Dual Adsorption Research Articles

On the Adsorption of Tetracycline by Calcined Magnesium‐Aluminum Hydrotalcites

Exploiting effective sorbents for antibiotic adsorption is highly desirable for the elimination of ecological risks from antibiotic contamination. In this study, MgAl-CO(3)(2-) hydrotalcites with different Mg/Al molar ratios were prepared and tetracycline (TC) adsorption to the hydrotalcites and calcined hydrotalcites was investigated by batch experiments. Calcined hydrotalcites had higher adsorption capacities compared to MgAl-CO(3)(2-) hydrotalcites. At low TC equilibrium concentrations, calcined hydrotalcites with differing Mg/Al ratios showed approximately identical TC uptakes. However, at high tetracycline concentration, greater TC adsorption capacity was observed for calcined hydrotalcite having a high Mg/Al ratio (i.e., 4.4). X-ray diffraction (XRD) characterization showed the presence of Mg-Al oxide solid solution in TC -loaded calcined hydrotalcite, suggesting that suspension of the calcined product in water and adsorption of TC had led to only partial reconstruction of the layered structure. We hypothesize that TC was adsorbed on the MgO surface at high equilibrium concentrations. The behavior of TC adsorption on the calcined hydrotalcite was well described by a dual adsorption model. Kinetic analysis suggested that at low adsorption levels, TC adsorption by calcined hydrotalcite could be modeled by both a pseudo second-order kinetics model and a nucleation-growth model. The present work demonstrates that calcined hydrotalcites may be promising adsorbents for effective removal of TC from water resources.

Surface plasmon resonance studies on molecularly imprinted films

AbstractNovel molecular recognition films were prepared from modified polysulfone having perillaldehyde moiety as a side group. The molecular recognition films were obtained from perillaldehyde polysulfone by adopting 9‐ethyladenine as a print molecule. The molecular recognition phenomena were studied by surface plasmon resonance (SPR) spectroscopy. Adsorption of adenosine (As) and guanosine (Gs) in the molecularly imprinted film was studied. Dual adsorption isotherms were observed for As in 9‐EA imprinted films, while nonspecific adsorption isotherms for Gs in those films. This revealed that the molecular recognition sites toward As were constructed in the films thus prepared. The apparent affinity constant toward As determined by using apparent adsorption isotherms ranged from 7.90 × 103 to 3.31 × 104 mol−1 dm3. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Experimental and modeling investigations of wastewater filtration

In an effort to make wastewater recycling risk-free, this research investigated the feasibility of using a waste material as filter for the removal of humic substances (HS), and ultimately the toxic hydrophobic organic compounds (HOC) attached to them. Based on the results of earlier studies, laboratory experiments were conducted in a large-scale set up to investigate with synthetic and real (municipal) wastewater, the effects of the flow rate, column diameter, and column height on the efficiency of the filtration process. Furthermore, with the experimental data, a mathematical model was calibrated and used to predict the performance of the filtration process under various conditions. The results of the investigation with the synthetic samples showed that all concentration-time profiles had a reversed ‘S’ shape, and at any given flow rate, the efficiency of the filtration increased when the height and/or diameter of the PPL column increased. However, it decreased when the flow rate increased. Under similar conditions, the filtration efficiency with municipal wastewater samples was much higher. The mathematical model predicted with more or less success the experimental data. Overall, this research confirmed that PPL can be used to remove HS. It also suggested that PPL may be able to remove HOC attached to HS. Nevertheless, further investigations are necessary to eliminate the release of background organics by PPL, and improve the model by taking into account the dual adsorption–filtration capability of its granules.

Biodegradation of polycyclic aromatic hydrocarbons in the natural waters of the Yellow River: Effects of high sediment content on biodegradation

The contamination of polycyclic aromatic hydrocarbons (PAHs) has become one of the major problems in the Yellow River of China. As the Yellow River is the most turbid large river in the world, it remains unknown to which extent the high suspended sediment content in the river may affect the fate and effect of PAHs. Here we report the effect of sediment on biodegradation of chrysene, benzo( a)pyrene and benzo( g, h, i)perylene with phenanthrene as a co-metabolism substrate in natural waters from the Yellow River. Biodegradation kinetics of the PAHs in the river water with various levels of sediment contents were studied in the laboratory by fitting with a biodegradation kinetics model for organic compounds not supporting growth. The results indicated that the biodegradation rates of PAHs increased with the sediment content in the water. When the sediment contents were 0, 4 and 10 g/l, the biodegradation rate constants of chrysene with the initial concentration of 3.80 μg/l were 0.053, 0.084 and 0.111 d −1, respectively. Further studies suggested the enhanced biodegradation rate in the presence of sediment was caused by the following mechanisms: (1) the population of PAH-degrading bacteria in the water system was found to increase with the sediment content; the bacteria population on sediment phase was far greater than that on water phase during the cultivation process; (2) the sorption of PAHs on the sediment phase was well described by the dual adsorption–partition model. Although the sorption capacity of PAH per unit weight of sediment decreased with the increase of the sediment content, the amount of sorbed PAH increased with the sediment content; and, (3) the desorption of PAHs from the solid phase led to a higher concentration near the water–sediment interface. Since the bacteria were also attached to the interface, this resulted in an increased contact chance between the bacteria and PAHs.

Lindane adsorption isotherms interpreted in terms of interaction free energies with porous media

Lindane adsorption isotherms on silica sand and alluvial loam were investigated by batch and column experiments and related to lindane interaction free energies with the porous media. These interaction free energies were highly dependent on the physico-chemical characteristics of lindane and the porous media and could be calculated by their surface thermodynamic properties. Silica sand displayed a single adsorption domain and lindane had a linear adsorption isotherm on silica sand. In contrast, alluvial loam exhibited dual adsorption domains, which could be interpreted by two linear adsorption isotherms. For heterogeneous porous media with multiple adsorption domains, such as alluvial loam, lindane first adsorbed onto domains of high adsorption potentials. When these domains were occupied, lindane began to adsorb onto domains of low adsorption potentials.

Dual solute adsorption of 2,4,6‐trichlorophenol and N‐[2‐(2,4,6‐trichlorophenoxy)propyl]amine on to activated carbon

Dual solute adsorption of 2,4,6‐trichlorophenol and N‐[2‐(2,4,6‐trichlorophenoxy)propyl]amine on to activated carbon

Analysis of Dual Diffusion and Non-linear Adsorption Isotherm with a Time Lag Method

This paper presents an application of the time lag method in the analysis of an adsorption system, where dual diffusion mechanism is assumed to exist and the equilibrium relationship between the fluid and adsorbed phases is non-linear. The derived time lag is expressed in terms of system parameters and operating conditions in the form of a quadrature. The feature of this solution is that the relative contribution of the pore and surface diffusions is a strong function of upstream pressure when the time lag experiment is operated over the non-linear range of the adsorption isotherm. It is this nice feature that we take advantage of to determine the pore and surface diffusivities without resorting to isolation of the pore diffusion by using non-adsorbing gas as a reference, as usually done in many other work. This advantage is not manifested in linear systems where the relative contribution of the pore and surface diffusions is a constant, rendering the delineation of these two processes impossible. Effects of various parameters on the utility of this time lag method are discussed in this paper, and application of the method is demonstrated with experimental data of sulfur dioxide adsorption onto Carbolac carbon (Proc. Roy. Soc., A271, 1–18, 1963).

Detailed Kinetics Modeling of Indium Phosphide Films in Mocvd Reactors

AbstractThe deposition kinetics of InP in MOCVD reactors is presented. The proposed chemical mechanism involves both gas phase and surface reactions. The fundamental hypothesis adopted in deriving the mechanism was a dual site dissociative adsorption of the precursors on the growing surface. In any case, all the rate constants either were taken from the literature or estimated through thermochemical methods. In addition, the deposition reactor was simulated by means of a monodimensional model that accounts for the main reactor features through the boundary layer theory.

Characterization of Acid-Base Property of ZrO<sub>2</sub> by Thermal Desorption: II. Dual Adsorption of NH<sub>3</sub> and CO<sub>2</sub>

Dual adsorption of nh3 and co2 has been used to study the acid property of zro2 in relation to its base property by tpd and ir spectroscopy. it is found that preadsorbed nh3 (or co2) has no inhibitory but a promotive effect to a postadsorption of co2 (or nh3) the increased adsorption of the postadsorbed moecules is most pronounced in the tpd curves at above 510 k. in the ir observation, the dual adsorption effect is characterized by a formation, on one hand, of a monodentate carbonate species which can not be formed in the single adsorption of co2, and by a strengthened bonding of nh3 to surface acid site (zr4+) on the other hand. these results suggest that there exists not only independently located acid and base sites, responsible for the adsorption of nh3 and co2, but some sites located closely(i.e acid-base pair sites). a surface induced through-bond acid-base interaction seems to be the nature of the dual adsorption effect.

Kimetic studies on liquid-phase hydrogenation of 1-methylnaphthalene using an improved basket reactor.

An improved basket reactor, equipped with a specially designed catalyst basket assembly to determine the exact starting time of reaction in batchwise experiments, was developed. The reactor was proved to be useful in experiments even under high temperature and pressure. Using this reactor, kinetic studies of liquid-phase hydrogenation of 1-methylnaphthalene were carried out as a model reaction of regeneration of hydrogen donor solvent for coal liquefaction and hydrotreating of polyaromatic sources of gas oil, in the range of 583–643 K temperature and 3.1–7.7 MPa hydrogen partial pressure over a commercial Co-Mo/γ-Al2O3 catalyst. To establish kinetic equations, the reaction equilibrium for conversion of 1-methylnaphthalene to methyltetralins was measured. Langmuir-Hinshelwood type kinetic equations, based on surface reaction between dual adsorption sites of hydrogen and reactants, fairly represented the effects of temperature and hydrogen partial pressure on the yields.

Determination of polymer‐solvent interaction parameters using piezoelectric crystals, with reference to the sorption of chemical warfare agents

AbstractPolymeric materials which show sensitivity to certain classes of organic vapors and give minimal responses from interferents are being sought for use as coatings on piezoelectric mass detection devices. The present work illustrates some simple methods for the determination of fundamental properties such as polymer‐solvent interaction parameters and diffusion constants, and relates these to the sensitivity and response time of the sensor. Polymers with a controlled variation in crosslink density were exposed to a variety of common solvents and vapors covering a range of solubility parameters. Seven non‐crosslinked amorphous polymeric materials were also assessed for their suitability as selective coatings for the detection of a range of chemical warfare vapors. Gross differences in the response characteristics of coated crystals immersed in liquids can be predicted, and an approximate guide to the relative rates of solvent penetration can also be obtained. More accurate predictions are hampered by the lack of knowledge of the specific interactions which occur within polymer–solvent pairs. Crosslinking the polymer film to enable operation in strongly solvating liquids has the effect of reducing the extent of swelling to a larger degree than expected on the basis of existing theories. The operation of coated crystals in the gas phase at very high vapor concentrations leads to a dual site adsorption process which can be described by the BET equation. At much lower vapor concentrations Henry's law appears to determine the response, and a simple solution model developed from partition theory for stationary phases in gas–liquid chromatography can be used to interpret the sensitivity of three non‐crosslinked amorphous polymeric films to DMMP, GA, GB, and GD. While adequately describing the responses of the organophosphorus esters, the model is not as satisfactory in predicting the interactions with HD. © 1993 John Wiley & Sons, Inc.

Acid-Base Bifunctional Behavior of ZrC2 in Dual Adsorption of CO2 and NH3

Abstract Temperature-programmed-desorption(TPD) profiles of NH3 and CO2 coadsorbed on ZrO2 revealed a progress of a new peak at around 553 K, which was not found when NH3 and CO2 were adsorbed individually. It was concluded that, though the most of the sites responsible to the adsorption of NH3 and CO2 were located independently, a part of them were located closely, where the pre-adsorbed NH3 molecule enhanced the adsorption of post-adsorbing CO2 molecules. This type of interaction was not found on either typical solid acid (SiO2–Al2O3 ; SA) or solid base (MgO).

Composite ZSM-5 zeolite/asbestos catalysts

A procedure has been developed which allows growth of the zeolite ZSM-5 in chrysotile (asbestos) fibers which have previously had magnesium partially leached out. The resulting materials, when used as catalysts in the conversion of methanol into hydrocarbons showed very interesting product selectivities: i.e., (a) at high magnesium leaching degree (MLD), relatively larger amounts of aromatics and isoparaffins were produced; and (b) at low MLD, light olefins were the main products in the gaseous phaseFrom NH3 absorption/temperature programmed desorption studies, it was suggested that at lower MLD (higher magnesium content) the dual acidic and basic adsorption sites were responsible for the enhanced production of light olefins from methanol conversion

THE EFFECT OF SURFACE HETEROGENEITY ON KINETIC OSCILLATIONS IN THE METHANATION OF CO

Abstract The kinetics of the methanation of CO have been analysed for oscillatory behavior. For a scheme involving dual site adsorption of H2, analytical conditions for isothermal oscillations have been derived. They show differences between a homogeneous and a heterogeneous surface of the catalyst. A common feature is that the ranges of oscillatory behavior on both types of surfaces are independent of the partial pressure of H2. However, they differ in the effect of the partial pressure of CO, and this fact is utilised to suggest a discrimination method.

Kinetics of Diffusion—Adsorption of Acid Dyes in Nylon

The process of diffusion—adsorption in the acid dye—nylon system has been analysed on the basis of a diffusion model incorporating instantaneous dual adsorption of the Langmuir and the Nernst type. The calculated dye‐concentration profiles obtained were in good agreement with experimental results previously reported for various acid dye—nylon systems. Furthermore, the model satisfactorily explained the concentration‐dependence of the diffusion coefficients of dyes derived experimentally by the Matano method.

Dual Adsorption of Polar Organic Compounds on Steel

Dual Adsorption of Polar Organic Compounds on Steel