Effects of molecular adsorption on the electronic structure of single-layer graphene

Adsorption Features of Tetrahalomethanes (CX4; X = F, Cl, and Br) on β12 Borophene and Pristine Graphene Nanosheets: A Comparative DFT Study

The potentiality of the β₁₂ borophene (β₁₂) and pristine graphene (GN) nanosheets to adsorb tetrahalomethanes (CX₄; X = F, Cl, and Br) were investigated using density functional theory (DFT) methods. To provide a thorough understanding of the adsorption process, tetrel (XC-X₃∙∙∙β₁₂/GN)- and halogen (X₃C-X∙∙∙β₁₂/GN)-oriented configurations were characterized at various adsorption sites. According to the energetic manifestations, the adsorption process of the CX₄∙∙∙β₁₂/GN complexes within the tetrel-oriented configuration led to more desirable negative adsorption energy (E_ads) values than that within the halogen-oriented analogs. Numerically, E_ads values of the CBr₄∙∙∙Br1@β₁₂ and T@GN complexes within tetrel-/halogen-oriented configurations were -12.33/-8.91 and -10.03/-6.00 kcal/mol, respectively. Frontier molecular orbital (FMO) results exhibited changes in the E_HOMO, E_LUMO, and E_gap values of the pure β₁₂ and GN nanosheets following the adsorption of CX₄ molecules. Bader charge transfer findings outlined the electron-donating property for the CX₄ molecules after adsorbing on the β₁₂ and GN nanosheets within the two modeled configurations, except the adsorbed CBr₄ molecule on the GN sheet within the tetrel-oriented configuration. Following the adsorption process, new bands and peaks were observed in the band structure and density of state (DOS) plots, respectively, with a larger number in the case of the tetrel-oriented configuration than in the halogen-oriented one. According to the solvent effect affirmations, adsorption energies of the CX₄∙∙∙β₁₂/GN complexes increased in the presence of a water medium. The results of this study will serve as a focal point for experimentalists to better comprehend the adsorption behavior of β₁₂ and GN nanosheets toward small toxic molecules.

Effects of strain and electric fields on the electronic transport properties of single-layer β12-borophene nanoribbons

Motivated by recent experimental and theoretical research on a monolayer of boron atoms, borophene, the transmission probability and current-voltage characteristics of β₁₂-borophene nanoribbons (BNRs) with zigzag and armchair edges have been calculated using the five-band tight-binding calculation, the Green's function approach, and the Landauer-Büttiker formalism. We focus on the effects of the geometrical parameters, perpendicular electric field, and external strain on the electronic transport properties of β₁₂-BNRs by considering the effects of the substrate. Our calculations show that the transmission coefficient and current of the system decrease by increasing the channel length, whereas increasing ribbon width leads to an increment in the transmission probability as well as the I-V characteristic of β₁₂-BNRs. Besides, the application of tensile strain causes a decrement in the current of the inversion symmetric model of the armchair β₁₂-BNR, whereas the current increases in the presence of compressive strain. We also observed a dip in the transmission spectrum of the biased β₁₂-BNR along the armchair direction which shows a metal-to-n-doped semiconductor phase transition in the device when applying a strong enough electric field. Moreover, the current of the inversion symmetric model of the β₁₂-BNR with zigzag and armchair edges increases with the application of a perpendicular electric field, while in the case of the homogeneous model, the application of an electric field enhances the current of the β₁₂-BNR only in the zigzag direction. These results provide insights for future experimental research and show that β₁₂-BNRs are potential candidates for next-generation electronic devices.

Cytotoxic aquatic pollutants and their removal by nanocomposite-based sorbents

Water is an extremely essential compound for human life and, hence, accessing drinking water is very important all over the world. Nowadays, due to the urbanization and industrialization, several noxious pollutants are discharged into water. Water pollution by various cytotoxic contaminants, e.g. heavy metal ions, drugs, pesticides, dyes, residues a drastic public health issue for human beings; hence, this topic has been receiving much attention for the specific approaches and technologies to remove hazardous contaminants from water and wastewater. In the current review, the cytotoxicity of different sorts of aquatic pollutants for mammalian is presented. In addition, we will overview the recent advances in various nanocomposite-based adsorbents and different approaches of pollutants removal from water/wastewater with several examples to provide a backdrop for future research.

Support effects in the adsorption of water on CVD graphene: an ultra-high vacuum adsorption study

Experimental data for water adsorption on CVD (chemical vapor deposition) graphene/SiO2 and graphene/Cu studied under ultra-high vacuum (UHV) conditions are discussed, focusing on support effects and hydrophobicity. Under UHV, it seems that graphene wettability is inversely related to wetting properties of the support. Graphene is not transparent to water wetting on the supports studied here.

Tunability of short-channel effects in MoS2 field-effect devices

MoS2 transistors have been electrically characterized and analyzed in terms of their vulnerability to short channel effects and their response to various environments. We find that the electrical performance of MoS2 flakes is governed by an unexpected dependence on the effective body thickness of the devices that in turn depends on the amount of intercalated water molecules that exist in the layered structure. In particular, a decrease in effective body thickness is observed in air compared to the "water-free" scenario. Moreover, we find that the doping stage of a MoS2 field-effect transistor (FET) is p-type despite the appearance of electron conduction, and the amount of p-doping is higher in air than in vacuum. Most importantly, our results indicate that device characteristics of MoS2 can be substantially impacted by tuning the device electrostatics. This can be accomplished by controlling the effectively active body thickness of the MoS2 FET employing intercalation and engineering of the effective barrier between individual MoS2 layers.

Molecular adsorption on graphene

Current studies addressing the engineering of charge carrier concentration and the electronic band gap in epitaxial graphene using molecular adsorbates are reviewed. The focus here is on interactions between the graphene surface and the adsorbed molecules, including small gas molecules (H(2)O, H(2), O(2), CO, NO(2), NO, and NH(3)), aromatic, and non-aromatic molecules (F4-TCNQ, PTCDA, TPA, Na-NH(2), An-CH(3), An-Br, Poly (ethylene imine) (PEI), and diazonium salts), and various biomolecules such as peptides, DNA fragments, and other derivatives. This is followed by a discussion on graphene-based gas sensor concepts. In reviewing the studies of the effects of molecular adsorption on graphene, it is evident that the strong manipulation of graphene's electronic structure, including p- and n-doping, is not only possible with molecular adsorbates, but that this approach appears to be superior compared to these exploiting edge effects, local defects, or strain. However, graphene-based gas sensors, albeit feasible because huge adsorbate-induced variations in the relative conductivity are possible, generally suffer from the lack of chemical selectivity.

The chemistry of imperfections in N-graphene

Many propositions have been already put forth for the practical use of N-graphene in various devices, such as batteries, sensors, ultracapacitors, and next generation electronics. However, the chemistry of nitrogen imperfections in this material still remains an enigma. Here we demonstrate a method to handle N-impurities in graphene, which allows efficient conversion of pyridinic N to graphitic N and therefore precise tuning of the charge carrier concentration. By applying photoemission spectroscopy and density functional calculations, we show that the electron doping effect of graphitic N is strongly suppressed by pyridinic N. As the latter is converted into the graphitic configuration, the efficiency of doping rises up to half of electron charge per N atom.

Electronic and dielectric properties of silicene functionalized with monomers, dimers and trimers of B, C and N atoms

First principle calculations have been performed to study the geometric, electronic and dielectric properties of low-buckled silicene with the adsorption of monomers, dimers and trimers of B, C and N atoms. A band gap opening has been achieved for all the C adsorbates, homo dimers of B and N, the hetero N–B dimer and the B–C–N trimer on silicene.

Photoinduced methylation of graphene

Covalent grafting of methyl groups onto the basal plane of graphene is achieved through a photochemical reaction between graphene and di-tert-butyl peroxide. The methylation of graphene is found to be reversible. The edge of single-layer graphene shows the largest methylation reactivity, which provides a route to tailor the edge state of graphene.

Engineering the work function of armchair graphene nanoribbons using strain and functional species: a first principles study

First principles density functional theory calculations were performed to study the effects of strain, edge passivation, and surface functional species on the structural and electronic properties of armchair graphene nanoribbons (AGNRs), with a particular focus on the work function. The work function was found to increase with uniaxial tensile strain and decrease with compression. The variation of the work function under strain is primarily due to the shift of the Fermi energy with strain. In addition, the relationship between the work function variation and the core level shift with strain is discussed. Distinct trends of the core level shift under tensile and compressive strain were discovered. For AGNRs with the edge carbon atoms passivated by oxygen, the work function is higher than for nanoribbons with the edge passivated by hydrogen under a moderate strain. The difference between the work functions in these two edge passivations is enlarged (reduced) under a sufficient tensile (compressive) strain. This has been correlated to a direct-indirect bandgap transition for tensile strains of about 4% and to a structural transformation for large compressive strains at about - 12%. Furthermore, the effect of the surface species decoration, such as H, F, or OH with different covering density, was investigated. It was found that the work function varies with the type and coverage of surface functional species. Decoration with F and OH increases the work function while H decreases it. The surface functional species were decorated on either one side or both sides of AGNRs. The difference in the work functions between one-sided and two-sided decorations was found to be relatively small, which may suggest an introduced surface dipole plays a minor role.