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Two approaches are presented here to analyze the absorption resonances between carbynes and cyclo[n]carbons, namely the analytical tight-binding model to calculate the optical selection rules of cumulenic atomic rings and chains and the ab initio time-dependent density functional theory for the optical investigation of polyynic carbon ring and chains. The optical absorption spectra of the carbon ring match that of the finite chain when their eigen energies align following theNring=2Nchain+2rule, which states that the number of atoms in an atomic ringNringis twice the number of atoms on a finite chainNchainwith two additional atoms. Two representative atomic chains are chosen for our numerical calculations, specifically carbynes withN=7and8carbon atoms as optical resonance spectra match to a recently synthesized carbon ring called cyclo[18]carbon. Despite the mismatch in resonance peaks, molecular orbital transitions of both carbynes N  = 7 and 8 and cyclo[18]carbon reveal a wave function symmetry change from inversion to reflection and vice versa for allowed molecular orbital transitions, which results in electron density redistribution along the polyynic carbyne axis or the cyclo[18]carbon circumference. Our investigation of the correlation of optical absorption peaks between carbynes and cyclo[n]carbons is a step towards enhancing the reliability of allotrope identification in advanced molecular device spectroscopy. Moreover, this work could facilitate the non-invasive, rapid and crucial assessment of these sensitive 1D allotropes by providing accurate descriptions of their electronic and optical properties, particularly in controlled synthesis environments., (© 2024 IOP Publishing Ltd.)

In this study, we investigated the reactivity of γ-graphyne (Gp) and its derivatives, Gp-CH 3 , Gp-COOH, Gp-CN, Gp-NO 2 , and Gp-SOH, for the removal of toxic heavy metal ions (Hg + 2 , Pb + 2 , and Cd + 2 ) from wastewater. From the analysis of the optimized structures, it was observed that all the compounds exhibited planar geometry. The dihedral angles (C9-C2-C1-C6 and C9-C2-C1-C6) were approximately 180.00°, indicating planarity in all molecular arrangements. To understand the electronic properties of the compounds, the HOMO (E H ) and LUMO (E L ) energies were calculated, and their energy gaps (E g ) were determined. The E H and E L values ranged between - 6.502 and - 8.192 eV and - 1.864 and - 3.773 eV, respectively, for all the compounds. Comparing the E H values, Gp-NO 2 exhibited the most stable HOMO, while Gp-CH 3 had the least stable structure. In terms of E L values, Gp-NO 2 had the most stable LUMO, while Gp-CH 3 was the least stable. The E g values followed the order: Gp-NO 2  < Gp-COOH < Gp-CN < Gp-SOH < Gp-CH3 < Gp, with Gp-NO 2 (4.41 eV) having the smallest energy gap. The density of states (DOS) analysis showed that the shape and functional group modifications affected the energy levels. Functionalization with electron-withdrawing (CN, NO 2 , COOH, SOH) or electron-donating (CH 3 ) groups reduced the energy gap. To specifically target the removal of heavy metal ions, the Gp-NO 2 ligand was selected for its high binding energy. Complexes of Gp-NO 2 -Cd, Gp-NO 2 -Hg, and Gp-NO 2 -Pb were optimized, and their properties were analyzed. The complexes were found to be planar, with metal-ligand bond distances within the range of 2.092→3.442 Å. The Gp-NO 2 -Pb complex exhibited the shortest bond length, indicating a stronger interaction due to the smaller size of Pb + 2 . The computed adsorption energy values (E ads ) indicated the stability of the complexes, with values ranging from - 0.035 to -4.199 eV. Non-covalent interaction (NCI) analysis was employed to investigate intermolecular interactions in Gp-NO 2 complexes. The analysis revealed distinct patterns of attractive and repulsive interactions, providing valuable insights into the binding preferences and steric effects of heavy metals., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Pure water is a key element for a sustainable and healthy environment of human inhabitation. Since major sources of water contamination are industrially generated heavy metal cations there is great demand for efficient methods of their treatment. Here, using density functional theory, we investigate the covalent organic framework's electronic and optical properties and their interaction with the most dangerous heavy metal pollutants, namely Hg +2 , Pb +2, and Cd +2 . We consider biphenyl boroxine covalent organic frameworks before and after chemical modification with CN, COOH, NH 2 , and NO 2 groups. In addition to the molecular geometries, such parameters as the dipole moment, chemical potential, electronegativity, chemical hardness, and binding energy are calculated. It is found that CN, COOH, and NO 2 functional groups are favorable for intermolecular bonding with harmful transition metals. The functionalization with the mentioned groups reduces the band gap of the pristine covalent organic frameworks and increases their reactivity. As a result, strong complexes with Cd +2 , Hg +2 , and Pb +2 can form, which, as follows from our calculations, can be detected by the red shift in their optical absorption spectra., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The electronic and adsorption properties of chemically modified square hexagonal boron nitride quantum dots are investigated using density functional theory calculations. The free energy and frequency calculations show that all the boron nitride flakes are stable before/after modification and metal adsorption. Edge modification significantly enhances the stability and interactivity of the flake. For instance, the free energy of binding decreases from -6.5 eV in the hydrogenated flake to -7.1 eV in the pristine one and the dipole moment increases from 4.5 D to 53.7 D, respectively. A wide spectrum of band gaps can also be achieved, where the band gap can be smoothly varied from ∼6 eV in edge fluorinated flakes to 0.2 in sulfurated ones. Six hydrated metals, Cd, Co, Cr, Cu, Fe, and Zn, are considered for adsorption by the flakes. The transition metals are highly selected by the flakes while heavy metals are weakly adsorbed. All hydrated metals are physically adsorbed by the edge and surface of hydrogenated flakes except Cu, which is chemically adsorbed. Chemical groups or elements attached to the flake strongly enhance the adsorption strength; the adsorption energy of hydrated Cr on the surface increases from 0.6 eV to 8.6 eV after attaching two COOH groups to the surface. Hydrogen evolution has also been observed through the adsorption process. The calculated low overpotential for the oxygen evolution reaction (0.52 V) and hydrogen adsorption strength (0.11 eV) for the hydrogen evolution reaction indicate that boron nitride quantum dots are not only potential candidates for the removal of different metals from wastewater but also for efficient water splitting.

Development of on-chip integrated carbon-based optoelectronic nanocircuits requires fast and non-invasive structural characterization of their building blocks. Recent advances in synthesis of single wall carbon nanotubes and graphene nanoribbons allow for their use as atomically precise building blocks. However, while cataloged experimental data are available for the structural characterization of carbon nanotubes, such an atlas is absent for graphene nanoribbons. Here we theoretically investigate the optical absorption resonances of armchair carbon nanotubes and zigzag graphene nanoribbons continuously spanning the tube (ribbon) transverse sizes from 0.5(0.4) nm to 8.1(12.8) nm. We show that the linear mapping is guaranteed between the tube and ribbon bulk resonance when the number of atoms in the tube unit cell is [Formula: see text], where [Formula: see text] is the number of atoms in the ribbon unit cell. Thus, an atlas of carbon nanotubes optical transitions can be mapped to an atlas of zigzag graphene nanoribbons.

Band gap control by an external field is useful in various optical, infrared and THz applications. However, widely tunable band gaps are still not practical due to a variety of reasons. Using the orthogonal tight-binding method for π-electrons, we have investigated the effect of the external electric field on a subclass of monolayer chevron-type graphene nanoribbons that can be referred to as jagged graphene nanoribbons. A classification of these ribbons was proposed and band gaps for applied fields up to the SiO2 breakdown strength (1 V nm(-1)) were calculated. According to the tight-binding model, band gap opening (or closing) takes place for some types of jagged graphene nanoribbons in the external electric field that lies on the plane of the structure and perpendicular to its longitudinal axis. Tunability of the band gap up to 0.6 eV is attainable for narrow ribbons. In the case of jagged ribbons with armchair edges larger jags forming a chevron pattern of the ribbon enhance the controllability of the band gap. For jagged ribbons with zigzag and armchair edges regions of linear and quadratic dependence of the band gap on the external electric field can be found that are useful in devices with controllable modulation of the band gap.