Waste glass-derived tobermorite carriers for Ag+ and Zn2+ Ions

In this study, the layer-lattice calcium silicate hydrate mineral, tobermorite, was synthesized from waste green or amber container glass and separately ion-exchanged with Ag+ or Zn2+ ions under batch conditions. Hydrothermal treatment of stoichiometrically adjusted mixtures of waste glass and calcium oxide in 4 M NaOH(aq) at 125 °C yielded tobermorite products of ~75% crystallinity with mean silicate chain lengths of 17 units after one week. Maximum uptake of Zn2+ ions, ~0.55 mmol g-1, occurred after 72 h and maximum uptake of Ag+ ions, ~0.59 mmol g-1, was established within 6 h. No significant differences in structure or ion-exchange behavior were observed be-tween the tobermorites derived from either green or amber glass. Composite membranes of the biopolymer, chitosan, incorporating the original or ion-exchanged tobermorite phases were pre-pared by solvent casting and their antimicrobial activities against S. aureus and E. coli were evalu-ated using the Kirby-Bauer assay. S. aureus and E. coli formed biofilms on the surfaces of pure chitosan and chitosan blended with the original tobermorites; whereas, the composites containing Zn2+-substituted tobermorites defended against bacterial colonization. Distinct clear zones were observed around the composites containing Ag+-substituted tobermorites which arose from the migration of the labile Ag+ ions from the lattices. This research has indicated that waste glass-derived tobermorites are functional carriers for antimicrobial ions with potential applications as fillers in polymeric composites to defend against the proliferation and transmission of patho-genic bacteria