Adsorption kinetics of acetic acid into ZnO/castor oil-derived polyurethanes.

The presence of a two-steps mechanism for AcOH uptake by the hybrids was demonstrated for the first time: a combination of Fickian diffusion and Case-II transport occurs in the COP matrix, and adsorption dominates acid uptake (followed by neutralization) at the particles surface. This mechanism is likely key to explain the enhanced performances of the hybrids vs activated charcoal and state-of-the-art tools to remove AcOH. The hybrids have high uptake capacity, and lower activation energies for the removal process than materials where the uptake of acid relies solely on adsorption. The size of the ZnO particles contributes to the process, i.e. nanoparticles form smaller and ramified fractal clusters that are able to adsorb AcOH more effectively than microparticles. These insights demonstrated the efficacy of the novel hybrids in art conservation, where the control of minimal concentrations of VOCs is crucial for the preventive conservation of masterpieces, and can be useful to other fields where efficient capture of acetic acid is critical (food industry, textile dyeing/printing, etc.).