Pristine graphene covalent functionalization with aromatic aziridines and their application in the sensing of volatile amines - an ab initio investigation.

Food quality is of paramount importance for public health safety. For instance, fish freshness can be assessed by sensing the volatile short chain alkylamines produced by spoiled fish. Functionalized graphene is a good candidate for the design of gas sensors for such compounds and therefore of interest as the basic material in food quality sensor devices. To shed theoretical insight in this direction, in the present work we investigate via first-principles density functional theory (DFT) simulations: (i) graphene functionalization via aziridine appendages and (ii) the adsorption of short chain alkylamines (methylamine MA, dimethylamine DMA, and trimethylamine TMA) on the chemically functionalized graphene sheets. Optimal geometries, adsorption energies, and projected density of states (PDOS) are computed using a DFT method. We show that nitrene reactive intermediates, formed by thermal or photo splitting of arylazides - p-carboxyphenyl azide (1a), p-carboxyperfluorophenyl azide (1b), and p-nitrophenyl azide (1c) - react with graphene to yield functionalized derivatives, with reaction energies >-1.0 eV and barriers of the order of 2.0 eV, and open a ∼0.3 to 0.5 eV band gap which is in principle apt for applications in sensing and electronic devices. The interaction between the amines and functionalized graphene, as demonstrated from the calculations of charge density differences showing regions of charge gain and others of charge depletion between the involved groups, occurs through hydrogen bonding with interaction energies ranging from -0.04 eV to -0.76 eV, and induce charge differences in the system, which in the case of p-carboxyperfluorophenyl azide (1b) are sizeable enough to be experimentally observable in sensing.

First-principles investigation of methanethiol adsorption and dissociation mechanisms on the high-Miller-index vicinal surface Cu(4 1 0).

In this work, we present detailed investigations of methanethiol adsorption on a Cu(4 1 0) surface within the framework of the self-consistent first-principles calculations as implemented in the Vienna ab initio simulation package (VASP). In particular, the adsorption sites, the surface coverage rate and electronic properties have been determined and compared to experimental values. The results indicate that the favorable adsorption site in the case of low coverage rate is a bridge on the step followed by the hollow site on the terrace. The adsorption significantly affects the outermost layer of the surface mainly for a higher coverage rate in a (2 × 2) supercell. The nature of the chemisorption process on the surface is analyzed by means of the density of states which, combined with charge density difference and atomic charge calculations, confirms the ionic character of the S-Cu bond. The specific effect of the presence of steps is highlighted by comparing the adsorption on the (1 0 0) terrace to the adsorption on the extended Cu(1 0 0) surface. Compared to the flat Cu(1 0 0), it is found here that while the stability is almost the same at p(2 × 2) coverage, the CH3S/Cu(4 1 0) becomes more stable than CH3S/Cu(1 0 0) at c(2 × 2) coverage with 0.30 eV per molecule. The mechanism of methanethiol dissociation is explored by the nudged elastic band method and demonstrates that the most favorable path is dissociation followed by migration of hydrogen from the step to its most stable position (hollow on the terrace) with energy barriers less than 0.5 eV.