Pilot study on sustainable antimicrobial chitosan-membranes for stone conservation: efficacy of natural compounds on baroque limestones from southeastern Sicily

This study investigates the development of chitosan-based membranes enriched with limonene and thymol as eco-friendly biocidal agents for the conservation of stone in Cultural Heritage. The membranes were characterized through spectroscopic, morphological and wettability analyses to assess the incorporation of the active compounds and their impact on structural and surface properties. Antimicrobial performance was evaluated in vitro against Escherichia coli and by applying the membranes to artificially inoculated limestone samples from southeastern Sicily (Southern Italy). Results showed that both the chemical nature and concentration of the additives significantly influenced membrane performance. Thymol-enriched membranes exhibited stronger and dose-dependent antimicrobial activity compared to limonene-based systems. Moreover, the petrophysical characteristics of the stone substrates affected treatment efficacy, highlighting the importance of material compatibility. Overall, the findings highlight the potential of chitosan membranes incorporating natural compounds as sustainable alternatives to conventional biocides and provides a basis for future in situ applications in stone conservation.