The Incorporation of Indigo Molecules in Sepiolite Tunnels

Abstract

Evidence for access of molecules the size of acetone or pyridine to the intracrystalline tunnels of nanofibre clay (sepiolite) has indicated formation of a new type of organic-inorganic nanocomposites. However, the introduction of larger molecules has been a recurring problem. It is now agreed that for indigo, the molecules are located on the external surface and at the ends of the fibres, thus blocking access to internal tunnels. We claim, however, that it is possible for indigo molecules to access the internal channels of sepiolite. FTIR and XRD analyses have provided evidence for folding of the sepiolite structure preheated at high temperature (above 350 degrees C). By comparison, we have shown that for indigo/sepiolite mixtures treated in the same conditions, no change in the crystalline structure of the sepiolite is observed, and that blue samples, related to Maya blue, with indigo molecules incorporated deeply enough into sepiolite to prevent folding of the tunnels, can be obtained. NMR, FTIR and thermal analysis confirm the interaction of indigo with the water coordinated to magnesium(II) and located inside the internal and external channels of sepiolite. Two other hypotheses are excluded; we show both that zeolitic water is not blocked in the tunnels by indigo, and that if thermal decomposition products of indigo can be formed, they are in a minority.

Diffusion Of Indigo Molecules Inside The Palygorskite Clay Channels

“…This observation strongly suggests that the folding of the clay is hindered in the presence of indigo. Such a prevention of folding due to the presence of indigo molecules into clay channels for an indigo@sepiolite hybrid 42 was reported by Ovarlez et al To our knowledge, this is the first time that this aspect 13/07/2012 is also shown for palygorskite. The long range structure of the palygorskite clay is thus affected by the presence of indigo, which is in agreement with the presence of the organic dye inside the channels of the clay.…”

“…Signet non défini., 31 . Transformation of indigo into an intermediate oxidized form, the dehydroindigo, has also been introduced 32,42 with possible bonding between nitrogen of the organic dye and aluminum site of palygorskite 33 . This study focalizes onto the dehydration/rehydration process and the structural evolution of the palygorskite clay in the absence and the presence of the indigo molecule.…”

Asbestiform sepiolite coated by aliphatic hydrocarbons from Perletoa, Aosta Valley Region (Western Alps, Italy): characterization, genesis and possible hazards

“…Data are consistent with previous works (Cannings, 1968;Hayashi et al, 1969;Mendelovici, 1973;Nagata et al, 1974;Prost, 1975;Mendelovici and Portillo, 1976;Post, 1978;Myriam et al, 1998;Frost et al, 2001;Jung and Grange, 2004;Ovarlez et al, 2009;Giustetto et al, 2010;Giustetto et al, 2011b;Bukas et al, 2013). Attribution of vibrational modes and related evolution with T rise are summarized in Table 3.…”

“…6) are consistent with previous works (Nagy and Bradley, 1955;Brauner and Preisinger, 1956;Martin Vivaldi and Cano Ruiz, 1956;Caillère and Hénin, 1957;Preisinger, 1959;Hayashi et al, 1969;Nagata et al, 1974;Rautureau and Mifsud, 1977;Ruiz et al, 1996;Weir et al, 2002;Hubbard et al, 2003;Ovarlez et al, 2006Ovarlez et al, , 2009. Although in sepiolite correlations between TGA features and structural changes are not straightforward nor partitioning among different kinds of water so strict (Mifsud et al, 1987), reasonable interpretations can be sketched.…”

“…Presence of the 3680 and 3674 cm -1 modes in the outgassed spectrum at 150 °C (pattern 4 in Fig. 7; Table 3) accounts for coexistence of folded and unfolded portions of the structure (Jung and Grange, 2004;Ovarlez et al, 2009). Furthermore, a broad signal appears at 3423 cm -1 which merits further discussion.…”