RES³T - Rossendorf Expert System for Surface and Sorption Thermodynamics

The influence of hydroxybenzoic acids (HAH_n), namely p-hydroxybenzoic acid (4-hydroxybenzoic acid, HPhbH) and protocatechuic acid (3,4-dihydroxybenzoic acid, HProtoH₂), on the adsorption of europium(III) onto α,γ-Al₂O₃ particles is studied as a function of acid concentration. After measuring the adsorption edge of the Eu(III)/α,γ-Al₂O₃ binary system, and using the previously studied binary component system Eu(III)/HAH_n—Moreau et al. (2015) Inorg. Chim. Acta 432, 81—, and HAH_n/α,γ-Al₂O₃—Moreau et al. (2013) Colloids Surf. A 435, 97—, it is evidenced that HPhbH does not enhance Eu(III) adsorption onto α,γ-Al₂O₃ in the Eu(III)/HPhbH/α,γ-Al₂O₃ ternary system. Conversely, HProtoH₂ enhances Eu(III) adsorption onto α,γ-Al₂O₃ in the Eu(III)/HProtoH₂/α,γ-Al₂O₃ ternary system. Adsorption of the acids are also found higher in the Eu(III)/acid/α,γ-Al₂O₃ ternary systems as compared with the corresponding binary systems assessing synergetic effects. For high HPhbH concentrations, a ternary surface species involving ≡AlOH surface sites, Eu(III), and PhbH^– is evidenced by time-resolved luminescence spectroscopy (TRLS). However, in the Eu(III)/HProtoH₂/α,γ-Al₂O₃ ternary system, chemical environment of Eu(III) is found to be very close to that in the Eu(III)/HProtoH₂ binary system. Ternary surface species could not be evidenced in the Eu(III)/HProtoH₂/α,γ-Al₂O₃ ternary system with TRLS because of the very short decay time of Eu(III) in the presence of protocatechuic acid.