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The possibility of using three types of NaOH-treated tea residues (green tea, pu-erh, and tieguanyin) as low-cost adsorbents for Cr(VI) treatment was investigated. The surface charge, composition, morphology, structure, and functional groups in the obtained biosorbents were characterized by pHzpc, cellulose content, SEM, BET, XRD, and FTIR spectroscopy. The nonlinear pseudo-first-order, pseudo-second-order, and Elovich models were used to investigate adsorption kinetics at various initial concentrations. The adsorption processes were more consistent with the pseudo-second-order kinetic model in the range of 5-50 mg L-1. The adsorption isotherm at 298 K was described using the nonlinear Langmuir, Freundlich, Temkin-Pyzhev, and Dubinin-Radushkevich models, indicating that the process was favorable and complex with maximum adsorption amounts of 6.15, 19.50, and 12.31 mg g-1 for green tea, pu-erh, and tieguanyin residues, respectively. Thermodynamic analysis revealed that the adsorption was a spontaneous, endothermic process. The results demonstrated that all materials had the potential to successfully remove Cr(VI) from the aqueous solution. [ABSTRACT FROM AUTHOR]

Chromium pollution represents a worldwide concern due to its high toxicity and bioaccumulation in organisms and ecosystems. An interesting material to remove metal ions from water is a whey-protein-based material elaborated by electrospinning, which is an emerging method to produce adsorbent membranes with diverse applications. The aim of this study was to prepare an adsorbent membrane of whey protein isolate (WPI) and polycaprolactone (PCL) by electrospinning to remove chromium ions from water. The adsorbent membrane was synthesized by a central composed design denaturing WPI using 2-Mercaptoethanol and mixing it with PCL to produce electrospun nanofibers. The adsorbent membrane was characterized by denaturation, Scanning Electron Microscope, Fourier-Transform Infrared Spectroscopy, Contact Angle, Thermogravimetric Analysis, and X-ray Photoelectron Spectrometry. The adsorption properties of this membrane were assessed in the removal of chromium. The removal performance of the membrane was enhanced by an increase in temperature showing an endothermic adsorption process. The adsorption process of chromium ions onto the nanofiber membrane followed the Sips adsorption isotherm, while the adsorption kinetics followed a pseudo-second kinetics where the maximum adsorption capacity was 31.0 mg/g at 30 °C and pH 2. This work provides a novel method to fabricate a hybrid membrane with amyloid-type fibrils of WPI and PCL, which is a promising adsorbent to remove heavy metal ions from water. [ABSTRACT FROM AUTHOR]

A theoretical physicochemical and thermodynamic investigation of the adsorption of heavy metals Zn2+, Cd2+, Ni2+, and Cu2+on carbon-based adsorbents was performed with statistical physics fundaments. Particularly, the experimental adsorption isotherms of heavy metal removal, at 30°C and pH 5, using adsorbents obtained from the pyrolysis of three biomasses (cauliflower cores, broccoli stalks, and coconut shell) were modelled and interpreted with a homogeneous statistical physics adsorption model. Calculations indicated that the heavy metal adsorption with these carbon-based materials was a multi-ionic process where several ions interact simultaneously with the same carboxylic functional group on the adsorbent surface. Adsorption capacities for these metal ions and adsorbents were correlated with electronegativity theory, which established that the adsorbate with the highest electronegativity was more readily adsorbed by the carboxylic functional groups available on the adsorbent surfaces. Also, the chemical compositions of biomass precursors explained achieved adsorption capacities for these metallic ions. The best adsorbent for heavy metal removal was obtained from CC biomass pyrolysis. Calculated adsorption energies for heavy metal removal could be associated with physisorption-type forces. Finally, the adsorption mechanism analysis was complemented with the determination of adsorption thermodynamic functions using the statistical physics. [ABSTRACT FROM AUTHOR]

Methane adsorption isotherm experiments on semianthracite (2.00-2.33% R o , max ) collected from the Xin'an coal mine, Henan Province, China, were conducted to investigate the effects of pore structure, coal quality, coal maceral, and coal rank on methane adsorption capacity with applications of univariate and multivariate analyses. Methane adsorption capacity varies significantly from 12.03 to 28.40 cm3/g. In univariate analysis, methane adsorption capacity has a strong positive correlation with pore specific surface area, weak positive correlations with pore volume and ash content, and weak negative correlations with moisture content and inertinite content. No correlation is observed between methane adsorption capacity and coal rank. In multivariate analysis, the mathematical model of methane adsorption capacity affected by the combined individual variables is established based on quantification theory I. There are similarities and differences between the two analyses. The similarities are that pore specific surface area has the greatest contribution to methane adsorption capacity, while coal rank has the least contribution. The differences are reflected in two aspects. Firstly, the other influencing factors contribute differently to methane adsorption capacity. Secondly, the positive or negative correlations of some influencing factors present the opposite. The mathematic model synthetically covers the combined effects of the influencing factors, which is more representative in evaluating methane adsorption capacity. [ABSTRACT FROM AUTHOR]

The separation of ethanol, propanol, and butanol from aqueous solutions was studied using adsorption on bone char. Adsorption kinetics and thermodynamic parameters of this separation method were studied at different conditions of pH and temperature. Results showed that the maximum adsorption capacities of these bioalcohols were obtained at pH 6 and 20°C. An exothermic separation was identified, which can be mainly associated to hydrophobic interactions between bone char surface and bioalcohols. Binary adsorption studies were also performed using mixtures of these bioalcohols. An antagonistic adsorption was observed for all bioalcohols where the ethanol and propanol separation was significantly affected by butanol. A model based on an artificial neural network was proposed to correlate both single and binary adsorption isotherms of these bioalcohols with bone char. It was concluded that the bone char could be an interesting adsorbent for the sustainable separation and recovery of bioalcohols from fermentation broths, which are actually considered emerging liquid biofuels and relevant industrial chemicals. [ABSTRACT FROM AUTHOR]

Magnetite nanoparticles (MNPs) synthesized from heated basalt were used to support a biocomposite prepared from muscovite (Mus) and carbohydrate polymer starch (St). The developed Mus/St/MNPs composite was characterized by XRD, FTIR, FESEM, TGA, DSC, and Zeta potential techniques. This multifunctional composite showed outstanding adsorption properties for hexavalent chromium (Cr(VI)) and methyl orange (MO) removal at 25–55 °C and pH 3.0. The adsorption isotherms were fitted to Langmuir model for Cr(VI) and Freundlich equation for MO. To understand microscopically these systems and to analyze their adsorption geometry and interactions mechanism, three statistical physics models were utilized. Theoretical calculations indicated that Cr(VI) ions were adsorbed on composite surface presenting a combination of horizontal and vertical positions, while the aggregated MO molecules displayed a non-parallel adsorption orientation and multi–interactions mechanism. The saturation adsorption capacity increased from 243.37 to 371.59 mg/g for Cr(VI) and 409.29 to 457.62 mg/g for MO at 25 and 55 °C (i.e., endothermic interactions). Cr(VI) and MO adsorption on Mus/St/MNPs was controlled by van der Waals forces, hydrogen bonding, and electrostatic interactions where the calculated adsorption energies were 12.5–30.62 kJ/mol. The utilized adsorbent was easily reactivated and reused several times where regenerated Mus/St/MNPs composite showed nearly 79 % of Cr(VI) and 85 % of MO adsorption capacities even after the fourth adsorption–desorption cycle. This study contributes to understand the physicochemical factors of Cr(VI) and MO adsorption on multifunctional adsorbents like MNPs/carbohydrate polymers/aluminosilicates interface. [ABSTRACT FROM AUTHOR]

Manganese–containing mica (Mn–mica) was synthesized at 200 °C/96 h using Mn–carbonate, Al–nitrate, silicic acid, and high KOH concentration under hydrothermal conditions. Mn–mica was characterized and tested as a new adsorbent for the removal of methyl orange (MO) dye from aqueous solutions. Compared to naturally occurring mica, the Mn–mica with manganese in the octahedral sheet resulted in enhanced MO uptake by four times at pH 3.0 and 25 °C. The pseudo–second order equation for kinetics and Freundlich equation for adsorption isotherm fitted well to the experimental data at all adsorption temperatures (i.e., 25, 40 and 55 °C). The decrease of Langmuir uptake capacity from 107.3 to 92.76 mg·g−1 within the temperature range of 25–55 °C suggested that MO adsorption is an exothermic process. The role of manganese in MO selectivity and the adsorption mechanism was analyzed via the physicochemical parameters of a multilayer adsorption model. The aggregated number of MO ions per Mn–mica active site (n) was superior to unity at all temperatures signifying a vertical geometry and a mechanism of multi–interactions. The active sites number (DM) of Mn–mica and the total removed MO layers (Nt) slightly changed with temperature. The decrease in the MO adsorption capacities (Qsat = n·DM·Nt) from 190.44 to 140.33 mg·g−1 in the temperature range of 25–55 °C was mainly controlled by the n parameter. The results of adsorption energies revealed that MO uptake was an exothermic (i.e., negative ΔE values) and a physisorption process (ΔE < 40 kJ mol −1). Accordingly, the adsorption of MO onto Mn–mica was governed by the number of active sites and the adsorption energy. This study offers insights into the manganese control of the interactions between MO ions and Mn–mica active sites. [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]

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]

Abstract A theoretical study of phenol adsorption on microwave-assisted activated carbons has been performed using statistical physics models. These models have been selected based on the adsorption isotherms profiles and applied to obtain a detailed explanation of the phenol adsorption mechanism and to understand the adsorbent performance. In particular, the phenol adsorption was analyzed using a model that assumed two layers with different adsorption energies. Modelling results, based on the number of phenol molecules adsorbed per site, suggested that two relative positions of phenol adsorbed on activated carbon surface could occur. Besides, at high temperatures, an aggregation phenomenon of phenol molecules was also hypothesized and interpreted. This adsorption process was associated to two adsorption energies that characterized the interactions between phenol – adsorbent and phenol – phenol molecules. The analysis of adsorption energies indicated that all interactions were weak resulting in a physisorption process. Highlights • Theoretical study of phenol adsorption on microwave-assisted activated carbons. • Application of the double layer model with two energies on adsorption isotherms. • Description of the adsorption geometry of phenol molecule. [ABSTRACT FROM AUTHOR]

[Display omitted] • Adsorption and recovery of butanol, propanol and ethanol from fertmentation wort. • The highest adsorption capacities for butanol, followed by propanol and ethanol. • Sips, Liu, and Hill best fitted the adsorption isotherms. • The interaction between bioalcohols and ACRS indicates that a physisorption. • The recovery of these bioalcohols from the use of ACRS is promising. This paper reports the study about the potential of activated carbon based on residual sludge from a beverage industry (ACRS) for the adsorption and recovery of butanol, propanol, and ethanol, at different temperatures through equilibrium isotherms. The results made it possible to verify that the highest adsorption capacities in ACRS were obtained for butanol with 24.64 mmol g−1, followed by propanol (19.31 mmol g−1) and ethanol (16.48 mmol g−1). This process was significantly and positively affected by the increase in temperature, giving it an endothermic character. Sips, Liu, and Hill best fitted the adsorption isotherms. The interaction analysis between bioalcohols and ACRS indicates that physisorption occurred. In conclusion, the recovery of these bioalcohols from the use of ACRS is promising given its ecological character, impacting the adsorption process's viability and low cost. [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]

Natural and carbonized pine-fruit shells (NPFS, and CPFS) were employed to study the adsorption of remazol black B dye (RBB) from aqueous solution. A theoretical analysis of the adsorption systems was performed via the statistical physics modeling of the experimental dye adsorption isotherms at 298–323 K and pH 3. Results showed that the adsorbent CPFS outperformed adsorbent NFPS for water decolorization. A multilayer advanced statistical physics model, which included monolayer and double layer adsorption scenarios, was employed to understand the RBB dye adsorption mechanism. Modeling analysis suggested that around two and three adsorbate layers were formed depending on the adsorption (i.e., adsorbent + dye RBB) systems at high temperature. The calculation of the linked dye molecules per leading adsorption site varied from 0.83 to 1.86 and from 1.10 to 2.88 for systems RBB-NPFS and RBB-CPFS, respectively. These results suggested that the dye RBB dye could be adsorbed on NPFS and CPFS surfaces via a non-horizontal orientation at tested operating conditions where the dye molecule aggregation phenomenon was present. Estimated adsorption energies confirmed an endothermic physisorption process for RBB dye removal. In summary, the statistical physics analysis provided a reliable interpretation of the adsorption mechanism of this textile pollutant on tested adsorbents. • Statistical physics analysis of the adsorption of dye remazol black B on pine-fruit shells was done. • Remazol black B adsorption mechanism was theoretically studied via isotherm modeling. • Remazol black B dye interacted with an inclined position on adsorbent surface. [ABSTRACT FROM AUTHOR]

• Single and binary adsorption of antibiotics on activated carbon was investigated. • Statistical physics modeling of antibiotics adsorption was performed. • Monolayer and competitive monolayer models explained the adsorption mechanism. • Antibiotic antagonistic adsorption was associated to statistical physics parameters. The adsorption mechanism of two antibiotics, namely amoxicillin (AMX) and tetracycline (TCN), on durian shell activated carbon (AC) was investigated in single and binary systems. Adsorption isotherms were determined under the same experimental conditions and they showed that the adsorption capacities of AMX were higher than those of TCN at all tested temperatures suggesting that this adsorbent preferred to remove AMX from the aqueous solution. It was also observed that all adsorption capacities decreased from single to binary systems, which was reasonably explained by an antagonistic adsorption between AMX and TCN on the active sites of AC creating an inhibition effect between these adsorbates. Monolayer and competitive monolayer models were developed via statistical physics theory and they were applied to explain and understand the adsorption mechanism of AMX and TCN via steric and energetic parameters. Results suggested that the parallel and non-parallel orientations of both antibiotics on the adsorbent surface of AC could be possible at tested experimental conditions. Modeling results demonstrated that the numbers of accepted antibiotic molecules per active site of AC varied with linear and inverse trends in single and binary systems, respectively, at all tested temperatures thus corroborating the adsorption inhibition effect caused by both adsorbates. An estimation of adsorption energies was also performed to describe and characterize the interactions between both antibiotics and AC surface. The assessment of the parameters of statistical physics models contributed to the explanation of the single and binary adsorption mechanisms of these water pollutants. [ABSTRACT FROM AUTHOR]