Halogen Adsorption Research Articles

Adsorption and reversible detection of toxic halogens gases at room temperature by two-dimensional Al2SSe for occupational sustainability

Current treatment for inhalational halogens poisoning involves providing supportive care, which includes administering humidified oxygen and managing the airway. Since toxic effects of halogens cannot be reversed, sensors with high sensitivity and good reversibility for detecting the relatively lower concentration yet noxious halogens becomes particularly significant and enticing. Herein, the structural and optoelectronic properties of toxic F2 and Cl2 gas molecules adsorbed on highly stable Al2SSe monolayer have been systematically studied by means of first-principles calculations based on density functional theory (DFT). Favorable adsorption sites of said molecules on Al2SSe were carefully examined. The relatively high, negative adsorption energy for F2 and Cl2 indicate that the adsorption process is exothermic and the molecules could be stably adsorbed on Al2SSe monolayer. This characteristic, combined with the substantial charge transfer (0.15–0.55 |e|), drastic change in work function, complete reversibility due to recovery time in 10−1 s scale and distinct optical response, render Al2SSe monolayer a viable option for utilization as either surface work functions transistor or optical chemical resistor for detecting these gases. Pearson correlation coefficient (PCC) analysis of theoretical recovery time and response value indicates that band gap change and electron transfer are the primary influencing factors. Selectivity analysis reveals that common compound forms of halogens and atmospheric molecules such as HF, HCl, N2, O2, H2 and H2O are either physically adsorbed or inert with extremely low adsorption energies on Al2SSe, prompting high F2 and Cl2 selectivity. These outcomes acclaim the exciting prospects of developing Al2SSe monolayer for specific, occupational related ultrahigh-sensitivity F2 and Cl2 sensing nanodevices.

Bromine Adsorption and Thermal Stability on Rh(111): A Combined XPS, LEED and DFT Study.

This study addresses a fundamental question in surface science: the adsorption of halogens on metal surfaces. Using synchrotron radiation-based high-resolution X-ray photoelectron spectroscopy (XPS), temperature-programmed XPS, low-energy electron diffraction (LEED) and density functional theory (DFT) calculations, we investigated the adsorption and thermal stability of bromine on Rh(111) in detail. The adsorption of elemental bromine on Rh(111) at 170 K was followed in situ by XPS in the Br 3d region, revealing two individual, coverage-dependent species, which we assign to fcc hollow- and bridge-bound atomic bromine. In addition, we find a significant shift in binding energy upon increasing coverage due to adsorbate-adsorbate interactions. Subsequent heating shows a high thermal stability of bromine on Rh(111) up to above 1000 K, indicating strong covalent bonding. To complement the XPS data, LEED was used to study the long-range order of bromine on Rh(111): we observe a (√3×√3)R30° structure for low coverages (≤0.33 ML) and a star-shaped compression structure for higher coverages (0.33-0.43 ML). Combining LEED and DFT calculations, we were able to visualize bromine adsorption on Rh(111) in real space for varying coverages.

A DFT investigation on the mechanical and structural properties of halogen- and metal-adsorbed silicene nanosheets

Herein, the effects of halogen and metal atomic adsorption on the mechanical and structural characteristics of silicene are studied using density functional theory (DFT) calculations. Cl, Br, Au, Ca, Ga, Li, and Na atoms are selected as the adsorption atoms. Moreover, the phonon dispersion and electron localization function are investigated to show the stability of considered nanostructures and to visualize the bonding properties, respectively. It is shown that the adsorption leads to decreasing the elastic and bulk moduli of some structures, while it increases them in some other structures. It is seen that except for Ca-adsorbed nanosheet, both the elastic and bulk moduli of all other structures decrease after adsorption. Furthermore, the isotropic behavior of all the studied nanosheets is indicated. The plastic behavior is also analyzed. It is revealed that the second critical strain of all nanosheets, except for SiBr and SiCl, decreases under uniaxial loading. However, under biaxial loading conditions, the second critical strain of Au-, Ca-, and Ga-adsorbed structures decreases, while in other structures (SiBr, SiCl, SiLi, and SiNa) the adsorption increases the yield strain.

Efficient heterogeneous photocatalytic C–C coupling of halogenated arenes mediated by metal cocatalyst

A moderate adsorption of benzyl halogens and appropriate kinetics of reaction intermediates are the keys to achieve efficient C–C coupling on the Ni/gCN photocatalyst.

Encapsulation and Adsorption of Halogens into Single-Walled Carbon Nanotubes

Functionalisation of single-walled carbon nanotubes (SWNTs) with atoms and molecules has the potential to prepare charge–transfer complexes for numerous applications. Here, we used density functional theory with dispersion correction (DFT + D) to examine the encapsulation and adsorption efficacy of single-walled carbon nanotubes to trap halogens. Our calculations show that encapsulation is exoergic with respect to gas-phase atoms. The stability of atoms inside SWNTs is revealed by the charge transfer between nanotubes and halogens. Encapsulation of halogens in the form of diatomic molecules is favourable with respect to both atoms and diatomic molecules as reference states. The adsorption of halogens on the outer surfaces of SWNTs is also exothermic. In all cases, the degree of encapsulation, adsorption, and charge transfer is reflected by the electronegativity of halogens.

Tuning the electronic and optical properties of molybdenite (MoS2) by adsorption of alkali metals and halogens

Electronic and optical properties of nanostructures formed by monolayer of molybdenite and with adsorption of alkali metals (Li, Na, K, Rb, Cs) and halogens (F, Cl, Br, I, At) on MoS2 are investigated by using the first principle calculations based on the density functional theory (DFT). The results suggest strong absorption peaks for pristine MoS2 in certain regions of the visible portion of the spectrum (~380–470 nm) and in the entire ultraviolet region. Structures formed by adsorption of Li, F, Cl, Br, I on MoS2 contribute to the red shift phenomenon where absorption peaks are seen to shift towards the lower energy range of the spectrum. However, a blue shift phenomenon is seen in other structures formed by the adsorption of At, Na, K, Rb, Cs over MoS2, where absorption peaks shift to higher energy range of the spectrum. Furthermore, high absorption is observed in the entire visible region (~400–790 nm) and UV region (below 360 nm) of the spectrum for all the adsorbed nanostructures. The measured dielectric constant is in line with the measured refractive index for all the adsorbed nanostructures.

Tuning optical and electronic properties of graphene oxide by surface adsorption of molecular halogens (X2 = I2, Br2, Cl2, and F2) for light harvesting

Surface adsorption of small molecules modulates both optical and electronic structure, which is beneficial for different applications. The molecular adsorption of halogens X2 (X2 = I2, Br2, Cl2, and F2) was investigated using density functional theory and the dispersion (Wb97xd) module. The electronic structure and optical properties of the pristine graphene oxide (GO) and its molecular complexes with halogens (GOI2, GOBr2, GOCl2, and GOF2) are explored. The adsorption of X2 (X2 = I2, Br2, and Cl2) molecules were stabilized by non-covalent lone pair-π bonding, (O)lp… π, interactions and π-π interactions. The F2 molecule were stabilized by lone pair-π bonding, (O)lp… π, as well as halogen bonding (XB). The GOX2 complexes were energetically stable and optically red shifted in polar solvents. The simulated optical absorption spectra at TD-DFT calculations of GOX2 complexes and TDOS uncover the presence of intermediate sates in the energy gap region, which is beneficial for harvest of visible light and photocatalysis.

Adsorption and sequential thermal release of F2 , Cl2 , and Br2 molecules by a porous organic cage material (CC3-R): Molecular dynamics and grand-canonical Monte Carlo simulations.

The adsorption-desorption behavior of fluorine, chlorine, and bromine molecules onto a crystalline porous organic cage, namely CC3-R was calculated at different temperatures using molecular dynamics (MD) and grand-canonical Monte Carlo (GCMC) simulations. Self-diffusion coefficients, radial distribution functions (RDF), and adsorption isotherms were calculated for this purpose. The results show that CC3-R has varied capacities to capture these halogens at ambient and high temperatures, so that the thermal release of fluorine is completed with increasing temperature up to around 70°C and chlorine molecules remain at the CC3-R surface up to 100°C and all bromine molecules are removed from the CC3-R surface at 200°C. We found that bromine self-diffusion was almost independent of temperature between 0 and 100°C in contrast to fluorine and chlorine. Among different diffusion regimes, Knudsen diffusion appears to have an important role in the adsorption of heavy halogens at higher temperatures.

Potential of Si14Ge14 and B14P14 nanocages as electrodes of metal-ion batteries: a theoretical investigation

In this study, the potential of Si14Ge14 and B14P14 as anode electrodes in metal-ion batteries by using of the density functional theory was investigated. The effects of halogen adsorption of the Si14Ge14 and B14P14 on potential of metal-ion batteries were examined. Results indicated that the B14P14 as anode in metal-ion batteries has higher potential than Si14Ge14. Results have shown that the K-ion battery has higher cell voltage and higher potential than Li-ion and Na-ion batteries. Results shown that the halogen adsorption of nanocages increases the cell voltage of studied metal-ion batteries. Results displayed that the F-metal-ion batteries have higher cell voltage and higher performance than Cl- and Br-metal-ion batteries. Finally, the F-B13P14 as anode electrode in the K-ion battery has the highest potential in industry.

Influence of hydrogen and halogen adsorption on the photocatalytic water splitting activity of C2N monolayer: A first-principles study

Adsorption of impurity atoms or molecules on the surface of photocatalysts may improve or worsen the photocatalytic activity due to chemical bond relaxations. Herein, we demonstrate the influence of molecular adsorbates such as H2, F2, Cl2, Br2, and I2 on the electronic properties and photocatalytic activity of the nitrogenated holey graphene (C2N) using hybrid density functional calculations including van der Waals interaction. Hydrogen and halogen molecules prefer to physisorb on the holey site except F2 which has substantial chemisorption. The halogens tend to draw electrons from C2N monolayer due to their high electronegativity and thereby introduce new band states which significantly alters the opto-electronic and photocatalytic properties. Although F2 and Br2 adsorbed C2N have favorable band edge positions, I2 adsorbed C2N is more promising for hydrogen production because of its appropriate band edge positions relative to the water redox potentials. Optical absorption spectra reveals that all these systems are visible light active and therefore they could harvest more incoming light. We have demonstrated here for the first time that intermediate bandgap states can be introduced in C2N system by adsorbing halogen molecules and our theoretical findings suggest that I2 adsorbed C2N monolayer is a promising candidate for photocatalytic water splitting.

Halogen Adsorption and Reaction with Bi2(Se,Te)3 and Bi/Bi2(Se,Te)3

Bi$_2$Se$_3$ and Bi$_2$Te$_3$, and these same surfaces covered with Bi films, are exposed to Br$_2$ and Cl$_2$ in ultra-high vacuum. Low energy electron diffraction (LEED) and low energy ion scattering (LEIS) are used to investigate the surface composition before and after halogen exposure. It is found that Br$_2$ weakly chemisorbs to the Se- or Te-terminated clean surfaces and light annealing removes the adsorbates restoring the intact surfaces. In contrast, halogens dissociatively adsorb onto surfaces covered with an additional bilayer of Bi, having a p-doping effect. Annealing these halogen-covered surfaces at 130{\deg}C causes Bi atoms to be chemically etched away and the surface reverts to a Se- or Te-termination. This work shows how halogen adsorption and reaction can be used to modify the surface termination of such materials.

Tuning the optical properties of phosphorene by adsorption of alkali metals and halogens

Optical properties of phosphorene are tuned by adsorption of alkali metals (Li and Na) and halogens (Br and Cl). It has been found that on increasing the size of alkali metals and halogen adsorbed phosphorene layer the absorption coefficient reduces and shifts towards visible region. The refractive index in alkali metal adsorbed phosphorene increases with size of phosphorene layer. For halogen adsorbed structure it decreases with increase in size of phosphorene layer. Optical absorption is observed to depend on both dielectric constant and refractive index. Since adsorption of alkali and halogen materials modifies the refractive index of phosphorene, absorption is seen to reduce in all cases where refractive index increases due to adsorption even when the dielectric constant was high.

Trends in Buckled and Planar Halogen-Doped Graphene for ORR Activity: A DFT Study

Owing to the sluggish oxygen reduction reaction (ORR), high-performance catalysts like Pt-based alloys are widely used to render the reaction practically useful in systems like fuel cells. Nonetheless, high costs and technical complications associated with such catalysts have encouraged the exploration of alternative ORR catalysts like heteroatom-doped carbon nanomaterials. To improve the catalytic activity of carbon, earlier studies used boron, nitrogen, phosphorus, sulfur, and selenium as dopants. In this paper, we perform density functional theory (DFT) calculations to explore the potential of halogens (X = F, Cl, Br, I) substituted within the two-dimensional structure of graphene. We also validate some of the results of previous experimental and theoretical studies on halogen-doped graphene. For example, we compare halogen adsorption and band structures of the resulting halogen-doped materials, as well as the possible influence of atomic size and atomic interactions (e.g., Br2/Br interactions, polyiodide formation) on their experimentally observed properties. Based on the resulting electronic and structural information, we then identify which among the buckled and planar forms of halogen-substituted graphene show the most promise for ORR activity. Finally, we compare this method of doping with previously studied methods like adsorption and edge-halogenation to provide additional insight on halogen doping.

Halogen bonding-assisted adsorption of iodoperfluoroarenes on a strong anion exchanger and its potential application in solid-phase extraction

The adsorption of iodoperfluoroarenes (IPFArs) by solid-liquid interfacial halogen bonding was investigated and preliminarily applied to solid-phase extraction (SPE). Based on 19F NMR titration experiments, UV spectrophotometric titrations, and chemical computations, silica gel functionalized with trimethylaminopropyl chloride (SAX) groups was chosen as a strong anion-exchanging adsorbent, since the solution-phase association ability of Cl− as halogen bond acceptor is superior to that of Br− or I−. Further explorations indicated that the adsorption of IPFArs is mainly driven by halogen bonding. The adsorption isotherms of 1,4-diiodotetrafluorobenzene (1,4-DITFB) and iodoperfluorobenzene (IPFB) were fitted by the Freundlich equation, while that of 1,2-diiodotetrafluorobenzene (1,2-DITFB) was fitted by the Langmuir equation. Such alternative adsorption models can meet the requirements of different self-assembly systems based on halogen bonding. In SPE applications, the adsorption efficiency of IPFArs on SAX is as follows: 1,4-DITFB≈1,2-DITFB>IPFB, with no significant adsorption of bromoperfluoroarenes. These results indicate promising applications of halogen bonding in the separation and enrichment of IPFArs.

First-principles studies on the effects of halogen adsorption on monolayer antimony.

Using first-principles calculations, we carry out systematic studies on the electronic, magnetic and structural properties of halogenated β-phase antimonene. We consider two different levels of halogen adatom coverage i.e. Θ = 1/8 and Θ = 1/18. It is found that F, Cl and Br adatoms act as acceptors whereas the I adatom acts as a donor. For a high coverage of Θ = 1/8, halogenated β-phase antimonene exhibits metallic characteristics. With a lower coverage of Θ = 1/18, through the adsorption of F, Cl and Br the semiconducting unstrained antimonene becomes metallic. In contrast, I-adsorbed antimonene remains semiconducting but exhibits magnetic behavior. We further investigate the effects of bi-axial strain on the halogenated β-phase antimonene. It is found that bi-axial strain can only induce ferromagnetism on the halogenated antimonene at Θ = 1/18. However, the ferromagnetism is suppressed when the applied strain is high. We uncover that the emergence of strain-dependent magnetism is attributed to the presence of localized states in the bandgap resulting from collective effects of bi-axial strain and the adsorption of halogen atoms.

Halogen adsorption at an As-stabilized β2–GaAs (001)–(2 × 4) surface

Halogen (F, Cl, Br, and I) adsorption at an As-stabilized GaAs (001) surface with the β2–(2 × 4) reconstruction is studied using the plane-wave projected-augmented wave method. The effect of halogens on the structural and electronic characteristics of the semiconductor surface is analyzed. The T2′ site at the missing row edge is shown to be the energetically most favorable for the adsorption of F, Cl, and Br, whereas I prefers the H3 site between adjacent arsenic dimers in the third layer from the surface. Ga-halogen bond formation suggests that charge is transferred via the depletion of occupied orbitals of the As-dimer surface atoms, which leads to the weakening of Ga–As bonds in the substrate. The weakening of bonds between substrate-surface atoms due to the interaction of halogens with the surface is estimated.

Trends and Regularities for Halogen Adsorption on Various Metal Surfaces

Work function changes induced by adsorbates play an important role in electrochemistry, where specially adsorbed ions directly influence the electrode potential through this parameter. Systematic density functional theory calculations were performed for fluorine, chlorine, bromine, and iodine adsorption on 29 close-packed metal surfaces. Through a large number of calculations, it was shown that similar geometry adsorption sites have very good linear relationships in terms of adsorption energies, the vertical distances between halogen atoms and the metal surfaces, the Bader net charges of the adsorbates, and the induced work function changes. Additionally, there is a linear relationship between bromine and chlorine for these surface properties. The fact that nearly half of the cases we investigated exhibit the work function decrease behavior indicates its generality in halogens adsorption situations.

Low-energy approximation in the theory of adsorption on graphene

The effect of the linear approximation of the electronic spectrum of single-layer graphene (low-energy approximation) on the magnitude of charge transfer between an adatom and graphene has been investigated. It has been shown that the implementation of this approximation for adsorption of alkali metals and halogens leads to a change in the occupation numbers of local and band states as compared to the results obtained in the model taking into account the entire spectrum. However, the total occupation numbers agree quite well.

Halogen Phases on Pd(110): Compression Structures, Domain Walls, and Corrosion

Halogens are used as modifiers in catalytic processes, notably including photocatalytic watersplitting; as redox-active species in dye-sensitized solar cells; and as etchants in device fabrication. Atomically resolved studies of the adsorption and reactivity of halogens on Pt and Pd surfaces are scarce in view of the prominent role these metals play in the mentioned applications. The present study reports phases of halogens on Pd(110) in the submonolayer coverage range as monitored by temperature-programmed desorption, low-energy electron diffraction, scanning tunneling microscopy, and density functional calculations. Domain wall and compression structures are observed, as is typical for halogens (except fluorine) on transition and noble metals, but not on Pt, where the bonding is much more site-specific and a different succession of phases is found. The reactivity of Br toward Pd(110) is greater than that of Cl, as judged by the corrosive attack and by the bond strength derived from the thermal desorption temperature. The results confirm that an ionic-bonding picture based on a large metal-to-halogen charge transfer is not valid for Pd and Pt. Rather, the bonding is predominantly covalent, and the reactivity does not obey simple intuitive rules.

Preparation and Characterization of Ag Nanoparticle-Embedded Blank and Ligand-Anchored Silica Gels

Ag nanoparticles, used for halogen (especially iodine) adsorption and an evaluation of halogen behavior, were embedded in synthesized inorganic-organic hybrid gels. In particular, an irradiation method using an electron beam plays a part in introducing Ag nanoparticles to the organofunctionalized silica gels from AgNO3 solutions in a simple way at atmospheric pressure and room temperature. For preparation of the Ag nanoparticle-embedded inorganic-organic hybrid gels, ligands of ethylenediamine (NH2CH2CH2NH-, TMSen) and mercapto (HS-) functionalized three-dimensional porous SiO2 sol-gels were first synthesized through hydrolysis and condensation reactions, and Ag nanoparticles were then embedded into the ethylenediamine- and mercapto-anchored silica gels each, through electron-beam irradiation. The addition of ligands yielded larger average pore sizes than the absence of any ligand. Moreover, the ethylenediamine ligand led to looser structures and better access of the Ag nanoparticles to the ethylenediamine-anchored gel. As a result, more Ag nanoparticles were introduced into the ethylenediamine-anchored gel. The preparation and characterization of Ag nanoparticle-embedded blank and ligand-anchored silica gels are discussed in detail.