A density functional theory (DFT) investigation of how small molecules and atmospheric pollutants relevant to art conservation adsorb on kaolinite

Abstract

The physio-chemical properties of the clay mineral kaolinite – the main component of porcelain – play a vital role in understanding how a porcelain object interacts with its environment. Understanding these interactions is imperative for the development of non-destructive yet effective conservation methods to preserve, treat, and restore porcelain objects of cultural heritage importance. To gain insight into the surface properties and behavior of kaolinite across a wide range of environments, we use density functional theory (DFT) to probe how a representative set of small molecules and atmospheric pollutants interact with a native kaolinite (001) surface, both in vacuum and with explicit hydration. By investigating selected atmospheric pollutants, acids, and sodium salts under different conditions, we identify the scenarios that are most disruptive to the native kaolinite surface. Specifically, we demonstrate that protic acids and sodium salts generally interact with the surface more strongly than common small molecule pollutants. Our results also indicate that adsorbates containing a central sulfur atom with a positive oxidation state are particularly deleterious to the kaolinite surface. Furthermore, to explore the interactions between a fired or partially fired porcelain object and relevant chemicals, we also model a partially dehydrated kaolinite surface and probe its interactions with three selected adsorbates. The trends elucidated throughout this study allow us to suggest a series of guidelines for the care of porcelain objects.