Specific ion effect on the point of zero charge of α-alumina and on the adsorption of 3,4-dihydroxybenzoic acid onto α-alumina surface

- NaCl exhibits critical salt concentration for adsorption density.
- At critical salt concentration adsorption density is equivalent to without salt.
- Below and above critical salt concentration adsorption density is different.
- Above critical salt concentration polarizability of ions governs adsorption density.
- At higher pH, the adsorption density depends on both specific ion effect and pHZPC.