Explanations of the possibility of optical monitoring of CRO42 anonous adsorption on carbon nanostructures by theoretical calculations of variable spectra
DOI:
https://doi.org/10.31548/energiya2019.02.082Abstract
Abstract. The search for new adsorption materials to create efficient water treatment schemes from heavy metals is an important scientific and technological task. Materials based on carbon nanostructured materials, in particular BNT, are considered as perspective adsorbents for such a task. The application of optical monitoring procedures for the adsorption process of heavy metal anions, in particular CrO42- anions, on carbon nanostructures can significantly improve the efficiency of cleaning methods and promote the creation of new effective environmental protection technologies. In this paper, the principal possibility of optical monitoring of adsorption (in particular, the detection of the fact of adsorption) of CrO42-anions on the surface of carbon nanostructures - BNT and graphene is analyzed. The analysis is based on the results of theoretical calculations of the Raman spectra and IR absorption of CrO42-anions, which were obtained in the approximation of TFG (DFT), "before" and "after" adsorption on the surface of carbon nanostructures.
The theoretical calculations of the electronic structure of BNT and graphene with adsorbed molecules on their surface were performed. The calculations were carried out using the software package Gaussian 09 in the framework of the theory of functional electronic density.
Two calculations have found two adsorption configurations of CrO42- anions on a single-layered sheet of graphene. It is found that for all adsorption configurations there are significant changes in the frequencies of valence vibrations of the most chromatic molecular anion. In the first configuration, the oscillation frequency ν1 (A1) increases by 122 cm-1 (from 858 to 980 cm-1) relative to the frequency of the corresponding variation of the "free" CrO42- molecular -anion. The oscillation ν3 (T2) undergoes degeneracy and also has considerably higher frequencies (1014, 1016 and 1036 cm-1), as compared to the case of "free" molecular anion. From these three components of the splitting, the most intense contribution to the spectrum of the CD gives the component with a frequency of 1016 cm-1 - it forms a separate band in the spectrum. In another adsorption configuration, the frequency of the valence fluctuation ν1 (A1) shifts slightly compared with the corresponding frequency of the free CrO42- anion (from 858 to 869 cm-1). In turn, the oscillation ν3 (T2) removes degeneration and it splits significantly: on three components with frequencies 725, 751 and 962 cm-1. Components with frequencies of 725 and 751 cm-1 form strips of the spectrum of a KI of another configuration that are absent in the spectrum of graphene without an adsorbed anion.
Calculated KR spectra and IR absorption of CrO42- molecular anions adsorbed on the surface of graphene and VNT (5.5) differ significantly (valence fluctuations are shifted by almost 100 cm-1) compared with the corresponding spectra of "free" CrO42- molecular anions, which proves the fundamental possibility of an experimental detection of the adsorption of CrO42-anions. Consequently, CR spectroscopy and IR absorption should be considered as promising methods for monitoring adsorption processes of MA CrO42- on the surface of carbon nanomaterials.
Key words: carbon, nanotubes, adsorption, molecules, electronic structure
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