Adsorption Isotherm Measurements Research Articles

Measurement of water vapor adsorption isotherms in mesoporous materials using the zero length column technique

Measurement of water adsorption isotherms is important for industrial applications and for the characterization of nanoporous materials. The zero-length column technique is used for the first time to measure the adsorption-desorption isotherm of water on a mesoporous adsorbent, SBA-15, up to 90% relative humidity at 298 K. The technique showed two key advantages; (a) The experimental flexibility for the measurement of continuous adsorption-desorption isotherms characterized by complex shapes and hysteresis loops; (b) The possibility to measure a complete set of adsorption-desorption isotherms and scanning curves in few days compared to several weeks needed with traditional gravimetric techniques. The adsorption isotherm measured was compared and validated against isotherms measured on a commercial gravimetric system designed for water vapor adsorption. For the system considered, the adsorption and desorption branches are very steep, and the zero-length column technique is shown to allow setting easily the starting point of the scanning curves.

Mid-infrared emissivity of nylon, cotton, acrylic, and polyester fabrics as a function of moisture content

The effectiveness of material to emit energy as thermal radiation is important in determining the apparent temperature in infrared thermographic measurements. For this reason, a number of measurements of the thermal emissivity in the mid-infrared thermographic (8–12 µm) region have been reported for fabrics. However, many fabrics adsorb moisture from the air, and condensed water has a relatively high thermal emissivity. In this manuscript, we report measurements of adsorption isotherms and mid-infrared thermal emissivity for nylon, cotton, polyester, and acrylic as a function of their moisture content in weight percent at temperatures just above ambient. We find that the order of water mass percentage gain for the fabrics in high humidity conditions are polyester < acrylic < nylon < cotton. The thermal emissivity is ∼0.88 independent of moisture content for the fabrics polyester, cotton, and nylon, while acrylic shows a pronounced increase in thermal emissivity as moisture content increases, ranging from ɛ ∼ 0.81 at low humidity conditions to ɛ ∼ 0.88 under high humidity conditions. In this work, emissivity measurements are made by imaging through a novel infrared window made from household cling wrap and interpreted with equations that are independent of window transmittance and sample temperature.

Stimuli-Responsive Ti-Organic Gels and Aerogels Derived from Ti-Oxo Clusters: Hierarchical Porosity and Photocatalytic Activity.

Herein, we report titanium-organic gels (TOGs) as new Ti-oxo-based materials that exhibit stimuli-responsive sol-gel transformations and hierarchical porosity upon the removal of solvent molecules. Heating a solution of Ti-oxo clusters and pyromellitic acid as a tetratopic ligand produces TOGs that readily become sols by applying physical stimuli such as shaking or vortexing under ambient conditions. Porous titanium-organic aerogels (TOAs) were obtained by the CO2 supercritical point drying (CPD) of the TOGs, and their porous structures were characterized by N2 adsorption and desorption isotherm measurements. These TOAs, based on the Ti-oxo clusters, possess hierarchical micro-, meso-, and macropores. Furthermore, accompanying the prominent photochromic phenomena, reduction of Ti4+ to Ti3+ was observed upon UV irradiation. The TOAs were successfully applied in the adsorption and photocatalytic degradation of several dye molecules. This research introduces a versatile method for preparing stimuli-responsive and porous Ti-oxo-based photocatalysts.

Effect of CO2 injection on adsorption of methane on shale from the Sichuan Basin in China

In order to understand the change of adsorption capacity of methane (CH4) after carbon dioxide (CO2) injection into shale at high pressure condition. The pore structure character and adsorption capacity of CH4 were analysed via low-pressure N2 adsorption and isothermal adsorption measurements for original and supercritical CO2 (ScCO2) treated shale samples from Jiaoshiba area in the Sichuan Basin. The results show that the ScCO2 treated samples have lower specific surface areas, less micropore and mesopore, and more macropore compare to original one. For ScCO2 treated shale samples, specific surface area and micropore decrease with increasing temperature. Furthermore, the absolute adsorption capacity of CH4 in original shale is higher than that in ScCO2 treated ones, indicating that micropore specific surface area is probably the main factor controlling adsorption capacity of CH4 on shale. For all samples, the absolute adsorption capacity of CH4 increase with increasing pressure from 0 MPa to 43 MPa and then tended to be stable.

Investigation of the Stabilization Mechanism of Air Stable n-Type Single-Walled Carbon Nanotubes Sheets Based on Adsorption Isotherm Measurements

In spite of the remarkable growth of microelectronics such as wearable devices, remote sensors, etc. On the market in recent years, almost all of them are still powered by batteries that are required to be recharged or replaced at stated periods. If these electronic devices can run continuously for an extended time without any external interference, the benefits would be further enhanced. One such solution is to produce energy from the human body heat, where the thermoelectric (TE) generation mechanism is used to generate electricity from temperature difference. The principle behind TE generation is the Seebeck effect. It is a phenomenon to produce potential difference from the temperature difference between the ends of a TE generator. The efficiency of this TE conversion can be evaluated by the figure of merit, ZT = S2σT/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and κ is the thermal conductivity. TE generators with a high Seebeck coefficient, high electrical conductivity, and low thermal conductivity are expected to have good TE properties. To fabricate the TE devices, p- and n-type materials are necessary and the research of TE materials using inorganic semiconductors such as Bi2Te3 have been done for a long time as they illustrate high performance more than ZT = 1. However, these materials contain rare and toxic elements and they are difficult to process. Therefore, among the several candidates including conducting polymers, single-walled carbon nanotubes (SWNTs) are emerged as the promising candidate due to their non-toxicity, processability, remarkable electrical and thermal conductivity, potentially large Seebeck coefficient and light weight. However, due to air oxidation, SWNTs show only p-type semiconducting property in air. In the development of the SWNTs-based TE devices, instability of the n-type SWNTs has been a crucial issue, since n-type SWNT are easily oxidized due to an electrophilic chemisorption of oxygen on the charge polarization.1 Under such background, we have reported that air-stable n-type SWNTs can be formed by adsorbing 2-(2-methoxyphenyl)-1,3-dimethyl-2,3-dihydro-1H-benzo [d] imidazole (o-MeO-DMBI). However, the stabilization mechanism is not clear. herefore, in this research we studied the stabilization mechanism based on the adsorption isotherm measurements, where the SWNT sheets were dipped in the ethanol solution of o-MeO-DMBI in different concentrations at 25 ºC. From the adsorption isotherm, we revealed that SWNTs sheets adsorbed below monolayer of o-MeO-DMBI showed unstable in n-type, while SWNT sheets adsorption of o-MeO-DMBI showed stable n-type property over full coverage3. 1) Zhu, X.-Q.; Zhang, M.-T.; Yu, A.; Wang, C.-H.; Cheng, J.-P. J. Am. Chem. Soc. 2008, 130, 2501. 2) Nakashima, Y.; Nakashima, N.; Fujigaya, T. Synthetic. Metals. 2017, 76, 225. 3) Nakashima, Y.; Yamaguchi, R.; Fujigaya, T. submitted.

Adsorption of 4-n-Nonylphenol, Carvacrol, and Ethanol onto Iron Oxide from Nonaqueous Hydrocarbon Solvents.

The adsorption of 4-n-nonylphenol (4NP), carvacrol, and ethanol onto the surface of iron oxide from nonaqueous solutions is presented. It is found that adsorption of 4NP from alkanes is strong and proceeds to monolayer formation, where the molecules are essentially "upright". However, at high relative concentrations, ethanol successfully out-competes 4NP for the iron oxide surface. Estimates of the enthalpy and entropy of binding of 4NP were found to be exothermic and entropically disfavored. Sum frequency generation vibrational spectroscopy data indicate some evidence of binding through a phenolate anion, despite the nonpolar, nonaqueous solvent. Carvacrol is also found to adsorb as a monolayer where the molecules are lying "flat". The adsorption of ethanol onto iron oxide from dodecane was investigated through the use of quantitative NMR, which is a convenient analytical technique for measuring adsorption isotherms. It was concluded that ethanol does not form adsorbed monolayers on the surface. Instead, it partitions onto the surface as a surface-enhanced local phase separation related to its poor solubility in alkane solvents.

Advances in modification of commercial activated carbon for enhancement of CO2 capture

A novel and inexpensive method of modification of textural properties of commercial activated carbons for enhancement of CO2 capture was investigated. The commercial activated carbons FPV, WG-12 and CWZ-22 were applied as a starting material, and KOH and K2CO3 were used as modification agents. The modification temperature was varied over the range of 600 °C to 850 °C, and the ratio of modification agent to carbon from 1 to 4 was studied. The adsorption of CO2 was examined on all the activated carbons at temperature 25 °C up to pressure of 1 bar. A close correlation between the CO2 adsorption and the pore size of activated carbons was revealed. The activated carbon exhibiting the CO2 adsorption of 5.8 mmol/g under pressure of 1 bar and temperature of 0 °C was successfully obtained as a result of modification by KOH. After selecting of the best sorbents, the adsorption of CO2 was performed in the temperature range from 25 °C to 160 °C and under pressure up to 35 bar. The measured adsorption isotherm of CO2 was fitted to the numerous adsorption equations. The Sips model was found to be the best. The isosteric heats of adsorption were also calculated.

Adsorption/desorption isotherms of CH4 and C2H6 on typical shale samples

CH4 and C2H6 are occupying components in shale gas. Determination of adsorption/desorption isotherms of CH4 and C2H6 on shale samples is significant for estimating the storage of shale resources in shale reservoirs. In this study, the thermogravimetric method is used to obtain the excess adsorption/desorption of CH4 and C2H6 on two typical shale samples. Simplified local density theory/Peng-Robinson equation of state (SLD-PR EOS) model is then applied to calculate the adsorbed density of CH4 and C2H6 on both shale samples, which is then applied to convert the measured excess adsorption into absolute adsorption values. Results show that C2H6 presents higher adsorption capacity than CH4 on shale samples, indicating the more affinity of C2H6 to the organic shale. Based on the predicted results from the SLD-PR EOS model, a reasonable agreement has been achieved with the measured adsorption isotherms, indicating the accuracy of the SLD-PR EOS model for predicting adsorption of CH4 and C2H6 on shale samples. In addition, the calculated adsorbed density of CH4 and C2H6 is a function of temperature and pressure, which agrees well with the results from the molecular simulations. The obtained absolute adsorption is always higher than the measured excess adsorption, emphasizing the importance of determination of adsorbed density in predicting the absolute adsorption of CH4 and C2H6 on shale. This study compares the adsorption/desorption behaviors of CH4 and C2H6 on typical shale samples, and more importantly, we propose a more efficient method, i.e., the SLD-PR EOS model, to calculate the absolute adsorption of CH4 and C2H6 on shale samples.

Synthesis of nanocomposites using xylan and graphite oxide for remediation of cationic dyes in aqueous solutions

Due to the rapid development of industrialization, the water resources on which we depend are facing unprecedented challenges. Dyes, as an indispensable substance in our lives, have caused great pollution to the water resources in nature, and the removal of dyes from wastewater is becoming an important topic. A porous xylan/poly(acrylic acid)/graphite oxide nanocomposite was prepared by graft polymerization and used for adsorption of cationic ethyl violet dye in wastewaters in this paper. Various techniques, i.e., Fourier-transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, elemental analysis, scanning electron microscopy, and ultraviolet-visible spectroscopy, were used to study this composite. Adsorption isotherm measurements showed that the composite's adsorption behavior fits the Langmuir isotherm adsorption model. Adsorption tests showed that this material has excellent adsorption properties; the maximum adsorption capacity for ethyl violet dye was 273.99 mg/g. Investigation of the adsorption mechanism indicated that electrostatic forces and π–π effects are mainly involved in adsorption. Desorption cycling tests showed that the adsorption efficiency of the composite was still over 95% after 3 cycles. These results show that this porous xylan/poly (acrylic acid)/graphite oxide nanocomposite has potential applications in cationic dye removal.

Pore evolution characteristics of Chinese marine shale in the thermal simulation experiment and the enlightenment for gas shale evaluation in South China

Although there are many similarities between the shale of Cambrian Qiongzhusi Formation and Ordovician Wufeng Formation–Silurian Longmaxi Formation in South China, including total organic carbon content (TOC) and thickness, the drilling results of shale gas exploration are very different. One of the reasons is the difference of the nano-pores number developed in organic matter between them. In order to reveal the causes, the black shale of Upper Proterozoic Xiamaling Formation in North China, which is similar to the marine source rock in Sichuan basin, was selected for the thermal simulation experiment, and the pore size and volume of the samples before and after the experiment were acquired by scanning electron microscopy (SEM) and nitrogen adsorption isotherm measurement. Through the SEM photographs, we found that the sizes of the organic pores in algae, dispersed organic matter and organic matter associated with clay minerals get bigger with the increasing maturity. The total pore volume, micro-pore volume and meso-pore volume of the shale acquired by nitrogen adsorption isotherm measurement increase with the increasing maturity, too. However, under the overburden pressure, micro-pore volume decreases at high maturity stage, indicating the pores in organic matter might be compressed. It is considered that the pore volume in organic matter of the shale of Qiongzhusi Formation might be compacted under greater confining pressure, which may be the reason why the pore structures of the two sets of marine shale in South China are different.

New perspectives on supercritical methane adsorption in shales and associated thermodynamics

Understanding methane adsorption behavior in shales is fundamental for optimizing shale gas development as the adsorbed methane is a large portion of the subsurface shale gas resource. However, the adsorption mechanism of supercritical methane in shales and associated thermodynamics are poorly understood because the equation of state of the adsorbed methane is unmeasurable. This work analyzed adsorption equilibria (up to 32MPa and 393.15K) using a rigorous framework that can account for non-ideal gas properties and accurately extrapolate absolute adsorption uptakes from measured adsorption isotherms. The framework also allows a straightforward calculation of thermodynamic potentials relevant to adsorption such as enthalpy and entropy. Modelling results show that methane adsorption isotherms in shale under different pressures and temperatures are represented by a two dimensional adsorption isotherm surface. The density of the adsorbed methane in shales depends on temperature and pressure, which is always lower than the liquid methane density but higher than the corresponding gaseous methane density. The temperature-dependent and pressure-dependent characteristics of adsorbed methane density leads to the corresponding temperature-dependent and pressure-dependent measured/absolute adsorption isotherms. The maximum adsorption uptake of shales is independent of temperature and pressure. The isosteric enthalpy/entropy of adsorption and enthalpy/entropy of adsorbed methane are found to be temperature- and surface coverage-dependent. These new findings therefore not only clarify some historical misunderstandings of methane adsorption in shales for engineering application, but also provide a novel framework for interpreting methane adsorption behavior in shales and for determining the associated thermodynamics.

Computational fluid dynamics modelling of the visible light photocatalytic oxidation process of toluene for indoor building materials with locally doped titanium dioxide

Computational fluid dynamics (CFD) is one of the promising methods that can precisely predict non-uniform air flow and contaminant distribution in indoor environments. The overarching objective of this study was to develop a mathematical model for describing the photocatalytic oxidation (PCO) reaction mechanism of gas phase toluene with titanium dioxide (TiO2)-bound indoor building materials. This mathematical model was developed based on Langmuir-Hinshelwood type kinetics and for the integration with CFD simulations as a wall surface boundary condition. The effects of gas phase toluene concentration, illuminance and humidity on the toluene oxidation reaction were considered with locally TiO2-doped building materials. Especially, humidity dependence was explicitly integrated as a competitive adsorption model between toluene and water vapour. Moreover, surface compositions of TiO2 and the substrate (ceramic tile in this study), and the physical adsorption properties of those materials, were modelled and integrated into the mathematical model. A 0.02 m3 chamber experiment and adsorption isotherm measurements were conducted to identify the model parameters. CFD analysis was carried out according to experimental scenarios, and an optimization procedure for the model parameters was proposed for their application as the boundary conditions in the CFD analysis.

Volumetric Measurements of Methane-Coal Adsorption and Desorption Isotherms—Effects of Equations of State and Implication for Initial Gas Reserves

This study presents the effects of equations of state (EOSs) on methane adsorption capacity, sorption hysteresis and initial gas reserves of a medium volatile bituminous coal. The sorption experiments were performed, at temperatures of 25 °C and 40 °C and up to 7MPa pressure, using a high-pressure volumetric analyzer (HPVA-II). The measured isotherms were parameterized with the modified (three-parameter) Langmuir model. Gas compressibility factors were calculated using six popular equations of state and the results were compared with those obtained using gas compressibility factors from NIST-Refprop® (which implies McCarty and Arp’s EOS for Z-factor of helium and Setzmann and Wagner’s EOS for that of methane). Significant variations were observed in the resulting isotherms and associated model parameters with EOS. Negligible hysteresis was observed with NIST-refprop at both experimental temperatures, with the desorption isotherm being slightly lower than the adsorption isotherm at 25 °C. Compared to NIST-refprop, it was observed that equations of state that gave lower values of Z-factor for methane resulted in “positive hysteresis”, (one in which the desorption isotherm is above the corresponding adsorption curve) and the more negatively deviated the Z-factors are, the bigger the observed hysteresis loop. Conversely, equations of state that gave positively deviated Z-factors of methane relatively produced “negative hysteresis” loops where the desorption isotherms are lower than the corresponding adsorption isotherms. Adsorbed gas accounted for over 90% of the calculated original gas in place (OGIP) and the larger the Langmuir volume, the larger the proportion of OGIP that was adsorbed.

Effects of energetic heterogeneity on gas adsorption and gas storage in geologic shale systems

Capturing heterogeneity in an adsorbate-adsorbent interaction is important to understand the underlying mechanisms controlling adsorption behavior; especially, for natural shale characterized by various mineral compositions and multi-scale pore sizes, its energetic heterogeneity is extremely complex. In this work, experimental investigations of methane adsorption on natural shale were conducted over a range of pressures (0.5–20 MPa) and temperatures (333–393 K), and a multi-site model was introduced to describe the measured adsorption isotherms. Specially, the adsorption energy distribution in our model is related to a pore-size and surface-property dependent function, rather than any traditionally assumed ones, such as Gaussian or exponential distributions. Besides, as an apparent indicator of adsorbent heterogeneity, isosteric heat was analyzed for our studied shales. Results showed that isosteric heat for an energetically homogeneous adsorbent is a constant, while the observed heat for our studied shales gradually decreases with an increase in surface coverage. This coverage-dependent heat is mainly controlled by the ordered occupation of gas molecules on heterogeneous adoption sites; in this respect, the most favorable sites with the highest energy are occupied first followed by secondary sites with lower energy. Furthermore, in application fields, our proposed model can be used to estimate total gas in place for a whole shale gas reservoir and gas resources contributed by individual pores. This work presents comprehensive knowledge about the effect of surface heterogeneity on methane adsorption on shale, and can thus be used as a solid foundation for accurately estimating gas storage and production in geologic systems.

Low pressure plasma functionalized cellulose fiber for the remediation of petroleum hydrocarbons polluted water.

This work reports the first example of effective purification, at laboratory level, of water polluted by petroleum hydrocarbons, by means of low pressure plasma fluorine grafted cellulose fiber extracted from Spanish Broom. In order to improve the affinity of the cellulosic surface towards water dispersed hydrocarbons, its original hydrophilic character was turned to super-hydrophobic, by a fluorine functionalization. Batch experiments were performed with the aim of studying kinetic and thermodynamic aspects of the adsorption process, as a function of the initial total hydrocarbon load and of the adsorbent amount. The kinetics data showed that the fiber removal efficiency ranged between 80-90% after one minute of contact time, in dependence of the initial hydrocarbon/fiber weight ratio (20-240 mg/g). A maximum adsorption capacity larger than 270 mg/g was estimated by fitting the adsorption isotherm measurements with the Langmuir model. It turned out that the functionalized fiber is capable to perform a significant hydrocarbons removal action if compared to other cellulosic materials reported in the literature. Finally, the efficiency of the plasma modified cellulose fiber, after iterative re-uses, was studied.

Measuring adsorption isotherms with a flowmeter and a pressure gauge

We revisit the quasi-equilibrium adsorption method as an inexpensive alternative to commercial volumetric apparatus for the measurement of gas adsorption isotherms. This method is based on how the pressure of a manifold containing the sample increases as a function of time when an adsorbing gas is introduced. We show that, under certain conditions, it is not necessary to employ ultra-low flow rates (i.e. below few cm3/h) to obtain reliable adsorption isotherms. Also, we show that by time-differentiating the mass balance equation, it is possible to obtain and measure directly the rates of adsorption. These new insights provide a low-cost and simple approach to the measurements of both adsorption equilibrium and rates.

Decoding gas-solid interaction effects on adsorption isotherm shape: II. Polar adsorptives

A unique set of 6 polar adsorptives of relatively large dipole moment and of increasing kinetic diameter were used to probe pore volumes available and their mechanism of adsorption on a well-characterised microporous carbon. Multiple adsorption isotherm measurements were made and repeatable results with relatively small standard deviations in amount adsorbed at low relative pressures were obtained. Inconsistencies were observed between calculated Gurvitsch volumes. Sources of these were analysed and identified as contributions from one or more of: (a) molecular sieve effects; (b) molecular packing effects, and; (c) 2D molecular structure formation due to hydrogen bonding. These inconsistencies were further studied by comparison with pore volumes derived via the Dubinin-Radushkevich (DR) equation. Qualitative analyses of the micropore filling processes were proposed, and substantiated by complementary DR analyses. Although most of the isotherms showed Type I character, recasting the relative pressure axis in logarithmic format highlighted clear differences as contributions from fluid-fluid and fluid-solid interactions during pore filling. Overall, the adsorptives were classified into three groups: (a) polar adsorptives with primarily specific interactions adsorbing as a condensation process over a relatively narrow relative pressure range in a medium and late pressure range (iso-PrOH, MeOH, 2-methyl, 2-butanol, H2O); (b) polar adsorptives with potential for non-specific interactions adsorbing as a condensation process over a relatively narrow pressure range in a medium pressure range (pyridine, iso-PrOH, 2-methyl, 2-butanol); and, (c) halogenated adsorptives adsorbing with an S-shaped uptake extending over a broad relative pressure (dichloromethane).

Comparison of SO2 with CO2 for recovering shale resources using low-field nuclear magnetic resonance

Adsorption isotherms of pure CH4, C2H6, CO2, and SO2 are measured on one typical shale sample using the static volumetric method. The adsorption capacity of the above four gases is then compared to elucidate the affinity of each gas species on shale. Nuclear magnetic resonance (NMR) technique is then used to investigate how SO2 and CO2 exert the influence on the adsorbed CH4 and C2H6 on the organic shale. Based on the measured adsorption isotherms, SO2 presents the strongest adsorption capacity among the four gases, and is followed by C2H6, CO2, and CH4. It suggests that SO2 can be served as a potential agent for recovering the heavier hydrocarbon species, i.e., C2H6, from organic shale, while CO2 may be only suitable for the shale CH4 recovery. After introducing CO2 or SO2, based on the variation of T2 spectrum of the “CH4 or C2H6-saturated” shale sample, we infer that the adsorbed CH4 can be readily replaced by CO2 and SO2 from shale surface. However, the adsorbed C2H6 molecules are less probably replaced by CO2 compared to SO2. In addition, the amount of desorbed CH4 and C2H6 resulted from CO2 is much smaller than that of SO2, suggesting the superiority of SO2 for shale resource recovery. We expect this strategy will inspire new perspectives for the recovery of shale resources using the method of flue-gas treatment.

Evaluation of the density and thickness of adsorbed methane in differently sized pores contributed by various components in a shale gas reservoir: A case study of the Longmaxi Shale in Southeast Chongqing, China

To investigate the densities and thicknesses of adsorbed methane in a shale gas reservoir, the Lower Silurian Longmaxi Shale in Southeast Chongqing was selected as a case study to establish models of the pore size distributions contributed by various components (PSDCVC), the amounts of methane adsorbed by various components (AMAVC) and the density and thickness of methane adsorbed by various components (DTMAVC). Based on the results of total organic carbon, carbon content in organic matter (OM), X-ray diffraction, methane isothermal adsorption and low-temperature nitrogen adsorption measurements, the pore size distributions and the amount of methane adsorbed by OM, clay and other minerals were calculated using the PSDCVC and AMAVC models. The average densities and thicknesses of adsorbed methane in pores with widths of <2 nm, 2–5 nm, 5–10 nm, 10–20 nm, 20–50 nm, 50–100 nm and 100–200 nm associated with OM, clay and other minerals under various conditions (i.e., temperatures of 30–70 °C and pressures of 1–10 MPa) were calculated using the DTMAVC model. The calculated data for the three analyzed samples using the PSDCVC and AMAVC models were compared with experimental results to determine the uncertainties of the two models. The density and thickness values of adsorbed methane in pores with various widths associated with OM, clay and other minerals decrease with increasing temperature and pore width and increase with increasing pressure. At the same temperature, pressure and pore width, the density and thickness values of adsorbed methane differ significantly among pores contributed by OM, clay and other minerals, exhibiting a decreasing trend from OM to clay to other minerals.

Carboxylic Anchoring Dye p-Ethyl Red Does Not Adsorb Directly onto TiO2 Particles in Protic Solvents

Adsorption of the carboxylic anchoring dye, p-ethyl red (p-ER), onto TiO2 nanoparticles in protic vs aprotic solvents was studied in situ using the surface-specific technique, second harmonic light scattering (SHS). Two different adsorption schemes were proposed to account for p-ER interactions with TiO2 under different solvent environments. In aprotic solvents, p-ER adsorbs directly onto TiO2. Conversely, in protic solvents, in which solvent molecules bind stronger than p-ER with TiO2, the dye molecules adsorb onto the solvent shell around the particle but not directly to the TiO2 surface. In addition, a portion of the p-ER molecules form hydrogen bonds with the protic solvent molecules. The two different adsorption models reproduce the measured adsorption isotherms detected by SHS. Specifically, the p-ER molecules adsorb with a smaller free energy change and a larger density in protic solvents than in aprotic solvents. Our results indicate that protic solvents are undesirable for administering adsorptio...