Microscopic investigation for the evaluation of atmospheric pressure non-equilibrium plasma technique used to remove contaminants from ancient Chinese murals

Abstract

• Dust and soot are the common deterioration aspects of ancient Chinese murals. • Atmospheric pressure non-equilibrium plasma has the efficiency in removing dust and soot. • The used cleaning parameters of plasma lead to the safe removal of contaminants. • Plasma cleaning causes inevitably damages the black pigment on the mural surface. • The cleaning mechanism of contaminants by the plasma technique is explained. Ancient Chinese murals suffered from long-time contamination, which caused the content of the painting to be unrecognized and the surface quality degradation. However, it is difficult to remove these contaminants on the mural surfaces without any damage to the substrate. Herein, atmospheric pressure non-equilibrium plasma (APNP) cleaning, as a potential tool to conserve and restore cultural heritage, was proposed to eliminate the contaminants on the surface of ancient Chinese murals. The experiments demonstrated that APNP was more suitable for cleaning hydrocarbon contaminants such as soot than dust. The soot containing carbonaceous particles on the mural surface could be removed entirely by APNP and did not cause significant changes to physicochemical properties on the mural interface. We found that critical plasma cleaning time and working distance were crucial for eliminating contaminants and protecting the surface of murals in an actual situation. Meanwhile, reactive molecular dynamics (RMD) simulations were performed to simulate the complex reaction processes of removing soot contaminants by APNP. During RMD simulation, the possible reaction pathway and evolution behavior of chemical bonds of reactive oxygen species dissociating carbonaceous molecules were analyzed. `The increased mobility capacity of atomic oxygen in the system facilitated the cleavage of carbonaceous molecular structures. .