Adsorption Of Hydrogen Fluoride Research Articles

Metal oxide modified MCM-41 on simultaneous removal of HF and HCl: Experimental and theoretical studies

To address the issue of harmful gases Hydrogen fluoride (HF) and hydrogen chloride (HCl) in metallurgical waste gas, this study utilized metal oxide modified molecular sieve (MCM-41) for their simultaneous removal. The adsorption and removal of HF and HCl are mainly influenced by alkaline sites and pore structure, with alkaline sites having a greater impact. MgO affects the alkaline site strength and pore structure, thereby facilitating the removal of HF and HCl. On the surface of the adsorbent, HF and HCl react to form MgF2 and MgCl2, which gradually reduces the adsorbent's performance. HF and HCl have a higher adsorption strength on the MgO surface, and the H…O interaction causes a more stable adsorption configuration. There is a competitive adsorption effect between HF and HCl, with HF having a preference for adsorbing on the MgO surface over HCl. The adsorption energies of HF and HCl are unlimited by adsorption effects. When the O atom in MgO is replaced by HF and HCl, Mg-F bonds, Mg-Cl bonds, and H-O bonds are formed, resulting in the formation of MgF2, MgCl2, and H2O. HF is easier to prioritize removal than HCl.

Investigations of the reaction mechanism of sodium with hydrogen fluoride to form sodium fluoride and the adsorption of hydrogen fluoride on sodium fluoride monomer and tetramer.

The reaction between Na and HF is a typical harpooning reaction which is of great interest due to its significance in understanding the elementary chemical reaction kinetics. This work aims to investigate the detailed reaction mechanisms of sodium with hydrogen fluoride and the adsorption of HF on the resultant NaF as well as the (NaF)4 tetramer. The results suggest that the reaction between Na and HF leads to the formation of sodium fluoride salt NaF and hydrogen gas. Na interacts with HF to form a complex HF···Na, and then the approaching of F atom of HF to Na results in a transition state H···F···Na. Accompanied by the broken of H-F bond, the bond forms between F and Na atoms as NaF, then the product NaF is yielded due to the removal of H atom. The resultant NaF can further form (NaF)4 tetramer. The interaction of NaF with HF leads to the complex NaF···HF; the form I as well as II of (NaF)4 can interact with HF to produce two complexes (i.e., (NaF)4(I-1)···HF, (NaF)4(I-2)···HF, (NaF)4(II-1)···HF and (NaF)4(II-2)···HF), but the form III of (NaF)4 can interact with HF to produce only one complex (NaF)4(III)···HF. These complexes were explored in terms of noncovalent interaction (NCI) and quantum theory of atoms in molecules (QTAIM) analyses. NCI analyses confirm the existences of attractive interactions in the complexes HF···Na, NaF···HF, (NaF)4(I-1)···HF, (NaF)4(I-2)···HF, (NaF)4(II-1)···HF and (NaF)4(II-2)···HF, and (NaF)4(III)···HF. QTAIM analyses suggest that the F···Na interaction forms in the HF···Na complex while the F···H hydrogen bonds form in NaF···HF, (NaF)4(I-1)···HF, (NaF)4(I-2)···HF, (NaF)4(II-1)···HF and (NaF)4(II-2)···HF, and (NaF)4(III)···HF complexes. Natural bond orbital (NBO) analyses were also applied to analyze the intermolecular donor-acceptor orbital interactions in these complexes. These results would provide valuable insight into the chemical reaction of Na and HF and the adsorption interaction between sodium fluoride salt and HF. The calculations were carried out at the M06-L/6-311++G(2d,2p) level of theory which were performed using the Gaussian16 program. Intrinsic reaction coordinate (IRC) calculations were carried out at the same level of theory to confirm that the obtained transition state was true. The molecular surface electrostatic potential (MSEP) was employed to understand how the complex forms. Quantum theory of atoms in molecules (QTAIM) and noncovalent interaction (NCI) analysis was used to know the topology parameters at bond critical points (BCPs) and intermolecular interactions in the complex and intermediate. The topology parameters and the BCP plots were obtained by the Multiwfn software.

A DFT + U-D3 Study of the Adsorption of Hydrogen Fluoride and Ethylene Carbonate on the Niobium-Doped (001), (011), and (111) Surfaces of Lithium Manganese Oxide

Cationic doping has been recommended as one of the most effective methods of reducing the number of trivalent manganese (Mn3+) ions that undergo a disproportionation reaction in lithium manganese oxide-based (LiMn2O4) lithium-ion batteries. However, the effect of surface doping on the major LiMn2O4 surfaces and their interactions with the electrolyte components is not yet fully understood. In this work, spin-polarised density functional theory-based calculations [DFT + U-D3 (BJ)] were employed to study the adsorption of the electrolyte components ethylene carbonate (EC) and hydrogen fluoride (HF) onto the Nb-doped major LiMn2O4 (001), (011), and (111) surfaces. During the substitution of niobium for manganese ions in the second surface layers (Nb second ), it was found that the (111) surface stability improves, resulting in an enhanced (111) plane on the morphology. However, replacing the first (Nb first ) as well as both top and sub-surface (Nb both ) layers of Mn atoms in the slabs maintains the same stability trend as in the pure pristine surfaces. Moreover, both adsorbates greatly preferred binding to the surfaces through the Nb instead of Mn atoms, and the largest adsorption energy was calculated for EC on the LiMn2O4 (011) surface doped on the Nb second site and for HF on the LiMn2O4 (111) surface doped on the Nb both site. Furthermore, the EC/HF adsorptions further enhance the stability of the Nb second (111) surface plane. However, minimal charge transfer was calculated for both HF and EC interacting with the pure and Nb-doped surfaces. Our findings are interesting, since exposing the (111) surface promotes the formation of a stable solid electrolyte interface (SEI), significantly reducing Mn dissolution and enhancing the adsorption of EC and HF.

First principle calculations including ab initio molecular dynamics studies for the activation of hydrogen fluoride on Ni(111)

The formation of an insulating nickel fluoride film on a nickel surface in contact with hydrogen fluoride (HF) is predicted to cause the low-voltage passivation of Ni anodes used in the Simons process. In this work, we examine the energetics of the activation of a single HF molecule adsorbing onto a Ni(111) surface using density functional theory with periodic boundary conditions. First, we calculate structures and energies of the minimum energy path towards dissociative chemisorption: physisorption intermediates, transition states and chemisorbed products. The calculated energies of the transition states are in the order of 380 meV, suggesting a surmountable activation barrier for chemisorption. To learn more in detail about the mechanism of the dissociative chemisorption, we additionally consider the adsorption of HF as a simulation of a molecular beam experiment by using ab initio molecular dynamics. Through analysis of the trajectories, the position of the center of mass of the HF molecule, upon collision with the Ni surface, is the most important factor for the probability of chemisorption. By comparison of the chemisorpion probability of an incoming HF molecule with the minimum energy path, we find that favorable HF impact angles for dissociative chemisorption do not correspond to the minimum energy path, due to the difference in mass between hydrogen and fluoride. The data points from the molecular dynamics simulations are fed into a neural network in order to fit a six-dimensional potential energy surface of HF on Ni(111), which is discussed.

Origin of enhanced thermal atomic layer etching of amorphous HfO2

HfO2 is a high-k material that is used in semiconductor devices. Atomic-level control of material processing is required for the fabrication of thin films of high-k materials at nanoscale device sizes. Thermal atomic layer etching (ALE) of metal oxides, in which up to one monolayer of material can be removed, can be achieved by sequential self-limiting fluorination and ligand-exchange reactions at elevated temperatures. First-principles-based atomic-level simulations using density functional theory can give deep insights into the precursor chemistry and the reactions that drive the etching of metal oxides. A previous study examined the hydrogen fluoride (HF) pulse in the first step in the thermal ALE process of crystalline HfO2 and ZrO2. This study examines the HF pulse on amorphous HfO2 using first-principles simulations. The Natarajan–Elliott analysis, a thermodynamic methodology, is used to compare reaction models representing the self-limiting and spontaneous etch processes taking place during an ALE pulse. For the HF pulse on amorphous HfO2, we found that thermodynamic barriers impeding spontaneous etching are present at ALE relevant temperatures. HF adsorption calculations on the amorphous oxide surface are studied to understand the mechanistic details of the HF pulse. An HF molecule adsorbs dissociatively by forming Hf–F and O–H bonds. HF coverages ranging from 1.1 ± 0.3 to 18.0 ± 0.3 HF/nm2 are investigated, and a mixture of molecularly and dissociatively adsorbed HF molecules is present at higher coverages. A theoretical etch rate of −0.82 ± 0.02 Å/cycle for amorphous HfO2 was calculated using a maximum coverage of 9.0 ± 0.3 Hf–F/nm2. This theoretical etch rate is greater than the theoretical etch rate for crystalline HfO2 that we previously calculated at −0.61 ± 0.02 Å/cycle. Undercoordinated atoms and void regions in amorphous HfO2 allow for more binding sites during fluorination, whereas crystalline HfO2 has a limited number of adsorption sites.

Equilibrium and Kinetic Adsorption of Hydrogen Fluoride onto Zeolite 3A

Equilibrium and kinetic adsorption behaviours of hydrogen fluoride (HF) onto zeolite 3A were investigated under different temperatures (298–338 K) and pressures (0.15–1.1 bar). The HF adsorption isotherms on zeolite 3A were well described by the Dubinin–Astakhov (DA) model. The isosteric heat of HF adsorption was calculated based on the DA model and Clausius–Clapeyron equation, and different kinetic models were used to analyze the HF adsorption kinetic. The results showed HF adsorption isotherms are type I of the IUPAC classification. The maximum adsorption capacities by the DA model are 0.443–0.5631 mg/g. The [Formula: see text] values decrease with increasing surface loading indicating the surface energy heterogeneity of zeolite 3A. The HF adsorption kinetics on zeolite 3A follows simple first-order kinetics. The calculated film diffusion parameter [Formula: see text] values show nonlinear characteristics with time. The order of magnitude of interparticle HF diffusion coefficient [Formula: see text] is 10−9 m2/s. The higher pressure and temperature are in favour of HF diffusion. The intraparticle diffusion curves for HF adsorption on zeolite 3A show quart-linear characteristics, indicating the presence of four consecutive HF adsorption steps including film diffusion, interparticle diffusion, intraparticle diffusion, and surface adsorption. The intraparticle diffusion is a rate-controlling stage.

HF and SiF4 adsorption on carbon graphite (1 1 1) surface in aqueous medium: A combined DFT and MD simulation approach

In this study, the adsorption properties of silicon tetrafluoride (SiF4) and hydrogen fluoride (HF) were investigated using density functional theory (DFT) and molecular dynamics (MD) simulation approaches. Many quantum chemical parameters related to the adsorption mechanism and global reactivity were calculated such as ELUMO, EHOMO, energy gap (ΔEgap), softness (S), chemical hardness (η), electronegativity (χ), chemical potential (µ), electrophilicity (ω), nucleophilicity (N), electrons transferred from molecules to graphite surface (ΔN), initial molecule-graphite interaction energy (Einteraction) and the energy change during the electronic back-donation process (ΔEb-d). The adsorption behaviors of the studied molecules on graphite (1 1 1) surface were investigated with the help of the molecular dynamics simulation. The optimum geometric configurations of the adsorption of SiF4 and HF on different possible sites in the graphite surface have been established. The corresponding adsorption energies, bond distances, Mulliken charges and electron density difference plots have been analyzed to understand the interaction at each site. The binding energies calculated for SiF4 were greater than those calculated for HF. The dynamic descriptors obtained were in good agreement with the results of quantum parameters.

Decomposition of tetrafluoromethane by reaction with CaO-enhanced zeolite

Tetrafluoromethane (CF4), the most stable perfluorocarbon, has a high global warming potential and high chemical stability. Various methods, including rotary kiln processing, plasma decomposition, and catalysts, are used to decompose CF4 before discharge to the atmosphere. However, these processes typically use a hydrolysis reaction to produce hydrogen fluoride (HF) and carbon dioxide, and the reactor needs to be made of specific materials to avoid corrosion from HF. In addition, adsorption or absorption of HF is required to render it harmless. Therefore, a dry process without HF production is desirable to decompose CF4.In this study, we investigated zeolite as a catalyst to promote the reaction between CaO and CF4. The effects of the zeolite type and mass fraction on CF4 decomposition were investigated. The catalytic activity of zeolite was in the order of mordenite (MOR) > ZSM-5 > Beta > Y. Ammonia temperature programmed desorption of the zeolites showed the order of the ratio of strong acid strength to weak acid strength agreed with the catalytic activity.A higher CaO mass fraction in the mixture meant the reaction could be carried out for longer. The optimum zeolite mass fraction and type were 10 % and MOR, respectively. This gave CF4 decomposition of > 90 % for about 5 h. The effect of the decomposition temperature was investigated at 923 and 973 K. Although the temperature did not affect CF4 decomposition, the CO2 selectivity changed greatly.

Density Functional Theory and Molecular Dynamics insights into the site-dependent adsorption of hydrogen fluoride on kaolinite

The removal of fluoride from water using adsorption on a low-cost mineral such as kaolinite is an important research topic. The present communication uses Density Functional Theory (DFT) and Molecular Dynamics (MD) based simulations to comprehensively investigate the adsorption behaviour of HF, one of the most predominant species of fluoride in the aqueous solutions, on the (0 0 1) surface of kaolinite. The optimum geometric configurations of adsorption of HF on different possible sites on the mineral surface have been established, and the corresponding adsorption energies, bond distances, Partial Density of States (PDOS), Mulliken charges and electron density difference plots have been analyzed to understand the interaction at each site. To explore the site-dependent adsorption behaviour, the interaction of HF has been investigated on different sites such as aluminium centres, surface oxygen atoms (both lying and upright) and cavity site (void space encircled by six aluminium centres). The analysis shows that the F atom has a strong tendency to form hydrogen bonds with the surface H atom on kaolinite. Among the three aforementioned types of adsorption sites considered, the “cavity” site is found to offer the greatest adsorption strength. Further, MD simulations have been undertaken to explain the effect of water on the adsorption and substantiate the bonding mechanism.

Experimental and theoretical assessment of the interactions of ionic liquids (ILs) with fluoridated compounds (HF, R-F) in organic medium

A liquid-liquid extraction procedure for the removal of fluoridated compounds [i.e., hydrogen fluoride (HF) and organic fluorides (R-F)] from alkylation gasoline (AG) using ionic liquids was studied both experimentally and theoretically. Synthesis and characterization of 1-butyl-3-methylimidazolium bromide, [C4MIM][Br], 1-butyl-3-metylimidazolium trifluoroacetate, [C4MIM][CF3COO], and 1-butyl-3-metylimidazolium bis(trifluoromethanesulphonyl)imide, [C4MIM][NTf2], ionic liquids (ILs) and its evaluation in the adsorption of HF and R-F species from organic medium (AG), was determined experimentally. Also the assessment of molecular interactions of HF with IL in the organic media was studied via Hybrid “QM (quantum mechanics)/MM (molecular mechanics)” Molecular Dynamics (MD) calculations. This QM/MM-MD simulations allowed the setting of a series of time equi-spaced HF-IL system configurations to evaluate interaction energies at QM theoretical level between HF and the closest ILs, as well as the mapping of Non-Covalent Interactions (NCI). Experiments indicate that fluoridated ILs are more efficient for HF extraction than brominated ILs. From the calculated interaction energies and NCI mapping it seems that the capacity of the anion of ILs to form hydrogen bonds with HF is the driving force in HF extraction.

Adsorption of hydrogen fluoride on alkaline earth fluoride surfaces: A first-principles study

We have performed periodic first-principles calculations for the adsorption of hydrogen fluoride on the three low index surfaces (111), (110) and (100) of alkaline earth metal fluorides MF2 (M = Ca, Sr and Ba). Adsorption energies were calculated using the two density functionals PBE and PBE0, Hartree–Fock and dispersion correction to PBE. We found that PBE and PBE0 yield similar adsorption energies, both predicting stronger adsorption than Hartree–Fock, and the largest energies were calculated with PBE-D3 correction. Adsorption structures and energies are discussed for different HF coverages, at the PBE level. Both, the interactions of HF with the surface fluorine anions and the interactions among the adsorbed HF molecules are found to play a crucial role in the adsorption process.

The role of boron nitride nanotube as a new chemical sensor and potential reservoir for hydrogen halides environmental pollutants

Density functional theory (DFT) studies on the interaction of hydrogen halides (HX) environmental pollutants and the boron nitride nanotubes (BNNTs) have been reported. To exploit the possibility of BNNTs as gas sensors, the adsorption of hydrogen fluoride (HF), hydrogen chloride (HCl) and hydrogen bromide (HBr) on the side wall of armchair (5,5) boron nitride nanotubes have been investigated. B3LYP/6-31G (d) level were used to analyze the structural and electronic properties of investigate sensor. The adsorption process were interpreted by highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO), quantum theory of atoms in molecules (QTAIM), natural bond orbital (NBO) and molecular electrostatic potential (MEP) analysis. Topological parameters of bond critical points have been used to calculate as measure of hydrogen bond (HB) strength. Stronger binding energy, larger charge transfer and charge density illustrate that HF gas possesses chemisorbed adsorption process. The obtained results also show the strongest HB in HF/BNNT complex. We expect that results could provide helpful information for the design of new BNNTs based sensing devices.

The effect of electron correlation on the adsorption of hydrogen fluoride and water on magnesium fluoride surfaces.

We have performed periodic density functional and periodic local MP2 calculations for the adsorption of hydrogen fluoride and water on the four low index surfaces (001), (100), (101) and (110) of magnesium fluoride. While the adsorption of HF is described well using B3LYP, MP2 is required for a good description of the adsorption of H2O. Post-optimization dispersion corrections of B3LYP are found to consistently overestimate the adsorption energy. The coordination of surface cations, the presence of hydroxyls on the surface, as well as the coverage appear to play an equally important role in the adsorption.

DFT study of the dissociative adsorption of HF on an AlN nanotube

Abstract We have investigated the adsorption of hydrogen fluoride (HF) on the AlN nanotube surface using density functional theory in terms of energetic, structural and electronic properties. By overcoming energy barriers of 27.90–52.30 kcal/mol, HF molecule is dissociated into H and F species on the tube surface and its molecular structure is not preserved after the adsorption process. Dissociation energies have been calculated to be −52.57 and −70.10 kcal/mol. The process has negligible effect on the electronic and field emission properties of the AlN nanotube. This process may increase the solubility of AlN nanotubes.

Density functional theory calculations of adsorption of hydrogen fluoride on titanium embedded graphene

In order to search for a gas sensor to detect hydrogen fluoride (HF), the adsorption of HF on transition metal-embedded graphene (TM/graphene) is investigated by density functional theory calculations. Compared with the relatively weak adsorption on other TM/graphene systems, HF molecule tends to be adsorbed on Ti/graphene with appreciable adsorption energy. Based on these calculations, two gas sensing mechanisms are proposed and revealed that both surface reconstruction and charge transfer result in a change of electronic conductance of Ti/graphene. Thus, this developed Ti/graphene would be an excellent candidate for sensing HF with lower cost and higher activity.

Surface Chemical Reaction Model of Silicon Dioxide Film Etching by Dilute Hydrogen Fluoride Using a Single Wafer Wet Etcher

A surface chemical reaction model of silicon dioxide film etching by hydrogen fluoride aqueous solution using a single wafer wet etcher was numerically evaluated taking into account the Langmuir-type rate theory and the transport phenomena. The surface reaction process was assumed to consist of three steps, such as (i) hydrogen fluoride adsorption at the silicon dioxide surface, (ii) chemical reaction of silicon dioxide with hydrogen fluoride and (iii) desorption of the by-product from the surface. The rate constants determined by calculation which could reproduce the silicon dioxide etching rate obtained by experiment. The rate limiting step was additionally evaluated.

Adsorption of hydrogen fluoride on SiC surfaces: A density functional theory study

We have carried out first-principles reaction path simulations of hydrogen fluoride (HF) adsorption at steps and terraces of 3C-silicon carbide (SiC) (111) surfaces to investigate initial processes in catalyst-referred etching (CARE). CARE is a novel abrasive-free planarization method and has been invented in our group. In SiC CARE, we use platinum as a catalyst and hydrofluoric acid (HF) solution as an etchant. A crystallographically undamaged and smooth SiC surface is obtained after CARE. In this study, we performed first-principles reaction path simulations using the Simulation Tool for Atom Technology (STATE) program package. Our results showed that the adsorption of HF molecules at step edges has lower activation barrier than that at terraces, and that HF adsorption at F-terminated surfaces is easier than that at OH-terminated surfaces.

Hydrogen fluoride adsorption and reaction on the α-Al2O3(0001) surface: A density functional theory study

The adsorption and reaction behaviors of HF on the α-Al(2)O(3)(0001) surface are systematically investigated using density functional theory method. By increasing the number of HF molecules in a p(2 × 1) α-Al(2)O(3)(0001) slab, we find that HF is chemically dissociated at low coverage; while both physical and dissociative adsorption occurs at a 3/2 monolayer (ML) coverage. At the same coverage (1.0 ML), diverse configurations of the dissociated HF are obtained in the p(2 × 1) model; while only one is observed in the p(1 × 1) slab due to its smaller surface area compared with the former one. Preliminary fluorination reaction study suggests that the total energy of two dissociated HF in the p(2 × 1) slab increases by 1.00 and 0.72 eV for the formation and desorption of water intermediate, respectively. The coadsorption behaviors of HF and H(2)O indicate that the pre-adsorbed water is unfavorable for the fluorination of Al(2)O(3), which is well consistent with the experimental results. The calculated density of states show that the peak of σ(H-F) disappears, while the peaks of σ(H-O) and σ(Al-F) are observed at -8.4 and -5 to -3 eV for the dissociated HF. Charge density difference analysis indicates that the dissociated F atom attracts electrons, while no obvious changes on electrons are observed for the surface Al atoms.

Adsorption of hydrogen fluoride onto activated carbon under vacuum conditions: Equilibrium, kinetic and thermodynamic investigations

In this study, the adsorption of HF gas by three types of activated carbon has been investigated under vacuum condition. The effects of experimental parameters such as initial pressure of the HF gas, contact time and temperature on adsorption process have been investigated. The results showed that the adsorption of the HF gas onto activated carbon increased by increasing initial pressure of gas, while it decreased with increase in temperature. The Freundlich isotherm model fitted the equilibrium data better than the other isotherm models. Using Langmuir isotherm model, the maximum adsorption capacities of the first type, the second type and third type of activated carbon were 226.4, 268.8 and 258.9 mg/g, respectively. Experimental data were also evaluated in terms of kinetic characteristics of adsorption and it was found that the adsorption process followed well pseudo-second-order kinetics. Thermodynamic parameters, the change of free energy (?G?), enthalpy (?H?) and entropy (?S?) of adsorption were calculated at the temperature range of 28-55?C. The results showed that the adsorption of HF on activated carbon is feasible, spontaneous and exothermic.

Hydrogen Fluoride Adsorption Ability of some Inorganic Compounds

Based on the traditional method of adsorption of the hydrogen fluoride, we mainly selected some typical inorganic compounds α-Al2O3, γ-Al2O3, CaF2and NaF as the adsorbents, studied and discussed the effect of their adsorption ability of the hydrogen fluoride gas. Comprehensive comparison showed that NaF was the best adsorbent for hydrogen fluoride gas. Meanwhile, as the raw materials for the production of hydrogen fluoride gas, CaF2was also used as an adsorbent, and the measurement showed that CaF2has barely adsorption ability for hydrogen fluoride gas. Using the electronic analytical balance and fourier transform infrared spectroscopy, the absorption efficacy of different inorganic compounds with equal quality for the same amount of hydrogen fluoride gas was analyzed and characterized.