Indigo/sepiolite nanohybrids: stability of natural pigments inspired by Maya blue

Maya blue is formed from insertion of indigo into palygorskite and sepiolite. Sepiolite and palygorskite are porous fibrous clays. Controlling the insertion, location and organisation of organic molecules in the cavities of nanotubes associated with the release or stability of these molecules is a crucial challenge in the evolution towards unusual properties in nanotechnologies. We validate simple FTIR analyses able to determine the location of indigo in or outside the pores of the fibres. Then, we compare the stability of indigo/palygorskite and indigo/sepiolite systems obtained from similar formulations. The heating treatment is stopped when all indigo is complexed with the clay. We show that in these conditions indigo/palygorskite is more stable than indigo/sepiolite. The formation of stable pigment is more complicated for indigo–sepiolite than for indigo–palygorskite.