Aldona Jankowska

Application of zeolites as matrices for pigments

Abstract Zeolites A mixed with various sodium polysulfides form ultramarine analogs of different colors upon thermal treatment. The resulting colors reflect the contribution of sulfur radical chromophores (mostly S 3 − and S 2 − ) and can be modified by choosing the polysulfide of adequate S chain length and by the conditions of thermal treatment. In some products the original LTA structure is retained. In the other cases (particularly when alkalinity of the mixture is increased) the transformation towards SOD takes place. Some natural zeolites (e.g. chabazite) have been used as starting material for the synthesis of ultramarine analogs of the SOD structure.

Structure and dynamics of S3− radicals in ultramarine-type pigment based on zeolite A: Electron spin resonance and electron spin echo studies

X-band electron spin resonance (ESR) spectra of S(3)(-) radicals in ultramarine analog (pigment) prepared from zeolite A and maintaining the original structure of parent zeolite were recorded in the temperature range of 4.2-380 K. Electron spin echo experiments (echo detected ESR, electron spin-lattice relaxation, and spin echo dephasing) were performed in the temperature range of 4.2-50 K. The rigid lattice g factors are g(x) = 2.0016, g(y) = 2.0505, and g(z) = 2.0355, and they are gradually averaged with temperature to the final collapse into a single line with g = 2.028 above 300 K. This is due to reorientations of S(3)(-) molecule between 12 possible orientations in the sodalite cage through the energy barrier of 2.4 kJ/mol. The low-lying orbital states of the open form of S(3)(-) molecule having C(2v) symmetry are considered and molecular orbital (MO) theory of the g factors is presented. The orbital mixing coefficients were calculated from experimental g factors and available theoretical orbital splitting. They indicate that the unpaired electron spin density in the ground state is localized mainly (about 50%) on the central sulfur atom of S(3)(-) anion radical, whereas in the excited electronic state the density is localized mainly on the lateral sulfur atoms (90%). A strong broadening of the ESR lines in directions around the twofold symmetry axis of the radical S(3)(-) molecule (z-axis) is discovered below 10 K. It is due to a distribution of the S-S-S bond angle value influencing mainly the energy of the (2)B(2)-symmetry MO. This effect is smeared out by molecular dynamics at higher temperatures. A distribution of the g factors is confirmed by the recovery of the spin system magnetization during spin-lattice relaxation measurements, which is described by a stretched exponential function. Both the spin-lattice relaxation and electron spin echo dephasing are governed by localized phonon mode of energy of about 40 cm(-1). Thus, the anion-radical S(3)(-) molecules are weakly bonded to the zeolite framework, and they do not participate in the phonon motion of the host lattice because of their own local dynamics.

Transformation of zeolite structures during synthesis of ultramarine analogues

XRD and IR analyses were applied to study the thermal synthesis of ultramarine by structural transformation of zeolites reacting with sulphur under alkaline conditions. Zeolites A, X and cancrinite are transformed to sodalite at high temperature (800°C) under highly alkaline conditions when sodium is the only alkali cation present. The original structure of the parent zeolites can be retained (particularly at low temperature) when the alkalinity is low. Other structures such as nepheline hydrate II, carnegieite, kaliophilite are detected in the coloured products obtained either at intermediate alkalinity or through the introduction of cations other than sodium into the reaction mixture.

Spontaneous crystallization of zincophosphate sodalite by means of dry substrate grinding

Zincophosphate sodalites can be obtained by simple grinding of the substrate salts [ZnCl2, Zn(NO3)2, Na2HPO4, Na2CO3] in a mortar, provided that at least one of the applied salts contains crystallization water.

Cesium Bearing Ultramarine Prepared From Zeolites

Abstract Pigments analogous to ultramarine with various colors including pink have been prepared mainly from zeolites A and also from X by a thermal treatment with sulfur and various amounts of Cs 2 CO 3 . The bulky Cs + cations introduced into zeolites reduce markedly a size of their pore openings and that of inner voids and subsequently affect the type and distribution of generated sulfur chromophores. It is likely that the chromophores in cesium-rich samples occupy rather the shrunken voids of α-cavities but not the sodalite units.

Spontaneous crystallization of zincophosphate sodalite and its modifications

The following study is a continuation of our research on spontaneous synthesis of sodium zincophosphate sodalite by a simple grinding of the substrate components ( e.g. , ZnCl 2 or Zn(NO 3 ) 2 , Na 2 HPO 4 , Na 2 CO 3 ). Rapid crystallization was used for the encapsulation of some substances (elemental sulphur, CdS, KBr, pyridine, hydroquinone) during sodalite structure formation. Attempts to increase the thermal stability of the resulting sodalite by adding some silicon or tin to the starting mixture brought about only a moderate improvement. The synthesis of potassium or ammonium derivatives of zincophosphate did not result in a sodalite structure.

Embedment of Methylene Blue in natural and synthetic phillipsite

Abstract Phillipsite was crystallized from a high siliceous aluminosilicate mixture containing Zn cations and methylene blue (MB). The presence of MB did not affect the crystallization, but it resulted in a substantial amount of dye being anchored to the zeolite, despite its narrow channels. Dye-free synthetic phillipsite modified with MB solution showed markedly lower dye content, which, however was considerably higher than those in the MB-treated natural phillipsite and mordenite. The ultra violet/visible (UV-vis) spectra of the dye-modified synthetic phillipsites indicated the presence of MB monomers and oligomers, whereas the spectra of the modified natural zeolites showed protonated MB also. The electron spin resonance spectra of samples crystallized with MB indicated the presence of paramagnetic species.

Inorganic Sulphur Pigments Based on Nanoporous Materials

Publisher Summary This chapter examines the use of zeolites and other molecular sieves for preparing sulfur pigments analogous to ultramarine. The conventional procedure with kaolin as a starting material can be supplemented by syntheses based on zeolites. The syntheses can be conducted in a broad range of temperatures including relatively low ones. Much lower (compared to kaolin) content of sulfur (or sulfur compounds) in mixture with zeolites suffices to obtain the products of intense colouration. The sulfur radical precursors can be introduced into zeolites either during their hydrothermal crystallization in the presence of sulfur compounds or during thermal treatment of zeolites mixed with sulfur (together with alkalis) or alkali sulfides. The thermal treatment of zeolites with radical precursors results in the formation of coloured products with maintained zeolite structures if low temperatures and low alkalinity of mixtures are applied. More drastic conditions always cause the structure transformation toward sodalite, provided that sodium is the only, or a very prevalent alkali cation in the mixture. Lack or deficit of Na cations results in recrystallization toward other structures. The application of zeolites allows to attain a broader range of product colours than during conventional synthesis from kaolin and substantially lowers the emission of polluting gases. The cations introduced into zeolites or applied as alkali sources influence the structure and coloration of the products. The sulfur pigments obtained from zeolites are more susceptible than the conventional ultramarine for a post-synthesis treatment with cations which results in a colour modification.

Modification of zincophosphate sodalite with silicon

Abstract We have found that the spontaneous crystallization of zincophosphate sodalite [1,2] from the mixture of substrate solutions at low temperatures can be simplified even more and the SOD structure can be achieved only by plain grinding of the substrates in the mortar. The crystallization water, however, must be present in at least one substrate salt to make the synthesis possible. Some molecules can be encapsulated in the β-cages during the instant synthesis. Since the zincophosphate sodalite is thermally unstable, attempts have been undertaken to increase its stability by means of introducing some silicon into the structure. The syntheses were conducted both with solutions of the substrates as well as by the grinding of solid salts. The modification with sodium silicate or H 2 SiF 6 disturbed the spontaneous crystallization and the structure SOD was attained after a much longer time. The instant syntheses still took place when limited amounts of TEOS (both in the solution as well as in the dry mixtures) were applied. The introduction of some silicone into the SOD structure does not improve the thermal stability very significantly (∼60°C). The larger amounts of silicon compounds introduced into the initial mixture were transformed mostly into amorphous silica.