Use of geopolymers as tunable and sustained silver ion release mediums

Silver was incorporated up to 3.4% (w/w) into the geopolymer structure via precipitation as Ag₂O by dispersing the geopolymer powder in an aqueous solution of AgNO₃. The precipitates were mainly located in the fine pores within the nanoparticles of the geopolymer network. The fine pores enabled the formation of very fine precipitates, mainly between 2 and 5 nm. The silver-incorporated geopolymer was found to have a sustained Ag⁺ release that can be tuned down by a thermal treatment, e.g., calcination. The Ag⁺ release amount could be reduced by about 30-fold after calcination at 850 °C. Calcination reduces the specific surface area, causes shrinkage, and makes the geopolymer structure less pervious. The size of the precipitates remains stable even up to 1050 °C, despite a large amount of sintering-related shrinkage. These results suggest that geopolymers could be a tunable Ag⁺ source for various antibacterial applications.