Ion Exchange in Geopolymers

Geopolymers have been widely used for construction and building materials. Nevertheless, some other applications have been found from their ability to be ion exchanged. An example is the encapsulation of heavy metals, but some others involve the ion exchange of the aluminosilicate structure to form photoactive particles or to link copper ions. In this chapter, we summarize some of the properties which make aluminosilicate inorganic polymer (geopolymers) ion exchangeable: the synthesized temperature, its effect over their porosity and their stoichiometric nature. Also, the effects of ion exchanging a geopolymer with an NH4+Cl, (NH4)2TiO2(C2O4)2 and (CH3)4N+Br are presented. The geopolymer was characterized by FT-IR, XRD, BET and MAS NMR, showing how a 100% of replacement was achieved for NH4+Cl. On the contrary, the efficiency was reduced in (NH4)2TiO2(C2O4)2 and (CH3)4N+Br, effect ascribed to the fact of the molecular size that did not allow the counterions to reach the aluminum atoms in the geopolymer. Finally, the procedure followed to ion exchange a metakaolinite-based geopolymer is described, and the potential applications related are presented