Double Layer Adsorption Model Research Articles

Physicochemical study of the adsorption of chlorophenols on activated carbon using an advanced double layer model

An advanced theoretical analysis was performed to elucidate the adsorption of 2,4-dichlorophenol and 4-chlorophenol on an activated carbon obtained from pine sawdust. In particular, a double layer adsorption model was used to estimate the number of chlorophenols molecules adsorbed per activated carbon functional group, the concentration of active sites from activated carbon surface involved in the adsorption mechanism, the saturation adsorption capacities and interaction energies to form the adsorbate layers on activated carbon. This theoretical investigation showed that the saturation adsorption capacities for the removal of 2,4-dichlorophenol and 4-chlorophenol were 167 and 130 mg/g, respectively. The adsorption of 2,4-dichlorophenol on activated carbon outperformed the 4-chlorophenol adsorption under tested experimental conditions. The adsorption of these compounds was endothermic and governed mainly by van der Waals interactions and hydrogen bonding. The adsorption of 2,4-dichlorophenol on activated carbon was a multimolecular process with the presence of an aggregation process in the aqueous solution, while a multi-docking adsorption mechanism occurred for the removal of 4-chlorophenol. Overall, this study contributes with theoretical insights on the removal of two emerging water pollutants by using activated carbon.

Insights into nitrobenzene adsorption mechanism on apricot stone activated carbon: A study via statistical physics models and thermodynamic analysis

Statistical physics modelling was performed to analyze the adsorption forces and the thermodynamics of the removal of nitrobenzene molecules using an activated carbon obtained from apricot stones. This adsorbent was prepared using phosphoric acid activation and exhibited a surface area of 1762 m2 g−1, total pore volume of 1.09 cm3 g−1 and an experimental maximum adsorption capacity of 295.63 mg g−1 for nitrobenzene at 298 K. The removal of this organic molecule was exothermic. A double layer adsorption model with two energies was utilized to calculate the main steric parameters for the removal of this compound. This model was employed to perform a thermodynamic analysis of this adsorption system. It was concluded that 2 and 3 adsorption sites can be involved for the removal of nitrobenzene molecules on activated carbon surface. Physical interaction forces were expected to participate in the removal of this pollutant. This activated carbon can be regenerated with NaOH thus offering the alternative of its recycling to reduce the removal costs of this organic molecule from water.

Insights into mass transfer mechanism and micro-interaction of melanoidin adsorption on polyethyleneimine-functionalised pomelo-peel-derived aerogel

Melanoidins are recalcitrant colouring and polluting polymers present in the effluent streams of molasses-based distilleries. Adsorption is the most prospective technology with ease of operation and high efficiency. Herein, the removal of melanoidins from spent wash was investigated by synthesising a polyethyleneimine (PEI) functionalised pomelo-peel (PP) derived aerogel (PEI-PPA). The PEI-PPA is distinguished by the porous network structure and abundant accessible functional groups (mainly protonated primary amine) that are conducive to the elimination of colouring contaminants (melanoidins). The incorporation of PEI into supporting matrices (i.e., PP–derived aerogel) effectively improved the melanoidin adsorption capacity (from a previous-best research of 230 mg/g to the current 615.70 mg/g), while the melanoidin removal rate reached 92.36 %. The independent gradient model and Hirshfeld surface analysis were used to investigated the possible electroweak interaction relationship between PEI-PPA and melanoidin. By analysing the number of melanoidin molecules bonded to each active site using a novel double-layer adsorption model, a mixed inclination (parallel and non-parallel orientation) of melanoidin onto the PEI-PPA surface was found. For the two mass transfer models fitted results, the adsorption onto the active sites (AOAS) model better described the behaviour of melanoidin adsorption by PEI-PPA than the external diffusion resistance–internal diffusion resistance (EDR–IDR) mixed model under the same conditions, revealing the AOAS was rate-controlling during the mass transfer process. AOAS both contained chemisorption and physisorption. The calculated rates of chemisorption were far higher than those of physisorption before equilibration, indicating chemisorption was main the rate-determining step. Altogether, this work proposed an effective conversion for PP into bio-adsorbent and provided a detailed analysis of mass transfer mechanism.

Adsorption of emerging pollutants on lignin-based activated carbon: Analysis of adsorption mechanism via characterization, kinetics and equilibrium studies

Lignin has been employed as a precursor to synthesize activated carbons with the aim of lignin-biomass revalorization. The properties of these activated carbons were compared, and the best adsorbent was employed to remove two emerging pollutants from water, acetaminophen and acetamiprid. The adsorption mechanisms of pharmaceutical and pesticide compounds were analyzed, modeled and interpreted via statistical physics models. In particular, adsorption kinetics and isotherms of acetaminophen and acetamiprid at temperatures between 20 and 60 °C were quantified experimentally. Equilibrium data were fitted to different statistical physics-based isotherm models to establish the corresponding adsorption mechanism. A double layer adsorption model with one type of functional group was the best to correlate and explain the removal of these organic molecules. Steric parameters for the adsorption of these organic compounds were also calculated thus determining that their adsorption was multi-molecular. At tested operating conditions, acetaminophen adsorption was endothermic, while acetamiprid removal was exothermic. Physical adsorption forces were expected to be responsible for the removal of both compounds. This study reports new insights on the adsorption mechanisms of relevant emerging pollutants commonly found in water worldwide.

Adsorption of dyes methyl violet and malachite green from aqueous solution on multi-step modified rice husk powder in single and binary systems: Characterization, adsorption behavior and physical interpretations

A novel modified rice husk (MRH) has been prepared for removing cationic dyes in both single system and binary system. SEM-EDS, FT-IR, XRD and XPS were used to characterize the physical and chemical properties of MRH. It showed that the maximum adsorption capacity of MRH for methyl violet (MV) and malachite green (MG) in single system was 154.49 and 996.97 mg g−1, while in binary system was 530.94 and 408.58 mg g−1, respectively. The experimental results showed that the pseudo-second-order kinetic model was better to describe the kinetic behavior of MV and MG adsorption. By using double layer adsorption model, we found that the nD for MV adsorption were 2.52, 2.65 and 3.34 at 298, 308 and 318 K, respectively, and the nD for MG adsorption were 4.59, 4.85 and 4.30, respectively. These results illustrated that multiple dye molecules were adsorbed on one adsorption site in non-parallel direction, indicating that the adsorption of dyes is multi-molecular mechanism. Furthermore, synergistic and antagonistic adsorption might be existed simultaneously in binary system. In summary, MRH has been shown well adsorption properties and reusability and our finding might provide a new idea for developing low-cost, efficient and reusable adsorbent to remove dyes from wastewater.

A novel approach to prepare efficient CO2 sorbents derived from alumina-extracted residue of coal ash

If a large amount of fly ashes produced by coal-fired power plants was not treated harmlessly, it will pose a serious threat to the ecological environment. As one of the high-valued utilization technologies of fly ash, the technology of extracting aluminum from coal ash produces large quantities of waste residue after acid leaching nevertheless. It is an economic and environmentally friendly way to recycle alumina-extracted residue (AR) as solid sorbent to capture CO2. In this study, using AR as raw material, we synthesized PEI modified solid sorbents by novel “wet gel impregnation” method (WGI) to enhanced CO2 capture. The effects of amine loading, adsorption temperature, and impregnation method on CO2 adsorption capacity and kinetics were investigated by thermogravimetric analysis (TGA). On this basis, a possible double-layer adsorption model was proposed, i.e., the PEI adsorption layer on the outer surface of sorbents and the internal isolation layer. The ratio of the two layers changed with the variation in PEI loading and adsorption temperature, resulting in the difference of adsorption capacity. The maximum CO2 adsorption capacity of 2.07 mmol/g was obtained under the amine loading of 40 wt% at 95 °C, and 100% CO2. Moreover, the stable adsorption capacity and high CO2 selectivity were maintained in five repeated adsorption-desorption cycles.

Theoretical assessment of the adsorption mechanism of ibuprofen, ampicillin, orange G and malachite green on a biomass functionalized with plasma

Theoretical assessment and interpretation of the adsorption mechanisms of pharmaceuticals (ibuprofen and ampicillin) and dyes (orange G and malachite green) on a biomass functionalized with a plasma treatment are reported in this paper. This theoretical study was performed via a double-layer adsorption model that was formulated from statistical physics. Modeling results indicated that the adsorption of tested organic adsorbates was affected by the molecular aggregation in the aqueous solution, which depended on the adsorption temperature. These molecules were adsorbed on the functionalized biomass surface via a non-flat orientation (i.e., they interacted with one functional group) at tested operating conditions where thermal agitation and steric hindrance could play a relevant role during the adsorption. Cocoa shell functionalized with plasma showed the highest adsorption for dyes especially orange G at 298 K. Adsorption capacities ranged from 10.32 to 26.14 mg/g, 10.54–15.55 mg/g, 6.31–13.76 mg/g and 4.2–6.54 mg/g for orange G, malachite green, ibuprofen and ampicillin, respectively. Exothermic adsorption energies were calculated for tested adsorbate molecules, which ranged from −10.17 to −18.11 kJ/mol thus indicating that physical forces were involved in the removal of these water pollutants. This study contributes to understand the physicochemical parameters that governed the adsorption of organic molecules on surface functionalized with plasma, which is an alternative for water treatment and purification.

Effective adsorption of dyes on an activated carbon prepared from carboxymethyl cellulose: Experiments, characterization and advanced modelling

• An activated carbon with a high surface area and outstanding dye adsorption properties was studied. • Dye adsorption isotherms were quantified at different temperatures. • Statistical physics model was used to attribute theoretical interpretation of dye adsorption mechanism. An activated carbon with a high surface area and outstanding adsorption properties was prepared for dye removal from water. The new adsorbent was obtained from the chemical activation and pyrolysis of sodium carboxymethyl cellulose (CMC). This activated carbon was employed to analyze and characterize the adsorption mechanism of three dye molecules: methyl violet, allura red and congo red. Different characterization techniques and experimental adsorption isotherms quantified at different temperatures (25–45 °C) were utilized to interpret the dye adsorption mechanism. A double layer adsorption model was employed to estimate the steric and energetic parameters associated with the adsorption of these dye molecules. The modelling results provided the possible adsorption orientations of these dyes on adsorbent surfaces at different operating temperatures and the number of bonded dye molecules per functional group of this adsorbent was also analyzed. Calculated adsorption energies showed that both exothermic and endothermic processes were feasible for these dyes and physical forces were involved in the adsorption mechanism. Overall, this new adsorbent showed a competitive performance for dye removal in aqueous solution and can be a potential option for industrial applications.

Preparation and characterization of a novel mountain soursop seeds powder adsorbent and its application for the removal of crystal violet and methylene blue from aqueous solutions

Abstract Herein, a novel mountain soursop seeds powder (MSSP) adsorbent was employed to explore the adsorption mechanism of two relevant environmental pollutants: crystal violet CV and methylene blue MB. As a first assessment to investigate the adsorption mechanism and to analyze the performance of this adsorbent, the dye adsorption isotherms were measured at 298–328 K and pH 8. Experimental results demonstrated that this adsorbent was more effective to remove the CV dye compared to MB dye from aqueous solution, thus concluding that it could utilized for the treatment of dye polluted industrial effluents. To further interpret the adsorption mechanism and to obtain a new physicochemical vision, a successful phenomenological theoretical analysis via double layer adsorption model was detailed in this paper. At high equilibrium concentration, the adsorbed quantities at saturation were calculated and they followed this sequence: Qsat (CV-MSSP) > Qsat (MB-MSSP). This theoretical finding explained the highest adsorption for CV dye at different temperatures and characterized analytically its affinity for tested adsorbates. The geometry inclination of tested dyes on MSSP adsorbent surface was described in the paper by analyzing the bonded number of CV and MB dye molecules per site. It was demonstrated that these dyes were adsorbed via a mixed orientation. Based on the estimated concentrations at half-saturation, the calculated adsorption energies suggested that the adsorption of CV and MB on MSSP adsorbent was endothermic. A general analytical description of the dye adsorption mechanism showed that the density of receptor sites and adsorption energies followed the same trend as the adsorption capacity, then they can be considered as the factors that governed this separation process.

Adsorption of acid green and procion red on a magnetic geopolymer based adsorbent: Experiments, characterization and theoretical treatment

A magnetic geopolymer (MG) was used as an effective adsorbent for water decolorization, in particular, for the removal of acid green (AG) and procion red (PR) from aqueous solutions. AG and PR dyes adsorption mechanism for this adsorbent was experimentally and theoretically characterized via the analysis and description of eight adsorption isotherms obtained at 298–328 K. Results showed that the AG dye was strongly adsorbed in comparison to PR dye. It was also concluded that the temperature showed a minor effect on the variation of the adsorption capacity for both dyes. An analytical double layer adsorption model was chosen to explain these experimental findings. This model contained theoretical parameters that can be utilized to understand the dyes adsorption mechanism. The temperature effect on all model parameters was analyzed concluding that this operating parameter had a minor effect on the number of accepted amount of AG and PR dyes per receptor site of MG adsorbent (n) and the density of receptor sites (Dm). The trends of parameters n and Dm led to a slightly variation of the adsorption capacity at saturation (Qsat = 2.n.Dm) as a function of temperature. Particularly, it was also concluded that AG and PR dyes retained their adsorption orientations on the magnetic geopolymer surface. Overall, it was established that the adsorption performance for the removal of AG dye could be associated to its short molecular size. Calculated adsorption energies varied from 18.55 to 29.14 kJ/mol and from 8.55 to 14.77 kJ/mol for the AG-GP and PR-GP systems, respectively. These adsorption energies indicated that physical interactions were involved during the adsorption mechanism of these water pollutants.

Interpretation of psychophysics response curves using statistical physics

Experimental gustatory curves have been fitted for four sugars (sucrose, fructose, glucose and maltitol), using a double layer adsorption model. Three parameters of the model are fitted, namely the number of molecules per site n, the maximum response RM and the concentration at half saturation C1/2. The behaviours of these parameters are discussed in relationship to each molecule’s characteristics.Starting from the double layer adsorption model, we determined (in addition) the adsorption energy of each molecule on taste receptor sites.The use of the threshold expression allowed us to gain information about the adsorption occupation rate of a receptor site which fires a minimal response at a gustatory nerve.Finally, by means of this model we could calculate the configurational entropy of the adsorption system, which can describe the order and disorder of the adsorbent surface.

On the statistical physics modeling of dye adsorption onto anionized nylon: Consequent new interpretations

AbstractExperimental adsorption isotherm of two basic dyes: Basic Blue 3 and Basic Red 24 from aqueous solution onto modified nylon 6,6 were analyzed by using a double layer adsorption model with two energy levels. Such model is based on statistical physics treatment. The parameters involved in the analytical expression of this model such as the fraction or the number of adsorbed dye molecule(s) per site, n, the receptor sites density, NM, and the energetic parameters, c1 and c2, were determined by fitting the experimental adsorption isotherms at four temperatures between 293 and 353 K with different degrees of grafting between 20 and 80%. The evolution of these parameters versus temperature and the grafting percent allows us to interpret and better understand this adsorption process at molecular level. Two different behaviors of the two dye molecules were highlighted according to their localized and non localized charges. The configurational entropy at various temperatures has also been studied. This parameter allowed to deduce some results related to the evolution of the disorder at the adsorption surface. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Acid dye adsorption onto cationized polyamide fibres. Modeling and consequent interpretations of model parameter behaviours

Experimental adsorption isotherms of four acid dyes named Acid Blue 25, Acid Yellow 99, Reactive Yellow 23, and Acid Blue 74 from aqueous solution onto cationized nylon-6,6 have been analyzed using a double layer adsorption model. The parameters involved in the analytical expression of this model such as the number or fraction of adsorbed dye molecule per site, n, the number of receptor sites per gram of adsorbent, N M , and the concentration at half-saturation, c 1 / 2 , are determined from adsorption isotherms at four temperatures between 293 and 353 K. The evolution of these parameters with temperature is discussed in relation with adsorption process and the behaviours of the different dyes taking into account their particular structure. The results are compared with those already published dealing with the adsorption of these same dyes onto cationized cotton. The configurational entropy at various temperatures has been studied. This parameter allowed to deduce some results related to the evolution of the disorder during the adsorption process.

Determination of Structure and Energetics for Gibbs Surface Adsorption Layers of Binary Liquid Mixture 2. Methanol + Water

Vapor/methanol and vapor/methanol-water mixture interfaces have been among the benchmark liquid interfaces under extensive experimental and theoretical investigation. In this report, we studied the orientation, structure and energetics of the vapor/methanol-water interface with newly developed techniques in sum frequency generation vibrational spectroscopy (SFG-VS). Different from the interpretations in previous SFG-VS studies for a more disordered interface at higher bulk methanol concentrations, we found that the methanol-water mixture interface is well ordered in the whole concentration region. We are able to do so because direct polarization null angle (PNA) measurement allowed us to accurately determine the CH3 orientation at the interface and to separate the orientational and interface density contributions to the SFG-VS signal. We found that the CH3 groups at the interface pointed out almost perpendicularly from the interface. We further found that this well-ordered vapor/methanol-water mixture interface has an antiparallel structure. With the double layer adsorption model (DAM) and Langmuir isotherm, the adsorption free energies for the first and second layer are obtained as -1.7 +/- 0.1 kcal/mol and 0.5 +/- 0.4 kcal/mol, respectively. Therefore, the second layer adsorption is slightly negative, and this means that replacement of the second layer water molecule with methanol molecule is energetically unfavorable. Comparing this interface with the vapor/acetone-water mixture interface reported previously, we are able to correlate the second layer adsorption free energy with the work of self-association using the pairwise self- and mutual interaction energies between the water and solute molecules. These results provided detailed microscopic structural evidences for understanding of liquid interfaces.

Determination of Structure and Energetics for Gibbs Surface Adsorption Layers of Binary Liquid Mixture 1. Acetone + Water

The orientation, structure, and energetics of the vapor/acetone-water interface are studied with sum frequency generation vibrational spectroscopy (SFG-VS). We used the polarization null angle (PNA) method in SFG-VS to accurately determine the interfacial acetone molecule orientation, and we found that the acetone molecule has its C=O group pointing into bulk phase, one CH3 group pointing up from the bulk, and the other CH3 group pointing into the bulk phase. This well-ordered interface layer induces an antiparallel structure in the second layer through dimer formation from either dipolar or hydrogen bond interactions. With a double-layer adsorption model (DAM) and Langmuir isotherm, the adsorption free energies for the first and second layer are determined as deltaG degrees (ads,1) = - 1.9 +/- 0.2 kcal /mol and deltaG degrees (ads,2) = - 0.9 +/- 0.2 kcal /mol, respectively. Since deltaG degrees (ads,1) is much larger than the thermal energy kT = 0.59 kcal /mol, and deltaG degrees (ads,2) is close to kT, the second layer has to be less ordered. Without either strong dipolar or hydrogen bonding interactions between the second and the third layer, the third layer should be randomly thermalized as in the bulk liquid. Therefore, the thickness of the interface is not more than two layers thick. These results are consistent with previous MD simulations for the vapor/pure acetone interface, and undoubtedly provide direct microscopic structural evidences and new insight for the understanding of liquid and liquid mixture interfaces. The experimental techniques and quantitative analysis methodology used for detailed measurement of the liquid mixture interfaces in this report can also be applied to liquid interfaces, as well as other molecular interfaces in general.

Theoretical consideration of the growth kinetics for GaAs and GaSb

An extended MOMBE growth kinetics model is proposed, based on the Robertson model, to explain both the GaAs growth rate variation and modulated beam mass spectroscopy data reported by Martin and Whitehouse. In this model, we assume that (1) MEGa molecules react with ethyl-radicals to form DEGa, (2) excessive group-V molecules on the surface suppress the decomposition of DEGa and enhance the desorption of DEGa, (3) reaction of DEGa with ethyl-radicals to form TEGa is negligible, and (4) effective surface coverage of excessive group-V atoms during growth is determined by the double layer adsorption model including desorption parameters for group-V molecules. The first assumption (1) is found to be a dominant process to explain the behaviour of DEGa desorption at high temperatures. This model can reproduce the dependences of both growth rate and desorbing rate of Ga alkyls on substrate temperature during GaAs MOMBE growth. The use of Sb instead of As produces a significant change in the growth rate variation with substrate temperature and group-V flux for the growth of GaSb, in spite of the use of the same TEGa flow rate. This can be rationalized by the difference in the desorption parameters for Sb and As.