First Step Of Adsorption Research Articles

Changing of Electrical Conductivity, Acidity Function Voltage of Potential Difference for Salicylic Acid and Substituted to Study Adsorption Mechanism on Alumina Surface and the Factors Affecting it

In this study and for the first time there are the use of the specific electrical conductivity, acidity function, difference potential for salicylic and acetyl salicylic acids (Aspirin) solution before and after adsorption to describe and elicit adsorption mechanism as followed :-MO¯ + H2O → MOH (first step)MOH + H+ → MOH2+ MOH2+ + Anion L¯ → MOH2+ -------- ¯ L (second step)Mo¯ ( alumina surface ) , ¯ L ( anione )The adsorption mechanism is represented by two steps the first is to change the charge of the alumina surface from the negative polarized charge to the positive polarized charge by adsorption of hydrogen ions and water molecules from the acid solution to the surface of the alumina by adsorption and the second step represented by the adsorption of the negative anion of the acid to the surface. Salicylic acid give (H+) and salicylate ions (anione) and the presence of hydroxyl group on ortho position helps in the stabilization of anion and increase acidity compared with acetyl group. The adsorption process leads to an increase of acidity function by means of the decrease of (H+) ions in the solution by transition from solution to surface of alumina. This is the first step of adsorption and the second step represented by the transition of salicylate ions. This in turn causes decrease of difference potential between the acidic solution and alumina surface. Decrease of (H+) ions in solution causes decrease in electrical conductivity of solution. All these changes clarify mechanism of ions transition and their type from the solution to surface.

Surface enhanced Raman spectroscopic (SERS) behavior of phenylpyruvates used in heterogeneous catalytic asymmetric cascade reaction

The strength and geometry of adsorption of substituted phenylpyruvates on silver surface was studied by means of surface enhanced Raman spectroscopy (SERS) using silver sol. 2′-nitrophenylpyruvates were used as starting materials in a newly developed heterogeneous catalytic asymmetric cascade reaction to produce substituted quinoline derivatives. Substituents on the aromatic ring of the starting materials had significant influence on the yield of the desired quinoline derivatives. Product selectivity of the transformation of nitrophenylpyruvates were enhanced by the acid added. The geometry and the strength of the adsorption are assumed to play an important role in the outcome of this reaction, so we have tried to find correlation between the structure of adsorbed phenylpyruvates and their catalytic performance. Based on the results of our spectroscopic measurements, the enol form is predominant in the series of phenylpyruvates in solid form and methanol solutions. Stronger adsorption of phenylpyruvates in acidic media through oxygen atoms was indicated by the increased enhancement in the SERS spectrum. The nitro group of 2′-nitrophenylpyruvates has no direct role in the adsorption on Ag surface. This observation has explained why the hydrogenation of the keto group (presumably via the enol form) occurs preferentially and why the formation of the undesired indole derivatives requiring reduction of the nitro group is suppressed. The SERS behavior has helped to get a closer look on the first step of adsorption of starting materials contributing to a better understanding of the cascade reaction studied, thus providing a better flexibility in catalyst design.

Graphene oxide chemically reduced and functionalized with KOH-PEI for efficient Cr(VI) adsorption and reduction in acidic medium

In this study, graphene oxide (GO), polyethyleneimine (PEI) and potassium hydroxide (KOH) were used to synthesize reduced graphene oxide (rGO/PEI-KOH) nanocomposite. The presence and grafting of PEI molecules on the reduced GO surface were assessed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) analyses. The rGO/PEI-KOH nanocomposite was successfully applied for hexavalent chromium, Cr(VI), wastewater elimination. The resulting rGO/PEI-KOH adsorbent was found to be highly effective for Cr(VI) removal at low pH values and achieved a maximum capacity of experimental adsorption of 398.9 mg/g, which is one of the highest sorption capacity of most GO- and PEI-based adsorbents reported in the literature up to date. Studying the adsorption mechanism, the sorption isotherm revealed that the modified-Langmuir model was the best fit and Cr(VI) removal follows a pseudo-second-order kinetics, with the predominance of intraparticle diffusion during the first step of adsorption. XPS analysis indicated the presence of appreciable amount of Cr(III) on the adsorbent surface, which suggests that the adsorbed Cr(VI) ions were effectively reduced to Cr(III) on the rGO/PEI-KOH adsorbent surface (∼70% of the total adsorbed Cr). Cr(VI) adsorption and subsequent reduction to Cr(III) both contributed to the Cr(VI) removal. The results of the present study highlight the benefits of rGO/PEI-KOH like low cost, environmentally friendly, large toxic Cr(VI) ions adsorption capacity and its effective reduction to less-toxic Cr(III).

Supercritical Fluid Atomic Layer Deposition: Base-Catalyzed Deposition of SiO2.

An in situ FTIR thin film technique was used to study the sequential atomic layer deposition (ALD) reactions of SiCl4, tetraethyl orthosilicate (TEOS) precursors, and water on nonporous silica powder using supercritical CO2 (sc-CO2) as the solvent. The IR work on nonporous powders was used to identify the reaction sequence for using a sc-CO2-based ALD to tune the pore size of a mesoporous silica. The IR studies showed that only trace adsorption of SiCl4 occurred on the silica, and this was due to the desiccating power of sc-CO2 to remove the adsorbed water from the surface. This was overcome by employing a three-step reaction scheme involving a first step of adsorption of triethylamine (TEA), followed by SiCl4 and then H2O. For TEOS, a three-step reaction sequence using TEA, TEOS, and then water offered no advantage, as the TEOS simply displaced the TEA from the silica surface. A two-step reaction involving the addition of TEOS followed by H2O in a second step did lead to silica film growth. However, higher growth rates were obtained when using a mixture of TEOS/TEA in the first step. The hydrolysis of the adsorbed TEOS was also much slower than that of the adsorbed SiCl4, and this was overcome by using a mixture of water/TEA during the second step. While the three-step process with SiCl4 showed a higher linear growth rate than obtained with two-step process using TEOS/TEA, its use was not practical, as the HCl generated led to corrosion of our sc-CO2 delivery system. However, when applying the two-step ALD reaction using TEOS on an MCM-41 powder, a 0.21 nm decrease in pore diameter was obtained after the first ALD cycle whereas further ALD cycles did not lead to further pore size reduction. This was attributed to the difficulty in removal of the H2O in the pores after the first cycle.

Dual-stimuli-sensitive microgels as a tool for stimulated spongelike adsorption of biomaterials for biosensor applications.

This work examines the fabrication regime and the properties of microgel and microgel/enzyme thin films adsorbed onto conductive substrates (graphite or gold). The films were formed via two sequential steps: the adsorption of a temperature- and pH-sensitive microgel synthesized by precipitation copolymerization of N-isopropylacrylamide (NIPAM) and 3-(N,N-dimethylamino)propylmethacrylamide (DMAPMA) (poly(NIPAM-co-DMAPMA) at the pH-condition corresponding to its noncharged state (first step of adsorption), followed by the enzyme, tyrosinase, adsorption at the pH-condition when the microgel and the enzyme are oppositely charged (second step of adsorption). The stimuli-sensitive properties of poly(NIPAM-co-DMAPMA) microgel were characterized by potentiometric titration and dynamic light scattering (DLS) in solution as well as by atomic force microscopy (AFM) and quartz crystal microbalance with dissipation monitoring (QCM-D) at solid interface. Enhanced deposition of poly(NIPAM-co-DMAPMA) microgel particles was shown at elevated temperatures exceeding the volume phase transition temperature (VPTT). The subsequent electrostatic interaction of the poly(NIPAM-co-DMAPMA) microgel matrix with tyrosinase was examined at different adsorption regimes. A considerable increase in the amount of the adsorbed enzyme was detected when the microgel film is first brought into a collapsed state but then was allowed to interact with the enzyme at T < VPTT. Spongelike approach to enzyme adsorption was applied for modification of screen-printed graphite electrodes by poly(NIPAM-co-DMAPMA)/tyrosinase films and the resultant biosensors for phenol were tested amperometrically. By temperature-induced stimulating both (i) poly(NIPAM-co-DMAPMA) microgel adsorption at T > VPTT and (ii) following spongelike tyrosinase loading at T < VPTT, we can achieve more than 3.5-fold increase in biosensor sensitivity for phenol assay. Thus, a very simple, novel, and fast strategy for physical entrapment of biomolecules by the polymeric matrix was proposed and tested. Being based on this unique stimuli-sensitive behavior of the microgel, this stimulated spongelike adsorption provides polymer films comprising concentrated biomaterial.

A new model based on multilayer kinetic adsorption mechanism for asphaltenes adsorption in porous media during dynamic condition

In this work, a new model based on multilayer kinetic adsorption mechanism has been proposed to account asphaltene adsorption in porous media under dynamic condition and the model was verified using experimental data obtained in this work and also with those reported in the literature. In the proposed model two steps are considered for asphaltene adsorption. The first step is taken as adsorption of asphaltenes on the surface of the porous media and the second step is taken as adsorption of asphaltenes on the asphaltenes already adsorbed on the porous media. The Crank-Nicholson method, central difference in space and trapezoidal rule in time, giving second order convergence in time was applied to develop a computer program using MATLAB software. Also, the Rung-Kutta fourth order scheme has been applied to calculate the volume fraction of asphaltene adsorption. The results show that the proposed model based on multilayer adsorption kinetic mechanism of aphaltene with the absolute average deviation 0.7% can predict more accurately the asphaltene adsorption experimental data in comparison to the previous models based on the monolayer adsorption kinetic and equilibrium mechanism. Sensitivity analysis shows that the proposed model is more sensitive to the first step of adsorption than the second step of adsorption. Also, a series of experiments was carried to investigate the asphaltene adsorption using UV–vis spectroscopy in order to study the effect of different parameters on asphaltene adsorption mechanisms during dynamic condition in porous media such as concentration, asphaltene composition, flow rate and type of porous media. The experimental results show that adsorption is controlled by the type of porous media rather than the asphaltene concentration of solution. Also, it was found that the adsorption process in porous media is controlled by kinetics mechanism during dynamic condition.

The interaction between water vapor and chitosan II: Computational study

Different models were used for both the exposed structures of chitosan and for water in the vapor state in the molecular modeling of the first step of adsorption of water on chitosan, taking into account water clustering phenomena upon adsorption, the water structure, and the effect of temperature on water structure (i.e., the presence of dimers or monomers). The degree of acetylation (DA) influences markedly the first step of water vapor adsorption on chitosan. Modeling results on the first step of adsorption were analyzed taking into account the ratio water dimer/water monomer and the species predominant as a function of ambient conditions (i.e., relative humidity (RH) and temperature (T)). From the experimental point of view, the ratio of water dimer/water monomer has a different effect on chitosans depending on its DA and adsorption temperature. We found that the adsorption of water monomer on a model of hydrated chitosan is favoured in almost −84 kJ mol−1 of steric energy, whereas the adsorption on dehydrated chitosan by only −21 kJ mol−1. The water–chitosan surface distance found in this work was 0.2 nm, whilst the literature values are between 0.245 nm and 0.309 nm for the hydrated chitosan crystalline structure. It was evident that at least two tetramers are required to represent the surface of chitosan.

XPS and ab initio study of the interaction of PbTe with molecular oxygen

Density functional (B3LYP) calculations have been performed to investigate the adsorption of O 2 ( 3 Σ g - ) molecule on the surface of cluster (PbTe) 4. To study the influence of point defects (namely, impurity atoms and cation and anion vacancies) on the reactivity of PbTe surface, clusters (PbTe) 3GeTe, (PbTe) 3GaTe, (PbTe) 3Te, and (PbTe) 3(Pb) were investigated. The adsorption of oxygen on the surface of (PbS) 4 cluster was calculated to evaluate the role of anions in the adsorption process. It was shown that the formation of the peroxide-like complex is the first step of adsorption. The calculated tendency to surface oxidation increases in sequence: PbTe with cation vacancies <PbS < pure PbTe < PbTe doped with Ga < PbTe doped with Ge < PbTe with anion vacancies. The results of quantum-chemical calculations correlate with X-ray photoelectron spectroscopy data.

Sphingomyelin content conditions insertion of daunorubicin within phosphatidylcholine monolayers

Cell death induced by the chemotherapeutic drug daunorubicin (DNR) implicates an apoptotic pathway originating at the plasma membrane and characterized by sphingomyelin (SM) hydrolysis and ceramide generation. The mechanisms by which such a drug (hypothetically passively diffusing across a structural membrane) can trigger SM hydrolysis is unknown, but raises the question of the precise interaction between DNR and membrane lipid constituents. In this initial study, using alternative current polarography together with voltammetry, we report that after a first step of adsorption, insertion of DNR within a condensed phosphatidylcholine monolayer was significantly facilitated by SM content.

Adsorption of 4,4’ ‐ iso propylidene diphenol and diphenylolpropane 4,4’ dioxyaceticacid from aqueous solution on kaolinite

Abstract The adsorption of 4,4 ‐ iso propylidene diphenol (Bis‐phenol A) and diphenylolpropane 4,4 dioxyaceticacid (Bis acid A2 ) on kaolinite type clay have been studied as the function of their solution concentration and temperature. The adsorption rates at low concentrations of Bis ‐ phenol A was found to fit the first‐order equation with two kinetic steps. In all cases, the first step of adsorption was more rapid than the second one. The results indicated that the adsorption rate is controlled by either a film diffusion or a intra‐particle diffusion. It can be concluded that the adsorption reaction begins with the film diffusion. Since the film‐diffusion rate is much higher than the rate of intra‐particle diffusion, the reaction is governed by intra‐particle diffusion in the second step. In the case of Bis acid A2 only one kinetic step was observed corresponding to the film diffusion mechanism. Using the Arrhenius equation, the activation energies for both systems were evaluated. The corresponding values of thermodynamic parameters were calculated using Eyring's equation of absolute reaction rate. The adsorption data of Bis ‐ phenol A and Bis acid A2 were fitted to Freundlich and B.E.T isotherms, respectively. The results could be interpreted in terms of a parallel orientation of Bis acid A2 molecules on the adsorbent surface.

Optical study of potassium growth on the Si(100) surface

The formation of the Si(100)/potassium interface has been studied by real-time surface reflectance spectroscopy, Auger electron spectroscopy and low energy electron diffraction. The changes of the Si optical reflectance have been followed as a function of the amount of K deposited at room temperature. The first step of adsorption gave rise to a phase transition which occurs at about 0.4 SML (where 1 SML corresponds to the saturation monolayer). The corresponding optical spectra displayed peculiar features which could be due to a symmetrization of the dimers at the silicon surface. Two growth processes could be distinguished, which yielded different equilibrium states: a ‘dynamic’ process observed during K evaporation (with a saturation larger than 1 SML) and a ‘static’ one which takes place after the evaporation has been stopped (saturation at 1 SML). The optical spectrum corresponding to the saturation of the dynamic process displays an absorption band which is interpreted as due to resonances in small K clusters, as observed in free K cluster experiments.