ИСТИНА

The adsorption of small analyte molecules (H2O, NH3, C2H5OH, and (CH3)2CO) and an indicator dye, 9-(diphenylamino)acridine (DPAA), on the surface of amor- phous silica particles is studied using electronic structure calculations at the DFT- D level of theory taking into account explicit corrections for van der Waals forces. Cluster models of three different types are used; two of them (Si10O11(OH)18 and Si20O27(OH)29) have been constructed using classical MD methods. The ef- fect of particle size, local environment, and the choice of the exchange-correlation functional and basis set on the adsorption energies is studied, and adsorption en- ergies are extrapolated to nanosized clusters. It is shown that the dye is more strongly bound to amorphous silica particles than the studied analyte molecules and that the energy of DPAA adsorption increases with the particle size, being at least twice as high as the energy of analyte adsorption for nanosized clusters. Electrostatic interactions play an important role in the adsorption of acridine dyes on the surface of silica nanoparticles [1]. We also studied the interaction of ana- lyte molecules in the gas phase with DPAA on dye/silica system. The electronic absorption spectra of the adsorbed dye are calculated within the TDDFT formal- ism and the effects of dye/analyte interactions are investigated. The spectral line broadening due to molecular vibrations is estimated within the Pekar model. A computationally efficient procedure is proposed for the prediction of changes in the absorption spectra of organic dyes adsorbed on silica upon their interaction with analytes. [1] V. Chashchikhin, E. Rykova and A. Bagaturyants, Phys. Chem. Chem. Phys. 13 (2011)1440-1447