No abstract

No abstract

Ion exchange of Na+ ions in a geopolymer by Cs+, NH4+, and Co2+ was used to characterize the accessibility of the inner volume of a Na‐geopolymer (Si/Al 1.8) and the size of the rings controlling the mobility of cations in the geopolymer matrix. Ultraviolet (UV)—visible (vis) spectroscopy of Co2+ ions in the Co2+‐exchanged geopolymer was used to characterize the local geometry of the Co2+ ions and the regularity and shape of local structures accommodating these Co2+ ions in the geopolymer matrix. Na‐geopolymers exhibit ion‐exchange properties similar to those of zeolites. All Na+ ions balancing Al atoms of the network of the as‐prepared geopolymer could be replaced (ion‐exchanged) by NH4+ or Co2+ ions. By analogy to zeolites, this indicates that all the Al atoms are accessible through rings containing at least eight Al and Si atoms. Co2+ ions in the geopolymer network are accommodated in two regular types of deformed six‐membered or eight‐membered rings. As indicated by the lower extent of Cs+ exchange, only one‐half of the Al atoms are simultaneously accessible through 10‐membered or larger rings. This indicates that neither regular alumosilicate six‐membered rings nor the hexagonal prisms typical of some zeolitic structures are present in the geopolymer network.

No abstract

No abstract

No abstract

No abstract

Geopolymers are generally XRD-amorphous materials; however recent research has proved that they contain nanometer particles probably with zeolitic structure. It has also been confirmed in our investigation that sodium in metakaolin-based geopolymer could be easily exchanged for other cations such as ammonium, cobalt, copper etc. Moreover, according to UV-VIS spectra of Co-geopolymer, it has been proven that the local arrangements of Co 2+ -extraframework ions in cationic positions correspond to those known in high-silica zeolites, such as mordenite, ZSM-5 or beta. A similar high level of ion exchange with various ions of transition metals has also been reached for metakaolin-slagbased geopolymers. Accordingly, it could be truly expected that these metal-exchanging geopolymers would show similar properties and potential applications as zeolites, while keeping the advantages of the geopolymers, such as simple synthesis procedure, easy molding into complicated shapes or forming thin highly adhesive layers. These novel applications, such as heterogeneous catalysis for environmental applications and active antibacterial thin coating of metal-geopolymers will be presented and discussed.