Inverse Gas Chromatography Measurements Research Articles

The driving force of water absorption in cementitious materials: An analysis of surface-free energies and pore structure

Upon the initial contact of hydrophilic cementitious materials with water, capillary absorption becomes the dominant phenomenon leading to durability deterioration of structures. The water absorption characteristics of such materials are governed by the interplay between pore structure and surface-free energies, with the latter being a factor often overlooked. In this study, advanced inverse gas chromatography (IGC) measurement techniques were employed to investigate the one-dimensional capillary water absorption of ordinary Portland cement (OPC) and alkali-activated slag (AAS). Results revealed water sorptivity values for OPC, AAS(NaOH), and AAS(Waterglass) as 0.0112, 0.0137, and 0.0187 mm/s0.5, respectively. This phenomenon can be attributed to the higher total surface-free energies observed at the liquid-solid interface in AAS materials, measuring 100.10 and 119.56 mJ/m2, compared with 74.25 mJ/m2 for OPC, consequently increasing capillary pressures. Moreover, it is observed that OPC exhibited a more complex pore tortuosity in comparison to AAS. This study underscores the dual role played by both capillary pressures and pore tortuosity in determining the water absorption characteristics of cementitious materials.

The ideal treatment for heart failer

The acid-base characteristics of the catalyst material are frequently linked to catalytic activity. Metal-organic frameworks (MOFs) have been tested as catalysts for a variety of processes. Based on the observed performance in diverse catalytic processes, Cu-BTC (with a well-defined crystalline structure) and Fe-BTC (with a gel-like porous structure) have both shown the presence of Lewis surface acid sites. In this study, researchers used Inverse Gas Chromatography (IGC) and n-butylamine thermal desorption analysis to assess the acid-base characteristics of both materials. Using acidic, basic, and amphoteric molecules, IGC experiments can access the acid-base characteristics of the material surface. The n-butylamine thermal desorption measurements, on the other hand, allow quantification of those acid and basic sites from the n-butylamine desorption curves of a sample previously saturated with that probe molecule. The Lewis acid properties obtained by both methodologies showed to be more pronounced for the Fe-BTC MOF sample. The IGC measurements exhibited values of acidity constants (KA) of 0.81 and 0.60 for Fe-BTC and Cu-BTC, respectively. Furthermore the n-butylamine thermo desorption experiments indicate total acidities of 2.06 and 0.49 mmol g−1 for Fe-BTC and Cu-BTC, respectively.

Relating Crystal Structure to Surface Properties: A Study on Quercetin Solid Forms.

The surface energy and surface chemistry of a crystal are of great importance when designing particles for a specific application, as these will impact both downstream manufacturing processes as well as final product quality. In this work, the surface properties of two different quercetin solvates (quercetin dihydrate and quercetin DMSO solvate) were studied using molecular (synthonic) modeling and experimental techniques, including inverse gas chromatography (IGC) and contact angle measurements, to establish a relationship between crystal structure and surface properties. The attachment energy model was used to predict morphologies and calculate surface properties through the study of their growth synthons. The modeling results confirmed the surface chemistry anisotropy for the two forms. For quercetin dihydrate, the {010} facets were found to grow mainly by nonpolar offset quercetin–quercetin stacking interactions, thus being hydrophobic, while the {100} facets were expected to be hydrophilic, growing by a polar quercetin–water hydrogen bond. For QDMSO, the dominant facet {002} grows by a strong polar quercetin–quercetin hydrogen bonding interaction, while the second most dominant facet {011} grows by nonpolar π–π stacking interactions. Water contact angle measurements and IGC confirmed a greater overall surface hydrophilicity for QDMSO compared to QDH and demonstrated surface energy heterogeneity for both structures. This work shows how synthonic modeling can help in the prediction of the surface nature of crystalline particles and guide the choice of parameters that will determine the optimal crystal form and final morphology for targeted surface properties, for example, the choice of crystallization conditions, choice of solvent, or presence of additives or impurities, which can direct the crystallization of a specific crystal form or crystal shape.

Determination of the surface thermodynamic characteristics and the structural isomer separation ability of new synthesized phenylbenzoate-based three-ring calamitic liquid crystals by inverse gas chromatography

Two different new calamitic liquid crystals (LCs), (4-[4-((S)-3,7-dimethyloctyloxy)phenoxy)carbonyl]phenyl 4-(n-decyloxy)benzoate (DPDEB) and 4-[4-((S)-3,7-dimethyloctyloxy)phenoxy)carbonyl]phenyl 4-(n-dodecyloxy)benzoate (DPDOB)) were synthesized and characterized using 1H-NMR, and 13C-NMR. The LC behavior of the target compounds was investigated by optical polarization microscopy (PM) and differential scanning calorimetry (DSC).The selectivity coefficients, a, of the structural isomers at infinite dilution for the DPDEB and DPDOB LCs were determined for butyl acetate, butyl alcohol and amyl alcohol isomers. Surface energy analysis has been performed using inverse gas chromatography (IGC). By using suitable solvents, the surface properties and separation power of isomers of DPDEB and DPDOB LCs were determined between 303.2 and 323.2 K. Experiments with LC's have been conducted at infinite dilution to the specific adsorption enthalpy and the specific adsorption free energy. IGC measurements exhibited values of acidity constants (KA) of 0.033 and 0.057 and basic constants (KD) of 0.176 and 0.242 for DPDEB and DPDOB, respectively. It has been found that all LCs show basic character.

Cleaving Method for Molecular Crystals and Its Application to Calculation of the Surface Free Energy of Crystalline β-d-Mannitol at Room Temperature.

Calculation of the surface free energy (SFE) is an important application of the thermodynamic integration (TI) methodology, which was mainly employed for atomic crystals (such as Lennard–Jones or metals). In this work, we present the calculation of the SFE of a molecular crystal using the cleaving technique which we implemented in the LAMMPS molecular dynamics package. We apply this methodology to a crystal of β-d-mannitol at room temperature and report the results for two types of force fields belonging to the GROMOS family: all atoms and united atoms. The results show strong dependence on the type of force field used, highlighting the need for the development of better force fields to model the surface properties of molecular crystals. In particular, we observe that the united-atoms force field, despite its higher degree of coarse graining compared to the all-atoms force field, produces SFE results in better agreement with the experimental results from inverse gas chromatography measurements.

Thermodynamic and separation properties of 4-(octyloxy) benzoic acid liquid crystals by inverse gas chromatography (IGC)

The thermodynamic properties of 4-(octyloxy) benzoic acid (OBA) liquid crystal (LC) were investigated at infinite dilution by inverse gas chromatography (IGC). The phase transition temperatures of OBA LC were determined by differential scanning calorimetry (DSC) and IGC. The thermodynamic region was determined to be between 160 and 170 °C. Specific retention volumes were calculated using IGC measurements to prepare retention diagrams. The results from the diagrams were used to characterize the thermodynamic properties of the OBA LCs. Based upon these properties, the solvents used in this study were determined to be unsuitable for OBA LCs. The separation of structural isomer series (butyl acetate, butyl alcohol, and amyl alcohol series) was studied by an OBA LC coated Chromosorb W stationary phase in the thermodynamic region. This system was able to distinguish the isomers according to the determined selectivity coefficients.

Characterization of diatomaceous earth coated with nitrated asphaltenes as superior adsorbent for removal of VOCs from gas phase in fixed bed column

Asphaltenes isolated from bitumen possess unusual adsorption characteristics that can be further enhanced by chemical modifications to promote interactions with VOCs’. Herein, nitrated asphaltenes are used as an active layer coated on a surface of a diatomaceous earth, in order to prepare an efficient adsorbent (AsfNitro). Breakthrough experiments with benzene, pyridine, and 1-nitropropane revealed significant increase in adsorption capacity, after deposition of nitrated asphaltenes, by 26, 12, and 8 times respectively. The adsorption capacity of AsfNitro for benzene per square meter of surface area is far more superior than for other adsorbents in use. Moreover, the AsfNitro exhibited excellent efficiency. For adsorption of 1-nitropropane and pyridine, almost 100% of the adsorbent’s bed was effectively used. Inverse gas chromatography measurements proved that nitrated asphaltenes were exclusively responsible for the adsorption properties, and the role of the diatomaceous earth was only to provide the surface area. Presented findings can be extended to other support materials and their inherent limitations for adsorption of VOCs can be overcome. Comparison of adsorption enthalpies demonstrated that common adsorbents e.g. activated carbons, cannot compete with AsfNitro in terms of sorbate-sorbent interactions. Additionally, contribution of chemisorption mechanism was recognized for AsfNitro, which indicate catalytic properties, and opens a new research field about asphaltenes’ novel practical applications. Application of asphaltenes in adsorption processes can be an effective procedure for risk mitigation of hazardous VOCs, accompanied by effective waste management and materials’ valorisation. Wasted adsorbent can be easily regenerated (without deterioration of surface properties), or blended in bitumen-aggregates mixes for road paving applications.

Physicochemical Gas-Solid Sorption Properties of Geologic Materials Using Inverse Gas Chromatography.

The goal of this study was to determine the physicochemical properties of a variety of geologic materials using inverse gas chromatography (IGC) by varying probe gas selection, temperature, carrier gas flow rate, and humidity. This is accomplished by measuring the level of interaction between the materials of interest and known probe gases. Identifying a material's physicochemical characteristics can help provide a better understanding of the transport of gaseous compounds in different geologic materials or between different geological layers under various conditions. Our research focused on measuring the enthalpy (heat) of adsorption, Henry's constant, and diffusion coefficients of a suite of geologic materials, including two soil types (sandy clay-loam and loam), quartz sand, salt, and bentonite clay, with various particle sizes. The reproducibility of IGC measurements for geologic materials, which are inherently heterogeneous, was also assessed in comparison to the reproducibility for more homogeneous synthetic materials. This involved determining the variability of physicochemical measurements obtained from different IGC approaches, instruments, and researchers. For the investigated IGC-determined parameters, the need for standardization became apparent, including the need for application-relevant reference materials. The inherent physical and chemical heterogeneities of soil and many geologic materials can make the prediction of sorption properties difficult. Characterizing the properties of individual organic and inorganic components can help elucidate the primary factors influencing sorption interactions in more complex mixtures. This research examined the capabilities and potential challenges of characterizing the gas sorption properties of geologic materials using IGC.

Surface characterization and synthesis of boron carbide and silicon carbide

Knowing the surface properties of ceramic materials is important to determine the area of use. The carbide-based ceramics namely boron carbide and silicon carbide were synthesized and characterized. The surface properties of boron carbide and silicon carbide ceramic materials were examined by the inverse gas chromatography method. Experiments of inverse gas chromatography were carried out to determine the specific adsorption free energy and the specific adsorption enthalpy corresponding to the acid-base properties of both materials. The inverse gas chromatography measurements exhibited values of acidity constants of 0.137 and 0.086 and basic constants of 0.104 and 0.077 for boron carbide and silicon carbide, respectively. The values obtained for and parameters indicated that boron carbide and silicon carbide have an acidic character.

Surface acid-base properties of Cu-BTC and Fe-BTC MOFs. An inverse gas chromatography and n-butylamine thermo desorption study

Catalytic activity is usually related to the acid-base properties of the catalyst material. Metal-organic frameworks (MOFs) have been evaluated as potential catalysts for several reactions. Cu-BTC (with a well-defined crystalline structure) and Fe-BTC (with a gel-like porous structure) have both shown the presence of Lewis surface acid sites based on the observed performance in different catalytic reactions. In this work, experiments of Inverse Gas Chromatography (IGC) and n-butylamine thermo desorption analysis were carried out in order to determine the acid-base properties of both materials. The IGC measurements allow to access the acid-base properties of the material surface by using acidic, basic and amphoteric molecules. Otherwise the n-butylamine thermo desorption measurements allow the quantification of those acid and basic sites from the n-butylamine desorption curves of a sample previously saturated with that probe molecule. The Lewis acid properties obtained by both methodologies showed to be more pronounced for the Fe-BTC MOF sample. The IGC measurements exhibited values of acidity constants (KA) of 0.81 and 0.60 for Fe-BTC and Cu-BTC, respectively. Furthermore the n-butylamine thermo desorption experiments indicate total acidities of 2.06 and 0.49 mmol g−1 for Fe-BTC and Cu-BTC, respectively.

Controllable Acid/Base Propriety of Sulfate Modified Mixed Metal Oxide Derived from Hydrotalcite for Synthesis of Propylene Carbonate

Ammonium persulfate modified mixed metal oxide derived from hydrotalcite with tunable acid/base properties can be prepared via thermal decomposition of Mg-Al hydrotalcite-type precursors and ammonium persulfate. By controlling the ammonium persulfate content, these sulphur mutated samples, denoted as SMgAlO-y (y = 1; 3; 5; 7), were investigated in this research. The resulted materials were characterized by XRD, SEM, FT-IR spectra, Py-IR spectra, XPS, Hammett indicator, CO2-TPD, as well as NH3-TPD. Furthermore, the acid-base property of the sample surface was determined by inverse gas chromatography measurements (IGC). Among all the obtained outcomes, the target SMgAlO-5 demonstrated the maximal Ka/Kb value, and it presented the highest activity as a catalyst in the synthesis of propylene carbonate (PC) through 1,2-propylene glycol and urea, giving the yield of 97.2% at the optimized reaction condition, which indicated that the PC yield counted on the synergic effect of the acidity and basicity on catalysts.

Adsorption of hydrocarbons commonly found in gasoline residues on household materials studied by inverse gas chromatography

The adsorption of hydrocarbons present in gasoline residues on household materials was investigated via inverse gas chromatography (IGC). A series of hydrocarbons (n-heptane, n-octane, n-nonane, toluene, p-xylene, and 1,2,4-trimethylbenzene) and three household materials (carpet fibers, cotton fabric, and cardboard) were selected in this work. IGC measurements using columns packed with these household materials were conducted to obtain molar enthalpies of adsorption of the selected hydrocarbons over the temperature range of 40 to 70 °C. Adsorption isotherms and Henry’s law solubility coefficients (S) were also determined at 40 °C. Results from our IGC measurements revealed that molar enthalpies of adsorption, adsorption isotherms, and solubility coefficients were largely dependent upon the structures and size of hydrocarbons and the choice of solid substrates. Measured molar enthalpies of adsorption became more exothermic with increasing size of hydrocarbons, ranging from −23.4 to −40.9 kJ/mol for carpet fibers, −36.2 to −48.2 kJ/mol for cotton fabric, and −30.1 to −52.5 kJ/mol for cardboard. From the adsorption isotherms and the measured retention times as a function of the injection amount, the adsorption affinity of hydrocarbons to the carpet fibers was found to be weaker than the affinity between hydrocarbon molecules, producing relatively lower solubility coefficients for all hydrocarbons than those measured on cotton fabric and cardboard. However, the adsorption affinities of hydrocarbons to both cotton fabric and cardboard were much stronger with increased solubility coefficients presumably due to the diffusion and dispersion of hydrocarbons through solid substrates. In particular, solubility coefficients of three aromatics on cardboard were significantly larger than those measured on carpet fibers and cotton fabric. This might be responsible for previously reported enhanced persistence of gasoline residues spiked on cardboard.

Electrolytic Surface Treatment for Improved Adhesion between Carbon Fibre and Polycarbonate.

To achieve good mechanical properties of carbon fibre-reinforced polycarbonate composites, the fibre-matrix adhesion must be dialled to an optimum level. The electrolytic surface treatment of carbon fibres during their production is one of the possible means of adapting the surface characteristics of the fibres. The production of a range of tailored fibres with varying surface treatments (adjusting the current, potential, and conductivity) was followed by contact angle, inverse gas chromatography and X-ray photoelectron spectroscopy measurements, which revealed a significant increase in polarity and hydroxyl, carboxyl, and nitrile groups on the fibre surface. Accordingly, an increase in the fibre-matrix interaction indicated by a higher interfacial shear strength was observed with the single fibre pull-out force-displacement curves. The statistical analysis identified the correlation between the process settings, fibre surface characteristics, and the performance of the fibres during single fibre pull-out testing.

Quantitative chemical analysis of volatile compounds via headspace-solid phase microextraction (HS-SPME) coupled with inverse gas chromatography (IGC)

The compositions of volatile compounds in headspace (HS) analyzed by a solid phase microextraction (SPME) sampling method usually differ from true compositions mainly because the partition coefficients for these compounds between headspace and a SPME fiber are not equal. In this paper we report an analytical strategy to more accurately quantify relative compositions of selected hydrocarbons present in gasoline residue by employing inverse gas chromatography (IGC) coupled with a HS-SPME sampling method. First, IGC measurements using a column packed with a solid support coated with polydimethylsiloxane (PDMS) were conducted to obtain the thermodynamic and chromatographic data needed for the estimation of the relative partition coefficients of n-heptane, toluene, and 1,2,4-trimethylbenzene (TMB) between headspace and a PDMS SPME fiber at 100 and 130 °C. Then, chemical analysis of headspace containing different compositions of vaporized n-heptane, toluene, and TMB were carried out via a PDMS SPME sampling method at 100 and 130 °C. Finally, the relative compositions of these vaporized compounds in headspace were estimated using compositions from a PDMS SPME sampling method and the relative partition coefficients from IGC. Our results showed that the estimated relative compositions of these compounds in headspace are comparable to true compositions obtained from direct headspace vapor analysis within reasonable relative errors.

Electrospun polylactic acid-chitosan composite: a bio-based alternative for inorganic composites for advanced application.

Fabricating novel materials for biomedical applications mostly require the use of biodegradable materials. In this work biodegradable materials like polylactic acid (PLA) and chitosan (CHS) were used for designing electrospun mats. This work reports the physical and chemical characterization of the PLA-CHS composite, prepared by the electrospinning technique using a mixed solvent system. The addition of chitosan into PLA, offered decrease in fiber diameter in the composites with uniformity in the distribution of fibers with an optimum at 0.4wt% CHS. The fiber formation and the reduction in fiber diameter were confirmed by the SEM micrograph. The inverse gas chromatography and contact angle measurements supported the increase of hydrophobicity of the composite membrane with increase of filler concentration. The weak interaction between PLA and chitosan was confirmed by Fourier transform infrared spectroscopy and thermal analysis. The stability of the composite was established by zeta potential measurements. Cytotoxicity studies of the membranes were also carried out and found that up to 0.6% CHS the composite material was noncytotoxic. The current findings are very important for the design and development of new materials based on polylactic acid-chitosan composites for environmental and biomedical applications.

Impact of Hydrophobic Organohybrid Silicas on the Stability of Ni2P Catalyst Phase in the Hydrodeoxygenation of Biophenols

AbstractHydrodeoxygenation (HDO) of lignocellulose‐derived pyrolysis oils offers an option to produce fuel substitutes. However, catalyst deactivation and stability constitute a significant issue. Herein, the dependence of stability and activity of Ni2P/SiO2 HDO catalysts on the support surface polarity is addressed in detail. The support surface polarity was adjusted by copolymerizing tetraethyl orthosilicate (TEOS) with different types and amounts of organosilanes by a sol–gel process in the presence of nickel nitrate and citric acid. After thermal treatment under an inert atmosphere, Ni/SiO2 precursors were formed. They were converted into Ni2P/SiO2 catalysts by using NaH2PO2 as a PH3 source. The catalyst surface polarity was characterized by inverse gas chromatography measurements of the free energy of methanol adsorption, and specific and dispersive surface energies derived from polar and nonpolar probe molecule adsorption. The correlation between catalyst performance and support surface polarity indicates that, to prevent deactivation of the catalyst by water under reaction conditions, the affinity of the support towards polar substances must be decreased below a threshold value.

Thermodynamic characterization of polymers

The central objective of this work is the presentation of a novel simple method for the characterization of polymers as regards their thermodynamic behavior in bulk phases and interfaces. For this purpose, LSER (Linear Solvation Energy Relationships) type molecular descriptors and polymer surface energies are derived, primarily, from Inverse Gas Chromatography (IGC) and contact angle measurements for a number of common polymers. The interconnection of these descriptors with the more familiar equation-of-state scaling constants from PVT measurements is explored. The characteristic LSER descriptors are used for the prediction of polymer – polymer miscibility as well as for handling IGC data for multicomponent systems. Emphasis is given on hydrogen-bonded polymer systems. As shown by a variety of examples, the efficiency and versatility of the method are particularly promising. The broader perspectives of this unified approach to solution thermodynamics are discussed.

Optimization of a microcontroller for the simultaneous logging of temperature and reversed-flow inverse gas chromatography measurements

ABSTRACTThe utilization of a microcontroller board, optimized for the simultaneous data logging of chromatographic information, the oven temperature, and remote transfer to a personal computer, is investigated, with the goal to extend the capabilities of a gas chromatograph (Shimadzu GC-14A) which does not include a built-in data logging module. An initial comparison of the chromatographic peaks obtained from solute injections, collected both by a dedicated analog-to-digital expansion card and the microcontroller board, demonstrated the latter’s ability to perform accurate analog signal digitization. Afterward, the evaporation of three organic liquids (methanol, acetone, and n-pentane) was studied by reversed-flow inverse gas chromatography. From the temperature variation of the experimentally determined rates, the respective thermodynamic functions of enthalpy and entropy changes of acetone and methanol evaporation were determined. The small deviations from the theoretical values indicate the reliability of the proposed methodology. More importantly, it was made apparent that by utilizing automatic data logging instead of the carrier gas flow reversal procedure, the monitoring of rapid physicochemical phenomena was performed with better accuracy, while the duration of the experiments was decreased with the reduced consumption of gas chromatographic consumables.

Characterization of the surface properties of cellulosic fibers in fibrous and ground forms by IGC and contact angle measurements

Surface properties of fibrous and ground cotton and linen were investigated by inverse gas chromatography (IGC) and the contact angle with different liquids was also measured on fabrics composed of both fibers. Results proved that dispersion component of surface tension (γ s d ) determined by IGC depends not only on the surface energy, but also on several factors influencing the adsorbability of probe molecules on the cellulosic substrates. For cotton samples, the trapping of n-alkanes among waxy molecules in the outer layer of fibers can be presumed. This effect results in larger γ s d for cotton fibers than for linen in spite of the higher wettability of the linen fabrics. Besides the surface energy and trapping effects, the grinding also influences the γ s d values. Specific enthalpy of adsorption (ΔH ) of polar probes could be determined on all linen samples, but only on the ground cotton sample. Lewis acid-base character calculated for linen and ground cotton samples depends on the same effects as the γ s d does. The similar ΔH A ab values of chloroform (acidic) and THF (basic) measured on each of the samples support the conclusion that the surface character is amphoteric, which is also proved by the high ΔH values of the amphoteric ethyl acetate and acetone probes.

Octyl Co‐grafted PrSO3H/SBA‐15: Tunable Hydrophobic Solid Acid Catalysts for Acetic Acid Esterification

AbstractPropylsulfonic acid (PrSO3H) derivatised solid acid catalysts have been prepared by post‐modification of mesoporous SBA‐15 silica with mercaptopropyltrimethoxysilane (MPTMS), and the impact of co‐derivatisation with octyltrimethoxysilane (OTMS) groups to impart hydrophobicity to the catalyst was investigated. Turnover frequencies (TOFs) for acetic acid esterification with methanol increase with PrSO3H surface coverage across both families, suggesting a cooperative effect between adjacent acid sites at high acid site densities. Esterification activity is further promoted upon co‐functionalisation with hydrophobic octyl chains, with inverse gas chromatography (IGC) measurements indicating that the increased activity correlates with decreased surface polarity or increased hydrophobicity.