Cobalt, nickel, and copper ion-exchanged on heterocyclic amine-intercalated titanium hydrogenphosphate compounds

Crystalline alpha-titanium hydrogenphosphate with a maximum theoretical ion-exchange capacity of 7.60 mmol g(-1) had aromatic organic 3- and 4-aminopyridine molecules inserted into the free lamellar space at 2.32 and 3.14 mmol g(-1). This expands the interlamellar distance from 760 to 1193 and 1261 pm, respectively. The effectiveness of these new matrices for exchanging cations at the solid/liquid interface dpends on the intercalated monoprotonated amines and gives cation-exchange order Cu2+ > Co2+ > Ni2+, not only from individual cationic solutions, but also when an equimolar mixture of these cations is employed. For the first procedure, copper had the most exchange ability giving 2.42 and 2.26 mmol g(-1). From the cation mixture, it presented ion-exchange capacities (1.91 and 1.80 mmol g(-1)), that are nearly four times that obtained for cobalt (0.560 and 0.384 mmol g(-1)). No significant values were obtained for nickel (0.084 and 0.039 mmol g(-1)) when present in the mixture. The X-ray diffraction patterns for copper-containing materials showed a reasonable increase of disorganization as the ion-exchange progressed, to change the original crystalline structure to an amorphous form. Carbon and nitrogen elemental analyses demonstrated a decrease in the amount of amine after the ion-exchange process, when compared to the respective precursors, reflecting successive displacement of the inserted organic molecule in the inorganic matrix. The favorable exchanging mechanism reaction seems to be associated with the diffusion of the cations inside the intercalated lamellar compounds.