Tiny culprits behind mighty Taj Mahal’s decay
doi:10.1038/nindia.2019.104 Published online 7 August 2019
Scientists have identified a key reason behind the degradation and discoloration of the marble surface of the Taj Mahal in Agra — carbon particulates of the nano scale1.
Through a careful examination of the black crust on the historic building’s marble surfaces, the scientists have revealed the presence of carbon particulates including carbon nano-tubes, graphene oxide and nano-carbon dots.
Their finding could help in the preservation of the 17th-century monument of love, a tourism hotspot.
The researchers used modern physico-chemical approaches to examine the Taj Mahal's surface. The report says that the high chemical activity of the nano carbons — in the presence of air and sunlight — generates several reactive oxygen species (ROS). These ROS are capable of responding to complicated chemical reactions on the surface of the marble in association with other deposits of plant origin and atmospheric aerosol containing microbial species. Such reactions cause the rapid degradation.
Also, the readily available gaseous nitrogenous pollutants produced by auto exhausts and refineries, when reacting with ROS, "produce reactive nitrogen species (RNS) capable of destroying marble surfaces, inflicting permanent damage to the Taj Mahal", the report says.
The presence of nano carbon dots smaller than five nanometres in the black crust were "clearly visualized in the TEM (transmission electron microscopy) images", the authors say, adding that a clear strategy was needed to prevent the further accumulation of such reactive species on the surface of the monument.
Meanwhile, a massive tree plantation in the nearby area, with frequent monitoring, maintenance, and restoration of the affected marble surface, "would be the only viable option to add life span to the monument", they say.