Nanostructured surfaces

Mechanisms of CrO42- anions and K2CrO4 quantum dots adsorption on the surface of carbon nanostructures 
V. Borysiuk1, S. Nedilko1, Yu. Hizhnyi1

1 Taras Shevchenko National University of Kyiv, Volodymyrska Street 64/13, 01601, Kyiv, Ukraine
E-mail: borysyukviktor@gmail.com

Removal of heavy metals from waste waters is a topical technological and industrial need.  One of the most promising methods of water purification from heavy metals is their adsorption by artificial adsorbents. At present, carbon nanostructured materials are intensively studied as adsorbents for efficient removal and storage of various toxic pollutants. The aim of this work is to clarify the mechanisms of the chromate compounds interaction with the surface of carbon nanotubes by theoretical modelling of the processes of molecular adsorption together with experimental studies of these processes by various , particularly, spectroscopic methods.
In this work we present results of the electronic structure calculations and related analysis for adsorption of CrO42- anions and K2CrO4 quantum dots (QDs) on the surface of several types of carbon nanotubes (CNTs). Geometry-optimized calculations of the electronic structures were carried out at the Density Functional Theory (DFT) level within molecular cluster approach using Gaussian 09 software package [1]. The binding energies, relaxed geometries, electronic charges, and vibrational spectra of studied chromate compounds in the adsorbed and in the “free” states were calculated and compared each other. 
The energies and oscillator strengths of the electronic transitions between the ground and excited states, as well as the optical absorption spectra of the “free” and adsorbed anions and QDs are calculated using time-dependent DFT (TD-DFT) approximation. Effects of water solvent on studied adsorption behavior were considered in a polarizable continuum model (PCM).
The Raman, IR absorption and photoluminescence spectra of the systems containing carbon nanostructures were experimentally measured before and after adsorption of chromate compounds. The spectra revealed substantial difference that confirms the principal possibility of optical monitoring of the adsorption processes. The observed behaviour of experimental spectra were discussed on the base of the obtained calculation results.

1.	Frisch M.J., Trucks G.W., Schlegel H.B., et al. // Gaussian 09 (Gaussian, Inc., Wallingford, CT, 2009).