Intercalation compounds of a smectite clay with an ammonium salt biocide and their possible use for conservation of cultural heritage

Ordered intercalation compounds between a smectite mineral clay (montmorillonite, Mt) and the ammonium salt mainly used for stone material disinfection procedures (i.e. N-Alkyl-N-benzyl-N,N-dimethylammonium chloride, shortly known as benzalkonium chloride, BAC), leading to an increase of interlayer distance from 1.3 nm up to 3.4 nm, have been prepared. The used clay/ammonium salt ratios are close to (or higher than) those often used for stone materials disinfection procedures for the conservation in cultural heritage. The prepared intercalated compounds have been studied as for their possible cation release in suitable aqueous media. Mt/BAC intercalate compounds are able to release only a fraction (if any) of the intercalated cations, eventually leading to a stable intermediate intercalate structure with interlayer distance not far from 1.9 nm, with a Mt/BAC ratio roughly equal to 4/1. The overall results indicate that Mt/BAC intercalates are possibly suitable for biocide applications in stone conservation procedures requiring both fast antimicrobial release and long-term biostatic effect.