Alkali-exchanged Y zeolites as superior deacidifying protective materials for paper relics: Effects of accessibility and strength of basic sites

Paper is the most important writing carrier and its degradation (acidification, aging, and ink removal) is a major issue in the protection of cultural heritage. In this work, we first propose alkali ion-exchanged Y zeolites (Ae-Y) as superior deacidification agents for paper. Their features such as the high surface area, adjustable alkali ion content, strength, good structural stability, and safety/non-toxicity or biocompatibility are very promising for preserving paper-based materials, as demonstrated by aging experiments carried out on both historical wood-pulp paper and modern hand-made bamboo paper samples. Through H2O-mediated dispersion of Ae-Y in target paper samples, the pH of the paper can be modified to a neutral or weakly basic state, and can be maintained for a long time even under harsh accelerated aging conditions. Meanwhile, the Ae-Y coating hardly alters the chromatic aberration and water wettability of papers. This new deacidifying agent does not trigger color changes in alkali-sensitive pigments (i.e., does not cause fading or blanching of pigments). Moreover, a systematic evaluation of the structure-performance relationship indicates the important roles of adequate accessible basic sites and controllable and mild basicity of Ae-Y in the long-term deacidification, anti-aging, and anti-fading effects exerted on paper relics. These findings not only shed light on the design of protective materials for paper-based cultural relics but also expand our knowledge on the deacidification and protection mechanisms of zeolites. [Display omitted] •Alkali ion-exchanged Y zeolites are proposed as deacidifying agents for paper.•They may be better alternatives in aqueous phase than generally used MgO and CaO.•Their superior performance is due to adequate accessible and mild basic sites.•The zeolite coatings hardly alter chromatic aberration and wettability of paper.•The zeolite coatings do not cause fading or blanching of alkali-sensitive pigments.