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Nowe metody syntezy pigmentów ultramarynowych z użyciem zeolitów

Jankowska A., Kowalak S.

Wiadomości Chemiczne

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2008

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[Z] 62, 7-8

659-682

EN

The natural ultramarine (lazurite, lapis lazuli) has been known and valued since the ancient times as semiprecious gem applied for jewelry, artistic works, decoration and painting. In Middle Ages it was used as excellent, but very expensive pigment. At the beginning of the nineteenth century a method of synthesis of artificial ultramarine has been discovered and it soon became a common inexpensive commercial product applied mostly for production of paints and as an optical brightener. The procedure included heating of the substrate mixtures (kaolin, sulfur, sodium carbonate, reducing agent) in kilns at high temperature (800°C). The technology of ultramarine production has not been substantially changed up to now, whereas the law regulations concerning environment protection imposed in the twentieth century could not accept a serious air pollution (SO2, H2S) always accompanying the production process. Therefore, searching for novel, environmentally friendly procedures becomes challenging. Ultramarine is an aluminosilicate with sodalite structure that contains sulfur anion-radicals (mostly •S3-) combined with Na+ cations embedded inside ?-cages. The sulfur radicals play a role of chromophores (•S3- blue, •S3- yellow). Sodalite is a zeolite and the sodalite units (?-cages) are constituents of structure of several zeolites (LTA, FAU, LTN, EMT). The use of zeolitic structures for encapsulation of sulfur anion radicals appeared very promising. The direct introduction of sulfur radicals from aprotic solutions of oligosulfides [27] was not successful but the thermal treatment of zeolites mixed with sulfur radical precursors (NaSn, S + alkalis) resulted in colored products analogous to ultramarine [24-26, 30, 31]. Zeolites A seem the most useful for preparation of sulfur pigments but other zeolites can be applied as well. The products of various colors (yellow, green blue and sometimes pinky) and shades can be obtained by choosing appropriate zeolite, radi-cal precursor, kind and content of alkaline cation in the initial mixture, temperature (400-800°C) and time of treatment. It was found that zeolite structure can be maintained upon the thermal treatment or it can be transformed (mostly towards SOD) under highly alkaline thermal treatment. The sulfur radicals can also be embedded inside smaller than ?-cages (e.g. CAN) which favors a generation of smaller radicals (i.e. •S2-) [39-42]. It is also possible to incorporate the sulfur compounds into zeolites during their crystallization and then a generation of radical upon heating. The sulfur pigments based on non aluminosilicate matrices (e.g. AlPO4-20) can be also obtained [38, 53]. Generally use of zeolites allows to obtain ultramarine-like pigments with broad range of colors under much milder than conventional conditions and with much lower emission of polluting agents.

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Application of the Molecular Sieves as Matrices for Chromophores Embedded in Their Cages

Kowalak S., Jankowska A.

Polish Journal of Chemistry

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2008

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Vol. 82, nr 1-2

131-140

EN

Zeolite matrices have been applied for embedment of sulfur radical chromophores inside the intra-crystalline cages. The thermal treatment of zeolites (200–800 graduate C) with sulfur radical precursors (oligosulfides, elemental sulfur and alkalis) led to colored products. Their coloration (yellow, green, blue) and structure depended on structure type of parent zeolite (LTA, FAU, SOD, ERI, CAN, GIS, STI, CHA, HEU), alkalinity of the initial mixture, temperature and time of thermal treatment. Synthesis at high temperatures under high alkalinity of mixtures always resulted in recrystallization of parent zeolites towards sodalite, whereas the mild preparation conditions did not affect the original structures of zeolites. Employing of zeolites as starting materials allows to extend the palette of achievable colors of ultramarine pigments.

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Theoretical studies on sulfur-containing radical ions

Carmichael I.

Nukleonika

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2000

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Vol. 45, nr 1

11-17

EN

Structures and properties are reported for pi-radical cations and for sigma-radical cations and anions, containing SS, SN and SO odd-electron bonds, from a variety of ab initio molecular orbital techniques and Density Functional Theory (DFT). Characteristic frequencies and absorption bands are determined to aid in the assignment of transient vibrational and optical spectra detected in pulse radiolysis experiments. Hyperfine coupling tensors are evaluated to facilitate the identification of these radicals by EPR spectroscopy. By comparison with predictions from accurate coupled-cluster based calculations in some simple model systems, DFT is shown to have difficulties in correctly describing the electronic structure of these radical ions. Useful linear relationships are uncovered between the computed lenght of the odd-electron bond and both the wavelenght of maximum optical absorption and the bond stretching frequency.