Ozone-loaded bacterial cellulose hydrogel: a sustainable antimicrobial solution for stone cleaning

The use of biocide-loaded hydrogels has recently been exploited for cleaning the biological attacks of cultural heritage and architectural stone materials. However, considering the drawbacks of traditional biocides, and the high costs of synthetic polymers, growing research for innovative and sustainable solutions are taking place. The aim of this work is to explore a bacterial cellulose (BC) hydrogel functionalized with ozone as a renewable, biodegradable, and easy-to-use antimicrobial remedy for stone biodeterioration. The BC microstructure was characterized by Field Emission-Scanning Electron Microscopy observation and high crystallinity was detected by X-ray diffraction analysis. Ozonated BC (OBC) hydrogels were tested against selected biodeteriogenic microorganisms in water suspension abolishing their viability, with its complete suppression after a 10-min and a 24-h treatment with OBC, for bacterial and fungal spores, respectively. Furthermore, the OBC was assessed on contaminated marble, brick, and biocalcarenitic stone specimens for simulating in situ conditions. A 100% reduction of microbial viability after a 24-h treatment was obtained. Successively, the shelf-life of the hydrogel and the antimicrobial activity were also evaluated after 30 days, demonstrating a subsequent cleaning efficiency along time. This research highlights the potential of the new ozonated BC hydrogel as a green and highly effective antimicrobial treatment, with advantages in sustainability.