Indigo@Silicalite: a New Organic−Inorganic Hybrid Pigment

In the search for stable and enduring organic colors, we have combined indigo, a historical and industrially important chromophore, with silicalite, the MFI zeolite. The resulting pigment presents high color durability against most external agents (e.g., light, temperature). This stability and its physical properties are explained by the association of indigo with an inert mineral, which is also influenced by formation conditions such as the initial indigo concentration and the thermal treatment. The formation of the indigo@silicalite hybrid, particularly diffusion of the organic molecule, is monitored by optical spectroscopies, thermogravimetric measurements, and X-ray diffraction. Color stability is attested when indigo enters the pores of the zeolitic host, thus forming a new pigment with characteristics similar to those of Maya Blue. This opens the way to the low-cost engineering of metal-free, nonhazardous pigment powders based on indigoid and other dyes.