Tuning the Dimensionality of Nano Ca(OH)₂ with Surfactants for Wall Painting Consolidation

As an effective conservation material for wall paintings, ancient paper, and stone artifacts, nano Ca(OH)₂ has been studied for more than two decades. However, the synthesis methods are expensive, complex, time-consuming, or require considerable energy. To tackle the issue, we report, in this study, a facile, large-scale, time saving, and economical method for synthesizing nano Ca(OH)₂ (∼90 nm) at room temperature. This is achieved by controlling crystal growth of Ca(OH)₂ at the (1010) facet (vertical direction) and (0001) facet (horizontal direction) with simultaneous addition of octyl phenyl polyoxyethylene ether (OPPE) and dimethylformamide (DMF) in the reaction. Density functional theory (DFT) calculations revealed that the crystal dimensionality tuning is caused by attaching OPPE to the (0001) facet and DMF to the ((Formula presented.)) facet of Ca(OH)₂. Experimental results showed that the synthesized nano Ca(OH)₂ has higher stability and carbonation degree than commercial Ca(OH)₂ and was used for consolidating a 1300-year-old tomb painting, which is a very important, precious, and heavily damaged national treasure of China. The results demonstrate that the nano Ca(OH)₂ shows excellent penetration into the painting, considerably improves the strength of the painting, and has no side effects on the color, pore distribution, and porosity of the painting. Our work will significantly facilitate the industrial production of nano Ca(OH)₂ and its application in cultural heritage conservation.