Isosteric Enthalpy Of Adsorption Research Articles

Porphyrin-based porous polyimides: Synthesis, porous structure, carbon dioxide adsorption

A novel dianhydride 3,3’-bis(3,4-dicarboxyphenoxy)-4,4’-diphenylethynyl biphenyl dianhydride (BPEBPDA) and a new tetramine monomer 5,10,15,20- tetra[4-[(3-aminophenyl)ethynyl]phenyl]porphyrin (TAPEPP) were successfully synthesized. Porphyrin-based polyimides (PPBPIs) were synthesized from BPEBPDA and porphyrin-based building blocks (TAPP and TAPEPP) via polymerization reactions. The porphyrin-based porous polyimide networks (PPBPI-CRs) were obtained from PPBPIs through thermal crosslinking reactions. The PPBPI-CRs exhibited BET surface areas (682 m2 g−1 and 693 m2 g−1) and CO2 uptakes (2.0 mmol g−1 and 1.67 mmol g−1 at 273 K and 1 bar) as well as the separation factors of CO2/N2 (37.63, 28.97) and CO2/CH4 (7.51, 5.61). Meanwhile, PPBPI-CRs showed an enhanced CO2 isosteric enthalpies of adsorption (25.1 kJ mol−1 and 30.1 kJ mol−1) than other porous polymers.

Comparative study of adsorption for m‐phenylenediamine in aqueous solution onto chemically modified resins

ABSTRACTFour kinds of hypercrosslinked resins (acidic resins labeled SAMR and TAMR and heterocyclic resins IDLMR and PRLMR) were synthesized as adsorbents to remove m‐phenylenediamine (MPD) from aqueous solution comparably. The Brunauer–Emmett–Teller specific surface area and pore size distribution of the two types of resins have been compared, and the infrared spectra of the resins confirm the presence of the modified groups. The adsorption isotherms illustrate that the Freundlich equation fits more appropriately than the Langmuir equation or the Temkin equation. In addition, the kinetic curves indicate that the pseudo‐second‐order model is a better fit than the pseudo‐first‐order model. The thermodynamic studies show that the isosteric adsorption enthalpy changes (ΔH) and the Gibbs free energy change (ΔG) are both negative, revealing that all of the adsorption processes are spontaneous and exothermic. All of the modified resins exhibit the best adsorption capacity at pH = 6.24. The results show that the acidic resins have better adsorption of MPD. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47378.

Testing the self-cleaning properties of a coordination polymer surface

It is well established that self-cleaning can be related to the hydrophobic or hydrophilic nature of a surface. Using adsorption chromatography, molecular simulations and wetting dynamics measurements, the self-cleaning properties of a new, strongly water resistant and hydrophilic cystine-containing coordination polymer (CP) were tested. Adsorption isotherms of n-octane and methanol were determined in the range of 313–343 K. Next the isosteric enthalpy of adsorption and the change in adsorption entropy were calculated to explain higher adsorption of methanol than n-butane. Performed chromatographic tests, molecular dynamics simulations and wetting dynamics experiments additionally prove that the Zn(Cys)2 CP is a promising material for the application in the preperation of self-cleaning surfaces or coatings.

Cation exchange modification of clinoptilolite –thermodynamic effects on adsorption separations of carbon dioxide, methane, and nitrogen

Abstract This study details an experimental analysis of the thermodynamics of adsorption equilibrium behaviour of pure CO2, CH4, and N2 gases on raw, Fe3+, Ca2+, and Cs+ cation exchanged clinoptilolite. Equilibrium adsorption isotherms were experimentally determined for CO2, CH4, and N2 at three different temperatures ranging from 303 K up to 363 K, at pressures up to 8.0atm using the microgravimetric technique. Kinetic adsorption uptake data was measured at different temperatures for CH4 and N2 gases, and the results were compared for raw and Ca2+ clinoptilolite. Heat of adsorption values were calculated for all three gases on the studied clinoptilolite samples using the chromatographic method. These results were compared to the isosteric adsorption enthalpies determined from the adsorption isotherms at different temperatures. The isosteric heat of adsorption was the highest for CO2 followed by CH4, and N2. Temperature dependent Sips, Toth, and Dual-Site Langmuir isotherm models were fitted with experimental data and selectivity factor values were calculated for CO2/CH4 and CH4/N2 gas separations using the regressed isotherm models. Ca2+ clinoptilolite shows the best potential for CO2/CH4 separations due to its high selectivity. However, higher temperatures are needed in order to compensate for the slow kinetic behaviour. For CH4/N2 separations, Fe3+ clinoptilolite selectivity displays both high values and less variability compared to Cs+ clinoptilolite over a broader range of temperatures and pressures.

Hydrogen Bonding of Acylamino-Modified Macroporous Cross-Linked Polystyrene Resins with Phenol

Hydrogen bonding plays an important role in the adsorption of organic compounds on polymeric adsorbents. Herein, three acylamino-modified macroporous cross-linked polystyrene resins, namely, PMVBA, PVBA, and PVBU, are synthesized and their adsorption of phenol is investigated in detail from hexane. The results indicate that about 3.70 mmol/g acylamino groups are uploaded on the resins, the adsorption of these resins to phenol is efficient, and the equilibrium capacity has an order of PVBU > PMVBA > PVBA. The isosteric enthalpy of adsorption is calculated, and it possesses a similar order of PVBU (−63.38 ± 9.2 kJ/mol) > PVBA (−55.81 ± 7.8 kJ/mol) > PMVBA (−39.87 ± 5.5 kJ/mol) at the zero fractional loading. Analysis of the adsorption mechanism suggests that hydrogen bonding is the main driving force for the adsorption, double hydrogen bonding is involved for phenol adsorption on PVBA and PVBU, and an approximate hexahydric ring is formed during this process.

Designed Synthesis of Mesoporous Solid-Supported Lewis Acid–Base Pairs and Their CO2 Adsorption Behaviors

Conventional amines and phosphines, such as diethylenetriamine, diphenylpropylphosphine, triethylamine, and tetramethylpiperidine, were grafted or impregnated on the surface of metalated SBA-15 materials, such as Ti-, Al-, and Zr-SBA-15, to generate air-stable solid-supported Lewis acid-base pairs. The Lewis acidity of the metalated materials before and after the introduction of Lewis bases was verified by means of pyridine adsorption-Fourier transform infrared spectroscopy. Detailed characterization of the materials was achieved by solid-state 13C and 31P MAS NMR spectroscopy, low-temperature N2 physisorption, X-ray photoelectron spectroscopy, and energy-dispersive X-ray mapping analyses. Study of their potential interactions with CO2 was performed using CO2 adsorption isotherm experiments, which provided new insights into their applicability as solid CO2 adsorbents. A correlation between solid-supported Lewis acid-base pair strength and the resulting affinity to CO2 is discussed based on the calculation of isosteric enthalpy of adsorption.

Charged porous organic frameworks bearing heteroatoms with enhanced isosteric enthalpies of gas adsorption.

Charged porous organic frameworks containing heteroatoms were synthesized via a Yamamoto-type Ullmann coupling reaction using potassium tetrakis(4-bromopyrazolyl)borate and tetrakis(4-chlorophenyl)phosphonium bromide as monomers. For the first time, a monomer containing boron atoms was successfully homocoupled to obtain a 3D charged porous organic framework. The heteroatoms and charges in the porous organic frameworks help to increase the interaction between the frameworks and the gases. Therefore the charged porous organic frameworks bearing heteroatoms synthesized in the present study exhibit high isosteric enthalpies of gas adsorption which surpass those of many other porous organic materials.

Quasi-Two-Dimensional Phase Transition of Methane Adsorbed in Cylindrical Silica Mesopores.

Using Monte Carlo and molecular dynamics simulations, we examine the adsorption of methane in cylindrical silica mesopores in an effort to understand a possible phase transition of adsorbed methane in MCM-41 and SBA-15 silica that was previously identified by an unexpected increase in the adsorbed fluid density following capillary condensation, as measured by small-angle neutron scattering (SANS) [Chiang, W-S., et al., Langmuir 2016, 32, 8849]. Our initial simulation results identify a roughly 10 % increase in the density of the liquidlike adsorbed phase for either an isotherm with increasing pressure or an isobar with decreasing temperature and that this densification is associated with a local maximum in the isosteric enthalpy of adsorption. Subsequent analysis of the simulated fluid, via computation of bond-orientational order parameters of specific annular layers of the adsorbed fluid, showed that the layers undergo an ordering transition from a disordered, amorphous state to one with two-dimensional hexagonal structure. Furthermore, this two-dimensional restructuring of the fluid occurs at the same thermodynamic state points as the aforementioned densification and local maximum in the isosteric enthalpy of adsorption. We thus conclude that the densification of the fluid is the result of structural reorganization, which is signaled by the maximum in the isosteric enthalpy. Owing to the qualitative similarity of the structural transitions in the simulated and experimental methane fluids, we propose this hexagonal reorganization as a plausible explanation of the densification observed in SANS measurements. Lastly, we speculate how this structural transition may impact the transport properties of the adsorbed fluid.

A Permanently Porous Yttrium-Organic Framework Based on an Extended Tridentate Phosphine Containing Linker.

The metal-organic framework [Y(tbpp)]·nDMF (1) was synthesized from yttrium(III) nitrate and the tritopic linker tris(4'-carboxy[1,1'-biphenyl]-4-yl)phosphine (H3tbpp). The distance between the coordinating atoms of the carboxylate groups of the extended tridentate phosphine linker is more than 1.8 nm, resulting in an average pore dimension of 0.9 nm in the noninterpenetrated metal-organic framework. The material exhibits high thermal stability and permanent porosity after removal of guest molecules from the one-dimensional pore system. The desolvated compound adsorbs nitrogen, argon, hydrogen, and carbon dioxide. Favorable adsorption of CO2 over N2 is predicted using ideal adsorbed solution theory (IAST). The isosteric enthalpies of adsorption of H2 and CO2 of -7 and -22 kJ mol-1, respectively, are representative for metal-organic frameworks with no accessible strong host-guest binding sites, despite the bifunctional nature of the organic ligand. The absence of strong specific adsorption sites was confirmed by in situ powder synchrotron X-ray diffraction of the reversible isobaric CO2 sorption process. Analysis of the diffraction data indicates that the CO2 molecules in the pores are disordered and nonlocalized. Despite this, it was possible to quantify the evolution of the occupation of the pores. CO2 is adsorbed at an approximately constant below 320 K from 10% loading to full capacity at 195 K.

Adsorption of p-chlorophenol on three amino-modified hyper-cross-linked resins

Three amino-modified hyper-cross-linked resins (HCP-M, HCP-E, and HCP-D) were synthesized, and they were evaluated for adsorption of p-chlorophenol from aqueous solution. The results indicated that the uploading amounts of the amino groups on the three resins followed an order of HCP-M<HCP-E<HCP-D, while their Brunauer-Emmett-Teller surface area had an opposite order. The three resins were efficient for adsorption of p-chlorophenol from aqueous solution and hydrogen bonding was the main driving force for the adsorption. The isosteric adsorption enthalpy at zero fractional loading had an order of HCP-M (−44.92kJ/mol)<HCP-E (−57.12kJ/mol)<HCP-D (−61.53kJ/mol). At the initial concentration of 502.1mg/L and the flow rate of 68mL/h, the saturated dynamic capacities of HCP-M, HCP-E, and HCP-D were 388.1, 394.3, and 318.1mg/g dry resin, respectively, and these resins could be completely regenerated and repeatedly used.

Characterization of nanostructured carbon CMK-3 by means of Monte Carlo simulations

A structural model of mesoporous carbon (CMK-3) prepared from the templating of SBA-15 silica materials named M_CMK3 and a mixed geometry model, representing the porous space as a collection of slit, cylindrical and M_CMK3 pores, is theoretically evaluated, developed and applied to the characterization of an experimental sample [1]. By using the Monte Carlo simulation method (off lattice), families of N2 adsorption isotherms are generated for cylindrical, slit and M_CMK3 geometries corresponding to different pore sizes. Then, the three geometric families of isotherms (kernels) are used to fit the experimental N2 adsorption data corresponding to CMK-3 materials, allowing for the determination of the micro and mesopore volume and the corresponding Pore Size Distribution (PSD). The same experimental data were fit using different mixed geometry models, and from the analysis of the effect of different kernels on the resulting PSD, it is concluded that the proposed mixed geometry model can capture in more detailed the textural and energetic features of nanostructured carbon CMK-3. Finally, using a virtual solid and pseudo-experimental adsorption data, the importance of the pore geometry and its effects on the PSD and isosteric enthalpy of adsorption are studied.

Enhanced CO₂ Adsorption on Activated Carbon Fibers Grafted with Nitrogen-Doped Carbon Nanotubes.

In this paper, multiscale composites formed by grafting N-doped carbon nanotubes (CNs) on the surface of polyamide (PAN)-based activated carbon fibers (ACFs) were investigated and their adsorption performance for CO2 was determined. The spaghetti-like and randomly oriented CNs were homogeneously grown onto ACFs. The pre-immersion of cobalt(II) ions for ACFs made the CNs grow above with a large pore size distribution, decreased the oxidation resistance, and exhibited different predominant N-functionalities after chemical vapor deposition processes. Specifically, the CNs grafted on ACFs with or without pre-immersion of cobalt(II) ions were characterized by the pyridine-like structures of six-member rings or pyrrolic/amine moieties, respectively. In addition, the loss of microporosity on the specific surface area and pore volume exceeded the gain from the generation of the defects from CNs. The adsorption capacity of CO2 decreased gradually with increasing temperature, implying that CO2 adsorption was exothermic. The adsorption capacities of CO2 at 25 °C and 1 atm were between 1.53 and 1.92 mmol/g and the Freundlich equation fit the adsorption data well. The isosteric enthalpy of adsorption, implying physical adsorption, indicated that the growth of CNTs on the ACFs benefit CO2 adsorption.

Fiber optic sensors based on hybrid phenyl-silica xerogel films to detect n-hexane: determination of the isosteric enthalpy of adsorption.

We investigated the response of three fiber optic sensing elements prepared at pH 10 from phenyltriethoxysilane (PhTEOS) and tetraethylsilane (TEOS) mixtures with 30, 40, and 50% PhTEOS in the silicon precursor mixture. The sensing elements are referred to as Ph30, Ph40 and Ph50, respectively. The films were synthesized by the sol–gel method and affixed to the end of optical fibers by the dip-coating technique. Fourier transform infrared spectroscopy, N2 adsorption–desorption at 77 K and X-ray diffraction analysis were used to characterize the xerogels. At a given pressure of n-hexane, the response of each sensing element decreased with temperature, indicating an exothermic process that confirmed the role of adsorption in the overall performance of the sensing elements. The isosteric adsorption enthalpies were obtained from the calibration curves at different temperatures. The magnitude of the isosteric enthalpy of n-hexane increased with the relative response and reached a plateau that stabilized at approximately −31 kJ mol−1 for Ph40 and Ph50 and at approximately −37 kJ mol−1 for Ph30. This indicates that the adsorbate–adsorbent interaction was dominant at lower relative pressure and condensation of the adsorbate on the mesopores was dominant at higher relative pressure.

Experimental studies on equilibrium adsorption isosteres and determination of the thermodynamic quantities of polar media on alumina Al2O3

Abstract The present work is a revieif of theoretical and experimental study on the adsorption performance of the adsorbent Alumina (Al2O3) used in the adsorption system. An experimental investigation on the equilibrium adsorption isosteres at low pressure (&lt; 1 atm) of working pairs Al2O3/H2O and Al2O3/C2H6O2 is carried out. The isovolume measurement method is adopted in the test setup to directly measure the saturated vapor pressures of working pairs at vapor-liquid equilibrium (dG=0 and dμi=0). Quantity adsorbed is determined from pressure, volume and temperature using gas law. The isosteric heat of adsorption is calculated from the slope of the plot of lnP versus 1/T different amounts of adsorbate onto adsorbent as follows: 0,01 vol% Al2O3/H2O; 0,03 vol% Al2O3/H2O; 0,1 vol% Al2O3/H2O; 0,01 vol% Al2O3/C2H6O2; 0,03 vol% Al2O3/C2H6O2; 0,1 vol% Al2O3/C2H6O2. This study shows that adsorption working pair Al2O3 C2H6O2 has better adsorption performances than those of the A2O3/H2O. Surface acidity! is a most important property! far both adsorption and catalysis and therefore is examined structure of active sites of alumina surface. Thermodynamic parameters such as isosteric heat of adsorption, isosteric enthalpy and entropy of adsorption are critical design variables in estimating the performance and predicting the mechanism of an adsorption process and are also one of the basic requirements for the characterization and optimization of an adsorption process

Thermodynamics of CO2 Adsorption on Polyethyleneimine Mesoporous Silica and Activated Carbon

A thermodynamic study of the enthalpies of adsorption of CO2 was conducted on polyethyleneimine 10k/ mesoporous silica (PEI-10k/MPS) and activated carbon (AC). These materials were chosen because of their high CO2 sorption capacities at about 85°C for PEI and about 20°C for the AC, therefore can capture CO2 with high efficiency in a wide temperature range. The absolute quantity of adsorbed CO2 as a function of equilibrium pressure at various temperatures was determined experimentally and fitted to isotherms of generalized Langmuir and Toth equations for PEI and AC, respectively. The adsorption of CO2 on PEI was favored with temperature revealing the endothermic nature of the process. On the other hand, CO2 adsorption on the AC was exothermic. The isosteric enthalpy of adsorption on PEI was about constant with CO2 loading at a value of 93 kJ.mol-1, confirming its chemical nature and corroboration with the Langmuir model. The corresponding isosteric enthalpy of the AC was in the range of ~-25 kJ.mol-1 and was continuously decreasing with CO2 loading; confirming the physisorption nature of the process and also that CO2/ CO2 interactions within the adsorption layer was significant.

Influence of temperature on water vapour sorption isotherms and kinetics of hardened cement paste and concrete

Water vapour sorption isotherms (WVSIs) have contributed significantly towards current knowledge of the porous nanostructure of cementitious materials and are an important component in modern durability calculations. In this paper, two newly developed multi-chamber testing apparatus for determining WVSIs of hardened cementitious materials are described. The adsorption, desorption and scanning behaviour of hardened cement paste and concrete are studied in detail over temperatures of 23°C to 80°C. Experiments provide confirmation of a monotonic reduction in sorption hysteresis with increasing temperature and show a disappearance of low humidity hysteresis by 60°C. Time and history dependence of apparent isosteric enthalpy of adsorption is demonstrated. Typically overlooked anomalous (non-Fickian) sorption kinetics are observed to significantly influence the equilibrium process. The magnitude and effect of temperature and humidity on kinetics is examined. Evidence supporting the role of microstructural change in observed size-independent kinetics and WVSI changes with temperature are discussed.

Organic adsorbates have higher affinities to fluorographene than to graphene

The large surfaces of two-dimensional carbon-based materials, such as graphene and fluorographene, are exposed to analytes, impurities and other guest molecules, so an understanding of the strength and nature of the molecule–surface interaction is essential for their practical applications. Using inverse gas chromatography, we determined the isosteric adsorption enthalpies and entropies of six volatile organic molecules (benzene, toluene, cyclohexane, n-hexane, 1,4-dioxane, and nitromethane) to graphene and graphite fluoride powders. The adsorption entropies of the molecules ranged from −17 to −34cal/molK and the maximum adsorption-induced entropy loss occurred for nitromethane at the high-energy sites. The enthalpies of bulkier adsorbates were almost coverage-independent on both surfaces and ranged from −11 to −14kcal/mol. Despite the fact that fluorographene has lower surface energy than graphene and graphene represents an ideal surface for the π–π stacking, the adsorbates had lower adsorption enthalpies to fluorographene than to graphene by ∼9%. These findings imply that bulkier airbone organic contaminants readily adsorb to the investigated surfaces and can modify the measured surface properties.

Adsorption of Cefocelis Hydrochloride on Macroporous Resin: Kinetics, Equilibrium, and Thermodynamic Studies

The adsorptions of Cefocelis hydrochloride in aqueous solution on macroporous resin (HP-20) were studied. On the basis of static experiments with HP-20 resin, the adsorption kinetics, isotherms, and thermodynamics of Cefocelis hydrochloride in aqueous solution on macroporous resin (HP-20) were investigated. Adsorption equilibrium data were correlated with the Langmuir and Freundlich equations. Adsorption data of kinetic were modeled using the Crank equation and fitting for the diffusion coefficient (De), and the value of the liquid film mass transfer coefficient (kf) was estimated from Carberry equation. Dynamic adsorption was performed on HP-20 resin packed in a glass column to obtain optimal parameters. The initial concentration, bed height, and residence time were considered to determine the dynamic test for the breakthrough curve. The values of thermodynamic parameters including the isosteric adsorption enthalpy (ΔH), free energy (ΔG), entropy (ΔS), and adsorption activation energy (Ea) demonstrated t...

NH2-MIL-125 as a promising material for adsorptive heat transformation and storage

With increasing demand for heating and cooling, the effective utilization of renewable and waste thermal energy becomes a significant challenge. Due to its high energy saving potential AHT (Adsorption Heat Transformation) has gained more and more interest during the last three decades. Large advances in the enhancement of AHT performance can be achieved with the development of new adsorbents. In this paper, the results of a comprehensive study on water adsorption on NH2-MIL-125 and evaluation of the feasibility of the “NH2-MIL-125 – water” working pair for AHT are presented. It is shown that NH2-MIL-125 exchanges 0.39 g H2O g−1 under typical adsorptive chilling cycle conditions, which exceeds the uptake variation for common and innovative adsorbents. NH2-MIL-125 can be regenerated at 348 K which allows use of low-temperature heat sources. The isosteric enthalpy of water adsorption varies from −49.7 ± 1.0 kJ mol−1 to −54.8 ± 2.0 kJ mol−1 at an uptake of 0.03–0.40 g g−1. The adsorption capacity and porosity of NH2-MIL-125 change slightly during the first adsorption cycle and then remain constant. Based on the data obtained, the efficiency and specific power of the chilling cycle utilizing the “NH2-MIL-125 – water” pair were assessed as 0.77–0.80 and 3.2 kW kg−1, respectively, which is of high practical interest.

A comparative study of several microporous materials to store methane by adsorption

Methane adsorption was studied in microporous materials with differences in their pore geometry and surface chemistry in order to evaluate the characteristics that enhance methane storage in porous materials. The studied materials included metal-organic frameworks (Cu-BTC, MIL-53 and ZIF-8), zeolites (5A and 13X) and an activated carbon (Maxsorb). Textural properties such as pore volume and specific surface area were studied by nitrogen adsorption–desorption isotherms. Methane adsorption was analyzed by means of measurements at low and high pressures (0–5000 kPa) at various temperatures (278–323 K). The effect of the adsorbate–adsorbent interaction was evaluated by the determination of the Henry constant using the adsorption data of methane at low pressures and 298 K. In addition, the isosteric enthalpy of adsorption using data of adsorption at several temperatures was obtained. A linear trend was observed between the Henry constant, the enthalpy of adsorption and the pore size, indicating that the latter is the most influential factor in the interaction of a microporous adsorbent and methane at room temperature. Also, it was found that the textural properties (i.e. specific surface and micropore volume) are directly related with the methane storage capacity at 298 K and 3.5 MPa. However, we obtained a deviation of this behavior for ZIF-8 that is related to its geometry and pore size.