Analysis of interaction between the organic dye methylene blue and the surface of AgCl(I) microcrystals

Abstract

We have used IR spectroscopy to study the nature of interaction between molecules of the organic dye methylene blue (MB) and the surface of AgCl(I) microcrystals. We recorded the IR absorption spectra of the organic dye methylene blue in the gas phase, adsorbed on the surface of AgCl(I) microcrystals, and also in the form of crystal hydrates. The results obtained allowed us to hypothesize that unsaturated dimethylamino groups and the sulfur atom in the heterocycle of this dye are the most active in the interaction between methylene blue molecules and the surface of AgCl(I) microcrystals. With the help of IR spectra of methylene blue crystal hydrates, we confirmed the significant role of OH groups during adsorption of molecules on the surface of AgCl(I) microcrystals. We suggest the possibility of formation of hydrogen bonds between the anions of the crystal lattice and the unsaturated dimethylamino groups as well as the sulfur atoms in the heterocycle, by formation of hydrogen bonds with the OH groups.Introduction. Development of modern optoelectronics has been determined by the possibilities for effective control of the parameters of optical radiation, including its frequency and intensity [1,2]. This is why there is considerable interest in searching for new materials having nonlinear properties that are exhibited even when the material is exposed to weak light fluxes. Heterogeneous systems based on a number of ionic/covalent crystals with adsorbed organic dye molecules occupy a special position among such media. In such systems, we observe sensitized anti-Stokes luminescence, arising when exposed to optical radiation with wavelengths coinciding with the absorption spectra of the adsorbed dye molecules and with low flux density (10 10 -10 15 photons/sec⋅cm 2 ) [3][4][5][6][7][8]. This phenomenon also occurs in microcrystals of AgCl 0.95 I 0.05 solid solutions with adsorbed methylene blue molecules [7]. However, despite the fact that obviously the anti-Stokes luminescence is two-photon in character, the detailed mechanism by which it arises remains controversial; it has been hypothesized that this luminescence is excited as a result of summing of the electronic excitation energy for two adsorbed dye molecules and its subsequent transfer to the crystal according to a cooperative mechanism [3]. One reason for such a situation is the lack of detailed information in the scientific literature about the nature of the interaction between the dye molecules and the surface of ionic/covalent crystals.At the same time, we should point out a number of attempts to establish the type of interaction between organic dye molecules (spectral sensitizer type) and the surface of silver halide crystals [9-16] using IR spectroscopy. For derivatives of benzothiazole and quinoline adsorbed on the surface of AgCl, AgBr, and AgI crystals, results have been obtained suggesting that interaction of these molecules with the surface involves the appearance of a coordination complex with a silver ion [10]. The considerable difference between t...

Mechanism of methylene blue removal from water by swelling clays

“…5. The vibration bands of MB matched well with the published data [36]. Most of the band positions in the wavenumbers of 1100-1700 cm −1 region red-shifted a few cm −1 except the band at 1595 cm −1 which blue-shifted to 1601 cm −1 after MB adsorbed on both minerals (Fig.…”

Fast dye removal from water by starch-based nanocomposites

“…For example, the broad band assigned to the hydrogen-bonded OH groups slightly shifted from 3454 to 4420 cm À1 accompanied by intensity decreasing. We suggest the formation of hydrogel bonds between the sulfur atoms in the heterocycles of MB and the OH groups present in the nanocomposite matrix [57]. Moreover, bands at 1723, 1599 and 1435 cm À1 originated by the stretch of the carboxyl groups (ACOOH) and the asymmetric and symmetric stretches of the carboxylate groups (ACOO À ) shifted to low wavenumber region (bands at 1712, 1574 and 1408 cm À1 , respectively) and changed intensity.…”

“…Moreover, bands at 1723, 1599 and 1435 cm À1 originated by the stretch of the carboxyl groups (ACOOH) and the asymmetric and symmetric stretches of the carboxylate groups (ACOO À ) shifted to low wavenumber region (bands at 1712, 1574 and 1408 cm À1 , respectively) and changed intensity. Such behavior is originated due to formation of hydrogen bonds between the negatively charged groups in the nanocomposite matrix and unsaturated dimethylamino groups of MB [57]. Finally, the band assigned to the vibration modes ascribed to methylene groups (at 2945 cm À1 ) shifted to 2923 cm À1 suggesting that other than electrostatic interactions between MB and the nanocomposite, hydrophobic interactions were also involved.…”

Characteristic features of charge transfer in the interaction between sensitizer molecules and AgCl(I) molecules

“…), is widely used in practice [1][2][3][4]. A special role is played by sensitization by organic dyes, due to the considerable diversity of their spectral characteristics, making it possible to design light energy detectors and converters having selective and conversely nonselective properties in the visible and near IR regions of the spectrum [1,4].In [5], for the example of methylene blue molecules adsorbed on the surface of AgCl(I) microcrystals, it is shown that they are bound to the crystal mainly by several active centers (the dimethylamino group and the sulfur atom of the heterocycle) via OH groups. Accordingly, a direct optical transition of electrons in the molecule to the conduction band is unlikely.…”

“…In [5], for the example of methylene blue molecules adsorbed on the surface of AgCl(I) microcrystals, it is shown that they are bound to the crystal mainly by several active centers (the dimethylamino group and the sulfur atom of the heterocycle) via OH groups. Accordingly, a direct optical transition of electrons in the molecule to the conduction band is unlikely.…”