Confinement effect on the adsorption from a binary liquid system near liquid/liquid phase separation

The preferential adsorption of one component of a binary system at the inner surfaces of mesoporous silica glasses was studied in a wide composition range at temperatures close to liquid/liquid phase separation. Confinement effects on the adsorption were investigated by using three controlled-pore glass (CPG-10) materials of different mean pore size (10 to 50 nm). For the experimental system (2-butoxyethanol+water), which exhibits an upper miscibility gap, strong preferential adsorption of water occurs, as the coexistence curve is approached at bulk compositions, at which water is the minority component. In this strong adsorption regime the area-related surface excess amount of adsorbed water decreases with decreasing pore width, while the shift in the volume-related mean composition of the pore liquid shows an opposite trend, i.e., greatest deviation from bulk composition occurring in the most narrow pores. A simple mean-field lattice model of a liquid mixture confined by parallel walls is adopted to rationalize these experimental findings. This model reproduces the main findings of the confinement effect on the adsorption near liquid/liquid phase separation.     

Adsorption volume and absolute adsorption: 2. Adsorption from liquid phase

A critical analysis of the isotherms of excess and absolute adsorption, as well as the adsorption space performed in the first part [1] is continued; however, as applied to the equilibrium physical adsorption from the liquid phase. The correct method is proposed for evaluating the adsorption volume of solid adsorbents with an arbitrary structure by the isotherm of excess adsorption of binary mixture of liquids. This method is successfully tested for nine different adsorption systems.     

Switchable-polarity solvents prepared with a single liquid component

Known liquids that can reversibly switch their polarity at atmospheric pressure are all prepared as mixtures of two liquid components; we now report a series of switchable-polarity solvents that consist, in their low-polarity form, of only a single liquid component, a secondary amine. These solvents operate in a polarity range that is significantly lower than those of previously reported switchable solvents. Application to the separation and purification of a polymer and recovery of a catalyst is described.     

The phase transition temperatures of a liquid crystal determined from FT-IR spectra explored by principal component analysis

The FT-IR spectra of a thin layer of pure 4-chloro-2'-hydroxy-4'-pentyloxyazobenzene (CHPAB) were studied as a function of temperature. A detailed analysis of the intensity variations was performed by a method based on principal component analysis (PCA). It was shown that the phase transition temperatures obtained by means of PCA and those determined by differential scanning calorimetry (DSC), the most widely used technique in the field, were nearly identical. The PCA results revealed that the transition from solid to a liquid crystalline (LC) phase (smectic A) is more drastic phase transition in terms of infrared absorption changes. The nematic to isotropic phase transition is much less infrared sensitive. Very much smaller absorption changes are associated with the transition between the smectic and nematic mesophases. The pattern of the intensity changes strictly is correlated with the orientation of the CHPAB molecules towards the surface windows due to the surface-induced homeotropic alignment of LC molecules. The important role of hydrogen bonding interaction on the observed transition is disclosed.     

Influence of temperature and pressure on the preferential adsorption of component of hydroorganic mobile phase in liquid chromatography

The excess isotherms of methanol and acetonitrile were measured on the series of C18 bonded phases. The measurements were done using the minor disturbance method. The goal of our work was to determine the influence of the temperature on the adsorption of two commonly used solvents. The influence on the mobile phase flow rate on the both organic solvent adsorption was also investigated. The effect of these two parameters was compared on the octadecyl packed columns with different coverage density and on the monolithic Chromolith column. Adsorption of both solvents decreases with the increase of the temperature. The increase of the pressure increases adsorption of methanol but decreases adsorption of acetonitrile.     

Dynamics of adsorption by zeolites from the liquid phase, simulated using data on adsorption statics

A mathematical model for calculation of the dynamics of liquid-phase adsorption in a fixed sorbent bed is constructed on the basis of material balance equations solved by numerical integration on the assumption of a constant mass-transfer coefficient and a limiting inner-diffusion resistance.     

Prediction of single component adsorption isotherms on microporous adsorbents

The adsorption of gases on microporous solids is a fundamental physical interaction which occurs in many technical processes, e.g. the heterogeneous catalysis or the purification of gases. In this context the adsorption equilibrium can determine the velocity and/or the capacity of the process. Therefore, it has to be known for designing purposes. The aim of this work has been the a priori prediction of the adsorption equilibria of arbitrary gases on microporous solids like zeolites and active carbon based only on the molecular properties of the adsorptive and the adsorbent. The adsorption isotherm is described completely from the Henry region over the transition zone to the saturation region. The quality of the model permits a first approximation of the planned process without further experimental effort.     

Potentiodynamic deposition of Prussian blue from a solution containing single component of ferricyanide and its mechanism investigation

Potentiodynamic techniques were used for the direct electrodeposition of Prussian blue nano-clusters from an acidic solution of ferricyanide. Electrochemical, EQCM, IR, AFM, and UV/vis measurements were carried out to characterize deposited nano-sized Prussian blue and to explore the formation mechanism. Results showed that ferricyanide could partially dissociate to free ferric and cyanide ions. The driving force of this dissociation is the formation of PB and the evolution of HCN. The optimal potential window for the potentiodynamic formation of PB from an acidic solution (pH 1.6) is between –0.5 V and 0.4 V. In addition, the influence of surface adsorption of CN^- ions on the formation of PB was discussed.Dedicated to Professor W. Vielstich on the occasion of his 80th birthday.     

Investigation of the adsorption mechanism of a peptide in reversed phase liquid chromatography,from pH controlled and uncontrolled solutions

The single-component equilibrium adsorption of the tripeptide Leucyl-Leucyl-Leucine (LLL) on a high-efficiency Jupiter Proteo column (C₁₂$C_{12}$) was investigated experimentally and modeled theoretically. The experimental equilibrium isotherms of LLL for adsorption on a C₁₂$C_{12}$ packing material from an aqueous solution of methanol (48%) and trifluoroacetic acid (0.1%) were measured by frontal analysis (FA). The FA measurements were done with two solutions, one in which the pH was controlled, the other in which it was not. Two solutions of LLL in the mobile phase were prepared (4.3 and 5.4 g/L) and their pH measured (2.94 and 2.88), respectively. The first solution was titrated with TFA to match the pH of the mobile phase (2.03), so its pH was controlled. The pH of the other solution was left uncontrolled. In both cases the isotherms could be modeled by a bi-Langmuir equation, a choice consistent with the bimodal affinity energy distribution (AED) obtained for LLL. The isotherm parameters derived from the inverse method (IM) of isotherm determination under controlled pH conditions (by fitting calculated profiles to experimental breakthrough profiles) are in a good agreement with those derived from the FA data. Under uncontrolled pH conditions, the application of IM suggests the coexistence of two different adsorption mechanisms. According to the isotherm parameters found by these three methods (FA, AED and IM), the C₁₂$C_{12}$-bonded silica can adsorb around 500 and 70 g/L of LLL under controlled and uncontrolled pH conditions, respectively. The adsorption of LLL on the C₁₂$C_{12}$ material strongly depends on the pH of the mobile phase and on the quantity of TFA added, which plays the role of an ion-pairing agent.     

Study of polymer-stabilised blue phase liquid crystal on a single substrate

One outstanding feature of the polymer-stabilised blue phase (PSBP) is that it is unnecessary to form an alignment film, which requires a high-temperature baking process. Therefore, PSBPs may enable flexible liquid crystal displays (LCDs) on plastic substrates. In this study, polymer stabilisation of a blue phase (BP) on a single substrate was performed without using a conventional sandwich-type cell, and the electro-optical properties are demonstrated to be similar to those of a sandwich-type PSBP LCD cell. It was experimentally shown that the oxygen which inhibits radical polymerisation is required to be excluded in order to complete the polymer stabilisation in blue phase.     

Probing the interface in vapor-deposited bimetallic Pd-Au and Pt-Au films by CO adsorption from the liquid phase

Bimetallic Pd-Au and Pt-Au and monometallic Pd, Pt, and Au films were prepared by physical vapor deposition. The resulting surfaces were characterized by means of XPS, AFM, and CO adsorption from the liquid phase (CH2Cl2) monitored by ATR-IR spectroscopy. CO adsorption combined with ATR-IR proved to be a very sensitive method for probing the degree of interdiffusion occurring at the interfaces whose properties were altered by variation of the Pd and Pt film thickness from 0.2 to 2 nm. Because no CO adsorption was observed on Au, the evaporation of Pt-group metals on Au allowed us to study the effect of dilution on the adsorption properties of the surfaces. At equivalent Pd film thickness, the evaporation of Au reduced the amount of adsorbed CO and caused the formation of 2-fold bridging CO, which was almost absent in monometallic surfaces. Additionally, the average particle size on Pd-Au surfaces was smaller than that on monometallic Pd surfaces. The results indicate that a Pd/Au diffuse interface is formed that affects the Pd particle size even more drastically than the simple decrease in Pd film thickness in monometallic surfaces. Pt-Au surfaces were less sensitive to CO adsorption, indicating that the two metals do not mix to a significant extent. The difference in the interfacial behavior of Pd and Pt in the bimetallic gold films is traced to the largely different Pd-Au and Pt-Au miscibility gaps.     

Isolation of ethanol from its aqueous solution by liquid phase adsorption and gas phase desorption using molecular sieving carbon

A novel bioethanol separation process was proposed in this study employing molecular sieving carbon (MSC) as an adsorbent, whose pore diameter is close to molecular size of ethanol. In the proposed process, fermentation broth is first introduced to the adsorption bed packed with MSC. In this step, ethanol is selectively adsorbed onto MSC, with highly enriching ethanol in the micropore of MSC. Subsequently, the concentrated ethanol is desorbed from MSC to gaseous phase, resulting in further purification of ethanol owing to a considerable difference in desorption rate between water and ethanol; Because of molecular sieving effect of MSC, the desorption rate of ethanol is much smaller than that of water. To establish this process, adsorption equilibrium and kinetics of ethanol on various MSCs were investigated in aqueous phase as the first step. Also, desorption kinetics of ethanol and water in gaseous phase were investigated. As a result, it was suggested that highly concentrated ethanol could be obtained with high recovery ratio through these simple operations, meaning the proposed process is quite promising.     

Measurement of adsorption energy between a solid adsorbent and a liquid adsorbate using differential scanning calorimetry

We report on a novel method involving the use of differential scanning calorimetry (DSC) in evaluation of adsorption energy between a liquid adsorbate and a solid adsorbent. The proof of concept is demonstrated by measuring the exothermic heat release due to the adsorption of automotive transmission fluid (ATF), the adsorbate, to a paper-based friction material used in automotive torque converters, the adsorbent. The novelty of the measurement technique involves initial freezing of the liquid adsorbate so that the initiation of the adsorption process can be identified. Our experimental results and theoretical calculations reveal that the adsorption energy of the friction paper and the summation of adsorption energies of each friction paper ingredient are in good agreement.     

Adsorption volume and absolute adsorption: 1. Adsorption from a gaseous phase

Important concepts of adsorption science, such as excess and absolute adsorption isotherms and adsorption space volume, are critically analyzed and their status is discussed. An adequate method is proposed for evaluating the adsorption volume of solid adsorbents having arbitrary structures from excess adsorption isotherms. The method is tested by the example of five adsorption systems examined at a wide range of equilibrium pressures.     

Analysis of phase change during pervaporation with single component permeation

Individual (single) component pervaporation study helped to address some of the basic curiosities for the process of pervaporation. Investigations were carried out to focus on the location of vaporization during single component pervaporation. A mathematical model was developed for single component permeation during pervaporation, assuming two zones inside the membrane; namely, liquid permeation and vapour permeation zones. Considering a pressure distribution across the thickness of the membrane, Kelvin equation (saturation vapour pressure gets modified inside the membrane due to permeant membrane interactions) proved to be useful in developing the model. According to the model assumptions, the sorbed liquid first transports as liquid; and as soon as it finds the region, where pressure is Kelvin pressure, it evaporates and continues to transport as vapor. Further, the developed model was found to be useful in describing the flux in terms of downstream pressure variations. Accordingly, location of vaporization was determined. It was observed that vapor phase transport dominates in the membrane at low downstream pressures. Importance of consideration for both the phases, during modeling, is discussed. Activity profile, determined across the membrane, was observed to be in agreement with the experimental observations (as per literature). The study may help to establish a fundamental framework in turn to model for binary and/or multi-component mixtures.     

High-resolution calorimetric investigation of the existence of a nematic phase for the dodecylcyanobiphenyl liquid crystal

We have employed high-resolution calorimetric techniques in order to investigate the unresolved issue of the existence of a nematic phase for the liquid crystal dodecylcyanobiphenyl. Various heating and cooling runs were performed on dodecylcyanobiphenyl samples of different origin and their analysis did not reveal any signature of a nematic phase. The calorimetric results are presented in detail and they are additionally supported by optical polarising microscopy observations.