Search on the surface charge density, in deprotonation Al-OH becomes Al-O- and the presence of cation like Na+ for example it becomes Al-O-Na+. See the papers attached.
The involved adsorption mechanism can be determined from XPS spectra analysis by evaluating the detected energy spectrum on the materials before and after adsorption.
what are the main reasons of differentiates in adsorption rates of different metal ( Cr+6 , Pb+2,Cd +2, Ni+2, ,… ions on one of nano metal oxides ( for example Tio2 , Fe2O3 , Al2O3,… ) ?