Influence Of Water Adsorption Research Articles

A modified Guggenheim-Anderson-Boer model for analyzing water sorption in coal

The presence of water can alter the mechanical properties of coal, which may not only cause roof falls during the coal mining process but also affect the hydraulic fracturing of coalbed methane (CBM) reservoirs. The nature of water adsorption properties in unconventional reservoir rocks has been the subject of several recent papers. However, the adsorption properties and adsorption mechanism of water in coal have not been thoroughly investigated. In this study, we carried out water vapor sorption experiments on four coal samples of different maturities. We found no linear relationship between maturity and water adsorption capacity. Furthermore, we proposed that the water adsorption mechanism in coal can be divided into two types: attached to oxygen functional groups and pore filling, which occur in hydrophilic pores and hydrophobic pores, respectively. Based on the above hypothesis, a modified Guggenheim-Anderson-Boer model was proposed to interpret water adsorption isotherms. It was concluded that the differences in the water adsorption characteristics of different coals under high humidity conditions were caused by the pore volume and the proportion of hydrophilic pores. We further analyzed the influence mechanism of water adsorption on methane adsorption under high relative humidity conditions. We found that the influence of water adsorption on methane adsorption in coal can be attributed to the water adsorption amount and proportion of hydrophilic pores.

Interaction of Nanodiamonds with Water: Impact of Surface Chemistry on Hydrophilicity, Aggregation and Electrical Properties.

In recent decades, nanodiamonds (NDs) have earned increasing interest in a wide variety of research fields, thanks to their excellent mechanical, chemical, and optical properties, together with the possibility of easily tuning their surface chemistry for the desired purpose. According to the application context, it is essential to acquire an extensive understanding of their interaction with water in terms of hydrophilicity, environmental adsorption, stability in solution, and impact on electrical properties. In this paper, we report on a systematic study of the effects of reducing and oxidizing thermal processes on ND surface water adsorption. Both detonation and milled NDs were analyzed by combining different techniques. Temperature-dependent infrared spectroscopy was employed to study ND surface chemistry and water adsorption, while dynamic light scattering allowed the evaluation of their behavior in solution. The influence of water adsorption on their electrical properties was also investigated and correlated with structural and optical information obtained via Raman/photoluminescence spectroscopy. In general, higher oxygen-containing surfaces exhibited higher hydrophilicity, better stability in solution, and higher electrical conduction, although for the latter the surface graphitic contribution was also crucial. Our results provide in-depth information on the hydrophilicity of NDs in relation to their surface chemical and physical properties, by also evaluating the impacts on their aggregation and electrical conductance.

Water Adsorption and Transport on Oxidized Two-Dimensional Carbon Materials.

Studies on the adsorption and transport of water molecules with oxidized two-dimensional (2 D) carbon materials have attracted increasing interest owing to their wide range of applications, such as sensing, energy conversion, and membrane separation. In this contribution, the interaction between water molecules and oxidized 2 D carbon materials (i.e., graphene oxide and graphdiyne oxide) is discussed, the influence of water adsorption and transport on the physicochemical properties of 2 D carbon materials is presented, and the recent progress on oxidized 2 D carbon material-based proton conduction, electricity generation, water transport, and humidity sensing is highlighted. The opportunities and challenges in these research fields are discussed, especially the structural stability and chemical modification of 2 D carbon materials.

The role of electrostatic charge in the adhesion of spherical particles onto planar surfaces in atmospheric systems

• Surface charge and humidity play strong roles in the adhesion of two surfaces. • Changes in adhesive force are greater for surfaces with higher charge densities. • The role of capillary force in surface adhesion is stronger for larger particles. • Humidity effects on the electrostatic force depend on surface hydrophobicity. The influence of electrostatic charge on the adhesive force between spherical particles and planar surfaces in atmospheric systems was studied using atomic force microscopy. Electrical bias was applied to modify the surface charge, and it was found that application of a stronger positive bias to a particle induces a stronger total adhesive force. The sensitivity of the system to changes in the bias depended on the surface charge density. For larger-size particles, the contribution of the electrostatic force decreased, and the capillary force became the major contributor to the total adhesive force. The influence of water adsorption on the total adhesive force and, specifically, on the contribution of the electrostatic force depended on the hydrophobicity of interacting surfaces. For a hydrophilic surface, water adsorption either attenuated the surface charge or screened the effect of surface potential. An excessive amount of adsorbed water provided a path to surface charge leakage, which might cancel out the electrostatic force, leading to a reduction in the adhesive force. Theoretically calculated forces were comparable with measured adhesive forces except for mica which has a highly localized surface potential. The results of this study provide information on the behavior of charged colloidal particles in atmospheric systems.

Modeling of a Thermo-chromatographic Pulse (TCP) as Radio-frequency (RF)-induced Selective Heating Effect

By utilizing the specific influence of water adsorption on the dielectric loss factor and, consequently, selective heating of the zeolite NaY in a radio-frequency (RF) electromagnetic field, a hot zone moving through the packed bed can be realized initiated by water injection. While the effect of water adsorption on RF heating and the phenomenon of the thermo-chromatographic pulse (TCP) itself were described in a previous paper, the present study presents a detailed model for the description and explanation of this effect. It involves the complex dependence of dielectric loss on temperature and moisture content, a diffusion model considering both hopping and Knudsen mechanisms and a power balance for a representative segment of the packed bed. The developed model was successfully applied to adequately describe various experimental situations observed for selective RF heating in a NaY zeolite bed.

A study of Ga layers on Si(1 0 0)-(2 × 1) by SR-PES: Influence of adsorbed water

Results for deposition and thermal annealing of gallium on the Si(1 0 0)-(2 × 1) surface achieved by synchrotron radiation photoelectron spectroscopy (SR-PES) and low energy electron diffraction (LEED) are presented. In addition to deposition of Ga on a clean surface, the influence of water adsorption on the arrangement of gallium atoms was also studied. The results on Ga deposition at a higher temperature (490 °C) are consistent with a Ga ad-dimer model showing equivalent bond arrangement of all Ga atoms for coverages up to 0.5 ML. The deposition onto a surface with adsorbed water at room temperature led to a disordered gallium growth. In this case gallium atoms bind to silicon dimers already binding fragments of adsorbed water. A subsequent annealing of these layers leads to a surface structure similar to the Ga-(2 × 2), however, it is less ordered, probably due to the presence of silicon oxides formed from water fragments.

Measurement and Analysis of Water Adsorption in Porous Silica Films

The influence of water adsorption on dielectric constants of the porous silica low- dielectric films was investigated. The amount of water adsorption inside pores was calculated by a capacitance value, a gas adsorption measurement, the BET (Brunauer, Emmett, and Teller) adsorption theory, and the Kirkwood microscopic theory of water dielectrics. A hexamethyldisilazane (HMDS) vapor treatment was introduced to make porous silica low- films hydrophobic, and the effect of the HMDS vapor treatment was investigated quantitatively. The BET adsorption at a low partial pressure of water vapor ( for the HMDS-treated film, for the nontreated film) was investigated by a capacitance value. The results showed that the BET adsorptions of the HMDS-treated and the nontreated films were almost the same. A water cluster formation inside pores, at a high partial pressure of water vapor ( for the HMDS-treated film and for the nontreated film), was investigated by a capacitance value and a gas adsorption measurement. The results showed that the HMDS vapor treatment suppressed the water cluster formation, and this suppression could lower the dielectric constant for the porous silica film.

Structural charge transfer in the aluminophosphate molecular sieves by diffuse reflectance spectroscopy

Influence of water adsorption in AlPO-5, SAPO-5, AlPO-11 and SAPO-11 has been studied with UV diffuse reflectance spectroscopy. The observed UV absorption spectra in the as-synthesized, template free and hydrated materials are related to the charge transfer processes between aluminum and oxygen atoms of the aluminophosphate and water molecules. As-synthesised materials show two distinct and well-defined bands at about 220 and 260–280 nm correlated to framework aluminum and organic templates, respectively. Upon calcination, the band of occluded template disappears and the band assigned to the framework aluminum shifts at about 240 nm. When the calcined samples are completely hydrated, broadening of the aluminum charge transfer band is observed. This is due to coordination of water molecules to the part of the framework aluminum. Broadening occurs more in AlPO-5 possibly because of higher water capacity and homogenity with respect to SAPO-5.

Effect of Salt on the Mechanism of Adsorption of Aromatics on Activated Carbon

The effect of KCl on the adsorption of phenol, toluene, and benzene on activated carbon, with different degrees of surface oxygenation, was investigated. Different trends of salt effect were observed for each compound. The observed KCl effects were interpreted on the basis of electrical charge neutralization on the carbon surface and the adsorbate molecules, water adsorption, and the “salt out” effect. In particular, water adsorption was found to be crucial in reducing the adsorption capacity of the activated carbon. The influence of water adsorption was more pronounced on carbon surfaces with higher amounts of oxygen-containing groups. This was additionally confirmed by measurements using flow microcalorimetry.

Electrocatalysis of Organic Oxidations: Influence of Water Adsorption on the Rate of Reaction

Current/potential responses of small organic molecules show as a characteristic feature an increase in anodic current when changing the potential in the cathodic direction. In situ infrared data on the adsorption of methanol, formic acid, and water at Pt(111) are used to develop a new model explaining these well-known catalytic effects. Since the strength of water adsorption increases with increasing potentials above 0.4 V, the adsorption of organic molecules has to be considered as a water displacement reaction. The reaction rate is thus the result of the concurrence of two processes that are oppositely affected by the potential: the rate of oxidation (charge transfer) and the rate of adsorption. In situ IR data and cyclic voltammograms for the oxidation of methanol and formic acid on a Pt(111) surface are presented and discussed. For comparison, data on CO oxidation are presented.

Positron spectroscopy of rehydrated pyrogeneous silica surface

Positron annihilation method has been used for investigating amorphous nonporous pyrogeneous silica of high purity. The influence of water adsorption on the structure of the silanol surface is shown. The effect of “swelling”, that is an increase of interglobular free volume at intermediate degrees of silica hydration has been observed.