SOM > ROD > NANO. This parameter remained unchanged with Al-substitution in SOM-akaganeite but it increased in ROD-akaganeites. The performance on the As(V) adsorption properties was also evaluated. The amount of As(V) adsorbed by NANO (mmol g-1) at saturation (Γmax) was three times larger than the correspondent to SOM. The pure and Al-SOM exhibited the highest Γmax (mmol m-2) indicating a highest surface reactivity towards As-adsorption. Taking into account these marked differences in the As(V) adsorption capacity of the various akaganeites, and their similarities in the structure, chemical composition and surface charge, it can be concluded that the textural characteristics are the main determinant of the adsorption properties.