Adsorption Of Different Molecules Research Articles

3D nanostructure prediction of porous carbons via gas adsorption

Structural characterization of porous carbon materials is critical for the evaluation of their synthesis procedures and performance. Throughout the last decades, many methods have been employed to determine porosity properties from gas adsorption such as surface area, pore size distribution (PSD) and real density. However, gas adsorption models use 1D structures of carbon nanopores, although adsorption and separation properties of nanoporous carbons are governed by 3D pore parameters. Estimating the 3D nanostructure of nanoporous carbons using gas adsorption would accelerate progress in research and implementation of nanoporous carbons. We report here a promising 3D pore nanostructural characterization from gas adsorption. Using atomistic simulations, we have generated a database of realistic 3D porous carbon structures spanning a wide range of pore sizes and geometries. After calculating their gas adsorption isotherms, we employed a numerical procedure to find the relative contribution for each of the structures to the adsorption isotherm of a nanoporous carbon sample. These contributions allowed us to estimate the surface area and pore size distribution of carbon materials; moreover (and perhaps more importantly!), we will show that the plausible 3D pore structures correlate very well with the local carbon structure as experimentally determined by high-resolution TEM observations and can successfully predict adsorption of different molecules. This is a powerful procedure that can be extended to other materials, and with enough computer power, to larger pore sizes.

Magnetic ε-Phosphorene for Sensing Greenhouse Gas Molecules.

It is critical for gas sensors that sense greenhouse gas molecules to have both good sensitivity and selectivity for water molecules in the ambient environment. Here, we study the charge transfer, IV curves, and electric field tuning of vanadium-doped monolayer ϵ-phosphorene as a sensor for NO, NO2, and H2O gas molecules via first-principle and transport calculations. We find that the paramagnetic toxic molecules of NO and NO2 have a high adsorption energy on V-ϵ-phosphorene, which originates from a large amount of charge transfer driven by the hybridisation of the localised spin states of the host with the molecular frontier orbital. Using the non-equilibrium Green's function, we investigate the IV responses with respect to the adsorption of different molecules to study the performance of gas molecule sensors. Our IV curves show a larger amount of changes in resistance of the paramagnetic NO and NO2 than nonmagnetic H2O gas molecules, suggesting both sensitivity and selectivity. Moreover, our calculations show that an applied external electric field (gate voltage) can effectively tune the amount of charge transfer. More charge transfer makes the sensor more sensitive to the molecule, while less charge transfer can reduce the adsorption energy and remove the adsorbed molecules, allowing for the repeated use of the sensor.

Adsorption of gas molecules on a C3N monolayer and the implications for NO2 sensors

Recent reports have raised exciting prospects for the use of C3N monolayers exhibiting excellent adsorptive properties in nanodevice applications. In this study, we carried out first-principle calculations to investigate the adsorption of NO2, NO, CO, HCN, NH3, CO2, H2, N2, CH4, H2O, O2, and N2O gas molecules on a C3N monolayer as well as its potential applications in gas sensor devices. Our results reveal that the chemisorption of NO2 can significantly influence the electronic properties of the C3N monolayer (e.g., changing semiconducting behavior to conducting behavior). In contrast, physisorption of the other gas molecules had little effect on the electronic properties of the C3N monolayer. These results suggest that the C3N monolayer is much more sensitive and selective to NO2 than to the other gases. The recovery time of NO2 at T = 300 K is only 0.62 s. Moreover, the optical properties of the C3N monolayer can be modified as a result of the adsorption of different molecules, especially the NO2 molecule. Thus, the C3N monolayer is a promising and desirable candidate for use as a suitable material in gas sensors for NO2 detection.

Evaluation of mesoporous silica and Nb-doped titanate as molecule carriers through adsorption/desorption study

Silica and Nb-doped titanate were evaluated as carriers of molecules with different characteristics on the basis of adsorption/desorption. Ovalbumin, gentamicin, and methyl blue were used as model molecules to study the adsorption onto these mesoporous materials as well as the possibility of desorption. Experiments were set to evaluate the kinetics of molecules’ adsorption and release as well as adsorption isotherms. Results show that Nb-doped titanate appeared to be a more suitable carrier than silica for all three molecules. Ovalbumin was adsorbed onto both evaluated materials in the highest amount. Additionally, linearized Langmuir isotherm model showed a good fit in describing the adsorption of different molecules onto silica and Nb-doped titanate.

Gas sensing properties of buckled bismuthene predicted by first-principles calculations.

First-principles calculations are used to study the structural, electronic, transport and optical properties of buckled bismuthene with the adsorption of various gas molecules such as CO, O2, H2O, NH3, SO2, NO and NO2. By considering the van der Waals interactions between the gas molecules and buckled bismuthene, we find that the buckled bismuthene shows superior gas sensing performance to other 2D materials such as graphene and MoS2. The adsorption of CO, O2, H2O and NH3 molecules is physisorption, whereas SO2, NO and NO2 are chemisorbed on the buckled bismuthene with large charge transfer and strong adsorption energy. After adsorption, charges are transferred from buckled bismuthene to the molecules and the quantum conductance is changed by the adsorbed molecules. Furthermore, the work function of buckled bismuthene is changed with the adsorption of different molecules. Our results show that the electronic, transport and optical properties of buckled bismuthene are sensitive to the adsorption of gas molecules, which suggests that buckled bismuthene holds great potential for application in gas sensors.

Towards the Manipulation of Defects and Dopants to Functionalise Graphene - a DFT Based Study and Development of New Theoretical Methods

Graphene is a material, which is exhibiting a rising research interest over the last few years due to its unique properties and various possible applications. Possible applications range from optical sensing and drug delivery up to fuel and solar cells as well as composite materials. Based on experimental findings, first principle theory of electronic structure calculations (DFT) shall be used to examine the effects of p/n-doping and defects on the material’s properties as to find a way of band gap tuning and to understand the underlying mechanisms of it. Not only graphene shall be examined in this context but also hexagonal Boron-Nitride Nanosheets (h-BNNs). Especially a radical functionalisation of h-BNNs with oxygen, nitrene and carbene is of interest. Based on DFT, IR spectra, Raman spectra and structural properties shall be computed and compared with experimental results. Density of States and Band structures shall be calculated as to understand the electronic properties of the examined materials. These results shall build the basis for working on further questions and to develop methods beyond DFT as to find a better description of the systems of interest. Further questions of interest are for example how the radicals adsorb on the h-BNNs, how magnetic impurities or the adsorption of magnetic materials change the properties of graphene or h-BNNs and how environmental effects influence the adsorption of different molecules on graphene. Methods describing dynamical correlations (e.g. Dynamic Mean Field Theory) are of interest in the context of working with strongly correlated materials. Furthermore, coarse grained methods offer a better description of dispersion forces and can be used to receive a better description of environmental effects. In this context, the development of double hybrid functionals may be of interest as well since they also tend to give a better description of dispersion forces. Another point of interest is the examination of charge transport properties with graphene-based electrodes, for example with methods based on the Landauer-formalism.

Surface Charge-Transfer Doping of Graphene Nanoflakes Containing Double-Vacancy (5-8-5) and Stone-Wales (55-77) Defects through Molecular Adsorption.

The adsorption of six electron donor-acceptor (D/A) organic molecules on various sizes of graphene nanoflakes (GNFs) containing two common defects, double-vacancy (5-8-5) and Stone-Wales (55-77), are investigated by means of ab initio DFT [M06-2X(-D3)/cc-pVDZ]. Different D/A molecules adsorb on a defect graphene (DG) surface with binding energies (ΔEb ) of about -12 to -28 kcal mol-1 . The ΔEb values for adsorption of molecules on the Stone-Wales GNF surface are higher than those on the double vacancy GNF surface. Moreover, binding energies increase by about 10 % with an increase in surface size. The nature of cooperative weak interactions is analyzed based on quantum theory of atoms in molecules, noncovalent interactions plot, and natural bond order analyses, and the dominant interaction is compared for different molecules. Electron density population analysis is used to explain the n- and p-type character of defect graphene nanoflakes (DGNFs) and also the change in electronic properties and reactivity parameters of DGNFs upon adsorption of different molecules and with increasing DGNF size. Results indicate that the HOMO-LUMO energy gap (Eg ) of DGNFs decreases upon adsorption of molecules. However, by increasing the size of DGNFs, the Eg and chemical hardness of all complexes decrease and the electrophilicity index increases. Furthermore, the values of the chemical potential of acceptor-DGNF complexes decrease with increasing size, whereas those of donor-DGNF complexes increase.

Reduction of graphene oxide/alginate composite hydrogels for enhanced adsorption of hydrophobic compounds

Carbon-based materials, consisting of graphene oxide (GO) or reduced GO (rGO), possess unique abilities to interact with various molecules. In particular, rGO materials hold great promise for adsorption and delivery applications of hydrophobic molecules. However, conventional production and/or usage of rGO in aqueous solution often causes severe aggregation due to its low water solubility and thus difficulties in handling and applications. In our study, to prevent the severe aggregation of GO during reduction and to achieve a high adsorption capacity with hydrophobic compounds, GO/alginate composite hydrogels were first prepared and then reduced in an aqueous ascorbic acid solution at 37 °C. Adsorption studies with a model hydrophobic substance, rhodamine B, revealed that the reduced composite hydrogels are more highly absorbent than the unreduced hydrogels. In addition, the adsorption properties of the composite hydrogels, which are consequences of hydrophobic and ionic interactions, could be modulated by controlling the degree of reduction for the adsorption of different molecules. The composite hydrogels embedding rGO can be very useful in applications related to drug delivery, waste treatment, and biosensing.

New Dynamic-Surface-Tension Analysis Yields Improved Residual Surfactant Measurements in Flowback and Produced Waters

Summary Surfactant is a significant component within fracturing-fluid additives that is used for enhancing oil and gas production following stimulation of unconventional reservoirs. To help ensure optimal applications of surfactants, operating and service companies have been searching for tools for tracking surfactant residuals in flowback and produced waters, which possibly can be correlated with well productivity. This paper discusses the residual surfactant concentration measured in produced water from example Barnett shale formation wells by use of a dynamic surface tension (DST) technique, which yields much more accurate measurements. DST measurement by maximum bubble-pressure technique is well-known, but it has not been used explicitly for the application of residual surfactant measurement in produced water. A comparison of DST includes evaluating the diffusion coefficient to the reaction kinetics of adsorption of a known molecule(s) in produced water. Short-time kinetics of adsorption of different molecules vary on the basis of chemical nature and molecular size. Ultraviolet–visible (UV–Vis) spectroscopy is used to confirm the results. An estimate of residual concentrations from UV–Vis appears to be coherent with DST-measurement values. Such measurements can be useful in determining the surfactant concentration during pumping and the surfactant performance during and after hydraulic-fracturing operations. Additionally, these measurements serve a vital role in tailoring the surfactant additive to specific reservoir conditions to achieve higher oil recovery. Real-time production results from these different wells are analyzed and appear dependent on the corresponding residual surfactant concentrations from produced waters. This unique technique is new to the authors’ knowledge for its use to study and analyze produced water for surfactant-additive concentration.

Understanding Gas-Induced Structural Deformation of ZIF-8.

ZIF-8 is a zeolitic imidazolate framework with very good thermal and chemical stability that opens up many applications that are not feasible by other metal-organic frameowrks (MOFs) and zeolites. Several works report the adsorption properties of ZIF-8 for strategic gases. However, despite the vast experimental corpus of data reported, there seems yet to be a dearth in the understanding of the gas adsorption properties. In this work we provide insights at a molecular level on the mechanisms governing the ZIF-8 structural deformation during molecular adsorption. We demonstrate that the ZIF-8 structural deformation during the adsorption of different molecules at cryogenic temperature goes beyond the gas-induced rotation of the imidazolate linkers. We combine experimental and simulation studies to demonstrate that this deformation is governed by the polarizability and molecular size and shape of the gases, and that the stepped adsorption behavior is defined by the packing arrangement of the guest inside the host.

Thermodynamic analysis of the breathing of amino-functionalized MIL-53(Al) upon CO 2 adsorption

Carbon dioxide gas adsorption in amino-functionalized MIL-53(Al) at various temperatures has been analysed in combination with temperature programmed XRD. Similarly to the regular MIL-53(Al) material, the so-called breathing phenomenon was shown to take place in the amino-MIL-53 upon adsorption of different molecules, i.e. the transition between a large-pore ( lp) and a narrow-pore ( np) structure. Using the osmotic thermodynamic model analysis, the temperature–loading phase diagram was derived. The overall diagram is similar to that for the regular MIL-53(Al), but a spectacular difference is the much larger stability domain of the np structure, which can be accounted for by the increased affinity for CO 2 due to the presence of the amino groups in the pore space.

Selective Nontemplated Adsorption of Organic Molecules on Nanofacets and the Role of Bonding Patterns

A key element of functionalizing nanocrystals with organic molecules is the nontemplated selective adsorption of different molecules on different facets. Here we report scanning-tunneling-microscopy images of perylene-3,4,9,10-tetracarboxylic-dianhydride and 2,5-dimethyl-N,N'-dicyanoquinonediimine on silver, demonstrating selective adsorption on different facets. We also report first-principles calculations that account for the data and show that bonding, which controls selectivity, occurs via the end atoms, while the molecule's midregion arches away from the substrate. The results are also consistent with data that have been interpreted in terms of bonding via the midregion.

Adsorption Thermodynamics of Sulfur- and Nitrogen-containing Molecules on NiMoS: A DFT Study

Detailed adsorption thermodynamic data of organosulfur and organonitrogen molecules on NiMoS hydrotreating catalyst active sites were studied by density-functional theory (DFT) calculations. Initially, the adsorption of the molecules on the NiMoS edge surface is studied, and the most stable configuration for each molecule is identified. The changes in electronic energy and zero point vibrational energy upon the adsorption of different molecules on the NiMoS surface are calculated. The contribution of adsorbed molecules, as well as gas phase molecules, to changes in entropy and C p values are obtained by calculating vibrational frequencies of adsorbed and free molecules. With these data, the changes in enthalpy, entropy, and free energy due to the adsorption on the NiMoS edge surface at different temperatures are determined. These data can be used to estimate the relative surface coverage of each type of species at different reaction conditions.

Adsorption of small molecules on the Pt(100) single crystal surface studied by Disappearance Potential Spectroscopy

Disappearance potential spectroscopy (DAPS) is used to elucidate the influence of H 2, O 2, NO, and CO adsorption and NO+H ads interaction on the electronic structure of the Pt(100)-(1×1) single crystal surface. DAP spectra obtained after adsorption of different molecules reveal the similar features related to excitation of platinum core electrons. Besides, a set of the pronounced individual satellites originating from the adsorbed species are also exhibited in DAP spectra. The locations of these satellites with respect to the substrate Fermi level are found to be comparable with the ionization potentials of the given adsorbed particle. It evidences the conjugate pathway of the primary electron energy consumption, which includes an ordinary threshold excitation of the substrate core electron accompanied by ionization of the adsorbed species.

Effect of ammonia and methylamine as coadsorbates on the adsorption behavior of benzene in NaBeta zeolite studied by FTIR spectroscopy

The single component (benzene, ammonia and methylamine) adsorption and the effect of coadsorbates such as ammonia and methylamine on the adsorption of benzene in NaBeta zeolite have been investigated by FTIR. The changes in the framework upon adsorption of different molecules have been checked and discussed. The benzene location in NaBeta zeolite with or without the presence of coadsorbates has been correlated with the structural and chemical properties of zeolite and with the interaction strength of ammonia, benzene and methylamine with NaBeta zeolite. It reveals that only cations, but not 12R windows of NaBeta are preferentiel adsorption sites for benzene even in the presence of coadsorbates such as ammonia and methylamine. The quantitative analysis on the amount of benzene adsorbed on cations when benzene is present alone suggests that all the cations present in NaBeta zeolite are accessible to benzene molecules. Ammonia and methylamine can interact not only with Na + ions via the lone pair on nitrogen atoms but also with the large number of silanols present in NaBeta zeolite. The interaction strength of ammonia, methylamine and benzene with NaBeta ranks in the order of methylamine/NaBeta>benzene/NaBeta>ammonia/NaBeta. The interaction of ammonia and methylamine with NaBeta causes an important modification of lattice parameter, indicating the deformation of zeolite framework. However, no significant deformation is observed upon adsorption of benzene alone. In spite of the deformation of zeolite framework, only adsorption of benzene in Na + ions has been observed and no change in the location of benzene in NaBeta zeolite is detected upon coadsorption of either ammonia or methylamine, being contrary to what we observed in KL zeolite upon coadsorption of methylamine and in NaEMT upon coadsorption of ammonia.

Aggregation of asphaltenes in organic solvents using surface tension measurements

The critical micelle concentrations (CMC) of four asphaltenes in different solvents were obtained by surface tension measurements. The CMC values ranged from 1 to 30 g/l and depended on the asphaltene and the solvent used. These values were empirically correlated to the Flory–Huggins interaction parameter. Molecular areas of the asphaltene molecules at the solvent–air interfaces were also calculated. The wide range in determined molecular areas (1.0–4.0 nm 2) can be attributed to significant differences in asphaltene–solvent interactions. As a consequence of these differences, the orientation of molecules at the interface can vary; a preferential adsorption of different molecules can also occur.

Partial or complete heterogeneous photocatalytic oxidation of neat toluene and 4-picoline in liquid organic oxygenated dispersions containing pure or iron-doped titania photocatalysts

The heterogeneous photocatalytic oxidation of neat toluene and 4-picoline in liquid organic oxygenated dispersions containing pure or iron-doped titania photocatalysts has been studied in a photochemical reactor radiating predominantly at 365–366 nm. The investigation correlates experimental conditions such as structural aspects, surface properties, concentration and chemical nature of the photocatalysts, and illumination times, with chemical yields and selectivity of products. For toluene, the main photocatalytic products found were benzaldehyde, benzyl alcohol and benzoic acid. In particular, our results show that traces of water present in the reaction system play an important role in the distribution of products. Likewise, the important role of the adsorption effects in photocatalysis based on semiconductors is emphasized. Thus, differences in the affinity and mode of the adsorption of different molecules (i.e., toluene, picolines) should give rise to differences in the distribution of the reaction products.