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The current study comprehensively investigates the adsorption behavior of chromium (Cr(III)) in wastewater using Algerian kaolinite clay. The structural and textural properties of the kaolinite clay are extensively characterized through a range of analytical methods, including XRD, FTIR, SEM-EDS, XPS, laser granulometry, N2 adsorption isotherm, and TGA–DTA. The point of zero charge and zeta potential are also assessed. Chromium adsorption reached equilibrium within five minutes, achieving a maximum removal rate of 99% at pH 5. Adsorption equilibrium is modeled using the Langmuir, Freundlich, Temkin, Elovich, and Dubinin–Radushkevitch equations, with the Langmuir isotherm accurately describing the adsorption process and yielding a maximum adsorption capacity of 8.422 mg/g for Cr(III). Thermodynamic parameters suggest the spontaneous and endothermic nature of Cr(III) sorption, with an activation energy of 26.665 kJ/mol, indicating the importance of diffusion in the sorption process. Furthermore, advanced DFT computations, including COSMO-RS, molecular orbitals, IGM, RDG, and QTAIM analyses, are conducted to elucidate the nature of adsorption, revealing strong binding interactions between Cr(III) ions and the kaolinite surface. The integration of theoretical and experimental data not only enhances the understanding of Cr(III) removal using kaolinite but also demonstrates the effectiveness of this clay adsorbent for wastewater treatment. Furthermore, this study highlights the synergistic application of empirical research and computational modeling in elucidating complex adsorption processes. [ABSTRACT FROM AUTHOR]

This study investigates the efficacy of adsorbents from locally sourced olive waste—encompassing olive skins, leaves, and pits, recovered from the initial centrifugation of olives (OWP)—and a composite with sodium alginate (OWPSA) for the removal of Cu2+ ions from synthetic wastewater. Experimental analyses conducted at room temperature, with an initial Cu2+ concentration of 50 mg/L and a solid/liquid ratio of 1 g/L, showed that the removal efficiencies were approximately 79.54% and 94.54% for OWP and OWPSA, respectively, highlighting the positive impact of alginate on adsorption capacity. Utilizing statistical physics isotherm models, particularly the single-layer model coupled to real gas (SLMRG), allowed us to robustly fit the experimental data, providing insights into the adsorption mechanisms. Thermodynamic parameters affirmed the spontaneity and endothermic nature of the processes. Adsorption kinetics were interpreted effectively using the pseudo-second-order (PSO) model. Molecular modeling investigations, including the conductor-like screening model for real solvents (COSMO-RS), density functional theory (DFT), and atom-in-molecule (AIM) analysis, unveiled intricate molecular interactions among the adsorbent components—cellulose, hemicellulose, lignin, and alginate—and the pollutant Cu2+, confirming their physically interactive nature. These findings emphasize the synergistic application of experimental and theoretical approaches, providing a comprehensive understanding of copper adsorption dynamics at the molecular level. This methodology holds promise for unraveling intricate processes across various adsorbent materials in wastewater treatment applications. [ABSTRACT FROM AUTHOR]

An activated carbon (AC) deriving from sludge is used in this research for the adsorption of two water pollutants, namely Reactive Black 5 (RB5) and Green Alizarin (GA) dyes, at different temperatures. The adsorption capacities varied from 277.2 to 312.69 mg/g for GA and from 225.82 to 256.02 mg/g for RB5. Comparatively, this adsorbent presents good performances in removing these dyes from wastewater. The application of physical models to adsorption experiments is advantageous to provide new insights into the dyes' adsorption mechanism. A dedicated physical adsorption model suggests that RB5 and GA dyes are adsorbed in a monolayer. Moreover, the orientation of RB5 and GA dyes on AC resulted in an angled position, determining a multi-molecular process. In addition, both dyes are adsorbed by the occurrence of an aggregation process, forming a dimer. The impact of temperature can be also interpreted, allowing concluding that it plays a relevant role in removing these dyes. The calculation and interpretation of adsorption energies show that the dyes are removed via an endothermic process, and physical forces are involved. [ABSTRACT FROM AUTHOR]

The paper describes a theoretical analysis of the adsorption of nicotinamide and propranolol onto a magnetic-activated carbon (MAC). For a better evaluation of the adsorption mechanism, adsorption isotherms expressing the variation of the adsorption capacity as function of adsorbate concentration were determined at different temperatures ranging from 20 to 45 °C. For both the analytes, experimental tests reveal that adsorption capacity increases with temperature. An advanced multi-layer model derived from the statistical physics is set for the interpretation of the entire adsorption data set. The modelling results show that the propranolol molecules change their adsorption orientation from a mixed (parallel and non-parallel) orientation to a multimolecular process. For nicotinamide, the aggregation of molecules is practically absent, except for the data at lower temperatures. The model allows stating that the adsorption of both the pharmaceutical compounds occurs via the formation of one or two layers on MAC adsorbent, the propranolol showing a higher tendency to form multiple layers. Finally, adsorption energy is estimated suggesting that the adsorption is endothermic and physical interactions are the responsible of the adsorption of both the compounds onto MAC adsorbent. [ABSTRACT FROM AUTHOR]

The paper describes a theoretical analysis of the adsorption of amoxicillin (AMX) onto two activated carbons pyrolysed at either 600 or 700 °C (PAC-600 and PAC-700). Series of experimental data are carried out at different temperatures ranging from 10 to 45 °C, as this is the first key factor to explain the adsorption mechanism of this pollutant. AMX adsorption capacity varied from 275 to 450 mg/g and between 276 and 454 mg/g for PAC-600 and PAC-700, respectively. It can be deduced that the pyrolysis temperature does not play a crucial role in AMX removal capacity of the adsorbents. A comparison with literature data shows that the retrieved adsorption capacities of both the adsorbents are very competitive for an effective water treatment. Physical models are applied to the two experimental data sets showing that a monolayer model with single energy is the best option to explain the AMX adsorption mechanism on both PAC-600 and PAC-700 adsorbents. The interpretation of the theoretical results points out that the AMX was not aggregated during the adsorption process. Under these experimental working conditions, it is noted that AMX is adsorbed almost via a parallel orientation on PAC-600 and PAC-700 adsorbents, reflecting that the adsorption is a multi-interaction mechanism. The model provides an estimation of the adsorption energy that allows the quantification of the interactions between the AMX and both PAC-600 and PAC-700 adsorbent surfaces; in both the cases, physical bindings are involved in AMX adsorption. [ABSTRACT FROM AUTHOR]

Permeable Adsorptive Barriers (PABs), filled with a commercial activated carbon, are tested as a technique for the remediation of a thallium (I)-contaminated aquifer located in the south of Italy. Thallium adsorption capacity of the activated carbon is experimentally determined through dedicated laboratory tests, allowing to obtain the main modelling parameters to describe the adsorption phenomena within the barrier. A 2D numerical model, solved by using a finite element approach via COMSOL Multi-physics®, is used to simulate the contaminant transport within the aquifer and for the PAB design. Investigations are carried out on an innovative barrier configuration, called Discontinuous Permeable Adsorptive Barrier (PAB-D). In addition, an optimization procedure is followed to determine the optimum PAB-D parameters, and to evaluate the total costs of the intervention. A PAB-D made by an array of wells having a diameter of 1.5 m and spaced at a distance of 4 m from each other, is shown to be the most cost-effective of those tested, and ensures the aquifer restoration within 80 years. The simulation outcomes demonstrate that the designed PAB-D is an effective tool for the remediation of the aquifer under analysis, since the contaminant concentration downstream of the barrier is below the thallium regulatory limit for groundwater, also accounting for possible desorption phenomena. Finally, the best PAB-D configuration is compared with a continuous barrier (PAB-C), resulting in a 32% saving of adsorbing material volume, and 36% of the overall costs for the PAB-D. [ABSTRACT FROM AUTHOR]

In this work, a modeling analysis based on experimental tests of cadmium/zinc adsorption, in both single-compound and binary systems, was carried out. All the experimental tests were conducted at constant pH (around neutrality) and temperature (20 °C). The experimental results showed that the zinc adsorption capacity was higher than that of cadmium and it does not depend on cadmium presence in binary system. Conversely, cadmium adsorption is affected by zinc presence. In order to provide good understanding of the adsorption process, two statistical physics models were proposed. A monolayer and exclusive extended monolayer models were applied to interpret the single-compound and binary adsorption isotherms of zinc and cadmium on activated carbon. Based on these models, the modeling analysis demonstrated that zinc is dominant in solution and more favorably adsorbed on activated carbon surface. For instance, in single-compound systems, the number of ions bound per each receptor site was n (Zn) = 2.12 > n (Cd) = 0.98. Thus, the receptor sites of activated carbon are more selective for Zn than for Cd. Moreover, the determination of adsorption energy through the adopted models confirmed that zinc is more favored for adsorption in single-compound system (adsorption energies equal to 12.12 and 7.12 kJ/mol for Zn and Cd, respectively) and its adsorption energy does not depend on the cadmium presence in binary system. Finally, the adsorption energy values suggested that single-compound and binary adsorption of zinc and cadmium is a physisorption. [ABSTRACT FROM AUTHOR]

In this work, the performances of a commercial activated carbon (Filtrasorb 400, provided by Calgon) were experimentally tested for the adsorption of different aromatic compounds, i.e., toluene and benzene from synthetic groundwater. Batch adsorption tests were carried out at constant pH (8) and four different temperatures (10–50 °C). The experimental equilibrium adsorption data were fitted with a new statistical physics model named as ‘multilayer model with saturation’ and established through the grand canonical ensemble in statistical physics. The characteristic model parameters of the adsorption isotherm such as the number of benzene or toluene molecule(s) per site, n, the receptor site densities, N M , the number of adsorbed layers (N L ) and the energetic parameter, (-ε 1 ) and (-ε 2 ), were estimated for the studied systems by a non-linear least square regression. These parameters were discussed and interpreted for their temperature dependence. The calculated thermodynamic parameters such as entropy, Gibbs free energy and internal energy from experimental data showed that the adsorption of benzene and toluene onto activated carbon Filtrasorb 400 was feasible, spontaneous and exothermic in nature. [ABSTRACT FROM AUTHOR]

Activated carbons (AC) were synthesized by a pyrolysis process and activation with water vapor of agricultural wastes, namely, apricot stones, peach stones, and olive stones, for CO2capture from a simulated flue gas. Kinetic and thermodynamic adsorption tests were carried out in a lab-scale fixed-bed column under operating conditions typical of a flue gas (i.e., P = 1 atm, CO2= 3–30%, T = 30°C). Experimental results showed that the AC derived from olive stones is characterized by a slightly faster saturation, due to a higher contribution of meso-macropores, while the AC derived from the apricot stones had the highest adsorption capacity, likely ascribed to a higher micropore volume and a narrower pore size distribution. Regeneration studies conducted on the AC derived from apricot stones showed that CO2adsorption is a reversible process and that the time to achieve a desired CO2recovery percentage is mainly controlled by temperature and, at less extent, by desorbing agent flow rate. [ABSTRACT FROM PUBLISHER]

This work deals with an innovative approach to design a permeable reactive barrier (PRB) filled with activated carbon, namely a permeable adsorptive barrier (PAB). A 2D numerical model, solved using a finite element approach via COMSOL Multi-physics, was used to describe the pollutant transport within groundwater and the pollutant adsorption onto the barrier. The PAB design procedure was applied to a benzene-contaminated aquifer situated in the metropolitan area of North Naples (Italy), lately hit the headlines as “Gomorra’s land”. Model results showed that PAB is an effective tool for the remediation of the aquifer under analysis, since the pollutant concentration downstream the barrier resulted everywhere lower than the regulatory limit set for groundwater. A sensitivity analysis was carried out to evaluate the influence of some site parameters on the PAB design, i.e. hydraulic conductivity and dispersivity. Finally, the simulation results allow estimating the long-term efficiency of the treatment system and the time required to achieve a complete restoration of the aquifer. [ABSTRACT FROM PUBLISHER]

In this work, the results of equilibrium and dynamic adsorption tests of hexavalent chromium, Cr (VI), on activated carbon are presented. Adsorption isotherms were determined at different levels of pH and temperature. Dynamic tests were carried out in terms of breakthrough curves of lab-scale fixed bed column at different pH, inlet concentration and flow rate. Both the adsorption isotherms and the breakthrough curves showed non-linear and unconventional trends. The experimental results revealed that chromium speciation played a key role in the adsorption process, also for the occurrence of Cr(VI)-to-Cr(III) reduction reactions. Equilibrium tests were interpreted in light of a multi-component Langmuir model supported by ion speciation analysis. For the interpretation of the adsorption dynamic tests, a mass transfer model was proposed. Dynamic tests at pH 11 were well described considering the external mass transfer as the rate controlling step. Differently, for dynamic tests at pH 6 the same model provided a satisfying description of the experimental breakthrough curves only until a sorbent coverage around 1.6 mg g −1 . Above this level, a marked reduction of the breakthrough curve slope was observed in response to a transition to an inter-particle adsorption mechanism. [ABSTRACT FROM AUTHOR]

In this work, a coal combustion ash (CCA) has been tested as an alternative low-cost sorbent to commercial activated carbons (GAC) for cadmium and zinc removal from polluted water. To this aim, the effect of pH and metal concentration on CCA adsorption capacity has been investigated, and a comparative analysis with GAC has been carried out in the same experimental conditions. Furthermore, in order to improve CCA adsorption capacity, two different activation treatments of raw CCA have been tested. In particular, the CCA was subjected to a gasification process conducted with steam and to different acidic treatments, conducted either with hydrochloric acid or nitric acid at different acid concentrations. Experimental results showed that all the acid treatments determined a substantial reduction of both cadmium and zinc adsorption capacity. Differently, the steam gasification determined a substantial increase in adsorption capacity with respect to raw CCA, in particular for zinc as its adsorption capacity resulted even higher than the correspondent of GAC. Finally, a thorough analysis of sorbent physical and chemical properties and of adsorption data allowed the individuation of the main cadmium/zinc adsorption mechanism both on CCA and activated carbon, adequately described by the Freundlich model. [ABSTRACT FROM AUTHOR]

Abstract: In this work, a new Real Adsorbed Solution Theory (RAST) model, for competitive multicomponent adsorption equilibrium correlation in liquid systems has been developed. The model is derived from Ideal Adsorbed Solution Theory; in its formulation it explicitly takes into account the non-ideal behavior shown by most of the adsorption systems. The occurrence of interactions among adsorbed molecules is accounted for by the introduction of activity coefficients, as a function of sorbates adsorption capacity and spreading pressure. These coefficients are experimentally evaluated through multicomponent adsorption isotherms determination, also considering single-compound adsorption isotherm parameters in the model formulation. The RAST model was tested on the experimental results of tetrachloroethylene/trichloroethylene (PCE/TCE) binary mixtures adsorption, obtained at constant temperature and different concentration ratio of the two compounds. This model, with the experimental determination of activity coefficients, allowed an accurate description of PCE/TCE binary adsorption experimental data, thus being a reliable instrument for the design of industrial adsorption equipment for wastewater containing a mixture of pollutants. [Copyright &y& Elsevier]

Abstract: Adsorption is an effective process to remove mercury from polluted waters. In spite of the great number of experiments on this subject, the assessment of the optimal working conditions for industrial processes is suffering the lack of reliable models to describe the main adsorption mechanisms. This paper presents a critical analysis of mercury adsorption on an activated carbon, based on the use of chemical speciation analysis to find out correlations between mercury adsorption and concentration of dissolved species. To support this analysis, a comprehensive experimental study on mercury adsorption at different mercury concentrations, temperatures and pH was carried out in model aqueous solutions. This study pointed out that mercury capture occurs mainly through adsorption of cationic species, the adsorption of anions being significant only for basic pH. Furthermore, it was shown that HgOH+ and Hg2+ are captured to a higher extent than HgCl+, but their adsorption is more sensitive to solution pH. Tests on the effect of temperature in a range from 10 to 55°C showed a peculiar non-monotonic trend for mercury solution containing chlorides. The chemical speciation and the assumption of adsorption exothermicity allow describing this experimental finding without considering the occurrence of different adsorption mechanisms at different temperature. [Copyright &y& Elsevier]

Abstract: For a proper design of multicomponent adsorption systems, the availability of reliable adsorption models is paramount. In this work, an experimental and modelling analysis of PCE/TCE adsorption, aimed at investigating adsorption capacities in a binary system, is carried out. All the experimental tests are conducted at constant pH and temperature. The analyte concentration is varied over a wide range in order to cover as much as possible real cases that could lead to different adsorption behaviours and, consequently, to different modelling results. Experimental data show that the PCE adsorption capacity does not depend on TCE presence, and the equilibrium final conditions are not related to different analyte adsorption rates. The equilibrium adsorption data are analyzed by using different adsorption models, namely Langmuir multicomponent, Ideal Adsorbed Solution Theory (IAST) and Predictive Real Adsorbed Solution Theory (PRAST) models. The Langmuir model provides the worst data prediction since its basic hypotheses do not reflect the physical behaviour of the system. The IAST model does not provide a satisfactory prediction of binary data except for low liquid concentration levels, as it underestimates the PCE adsorption capacity and overestimates TCE. It follows that when the solid coverage increases, the PCE–TCE mixture behaviour is not ideal. Finally, the PRAST model, here developed for liquid systems for the first time, is considered in order to take into account a non-ideal system by including activity coefficients. The PRAST model provides a very good prediction of PCE adsorption experimental data but it is not useful to predict TCE adsorption data, its performance being even worse than IAST. The inability of the model to correctly predict both isotherms simultaneously lies in the particular type of non-ideality of the system itself, as shown by experimental data. [Copyright &y& Elsevier]

A procedure to optimize the design of a Permeable Adsorptive Barrier (PAB) for the remediation of a contaminated aquifer is presented in this paper. A computer code, including different routines that describe the groundwater contaminant transport and the pollutant capture by adsorption in unsteady conditions over the barrier solid surface, has been developed. The complete characterization of the chemical–physical interactions between adsorbing solids and the contaminated water, required by the computer code, has been obtained by experimental measurements. A case study in which the procedure developed has been applied to a tetrachloroethylene (PCE)-contaminated aquifer near a solid waste landfill, in the district of Napoli (Italy), is also presented and the main dimensions of the barrier (length and width) have been evaluated. Model results show that PAB is effective for the remediation of a PCE-contaminated aquifer, since the concentration of PCE flowing out of the barrier is everywhere always lower than the concentration limit provided for in the Italian regulations on groundwater quality. [Copyright &y& Elsevier]

Abstract: In this work, an experimental study aimed at the assessment of the factors affecting the adsorption of trichloroethylene (TCE) from water solutions onto activated carbons is presented. The influence of sorbent properties, such as B.E.T. surface area, micropore volume, chemical composition and acid/basic surface functional groups on TCE adsorption capacity is experimentally assessed by testing a set of 12 sorbents. Moreover, the effect of the presence of other species in solution, such as sodium acetate and tetrachloroethylene (PCE), is studied through parametric TCE adsorption isotherms realization. The experimental results show that the TCE adsorption capacity is promoted by a high B.E.T. surface area, micropore volume and C content and it is significantly affected by the presence of a non-ionic compound of similar structure (PCE), however it does not depend on the presence of an organic salt (sodium acetate). These results confirm that neither TCE–carbon ionic interaction nor sorbent ionization phenomena are involved in the TCE adsorption, since its mechanism is based on dispersion forces (London–Van Der Walls interaction). A thorough analysis of the experimental data set suggests that, in consideration of the TCE adsorption mechanism, the maximization of basal plane extent (as the B.E.T. surface area) and its effective fraction (as the C content) is a valid criterion to select or synthesize a new suitable sorbent for TCE adsorption from waters. [Copyright &y& Elsevier]

Abstract: Adsorption processes have long been used in water and wastewater treatment and a deterministic approach has been often adopted for the analysis of fundamental mechanisms. In this research, a new approach based on statistical treatment of modelling data is adopted for the analysis of trichloroethylene (TCE) adsorption on granular activated carbon (GAC) from synthetic groundwater. The work starts from an experimental analysis aimed at the assessment of the influence of thermodynamic parameters (concentration, pH, salinity, temperature and the presence of an organic non-ionic compound, i.e. ethyl acetate) on TCE adsorption capacity. A wide range of process parameters have been considered to simulate highly polluted groundwater, as when leachate infiltrations occur at solid waste landfill. Experimental results show that adsorption capacity decreases by increasing the temperature and the ethyl acetate concentration, while neither pH nor salinity have any influence. A thorough understanding of adsorption mechanism and the individuation of the model with highest physical and mathematical significance is carried out by a thermodynamic analysis and a statistical methodology based on Analysis of Variance (ANOVA). The latter indicates that in dilute solutions the Freundlich model is the best data fitting model for TCE adsorption, among those which are commonly adopted. [Copyright &y& Elsevier]

Abstract: The design of adsorber units is mainly dependent on the equilibrium adsorption capacity of the sorbent in the working conditions. At the moment, these data are available in a limited number of experimental conditions and, for the case of activated carbon, there are no predictive models to assess the adsorption capacity as a function of the process parameters. This makes the adsorber design a complex and approximated task. In this work, a model for the description of metallic ions adsorption onto activated carbon is presented. The model starts from an evaluation of ion speciation and it considers the approach of the multi-component Langmuir model to correlate the metal uptake to the ion concentration in solution. The model has been used to analyse available experimental data on the adsorption of As(V), Cd(II), Cr(III) and Cr(VI) ions on activated carbon. A good matching between experimental results and model predictions has been obtained for all the investigated conditions. [Copyright &y& Elsevier]

Biomethane, a renewable form of natural gas, can be produced by biogas upgrading and its utilization is incentivized to mitigate CO 2 emissions. In this work, biogas upgrading via adsorption on commercial carbonaceous adsorbents, an activated carbon (AC) provided by Desotec and two carbon molecular sieves (CMSs) produced by Carbotech and Xintao, is experimentally investigated in a fixed-bed column, testing CO 2 /CH 4 mixtures at different concentrations as feed gas. The experimental campaign highlights that AC has a higher adsorption capacity for both CO 2 and CH 4 , as well as better kinetic performances (i.e. higher bed usage efficiency and lower desorption times), than CMSs. On the other hand, the CMSs show a much lower CH 4 adsorption capacity than the AC due to their combined thermodynamic/kinetic sieving properties, which emerge from dynamic breakthrough curves and equilibrium adsorption data alike. Therefore, the CMSs show a much higher selectivity for the separation of the CO 2 /CH 4 mixture, and Xintao sample shows a better overall performance thanks to its faster kinetics; moreover, experimental cyclic adsorption/desorption runs on Xintao confirmed its complete regenerability. Breakthrough curves modelling, performed in MATLAB environment and aimed at evaluating the CO 2 mass transfer coefficients, points out that intraparticle diffusion is the rate-limiting step for CO 2 adsorption process. It can be concluded that CMSs show better performances for biogas upgrading due to their high selectivity and despite their lower CO 2 adsorption capacity, which cannot be taken as the main controlling parameter in the adsorbent selection devoted to this specific application. [Display omitted] • Carbon molecular sieves outperform activated carbon for CO 2 /CH 4 separation. • Equilibrium/kinetic sieving effects emerge from breakthrough and equilibrium data. • Intraparticle diffusion is the rate-limiting step for the adsorption process. • Constant CO 2 adsorption capacity for cyclic reuse and desorption at 80 °C. • Selectivity and kinetics are the leading parameters for an optimal adsorbent choice. [ABSTRACT FROM AUTHOR]

• Copper and zinc ions adsorption kinetics and isotherms on cancrinite were studied. • Metal adsorption isotherms were investigated in single and binary systems. • Statistical physics models were used to understand the adsorption mechanism. • Adsorption thermodynamic parameters were calculated and interpreted. Adsorption isotherms of Cu2+ and Zn2+ onto cancrinite were investigated in single-compound and binary systems at pH 6.0 and room temperature. The maximum adsorption capacity of Cu2+ was higher than Zn2+ in both the systems. This result could be related to Pauling electronegativity and hydrated ionic radius of these metals, making the cancrinite more selective for Cu2+ than Zn2. The separation factor (α C u , Z n) was greater than unity confirming the higher selectivity for Cu2+ adsorption. Langmuir and Freundlich models fitted well the single-compound adsorption isotherms. In order to obtain a better interpretation of the adsorption of Cu2+ and Zn2+ in single and binary systems, a monolayer and an exclusive extended monolayer models were adopted. According to these statistical physics models results, the receptor sites of cancrinite showed to be more selective for Cu2+ (n = 0.94) than Zn2+ (n = 0.77) in single-compound systems. Due to the competitive effect arising between Cu2+ and Zn2+ on the same receptor site, the n values were reduced in binary system to 0.68 and 0.39 for Cu2+ and Zn2+, respectively. Furthermore, the adsorption energies in single-compound systems were equal to 23.78 and 19.23 kJ/mol for Cu2+ and Zn2+, respectively. In binary system, the adsorption energies of the studied ions decreased and their values in all the systems indicated the existence of a physisorption process. The reduction of the adsorbed capacity ratio between the binary and single-compound systems (i.e. Q b /Q s) highlighted the antagonistic effect between copper and zinc ions. Finally, thermodynamic parameters were investigated in detail. [ABSTRACT FROM AUTHOR]

In this research, the adsorption isotherms of Methylene Blue (MB) and Basic Yellow 28 (BY28) on agricultural Algerian olive cake waste (AAOCW) were modeled at molecular level using statistical physics and COSMO–RS theories. This molecular modeling aimed to demonstrate an alternative way to describe the interactions between dyes and adsorbents. The adsorption equilibrium isotherms of MB and BY28 on AAOCW were constructed at different temperatures. The statistical physics model was used to quantify the number of adsorbed dye molecules per site, the anchorage number, the receptor sites density, the adsorbed quantity at saturation, the concentration at half saturation and the molar adsorption energy. The COSMO–RS theory was used to quantify the interaction energies: Electrostatic, hydrogen bonding and Van der Waals. σ–Profile and σ–potential were calculated to show the ability of each of the two dyes to interact with every adsorbent site. It was demonstrated that statistical physics and COSMO–RS theories are confident ways to elucidate the interactions between dye molecules and adsorbent surface at a molecular level. [ABSTRACT FROM AUTHOR]

• The adsorption of two industrial pollutants on polyurethane/chitosan adsorbent foam was developed. • Estimation of the total number of formed layers was determined. • Description of the adsorbent performance via the calculation of the maximum adsorption capacity. • Calculation of adsorption energy at different temperatures. This work presents an application of a multilayer model derived from statistical physics to the adsorption experimental data of two industrial pollutants, namely perfluorohexanesulfonic (PFHxS) and Perfluorobutanesulfonic (PFBS) acids on a bio–based polyurethane /chitosan(PU/CH) adsorbent foam, at T = 298–328 K and pH 4. This model shows that the number of PFHxS and PFBS layers formed on adsorbent surface increases from 1.61 to 3.80, and from 1.56 to 2.26 respectively by increasing the temperature.This means that the adsorbate molecules are arranged on a variable number of layers. For instance, at 328 K, it was deduced that around 80 % of PFHxS acid was taken up by the PU/CH composite, forming a total of four layers, whereas the remaining 20 % contributed to the formation of three layers. The estimation and analysis of the number of molecules bound per active site is useful to understand the adsorption mechanism. PFHxS and PFBS adsorb on PU/CH in non-parallel configuration, through a multimolecular docking characterized by more than one molecule per active site. The PU/CH performances are investigated in terms of the maximum adsorption capacity of both the tested industrial pollutants, retrieving similar values for both PFHxS and PFBS. Two adsorption energies are calculated showing that physical forces are contributing to remove these pollutants. Interstingly, thermodynamic calculations are also introduced and interpreted to understand the adsorption mechanism at macroscopic level. These theoretical scientific evidences provide a plausible explanation of the PFHxS and PFBS adsorption mechanisms and contribute to understand this interfacial process at the molecular level. [ABSTRACT FROM AUTHOR]

Abstract: This paper is collocated after two other works in which sieved or demineralized coal combustion ashes were used as cadmium (Cd2+) sorbent for water treatments, and the changes in raw ash properties were followed upon steam- and CO2-gasification. In the present paper, ash samples activated by steam- or CO2-gasification were used to adsorb Cd2+ in model aqueous solutions, to elucidate the relationships among ash properties, gasification treatments, properties of the gasified ash and its sorption behavior. To this end, equilibrium and kinetic cadmium adsorption tests were carried out using the gasified ash (treated with either steam or CO2) as sorbent and under fixed operating conditions (for example, the contact time was 7days and the initial Cd2+ concentration in the aqueous solution to be treated varied between 5 and 50mgL−1 for equilibrium tests, while kinetic tests were carried out for times ranging from 10min to 7days using an initial Cd2+ concentration equal to 50mgL−1). Results were expressed in terms of adsorption isotherms, removal efficiency and kinetic curves. Post-processing of experimental data allowed to provide estimations of relevant parameters such as the equilibrium and the kinetic constants, the separation factor, the initial adsorption rate, the characteristic adsorption time. Besides a direct confrontation between the two gasification treatments, results were also compared with former experiments on the same raw material, and with the main outcomes emerging from the pertinent literature, confirming that the gasified materials resulted as very attractive sorbents for Cd2+ capture from wastewaters. [Copyright &y& Elsevier]

The removal of a benzodiazepine (clorazepate, CLZ) from aqueous solution by adsorption onto maghnite clay is investigated supported by theoretical simulations. The Fourier-transform infrared (FTIR), Ultraviolet (UV), X-ray diffraction (XRD), and scanning electron microscope (SEM) analyses were used to characterize the adsorbent. To individuate the optimum conditions for adsorption, equilibrium, and kinetic tests are performed to assess the efficiency of this adsorbent to remove CLZ from polluted water in different operating conditions like pH, initial concentration, adsorbent dosage, and contact time. Adsorption is maximum at low pH, and it is mainly driven by electrostatic interactions between the benzenic ring of CLZ molecule and the montmorillonite layer of maghnite adsorbent. The kinetics obeys to the pseudo-first-order kinetic model, while the Freundlich isotherm model was found to better describe the adsorption equilibrium. The maximum observed adsorption amount of CLZ onto maghnite was about 50 mg g−1 at pH 4.66. A complementary theoretical study is performed to quantify the CLZ/maghnite interactions using Monte Carlo simulations. Interestingly, the results show that the CLZ assumes a horizontal position on the maghnite surface upon adsorption, characterized by high energy adsorption. Unlabelled Image • A benzodiazepine (Clorazepate) is removed from water by adsorption onto maghnite. • Adsorption is maximum at acidic pH and occurs by electrostatic interactions. • The pseudo-first order kinetic model better describes the experimental data. • Monte Carlo simulations suggest that adsorption occurs by horizontal bond. • Clorazepat is adsorbed more than water molecules onto maghnite surface. [ABSTRACT FROM AUTHOR]

• Advanced adsorption models are derived from statistical physics formalism. • CO 2 adsorption isotherms are successfully modelled by saturated multilayer model. • Steric and energetic analysis of CO 2 sorption mechanism is provided. • Thermodynamic adsorption functions confirm the exothermic character of adsorption. Three different activated carbons, namely Aquacarb 207EA (AQ), Organosorb-10 (OR-10) and Organosorb-10AA (OR10-AA) are investigated for carbon dioxide (CO 2) adsorption from simulated flue-gas, which is one of the promising approaches to mitigate global warming. Adsorption isotherms are determined at three temperatures (303 K, 323 K and 353 K) and over a wide CO 2 partial pressure range (0.03–0.3 bar), in a dynamic lab-scale experimental apparatus. Experimental results show that CO 2 adsorption capacity is affected by micropore volume, while the chemical properties (mainly pH PZC and acid functional groups) seem to play a secondary role. The CO 2 adsorption isotherms are interpreted by three advanced models derived from statistical physics. The selected model allows retrieving useful information about the sorption process by determining the number of captured CO 2 molecules per site (n ms), the density of receptor sites (D sr), the total number of adsorbed layers (N c) and the energetic parameters (− ε 1) and (− ε 2). The modeling analysis suggests that the captured CO 2 molecules aggregate upon adsorption and are anchored with a perpendicular position on the adsorbents surface. The total numbers of adsorbed layers range from 3.12 to 5.56 for the three adsorption systems, and the value increases with temperature as if the diminution of active sites available for CO 2 capture on adsorbent surface was partially counterbalanced by a multilayer adsorption mechanism. The adsorption energies retrieved from data analysis are in the range from −11.39 to −21.10 kJ/mol, confirming that, for the investigated systems, adsorption is exothermic and based on physisorption. Finally, the site energy distribution is also estimated to corroborate the surface heterogeneity and the physical nature of the adsorbate/adsorbent interactions. [ABSTRACT FROM AUTHOR]

The reactive adsorption of H 2 S on CuO-ZnO dispersed onto activated carbon was investigated in different gas streams, containing either O 2 , H 2 O or O 2 /H 2 O, at room temperature and in a lab-scale fixed-bed reactor. Sorbents performances were analysed in terms of H 2 S capture rate and capacity, and results correlated with the sulphur species formed upon adsorption under different experimental conditions. Temperature Programmed Desorption (TPD), porosimetric and XPS analyses were performed in order to support the adsorption dynamic tests. The co-presence of O 2 and H 2 O caused a remarkable increase in H 2 S adsorption capacity, in particular for Cu-containing sorbents, favouring the formation of various sulphur species such as sulphides, sulphates and, above all, elemental sulphur. The analysis of the experimental data set showed the occurrence of two main H 2 S oxidation mechanisms with different rates: the first one quickly formed metal sulphates utilizing lattice oxygen from metal oxide clusters or superficial oxygen species; the second process was slower and required moisture and molecular oxygen in the feed gas to catalytically form elemental sulphur chains that progressively filled-up the sorbent microporosity. Image 1 • Enhanced H 2 S capacity of CuO-ZnO/AC sorbents with O 2 and H 2 O. • Reactive adsorption mechanism starts with the initial fast formation of metal sulphates. • CuO catalyzes H 2 S oxidation to elemental S in the presence of H 2 O and O 2. • Large sorption capacity related to the filling up of micropores with elemental S. [ABSTRACT FROM AUTHOR]

The simultaneous adsorption of three pollutants cobalt (Co), methylene blue (MB) and nickel (Ni) on a modified chitin surface from ternary systems was investigated. Multicomponent experimental adsorption data were determined at 298–328 K and pH 6. These experimental studies indicated that Ni adsorption was higher than those obtained for Co and MB. The multicomponent adsorption mechanism of this ternary system was analyzed with statistical physics theory where a set of new models with different hypotheses was developed and tested. Results showed that an adsorption model assuming that the pollutants Co, MB and Ni were adsorbed on three different types of modified chitin receptor sites was the most appropriate. This model was also utilized to calculate the corresponding adsorption energies to describe the possible interactions between these adsorbates and the surface of modified chitin. A general analysis of trends and magnitude of the model parameters provided a deeper understanding of the ternary adsorption mechanism at molecular level. Macroscopically, the ternary adsorption mechanism was interpreted via a calculation of three thermodynamic functions. [ABSTRACT FROM AUTHOR]

• The adsorption of two pharmaceutical pollutants on activated carbon was studied. • The application of an advanced theoretical model allowed studying the adsorption mechanism. • The adsorption geometry of both pharmaceuticals was determined at different temperatures. • The adsorption energies were calculated for each adsorption layer. In this work, the adsorption mechanism of two pharmaceutical pollutants, paracetamol (PCM) and nimesulide (NMS), on activated carbon (AC) is elucidated via advanced modelling. Adsorption isotherms of PCM and NMS on a selected AC are obtained in the temperature range of 298–328 K. A physical model is applied to the experimental data set, assuming that the PCM and NMS molecules formed two layers on the AC, through the contribution of two adsorption energies. This theoretical analysis shows that the saturation adsorption capacities decrease with temperature from 259.27 to 211.82 mg/g for NMS and from 114.79 to 73.49 mg/g for PCM. This trend indicates that the tested AC has higher performances in removing NMS than PCM. The analysis of model parameters indicates that the number of molecules bound per active site (n) for the NMS-AC system are greater than unity for all the investigated temperatures, while it results to be equal to unity for PCM-AC system. This result allows concluding that an aggregation occurs during the adsorption of both the compounds, which are removed via interactions with one AC functional group. Different adsorption energies are determined, showing that the adsorption of NMS and PCM occurs via physisorption. Overall, this paper reports new theoretical assessments of PCM and NMS adsorption mechanism onto activated carbon via the adopted statistical physics model. [ABSTRACT FROM AUTHOR]

Highlights • Serpentine was treated by a solution of CTAB/H 2 O 2 to produce MSP adsorbent. • Adsorption of Cr (VI) and fluoride by MSP in single and binary systems was studied. • Statistical physics models were used to understand adsorption mechanisms. • Active sites in MSP were more selective for F than Cr (VI) in the studied systems. Abstract Single-compound and binary adsorption isotherms of hexavalent chromium (Cr (VI)) and fluoride (F) ions onto surfactant–modified serpentine (MSP) are investigated at different temperatures (298, 308 and 318 K) and constant pH (2.0). For each temperature, F is adsorbed more than Cr(VI), in both single-compound and binary systems, mainly due to both higher electronegativity and number of active receptor sites (i.e., hydroxyl groups) on adsorbent surface. Moreover, in binary systems, both the adsorbates showed a reduction in their adsorption capacities, testifying the occurrence of competitive adsorption mechanisms. Classical models fit the experimental results but are not able to provide important information about the adsorption mechanisms. In order to understand the mechanism of Cr(VI) and F adsorption, the parameters of two advanced statistical physics models are determined and interpreted. For Cr(VI), more than one ion is adsorbed on a same active site (multimolecular mechanism), likely by an ion exchange mechanism between chromium anions/cations and the protonated/non-protonated OH groups of the MSP surface. For F, a multi-docking mechanism occurs (i.e. more than one active site is needed to bond one F ion), likely associated with electrostatic interactions between MSP active sites and the adsorbed ions. Sterically, the receptor sites density (N M) is found to be the main parameter controlling the adsorption capacities of the adsorbed ions and their difference, confirming the predominance of F ions. The adsorption capacity ratio between single-compound and binary values (i.e. Q b /Q s) indicates that Cr(VI) adsorption slightly decreases in the presence of F, allowing to quantify the competition between ions. The estimated adsorption energies for the investigated systems well represent the endothermic adsorption of both Cr(VI) and F, having a physical reversible character. [ABSTRACT FROM AUTHOR]

Herein, a chitosan/polyamide nanofibers (CPN)-based adsorbent is employed to interpret the adsorption mechanism of two dyes, namely Reactive Black 5 (RB5) and Ponceau 4R (P4R), at different temperatures. Based on experimental results, the adsorption isotherms of RB5 and P4R dyes indicate that the separation process tends to a saturation plateau at high concentration, also suggesting that the dyes adsorption process occurs with the formation of a finite number of layers. To provide a reasonable explanation of the dyes adsorption mechanisms, three statistical physics models are used and discussed. The advanced modelling analysis reveals that the adsorption of both dyes occurs by the formation of two different adsorbed layers on CPN surface. Based on the application of the best statistical physics adsorption model, it was deduced that both dyes were anchored with horizontal and non-horizontal positions on CPN surface depending on temperature, which was concluded by investigation the captured number of dye molecules per CPN adsorbent site during the adsorption process. Based on these theoretical results, it was noted that the adsorption capacities at saturation followed this sequence: Q (P4R) > Q (RB5) for all investigated temperatures (i.e., 222.4, 261.3, 352.8, 482.2 mg/g for P4R and 198.6, 267.7, 288.2, 352.5 mg/g for RB5), indicating that CPN adsorbent was more effective for the P4R dye removal. The adsorption energies are studied to explain the difference in the interactions between dyes and adsorbent surface (P4R-CPN, RB5-CPN), and between these dyes (P4R-P4R, RB5-RB5), indicating that the removal of these adsorbates was based on a physisorption mechanism where a desorption process is possible. Comparing the estimated parameters of the best statistical physics model, it was concluded that both steric and energetic factors are mainly responsible for the adsorption of P4R and RB5 dyes on CPN. • Investigation of dyes adsorption via advanced modelling analysis. • Study of adsorbate-adsorbent, and adsorbate-adsorbate interactions. • Description of adsorption mechanism through steric and energetic factors. [ABSTRACT FROM AUTHOR]

Abstract In this work, agro-wastes coming from soursop (peel, seeds and pulp fiber) and sugarcane (bagasse) are used as low-cost biosorbents to remove methylene blue (MB) from aqueous media. Batch experiments are performed under different experimental conditions investigating the effects of biosorbent amount, dye concentration and stirring rate. The best results were found using soursop wastes for a MB concentration of 100 mg L−1, using 0.75 g of residue and a stirring rate of 110 rpm, removing a percentage above 90%. Theoretically, adsorption kinetic can be successfully described by the pseudo-second order model. Redlich-Peterson and Sips models are adopted to interpret the equilibrium adsorption of MB on sugarcane bagasse and soursop residue, respectively. Interestingly, the monolayer model with single energy derived by statistical physics theory is also applied for a deeper explanation of the adsorption mechanism of MB on both the adsorbents. The application of this model allows defining the adsorption geometry of the investigated adsorbate and provides important information about the interactions between the adsorbate and sorbents. In particular, the modelling analysis by statistical physics allows defining that the dye molecules are adsorbed in vertical position and the adsorption process is multi-molecular (i.e. n > 1). Finally, the estimation of adsorption energy suggested that MB adsorption on biosorbent is a physisorption process. [ABSTRACT FROM AUTHOR]

Highlights • Bentonite-chitosan adsorbent was synthetized and applied in heavy metal adsorption. • Single and binary adsorption of Cd2+ and Pb2+ on bentonite-chitosan composite was analyzed. • Statistical physics models were applied to understand the adsorption mechanisms. Abstract In this study, a bentonite-chitosan composite was tested for the single and binary adsorption of Cd2+ and Pb2+ ions at constant pH (6) and different temperatures (30, 40, and 50 °C). For both adsorbates, the adsorption capacities decreased in binary systems due to an antagonistic adsorption effect. Statistical physics models were used to analyze the adsorption isotherms and to attribute microscopic interpretations to the experimental evidences at a molecular level. Specifically, a monolayer model with one energy and an exclusive extended monolayer model were applied to single and binary adsorption data, respectively. The crossing of the experimental and modelling results proved that Cd2+ ion was more adsorbed in the binary system. The modelling analysis allowed determining that the numbers of ions linked per adsorbent site varied significantly in binary system with respect to single-compound ones, thus confirming that an inhibition effect occured. Finally, the adsorption energy was estimated for both adsorption systems indicating the occurrence of an endothermic adsorption. Moreover, adsorption energies showed concordant trends with the corresponding adsorption capacities of both Cd2+ and Pb2+, hence being able to describe the adsorption phenomena. [ABSTRACT FROM AUTHOR]

A new adsorbent (amphoteric adsorbent coating: AAC) based on composite coating with amphoteric functionality was employed to study the adsorption mechanism of Brilliant Green (BG) and Acid Red 1 (AR1) dyes. This adsorbent was prepared as a coating and supported on cotton cloth by application of a facile method, based on the combined use of smectite-based clay powder, acrylic polymer emulsion (APE) and cationic polyelectrolyte. The novel adsorbent coating was characterized by FE-SEM, EDX, zeta potential and FTIR analysis. Subsequently, the equilibrium adsorption isotherms of AR1 and BG dyes were performed and analyzed at different temperatures (from 303 to 343 K) in order to achieve a thorough comprehension of dyes adsorption mechanism. To this aim, a multilayer model with saturation was developed using statistical physics theory and was applied as a sophisticated tool for data interpretation. The correlations of experimental and theoretical results allowed to understand two distinct behaviours for the adsorption of AR1 and of BG dyes, which were related to the formation of two different adsorbed layers and a variable number of layers, respectively. Based on the parameter of the adopted model, the adsorption geometry of dyes has been described at different temperatures. Interestingly, the adsorption process was energetically typified by estimation of the adsorption energies, which indicated that the adsorption of AR1 and BG dyes were exothermic and endothermic, respectively. [ABSTRACT FROM AUTHOR]

Abstract The adsorption of Pb(II) and Hg(II) ions on bentonite-alginate composite (BAC) is investigated in both single-compound and binary systems, at three different temperatures. For a better interpretation and comparison, all the adsorption equilibrium isotherms are recorded under identical conditions. A simple examination of all adsorption equilibrium isotherms shows that the bentonite-alginate composite is more effective for Pb (II) adsorption than for Hg (II) and the adsorption capacity is reduced in binary system, reflecting a competitive effect between the Pb (II) and Hg (II). To explain the single and binary processes and the corresponding mechanisms, Hill and competitive Hill models are applied. The adsorption geometry can be determined at different temperatures by an estimation of the number of ions captured per BAC adsorbent site. Based on these models, it is shown that the affinity sequence in all adsorption systems is: Pb (II) - Hg (II). This behavior can be explained and corroborated by an energetic analysis deduced from these models. Finally, in order to deepen the interpretation of single-compound and binary adsorption, the conductor-like screening model (COSMO-RS) was tested and applied to calculate the total interaction energies between heavy metals and BAC adsorbent. The evaluation of energies deduced from COSMO-RS model indicated that the electrostatic misfit interaction energy may play the main role in the heavy metals ions adsorption in tested systems. Highlights • Pb and Hg adsorption on bentonite-alginate composite has been studied. • Metal adsorption could be a combination of physical and chemical interactions. • COSMO-RS model was applied in metal adsorption. • Electrostatic misfit energy played the main role in metal adsorption. [ABSTRACT FROM AUTHOR]

The paper is a complementary study of Food Yellow 4 and Food Blue 2 adsorption in single-compound and binary systems on modified chitosan (CC-chitosan), using statistical physics and Ideal Adsorbed Solution Theory (IAST) models. In order to provide new macroscopic interpretations of adsorption mechanisms, three thermodynamic functions were determined, such as configurationally entropy, free enthalpy and internal energy. The configurationally entropy trend showed that the dye molecules have plenty possibilities/positions to be docked on empty receptor sites at low concentrations, but limited possibilities at high equilibrium concentrations. The study of the free enthalpy and internal energy confirmed that the adsorption process in single-compound and binary systems is spontaneous. The second theoretical approach is based on the IAST model to predict the multicomponent adsorption isotherms using single-compound isotherm data. The IAST model provides a very good prediction of binary adsorption data, for both the adsorbates. Best results were obtained for Food Yellow 4 adsorption data; while for Food Blue 2 an increasing deviation between experimental and modeling binary adsorption data can be observed along with increasing concentration. Finally, the IAST model correctly described the decrease in adsorption capacity of both the dyes from single-compound to binary system, due to competition effects. [ABSTRACT FROM AUTHOR]

• A new activated carbon was used for ibuprofen and paracetamol adsorption. • The adsorption mechanism of paracetamol and ibuprofen was investigated. • A double layer model (DLM) is adopted in order to provide an interpretation of the adsorption mechanisms. • Adsorption was occurred as a multi-molecular process via physical interactions. The paper reports an experimental and theoretical work about the adsorption of paracetamol (PCM) and ibuprofen (IBP) onto a new activated carbon synthesized starting from the tree pods deriving from Erythrina speciosa. The adsorbent shows good porous properties, with a BET surface area of 795.1 m2/g, and an average pore volume of 0.422 cm3 g−1. Adsorption tests are carried out by varying the most important operating parameters. The adsorption capacity of both IBP and PCM results to be maximum at pH = 3, i.e., where the adsorbate molecules are found in neutral form. Adsorption isotherms indicated that IBP adsorption capacity increases with temperature up to 96.28 mg g−1, while an opposite trendwas retrieved for PCM, which decreased until 50.40 mg g−1. For a theoretical analysis, a double layer model (DLM) is adopted in order to provide an interpretation of the occurring adsorption mechanisms. The theoretical approach indicates that both IBP and PCM are adsorbed bya multi-molecular way, i.e. each functional group on the adsorbent surface accommodates more than one molecule at the same time. Finally, the adsorption energy reveals that a physical adsorption is responsible for both IBP and PCM adsorption on the synthesized adsorbent. [ABSTRACT FROM AUTHOR]

• Adsorption of potential toxic dyes (methylene blue and crystal violet) was studied. • A promising adsorbent was produced and tested during adsorption tests. • A physical model was applied on the entire adsorption data set. • Steric explanations supported a better understanding of the adsorption mechanism. • Two energies described the interactive effects of the adsorption systems. This paper analyzes the adsorption of two potential toxic dyes, i.e. methylene blue (MB) and crystal violet (CV) onto Bauhinia forficata residual fruit powder (BFRFP) as a new promising adsorbent. The experiments aimed at retrievement of adsorption data are carried out at T = 298–328 K and are coupled with an adsorbent characterization to better highlight the MB and CV dyes adsorption mechanism. MB adsorption capacity at saturation (ACS) varies from 181.48 to 201 mg.g−1, while for CV dye, it ranges from 263.06 to 282.61 mg.g−1. This difference is not very significant but reflects that the BFRFP has a higher affinity to remove CV dye. Comparing with some alternative adsorbents, the BFRFP adsorbent shows to be a competitive material for the removal of MB and CV dyes from polluted water. A model assuming that MB and CV dyes are removed via a formation of two layers on BFRFP is chosen as the one that, from a physical point of view, better interpret their adsorption mechanisms. The prediction of the number of dyes adsorbed on BFRFP is approximately equal to 1 for both the dyes, testifying that they are removed without an aggregation process and with slanted position. The physical model generates two energies to describe the interactive effects between both dyes and BFRFP adsorbent (dye- BFRFP) and between dyes (dye-dye). Results show that physical interactions occur during the adsorption process. [ABSTRACT FROM AUTHOR]

• A new adsorbent was prepared from the residue of Butiacapitate. • The adsorption of pharmaceutical molecules was studied. • Adsorption of ketoprofen was endothermic, while paracetamol was exothermic. • A double-layer model with two energies deriving from statistical physics was applied. • This study highlights the important aspects of the adsorption mechanism. This paper describes the removal process via adsorption of paracetamol (PRC) and ketoprofen (KTP) on activated charcoal prepared from the residue of the fruit of Butiacapitate. Some adsorbent characterizations are carried out for a plausible analysis of the adsorption results and for the description of adsorption mechanism. Modelling investigations show that the double layer derived from statistical physiscs can be adopted to interpret the adsorption data. Interestingly, the adsorption mechanism can be elucidated via the model parameters determined at different temperatures. The performance of the adsorbent in terms of maximum adsorption capacity increased from 101.16 to 134.52 mg/g for KTP molecules and decreased from 98.19 to 73 mg/g for PRC molecules, by increasing the temperature, which are in line with the experimental values retrieved. These tendencies of adsorption capacities may be related to the behavior of the number of PRC and KTP pharmaceuticals captured per functional group of the adsorbent. Overall, the modeling results show also that the values of adsorption energies associated to the two layers of KTP and PRC molecules on the adsorbent surface are lower than 40 kJ/mol, implying that only physical type interactions occur in the removal process of these pharmaceutical molecules. [ABSTRACT FROM AUTHOR]

In this paper, the adsorption of the herbicide 2,4-D and the drug ketoprofen on wheat husks Fagopyrum esculentum treated with H 2 SO 4 is experimentally and analytically analyzed. The adsorbent is fully characterized through some techniques such as FT-IR, SEM, and XRD. Adsorption tests are carried out to optimize the performances in terms of adsorbent dosage and solution pH. Subsequently, the impact of temperature is determined through the realization of adsorption isotherms. A multilayer model is employed to microscopically interpret the adsorption mechanism of both the investigated compounds. The modelling analysis shows that the number of molecules bound per adsorption site varied from 0.68 to 2.77 and from 2.23 to 3.59 for ketoprofen and herbicide 2,4-D, respectively. These estimated values testify that an aggregation process occurs during adsorption. The global number of formed layers of each adsorbate is also determined, showing a significant reduction from 5.73 to 2.61 for ketoprofen and from 1.79 to 1.5 for herbicide 2,4-D with the temperature. For a complete understanding of the adsorption mechanism, the saturation adsorption capacity and adsorption energy were calculated and interpreted. Overall, it may be inferred that physical interactions govern how these contaminants adsorb on the tested adsorbent. [Display omitted] • The adsorption of the herbicide 2,4-D and the drug ketoprofen was investigated. • The wheat husks Fagopyrum esculentum was employed as an adsorbent. • Application of physical adsorption model to ascribe new interpretations of the adsorption mechanism. • Description of the adsorption orientation of both pollutants. • Estimation and interpretation of adsorption energies. [ABSTRACT FROM AUTHOR]

• Application of physical model with two adsorption energies. • The adsorption is a multi-cationic process. • Determination of adsorption energies for both functional groups. • Study the impact of temperature on all model parameters. In this work, the adsorption of Cd2+, Pb2+, and Hg2+ ions onto multi-walled carbon nanotubes (MWCNTs) functionalized with COOH is investigated as a function of temperature (298–328 K). For all the investigated ions, adsorption shows the classical exothermic behavior, as adsorption capacity decreases by increasing the temperature. Moreover, a saturation value of adsorption capacity is reached for all the metal cations, testifying the possible formation of a monolayer on the adsorbent surface. Two adsorption models derived from statistical physics are tested to address the investigated system's behavior. The monolayer with double functional groups is selected as the best fitting one. The analysis of model parameters shows that the adsorption of the investigated metals is multi-cationic, i.e. each functional group can adsorb several ions simultaneously. Moreover, an increase in temperature determines a decrease in the density of functional groups; for Cd2+ and Pb2+ ions it is associated with an adsorption capacity on the first functional group higher than the corresponding value obtained for the second, while for Hg2+ ions, an opposite result is retrieved. Finally, adsorption energies are determined for both the functional groups, resulting in the typical range of physical adsorption. [ABSTRACT FROM AUTHOR]

This paper proposes a process for reducing the content of copper and zinc in polluted soils and a combined photocatalytic-physical process for the treatment of the soil washing effluents. For this purpose, real soil samples were taken from the “Land of Fires”, a region in Southern Italy which is known for its high incidence of cancer mortality. Ethylenediamine- N,N ′-disuccinic acid (EDDS) was used to extract the heavy metals from the contaminated soil. The soil washing effluents were treated through a sequence of photocatalytic and adsorption processes to lower the concentration values of metals (Cu, Zn, Fe and Mn) below the limits of national legislation for discharge in municipal sewers and to remove the EDDS from the soil washing solutions. Ecotoxicological tests, using different living organisms ( Daphnia magna , Vibrio fischeri , Pseudokirchneriella subcapitata and Lepidium sativum ), were performed on the soil washing effluents before and after the treatments to assess the effects of the proposed combined process on the ecotoxicity of the soil washing solutions. [ABSTRACT FROM AUTHOR]

This work is an experimental analysis of the adsorption of ibuprofen (IBP) onto a granular activated carbon. Ibuprofen is a NSAID (non-steroidal anti-inflammatory drug) and is now an emerging contaminant of the aquatic environment. The effect of IBP concentration, pH and temperature on the equilibrium adsorption capacity is investigated through batch tests. The experimental results show that the highest adsorption capacity is observed under acidic pH and high temperature conditions. The combined effect of pH and temperature on IBP dissociation in water seems to play a major role in determining the IBP adsorption capacity of the activated carbon. Low pH and high temperature, in fact, reduce the IBP dissociation grade and increase the concentration of the non-ionized IBP species, which is likely to have a higher adsorption capacity with respect to the ionized one. The study puts forward a model to describe the IBP adsorption mechanism considering the variability of the dissociation grade. The model is based on the multicomponent Langmuir adsorption theory applied to the ionic species in solution. It shows that the adsorption capacity is strictly dependent on the IBP speciation in solution, allowing for a correct interpretation of the effects pH and temperature on IBP adsorption capacity. Finally, one of the main goals of this model is to preserve the exothermicity of the adsorption phenomena despite the trend observed in the experimental results: the increase in adsorption capacity with temperature appears to be related to a lower level of IBP dissociation. [ABSTRACT FROM AUTHOR]

• Quaternary adsorption of Cu2+, Co2+, Ni2+ and Ag+ ions was investigated. • Development of a new quaternary adsorption model. • Adsorption of Cu2+, Co2+ and Ni2+ ions was endothermic, while the Ag+ adsorption was exothermic. • Ag+ adsorption was reduced from single-compound to quaternary system. Quaternary adsorption of Cu2+, Co2+, Ni2+ and Ag+ ions on an adsorbent obtained from the alkaline fusion of wastewater treatment sludge was investigated. Adsorption tests in both single-compound and quaternary systems were carried out and the analysis of adsorption mechanism was done by the application of a new quaternary model. This model was developed from a general methodology based on the application of grand canonical ensemble in statistical physics. This adsorbent was characterized by different analytical techniques. Experimental data showed that the adsorption of Cu2+, Co2+and Ni2+ ions was endothermic, while the Ag+ adsorption was exothermic. Ag+ adsorption was significantly reduced from single-compound to quaternary system due to the competitive effect caused by the other divalent ions, while the adsorption capacities of Cu2+, Co2+ and Ni2+ were not significantly affected in the multicomponent solution. A significant competitive effect of Cu2+, Co2+ and Ni2+ ions on the adsorption of Ag+ ions occurred. Modelling analysis showed that the adsorption of Cu2+, Co2+ and Ni2+ ions was a multi-ionic process at all tested temperatures, while the adsorption of Ag+ was a multi-ionic process only at low temperatures (298 and 308 K). Finally, the statistical physics model confirmed that the adsorption energies corresponded to physical interactions forces and the water molecule adsorption played a relevant role during the removal of these trace metals. [ABSTRACT FROM AUTHOR]

Adsorption of two organic pollutants (2-nitrophenol: 2-NRP and ketoprofen: KTP) on activated carbon produced from wastes deriving from a winery industry is investigated in the paper. Experimental data retrieved at T = 298–328 K indicate that, in the investigated equilibrium concentrations, a saturation phenomenon is reached for ketoprofen, while for 2-nitrophenol steeper curves are observed. For both the adsorbates, an increase in temperature determines a reduction of adsorption capacity. A modelling analysis via statistic physics models demonstrates that a double layer model is perfectly suitable to describe the adsorption mechanisms of both the investigated adsorbates. In light of the number of bonded molecules per adsorption site, the inclination of both the molecules upon adsorption is described. The obtained results suggest that they are adsorbed via both parallel and non parallel orientations, depending on the systems and temperature. Adsorption capacity variation is controlled by the number of bonded molecules per adsorption site and the density of receptor sites. Adsorption energy results show that physical interactions are responsible of the adsorption of both the pollutants. Finally, the results demonstrate that our adsorbent has an outstanding adsorption capacity which makes it promising for water depollution. • An activated carbon was employed to study the adsorption of 2-nitrophenol and ketoprofen. • Characterization of this adsorbent via numerous techniques was performed. • The adsorption mechanism was interpreted an advanced modelling. • The adsorbent has an outstanding adsorption capacity. [ABSTRACT FROM AUTHOR]

The goal of this work is the study of the adsorption of Diclofenac (DCF) on a magnetic composite made by metal oxide dispersion onto chitosan (ZnFe 2 O 4 /CMC). The adsorption isotherms at four temperatures (298, 308,318 and 328 K) and pH = 3 are interpreted in the light of an adsorption model derived from the statistical physics formalism, which includes the calculation of physicochemical parameters with defined physical meaning. Specifically, the adsorption process is interpreted in light of the number of DCF molecules adsorbed per site (n), which increases with temperature, and the density of receptor sites (N M), which shows a similar trend. The values of the calculated adsorption energy (ΔE 1 and ΔE 2) confirmed that the interaction between the DCF molecules and ZnFe 2 O 4 /CMC takes place via physical forces. Overall, the hydrogen bonds are identified as the main bonding interactions of DCF molecules on the ZnFe 2 O 4 /CMC surface. Interestingly, thermodynamic potential functions are determined for a complete adsorption characterization, which included also the adsorption energy distribution (AED) determination of DCF adsorption onto the ZnFe 2 O 4 /CMC. • Modelling of adsorption isotherms of Diclofenac (DCF) on a magnetic composite. • Steric and energetic parameters were interpreted. • Thermodynamic study was developed and interpreted in the paper. • AED is involved in the adsorption of Diclofenac (DCF) on a magnetic composite. [ABSTRACT FROM AUTHOR]

• Thermal treatment enables the generation of new micropores for activated carbon. • Activated carbon prepared from biomass exhibits excellent methylene blue removal. • Statistical physics approach showed that MB lies parallel on the adsorbents. • Isosteric heat of adsorption allows to investigate the surface heterogeneity. • MEP map and Fukui index highlight the adsorption reactive sites. The fundamental phenomena involved in methylene blue adsorption onto three different activated carbons (a raw adsorbent and two samples derived from either chemical or thermal treatment of the raw sample) are elucidated by coupling different multi-physics modeling approaches. Statistical physics approach leads to understand that methylene blue adsorption is mainly affected by the porosity of sorbents rather than their functional groups. Electrostatic interactions, Van der Waals forces or hydrogen bonding might occur between dye cations and carboxylate anions on adsorbent surface. The quantum chemical calculations suggest that dispersive interactions and pore characteristics of the activated carbon derived from thermal treatment predominantly contribute. The investigated reactive sites show that the same preferable sites for both electrophilic and nucleophilic attacks are detected for the sample derived from thermal treatment, allowing explaining the best performances of this adsorbent. Finally, the most stable energy configuration of methylene blue adsorption on activated carbon is obtained by Monte Carlo simulations. Image, graphical abstract [ABSTRACT FROM AUTHOR]

This study investigates the n-pentane adsorption performances on different activated carbons both as raw and modified by means of either chemical (amination with ammonium hydroxide) or thermal (carbonization at 1273 K) treatments. The raw, chemically and physically modified activated carbons were tested for n-pentane adsorption at 261 K in a volumetric apparatus. Maximum adsorption capacity values of 13, 11.7 and 9.1 μmol g−1 were obtained for the thermally, chemically and raw activated carbons, respectively, thus testifying the effectiveness of the treatment methods in improving the n-pentane adsorption capacity of the parent sorbent, due to an increase in the content of both acidic and basic functional groups. On the other hand, at low n-pentane partial pressures the volume of ultramicropores appears the ruling faction in determining a higher sorbent capture capacity. Kinetic adsorption data were successfully modelled according to the fractal-like Vermeulen model, and the outcomes suggested a more marked time-dependence of the intraparticle diffusivity for the chemically treated sample, likely related to a greater surface heterogeneity of this sample. Immersion enthalpy data also suggested that weaker adsorbate-adsorbent interactions promote a faster diffusion process. Volumetric apparatus for gases adsorption: 1. Thermostat. 2. Thermostat controller. 3. Variac transformer. 4. Cell sample holder with activated carbon. 5. Valve to the sample holder. 6. Adsorbate holder. 7. Valve to the solvent holder. 8. Equilibrium tank. 9. Diffuser. 10. Vacuum pump. 11. Pressure controller # 1. 12. Pressure controller # 2. 13. Control panel. 14. Voltmeter. 15. Data register. Image 1 • The adsorption of n-pentane onto modified activated carbons is investigated. • Chemical and physical adsorbent modifications influence n-pentane capture capacity. • Basic and acidic oxygen groups on activated carbon favor n-pentane adsorption. • Fractal-like Vermeulen equation describes n-pentane adsorption kinetic evolution. • Intraparticle transport is influenced by adsorbate/adsorbent interaction energy. [ABSTRACT FROM AUTHOR]

In this work, the effect of salts on the adsorption of a textile pollutant (Methylene blue: MB) on comminuted raw avocado seeds (CRAS) was interpreted via a physical monolayer model (PMM). To this aim, ten MB adsorption isotherms were determined at 25 °C and pH 10 in the presence of the next salts: NaCl, Na 2 CO 3 , Na 2 SO 3 , NaHCO 3, C 6 H 5 Na 3 O 7 , NaHSO 3, Na 2 B 4 O 7 ·10H 2 O, Na 2 S 2 O 3, NaNO 2 and Na 2 HPO 4. Under the same experimental conditions, a further adsorption isotherm was also determined without any salt addition and taken as reference data. In order to achieve a theoretical interpretation of the experimental data and to address the effect of salts on adsorption mechanism, a physical monolayer model (PMM) was applied to all the retrieved data. The model showed that Na 2 CO 3 , NaHCO 3 , Na 2 B 4 O 7 , Na 2 S 2 O 3 , and NaNO 2 salts have no effect on the adsorption of MB dye, while the presence of NaCl, Na 2 SO 3 , C 6 H 5 Na 3 O 7 , NaHSO 3 and Na 2 HPO 4 salts in the solution caused a slight decrement of MB adsorption capacity due to a competitive effect between MB dye and salts on CRAS adsorption site. The modeling analysis showed that MB was adsorbed with a mixed parallel and non-parallel orientation on CRAS adsorbent surface. Moreover, the adsorption energies varied from 19.44 to 22.36 kJ/mol in tested systems. Adsorption energy values revealed that the process evolved via a physical adsorption, regardless the salt present in solution. All the investigated salts did not functionalize the CRAS adsorbent surface and also did not change the interaction energy between MB molecules and the adsorbent receptor sites. The interpretation of all the model parameters contributed to explain the adsorption mechanism of MB dye on CRAS. Specifically, the effect of salt on the reduction of MB adsorption capacity seems to be likely due to both steric hindrance effect and to MB molecule aggregation hindrance exerted by the salts, which prevented the formation of subsequent MB adsorbed layers, thus limiting its overall adsorption capacity. • MB dye adsorption mechanism was analyzed via statistical physical modeling. • Salts effect on dye adsorption on a lignocellulosic biomass was performed. • Description of the adsorption mechanism through an energetic factor. [ABSTRACT FROM AUTHOR]

• Adsorption of Indigotine blue dye (IBD) on the CoFe 2 O 4 /CMC was studied. • Adsorption mechanism was analyzed and interpreted with the multilayer statistical physics model. • Adsorption occurs by aggregation of IBD molecules on the CoFe 2 O 4 /CMC surface. • Adsorption of IBD onto CoFe 2 O 4 /CMC is endothermic, spontaneous and multilayer. An advanced model is applied to analytically explore the adsorption mechanism of Indigotine blue dye (IBD) onto a CoFe 2 O 4 /chitosan magnetic composite (CoFe 2 O 4 /CMC). Contrary to the classical adsorption models, the model is defined starting from the statistical physics theory and it is a generalized model containing numerous parameters having a defined physical meaning. Experimental evidences based on equilibrium data at four temperatures (298−328 K) are analyzed for a useful analytical interpretation. The analysis of the data via the advanced model indicates that the number of IBD linked per CoFe 2 O 4 /CMC active site (n) varied from 3.65 to 3.83, also demonstrating that the orientation (adsorption geometry) of the IBD dye on CoFe 2 O 4 /CMC surface is angled and affected by the temperature. Based on these values, it can be deduced that the adsorption mechanism at all the investigated temperatures is a multi-molecular process. It is also demonstrated that an increment in the temperature leads to a positive evolution of the adsorption capacity (Q sat) from 224.81 mg/g at T = 298 K to 289.87 mg/g at T = 328 K, testifying that the adsorption process is overall endothermic. This theoretical evidence is corroborated by the estimation of the adsorption energies (Δ E 1 a and Δ E 2 a), which indicated that physical interactions between IBD molecules and the CoFe 2 O 4 /CMC receptor sites and among IBD-IBD molecules take place. Finally, three thermodynamic parameters are determined for a further insight into the interpretation of the adsorption mechanism. The adsorption configurational entropy (S ad) evolution allows confirming the occurrence of different adsorbed layers (N C = 1+N 2), while the Gibbs adsorption free energy (G ad) confirmed that the process is spontaneous. [ABSTRACT FROM AUTHOR]