Adsorption

Zeta potential of liposomes is often measured in studies of their properties and/or applications. However, there are not many papers published in which zeta potential was determined during enzymatic reaction of a lipid. Therefore in this paper size, polydispersity index, and zeta potentials of 1,2-dipalmitoylsn-glycero-3-phosphatidylcholine (DPPC) and 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) liposomes were investigated in 1 mM NaCl (pH 6.2) and phosphate buffer (pH 8.1) during 60 min of phospholipase C action at 20 and 37 °C. The hydrocarbon chains saturation differ these two phospholipids what appears in some differences in the zeta potential changes during the hydrolysis reaction run. The polydispersity index of the liposomes indicates that they are relatively stable and monodisperse, except for DPPC in phosphate buffer where up to 30 % of the initial amount forms larger size moieties, possibly aggregates of the liposomes, enzyme and the hydrolysis products. However, in this buffer zeta potential of the liposomes practically does not change during PLC action. Also the changes of zeta potential of DOPC liposomes are minor, although their negative values are much smaller than those of DPPC at both temperatures. These small changes of the potential may be due to compression of the diffuse double layer by present phosphate buffer. However, distinct changes of the zeta potentials in the presence of PLC take place in NaCl solution. The observed changes can be explained by reorientation of the phospholipid polar heads and their different density on DPPC and DOPC surface of the liposomes. Although it appeared that the zeta potential is not a very sensitive parameter for tracking the hydrolysis reaction in phosphate buffer, generally zeta potential enables the characterization of such reactions through determination of electrokinetic properties of liposomes as well as the polydispersity and size distribution of the liposomes do.

The interactions between phenol molecules and activated carbons were investigated in order to understand the adsorption mechanism of this aromatic compound. A series of activated carbons with varied chemical composition but similar porous features were synthesized and submitted to phenol exposure from aqueous phase, followed by thermogravimetric analysis and identification of the desorbed species by temperature programmed desorption coupled with mass spectrometry. Based on these experiments, both physi- and chemisorption sites for phenol were identified on the activated carbons. Our results demonstrate that physisorption of phenol depends strictly on the porosity of the activated carbons, whereas chemisorption depends on the availability of the basal planes in the activated carbons. Thus, oxidation of the carbon can suppress the fraction of chemisorbed phenol since the surface functionalities incorporate to the edges of the basal planes; notwithstanding, hydrophilic carbons may present a small but not negligible contribution of chemisorbed phenol depending on the extent of the functionalization. Moreover, these adsorption sites (chemi-) are recovered by simply removal of the surface functionalities after thermal annealing.

The adsorption behaviors of arsenic As(V) on the iron modified attapulgite (Fe/ATP) were studied. Two types of Fe/ATP nanoparticles, including Fe(III)/ATP and Fe(II,III)/ATP were prepared by ultrasonic co-precipitation method and characterized using SEM, XRD, XPS, FT-IR and zeta potential analyses. The adsorption isotherms of As(V) on Fe/ATP were well fitted by Freundlich model. The adsorption kinetics data were followed by the pseudo-second-order model with the pseud-second-order rate constant (k, min−1) of − 0.033 for Fe(III)/ATP and − 0.037 for Fe(II,III)/ATP, respectively. Adsorption capacities of Fe/ATP were 5–6 times higher than ATP (5.2 mg g‒1). The Fe–O(H) groups on Fe/ATP contributed to the strong interaction for As(V), confirmed with FT-IR and XPS analyses. The higher adsorption capacity of Fe(III)/ATP than that of Fe(II,III)/ATP was attributed to more surface hydroxyl groups on Fe(III)/ATP. Surface complexation models and density functional theory calculations demonstrated that As(V) sorption on Fe/ATP was by virtue of the formation of monodentate complexes.

h-BN monolayer as a novel 2D nanomaterial has raised great attention for sensing application in recent years. In this work, we using DFT method investigate the Pd-doping behavior on the pristine h-BN monolayer as well as related adsorption and sensing performance upon three SF6 decomposed species to explore its sensing potential. Our results indicate that n-typing doping is identified after Pd atom is doped on the h-BN monolayer, forming a novel chemical bond of Pd–N with length of 2.16 Å. The adsorption performance of Pd–BN monolayer upon SF6 decomposed species is in order as SOF2 > SO2 > SO2F2, with Ead of 0.94, 0.83 and 0.48 eV, respectively. After gas adsorption, the bandgap of Pd–BN monolayer is remarkably changed, making it possible for use of a resistance-type gas sensor. The sensitivity is obtained as − 41.04%, − 108.14% and 2.55% for SO2, SOF2 and SO2F2 systems, respectively, which implies the superior sensing behavior upon SOF2 at room temperature. Our work is meaningful to propose a novel sensing nanomaterial for detection of SF6 decomposed species, bridging the distance to evaluate the operation status of SF6 insulation devices.

A simple graphical approach for complex pressure swing adsorption (PSA) cycle scheduling has been developed. This new methodology involves a priori specifying the cycle steps, their sequence, and the number of beds, and then following a systematic procedure that requires filling in a 2-D grid based on a few simple rules, some heuristics and some experience. The outcome or solution is a grid comprised of columns that represent the total cycle time, rows that represent the total number of beds, and cells that represent the duration of each cycle step, i.e., the complete cycle schedule. This new approach has been tested successfully against several cycle schedules taken from the literature, including a two-bed four-step Skarstrom cycle, a four-bed nine-step process with two equalization steps, a nine-bed eleven-step process with three pressure equalization steps, and a six-bed thirteen-step process with four pressure equalization steps and four idle steps. This approach also revealed the existence of numerous cycle schedules for each bed and cycle step combination examined. Although it cannot identify the total number of permutations or which one is better, it does provide a very straightforward way to determine some of the possible cycle schedules of virtually any PSA process that can be conceived.

This paper examines the possibility to use a single neural network to model and predict a wide array of standard adsorption isotherm behaviour. Series of isotherm data were generated from the four most common isotherm equations (Langmuir, Freundlich, Sips and Toth) and the data were fitted with a unique neural network structure. Results showed that a single neural network with a hidden layer having three neurons, including the bias neuron, was able to represent very accurately the adsorption isotherm data in all cases. Similarly, a neural network with four hidden neurons, including the bias, was able to predict very accurately the temperature dependency of adsorption data.

Adsorption of acetazolamide (ACT) and formation of a mixed adsorption layers of acetazolamide (ACT)—sodium 1-decanesulfonate (SDS) and acetazolamide—hexadecyltrimethylammonium bromide (CTAB) at the R-AgLAFe/chlorates(VII) interface are described. The systems were characterized by the measurements of differential capacity, potential of zero charge, and surface tension at this potential. The adsorption parameters determined in the studied systems indicate the SDS domination in the adsorption equilibria and the competitive adsorption between the ACT—SDS or mixed micelles. However, acetazolamide dominates at adsorption equilibria of the ACT—CTAB mixture.

Calculations are presented to illustrate the dependence of capillary adsorption upon the interactions present in model pores. The sequence of phase transitions at zero temperature is determined for a Lennard-Jones lattice gas in a pore consisting of 4 × 4 × ∞ sites. The dependence of the specific filling sequence upon the comparative strength of the gas-pore wall and the gas-gas interaction well-depths is determined. Grand canonical Monte Carlo simulations of sorption at finite temperature in the continuum version of the same model pore are also reported. Both the theory and the simulations were performed with variable gas-solid and gas-gas energy well-depths. At a temperature of 90 K, the gas-solid heterogeneity associated with atoms adsorbed in the corners, on the walls and in the interior pore volume gives rise to sequential adsorption similar to that observed in the lattice gas calculation at 0 K. A gradual approach to non-wetting behavior is observed as the gas-solid well-depth decreases. Values of the gas-solid well-depth needed to produce pore filling at saturation (i.e., “pore-wetting”) are discussed.

We have used Grand Canonical Monte Carlo simulation to study argon adsorption at 87 K in wedge shaped mesopores. The structural parameters, including mean pore size, wall length and wedge angle, were varied to investigate their effects on the size, shape and the position of the hysteresis loop. Although the effects of pore size have been studied previously, the wall length and wedge angle have received little attention. We find that the wedge angle can have a significant effect on the existence, position, size and shape of the hysteresis loop, while the wall length affects the adsorptive capacity associated with the loop and the behaviour of the isotherm beyond the loop. The results of this work have far-reaching consequences for the characterization of pore size distribution where it is commonly assumed, when constructing a kernel of local isotherms, that pore size is uniform, since even a small deviation from a constant pore width can shift the condensation and evaporation pressures significantly and thus lead to an incorrect estimation of pore size.

In this study, the monocomponent adsorption of benzene, toluene and o-xylene (BTX) compounds, as model contaminants present in the petrochemical wastewaters, was investigated using three types of adsorbents: activated carbon (Carbon CD 500), a polymeric resin (MN-202) and a modified clay (Claytone-40). Langmuir and Freundlich models were able to fit well the equilibrium experimental data. The BTX adsorption capacity increased in the following order: Claytone-40 < CD 500 < MN-202. The maximum uptake capacity of MN-202, given by the Langmuir fitting parameter, for benzene, toluene and o-xylene was 0.8 ± 0.1, 0.70 ± 0.08 and 0.63 ± 0.06 mmol/g at 26 °C. Desorption kinetics for polymeric resin with 50 % methanol solution were fast being able to reuse the resin in consecutive adsorption/desorption cycles without loss of sorption capacity. The adsorptive behaviour at batch system was modelled using a mass transfer kinetic model, considering that the sorption rate is controlled by a linear driving force model, which successfully predicts benzene, toluene and o-xylene concentration profiles, with homogeneous diffusivity coefficients, D h , between 3.8 × 10−10 and 3.6 × 10−9 cm2/s. In general, benzene diffuses faster than toluene and o-xylene, which is in agreement with molecular diffusivity in water.