Silver nanoparticles in building materials for environment protection against microorganisms

Gypsum and grout are finishing materials found in almost all constructions. Specifically, gypsum has been widely used because of its low cost in the composition of drywall. However, in humid environments, they are susceptible to microorganism infestation. In this work, silver nanoparticles (Ag-NPs) were incorporated to gypsum (643 and 321 ppm) and grout (227 ppm) and the antimicrobial activity tested. The MIC value for Ag-NPs solution was 26.8 µg ml⁻¹ for Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli and 428 µg ml⁻¹ for the A. Niger. Another MIC test with specimen component dilutions indicated that grout and gypsum do not exhibit antibacterial activity against S. aureus. However, when incorporated with Ag-NPs, both grout and gypsum demonstrate growth inhibition. In a biofilm test performed with S. aureus, SEM images revealed crenation of bacteria in contact with specimens containing Ag-NPs. The addition of Ag-NPs causes change in color that was measured through CIELAB (International Commission on Illumination) color coordinates. There is no difference in the L value parameter (lightness) for all materials tested. However, the comparison between the parameters a (green–red coordinate) and b (blue–yellow) for gypsum and grout results in a statistically significant difference (p < 0.05, Kruskal). The values of b increase as the Ag-NPs concentration increases because of the yellowish coloration of the solution. It can be concluded that Ag-NPs can be incorporated to gypsum and grout, maintaining its antimicrobial feature improving the material properties, which can benefit health and the environment.