Antifouling nanodevices for the development of an innovative multifunctional coating

Abstract

Most historical buildings and monuments, that are a seamless part of our urban landscape, use natural stone as the main construction material and are subject to a deterioration process. In particular, the urban environment determines and accelerates the deterioration of outdoor surfaces, due to pollution and high concentration of fine particulate. In addition, biotic factors, e.g. microorganisms, are among the most common agents of stone damage. Given the large number and the different nature of the degradation processes, finding a solution to the deterioration of stone materials is a challenging issue. For this reason, the maintenance of outdoor stone materials and ornamentation requires an enormous investment both in terms of time as well as in terms of funding, along with specific need for a continuous update of the restorers’ know-how and skills. This thesis deals with the biodeterioration of stone materials, and proposes innovative solutions for the reduction of the environmental impact, which increase the effectiveness of the restoration treatments over time. In detail, the realization of a self-cleaning coating with antifouling properties is pursued. A hybrid nanocomposite coating, containing TiO2 nanoparticles and two different kinds of silica nanocontainers with antifouling properties, is realized, characterized and tested. The first part of the thesis reports the synthesis and the optimization of the empty of silica nanocontainers with core-shell structure, namely nanocapsules (Si-NC). In particular, the influence of the synthesis parameters, such stirring condition and dripping methods of the silica precursor, on the size and the textural properties of the final nanocapsules is analyzed. Conversely, the synthesis protocol of mesoporous silica nanoparticles (Si-MNP) was already established [112], but the application to the in situ entrapment of the active compounds (e.g. biocides), to the best of our knowledge, has not been reported so far. After the optimization and the characterization of the both empty silica nanocontainers, the encapsulation and the in situ entrapment of a commercial biocide (2-mercaptobenzothiazole) was explored. Special attention was addressed to understand how the biocides molecules are confined in the two different silica nanosystems. Successively, the synthesis conditions to encapsulate two environmentally-friendly biocides (the zosteric acid sodium salt and the usnic acid) were explored. The aim was to minimize the release in the environment of low eco-compatibility compounds: on one side using the technology of the silica nanocontainers to control the release over time and to increase the efficacy of the treatment, on the other side applying the environmentally-friendly biocides. The effects of each active compound on the two different silica nanocontainers will evaluate not only from the morphological point of view, but also from the textural and the structural point of view. At the end, in order to evaluate the role of nanoparticles in the determination of coating properties, the addition of different amount of the two silica nanosystems and TiO2 nanoparticles into a non commercial coating formulation were tested.