Environmentally friendly ZnO/Castor oil polyurethane composites for the gas-phase adsorption of acetic acid.

Acetic acid, a common pollutant present in museums and art galleries, can irreversibly damage works of art. Herein, a sustainable and scalable synthesis of zinc oxide-castor oil polyurethane hybrids (ZnO/COPs), to be used as acetic acid removers in the preventive conservation of Cultural Heritage, is reported. The adsorption capacities of ZnO/COPs were studied in saturated acetic acid atmosphere, at low acetic acid gas concentration, and inside a wooden crate (naturally emitting acetic acid) representative of those used in the storage deposits of museums and art collections. Upon exposure, acetic acid interacts with the castor oil polyurethane and diffuses to the surface of ZnO particles where is stably fixed as zinc acetate crystals. Zinc acetate domains form homogeneously on the surface and are distributed evenly within the ZnO/COPs, thanks to weak interactions between the polyurethane matrix and acetic acid that favour the transport of the acid up to reach the zinc oxide surfaces, resulting in a synergistic effect. The ZnO/COPs composites showed significantly enhanced adsorption capacities of acetic acid surpassing those of the activated carbon benchmark, with the advantage of being easily handled and movable, without the health issues and risks associated to the use of non-confined micro/nano-powders.

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Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.