Sorption of 2,2′‐bipyridine on clays and oxides

The sorption of 2,2′‐bipyridine onto some clays and oxides was studied as a function of concentration, pH, time and the exchangeable cation of the clays. The reaction was found to include both physical, cation exchange, and chemisorption, was irreversible and multilayered at high concentrations. The sorption was also pH dependent attaining a maximum in the pH range 4.5 to 5.5 depending on the sorbent; this dependence was attributed to chemisorption. The maximum in sorption was observed to take place above the pH value where the molecular form is the only bipyridine species present in solution thus indicating its preference by the sorbents over the positive species. Chemisorption, ion exchange against metalic cations and molecular aggregation on the surface are the factors thought to be responsible for the desorption of bipyridine at pH values beyond that at the maximum sorption.