Search

For adsorption chillers or desiccant systems, thin film adsorbents coated on heat exchanger surfaces contribute to enhance adsorption/desorption rate of vapor, due to low thermal resistance leading to quick exothermic/endothermic heat exchange with external cooling/hot fluid. They enable to downsize adsorbent heat exchanger in systems. In the present study, a silica gel thin film synthesized on aluminum plate was proposed as a novel adsorbent. Pore structure of this new adsorbent changed during 15 months after synthesis: pore diameter enlarging and specific surface area decreasing. Upon this, the influence of time elapsed after synthesis on equilibrium adsorption of water vapor was examined under various adsorbing conditions until 22 months after synthesis. The equilibrium showed S-shape curve characteristics with respect to relative humidity, and decreased monotonously with elapsed time in wide relative humidity range, which was attributed to the pore structure change. Decreasing of equilibrium was not seen after 15 months from synthesis, that is, stabilization was attained. The equilibrium reduction in low relative humidity range was analyzed with the BET equation. Moreover, relative humidity of capillary condensation occurring was compared to the Kelvin equation. Finally, the equilibrium was formulated which reproduced well the measurements over the entire relative humidity range. [Display omitted] • Vapor adsorption on a silica gel thin film synthesized directly on an aluminum plate. • Long-term data acquisition of equilibrium adsorption amount after the film synthesis. • Equilibrium decreased monotonously with time elapse due to the pore structure change. • Decrease finished after 15 months from film synthesis or with 4 ad/desorption cycles. • Equilibrium was formulated to predict chiller or desiccant performance with the film. [ABSTRACT FROM AUTHOR]

[Display omitted] • Deep investigation into activated carbon (AC) for diclofenac potassium (DP) removal. • Statistical physics and experimental studies of AC-DP interaction. • The DP removal process forms a double layer in AC with a single energy involved. • Physical interactions predominate, and higher temperatures enhance removal. This study aims to contribute to understanding the removal processes of diclofenac potassium (DP) medicine in wastewater treatment systems, employing activated carbon (AC) as an adsorbent. To achieve this goal, a multidisciplinary approach was adopted, integrating experimental and theoretical analyses of equilibrium data regarding the adsorption of DP on AC. Five statistical physics models were applied to determine the model best for the adsorption process. The selection of the most appropriate model considered both the performance of the models and the analysis of the estimated parameters. Statistically, all models exhibited satisfactory results. However, when analyzing the estimated parameters, the double-layer model with single adsorption energy emerged as the most suitable model to describe the analyzed process. Based on the chosen model's parameters, we observed that as the temperature increases, the number of active sites occupied during adsorption and their availability on the adsorbent also increases. However, the number of available adsorption sites decreases as the temperature rises. The half-saturation concentration, in turn, increases with increasing temperature, suggesting that the process is favored when temperatures above room temperature are used. Additionally, higher temperatures provide better removal results, indicating that DP molecules' non-parallel and parallel orientations on the AC surface favor the adsorption process. Finally, our combined results led to the proposal of a mechanism for DP adsorption on AC, which is based on physical adsorption interactions between adsorbate-adsorbent and adsorbate–adsorbate. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cellulose fibers/ohillipsite composite was used in the uptake of different Se ions. • The Q sat of Se (VI) and Se(IV) are 144.7 mg/g and 196.4 mg/g, respectively. • The uptake behavior of the Se ions follow Langmuir and Pseudo-First order models. • The uptake energies (<40 kJ/mol) suggesting physisorption reactions. • The uptake of the three Se ions occurred by exothermic and spontaneous reactions. Natural zeolite of the phillipsite phase was integrated into biocomposite with cellulose fibers (CF/Ph) and characterized as an effective and environmental adsorbent for both selenite (Se (IV)) and selenate (Se (VI)). The retention studies were performed based on the experimental factors in addition to both classic and advanced equilibrium modeling. The composite showed enhanced retention properties for both Se (IV) (196.4 mg/g) and Se (VI) (144.7 mg/g) as compared to raw phillipsite (Se (IV) (142.13 mg/g) and Se (VI) (113 mg/g)) and cellulose (Se (IV) (42.5 mg/g) and Se (VI) (6.4 mg/g)). Based on the synergetic parameters, the integration process enhanced the quantities of the existing active sites at a considerable rate (Nm = 57.3 mg/g (Se (IV)) and 48 mg/g (Se (VI))) as compared to phillipsite and cellulose. The number of the two adsorbed selenium ions is about 4, demonstrating multi-ionic uptake of them in vertical orientations. The energetic investigation (9–11 kJ/mol) validates the retention of two forms of selenium by mainly physical mechanistic processes (dipole bonding and/or van der Waals forces and/or hydrogen bonding). Regarding the thermodynamic functions, the reported behaviors demonstrate the exothermic and spontaneous uptake of both selenite (Se (IV)) and selenate (Se (VI)) by CF/Ph. Also, the composite possesses remarkable recyclability and higher efficiency as compared to several studied structures and can be applied in realistic remediation process even in existence of other chemical contaminants. [ABSTRACT FROM AUTHOR]

• PFAS adsorbed in GAC was maximumly extracted by 60-min methanol-sonication method. • Carboxylic PFAS with log D ow values <1was greater in deeper parts of GAC filter. • Once adsorbed, short-chain PFAS desorbed and migrated downward in GAC filter. • Desorption potential was defined as desorption to PFAS-free water per unit GAC mass. • The ratio of the desorption potential to load was lower for more hydrophobic PFAS. Activated carbon adsorption is an effective method for removing perfluoroalkyl substances (PFAS) from water. However, the observation that higher concentrations of PFAS are observed after treatment than before (i.e., desorption) is an important, unsolved issue. In this study, to elucidate PFAS desorption and its relationship with PFAS properties, we conducted solvent extraction and long-term desorption experiments using granular activated carbon (GAC) that had been loaded with PFAS in two actual drinking water treatment plants. The amount of PFAS extracted from GAC depended on the depth in the GAC filter; longer-chain and hydrophobic PFAS were present in relatively higher amounts in the shallow part compared to the deep part of the GAC filter, whereas shorter-chain and hydrophilic PFAS were present in relatively higher amounts in the deep part compared to the shallow part. This pattern was probably due to a chromatographic effect by which hydrophilic PFAS adsorbed once, subsequently desorbed, and migrated from the shallow part of the GAC filter to the deeper part. The desorption potential of PFAS to water (i.e., the maximum amount of PFAS desorbed to water per unit mass of GAC) was estimated by conducting long-term bottle-point desorption tests and analyzing the relationship between the equilibrium water-phase concentration of PFAS in a bottle containing GAC and the amount of PFAS desorbed to water per unit GAC mass. The desorption ratio (ratio of desorption potential to loading) was the highest for PFAS for which the logarithm of the octanol/water distribution coefficient (Log D OW) ranged from −1 to 1. The implication was that most of those PFAS removed by GAC were likely to return to the water as the external water-phase concentrations dropped. The decrease of the desorption ratio to 20 % as Log D OW increased suggested irreversible adsorption due to hydrophobic affinity. [Display omitted] [ABSTRACT FROM AUTHOR]

Magnesium-trapped hydroxyapatite (Mg.HP) was hybridized with cellulose fiber to produce a bio-composite (CLF/HP) with enhanced adsorption affinities for two types of toxic pesticides (chlorpyrifos (CF) and omethoate (OM)). The enhancement influence of the hybridized cellulose on the adsorption performances of Mg.HP was illustrated based on the determined steric and energetic factors. The computed CF and OM adsorption performances of CLF/HP during the saturation phases are 279.8 mg/g and 317.9 mg/g, respectively, which are significantly higher than the determined values using Mg/HP (143.4 mg/g (CF) and 145.3 mg/g (OM)). The steric analysis demonstrates a strong impact of the hybridization process on the reactivity of the surface of the composite. While CLF/HP reflects effective uptake site densities (Nm) of 93.3 mg/g (CF) and 135.3 mg/g (OM), the estimated values for Mg.HP are 51.2 mg/g (CF) and 46.11 mg/g (OM), which explain the reported enhancement in the adsorption performances of the composite. The capacity of each uptake site to be occupied with more than one molecule (n (CF) = 3–3.74 and n (OM) = 2.35–3.54) suggests multimolecular uptake. The energetic factors suggested physical mechanistic processes of spontaneous and exothermic behaviors either during the uptake of CF or OM. [ABSTRACT FROM AUTHOR]

• Vapor pressure correlations compiled for 38 refrigerants and 262 working pairs. • Refrigerants include water, ammonia, CO 2 , alcohols, HFCs, HFOs, and hydrocarbons. • Generalized vapor pressure functional forms enable cross comparisons. • Correlation valid ranges are provided where available. • An enabling dataset for thermodynamic simulations of sorption systems. Sorption devices are important tools for the efficient utilization of fuels and waste heat. Amid a tremendous diversity of cycles and applications, all sorption systems have an equilibrium vapor pressure that depends on the sorbent temperature and composition. The vapor pressure properties of working fluids are reported in the literature in a variety of ways, which impedes wide-ranging cross comparisons or screening studies for novel applications. This work compiles equilibrium vapor pressure properties for 123 liquid absorbents with 31 absorbates and 139 solid adsorbents with 16 adsorbates. The adsorption pairs are represented with six functional forms. Most of the absorption pairs are represented with 10 functional forms, plus several that are represented with custom empirical equations. Because the functional forms used in the literature vary widely, in this work each functional form was generalized. This paper is designed to facilitate comparisons of working fluid properties for screening studies, provide a quick reference to existing research, and present a framework for standardizing the reportage of vapor pressure equilibrium data for existing and future working pairs. [ABSTRACT FROM AUTHOR]

• Novel sodalite form produced from muscovite for the removal of inorganic se ions. • The q max of se (VI) and Se(IV) by sodalite are 149 mg/g and 255 mg/g, respectively. • The uptake behavior of both ions follow langmuir and pseudo-second order models. • The uptake energies of the se ions (< 8 kJ/mol) suggesting physisorption reactions. • The uptake of the se ions occurred by exothermic and spontaneous reactions. Muscovite flakes were applied in the synthesis of three types of sodalite with different morphologies by hydrothermal processes for 24 h, 48 h, and 72 h. The synthetic sample after 72 h (S-72) showed the best surface area (105 m2/g), morphological features, and ion exchange capacity (71.3 meq/100 g). The S-72 was applied for effective retention of both Se (VI) and Se (IV) ions in batch adsorption studies. The retention capacities of Se (VI) and Se (IV) ions using S-72 sodalite are 149 mg/g and 255 mg/g, respectively after an equilibration time of 300 min and 360 min. The kinetic assessment suggested Pseudo-second order behavior for the retention of both Se (VI) and Se (IV). The equilibrium studies of their retention reactions demonstrated Langmuir isotherm behavior and monolayer form for the homogeneously adsorbed Se (VI) and Se (IV) ions on the surface of sodalite. The Gaussian energies (> 8 KJ/mol), enthalpies (< 80 KJ/mol), and Gibbs free energies (< 40 KJ/mol) for both Se (VI) and Se (IV) suggested physical reactions related to coulumbic attractive forces or ion exchange process. Based on the thermodynamic investigations, the Se (VI) and Se (IV) retention reactions are of exothermic, favourable, and spontaneous properties. The removal percentages of Se (VI) and Se (IV) ions by sodalite in the coexisting of Pb2+, Zn2+, PO 4 −3, and NH4+ ions are of significant values either in pH 2 or pH 7. [Display omitted] [ABSTRACT FROM AUTHOR]

The widespread of mixtures formed by polyelectrolytes and oppositely charged surfactants in different industrial sectors requires a thorough understanding of the physicochemical bases governing their interactions. These interactions lead to the formation of polyelectrolyte–surfactant aggregates, with the presence of such aggregates in the aqueous mixtures impacting decisively on their bulk and interfacial properties. Furthermore, the broad range of morphologies, sizes, and properties of the aggregates makes it necessary to obtain a comprehensive picture describing their behavior and properties to be able to exploit their possible applications. This review is aimed to shed light on some of the most relevant physicochemical aspects involved in the complexation process of polyelectrolyte–surfactant mixtures, paying special attention to the formation of nonequilibrium states (kinetically trapped aggregates), and how these impact on the interaction of the complexes with interfaces, both fluid/fluid and solid/fluid. Image 1 • Oppositely charged polyelectrolyte-surfactant form complex in solution. • One-phase and phase-separated systems can be defined as the composition of the mixtures is changed. • Thermodynamic considerations do not account for the whole description of the physicochemical behavior of polyelectrolyte–surfactant mixtures. • Nonequilibrium effects impact decisively in the behavior of polyelectrolyte–surfactant mixtures. • Complexes formed in solution affect the properties of interfaces on their adsorption. [ABSTRACT FROM AUTHOR]

• Analysing adsorption and thermal regeneration of water on 13X by Equilibrium Theory. • Proposing optimal hot purge gas temperature in regenerating a humid adsorption column. • Validating the proposed guideline with full numerical simulation and ideal work calculation. A Thermal Swing Adsorption (TSA) process has been widely commercialised for its application to air drying. In designing an air-drying TSA, zeolite 13X is chosen as a desiccant when required to produce a very low dew point dry air due to its highly nonlinear, favourable isotherm. It is essential to make use of an external hot purge gas in producing such an extremely low dew point dry air, as the column has to be regenerated thoroughly for the next adsorption step. In case of the externally heated TSA, usage of a hot purge gas gives rise to huge energy consumption. Also the cycle time has to be made as short as possible to enhance the bed productivity. To optimise this energy-intensive process, it is crucial to find an optimal hot purge gas temperature at which the column can be regenerated as quickly as possible with less energy consumed. In this study, Equilibrium Theory approach was taken to analyse the thermal regeneration breakthrough of a zeolite 13X column saturated with a water vapour in which the equilibrium isotherm is estimated by Toth or Aranovich-Donohue isotherms. As a result of Equilibrium Theory analysis, it was found that the trailing front of a thermal regeneration breakthrough would exhibit a transition of the shape from simple to shock wave with increasing purge gas temperature. The purge gas temperature has to be chosen so that after thermal regeneration the targeted water vapour concentration remaining in the column lies within the concentration range occupied by the shock wave. A useful correlation that relates the targeted dew point of the remaining water vapour with the purge gas temperature was proposed. The presence of the optimal hot purge gas temperature estimated by Equilibrium Theory was validated by both full numerical simulation and ideal work consumption. [ABSTRACT FROM AUTHOR]

• Method proposed for diluted (constant velocity) and isothermal cases. • Adsorption breakthrough curves are integrated to capacity curves. • Capacity curves allow to obtain adsorbed quantities in equilibrium with intermediate zones. • Equilibria were obtained from breakthrough curves of alcohols on all-silica beta zeolite. • Two, instead of one, equilibrium points could be obtained from one breakthrough curve. Adsorption mixture equilibrium data remains challenging to obtain. An established technique is the adsorption breakthrough experiment where the final adsorbed capacities are determined. A graphical method to obtain adsorbed amounts from the intermediate plateaus in the breakthrough curves is proposed in this work. The method is proposed for isothermal, diluted breakthrough tests. Via an integrated capacity curve, the intermediate regions can be extrapolated to extract additional equilibrium points beyond the final state without the need for a multicomponent model. If the column is preloaded, the extra equilibrium points can correspond to multicomponent mixtures as multiple species can have non-zero intermediate concentration plateaus. The method is demonstrated on various simulated examples and then applied on breakthrough data from non-preloaded and preloaded columns of all-silica beta zeolite for diluted methanol/ethanol and diluted ethanol/isobutanol mixtures. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synthesis of CeIV-ZrIV-LaIII hybrid oxide (CZL) and characterizations. • Systematic F− and Cu(II) extraction from water with CZL. • Best fit pseudo-second-order kinetic model, implying the chemisorption mechanism. • High amounts of F− and Cu(II) extraction at optimized conditions were reported to be 213.99 and 61.52 mg g−1, respectively. • Combined coulombic and ion-exchange phenomena are the extraction mechanisms. We report herein the tailored preparation and characterization insight of hybrid CeIV-ZrIV-LaIII hydrous oxide (CZL) and application as a solid-phase extractor towards F− and Cu(II) to reduce water contamination levels. Obviously, characterization of the as-prepared sample was done using electron microscopy (TEM, SEM), energy-dispersive X-ray spectroscopy (EDS), Föurier transform infrared (FT-IR) spectroscopy, BET surface analyzer, powder X-ray diffraction (p-XRD), and Zeta meter and reported. The BET analysis indicates very high surface area 219.971 m2 g−1 and pore volume 0.1374 cm3 g−1 of CZL, the value get decreased after adsorbing the Cu(II) and F−, this indicates interior surface involved on the adsorption process. Transfer of F− and/Cu(II) from aqueous phases over the CZL surfaces was investigated at optimized pH adopting batch procedure. The parameters investigated are the effects of concentration, reaction time and co-existing ions. Kinetically seen distribution of both F− and Cu(II) agree best with the pseudo-second-order model. Fitness of the equilibrium data with isotherm models has confirmed almost monolayer surface coverage; and computed ΔH0, ΔS0, and ΔG0 have suggested the spontaneous nature of the reactions. The order of percentage of F− transfer declines in presence of ions occurring in water as HCO 3 − > PO 4 3− > SO 4 2− > NO 3 − > Cl−. The exhausted CZL material is regenerated using NaOH (pH 12) solution. At optimal circumstances, the CZL shows Langmuir monolayer capacity of 213.99 mg g−1 and 61.52 mg g−1 respectively, for F− and Cu(II), which are greater than previously reported some materials. Overall, the CZL is an efficient material for extracting F− and Cu(II) from their aqueous phases. [ABSTRACT FROM AUTHOR]

• The triazine-based porous polymers were developed by one-pot strategy under mild conditions. • The polymers had relatively high BET surface area and hierarchical porosity. • The Langmuir model described the equilibrium data well with the maximum capacity of 229.9 mg/g. • The Hg2+ concentration at the initial concentration of 6.0 ppm reduced to 4 ppb after 40 min. • The embedded carbonyl, triazine ring, and amino groups had strong chelating coordination with Hg2+. The triazine-based porous organic polymers were synthesized by a one-pot amidation polycondensation reaction and they were applied for Hg2+ removal from aqueous solution. The results showed that these polymers had high Brunauer-Emmett-Teller (BET) surface area (404–521 m2/g) and hierarchical porosity with dominated micropores and mesopores. The equilibrium data for Hg2+ adsorption followed the Langmuir model with the maximum capacity of 229.9 mg/g. The Hg2+ concentration at the initial concentration of 6.0 ppm reduced to 6 ppb after 20 min, verifying its fast and deep treatment of Hg2+ wastewater. The adsorption was rapid and the pseudo-second-order rate model characterized the kinetic data perfectly. Moreover, the polymers exhibited excellent selectivity, easy regeneration, and superior reusability, indicative of their outstanding performance for Hg2+ removal. Analysis of the adsorption mechanism revealed that the embedded carboxyl, triazine ring, and amino groups played significant role due to the strong chelating coordination of the oxygen and nitrogen with Hg2+. [ABSTRACT FROM AUTHOR]

• The two polar-modified hyper-cross-linked resins were synthesized. • The two polar-modified hyper-cross-linked resins had different pore structure. • The effect of certain factors on the adsorption process was evaluated. • Kinetic, isotherm, mechanism and thermodynamic studies were performed. • The frontier orbital energy of the adsorbents and adsorbate were calculated. Two polar monomers, Trimellitic anhydride and o-phthalic anhydride, are employed to copolymerize with the non-porous gel-type chloromethylated poly(styrene-divinylbenzene) (NP-CLPs), and synthesized two polar-modified hyper-cross-lined resins. The resins were efficient for adsorption of o-tolylthiourea, and possessed the largest equilibrium capacity (221.2 mg/g for TMAMR, and 206.7 mg/g for PAMR). The influences of adsorption temperature, solution pH, and salt content of the solution were studied by the static adsorption method. The Freundlich and Langmuir isotherm model were used to fit equilibrium data for all investigative temperatures (288–318 K). The Langmuir model was better than the Freundlich model at 288 K; however, with the increasing temperature the Freundlich and Langmuir models could all well describe the isotherm data. The thermodynamic parameters (Δ H 0, Δ S 0, and Δ G 0) showed that the adsorption of o-tolylthiourea was feasible, exothermic, and spontaneous from 288 K to 318 K. The kinetic data were fitted by pseudo-first order, pseudo-second order, and intraparticle diffusion equations. Differences in adsorption of o-tolylthiourea between TMAMR and PAMR resins were interpreted by the frontier orbital energy level difference between resins and o-tolylthiourea calculated with the semi-empirical method AM1. [ABSTRACT FROM AUTHOR]

• Suitable isotherm models for water vapor adsorption by lignocellulose biosorbents. • Surface affinity and heat of adsorption obtained from different models. • Dynamic transport of water in pores visualized using optical microscopy. • Heat of adsorption as a function of surface loading and heterogeneity. Water vapor is to be separated from industrial gaseous streams at reduced costs. Natural lignocellulose materials have demonstrated a high water adsorption capacity and great potential in industrial gas dehydration, specifically natural gas dehydration. In this work, flax shives, a representative of abundant lignocellulose materials generated as by-products of agriculture industry, was chosen as a model to investigate their water adsorption. The focus of this work is on analyzing the surface morphology and the chemistry of the material, and investigating the effects of key parameters on the equilibrium, isotherms, surface affinity, and heat of water adsorption. The results showed that total operating pressure had the most significant effect on the equilibrium, followed by the temperature. The shape of water adsorption isotherm was changed from type III to type I as the total operating pressure was decreased and temperature was increased. The Anderson, Toth, and multi-site Langmuir models successfully described the isotherms obtained at various operating conditions. The modeling results were further used to determine the standard heat of adsorption, isosteric heat, heat of individual sites, and excess heat of liquefaction that the second and subsequent adsorbed layers released. In addition, the material surface was characterized by FE-SEM and FTIR, and the water transport through the material's structure was visualized using optical microscopy images and video. These findings contributed to the fundamental science of water adsorption and natural lignocellulose materials and provided information for the design of drying processes based on adsorption and related interface sciences. [ABSTRACT FROM AUTHOR]

Graphical abstract Effect of temperature on pseudo-second-order kinetics of aniline onto the natural kaolinite (a) and activated kaolinite (b) (25 mg L−1 initial solution concentration). Highlights • The kinetics of aniline on native (NK) and acid activated (AK) kaolinites were best described by a pseudo-second-order kinetic model. • According to Langmuir, Freundlich and Dubinin-Redushkevich models aniline are favourably adsorbed by NK and AK. • Thermodynamic quantities show that the adsorption processes were endothermic, feasible and spontaneous. Abstract In this study, the adsorption kinetics, equilibrium and thermodynamics of aniline on native (NK) and acid activated (AK) kaolinites were examined. It was shown that modification of kaolinite with acid not only increases the adsorption capacity of the adsorbent from 109.89 to 256.41 mgg−1for aniline but also its initial sorption rate for aniline, suggesting the activated kaolinite with higher adsorption capacity have great potential application in removal of aniline from water and wastewater. Adsorption efficiency for AK reached at about 91% while it was at about 75% for NK. The kinetics of adsorption of aniline was discussed using three kinetic models, the pseudo-first-order, the pseudo-second-order and the intra-particle diffusion model. The experimental data fitted very well the pseudo-second-order kinetic model due to the higher correlation coefficient and lower sum of squared errors (SSE,%) values, and a good agreement between the experimental and the calculated qe values. Experimental results were also analysed by the Langmuir, Freundlich and Dubinin–Redushkevich (D–R) isotherm models. R L separation factor for Langmuir and the n value for Freundlich isotherm show that aniline are favourably adsorbed by NK and AK. The negative value of ΔG and positive value of ΔS showed that the adsorption of aniline onto NK and AK was feasible and spontaneous. The positive value of ΔH confirmed the endothermic nature of adsorption. [ABSTRACT FROM AUTHOR]

• Diclofenac, a pharmaceutical wastewater pollutant, was adsorbed onto GO sheets. • Optimum conditions: dosage 0.16 g/L, concentration 400 mg/L, 14.75 min and 40°C. • Adsorption equilibrium was best described by the Langmuir model. • Adsorption kinetic was well described by the pseudo-second-order kinetic model. • Intraparticle diffusion plot indicated that the process has multiple rate-limiting steps. Diclofenac is a pharmaceutical compound which is listed as a priority substance to be removed from wastewater. The current research investigated the adsorption of diclofenac using graphene oxide (GO) which was characterized by Fourier transform infrared, scanning electron microscopy, X-ray diffraction, transmission electron microscopy and Raman spectroscopy. Response surface methodology was employed to optimize the adsorption of diclofenac onto GO based on central-composite design. According to the developed model, the dominant parameters affecting the process were dosage and initial concentration. The optimum adsorption conditions were dosage of 0.16 g/L, time of 14.75 min, initial concentration of 400 mg/L and temperature of 40°C. Under these conditions, GO exhibited a maximum adsorption capacity of 653.91 mg/g for diclofenac. The diclofenac uptake by GO was consistent with the Langmuir adsorption and pseudo-second-order kinetic models. The active binding sites for diclofenac in GO might be hydroxyl, carboxyl and alkoxy as determined by FTIR analysis. The results provided sufficient evidence to support GO as a promising adsorbent for removal of diclofenac in aqueous solution. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Abstract The fly ash from the Corner Brook Pulp and Paper (CBPP) mill was used in this study as the raw material for the preparation of a low-cost adsorbent for arsenic removal from the well water of Bell Island. The CBPP fly ash was physically activated in two different ways: (a) activation with pure CO 2 (CAC) with the iodine number and methylene value of 704.53 mg/g and 292.32 mg/g, respectively; and (b) activation with a mixture of CO 2 and steam (CSAC) with the iodine number and methylene value of 1119.98 mg/g and 358.95 mg/g, respectively, at the optimized temperature of 850 °C and the time of 2 h for both activations. The BET surface areas of the CAC and CSAC at the optimized conditions were 847.26 m2/g and 1146.25 m2/g, respectively. The optimized CSAC was used for impregnation with iron (III) chloride (FeCl 3) with different concentrations (0.01 M to 1 M). The study shows that the adsorbent impregnated with 0.1 M FeCl 3 is the most efficient adsorbent for arsenic removal. Isotherm analysis shows that the Langmuir model better describes the equilibrium behavior of the arsenic adsorption from both local well water and synthesized water compared to the other models. The maximum arsenic adsorption capacity was 35.6 μg/g of carbon for local well water and 1428.6 μg/g of carbon for synthesized water. Furthermore, the kinetic behavior of arsenic adsorption from synthesized and local well water was well depicted by the pseudo-second order kinetic model. Graphical abstract Unlabelled Image Highlights • Higher surface and pore volume achieved through the activation with the mixture of steam and CO 2 • Iron impregnation of the adsorbent significantly increases the removal efficiency of arsenic. • Langmuir model better describes the equilibrium behavior of arsenic adsorption. [ABSTRACT FROM AUTHOR]

Highlights • Three kinds of water-insoluble alginate-based nanofiber membranes were prepared. • The maximum actual adsorption capacity of nanofiber membranes can reach 2230 mg/g. • Separation experiment shows that separation efficiency reaches 97.33%. • Controlled synthesis membranes are applied to different adsorption environments. Abstract Herein, the three kinds of water-insoluble alginate-based nanofiber membranes were prepared by electrospinning and followed with crosslinking by calcium chloride (CaCl 2), glutaraldehyde vapor (GA), and trifluoroacetic acid (TFA) crosslinking, respectively. All the sodium alginate(SA) nanofiber membranes present excellent integrated adsorption performance toward methylene blue (MB). Among these, CaCl 2 crosslinked SA membranes exhibit the maximum actual adsorption capacity of 2230 mg/g and shortest adsorption equilibrium time of 50 min to date. On the basis of the selective adsorption of SA, the nanofiber membranes can separate MB/ methyl orange (MO) mixture solution and maintain high separation efficiency even after five cycles. In addition, respective applicable condition for differentially crosslinked SA nanofiber membranes was evaluated. The TFA crosslinked membranes have the least reduction in the adsorption capacity in acidic environment and GA crosslinked membranes adsorb better in alkaline environment. For seawater environment, GA crosslinked membranes show obvious adsorption performance than other crosslinked membranes. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Microwave-assisted hydrothermal carbonization of rice straw. • Relation between microwave conditions and hydrochars' physical-chemical properties. • Adsorption of three organics and two heavy metals on the hydrochars. Abstract A series of rice straw hydrochars were produced through a microwave-assisted hydrothermal treatment method, characterized and used for the adsorption of three organics and two heavy metals from aqueous solutions. The hydrochars have carbon contents from 37.44% to 43.31%, are rich in oxygen containing functional groups, and the equilibrium of hydrothermal carbonization reactions could be reached rapidly in microwave environment. The hydrochars can effectively adsorb the model pollutants, the maximum adsorption capacities of Congo red, berberine hydrochloride and 2-naphthol at 298 K and initial concentration of 0.5 mg/mL were 222.1, 174.0 and 48.7 mg/g, respectively, and those of Zn2+ and Cu2+ were 112.8 and 144.9 mg/g, respectively. Adsorption thermodynamic parameters were calculated. These results suggest that microwave-assisted hydrothermal treatment is an effective method for the rapid production of hydrochars, and rice straw hydrochars are promising adsorbents for the removal of water pollutants such as organics and heavy metals. [ABSTRACT FROM AUTHOR]

Graphical abstract Breakthrough curves of acetaldehyde and acetone in binary system. Highlights • Adsorption isotherms of acetaldehyde/acetone onto coconut shell activated carbon were obtained in single and binary systems. • Henry's law constant and the selectivity were investigated to understand adsorbent and adsorbate affinity. • Integral free energy functions were useful parameters to understand adsorption behavior. • Adsorbed acetaldehyde was displaced by acetone in co-adsorption system. Abstract The adsorption characteristics of acetaldehyde/acetone onto coconut shell activated carbon (CSAC) were investigated with a dynamic apparatus. The Langmuir, Freundlich and Sips models were used to analyze the adsorption isotherm data in single gas system, revealing that the Freundlich model most suitably described the adsorption of the two gases. Henry's law constant and the selectivity were investigated based on adsorption isotherms to understand adsorbent and adsorbate affinity. A thermodynamic study also revealed that the adsorptions were exothermic and phyiscal. The adsorption of these studied gases is likely to be heterogeneous. Acetone formed the more ordered configuration on CSAC, but molecular acetaldehyde has higher degree of freedom. For the binary adsorption system, the equilibrium data fit well with the Extended Freundlich model. The competitive adsorption experiment indicated that acetone was more selectively adsorbed than acetaldehyde on CSAC. In particular, because of the displacement of adsorbed acetaldehyde by acetone the acetaldehyde demonstrated a maximum excess concentration. [ABSTRACT FROM AUTHOR]

Abstract The kinetic and equilibrium parameters of the quantitative adsorption for Indigo Carmine (IC) removed by commercial activated carbon (AC) were studied by UV–visible absorption spectroscopy. AC with a high specific surface area (1250.320 m2/g) was characterized by the Brunauer–Emmett–Teller (BET) method and point of zero charge (pzc). The effect of the initial dye concentration (10–60 mg/L), contact time (0–90 min), pH (1−12), agitation speed (0–600 rpm), adsorbent dose (1–10 g/L) and temperature (298–323 K) were determined to find the optimal conditions for a maximum adsorption. The adsorption mechanism of Indigo Carmine onto AC was studied using the first pseudo order, second pseudo order and Elovich kinetics models. The adsorptions kinetic were found to follow a pseudo second order kinetic model with a determination coefficient (R2) of 0.999. To get an idea on the adsorption mechanism, we applied the Webber-Morris diffusion model. The equilibrium adsorption data for Indigo Carmine on AC were analyzed by the Langmuir, Freundlich, Elovich, Dubinin and Temkin models. The results indicate that the Langmuir model provides the best correlation at 25 °C (q max = 79.49 mg/g) and Dubinin at 40 °C (q max = 298.34 mg/g). The adsorption isotherms at different temperatures have been used for the determination of thermodynamic parameters such as free energy (ΔG° = −0.071 to −1.050 kJ/mol), enthalpy (ΔH° = 28.11 kJ/mol), entropy (ΔS° = 0.093 kJ/mol·K) and activation energy (Ea) of 51.06 kJ/mol of adsorption. The negative ΔG° and positive ΔH° values indicate that the overall adsorption is spontaneous and endothermic. Highlights • An activated carbon is used to remove Indigo Carmine (IC) from aqueous solution. • The equilibrium experimental data were well fitted by the Langmuir and Dubinin isotherms models. • Under optimized conditions, 79.49 mg/g at 25 °C and 298·34 mg/g at 40 °C of the dye could be removed from solution. • The adsorption of the dye follows the pseudo-second order kinetic model. • A thermodynamic study showed the spontaneous and endothermic nature of the adsorption. [ABSTRACT FROM AUTHOR]

Isotherms are of paramount importance for the interpretation of adsorption and ion exchange mechanisms and the design of separation and catalytic processes. Although the literature on sorption isotherms is rich, most of experiments and models employed are limited to systems that obey simple equilibrium isotherms, such as linear, favorable (convex-upward) or unfavorable (concave-upward). This paper deals with the rather overlooked S-shaped isotherms and their dimensionless forms, which are of great importance for the modeling of separation processes and interpretation of equilibrium data. A review on the physical significance and applications of S-shaped isotherms in adsorption and ion exchange process is also presented. [ABSTRACT FROM AUTHOR]

Bio-nanosilica was obtained from rice husk thought an alternative ultrasound process and, the material was used to adsorb Crystal Violet (CV) dye from aqueous effluents. Ultrasound modified bio-nanosilica (UM-nSiO 2 ) presented better characteristics than standard nano-silica (nSiO 2 ), demonstrating that ultrasound technique has great potential to generate a promising material for adsorption purposes. The adsorption study was carried out by the kinetic curves, equilibrium isotherms and thermodynamics. Pseudo-second order model was the best to represent the kinetic curves. To represent the equilibrium curves, BET and Freundlich were suitable. Bio-nanosilica attained adsorption capacity of 495 mg g −1 and removal percentage of 98%, being an efficient adsorbent for CV dye. [ABSTRACT FROM AUTHOR]

• Li 4 SiO 4 -CO 2 reaction is experimentally, kinetically and thermodynamically analyzed. • Equilibrium, adsorption, desorption & circulation processes are separately studied. • Empirical formula of practical equilibrium temperature vs CO 2 pressure is deduced. High-temperature carbon capture by using Li 4 SiO 4 -based solid adsorbent has been considered as a promising approach for mitigating fossil fuel-related CO 2 emission due to its relatively high capacity and excellent cyclic stability. From the aspects of experimental tests, kinetic calculations and thermodynamic analyses, this work systematically investigated four important parts during the looping carbon capture process of Li 4 SiO 4 , including the reaction equilibrium, the CO 2 adsorption, the CO 2 desorption and the cyclic ad-desorption. Firstly, the theoretical and experimental equilibrium boundary and corresponding thermodynamic parameters of Li 4 SiO 4 -CO 2 reaction system were calculated and an empirical formula about the practical equilibrium temperature was provided. Then, the CO 2 adsorption and desorption processes were kinetically and thermodynamically analyzed by the Jander-Zhang model and the initial reaction rate model, respectively. Finally, the key adsorption and desorption parameters of Li 4 SiO 4 within 10 ad-desorption cycles were calculated and the mechanisms were concluded. All above conclusions could provide theoretical guidance for the future development of Li 4 SiO 4 during the cyclic CO 2 adsorption–desorption processes. [ABSTRACT FROM AUTHOR]

The development of a compact, efficient, reliable thermal diode is crucial to improve advanced thermal management efficiency and controllability, and to enable brand new applications such as thermal logic gates and computers. In this study, we examine a nanoscale and efficient capillary-controlled thermal diode mechanism in Ar-filled Pt-based heterogeneous nanoporous structures, using Grand Canonical Monte Carlo (GCMC) simulation combined with Non-Equilibrium Molecular Dynamics (NEMD) simulation at the temperature range of 70–150 K and the pressure of 1.66 atm. Results show that the large thermal conductivity contrast between the controlled adsorption and capillary states using the structural heterogeneity (nanopillars on only one surface) and/or material heterogeneity (two different materials for nanogap surfaces) allows for the maximum thermal rectification ratio, R max  ∼ 140 with minimal hysteresis under the cyclic operating temperatures −40 K < Δ T  < +40 K. It is also found that the material heterogeneity is equivalent to the structural heterogeneity for minimizing the hysteresis in adsorption-capillary transition, but the heat flux across the nanogap with the material heterogeneity reduces due to weaker Ar-solid interaction. The coupled structural-material heterogeneity for the capillary-driven thermal diode is also discussed. The obtained results pave pathways for advanced thermal management systems such as thermal transistors, thermal logic gates, and computers. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The adsorbent has a highly ordered, multilayer-like composite structure. • The sorption process followed the pseudo-second-order kinetic model. • Adsorption of Cd2+, Ni2+ and Cr3+ ions onto the surface of OPC was heterogeneous. • Thermodynamic studies suggested physical adsorption for the removal of, Pb2+. • Physico-chemical process may be involved in the adsorption of Cd2+, Ni2+ and Cr3+. Abstract The efficiency of oil palm calyxes (OPC) in removing heavy metals from aqueous solution is presented in this report. Qualitative analyses showed the participation of hydroxyl, carboxylate and methoxyl groups in the binding process. OPC surface was observed to be amorphous, highly ordered and multilayered. Quantitative analyses indicated that the removal of Cd2+, Pb2+ and Ni2+ occurred at fast kinetics, with uptake of 38.24, 47.66 and 32.61 mg/g respectively, after 5 min. Optimum Cr3+ adsorption was however not reached after 3 h, indicating slow kinetics. Pseudo-second-order model best described the kinetics of the adsorption, suggesting chemisorption as the rate-limiting step. Metal uptake increased with rise in adsorbate concentration. However, no further rise in uptake was observed with increase in Pb2+ concentration beyond 200 mg/L. Data from the sorption of Cd2+, Ni2+ and Cr3+ were best described by Freundlich isotherm, while those of Pb2+ obeyed Langmuir isotherm, with maximum adsorption capacity (q max) of 120.48 mg/g. Thermodynamic studies indicated that the removal of Cd2+, Ni2+ and Cr3+ was exothermic and occurred with decreased disorderliness, while Pb2+ removal was endothermic with increased entropy. The negative values of ΔG° indicated the spontaneity of the biosorption of Cd2+, Pb2+, Ni2+ and Cr3+ onto OPC. [ABSTRACT FROM AUTHOR]

Homogeneous Surface Diffusion Model (HSDM) has been widely used to simulate the breakthrough of organic micropollutants in fixed-bed adsorbers, but its practical applicability in real-scale conditions is not fully established. In this study we proposed a validated methodology to support the assessment of full-scale GAC adsorbers, providing a sound framework for a sustainable management. Specifically, we predicted the breakthrough of volatile organic compounds by the HSDM applied to full-scale granular activated carbon (GAC) adsorbers treating a complex groundwater matrix. Isotherm and short bed adsorber (SBA) tests were conducted to obtain equilibrium and mass-transfer coefficients for two contaminants (chloroform and perchloroethylene, PCE) and two GACs. Isotherm data were well described by Freundlich and Langmuir models, showing that single-component isotherms can be also used in complex water matrices, indirectly taking into account competition phenomena into the estimated parameters. The fitting of SBA data by HSDM was effective for chloroform, while PCE results were not well described, indicating that the combination of isotherm and SBA experiments to estimate HSDM parameters is not always effective, but it can depend on the characteristics of the adsorbate. Breakthrough data from the monitoring of two full-scale adsorbers were finally used to validate HSDM parameters for chloroform: its breakthrough was effectively simulated, w ithout introducing any competition effect in HSDM equations. The model well reproduced also the release of the contaminant (resulting in chromatographic effect) by considering the variation of its influent concentration over time. [ABSTRACT FROM AUTHOR]

Prolong consumption of arsenic-rich drinking water causes serious health problem. Aiming to minimize the problem, it is attempted to develop cheap and advanced materials for arsenic extraction from the contaminated water. Thus, multifunctional graphene oxide (GO)-incorporated iron-aluminium mixed oxide (GIAMO) composite has been prepared with five different GO content, and evaluated by batch method for the arsenic(III) removal efficiency. Among the as-prepared GIAMO samples, three samples consisting 1.0, 2.0 and 3.0 g of GO show equally good (92–95%) arsenic(III) removal efficiency, which is 30–35% higher than pristine iron-aluminium oxide (IAMO) from an aqueous solution (5.0 mg As III ·L −1 ) at pH 7.0 (± 0.2) and 303 K. Thus, 1.0 g GO-inserted GIAMO (GIAMO-1) sample was characterized as microcrystalline (10–15 nm) with BET surface area about 1.45 times higher than IAMO and investigated for the arsenic(III) adsorption. Optimized pH for arsenic(III) adsorption is 6.0–8.0. The kinetic data agree more closely with pseudo-first order equation (R 2  = 0.98–0.99) than pseudo-second order equation (R 2  = 0.92–0.93). The equilibrium data describe the Langmuir isotherm (R 2  = 0.97–0.98) better than the Freundlich isotherm (R 2  = 0.91–0.92), showing the Langmuir monolayer capacity 42.2836 mg·g −1 at 293 K which drops to 24.9170 mg·g −1 at 313 K. High negative enthalpy change (ΔH° ∼ −224 kJ. mol −1 ) is responsible for the spontaneous reaction (ΔG° = negative) despite unfavorable entropy change (ΔS° = −0.71 kJ. mol −1 ). The order of competitive effect of PO 4 3− , SO 4 2− and HCO 3 − on arsenic(III) removal efficiency is PO 4 3−  > SO 4 2−  > HCO 3 − . However, the high HCO 3 − (> 200 mg·L −1 ) enhances the arsenic(III) removal efficiency of this material. 2.0 M NaOH can regenerate arsenic adsorbed GIAMO-1 only up to 50–60%. 0.65 g. of composite per L of high arsenic (As total : 0.115 mg L −1 ) groundwater can upgrade to potable standard, encouraging possible safe use for high arsenic water treatment. Highly negative enthalpy change, poor regeneration, FTIR, XRD and CV analyses of arsenic-rich solid suggested that arsenic(III) is stabilized over the solid surface without oxidation by surface complex formation. [ABSTRACT FROM AUTHOR]

Tenuazonic acid is a fungal secondary metabolite that is produced by a number of Alternaria species and is therefore a natural contaminant of food and feed samples. The aim of this study was to investigate the adsorption kinetics and isotherms of tenuazonic acid (TeA) from citrus juice using inactivated lactic acid bacteria (LAB). The results showed that inactivated LAB-20023 could significantly reduce TeA from contaminated fruit juice. The kinetic models indicated that the biosorption process of TeA onto inactivated cells from fruit juice obeys a pseudo-second-order model rather than a pseudo-first-order kinetic model at all studied temperatures and initial concentrations. The equilibrium data were fitted to Langmuir and Freundlich isotherm models, and the results showed that the adsorption equilibrium was best described by the Freundlich isotherm. [ABSTRACT FROM AUTHOR]

The effective use of the sorption properties of different clays as sorbents for the removal of dyes from wastewater has currently received much attention because of the eco-friendly nature of clay materials. Dyes are complex class of organic compound having wide range of applications in textile and food industries and a large amount of dyes are wasted, which get mixed in natural water resources. Mixing of dyes in water resources must be prohibited for the safety of natural ecosystem. The adsorbents (natural and modified) have been successfully used for the adsorption of dyes form wastewater. This review article highlights the importance of clay (raw and modified) as an adsorbent for the adsorption of dyes from textile wastewater. Appropriate conditions for clay-dye system and adsorption capacities of a variety of clays are presented and sorption process is critically analyzed. Studies reported the clays as an adsorbent from 2004 to 2016 are included and different properties for the utilization of clay and clay-based adsorbents are discussed. Based on studies, it was found that the clays (natural and modified) are affective adsorbents for the purification of wastewater containing dyes. [ABSTRACT FROM AUTHOR]

The objective of this work is to study the synthesis of Mg-Al-D2EHPA and its efficiency to remove the Cu 2+ ions from aqueous solutions. Mg-Al-CO 3 was synthesized by co-precipitation method, calcined and modified with D2EHPA surfactant. Batch tests of sorption were carried out with synthetic solutions of Cu 2+ prepared using deionized water. Experimental data of sorption were fitted using several kinetic and equilibrium models. Results show that the intercalation of D2EHPA increases the interlamellar space from 7.65 to 26.28 Å with a bilayer arrangement of surfactants ions. It was also found that Cu 2+ ions uptake is rapid and reaches its maximum value (qm = 68.66 mg/g) after 60 min. The kinetic data are well described by the pseudo-second-order model, and reveal that the intra-particle diffusion is involved in the kinetic mechanism. Also, equilibrium study shows that the sorption is of a physical type and Freundlich model best fit the isotherm data. [ABSTRACT FROM AUTHOR]

The present work deals with the study of adsorption of isonicotinic acid (iNA) onto Amberlite IR120 H. Equilibrium and kinetic experiments are carried out to determine the effect of adsorbent dose (10 g/L to 70 g/L) initial concentration of iNA (0.01 M to 0.05 M), contact time (0 to 40 min) and temperature (298 to 333 K) on the capacity of the adsorbent. With an increase in the adsorbent dosage, the uptake capacity of adsorbent is found to decrease but with an enhancement in the recovery efficiency. The optimum dosage of adsorbent is found to be 50 g/L. In the kinetic experiments, the percentage removal of iNA reaches to a constant value of 95% with Amberlite IR120 H (50 g/L) after 30 min. Increased temperature shows reverse trend in the removal efficiency of iNA. The change in enthalpy and entropy are estimated to be − 8.80 kJ/mol and − 19.78 J/mol/K, respectively. Equilibrium data are analyzed by using Langmuir, Freundlich and Temkin isotherm models. Kinetic models such as pseudo-first order, pseudo-second order and intra particle diffusion models are used to predict the kinetics of the adsorption process by Amberlite IR120 H for the removal of iNA. [ABSTRACT FROM AUTHOR]

In this study, AB113 dye was successfully sequestered using a novel adsorbent made of mixed fish scales (MFS). The influence of adsorbent dosage, initial pH, temperature, initial concentration and contact time on the adsorption performance was investigated. The surface chemistry and morphology of the adsorbent were examined by FTIR, TGA and SEM. Amides, phosphate and carbonate groups were evidently responsible for the high affinity of MFS towards the dye. The adsorption equilibrium and kinetic were well described by Langmuir and pseudo-second-order models, respectively. The maximum adsorption capacities of MFS were 145.3–157.3 mg/g at 30–50 °C. The adsorption of AB113 dye onto the adsorbent was exothermic and spontaneous as reflected by the negative enthalpy and Gibbs energy changes. The results support MFS as a potential adsorbent for AB113 dye removal. [ABSTRACT FROM AUTHOR]

Rice bran is a major by-product of the rice milling industry and is abundant in Taiwan. This study proposed a simple method for modifying rice bran to make it a low-cost adsorbent to remove reactive blue 4 (RB4) from aqueous solutions. The effects of independent variables such as dye concentration (100–500 ppm), adsorbent dosage (20–120 mg) and temperature (30–60 °C) on the dye adsorption capacity of the modified rice bran adsorbent were investigated by using the response surface methodology (RSM). The results showed that the dye maximum adsorption capacity of the modified rice bran adsorbent was 151.3 mg g −1 with respect to a dye concentration of 500 ppm, adsorbent dosage of 65.36 mg, and temperature of 60 °C. The adsorption kinetics data followed the pseudo-second-order kinetic model, and the isotherm data fit the Langmuir isotherm model well. The maximum monolayer adsorption capacity was 178.57–185.19 mg g −1 , which was comparable to that of other agricultural waste adsorbents used to remove RB4 from aqueous solutions in the literature. The thermodynamics analysis results indicated that the adsorption of RB4 onto the modified rice bran adsorbent is an endothermic, spontaneous monolayer adsorption that occurs through a physical process. [ABSTRACT FROM AUTHOR]

Models of adsorptive desulfurization to remove the major refractory sulfur compounds, such as thiophene (T), benzothiophene (BT) and dibenzothiophene (DBT) in decahydronaphthalene (DHN), were investigated. The experimental desulfurization of naphthenic oils using activated carbon was conducted in an adsorption system at different temperatures. The adsorptive capacity and selectivity of the adsorbent for sulfur compounds and the effects of coexisting inhibitors on the adsorption performance were examined. The activated carbon showed high capacity and selectivity in the adsorptive desulfurization of naphthenic oil. Water, carbazole, naphthalene and phenol in synthetic naphthenic oil have a strong inhibiting effect on the desulfurization performance of the adsorbent at 100 °C. Increasing the temperature to 150 °C can significantly improve the performance of the adsorbent in the desulfurization of real naphthenic oils. The results showed that the activated carbon exhibited a remarkable adsorption performance. The adsorption capacities reached 1.6 × 10 −2 , 2.0 × 10 −2 and 1.9 × 10 −2 kg kg −1 for T, BT and DBT in DHN, respectively. The Langmuir-Freundlich and Toth isotherm models provided good fits with the experimental equilibrium data for the real naphthenic oils. The kinetic results for the real naphthenic oils showed that the adsorption process can be described by a second-order mass transfer model. The results revealed that a temperature increase favors the sulfur adsorption kinetics and there was a greater diffusivity resistance for heavier oils. The data obtained showed effective diffusivity coefficients of between 7.5 × 10 −15 and 2.6 × 10 −13 m 2 s −1 and mass transfer coefficients for the external fluid film ranging from 8.3 × 10 −8 to 4.9 × 10 −7 m s −1 . [ABSTRACT FROM AUTHOR]

The kinetic regularities and thermodynamics of adsorption of one of the most common pharmaceutical pollutants diclofenac (DCF) on Fe 2 O 3 -pillared montmorillonites (Fe-PMts) have been first studied. Fe-PMts were synthesized by intercalation of natural montmorillonite with iron polyoxocations, followed by heat treatment at 623 and 723 K. The structural and textural characteristics have been studied by XRD, IR, SEM and low temperature N 2 adsorption. It has been established that the pillaring lead to an increase in the specific surface of the natural clay by 2.4 times and an increase in the sorption capacity with respect to DCF up to 80 times. The main physicochemical parameters affecting the DCF adsorption were the pH, sorbent content, DCF concentration, and temperature. The specific DCF adsorption increased with decreasing pH, sorbent content, temperature, and with an increase in the initial DCF concentration. An analysis of the kinetic data and the adsorption isotherm was carried out using pseudo-first and pseudo-second order kinetic models, intraparticle diffusion model, and Langmuir and Freundlich adsorption models. The kinetic data of DCF adsorption were in agreement with the pseudo-second order kinetics model, and the adsorption isotherm was in good agreement with the Langmuir model with maximum adsorption capacity of 103.1 mg·g−1 at pH 5.9. DCF adsorption on Fe-PMt was a spontaneous and exothermic process based on the values of the thermodynamic parameters. The results of the study showed that Fe-PMt was an effective sorbent for removing DCF from aqueous solutions and could be used in pharmaceutical wastewater treatment as a cheap and environmentally friendly sorbent. [ABSTRACT FROM AUTHOR]

This study explores the adsorption capacity of carboxymethyl-β-cyclodextrin (CMβ-CD) functionalized chitosan (CS) impregnated with water-insoluble epichlorohydrin cross-linked β-cyclodextrin polymer (β-CDP) to yield CS-β-CDP-CMβ-CD composite beads for the removal of toxic Cd (II) ions from aqueous solutions. Characterization of the adsorbent was performed with XPS, FTIR, NMR, BET and SEM. The synergistic effect was expected and found at removing Cd (II) with a sorption capacity exceeding 378 mg g −1 (approximately 3.37 mmol g −1 ), which is higher than any other existing technology. The removal of Cd (II) was found maximum at pH 6.5. The rate reduction can be expressed by pseudo-second-order reaction kinetics. Thermodynamic parameters such as the enthalpy (Δ H 0 ), entropy (Δ S 0 ), and free energy change (Δ G 0 ) suggest the endothermic adsorption of Cd (II) in solution. The activation energy was calculated to be 65.62 kJ mol −1 indicating a chemisorption process. The regeneration and reusability of the adsorbent were found suitable for in situ application of this technology for Cd remediation. The Langmuir isotherm model, which is effective for analyzing equilibrium data, indicated both monolayer adsorption and chemisorption. The intraparticle diffusion model indicated both film diffusion and intraparticle diffusion as the rate limiting steps. Thus, the synthesized CS-β-CDP-CMβ-CD beads showed good adsorption selectivity for Cd (II) having excellent regeneration and reusability. [ABSTRACT FROM AUTHOR]

With increasing social and economic developmental activities, high grade energy sources are depleting at faster rate and also inviting menace of environmental problems. Therefore, to reduce dependency on high grade energy sources for cooling applications and to protect environment, adsorption cooling systems are promising alternatives that are powered by low grade heat sources like solar heat, industrial/automobile waste heat etc. and also use environment friendly refrigerants. But, these systems have still low performances, large size and high cost. Therefore, in order to overcome these difficulties, many researchers are focussing on different ways to improve heat and mass transfers in the heat exchangers of the system to enhance its performance. These strategies include the use of advanced adsorbent material and advanced adsorption cycles, design improvement in heat exchangers and development of mathematical models for optimization of design/operating parameters of the cooling systems. In this paper, various mathematical models for adsorption systems are presented that include thermodynamic models, lumped parameters models; and heat and mass transfer models. These models include equations governing the heat and mass transfer in the main components of the cooling systems. The advantages of this method are that it can produce large volumes of results at no more cost and it is very cheap to perform parametric studies, for instance, to optimize equipment performance. The various numerical methods and experimental validations have been also presented and discussed. [ABSTRACT FROM AUTHOR]

Levulinic acid (LA) from aqueous solutions was removed by using commercial adsorbent Amberlite XAD-4 (XAD-4). The equilibrium and kinetic studies were performed to investigate the effect of adsorbent amount (1 g to 3.5 g at 298 K, 308 K and 318 K), initial acid concentration (2 g·L − 1 to 4 g·L − 1 at 298 K, 308 K and 318 K), and contact time ( t , 10 min to 90 min at 298 K) on the capability of XAD-4. The uptake capability and removal efficiency of XAD-4 for the adsorption of LA was observed to increase by increasing amount of adsorbent. In the equilibrium experiments of LA adsorption, adsorption capacity value was increased to 26.85 mg·g − 1 from 10 mg·g − 1 at 298 K with an increase in the amount of XAD-4. In the kinetic studies, the equilibrium time of 70 min was obtained. Also equilibrium study was performed at three different temperatures, 298, 308 and 318 K. The maximum removal was obtained at 298 K. Thermodynamic model parameters such as ∆ G °, ∆ H ° and ∆ S ° are estimated at three different LA concentration (2 g·L − 1 , 3 g·L − 1 and 4 g·L − 1 ). Different isotherm and kinetic models were applied to estimate the equilibrium and kinetic parameters. [ABSTRACT FROM AUTHOR]

In this article, we have presented the studies regarding the improvements of the adsorption performance of a styrene-12% divinylbenzene copolymer functionalized with aminophosphonate groups in the removal process of thallium ions from aqueous solutions, by impregnation of the solid support with trihexyl(tetradecyl)phosphonium chloride (Cyphos IL-101). The use of ionic liquid impregnated polymer as adsorbent in the removal process of radionuclides presents higher adsorption performance because, in this case, the advantages of the ionic liquids are combined with the properties of the solid support. Until now the ionic liquids were intensive studied in the removal process of radionuclides from aqueous solutions but using the liquid-liquid extraction. In our case these are used in the solid-liquid separation process, a smaller quantity of ionic liquids being used (which decrease the cost of the adsorption process), and the loss of the ionic liquids in the aqueous phase being avoided. The ultrasonication method used for the impregnation of the ionic liquids onto the solid support is also a new and original one. The impregnation of the solid support with Cyphos IL-101 significantly increased its adsorption performance in the removal process of Tl(I) ions from aqueous solutions. [ABSTRACT FROM AUTHOR]

An efficient activated carbon was prepared using palm oil mill effluent as a precursor. The adsorption capacity of activated carbon for lead ion and zinc ion from aqueous media was investigated under equilibrium conditions between 303.15 and 353.15 K. The activated carbon was analyzed using fourier transform infrared spectroscopy, field emission scanning electron microscope, energy dispersive X-Ray, and Nitrogen adsorption-desorption analysis. The adsorption capacity of activated carbon was studied by varying adsorbent dosage, contact time, and temperature. The equilibrium time was attained after 50 min for both ions. The data analysis was performed with different isotherm and kinetic models. Pseudo-second-order kinetic rather than pseudo first-order model is best fitted for both lead ion and zinc ion removal from wastewater. Further, the rate-determining step for both metal ions is chemisorption based on the suitability of the Elovich equation. Langmuir model provides the best fit for both removal of lead ion and zinc ion. The thermodynamic parameters shows the feasibility of adsorption of both ions is endothermic. [ABSTRACT FROM AUTHOR]

The uptake of ethylsulfate (ES − ), hexylsulfate (HS − ), and dodecylsulfate (DS − ) anions by Mg–Al oxide in aqueous solution was examined through adsorption equilibrium and kinetic modelling. The removal of ES − , HS − , and DS − by Mg–Al oxide proceeded as diffusion-controlled reactions exhibiting Langmuir-type adsorption isotherms. The maximum amounts of adsorption are ordered as DS − > HS − > ES − . Mg–Al oxide preferentially reacts with the organic anion with lower charge density, because the effect of hydrophobic interactions in these cases is stronger than that of electrostatic interactions. In the first stage of reaction, Mg–Al oxide, which is prepared by the thermal decomposition of Mg–Al layered double hydroxides (LDHs) intercalated with CO 3 2− (CO 3 ·Mg–Al LDH), rehydrates and combines with alkylsulfate to reconstruct the LDH structure. Then the alkylsulfate anions intercalated in the interlayer of the LDH attracted other anions in the solution via hydrophobic interactions, thereby promoting their removal by Mg–Al oxide. DS − was removed with the highest efficiency followed by HS − , because the hydrophobic attraction between DS − anions is stronger than that between HS − , which is stronger than that between ES − . At low initial concentrations (C 0 ), the intercalated alkylsulfates are likely oriented parallel to the brucite-like host layers of Mg–Al LDH. With increasing C 0 , pairs of alkyl chains in DS − and HS − may overlap due to the hydrophobic interaction, while the alkyl chains in DS − are likely arranged perpendicular to the host layers to form bilayers. [ABSTRACT FROM AUTHOR]

Environmental pollution by textile dye-based wastewater raises a vital call for consideration to industrialists and scientists due to its influence on the ecosystem. In this study, zinc oxide (ZnO), copper oxide (CuO), Manganese dioxide (MnO 2), and Magnesium Oxide (MgO) nanoparticles were successfully synthesized from Leucaena leucocephala leaves for the removal of Reactive Golden Yellow-145 (RY-145) and Direct Red-31 (DR-31) dyes. The nanoparticles were characterized by scanning electron microscope (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). Optimization of various operating parameters like initial dye concentration, pH, temperature, contact time, and dose of nanoparticles was investigated. The results showed that Leucaena leucocephala leaf-mediated ZnO, CuO, MnO 2 , and MgO nanoparticles presented the highest adsorption capacities for RY-145 of 47.50 (mg/g), 65.53(mg/g), 53.62 (mg/g), and 58.72 (mg/g) respectively, with optimized parameter values of pH solution, contact time, adsorbent dose, initial dye concentration, and temperature were 3, 75 min, 0.05 g/50 mL, 100 mg/L and 25° C on 124 rpm, correspondingly. DR-31 presented the highest adsorption capacities of 57.08 (mg/g), 83.47(mg/g), 67.36 (mg/g), and 72.53 (mg/g) respectively at optimized parameter values of pH solution, contact time, adsorbent dose, initial dye concentration and temperature were 2 and 3, 60min, 0.05 g/50 mL, 100 mg/L and 25° C on 124 rpm. The surfactants and electrolytes effects were also scrutinized on dyes' adsorption. The surfactants and electrolytes' existence in the aqueous media reduced the adsorption of dye because of the competition for limited binding sites. The RY-145 and DR-31 adsorbents adsorption efficiencies were found in following order; MgO (65.52% and 83.47%) > MnO 2 (58.72% and 72.53%) > CuO (53.62% and 67.36%) > ZnO (47.50% and 57.08%). The adsorption-based dye data were scrutinized using various isotherms, kinetics, and thermodynamics models. The studies presented that the adsorption processes were well fitted to pseudo-second-order kinetics since correlation coefficient (R2) values ranged from 0.994 to 0.999 and Intraparticle diffusion models correlation coefficient values ranged from 0.88 to 0.97, their values were relatively near the experimental values signify the adsorption kinetics in both dyes. Both dyes adsorption on green nano-adsorbents followed a Langmuir isotherm due to decent correlation coefficient values of 0.999 with value of 59.17 (mg/g), 66.22 (mg/g), 72.99 (mg/g), and 81.30 (mg/g) respectively for DR-31 and 47.62 (mg/g), 53.763 (mg/g), 58.48 (mg/g), and 64.93 (mg/g) for RY-145 with monolayer coverage. RY-145 also followed Temkin and Doubinin Radushkevich's isotherm. The thermodynamics investigations revealed spontaneous dyes adsorption onto MgO and MnO 2, ZnO is non-spontaneous in both dyes while CuO is spontaneous in DR-31 and non-spontaneous in RY-145. The maximum desorption of 78–86% was attained using the 0.2 N and 0.4 N NaOH for adsorbed RY-145 and DR-31 dye respectively. The desorption data was favorable as the Leucaena leucocephala leaf-mediated ZnO, CuO, MnO 2 , and MgO nanoparticles adsorbents were utilized several cycles and have stability This experimental study also determines the potential efficacy of green nano-adsorbents for the removal of dye from the real textile effluent. In addition, a phytotoxicity investigation of used green nano-adsorbents is carried out on the pea seeds, to demonstrate their sustainability from a real environmental point of view. Thus, Because of their promising efficiency, green ZnO, CuO, MnO 2 , and MgO nanoparticles have the potential to apply for dye adsorption from textile wastewater. [Display omitted] • ZnO, CuO, MnO 2 , and MgO nanoparticles were synthesized using Leucaena leucocephala. • Adsorptive removal of Reactive Golden Yellow-145 and Direct Red-31 by green nano adsorbent. • Adsorption processes were well fitted to Langmuir isotherm, pseudo-second-order kinetics and Intraparticle diffusion models. • RY-145 and DR-31 adsorption efficiencies order on green nano-adsorbents; MgO > MnO 2 > CuO > ZnO. • Desorption and reusability studies indicated excellent results and stability. [ABSTRACT FROM AUTHOR]

The standard Gibbs free energy, enthalpy and entropy change data for adsorption equilibrium reported in biosorption literature during January 2013–May2016 were listed. Since the studied biosorption systems are all near-equilibrium processes, the enthalpy and entropy change data evaluated by fitting temperature-dependent free energy data using van Hoff’s equation reveal a compensation artifact. Additional confusion is introduced with arbitrarily chosen adsorbate concentration unit in bulk solution that added free energy change of mixing into the reported free energy and enthalpy change data. Different standard states may be chosen for properly describing biosorption processes; however, this makes the general comparison between data from different systems inappropriate. No conclusion should be drawn based on unjustified thermodynamic parameters reported in biosorption studies. [ABSTRACT FROM AUTHOR]

In this study, cucurbit[8]uril (CB[8]) was utilized as a kind of new adsorbent to remove Pb 2 + ions from aqueous solution. With the solution pH increased from 2 to 6, the removal efficiency of adsorption increased from 55.6% to 74.5%correspondingly. The uptake of Pb 2 + increased rapidly in the initial 30 min, and then the adsorption rate became slower. The Pseudo-second order model could be used to interpret the adsorption kinetics satisfactorily; and the rate determining step in Pb 2 + adsorption onto CB[8] was the external mass transfer step. Equilibrium isotherm study reveals that the Langmuir model gave a better fitting result than Freundlich model. The maximum adsorption capacity calculated by the Langmuir model was 152.67 mg/g for 298 K, 149.70 mg/g for 313 K and 136.42 mg/g for 323 K, respectively. The adsorption is a spontaneous process of exothermic nature. The effect of the adsorbent dosage and the influences of solution pH and co-existing cations were also investigated. The CB[8] was synthesized and characterized by 1 H NMR, IR, ESI-MS spectra, SEM-EDAX, Zeta-potential and BET-analysis. The adsorption mechanism was due to the coordination between CB[8] molecule and Pb 2 + ions. [ABSTRACT FROM AUTHOR]

As reported in our previous work, crosslinked polymeric adsorbents with high microporous surface areas are proper for glabridin adsorption. In addition, adsorption capacity of the microporous and mesoporous self-crosslinked polystyrene resin XT2-10 was superior to that of the optimal commercial adsorbent BMKB-1 under the same conditions. However, there is still room for further improvement. Based on this, in the following study, a series of novel hypercrosslinked polymeric adsorbents modified with acetylaniline as the cross-linked bridge (labeled as XT8-0, XT8-4, XT8-6, XT8-8 and XT8-10) were synthesized from macroporous crosslinked chloromethylated polystyrene by adding different quantity of acetylaniline in the Friedel–Crafts reaction. The microporous surface areas of hypercrosslinked polymeric resins XT8 occupied more than 55% of the total BET surface areas and these resins were evaluated for adsorption of glabridin. Among the synthesized five resins, XT8-8 possessed the largest adsorption capacity toward glabridin, and it was superior to the previous synthesized self-crosslinked polystyrene resin XT2-10 and much better than the optimal commercial resin BMKB-1. The isotherms could be fitted by Freundlich model and the adsorption was shown to be an exothermic process. The kinetic curves could be characterized by pseudo-second-order rate equation and the adsorption rate of glabridin on XT8-8 was controlled by both intraparticle diffusion and external diffusion. The enthalpy Δ H , Gibb’s free energy Δ G and entropy Δ S were calculated to be negative. The reusability of the modified resins was also assessed and the modified resins exhibited considerable reusability. The remarkable adsorption behaviors of XT8-8 were due to its suitable structural design and modification. The hypercrosslinked resins being developed were promising alternatives to commercial adsorbents for adsorbing glabridin and other flavones from herbal plants. [ABSTRACT FROM AUTHOR]

The present work addresses the kinetics, thermodynamics, and equilibrium of α-toluic acid adsorption onto calcium peroxide (CaO 2 ) nanoparticles. CaO 2 nanoparticles were synthesized by chemical precipitation method and characterized using XRD, TEM, and FT-IR. Characterization results confirmed that CaO 2 nanoparticles were in the size range of 5–15 nm. The rate of α-toluic acid adsorption was determined by fitting the batch adsorption experimental data with pseudo first order, pseudo second order, Elovich, intra-particle diffusion, fractional power, and Bangham kinetic models. Amongst all models, the pseudo second order model showed good correlation with a rate constant, k 2 = 8.53 × 10 −5 g mg −1 min −1 . Thermodynamic parameters (Δ G °, Δ H °, and Δ S °) showed that adsorption is more favorable at low temperature, and an exothermic process. The equilibrium data were analyzed with Langmuir, Freundlich, Temkin, Toth, and Radke-Prausnitz isotherms, and the best fit was observed with Langmuir isotherm suggesting monolayer and chemisorption of α-toluic acid. This was also confirmed from error analysis. On quantitative basis, the adsorption capacity of CaO 2 nanoparticle adsorbent was found to be around 30% higher as compared to the conventional CaO 2 . Based on FT-IR analysis, a mechanism for α-toluic acid removal from aqueous solution using CaO 2 nanoparticles was proposed. [ABSTRACT FROM AUTHOR]

In the present paper, Amberlite XAD-16 was chosen as an advantageous macroporous polymeric resin and functionalized with NO 2 (electron-acceptor) and NH 2 (electron-donor) groups via known reactions to prepare two new functional macroporous resins, NO 2 -XAD-16 and NH 2 -XAD-16 respectively, and kinetics, equilibrium, thermodynamic and other adsorption properties of these two functionalized polymers toward tetracycline antibiotic were compared with those of conventional XAD-16. Effect of various physicochemical factors was investigated. The equilibrium experimental data were followed by Langmuir model, and the calculated maximum adsorption capacities in terms of monolayer adsorption were in agreement with those obtained from the experiments. The experimental kinetic data was best fitted with pseudo second order, with higher k 2 values for NO 2 -XAD-16 compared to XAD-16 and NH 2 -XAD-16. The calculated thermodynamic parameters of the adsorption (∆G º , ∆H º and ∆S º ) showed that the adsorption of tetracycline onto all three polymeric resins is feasible, spontaneous and endothermic under the conditions employed. However, the thermodynamic studies indicated the more feasibility, spontaneity and favorability of tetracycline adsorption onto NO 2 -XAD-16 polymeric beads. Overall, comparative outcomes indicated that the functional group with electron-acceptor ability (-NO 2 ) is the best choice for modifying XAD-16 beads for their application in the adsorption of tetracycline from aqueous solutions. [ABSTRACT FROM AUTHOR]

Textile dyehouses generate high volumes of coloured wastewaters, which require convenient treatment in order to avoid water bodies' contamination, adverse effects to aquatic life and risks to human health. The complete decolourisation of such contaminated waters in a cost-effective manner is still a challenge nowadays. This work focuses on the use of a clayey material as a low-cost adsorbent for a basic textile dye (Red 46), commonly used in acrylic fibres dyeing. The bentonitic clay (49% of montmorillonite) presents a considerable (50 cmol c /kg) cationic exchange capacity and a porosity of 10%. Dye adsorption kinetics was successfully described by a pseudo-second order model, resulting an average kinetic constant of 0.23 g dye g clay − 1 min − 1 . Adsorption equilibrium was reached in 12–24 h and data were successfully fitted to Freundlich and Langmuir equations. The maximum adsorption capacity predicted by the Langmuir model depends on the pH, varying between 217 mg/g at pH 8 and 584 mg/g at pH 9 (25 °C). Increasing the temperature from 25 to 35 °C also led to an increase in adsorbed amounts. In addition to the excellent adsorption performance, the clay showed a great affinity to the dye, indicating high propensity to complete decoulorization of textile dyeing wastewaters. The results obtained in the present work show that a natural, readily-available and cheap material i.e. a bentonitic clay can be used as an effective and environmentally-friendly adsorbent for basic dyes. [ABSTRACT FROM AUTHOR]