Surface Adsorption Properties Research Articles

On the Adsorption Properties of Surface Chemically Pure CHAPS at the Air/Water Interface

CHAPS, a surface-active derivative of the steroids' basic structure of the cholic acid [3-[(3-cholamidopropyl)dimethyl-ammonio]-1-propanesulfonate] has become a very important material in biological and pharmaceutical application. Investigations of the adsorption properties of aqueous, surface-chemically pure CHAPS solutions at the air/water interface were performed using surface tension and surface potential measurements. Unlike ordinary extended-chain surfactants, the amphiphilic structure of CHAPS is prone to adopt different concentration-dependent surface states of the adsorption layer. These are well reflected in the adsorption isotherm and in the electric surface properties. They are explained by changes in the adsorbate molecule's orientation and/or conformation as a result of the latter's different surface area demand. The versatile favorable application properties of the CHAPS molecule are obviously due to its complicated molecular structure, which enables it to comply with rather different interfacial and colloidal challenges.

Effect of pH on the removal of Victoria blue by adsorption

The removal of Victoria blue dye form water and waste water by adsorption on China clay is greatly influenced by the pH of the medium. The pH of the adsorbate solution effect the nature of the surface properties of adsorbents the degree of ionization and speciation of aqueous adsorbate species and ultimately the rate and extent of the adsorption. The initial concentration of the dye taken was 1.0 × 10-6 M and the China were agitated at 30° C (±°C). The pH of the dye solution was changed from 3.0 to 8.0 using NaOH or HCI solutions of appropriate strength. The results the variation in adsorption with different pH have been recorded.

The adsorption properties of surface modified activated carbon fibers for hydrogen storages

In this study, activated carbon fibers (ACFs) with high surface area and pore volume have been modified by Ni doping and fluorination. The surface modified ACFs were characterized by BET surface area, SEM/EDS, XRD, and Raman spectroscopy. The changes in pore structure and surface properties of these modified ACFs were correlated with hydrogen storage capabilities. After fluorination treatment, although the micropore volume of ACF was decreased, amounts of hydrogen storage were found to increase. Additionally, micropore volume on ACFs was found to be unchanged with Ni doping, hydrogen storage capacities were considerably increased due to the effect of catalytic activation of nickel. Though fluorination of ACFs increases hydrogen affinity, the effect of catalytic activation of nickel is more prominent, and thus led to better hydrogen storage. Hence, it was concluded that hydrogen storage capacity was related to micropore volumes, Pore size distribution (PSD) and surface properties of ACFs as well as specific surface areas.

Surface structure and adsorption properties of multiwalled carbon nanotubes

The pore structure, sorption parameters, and chemical composition of the surface of multiwalled carbon nanotubes synthesized by catalytic pyrolysis were determined. The dependences of the amount of cholic acid adsorbed by the nanotube surface on time, pH, and concentration of an equilibrium solution were studied. Physical adsorption of cholic acid is mainly the outcome of nonspecific interactions between the acid and the surface of the nanotubes.

Modification of the Surface Adsorption Properties of Alumina-Supported Pd Catalysts for the Electrocatalytic Hydrogenation of Phenol

The electrocatalytic hydrogenation (ECH) of phenol has been studied using palladium supported on gamma-alumina (10% Pd-Al2O3) catalysts. The catalyst powders were suspended in aqueous supporting electrolyte solutions containing methanol and short-chain aliphatic acids (acetic acid, propionic acid, or butyric acid) and were dynamically circulated through a reticulated vitreous carbon cathode. The efficiency of the hydrogenation process was measured as a function of the total electrolytic charge and was compared for different types of supporting electrolyte and for various solvent compositions. Our results show that these experimental parameters strongly affect the overall ECH efficiency of phenol. The ECH efficiency and yields vary inversely with the quantity of methanol present in the electrolytic solutions, whereas the presence of aliphatic carboxylic acids increased the ECH efficiency in proportion to the chain length of the specific acids employed. In all cases, ECH efficiency was directly correlated with the adsorption properties of phenol onto the Pd-alumina catalyst in the studied electrolyte solution, as measured independently using dynamic adsorption isotherms. It is shown that the alumina surface binds the aliphatic acids via the carboxylate terminations and transforms the catalyst into an organically functionalized material. Temperature-programmed mass spectrometry analysis and diffuse-reflectance infrared spectroscopy measurements confirm that the organic acids are stably bound to the alumina surface below 200 degrees C, with coverages that are independent of the acid chain length. These reproducibly functionalized alumina surfaces control the adsorption/desorption equilibrium of the target phenol molecules and allow us to prepare new electrocatalytic materials to enhance the efficiency of the ECH process. The in situ grafting of specific aliphatic acids on general purpose Pd-alumina catalysts offers a new and flexible mechanism to control the ECH process to enhance the selectivity, efficiency, and yields according to the properties of the specific target molecule.

Hydrophobicity and catalytic properties of Ti-MFI zeolites synthesized by microwave and conventional heating

Ti-incorporated MFI zeolite (Ti-MFI-MW) has been synthesized with microwave heating. Their physicochemical properties such as surface hydrophobicity, and adsorption and catalytic properties have been compared with those of Ti-incorporated MFI zeolite (Ti-MFI-CH) prepared by conventional hydrothermal method. Competitive adsorption measurements with toluene and water revealed that the hydrophobicity index of Ti-MFI-MW (8.0) is higher than that of Ti-MFI-CH (6.2). IR spectra showed that Ti-MFI-MW also has a lower content of surface hydroxyl groups and adsorbs a larger amount of 1-hexene than Ti-MFI-CH. These results pointed out that Ti-MFI-MW is more hydrophobic than Ti-MFI-CH. Epoxidation reactions of 1-hexene and styrene with hydrogen peroxide have been conducted to investigate catalytic properties of the Ti-MFI zeolites according to the synthesis method. The conversions and epoxide selectivities over Ti-MFI-MW are higher than those over Ti-MFI-CH due to the enhanced surface hydrophobicity.

Effects of activation time on the properties and structure of polyacrylonitrile‐based activated carbon hollow fiber

AbstractPolyacrylonitrile (PAN) hollow fibers were pretreated with ammonium dibasic phosphate, then further oxidized in air, carbonized in nitrogen, and activated with carbon dioxide. The effects of activation time of a precursor fiber on the microstructure, specific surface area, pore‐size distribution, and adsorption properties of PAN‐based activated carbon hollow fibers (PAN‐ACHF) were studied in this work. The BET surface area of PAN‐ACHF and surface area of mesopores gradually increase with activation time extending, and reach the maximum values, 780 and 180 m2 g−1, respectively, when fibers are activated at 800°C for 100 min. The adsorption ratio to creatinine changes little with activation time extending and all values over all activation time are above 90%. The adsorption ratio to VB12 gradually increases with activation time extending before 60 min, and then becomes relatively constant from 60 to 100 min. The number of pores on the surface of PAN‐ACHF increases with activation time extending. The amount of mesopores in PAN‐ACHF made of fibers activated for different time increases with activation time extending and the dominant pore sizes of mesopores in PAN‐ACHF range from 2 to 5 nm. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 2565–2569, 2006

Changes in the Surface Chemistry and Adsorptive Properties of Active Carbon Previously Oxidized and Heat-Treated at Various Temperatures. III. Studies of the Adsorption of Organic Solutes from Aqueous Solutions

The dependence between the surface chemistry characteristics of thermally modified active carbon samples with previously oxidized surfaces and their ability to adsorb organic solutes from aqueous solutions was investigated. The characteristics of the surface functional groups and the porous structure of the samples obtained were estimated using various experimental methods. The adsorption isotherms of nitrobenzene and 4-nitrophenol from dilute aqueous solutions onto all the carbon samples obtained were measured. The experimental systems were analyzed in terms of the theory of adsorption onto energetically heterogeneous solids. The relationships between the optimized isotherm parameters, i.e. equilibrium constants and heterogeneity parameters, and the characteristics of the active carbons were discussed.

A Comparative Study of Nitrogen Physisorption on Different C70 Crystal Structures Using an Ab Initio Based Potential

Quantum mechanical calculations are performed using the recently developed hybrid method for interaction energies to determine atom site Lennard-Jones potential parameters for the interactions of molecular nitrogen with C(70) molecules. This ab initio based potential is used in grand canonical Monte Carlo simulations to predict surface adsorption properties of N(2) on five known C(70) structures: rhombohedral, fcc, ideal hcp, deformed hcp, and monoclinic crystals. Because of the presence of five-membered carbon rings and the surface curvature of C(70) molecule, the Lennard-Jones potential parameters for nitrogen-carbon interactions obtained from ab initio based calculations are found to be different from that with planar graphite. The simulation results obtained from these two sets of force fields are compared and shown to differ, particularly at low coverage, where the nitrogen-carbon interactions are more important than the nitrogen-nitrogen interactions. The surface area, monolayer capacity, and isosteric heat of adsorption are calculated for various C(70) crystals and found to change appreciably as a result of the shear-induced phase transformation from hcp to rhombohedral lattice.

Adsorption properties of the corundum surface in corundum-based refractories

Distribution of the adsorption sites in fused corundum is studied depending on the fractional composition of the material and specific surface of its finely ground fractions. Treatment of the corundum surface with a phenolic resin is shown to affect, both quantitatively and qualitatively, the distribution of acid-base adsorption sites.

Evaluation of different zeolites in their parent and protonated forms for the catalytic combustion of hexane and benzene

Deep oxidation of benzene and n-hexane over NaX, CaA and ZSM-5 zeolites in their parent and protonated forms has been studied in the present work. Chemical composition was determined by ICP-MS, varying the Si/Al ratio between 1 and 11.38. Parent and protonated zeolites were characterized by X-ray diffraction (XRD), N 2 physisorption, ammonia temperature-programmed desorption (NH 3-TPD) and inverse gas chromatography (IGC). Catalytic activities were evaluated by recording the light-off curves in a pulsed flow microreactor. Reactivity (expressed in terms of ignition temperatures) was correlated with surface acidity (strength and concentration of acid sites), morphological parameters and adsorption properties. ZSM-5 and X Zeolites present the best catalytic performance for the catalytic oxidation of benzene and n-hexane, respectively. Results obtained indicate that the catalytic activity for n-hexane oxidation strongly depends on the strength of the interaction between the organic molecule and the catalyst, whereas in the case of benzene, the adsorption capacity of the material plays a key role on the catalytic activity.

Investigation of factors affecting the adsorption of functional molecules onto gel silicas: 1. Flow microcalorimetry and infrared spectroscopy

Flow microcalorimetry and infrared spectroscopy were used to study the surface structure and adsorptive properties of a series of calcined and uncalcined porous silicas. The adsorbates dl-menthol, ( r)-(+)-limonene, ( + / − ) -citronellal and carvone were selected for their functionality, that included carbonyl, vinylic and hydroxyl groups. The amounts of probe retained by the silicas together with the energy exchange involved in the adsorption/desorption process were determined by flow microcalorimetry. The functional groups involved in these interactions were studied by means of infrared spectroscopy. It was observed that the strongest interactions with the silica surface took place through hydrogen bonding onto the surface silanol. The most retentive probes were found to be those with a carbonyl group in their structure. Adsorption onto calcined silicas was found to be less energetic than onto the equivalent calcined samples. The adsorption densities were compared with theoretical predictions based on molecular models. In all cases apart from citronellal monolayer coverage were not observed due to steric effects.

Experimental design methodology for the preparation of carbonaceous sorbents from sewage sludge by chemical activation––application to air and water treatments

The objective of this study is to optimize experimental conditions of sorbent preparation from sewage sludge using experimental design methodology. Series of carbonaceous sorbents have been prepared by chemical activation with sulfuric acid. The sorbents produced were characterized, and their properties (surface chemistry, porous and adsorptive properties) were analyzed as a function of the experimental conditions (impregnation ratio, activation temperature and time). Carbonaceous sorbents developed from sludge allow copper ion, phenol and dyes (Acid Red 18 and Basic Violet 4) to be removed from aqueous solution as well as VOC from gas phase. Indeed, according to experimental conditions, copper adsorption capacity varies from 77 to 83 mg g −1, phenol adsorption capacity varies between 41 and 53 mg g −1 and VOC adsorption capacities (acetone and toluene) range from 12 to 54 mg g −1. Each response has been described by a second-order model that was found to be appropriate to predict most of the responses in every experimental region. The most influential factors on each experimental design response have been identified. Regions in which optimum values of each factor were achieved for preparation of activated carbons suitable for use in wastewater and gas treatments have been determined using response surfaces methodology. In order to have a high mass yield and to minimize the energetic cost of the process, the following optimal conditions, 1.5 g of H 2SO 4 g −1 of sludge, 700 °C and 145 min are more appropriate for use of activated carbon from sludge in water and gas treatments.

Electrode Potential-Dependent Stages in OH ads Formation on the Pt3Cr Alloy (111) Surface

Results of a periodic spin-density-functional theory study of the electronic structure and the local adsorption properties of the alloy surface are presented. A slab composed of four-atom-layer is used to model the (111) surface of the bulk phase with the two topmost layers and adsorbed species allowed to relax. Adsorption energies for OH and have been calculated as functions of initial OH coverage. Using these energies in a model based on reaction energies for acid electrolyte, we have calculated reversible potential shifts, for formation from on different surface sites of the alloy relative to the Pt(111) surface. For the first 0.25 monolayer (ML) coverage, and OH are more stable on the Cr sites and a V is calculated. For the next 0.25 ML instalment, forming on Pt, V. Shifts in for going to 0.75 and 1 ML coverage are both positive. Hydrogen bonding between adsorbed molecules plays a role at higher coverage. adsorption was studied on the 0.5 ML covered surface and was found to bond more weakly than allowing us to suggest that if the sputtered alloy surface is active toward reduction, as the sputtered and surfaces are, Pt islands may be responsible. © 2004 The Electrochemical Society. All rights reserved.

Surface Composition and Adsorption Properties of Activated Carbon Cloth

Surface Composition and Adsorption Properties of Activated Carbon Cloth

Effects of cation exchange on the pore and surface structure and adsorption characteristics of montmorillonite

Ca-montmorillonite was exchanged with the metal cations, titanium, iron, and copper and the ion-exchange effects on the surface area, pore structure and adsorption property of the montmorillonite were studied. The changes in the pore structure and the surface roughness of the montmorillonite were first characterized based on the classical and fractal analyses of the nitrogen adsorption isotherms as well as the XRD and TGA/DSC patterns. Then, the adsorption isotherms of benzene, hexane, and cyclohexane were measured to identify how exchange process affected the adsorption characteristics of the montmorillonite. It was found that the ion-exchange processes could induce enormous changes in the surface and pore structure of montmorillonite and these changes could be interpreted with the coverture of the surface roughness (surface screening effect), the inhibition of the movement of nitrogen molecule into pores (pore blocking effect), and the interlamellar expansion of the montmorillonite (pore opening effect). The effect of alterations of the surface area and the pore structure on the adsorption characteristics of montmorillonite was discussed.

Photodecomposition and Surface Adsorption of Methylene Blue on TiO<sub>2</sub> Nanofluid Prepared by ASNSS

This study proposes a low-pressure control method for an arc-submerged nanoparticle synthesis system (ASNSS) developed for TiO 2 nanoparticle fabrication. The photocatalytic and surface adsorptive activity of TiO 2 nanofluid is examined via the decomposition of methylene blue. Experimental results show that the ASNSS can successfully prepare anatase TiO 2 . The rate constant of photocalalytic reaction of TiO 2 nanoparticles for methylene blue is 0.0345 (min - 1 ), and the rate constant of surface adsorption of methylene blue on TiO 2 is 0.0437 (min - 1 ). Experimental results indicate that the TiO 2 nanofluid prepared by the ASNSS has excellent photocatalytic activity and surface adsorption property for degradation of methylene blue.

Characterization and application of a new natural catalyst

This paper is focused on the characterization and study of the catalytic properties of a natural soil from Etla, Oaxaca, Mexico. Thus, X-ray diffraction, energy dispersive spectroscopy, scanning electron microscopy, thermal methods, infrared spectroscopy, 27 Al and 29 Si solid-state NMR spectroscopy and surface adsorption properties (N2-BET) analyses for the target material were carried out. Additionally, in order to test the potential and effectiveness of this material as Lewis acid catalyst, a set of experiments for the promotion of various 1,3-oxathiolanes as well as ortho and para benzyltoluenes were carried out. It was found that the catalytic activity for these reactions depends on the amount of soil, the reaction time and the pyridine concentration used as competitive inhibitor. Finally, the studies on the characterization and uses of the soil were thought in order to contribute to the aim of the green chemistry, by using and promoting friendly environment natural materials.

Surface Tension and Adsorption Properties of a Series of Bolaamphiphilic Poly(fluorooxetane)s

Studies of surface tension, adsorption parameters, and dynamic surface tension were performed on a series of bolaamphiphilic α,ω-(diammonium disulfato)poly(fluorooxetane)s of several perfluoroalkyl chain lengths. Similar measurements were performed on a small-molecule, anionic fluorosurfactant with a −C8F17 perfluoroalkyl group that is known to be an effective flow and leveling aid in aqueous coatings. Molecular area demands for the poly(fluorooxetane)s were found to be relatively small for a polymeric species and may indicate a change in conformation between bulk solution and interface. Other adsorption parameters were found to be similar to those of the small-molecule fluorosurfactant. Diffusion coefficients were found to be slightly smaller for the poly(fluorooxetane)s compared to the small-molecule fluorosurfactant.

Adsorption/Oxidation of CH3SH on Activated Carbons Containing Nitrogen

Activated carbons of different origins were impregnated with urea and heat-treated at 450 and 950 °C. Surface properties of adsorbents were evaluated using nitrogen adsorption, potentiometric titration, Boehm titration, elemental analysis, and thermal analysis. Then, the CH3SH breakthrough capacity tests were carried out and the adsorption capacities were evaluated. The results showed that the amount adsorbed depends strongly on the modification conditions of the carbon surface. It increased from 1.4 to 10 times after introduction of nitrogen species. Immobilization of methyl mercaptan on the surface is likely governed by the redox process, and basic nitrogen groups can act as catalysts for electron transfer from sulfur to oxygen. Dimethyl disulfide and methyl methanethiosulfonate are the main products of methyl mercaptan oxidation.