Polydopamine-Modified Nanolime with High Kinetic Stability in Water for the Consolidation of Stone Relics

As a promising inorganic nanomaterial for the conservation of arenaceous sandstone-based relics such as wall painting, ancient building, stone heritage etc., nanolime (NL) has drawn increasing attention in recent years. Usually, NL needs to be dispersed into an alcoholic solution when applied. Nevertheless, a back-migration phenomenon of NL to the surface of the stone and delayed carbonation of NL enabled by alcohol do not guarantee good preservation effects. Dispersing NL into water can avoid the above issues. However, NL water suspension shows extremely poor kinetic stability, greatly restricting the penetration of NL into stone relics as well as bringing unfavorable impacts to the treated stone heritage. Here, we develop a facile method to synthesize polydopamine (PDA)-modified NL (PDA@NL). Characterizations demonstrate that PDA is uniformly distributed on the surface of NL particles though hydrogen bonds. In addition, the presence of PDA reduces the size of NL particles and achieves the highest specific surface area of NL reported to date. More importantly, water suspension of PDA@NL is far more stable than that of pure NL. The kinetic stability mechanism of PDA@NL in water is attributed to the lessened spatial interactions between NL particles, which is realized by the coverage of PDA on the surface of NL particles. Furthermore, the coverage of PDA does not inhibit carbonation. Within 105 h, NL in PDA@NL completes carbonation and obtains 93.7% calcite, which is comparable to that of NL suspension. Permeability tests prove that the PDA@NL suspension penetrates far deeper through stone specimens compared with the NL suspension. Additionally, PDA@NL presents good consolidation performances for stone samples. Our work opens a new direction for the modification of NL that will boost the studies of NL-modified materials as well as the conservation of cultural heritage.