Some features of 2 and 4-aminopyridines anchored on silica gel: Properties and chemisorption of metal(II) chlorides in non-aqueous solutions

Silica gel surfaces modified with 2- or 4-aminopyridine groups were used to adsorb MCl₂ (M = Co, Ni, Cu, Zn) from ethanol and acetone solutions at 298 K. The chemisorption isotherms fitted a modified Langmuir equation very well and are similar for all cations. The capacity of anchored 4-aminopyridine (SIL4) in adsorbing the metallic ion is larger than that of the immobilized 2-aminopyridine (SIL2). The maximum retention capacity has the sequence Cu> Co> Zn in acetone for both surfaces, and Zn> Co> Cu> Ni for SIL2, and Zn> Cu> Co> Ni for SIL4 in ethanol. For a given cation, the variation in enthalpy of solvent-solute exchange on the surface is always larger in ethanol. This process seems to be related to the enthalpy of solvation of the cation involved in the exchange.