Adsorption Rate Coefficient Research Articles

Modelling CO2 adsorption dynamics onto amine-functionalised sorbents: A fractal-like kinetic perspective

In this article we applied a fractal-like Vermeulen model to describe kinetic data selected from literature case-studies for CO2 adsorption onto amine-functionalised sorbents. The statistical analysis based on the Akaike information criterion demonstrated a better fitting performance of the fractal-like model with respect to its canonical counterpart in describing experimental profiles of coverage degree in the entire time range explored. The canonical kinetic model generally provided a satisfying description of dynamic data only in the early stages of the process. The fractal model accounts for the presence of an instantaneous rate coefficient which ranged between orders 10−2 and 1 min−1. Parameters derived from the fractal-like model demonstrated that the diffusion process at the beginning of adsorption is enhanced when the sorbent has a pore network easily accessible for the adsorbate. This happens when the sorbent is characterised by a wider mean pore diameter and greater specific pore volume, and when the process temperature is raised. The heterogeneity parameter of the fractal-like model affects the time-decay of the adsorption rate coefficient. This parameter ranged between 0.16 and 0.85, and it is higher when the porous material is both rapidly occupied by CO2 molecules and displays a wider pore size distribution.

Design and development of radioactive xenon gas purification and analysis system based on molecular sieves

The dynamic adsorption of xenon on molecular sieve packed columns was investigated. The modified Wheeler-Jonas equation was used to describe adsorption parameters such as adsorption capacity and adsorption rate coefficient. Different experimental conditions were accomplished to study their effects and to touch appropriate adsorbing circumstances. Respectable consistency was reached between experimental and modeled values. A purification and analysis setup was developed for radioactive xenon gas determination. Standard sample analysis results approved acceptable quantification accuracy.

Kinetics of heavy metal adsorption and desorption in soil: Developing a unified model based on chemical speciation

Predicting the kinetics of heavy metal adsorption and desorption in soil requires consideration of multiple heterogeneous soil binding sites and variations of reaction chemistry conditions. Although chemical speciation models have been developed for predicting the equilibrium of metal adsorption on soil organic matter (SOM) and important mineral phases (e.g. Fe and Al (hydr)oxides), there is still a lack of modeling tools for predicting the kinetics of metal adsorption and desorption reactions in soil. In this study, we developed a unified model for the kinetics of heavy metal adsorption and desorption in soil based on the equilibrium models WHAM 7 and CD-MUSIC, which specifically consider metal kinetic reactions with multiple binding sites of SOM and soil minerals simultaneously. For each specific binding site, metal adsorption and desorption rate coefficients were constrained by the local equilibrium partition coefficients predicted by WHAM 7 or CD-MUSIC, and, for each metal, the desorption rate coefficients of various binding sites were constrained by their metal binding constants with those sites. The model had only one fitting parameter for each soil binding phase, and all other parameters were derived from WHAM 7 and CD-MUSIC. A stirred-flow method was used to study the kinetics of Cd, Cu, Ni, Pb, and Zn adsorption and desorption in multiple soils under various pH and metal concentrations, and the model successfully reproduced most of the kinetic data. We quantitatively elucidated the significance of different soil components and important soil binding sites during the adsorption and desorption kinetic processes. Our model has provided a theoretical framework to predict metal adsorption and desorption kinetics, which can be further used to predict the dynamic behavior of heavy metals in soil under various natural conditions by coupling other important soil processes.

Kinetics, mechanism, isotherm and thermodynamic studies of liquid phase adsorption of Pb2+ onto wood activated carbon supported zerovalent iron (WAC-ZVI) nanocomposite

AbstractThe kinetics, mechanism, isotherm, and thermodynamics of adsorption of Pb2+ onto wood-activated carbon-supported zerovalent iron (WAC-nZVI) nanocomposite was successfully studied. WAC-nZVI was characterized by a combination of spectroscopic and analytical techniques (BET, PZC, FTIR, SEM, and EDX). BET surface area was 101.50 m2/g and BJH Adsorption average pore diameter 116.73 A. The adsorption of Pb2+ studied in batch process depends on various operational parameters ranging from effect of pH to ionic strength. Kinetics data were best described by pseudo-second-order model based on high initial adsorption rate, h2 (166.67 mgg−1 min−1) and correlation coefficient (R2 > 0.99). The mechanism was controlled by both external and intraparticle diffusion models confirmed by Bangham and Boyd models. Equilibrium data were fitted to seven isotherm models. The Langmuir monolayer adsorption capacity (77.52 m2/g) surpassed those previously investigated for adsorption of Pb2+ onto nanoadsorbents. Validity of k...

Factors influencing phosphorus adsorption onto sediment in a dynamic environment

The adsorption of phosphorus onto sediment in a batch reactor and a dynamic flume was studied experimentally. The effect of velocity, sediment transport patterns, sediment supply, and phosphorus added to water was investigated in the two systems. Results showed that the equilibrium isotherm adsorption was better described using the Langmuir model. The adsorption amount increased as the initial phosphorus concentration in water increased before reaching saturation state, which was described as maximum amount of adsorption; the rate of increase in adsorption however decreased because of the limit adsorption sites and the increasing desorption. The kinetics of soluble reactive phosphorus (SRP) in water over time in both the batch reactor and the dynamic flume were well described using a pseudo-second order equation that gave good predictions of both the adsorption rate at the initial stage and the amount of adsorption in a state of quasi-equilibrium. The amount of adsorption per unit mass of sediment in the quasi-equilibrium state increased as the initial phosphorus concentration in water increased or as the sediment concentration decreased. In the quasi-equilibrium state, the adsorption amount of the SRP fluctuated within a larger range in the dynamic flume than in the batch reactor, because of continuous exchange between the suspended sediment and the bed sediment in the flume. The adsorption rate of the suspended sediment was greater than that of the bed sediment. The amount of adsorption decreased as the velocity increased when the phosphorus concentration was low, while it increased when the phosphorus concentration was high, as a result of a different concentration gradient at the water–sediment interface. The distribution coefficient and the adsorption rate coefficient both decreased as the initial phosphorus concentration increased when the sediment concentration was fixed. The variation of the distribution coefficient (KD) indicated that the adsorption amount at equilibrium in the dynamic flume was larger than that in a quiescent environment when the phosphorus concentration was low, while the difference between the two systems was small when the phosphorus concentrations were high. However, the KD value in both the flume and in static conditions was smaller than the value for the continuous disturbed environment in the batch reactor, indicating that the adsorption capacity was over-estimated in the latter.

Preparation of ordered macroporous cinchonine molecularly imprinted polymers and comparative study of their structure and binding properties with traditional bulk molecularly imprinted polymers

Three-dimensionally ordered macroporous molecularly imprinted polymers (MMIPs) were prepared by a combination of the colloidal crystal template method and the molecular imprinting technique. Traditional bulk molecularly imprinted polymers (BMIPs) were simultaneously synthesized with the same recipe as the MMIPs by using methacrylic acid as functional monomer, ethylene glycol dimethacrylate as crosslinker and chloroform as porogen. SEM and Brunauer − Emmett − Teller measurements show that MMIPs have a more regular macroporous structure, a narrower macropore distribution and a greater surface area and porosity compared with BMIPs. The isothermal and kinetic data of both polymers can be fitted with the Freundlich model and a pseudo-second-order equation, respectively. Their specificities to the template molecules are also similar. However, the binding capability, adsorption rate coefficient and internal effective diffusion coefficient of the MMIPs are higher than for the BMIPs when the particle size is above 54 µm. © 2015 Society of Chemical Industry

Transport of Antibiotic Resistance Plasmids in Porous Media

Antibiotic resistance plasmids play important roles in resistance buildup and spread in soil and groundwater. However, very limited work has been reported in the literature to examine the transport behavior of free resistance plasmids in the environment. In this work, the transport of eight resistance plasmid vectors (pUC18, pBlueScript II SK(+), pBR322, pFastBac HT A, pBABE‐Puro, pcDNA3.1(+)/myc‐His A, pcDNA3.1(+)/Flag‐His A+ATM, and pAdEasy‐1) in quartz sand was investigated through packed column experiments. At ionic strengths up to 0.05 mol L−1 in NaCl solutions and 0.006 mol L−1 in CaCl2 solutions, adsorption rate coefficients of all the plasmids examined were <0.19 h−1 at a fluid velocity of 6.1 m d−1. This result indicates that under environmentally relevant flow and solution chemistry conditions, free plasmids may transport across significant distances and may have the potential to spread antibiotic resistance to much larger areas and more receptors in the environment. As ionic strength increased, adsorption of plasmids in CaCl2 solutions increased dramatically. Adsorbed plasmids could be partly desorbed at reduced ionic strengths. These observations indicate that the transport behavior of free plasmids is very similar to the transport of colloids commonly examined in the literature (e.g., latex microspheres and bacteria). No noticeable difference in breakthrough concentrations of linear and supercoiled plasmids was observed. At higher ionic strengths (0.02 and 0.05 mol L−1) in CaCl2, the size of the plasmids was found to play a predominant role in governing their transport under identical flow and solution chemistry conditions.

Kinetics of Hg(II) exchange between organic ligands, goethite, and natural organic matter studied with an enriched stable isotope approach.

The mobility and bioavailability of toxic Hg(II) in the environment strongly depends on its interactions with natural organic matter (NOM) and mineral surfaces. Using an enriched stable isotope approach, we investigated the exchange of Hg(II) between dissolved species (inorganically complexed or cysteine-, EDTA-, or NOM-bound) and solid-bound Hg(II) (carboxyl-/thiol-resin or goethite) over 30 days under constant conditions (pH, Hg and ligand concentrations). The Hg(II)-exchange was initially fast, followed by a slower phase, and depended on the properties of the dissolved ligands and sorbents. The results were described by a kinetic model allowing the simultaneous determination of adsorption and desorption rate coefficients. The time scales required to reach equilibrium with the carboxyl-resin varied greatly from 1.2 days for Hg(OH)2 to 16 days for Hg(II)-cysteine complexes and approximately 250 days for EDTA-bound Hg(II). Other experiments could not be described by an equilibrium model, suggesting that a significant fraction of total-bound Hg was present in a non-exchangeable form (thiol-resin and NOM: 53-58%; goethite: 22-29%). Based on the slow and incomplete exchange of Hg(II) described in this study, we suggest that kinetic effects must be considered to a greater extent in the assessment of the fate of Hg in the environment and the design of experimental studies, for example, for stability constant determination or metal isotope fractionation during sorption.

Layered double hydroxide–alginate/polyvinyl alcohol beads: fabrication and phosphate removal from aqueous solution

In the water treatment field, powder form of layered double hydroxides (LDHs) has wide applications in adsorptions. However, its applications are limited because of low hydraulic conductivity. Here, LDH–alginate/polyvinyl alcohol (PVA) beads were fabricated by entrapment of the Mg–Al LDH powder into alginate/PVA beads. The obtained Mg–Al LDH–alginate/PVA beads were characterized by X-ray diffraction scanning electron microscopy. Their performance for phosphate removal by batch and column adsorption mode was evaluated. The Mg–Al LDH–alginate/PVA beads were found to be efficient adsorbents for phosphate removal. Batch adsorption experiment showed that the phosphate sorption process on the Mg–Al LDH–alginate/PVA beads followed pseudo-second-order reaction order kinetic model and the adsorption isotherm date could be simulated using both Langmiur and Freundlich models. In the column study, the flow rate and inlet phosphate concentration were maintained at 29.62 m3/m2 h and 10 mgP/L, respectively. Using 20 cm column depth, the breakthrough and exhaust time were found to be 5 and 31 h, respectively. The percentage of phosphate removal by column was 80.09%. The values of adsorption rate coefficient (K) and the adsorption capacity coefficient (N) were 0.0125 L/mg h and 258.32 mg/L, respectively.

Entrapment of Mg−Al layered double hydroxide into alginate/polyvinyl alcohol beads for water remediation

Mg−Al LDH-alginate/PVA beads were fabricated by entrapment of the Mg−Al LDH powder into alginate/PVA beads. This study has demonstrated the potential use of this technique in environmental remediation using nitrate as a model contaminant. The obtained Mg−Al LDH-alginate/PVA beads were characterized by X-ray diffraction and scan electron microscopy. Batch adsorption experiment showed that the nitrate sorption process on the Mg−Al LDH-alginate/PVA beads followed pseudo-second-order reaction kinetic model and the adsorption isotherm date showed that the Langmuir isotherm was more appropriate at describing the experimental results than the Freundlich isotherm. In the column study the flow rate and inlet nitrate concentration were maintained at 24.84 m3/m2 h and 25 mg N/L, respectively. Using 15 cm column bed depth, the breakthrough and exhaust time found were 8 and 28 h, respectively. The percentage of nitrate removal by column was 67.10. The value of adsorption rate coefficient (K) and the adsorption capacity coefficient (N) were 0.0045 L/mg h and 475.67 mg/L, respectively.

Synthesis of α‐cellulose/polypyrrole composite for the removal of reactive red dye from aqueous solution: Kinetics and equilibrium modeling

In this work, a composite from α‐cellulose coated with conducting polypyrrole by in situ polymerization using potassium persulfate as oxidant was obtained. The composite was characterized by fourier transform infrared (FTIR) spectroscopy, cyclic voltammetry, UV/Vis spectroscopy, and scanning electron microscopy (SEM) analysis showed homogeneous coating of α‐cellulose with polypyrrole (PPy) to produce a composite with a conductivity of 3.5 × 10−5 S/m. Batch aqueous adsorption experiments of the reactive red 120 (RR120) dye onto the synthesized material were conducted. The results showed that this composite is an efficient adsorbent for RR120 dye removal. For the adsorption experiments set to an initial pH of 3.9, the adsorption capacity was 15.6 mg of dye/g of composite for an equilibrium concentration (in the liquid) of RR120 dye equal to 1,000 mg/L, whereas a value of 96.1 mg of dye/g of composite was obtained when the solution pH was set to 2.0 for the same equilibrium concentration. When performing adsorption experiments using pure α‐cellulose, dye adsorption was insignificant at any pH value. Adsorption isotherm for RR120 was described by a typical Freundlich model. The transient adsorption of RR120 on the synthesized composite was described by a general three‐resistance model that includes the transport on the film that surrounds the composite particles, diffusion inside the particles, and adsorption on the surface of the particles. A fitting of the uptake curves was performed allowing the estimation of values for the effective diffusivity, D0, and the adsorption rate coefficient, k1. For the adsorption experiments with an initial pH value set to 3.9, D0 was estimated as 1.05 × 10−10 m2/s, whereas k1 was 1.65 × 10−4 Ln/g mgn − 1 s; the corresponding values of k1 at pH = 2 and 9.0 were 3.18 × 10−4 and 5.16 × 10−5, respectively. POLYM. COMPOS., 36:312–321, 2015. © 2014 Society of Plastics Engineers

Fractal-Like Kinetics for Adsorption on Heterogeneous Solid Surfaces

A physical meaning of the fractal-like concept has been represented for kinetics of adsorption on energetically heterogeneous solid surfaces. This study shows that the adsorption kinetics at the solid/solution interface in a real system with different types of surface sites and then with different affinity for adsorption can be described by a fractal-like approach. On the basis of this study, the history of process can affect the rate of process, and therefore the observed adsorption rate coefficient is a function of time. Employing this concept to extend some kinetic models leads to obtaining different fractal-like kinetic models that can be utilized to simulate adsorption kinetics in systems with heterogeneous surfaces. The simulation of experimental kinetic data with fractal-like equations for the heterogeneous surfaces and the fact that their equilibrium data follow the Langmuir–Freundlich (Sips) isotherm indicate the applicability of these equations for real systems. The obtained results show that th...

In Situ and Real Time Characterization of Spontaneous Grafting of Aryldiazonium Salts at Carbon Surfaces

Aryldiazonium cations are widely used to covalently functionalize carbon substrates that display a wide range of composition, from 100% sp2 such as graphite or graphene to 100% sp3 such as diamond and nanodiamond. In this work we investigated the effect that changes in carbon composition have on aryldiazonium adsorption rates and surface reaction mechanism. Quartz crystal microbalance (QCM) was used to investigate the rates of adsorption in situ and in real time at two amorphous carbon substrates, one with high sp2 content (a-C) and one with high sp3 content (a-C:H). A reversible Langmuir adsorption model was found to satisfactorily describe adsorption at a-C:H, yielding an adsorption rate coefficient ka = 3.1 M–1 s–1 and a free energy of adsorption ΔGa = −20.1 kJ mol–1. This model, on the other hand, could not be applied for the interpretation of adsorption curves at a-C. Using electrochemical methods and X-ray photoelectron spectroscopy (XPS), we found that adlayers formed at a-C:H and a-C surfaces differ considerably in composition; in particular, a-C surfaces were found to display higher rates of dediazoniation with respect to a-C:H surfaces. Our findings are interpreted and discussed in the context of current proposed mechanisms for aryldiazonium reactions at surfaces that consist of an adsorption/desorption step followed by a chemisorption via dediazoniation step. Our observations are consistent with proposed mechanisms and strongly suggest that differences in carbon composition result in differences in the relative magnitude of adsorption and chemisorptions rate coefficients.

Modeling of catalytic activity of an Al2O3 surface on the basis of the first principles

The adsorption, desorption, impact, and associative heterogeneous recombination rate coefficients are determined for atomic oxygen in the temperature range between 500 and 2000 K on the basis of quantum chemical data on the energy of interaction of atomic and molecular oxygen with the clusters that model an α-Al203 surface. These coefficients are used to calculate the heterogeneous recombination probabilities and the heat fluxes to the surface under the conditions similar to those of the MESOX facility.

An exponential kinetic model for adsorption at solid/solution interface

An exponential kinetic model has been proposed for modeling of adsorption kinetics at the solid/solution interface. This new equation was compared with pseudo first-order (PFO) and pseudo second-order (PSO) equations as the well-known two parametric models. Based on numerically generated data points (t,q) by using of statistical rate theory equation for homogeneous surfaces, it has been shown that we can use the new model for homogeneous solid surfaces as well as the pseudo second-order model. Moreover, the driving force of new model is a combination of driving forces of PFO and PSO equations. However, using Langmuir–Freundlich equation to generate kinetic data for heterogeneous surfaces, it has been shown that the kinetic data can be described by PFO model when the adsorption rate coefficient is smaller than the desorption rate coefficient; but, when the adsorption rate coefficient is bigger than the desorption rate coefficient, which is more favorite for practical application, the new exponential model shows better agreement with kinetic data. The main advantage of using the new model for heterogeneous systems is its simplicity in comparison with Langmuir–Freundlich kinetic model which there is no analytical solution for it. Finally, the results of fitting to the experimental data represent that exponential model can describe kinetics of adsorption for both homo- and heterogeneous systems very well.

Dynamics of Interactions Between HF and Hafnium Oxide During Surface Preparation of High-K Dielectrics

The interactions of HF with hafnium oxide are important aspects of the post-etch cleaning of high-k dielectrics. The dynamics of these interactions during typical wafer rinsing are studied using a quartz crystal microbalance (QCM) equipped with a flow-through cell. A process model is developed showing that the overall rinse process consists of three simultaneous steps: adsorption, desorption, and etching involving fluoride species. The model is validated using the experimental data obtained in QCM. The key parameters of these process steps, namely, adsorption, desorption, and etch rate coefficients are determined using the combined experimental measurement and process modeling.

Characteristics of cationic Red X-GRL biosorption by anaerobic activated sludge

Anaerobic activated sludge (AAS) was employed for the adsorption of cationic Red X-GRL (X-GRL) from aqueous solutions. The X-GRL uptakes decreased with increases in temperature and salinity, while it was improved with increase in pH. The adsorption of X-GRL by AAS had a better agreement with a fractal-like Langmuir isotherm than a typical Langmuir isotherm. The adsorption rate coefficients at different time had a power-law relationship with time. The surface dimension was positively related to the X-GRL uptakes. The X-GRL uptake by the EPS accounted for only ∼19% of the total adsorption. The X-GRL adsorption was therefore largely attributed to the active groups on the cell wall. FTIR analysis showed that –CH2 and –NH2 groups were not responsible for the adsorption, which indicated chemical adsorption was negligible.

Separation and recovery of lead from a low concentration solution of lead(II) and zinc(II) using the hydrolysis production of poly styrene-co-maleic anhydride

The Pb Zn separation/preconcentration technique, based on the complex formation reaction of Pb(II) and Zn(II), using a copolymer poly(styrene-co-maleic anhydride) (PSMA), without adding any carrier element was developed. The effects of several experimental parameters such as solution pH, temperature and adsorption time were studied. The experimental results show that the PSMA resin–Pb equilibrium was achieved in 2 min and the Pb(II) loading capacity is up to 641.62 mg g −1 in aqueous solution under optimum conditions, which is much higher than the Zn(II) loading capacity within 80 min. The adsorption test for Pb(II) indicates that PSMA can recover Pb(II) from a mixed solution of Pb(II), Zn(II) and light metals such as Ca(II) and Mg(II) with higher adsorption rate and larger selective coefficient. A further study indicates that PSMA as chelating resins recovering Pb(II) can be regenerated via mineral acid (6 M H 2SO 4). PSMA was synthesized by radical polymerization and tested as an adsorbent for the selective recovery of Pb(II). In addition, the formation procedure and structure of Pb–PSMA complex were also studied. Both the PSMA and the Pb–PSMA complex were characterized by means of FTIR spectroscopy, elemental analysis, gel permeation chromatography (GPC) and atomic absorption spectrometry (AAS).

Adsorption of cationic dyes on poly(acrylic acid‐co‐sodium acrylate‐co‐acrylamide) superabsorbents

AbstractInverse suspension polymerization was carried out to synthesize poly(acrylic acid‐co‐sodium acrylate‐co‐acrylamide) superabsorbent polymers (SAPs) crosslinked with ethylene glycol dimethacrylate (EGDMA). The equilibrium swelling capacities of the SAPs, determined by swelling them in DI water, were found to vary with the acrylamide (AM) content. The SAPs were used to adsorb four cationic dyes (Acriflavine, Auramine‐O, Azure‐I and Pyronin‐Y). The effect of AM content in the SAPs on the adsorption of the cationic dyes was investigated. Different initial concentrations of Azure‐I were used with the same amount of the SAP to explore the effect of initial dye concentration on the adsorption. The effect of the adsorbent amount was investigated by taking different amounts of SAP with a fixed initial concentration of Acriflavine. The kinetics of the dye adsorption was modeled by a first order model and the equilibrium amount of the dye adsorbed, adsorption rate coefficients, removal efficiency and partition coefficients were determined. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Determining the Fundamental Kinetic Parameters for Rinsing and Cleaning of Hafnium-Based High-k Materials

The interactions of HF with hafnium oxide are important during post-etch cleaning of high-k dielectrics. The dynamics of these interactions during the rinse process are studied using a quartz crystal microbalance (QCM) equipped with a flow-through cell. A process model is developed showing that the overall process consists of three simultaneous process steps: adsorption, desorption and etching involving fluoride species. The model was validated using the experimental data obtained in QCM. The key parameters of these process steps namely adsorption, desorption and etch rate coefficients were determined using the combined experimental measurement and process modeling.