Density functional calculation of graphene monolayer for detecting carcinogenic heavy metals in water

Zhao, Yimiao (2022) Density functional calculation of graphene monolayer for detecting carcinogenic heavy metals in water. Memorial University of Newfoundland. (Unpublished)

[English] PDF (Undergraduate Honours Thesis) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (4MB)

Abstract

The thesis discusses the ability of graphene monolayer for the possible detection of carcinogenic heavy metals like Arsenic (As), Cadmium (Cd), Chromium (Cr), Mercury (Hg), and Lead (Pb) present in water as the most common pollutants. These highly toxic and nonbiodegradable carcinogenic chemicals are responsible for various allergies and intractable diseases. The density functional theory (DFT) has been used to perform the calculations of electronic properties to understand the response of graphene towards heavy metals both in a vacuum and aqueous environments. DFT calculations have been done using the Gaussian 16 software package. The geometries of each calculated compound, either as graphene or complex (heavy metal and adsorbed graphene) have been optimized via B3LYP with the basis set of def2SVP. A 4 x 5 graphene (defined as a graphene with 4 carbon atoms time 5 carbon atoms) has been modeled and optimized, as well as other compounds. Energetics of heavy metal and water molecules with pristine graphene in both vacuum and aqueous environments are studied by the variations in binding distances and binding energies. The energetics study reveals that As and Cr show adsorption on the surface with higher binding energies and smaller binding distances in comparison with the other three carcinogenic heavy metals. To further understand the possible detection capability of graphene monolayer calculations of the density of states (DOS), the highest occupied molecular orbital (HOMO), and the lowest unoccupied molecular orbital (LUMO) were performed. The energy difference between occupied orbitals and virtual orbitals shown on DOS profiles are HOMO and LUMO energy gaps. The calculations show that As, Pb or Cr with graphene has lower HOMO and LUMO energy gap than pristine graphene in vacuum. As, Pb, Cd or Cr with graphene in water has a lower energy gap than pristine graphene. Lower HOMO and LUMO energy gap leads to an increase in the charge transfer, which may contribute to the absorption behaviors of heavy metals on graphene indcating a potential candidate for the detection of heavy metals. Cd only confirms its feasibility for detection in a water environment. The binding energies of Cr are -20.78 eV and -16.18 eV in vacuum and water, respectively. The HOMO and LUMO energy gaps are 0.87 eV and 0.99 eV in vacuum and water, respectively. In comparison with the other four carcinogenic heavy metals, the graphene monolayer shows better detection capability with Cr in both vacuum and aqueous environments.

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