Removal of Sr2+ Ions by Ta-Doped Hexagonal WO3: Zeta Potential Measurements and Adsorption Mechanism Determination

The adsorption of Sr2+ ions onto Ta-doped hex-WO3 nanomaterials was studied by measuring the zeta potentials of the powder nanoparticles and by determining the adsorption isotherm and adsorption mechanism. Five important results were obtained: (1) the zeta potential values of the Ta-doped hex-WO3 suspensions in different electrolyte solutions, within the studied pH ranges, increased with an increase in electrolyte valence; and (2) the zeta potential of the Ta-doped hex-WO3 suspensions increased with an increase in ionic strength. (3) Sr2+ ion adsorption increased with a decrease in temperature and ionic strength. (4) The adsorption enthalpy was calculated as 47 kJ·mol-1, and the interaction between the Ta-doped hex-WO3 surface and Sr2+ ions was concluded to be chemical in nature. (5) The adsorption of Sr2+ ions onto the Ta-doped hex-WO3 was attributed to surface chemical adsorption and ion exchange (in tunnels).