Gas phase vs. liquid phase: monitoring H2 and CO adsorption phenomena on Pt/Al2O3 by IR spectroscopy

The adsorption phenomena occurring at the surface of a highly-dispersed Pt/Al2O3 catalyst for hydrogenation reactions were thoroughly investigated in the gas-phase by transmission IR spectroscopy and in the liquid-phase by...

Isotope Exchange Kinetics in Clay-Water System

<p>Knowledge of reactions at solid/liquid and solid/gas interfaces is of great importance in the study of all adsorption phenomena. Techniques that enable a study of molecules (liquid or gaseous) adsorbed onto a surface may be divided into two categories: (a) those that upset the equilibrium between molecules in the gaseous (or liquid) phase above the solid surface and molecules actually adsorbed onto it, and (b) those that do not. Those techniques that do not disturb this equilibrium will give results that would be expected to have greater reliability than those obtained from techniques that upset this equilibrium (for example by heating or by affecting one component of the equilibrium by titration, precipitation etc.) In an endeavour to study the properties of water adsorbed onto various substances such as clay, wool and textile fibres without affecting the equilibrium the technique of isotopic exchange has been developed. Essentially the procedure is to take a closed adsorber system in equilibrium with a gas (or liquid), part of which is in the sensitive region of a geiger counter, and to add a very small amount of radioactively labelled gas (or liquid) to the system. The adsorber is placed in the bottom of a geiger counter out of the sensitive volume and a known fraction of gas (or liquid) is in the sensitive volume. As the system is at equilibrium there is continuous exchange between the adsorbed molecules on the sample and the molecules in the gaseous (or liquid) state. Thus, when a very small amount, by weight, of the radioactively labelled gas (or liquid) is added to the system, exchange will take place with the non-radioactive molecules adsorbed on the surface of the material under study. Thus radioactivity will be removed from the sensitive volume of the geiger counter and adsorbed onto the surface of the material, and so the specific activity (count rate), as measured with the geiger counter, will drop. The advantage of this technique is that the equilibrium between the adsorbed molecules and the free gas (or liquid) is not disturbed. The actual amount of radioactive material added is so minute that there is no effective change in the concentration of the free gas (or liquid).</p>

Isotope Exchange Kinetics in Clay-Water System

<p>Knowledge of reactions at solid/liquid and solid/gas interfaces is of great importance in the study of all adsorption phenomena. Techniques that enable a study of molecules (liquid or gaseous) adsorbed onto a surface may be divided into two categories: (a) those that upset the equilibrium between molecules in the gaseous (or liquid) phase above the solid surface and molecules actually adsorbed onto it, and (b) those that do not. Those techniques that do not disturb this equilibrium will give results that would be expected to have greater reliability than those obtained from techniques that upset this equilibrium (for example by heating or by affecting one component of the equilibrium by titration, precipitation etc.) In an endeavour to study the properties of water adsorbed onto various substances such as clay, wool and textile fibres without affecting the equilibrium the technique of isotopic exchange has been developed. Essentially the procedure is to take a closed adsorber system in equilibrium with a gas (or liquid), part of which is in the sensitive region of a geiger counter, and to add a very small amount of radioactively labelled gas (or liquid) to the system. The adsorber is placed in the bottom of a geiger counter out of the sensitive volume and a known fraction of gas (or liquid) is in the sensitive volume. As the system is at equilibrium there is continuous exchange between the adsorbed molecules on the sample and the molecules in the gaseous (or liquid) state. Thus, when a very small amount, by weight, of the radioactively labelled gas (or liquid) is added to the system, exchange will take place with the non-radioactive molecules adsorbed on the surface of the material under study. Thus radioactivity will be removed from the sensitive volume of the geiger counter and adsorbed onto the surface of the material, and so the specific activity (count rate), as measured with the geiger counter, will drop. The advantage of this technique is that the equilibrium between the adsorbed molecules and the free gas (or liquid) is not disturbed. The actual amount of radioactive material added is so minute that there is no effective change in the concentration of the free gas (or liquid).</p>

The effect of temperature and pressure on nitrogen adsorption in amorphous silica

Nitrogen is an element that is widely found in nature can be used as a gas that is absorbed to help characterize materials, especially on the surface of the material. According to Brunauer – Emmet - Teller (BET) is a theory where nitrogen is used as a gas characterizing material because of its ability to high purity and can interact with solid elements and inert. BET can only produce quantitative data and does not show adsorption phenomena. Molecular dynamics simulation is conducted to observe the phenomena during nitrogen adsorption in amorphous silica, a porous material with a large surface area. In this study, the molecular dynamics simulations are arranged in a state of isotherm, where the temperature used is three variables: 77 K, 100 K, and 150 K in the variation of pressure used 1, 3, 5, 7, and 10 atm for each equilibrium. In molecular dynamics simulation to simulate the interaction between atoms based on Coulomb force is using Lennard-Jones Potential. Based on the simulation results obtain, it was found that at 77 K temperature had the optimal ability to adsorb nitrogen compared to 100 K and 150 K. The higher the pressure given in the system, it will increase the amount of nitrogen adsorbed.

Two-Scale Investigation of the Retention Behavior of a Well-Graded Mixed Soil

The hydraulic characterization of mixed compacted soils is helpful for the design of earthworks subjected to drying–wetting cycles. When the mixed soil is well-graded and made of both coarse and fine fractions, its matric suction may also be due to the short-range adsorption phenomena, as for the soil investigated in this research work. A silty–clayey sand was created by a mixing procedure and experimentally investigated at two different scales. Physical modeling of an infiltration process was performed, allowing an inverse numerical analysis to infer the water retention and the hydraulic conductivity functions of the soil, whereas element testing on soil specimens allowed direct determination of the same equations. In the article, problems related to the employed suction measurement techniques have been pointed out and discussed. By this two-scale combined strategy, features of the soil hydraulic behavior, such as the wetting collapse, the shrinkage during drying, and the loop of hysteresis, were also determined.

Adsorption phenomena at the interface between mercury and solutions containing choline chloride, ethylene glycol and water

Adsorption of the components of deep eutectic solvent ethaline (ethylene glycol and choline chloride) on mercury electrode is investigated by electrocapillary measurements. It is determined that choline cations are mainly adsorbed on the negatively charged surface of mercury, while chloride anions are mainly adsorbed on the positively charged surface. The corresponding values of free energies of adsorption and interactions of adsorbate and solvent with metal are calculated and analyzed. An anomalous increase in both the apparent value of the adsorption at limiting coverage and the free energy of the interaction of the choline cation with mercury is observed in the transition from aqueous to ethylene glycol solutions, which is explained by the formation of complexes in a surface layer that exist in deep eutectic solvents and are capable of adsorbing on the electrode surface. The free energy of interaction with the mercury surface is higher than the energy of squeezing out from the volume of the solution onto its surface, which indicates the specific interaction of the adsorbate with mercury. A marked decrease in interfacial tension on both branches of the electrocapillary curve is observed when water is added to ethaline.

Halloysite nanotubes-based nanocomposites for the hydrophobization of hydraulic mortar

The treatment of stone surfaces for their protection from ageing caused by natural and anthropogenic effects is an open issue in materials development for Cultural Heritage. We thought interesting to verify the suitability of a modified cellulose biofilm filled with halloysite nanotubes as wax compatibilizers to design a protecting layer. A hydraulic mortar was selected as a stone prototype. To improve the physico-chemical properties of the covering layer, wax microparticles have been incorporated to control transport, consolidation and wettability features. In particular, different application protocols have been studied, namely brushing and spraying, to assess whether the proposed procedures can be scaled up. Colorimetric analysis has been carried out to evidence the applicability in terms of color alteration after the treatment. Water adhesion was investigated by measuring the contact angle values as a function of time to obtain information on spreading and adsorption phenomena. These physico-chemical properties have been correlated to the microstructure evidenced by both electron and optical microscopies. Graphic abstract

Removal of Pharmaceutical Residues from Wastewater using Activated Carbon from Rice Husks

The presence of pharmaceutical residues in discharges that end up in rivers is a growing concern for the disruption of aquatic ecosystems and human health. The risk of exposure to these medical wastes becomes greater because they are not biodegradable even after sewage treatment. This study aimed to remove trimethoprim (antibiotic), paracetamol (painkiller), and nevirapine (anti-retroviral) from wastewater using activated carbon made from rice husks, an agricultural waste that was investigated as a potential adsorbent. The instrument used for analysis was a liquid chromatography-tandem mass spectrometer (LC-MS/MS). The powdered carbon of rice husks was carbonated at a temperature of 500oC and then activated by phosphoric acid to increase its porosity. After activation, it was successfully characterized by the use of Scanning electron microscopy which showed irregular cavities with open fine pores. Fourier transform infrared showed different functional groups which determined adsorbent- adsorbate interactions while X-ray diffraction revealed amorphous particle arrangement. The effects of the adsorbent dose, contact time, pH, and initial drug concentration were studied. Freundlich and Langmuir's isotherms were used in the evaluation of adsorption phenomena. Thus, obtained results showed that rice husks activated carbon is an effective adsorbent.