Properties of methylene blue in the presence of zeolite nanoparticles

Abstract

The interactions between methylene blue (MB) and zeolite nanocrystals in water suspensions are investigated. The zeolite nanocrystals (diameter of 40–70 nm) with BEA-, LTL- and LTA-type framework structures with pore size of 7.3, 7.1 and 4.1 Å, respectively, are chosen to evaluate their effect on the stabilization of the MB (7.0 × 16 Å) in their pores and on the crystals surface. It is found that the MB molecules enter the channels of the LTL-type zeolite nanocrystals, while the BEA-type zeolite is partially filled by the MB due to the presence of organic agent (tetraethylammonium cations) in the channels. The highly hydrophilic surface of the LTA-type nanocrystals with pore size smaller than the size of MB is strongly modified, but no MB molecules in the LTA-zeolite channels are present due to pore size restriction. The UV-vis characterization of the suspensions containing zeolite nanocrystals and MB (samples LTL-MB, BEA-MB and LTA-MB) reveal a shift in the absorption maximum (581 nm) with 16.5 nm for BEA, 15.5 nm for LTL, and 13.5 nm for LTA zeolite crystals. The absorption maximum in the three suspensions shifts to shorter wavelengths (blue shift) with time, and only the LTA-MB sample returns to 581 nm after 8 minutes that corresponds to the original wavelength of the free MB molecule in water. The observed blue shift for samples BEA-MB and LTL-MB is explained with the penetration and stabilization of MB molecules in the zeolite pores. The zeolite nanocrystals in the presence of MB show high stability in water suspensions, which make them a promising matrix for preparation of water-soluble photopolymers. Photopolymers for full colors holography with expanded wavelength sensitivity range based on addition of more than one sensitizer (MB, erythrosine B and acriflavine stabilized in zeolite nanocrystals) are under development.