Mayan inspired nanocomposite materials: An overview

Maya Blue is a famous pigment used by ancient Mayas, renowned for its stability, formed after a heatinginduced encapsulation and bonding of the indigo dye inside the nano-tunnels crossing the structure of the clay mineral palygorskite. Such a discovery led to an inspiration: if Mayas made it blue, someone else could have made it any other colour! Some red dyes were thus complexed with palygorskite so to check, using a multi-analytical approach (including molecular mechanics, UV-Vis, FT-IR and SER spectroscopies and TGA-GC-MS), whether the ensuing compounds might have shown physical/chemical features similar to their notorious 'blue brother'. Two of the tested dyes gave notable results. When alizarin is grafted on palygorskite, a composite is formed that changes colour (orange-to-purple) after pH variations. Methyl red forms instead a stable red/purple complex with palygorskite, suffering no colour change despite severe acid/alkali attacks. Surface interactions form between alizarin and palygorskite, thus allowing the dye to maintain its sensitivity (and colour change) with pH. Conversely, methyl red can diffuse and bind in the clay nano-pores, forming supramolecular host/guest interactions responsible for the composite stability.