Adsorption Of Benzene Molecules Research Articles

Double-walled Al-based MOF with large microporous specific surface area for trace benzene adsorption.

Double-walled metal-organic frameworks (MOFs), synthesized using Zn and Co, are potential porous materials for trace benzene adsorption. Aluminum is with low-toxicity and abundance in nature, in comparison with Zn and Co. Therefore, a double-walled Al-based MOF, named as ZJU-520(Al), with large microporous specific surface area of 2235 m2 g-1, pore size distribution in the range of 9.26-12.99 Å and excellent chemical stability, was synthesized. ZJU-520(Al) is consisted by helical chain of AlO6 clusters and 4,6-Di(4-carboxyphenyl)pyrimidine ligands. Trace benzene adsorption of ZJU-520(Al) is up to 5.98 mmol g-1 at 298 K and P/P0 = 0.01. Adsorbed benzene molecules are trapped on two types of sites. One (site I) is near the AlO6 clusters, another (site II) is near the N atom of ligands, using Grand Canonical Monte Carlo simulations. ZJU-520(Al) can effectively separate trace benzene from mixed vapor flow of benzene and cyclohexane, due to the adsorption affinity of benzene higher than that of cyclohexane. Therefore, ZJU-520(Al) is a potential adsorbent for trace benzene adsorption and benzene/cyclohexane separation.

Effect of pore size distribution of biomass activated carbon adsorbents on the adsorption capacity

AbstractBACKGROUNDIn order to investigate the correlation between the pore size distribution of biomass activated carbon adsorbents (BACAs) and VOCs (volatile organic compounds) adsorption/desorption performance. Four BACAs with same specific surface area but different pore size distribution were prepared under different experimental conditions and processes.RESULTSThe impact of the pore size distribution of BACAs on the adsorption/desorption performance of benzene, toluene and xylene was investigated. The results indicated that the adsorption ability of the prepared BACAs for benzene, toluene and xylene was mostly affected by the pore sizes distributed in the 2.60 ~ 3.25, 2.68 ~ 3.35and 4.20 ~ 4.90 nm ranges, respectively, when the studied BACAs had similar specific surface area (SBET ≈ 1080 m2 g−1). However, the desorption amount of adsorbed benzene molecules mainly relied on the pore structures of BACAs having pore sizes in the 3.95 ~ 4.60 nm range.CONCLUSIONThe pore structures of BACAs distributed in different pore size ranges have various effects on the phenyl VOCs adsorption capacity. Benzene adsorption on the BACAs was mainly affected by the microporous structures. The pore structure with larger pore size was more favorable for the desorption of the adsorbed toluene and xylene molecules compared to the adsorbed benzene molecules. Benzene, toluene and xylene had low residual rates in the studied activated carbon adsorbents attesting to their superior regenerative properties. This work could provide an important reference for the design, preparation, and selection of activated carbon adsorbents for the adsorption capacity of benzene, toluene and xylene. © 2024 Society of Chemical Industry (SCI).

Control of the pore chemistry in metal-organic frameworks for efficient adsorption of benzene and separation of benzene/cyclohexane

Control of the pore chemistry in metal-organic frameworks for efficient adsorption of benzene and separation of benzene/cyclohexane

Substitution (CH3, Cl, or Br) effects of the imidazolate linker on benzene adsorption kinetics for the zeolitic imidazolate framework (ZIF)-8.

Herein, the time dependence of benzene adsorption uptake was examined for ZIF-8, Cl-ZIF-8, and Br-ZIF-8 and analysed using an intra-crystalline (Fick's) diffusion model, yielding the diffusion coefficient and saturated adsorption amount of benzene. The saturated adsorption amount of benzene decreased in the order of ZIF-8, Cl-ZIF-8, and Br-ZIF-8. Notably, ZIF-8, with an intermediate pore volume among the three specimens, accommodated the greatest number of molecules (5.5 molecules per micropore). The activation energy, Ea, and the pre-exponential factor, D0, for benzene diffusion increased in the order of ZIF-8, Cl-ZIF-8, and Br-ZIF-8. These findings suggest that the 2-methylimidazolate moiety forms an effective attraction interaction with benzene molecules. The D0 values also yielded the activation entropy, ΔS‡, in the transition state when a benzene molecule passed through a six-membered ring aperture. The ΔS‡ values at 303 K were negative, and their absolute values increased in the order of Br-ZIF-8, Cl-ZIF-8, and ZIF-8. Considering the degree of freedom of translation and rotation of the benzene molecule and the vibration and disorder of the linker, we found that the differences in ΔS‡ were caused by the dynamic local structure of the six-membered ring aperture among the ZIF-8 analogues. Furthermore, infrared spectroscopy revealed a low-wavenumber shift of the C-H stretching band in both the imidazolate moiety and adsorbed benzene molecules. A solid-state 13C-nuclear magnetic resonance spectrum presented a downfield shift of 13C resonance peaks in the imidazolate moiety, suggesting that CH/π interactions reasonably explain the intermolecular interaction between the imidazolate moiety (including the methyl group) and π-electrons of benzene.

Domains of the adsorbed benzene monolayer on graphene

We consider the adsorbed benzene monolayer on graphene and show that the monolayer’s structure can be very complicated even for benzene, the simplest representative of the cyclic hydrocarbons. We base this on previous the first principal investigations, which found different energy states of the adsorbed benzene molecule. We find the existence of the six domains (star domains) for the stable molecular monolayer. The representatives of these domains (grains) at the graphene hexagonal layer are star vectors that describe transitions from symmetric high energy state into the stable low symmetric position. In the hexagon lattice of any benzene close pack domain, we introduce the primitive unit vectors, which are twice longer than the graphene primitive unit ones. The symmetry elements of the adsorbed benzene monolayer on graphene are found, left and right domains are introduced. Besides, half-translation of the benzene domains on the graphene primitive unit vectors leads to a further increase in the variety of the domain types. We introduce the selection procedure to decrease the number of the possible domains, find zero-block cells, and the complete number of the benzene domains — eight. We find all types of the structural domains and show their relation with the graphene unit cell construction.

The vibrational properties of benzene on an ordered water ice surface

ABSTRACT We present a hybrid CCSD(T) + PBE-D3 approach to calculating the vibrational signatures for gas-phase benzene and benzene adsorbed on an ordered water ice surface. We compare the results of our method against experimentally recorded spectra and calculations performed using PBE-D3-only approaches (harmonic and anharmonic). Calculations use a proton ordered XIh water ice surface consisting of 288 water molecules, and results are compared against experimental spectra recorded for an ASW ice surface. We show the importance of including a water ice surface into spectroscopic calculations, owing to the resulting differences in vibrational modes, frequencies, and intensities of transitions seen in the IR spectrum. The overall intensity pattern shifts from a dominating ν11 band in the gas-phase to several high-intensity carriers for an IR spectrum of adsorbed benzene. When used for adsorbed benzene, the hybrid approach presented here achieves an RMSD for IR active modes of 21 cm−1, compared to 72 cm−1 and 49 cm−1 for the anharmonic and harmonic PBE-D3 approaches, respectively. Our hybrid model for gaseous benzene also achieves the best results when compared to experiment, with an RMSD for IR active modes of 24 cm−1, compared to 55 cm−1 and 31 cm−1 for the anharmonic and harmonic PBE-D3 approaches, respectively. To facilitate assignment, we generate and provide a correspondence graph between the normal modes of the gaseous and adsorbed benzene molecules. Finally, we calculate the frequency shifts, Δν, of adsorbed benzene relative to its gas-phase to highlight the effects of surface interactions on vibrational bands and evaluate the suitability of our chosen dispersion-corrected density functional theory.

Tuning Electronic and Magnetic Properties of Two-Dimensional Ferromagnetic Semiconductor CrI3 through Adsorption of Benzene

Two-dimensional (2D) ferromagnetic (FM) semiconductor chromium triiodide (CrI3) has attracted much attention because of its long-range two-dimensional (2D) FM order and tunable interlayer magnetic coupling. In the present work, the electronic and magnetic properties of CrI3 monolayer adsorbing benzene molecules (denoted as C6H6@CrI3) is systematically investigated by means of first-principles calculations, which gives a better understanding and particular opportunity of crafting desired properties of this material. It is found that the adsorption of benzene molecules can enhance the optical absorption and FM couplings of CrI3 monolayer. The enhancement of FM coupling is independent of the adsorption concentration of benzene molecules. We hope that these findings will bring additional interest to the newly experimentally synthesized 2D FM semiconductor.

The modification of benzene adsorption on zigzag single-wall carbon nanotubes by carboxylation

In this work, the adsorption of benzene molecule on (10,0) functionalized zigzag single-wall carbon nanotubes was studied using density functional theory. Geometric structures, adsorption energies and electronic properties of five supercells were investigated. It was found that the carboxylation causes a notable increment in the adsorption capability of SWCNT in uptaking benzene as a pollutant molecule. The highest absorbency was achieved when benzene molecule had interaction with both SWCNT and COOH functional group through π-π interaction and hydrogen bonding.

Effect of Polarity of Activated Carbon Surface, Solvent and Adsorbate on Adsorption of Aromatic Compounds from Liquid Phase.

In this study, introduction of acidic functional groups onto a carbon surface and their removal were carried out through two oxidation methods and outgassing to investigate the adsorption mechanism of aromatic compounds which have different polarity (benzene and nitrobenzene). Adsorption experiments for these aromatics in aqueous solution and n-hexane solution were conducted in order to obtain the adsorption isotherms for commercial activated carbon (BAC) as a starting material, its two types of oxidized BAC samples (OXs), and their outgassed samples at 900 °C (OGs). Adsorption and desorption kinetics of nitrobenzene for the BAC, OXs and OGs in aqueous solution were also examined. The results showed that the adsorption of benzene molecules was significantly hindered by abundant acidic functional groups in aqueous solution, whereas the adsorbed amount of nitrobenzene on OXs gradually increased as the solution concentration increased, indicating that nitrobenzene can adsorb favourably on a hydrophilic surface due to its high dipole moment, in contrast to benzene. In n-hexane solution, it was difficult for benzene to adsorb on any sample owing to the high affinity between benzene and n-hexane solvent. On the other hand, adsorbed amounts of nitrobenzene on OXs were larger than those of OGs in n-hexane solution, implying that nitrobenzene can adsorb two adsorption sites, graphene layers and surface acidic functional groups. The observed adsorption and desorption rate constants of nitrobenzene on the OXs were lower than those on the BAC due to disturbance of diffusion by the acidic functional groups.

Adsorption of Benzene on 4H-SiC (0001) Surface: First Principles Calculations

We study adsorption of the benzene molecule on the Si terminated (0001) surface of 4H-SiC by performing rst principles calculations in the framework of density functional theory. We nd out that chemical reaction leading to the chemisorption of benzene on the surface has endothermic character. The adsorbed benzene molecule is bounded to two surface Si atoms and it does not lose its integrity, however, it undergoes strong deformations and causes distortion of the substrate. We analyze also changes in the electronic structure caused by benzene adsorption.

Modification of the structural and electronic properties of graphene by the benzene molecule adsorption

Abstract A survey of the literature data on the adsorption of benzene on graphene or carbon nanotubes indicates that the distance between the graphene sheet and benzene molecule is determined from weak van der Waals forces (∼3.40 A). In our theoretical study, it was found that the benzene/graphene structure (in a specific configuration with carbon atoms located at the atop positions, stacked directly on the top of each other) forms strong covalent bonds, if the distance between the graphene and benzene is about 1.60 A. Such a short distance corresponds to about a half of the usual separation between the graphite layers. It was also shown that at such a short distance the carbon atoms of the benzene molecule move towards the graphene sheet, whereas the hydrogen atoms move in a different direction, thus breaking the benzene planar structure. In addition to the structural optimization, the calculated electronic and optical properties (significantly modified by the adsorbed benzene molecule) are presented as well.

Computer Simulation of Benzene–Water Mixture Adsorption in Graphitic Slit Pores

The adsorption of mixtures of benzene–water in graphitic slit pores has been studied using Monte Carlo simulation. It is shown that the adsorption of the mixture starts with the adsorption of benzene molecules on the graphite surface which then act as anchors for water molecules to adsorb. High loadings of water in a slit pore significantly affect the arrangement and orientation of benzene molecules. When the water density in the pore approaches its bulk liquid density, water molecules displace some benzene molecules from the surface, and the benzene sorption process switches from adsorption to an absorption mechanism. We have also studied the influence of the external vapor composition on the adsorption isotherms of benzene and water. It is observed that a high concentration of benzene in the vapor phase facilitates the adsorption of both benzene and water in such a manner that the condensation pressure of benzene and the onset pressure of water adsorption shift to lower values. At high pressures, the adsorption of water is dominant at the expense of benzene adsorption. This interesting finding calls for a review of the concept of graphite surface hydrophobicity when water is coadsorbed with hydrocarbons.

Rice-ball structures of iron–benzene clusters, Fe 4–(C 6H 6) m, m ⩽ 3. A density functional study

Geometrical rice-ball structures of the Fe 4 cluster with capped adsorbed benzene molecules for neutral, anion, and cation species, Fe 4–(C 6H 6) m ( m ⩽ 3), are studied by means of all-electron calculations done with the BPW91 approach of density functional theory jointly with 6-311++G(2d, 2p) basis sets. Electronic properties like ionization energies and electron affinities as well as binding energies are estimated and are in good agreement with recently reported experimental results. The computed IR spectra for these species show vibrational bands near those of the isolated benzene molecule and some forbidden IR modes of this ligand become IR active in Fe 4–(C 6H 6) m ( m ⩽ 3). The metal-benzene bonding issue was studied through the contour plots of molecular orbitals, showing signatures of metal–carbon bonding, originated from the 3d electrons of Fe 4 and the 2pπ electrons of benzene.

Reversible structural change of host framework triggered by desorption and adsorption of guest benzene molecules in Fe(NCS) 2(bpp) 2·2(benzene) (bpp = 1,3-bis(4-pyridyl)propane)

Assembled iron complex Fe(NCS) 2(bpp) 2·2(benzene) (bpp = 1,3-bis(4-pyridyl)propane), enclathrating benzene molecules, has been synthesized and its host framework was 1D chain structure. By releasing benzene molecules, the host framework changed to 2D interpenetrated structure. The desorbed complex enclathrated benzene molecules again and the host framework returned to 1D structure. Although the spin state remained in the high spin upon the desorption and adsorption of the benzene molecules, 57Fe Mössbauer spectra revealed that the symmetry around iron atom changed depending on the sorption. The reversible structural change of host framework was tried to explain by two factors: the crystal stability by making up the interstitial space and the conformer stability in coordinated bridging ligand bpp.

Adsorption and Structure of Benzene on Silica Surfaces and in Nanopores

Grand canonical Monte Carlo simulations are used to study the adsorption of benzene on atomistic silica surfaces and in cylindrical nanopores. The effect of temperature and surface chemistry is addressed by studying the adsorption of benzene at 293 and 323 K on both fully and partially hydroxylated silica surfaces or nanopores. We also consider the adsorption of benzene in a cylindrical nanopore of diameter D=3.6 nm and compare our results with those obtained for planar surfaces. The structure of benzene in the vicinity of the planar surface and confined in the cylindrical nanopore is determined by calculating orientational order parameters and examining positional pair correlation functions. The density profiles of adsorbed benzene reveal the strong layering of the adsorbate, which decays with the distance from the silica surface. At a given temperature and at low pressures, the film adsorbed at the fully hydroxylated silica surface is larger than that for the partially hydroxylated silica surface. This result is due to an increase in the density of silanol groups that induces an increase in the polarity of the silica surface, which becomes more attractive for the adsorbate. Our results also suggest that the benzene molecules prefer an orientation in which their ring is nearly perpendicular to the surface when fully hydroxylated surfaces are considered. When partially hydroxylated surfaces are considered, a second preferential orientation is observed where the benzene ring forms an angle of approximately 50 degrees with the silica surface. In this case, the average orientation of the benzene molecules appears disordered as in the bulk phase. These results suggest that determining the experimental orientation of benzene in the vicinity of a silica surface is a difficult task even when the surface chemistry is known. Capillary condensation in the nanopores involves a transition from a partially filled pore (a thin film adsorbed at the pore surface) to a completely filled pore configuration where the confined liquid coexists at equilibrium with the external gas phase. The disordered orientation of the adsorbed benzene molecules in the case of the partially hydroxylated surface favors the condensation of benzene molecules (the condensation pressure for this substrate is lower than that for the fully hydroxylated surface). Finally, these results are consistent with the structural analysis, showing that (1) benzene tends to relax its liquid structure a little in order to optimize its molecular arrangement near the pore wall and (2) the disordering of the liquid structure induced by the surface becomes stronger as the interaction with the pore wall increases.

UV-Raman and Fluorescence Spectroscopy of Benzene Adsorbed Inside Zeolite Pores

UV-Raman spectroscopy was used to investigate the host−guest interactions of benzene molecules adsorbed within siliceous MFI. With use of 244 nm ultraviolet laser light as the excitation source, several new peaks appear in the spectra. These peaks are not expected from normal Raman scattering of liquid benzene and not seen in the FT-Raman spectra of benzene in silicalite, but appear in the UV-Raman spectra because of the Raman resonance effect. Further investigations diminish the possibility that the new peaks are due to laser-induced chemical reactions. The fluorescence spectra show the fluorescence bands of benzene with vibration progressions, which suggests that the adsorbed benzene molecules are not clustered. Considering that the dimensions of benzene molecules closely match the channel sizes of MFI, it is proposed that the symmetry of D6h-benzene in the excited state degrades to lower symmetry upon adsorption due to compression of benzene molecules inside MFI pores. In support of this result, UV-Ram...

Catalytic reduction of NO in the presence of benzene on a Pt(3 3 2) surface

The catalytic reduction of NO in the presence of benzene on the surface of Pt(3 3 2) has been studied using Fourier transform infra red reflection-absorption spectroscopy (FTIR-RAS) and thermal desorption spectroscopy (TDS). IR spectra show that while the presence of benzene molecules at low coverage (e.g., following an exposure of just 0.25 L) promotes NO–Pt interaction, the adsorption of NO on Pt(3 3 2) at higher benzene coverages is suppressed. It is also shown that there are no strong interactions between the adsorbed NO molecules and the benzene itself or benzene-derived hydrocarbons, which can lead to the formation of intermediate species that are essential for N 2 production. TDS results show that the adsorbed benzene molecules undergo dehydrogenation accompanied by hydrogen desorption starting at 300 K and achieving a maximum at 394 K. Subsequent dehydrogenation of the benzene-derived hydrocarbons then begins with hydrogen desorption starting at 500 K. N 2 desorption from NO adlayers on clean Pt(3 3 2) surface becomes significant at temperatures higher than 400 K, giving rise to a peak at 465 K. This peak corresponds to N 2 desorption from NO dissociation on step sites. The presence of benzene promotes N 2 desorption, depending on the benzene coverage. When the benzene exposure is 0.25 L, the N 2 desorption peak at 459 K is dramatically increased. Increasing benzene coverage also results in the intensification of N 2 desorption at ∼410 K. At benzene exposures of 2.4 L, N 2 desorption develops as a broad peak with a maximum at ∼439 K. It is concluded that the catalytic reduction of NO by platinum in the presence of benzene proceeds by NO decomposition and subsequent oxygen removal at temperatures lower than 500 K, and NO dissociation is a rate-limiting step. The contribution of benzene to N 2 desorption is mainly attributed to providing a source of H, which quickly reacts with NO-derived atomic O, leaving the surface with more vacant sites for further NO dissociation.

Magnetic moments of bare and benzene-capped cobalt clusters

Magnetic moments of bare cobalt clusters Co(n) (n=7-32) and benzene-capped cobalt clusters Co(n)(bz)(m) have been measured at temperatures ranging from 54 to 150 K using a molecular beam deflection method. It was observed that Co(12-32) produced at temperatures greater than approximately 100 K display high-field-seeking behavior at all temperatures in the range investigated, indicating that they are superparamagnetic species. At temperatures below approximately 100 K, the field-on beam profiles of Co(7-11) and some larger clusters displayed substantial symmetric broadening, indicating that some fraction of the clusters in the beam were no longer superparamagnetic, but rather were in a blocked (locked-moment) state. In the superparamagnetic regime (T=150 K) Co(n) clusters in the n=7-32 size range were found to possess per-atom moments ranging from 1.96+/-0.04 micro(b)(Co(24)) to 2.53+/-0.04 micro(b)(Co(16)), significantly above the bulk value of 1.72 micro(b). Locked-moment isomers were found to display moments of approximately 1 micro(b) per atom. Cobalt clusters containing a layer of adsorbed benzene molecules were found to possess significantly lower moments per cobalt atom than the corresponding bare cobalt clusters.

Adsorption of Benzene on Graphitized Thermal Carbon Black: Reduction of the Quadrupole Moment in the Adsorbed Phase

The performance of intermolecular potential models on the adsorption of benzene on graphitized thermal carbon black at various temperatures is investigated. Two models contain only dispersive sites, whereas the other two models account explicitly for the dispersive and electrostatic sites. Using numerous data in the literature on benzene adsorption on graphitized thermal carbon black at various temperatures, we have found that the effect of surface mediation on interaction between adsorbed benzene molecules must be accounted for to describe correctly the adsorption isotherm as well as the isosteric heat. Among the two models with partial charges tested, the WSKS model of Wick et al. that has only six dispersive sites and three discrete partial charges is better than the very expensive all-atom model of Jorgensen and Severance. Adsorbed benzene molecules on graphitized thermal carbon black have a complex orientation with respect to distance from the surface and also with respect to loading. At low loadings, they adopt the parallel configuration relative to the graphene surface, whereas at higher loadings (still less than monolayer coverage) some molecules adopt a slant orientation to maximize the fluid-fluid interaction. For loadings in the multilayer region, the orientation of molecules in the first layer is influenced by the presence of molecules in the second layer. The data that are used in this article come from the work of Isirikyan and Kiselev, Pierotti and Smallwood, Pierce and Ewing, Belyakova, Kiselev, and Kovaleva, and Carrott et al.

Coverage-dependent adsorption behavior of benzene on Si(100): A high-resolution photoemission study

The adsorption of benzene molecules on Si(100) is investigated by high-resolution core-level photoelectron spectroscopy using synchrotron radiation as well as ultraviolet photoelectron spectroscopy (UPS) for valence bands. The C $1s$ photoelectron spectra of benzene adsorbates are found to consist of two different components, which represent carbon atoms with or without a direct $\mathrm{Si}\ensuremath{-}\mathrm{C}$ bond. The population ratio of these two components exhibits a drastic change upon increasing the molecular coverage. This is explained by the coverage-dependent change of the adsorbate structure, which is corroborated by the noticeable variation of the molecular orbitals in the valence bands as observed by UPS. From these results, it is deduced that the population of the di-$\ensuremath{\sigma}$ structure increases significantly at a high coverage over the tetra-$\ensuremath{\sigma}$ structure which is energetically favored at a low coverage. This indicates the importance of the interaction between the adsorbate molecules at a high coverage.