Search

The present study investigated crystal violet removal by modifying the chestnut shell with a chemical activation method. For this purpose, H2SO4 and NaOH pretreatments were applied to the chestnut shell and the pretreatment method that gave the best performance under the same conditions was determined. The best adsorption efficiency was achieved with the NaOH pretreatment (99.06%) and the crystal violet adsorption reached equilibrium within 60 min. After selecting the best chemical activation method, the modified chestnut shell was characterized before and after adsorption (FTIR and SEM). Furthermore, the effects of parameters such as pH, initial crystal violet concentration, adsorbent dosage, temperature, and contact time were observed. Moreover, isotherm, kinetics and thermodynamics of the adsorption process were researched in detail. The best results were obtained with the Langmuir isotherm model (R2=0.99) and the pseudo-second-order kinetic model (R2=0.99). Thermodynamic parameters showed that the adsorption process is spontaneous, endothermic and feasible. [ABSTRACT FROM AUTHOR]

Heavy metal contamination is a major concern, and the adsorption process is regarded as one of the most efficient water remediation processes to deal with it. Herein, we modified fly ash by a microwave-assisted hydrothermal process to enhance its adsorption capacity and tested the material toward Cd(II) and Cu(II). Characterization of the adsorbents was performed by several techniques in detail to elucidate considerable structural changes such as cracking of spherical morphology, increase in surface area and changing of the chemical composition. Then batch adsorption was performed under different conditions to investigate the equilibrium, kinetics, and thermodynamics of the process. NaOH-modified fly ash considerably has a higher adsorption performance than that of the as-received sample for both ions. The highest adsorption capacity of modified fly ash was achieved as 133.8 and 95.7 mg/g for Cd(II) and Cu(II), respectively. The kinetics and isotherms could be perfectly reflected by a pseudo-second-order rate equation and the Freundlich model, while thermodynamics confirmed the endothermicity of the process. [ABSTRACT FROM AUTHOR]

This study investigated the performance of lemongrass (Cymbopogon nardus) leaves biowaste (LLB) to adsorb methylene blue (MB) dye from an aqueous solution using the batch method. Batch experiments were conducted in order to evaluate the effect of initial MB concentration, pH, contact time, and temperature. Point of zero charge measurement demonstrated that the LLB is anionic in a wide range of pH values (pH > 6.7) that support the adsorption of cationic contaminants. The adsorption process pursued Langmuir isotherm (R2 = 0.9960) and pseudo-second-order kinetic model (R2 = 0.9960) best fitted with a maximum capacity of 43.16 mg g−1 at room temperature. The adsorption process was spontaneous and exothermic. FT-IR spectra and SEM-EDX characterization before and after adsorption affirmed the interaction of MB dye onto the LLB. It is suggested that the adsorption of the dye proceeds via electrostatic attraction, cationic exchange, π-π bonding, and hydrogen bonding, while the role of pore filling is modest. LLB has good reusability, as evidenced by four cycles of desorption using 30% acetic acid as the eluent. The optimum conditions were applied to real wastewater with a removal efficiency was 93.58% at pH 9. Therefore, the LLB could be an effective adsorbent for removing MB dye from wastewater. [ABSTRACT FROM AUTHOR]

This study was aimed at evaluating the isotherm of lead(II), manganese(II), and cadmium(II) adsorption in single and multimetal solutions using Nigerian bentonite. The natural and calcined clays were characterized for specific surface area, surface morphology, elemental composition, and cation exchange capacity (CEC). The adsorption data were analyzed and interpreted using isotherm models. The natural bentonite exhibits a specific surface area of 23.5 m2/g and a CEC value of 47.7 mEq/100 g and displays a higher adsorption capacity of all heavy metals in both single and multimetal solutions than the calcined bentonite. The removal of lead(II) by natural bentonite in single-component system is 0.0448 mmol/g. The order of selectivity is lead(II) > cadmium(II) > manganese(II). Result also shows that both clays demonstrate a preferable adsorption toward lead(II). Lead(II) adsorption is less affected by the presence of counter cations in multimetal solution. The adsorption of heavy metals onto Dijah-Monkin bentonite is site selective and site specific, and the adsorption data are well presented by the Langmuir model. The CEC could be the primary mechanism for the uptake of heavy metals, and the removal capacity was shown to depend on the ionic radius of metal ions. [ABSTRACT FROM AUTHOR]

Metal organic frameworks (MOFs) have become material of special attention due to their high porosity and large surface area. Adsorptive removal of ciprofloxacin hydrochloride using MOFs from aqueous waste and real wastewater has been studied in this work. The MOF-5 synthesized showed higher adsorption capacity as compared to activated charcoal. The adsorption satisfies the pseudo-second-order kinetic model and adsorption isotherm is very well explained by the Freundlich and the Sips isotherm. The adsorption mechanism may be explained by the electrostatic interactions of the pharmaceutical compounds and the MOF-5 surface. Finally, it can be concluded that MOF-5 has shown a great potential for their application in wastewater treatment technology development. [ABSTRACT FROM AUTHOR]

The objective of this work was to study the efficiency of activated carbon prepared from agricultural waste (olive stones; OS) on diclofenac (DCF) adsorption in aqueous solutions. The prepared charcoals were characterized by Fourier transform infrared (FTIR), scanning electron microscopy (SEM)/Energy Dispersive X-Ray Analyser (EDX), and Brunauer-Emmett-Teller (BET) analysis techniques. The results show that DCF adsorption is favorable in acid medium and low temperature. The adsorption kinetics follows a pseudo-second-order kinetic model. The adsorption was found to be spontaneous (ΔG° < 0) for OS600°C, whereas the negative values of the enthalpy (ΔH°) suggest an exothermic adsorption for both adsorbents. [ABSTRACT FROM AUTHOR]

Adhesion of bacteria to clay minerals is of great importance in both natural soil environments and technological applications. In the present study, equilibrium experiments along with Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and energy-dispersive X-ray analysis (EDX) were used to investigate the adhesion of Pseudomonas putida to the palygorskite and sepiolite clay minerals. The results showed that bacterial adhesion was rapid and reached equilibrium within 30 min. Equilibrium data showed that sepiolite has higher capacity and affinity than palygorskite for P. putida retention. Mixed FT-IR peak features of the clay minerals and P. putida were observed in the clay–bacteria complex spectra, indicating significant adhesion of P. putida to the minerals. However, some differences in the position of the individual bands were observed between infrared spectra obtained for pure bacteria or clay minerals and their corresponding clay–bacteria complexes, which are believed to be related to clay–bacteria interactions via different mechanisms. SEM/EDX analysis demonstrated fine fibrous clay particles adhered to the surface of individual P. putida cells. The results revealed rapid and close interactions of palygorskite and sepiolite with P. putida cells, which is important for better understanding the fate of bacteria in soil systems dominated by fibrous clay minerals and their practical applications in bioengineering and biotechnology. [ABSTRACT FROM AUTHOR]

The textile industry is responsible for discarding wastewater contaminated with dyes. The timber industry generates waste in the form of sawdust. The aim of the present study was to evaluate the adsorptive potential of sawdust obtained from the Aspidosperma polyneuron tree for the removal of the textile dye from wastewater. Sawdust was subjected to different pre-treatments (acid, alkaline and polyethyleneimine) in order to increase its adsorption capacity. Based on the results from the isotherms, treatment with polyethyleneimine (PEI) led to the greatest adsorption capacity and fits the Freundlich model, indicating cooperative adsorption. Other treatments with sawdust best fit the Langmuir model, but the untreated sawdust presented better results than the treated sawdust. These results were only surpassed by sawdust treated with PEI. A. polyneuron revealed good potential for use as an adsorbent to remove dyes, which is a novel result, since to date there is no study on its use as a sorbent material. [ABSTRACT FROM AUTHOR]

The presence of water in coal presents a technological challenge for its industrial use in energetic processes. Water tends to negatively affect the coal quality and its net heating value (NHV), in addition to affecting its transportation costs. Therefore, this study aims to investigate the effects of glycerol and temperature on water adsorption onto systematically modified coals. A Colombian bituminous coal sample was used as support for being modified with glycerol. The virgin coal and modified coal were characterized by nitrogen adsorption at 77 K (SBET), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, elemental analysis (C–H–N elemental), and thermogravimetric analysis (TGA). The results showed that the water uptake decreased as the amount of glycerol on the coal surface increased. The optimum concentration of 8 wt% of glycerol impregnated on the coal minimized water adsorption. Over a range of water activity evaluations, this amount of glycerol (C8) reduced water adsorption by approximately 60% compared with nonimpregnated coal (C0). As expected, water uptake decreased with increasing temperature. These results are reflected in the NHV with an increase of 17% for the C8 sample compared with the other samples evaluated. The Talu and Meunier model was used to fit the experimental adsorption isotherms, and the mean square root error (MSRE%) was lower than 10%. The isosteric heat of sorption (IHS) for coal tends to decrease as the amount of adsorbed water increases. In addition, the value of IHS decreases as the concentration of glycerol increases due to the blocking of polar adsorption sites present on the coal surface, which are the main regions of low uptake of adsorbed water. Additionally, the Gibbs free energy was found to have negative values, which corroborates the spontaneous adsorption process. [ABSTRACT FROM PUBLISHER]

We studied the adsorption of Brilliant Yellow (BY) from aqueous solutions onto sepiolite and determined the adsorption equilibrium isotherms. We applied pseudo-first-order and pseudo-second-order kinetic models; the adsorption of BY onto sepiolite was best described by the pseudo-second-order kinetic model. The experimental data obtained at different temperatures were analyzed using various isotherm models; the Koble-Corrigan isotherm model provided the best fits for the BY adsorption data at all temperatures. The thermodynamic parameters of the BY adsorption onto sepiolite indicated that the adsorption process is spontaneous and exothermic in nature. [ABSTRACT FROM AUTHOR]

Methane storage was studied on the wet activated carbons by hydrate formation in the mesopore structures. Coconut shell was used as a raw material for preparation of the activated carbon samples. These highly mesoporous samples were prepared by the combination of both physical and chemical activation processes. After wetting the adsorbents with a constant water/carbon weight ratio (R) close to 1, the isotherms were obtained at 2°C up to the pressure of 80 bars. Wetted carbons exhibited stepwise isotherms at the critical pressure in the pressure range of 25–50 bars depending on the activated carbon samples. At this critical pressure, hydrate formation took place slowly. The amounts of methane uptake at 80 bars were obtained ranging from 14.9 to 24.8 mmol.g–1based on the dry adsorbent for different samples. By considering the density of activated carbon samples, the amounts of methane storage varied in the range of 185–237 V/V. [ABSTRACT FROM PUBLISHER]

In the present study, adsorption capacity of mercury(II) on β-zeolite, zeolite Y, and mordenite is investigated. It has been observed that removal rate of Hg(II) is better with zeolite Y than β-zeolite and mordenite, whereas, adsorption capacity of β-zeolite is found to be more than that of zeolite Y and mordenite. Five equilibrium isotherms have been tested to fit the adsorption data. The kinetic data are analyzed using the pseudo-first order, pseudo-second order, and diffusion models. The Freundlich isotherm model shows better fit for β-zeolite and zeolite Y, whereas, in the case of mordenite, Temkin isotherm fits the data well. The kinetic data of adsorption of Hg(II) on β-zeolite, zeolite Y, and mordenite fit well with pseudo-second order. Diffusion studies show that the adsorption of mercury on β-zeolite and zeolite Y are intraparticle diffusion controlled, and mordenite is film-diffusion controlled. [ABSTRACT FROM AUTHOR]

In this study, the adsorption behavior of Basic Red 46 (BR 46) in aqueous solutions by single-walled carbon nanotube (SWCNTs) and functionalized SWCNTs having covalent attachments of carboxylic group (SWCNT-COOH) surface as adsorbents were investigated. The adsorption equilibrium data were analyzed using various adsorption isotherms, and the results have shown that adsorption behavior of BR 46 could be described reasonably well by a generalized isotherm. Kinetic studies indicated adsorption of BR 46 by SWCNTs and SWCNT-COOH surfaces follows a pseudo-order model. The maximum adsorption capacities of BR46 by SWCNTs and SWCNT-COOH surfaces are reported at 298 K, 38.35 and 49.45 mg/g, respectively. The adsorption of BR 46 depends on the initial pH of the solution with maximum uptake occurring at about pH 9. Decrease in the absolute value of ΔG0 with increasing temperature indicates that higher temperatures hardship the adsorption. The negative value of ΔH0 reflects an exothermic adsorption and indicates that the adsorption is favored at low temperature. The negative entropy states that the adsorption of BR 46 by SWCNT-COOH and SWCNTs surfaces are orderly adsorbed by the surfaces. [ABSTRACT FROM AUTHOR]

The present study explores the ability of surfactant modified bamboo sawdust in removing zinc (II) ions from aqueous solutions. The modified bamboo sawdust is characterized by surface area analysis, Scanning Electron Microscope, and Fourier Transform Infrared and X-ray fluorescence analysis. Adsorption isotherm and kinetic models were used to study the adsorption characteristics of zinc (II) ions onto modified bamboo sawdust. The equilibrium adsorption isotherm data were fitted into the Langmuir and Freundlich adsorption isotherms. It was found that modified bamboo sawdust yielded maximum adsorption capacity of 111.12 mg/g at 50°C for zinc (II) ions. The kinetic data obtained at different initial concentrations were analyzed using first-order-reversible reaction, pseudo-first-order, and pseudo-second-order models. The results provide strong evidence to support the hypothesis of adsorption mechanism. [ABSTRACT FROM PUBLISHER]

The adsorption of a synthetic textile dye (Remazol Brilliant Black Reactive) on cocoa pod husk-based activated carbon was investigated in batch process. The adsorbent prepared was characterized by gas adsorption surface analysis (Brunauer Emmett Teller, BET), scanning electron microscopy, and Fourier transform infrared spectroscopy. The effects of initial dye concentration, contact time, solution temperature, and solution pH were evaluated. Equilibrium data were fitted to Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm models, the first being the best with maximum monolayer coverage of 111 mg g-1. Kinetic data were fitted into pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich models; the pseudo second-order model provided the best correlation. Maximum adsorption was observed at pH 7. Standard free energy, standard enthalpy, and standard entropy were also calculated. The adsorption interaction was found to be endothermic and spontaneous. Both the mean free energy of adsorption and the activation energy show that the mechanism is by physisorption. [ABSTRACT FROM AUTHOR]

The present study explores the ability of a new adsorbent-conch shell powder (CSP) in removing Malachite Green from aqueous solutions. The effect of various process parameters, namely initial solution pH, temperature, initial dye concentration, adsorbent dose, and contact time was investigated. Adsorption equilibrium data were well described by the Langmuir isotherm with maximum adsorption capacity of 92.25 mg g-1 at 303 K. The kinetic data conformed to the pseudo-second-order kinetic model. A thermodynamic study showed the spontaneous nature and feasibility of the adsorption process. The results provide strong evidence to support the hypothesis of adsorption mechanism. [ABSTRACT FROM AUTHOR]

Batch adsorption study was carried out to remove excess fluoride from water using pyrophyllite. Result showed that adsorption of fluoride was rapid in first 20 min and thereafter increased slowly to reach the equilibrium in about 2 hrs. About 85% removal efficiency was obtained within 2 hrs at an adsorbent dose of 4 g/L for initial fluoride concentration of 10 mg/L. Maximum fluoride adsorption takes place at pH 4.9. Thermodynamic parameters such as Gibb's free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) changes were determined for the adsorption process. Negative ΔH° value signified that the adsorption process was exothermic in nature. From the kinetic study it was found that fluoride adsorption by pyrophyllite followed pseudo-second-order kinetics with an average rate constant of 0.92 g/mg · min. Intraparticle diffusion model was studied to determine the rate limiting step of the adsorption process. The system followed the Langmuir isotherm with maximum adsorption capacity of 2.2 mg/g of fluoride. [ABSTRACT FROM AUTHOR]

The adsorptive performances of alkaline treated peat have been investigated for the removal of Pb(II), Co(II), and Ni(II) ions from aqueous solutions. The influence of initial metal ions concentration and equilibrium contact time was studied in a series of batch experiments, in comparison with natural peat. An increasing of adsorption capacity of alkaline treated peat was obtained for all studied heavy metals (23.07% - Pb(II), 23.53% - Co(II), and 26.19% - Ni(II)). The Langmuir isotherm model was the best model for the mathematical description of studied heavy metals adsorption on alkaline treated peat. A significant decrease of equilibrium contact time in case of alkaline treated peat was also found. The kinetics of Pb(II), Co(II), and Ni(II) uptake by alkaline treated peat followed the pseudo-second order mechanism. The FT-IR spectrometry analysis showed that carboxylic (-COO-) and hydroxyl (-OH) groups play an important role in the heavy metals binding process. The heavy metal could by easily eluted from the loaded adsorbent with 0.1 mol/L HCl and the adsorbent may be reused in several adsorption/desorption cycles. The alkaline treated peat has better adsorption characteristics for the removal of heavy metals from aqueous solutions, and the cost of this treatment is very low. [ABSTRACT FROM AUTHOR]

In this work, a new simple correlation has been derived for the prediction of the bulk porosity decline during nanofiltration of a salty (ionic) solution using the PVD membrane. This model has been developed on the basis of the adsorption of the cations available in the feed onto the membrane. Therefore, three adsorption isotherms were tested and fitted to the equilibrium adsorption data, and the Freundlich isotherm was subsequently realized as the best choice. The porosity model included two adjustable parameters which can be determined theoretically and experimentally. Adsorption isotherms were combined for the determination of the first parameter and a novel method called 'Flux test' was developed for the other parameter estimation. A reasonable agreement was observed between experimental- and model-predicted porosity. The model's ability of estimation indicates a little decrease at higher pressures due to approaching an unfavorable equilibrium adsorption condition and deviation from the isotherm's parameters from the actual equilibrium amounts to this situation. [ABSTRACT FROM AUTHOR]

In this study, removal of arsenazo(ΙΙΙ) using activated carbon (AC) and multiwalled carbon nanotubes and of methyl red using AC from waste water is reported. The influences of pH, temperature, concentration of the dye, amount of adsorbents, particle size of adsorbent, and contact time on the efficiency of removal from aqueous solution are investigated. Adsorption experiments indicate that the extent of adsorption is strongly dependent on the pH of the solution. Changes in free energy of adsorption ( [image omitted]), enthalpy ( [image omitted]), and entropy ( [image omitted]) are calculated to understand the nature of adsorption. The calculated values of [image omitted] indicate that the adsorption process is spontaneous. The estimated values of [image omitted] and [image omitted] are positive which indicates that the adsorption process is endothermic and that the dye molecules are organized on the adsorbent surface in a more random fashion than in solution. The dye adsorption process follows a pseudo-second-order model under involvement of an intra-particle diffusion mechanism. Standard adsorption isotherms are used to fit the experimental data. [ABSTRACT FROM AUTHOR]

The adsorption characteristics of Pb2+ on pre-boiled treated onion skins (PTOS) and formaldehyde-treated onion skins (FTOS) were evaluated. The effects of Pb2+ initial concentration, agitation rate, solution pH, and temperature on Pb2+ adsorption were investigated in batch systems. Pb2+ adsorption was found to increase with increase in initial concentration. The point of zero net charge (PZC) was 6.53. The optimum pH for the maximum removal of Pb2+ was 6.0. The adsorption equilibrium data was best represented by the Langmuir isotherm model for FTOS and the Freundlich isotherm model for PTOS. The maximum amounts of Pb2+ adsorbed (qm), as evaluated by the Langmuir isotherm, was 200 mgg-1 for FTOS. The efficiencies of PTOS and FTOS for Pb2+ removal were 84,8.0% and 93.5% at 0.15 g/200 mL-1 adsorbent dose, respectively. (C0 = 50 mg L-1). Study concluded that onion skins, a waste material, have good potential as an adsorbent to remove toxic metals like Pb2+ from water. Boehm titration analysis was conducted to determine the surface groups. It was found that the adsorption kinetics of Pb2+ obeyed pseudo-first-order kinetic model as based on Δq (%) values. FTIR and SEM images before and after adsorption was recorded to explore changes in adsorbent-surface morphology. Activation energy (Ea) was obtained as 25.596 kJ/mol. [ABSTRACT FROM AUTHOR]

This study was performed to assess the effects of clearing and cultivation on phosphate sorption kinetics and equilibria as well as phosphate buffering behavior of soils in forest and rangelands from Zagros area, western Iran. Total phosphorus and its organic and inorganic fractions were also determined for the soils according to reference methods. The results showed that clearing and cultivation practices caused a significant increase in soil total and total inorganic phosphorus in the forest soils, but a decrease was observed in the rangeland study area. The concentration of soil organic phosphorus, however, decreased in both forest and rangeland soils after long-term cultivation. Phosphate sorption behavior of the soils was also affected by the land-use changes. The time-dependent sorption data for soils of both protected and disturbed sites were adequately fitted by Power function, Elovich and Parabolic diffusion equations. Kinetic parameters related to rate of phosphate sorption including “specific sorption rate at unit time” and “apparent diffusion coefficient” derived from the models were markedly increased after the land-use conversion. The equilibrium-based phosphate sorption on the soils was significantly described by Langmuir and Freundlich isotherms. Sorption capacity and buffering indices of phosphate, calculated from the isothermal equations, also increased in the cultivated soils as compared to the corresponding soils of the protected sites. The results demonstrated that land-use conversion from natural forest and rangeland to agriculture could significantly influence the distribution and sorption of phosphate in the studied soils which should be considered in sustainable land management in the Zagros area. [ABSTRACT FROM AUTHOR]

The efficacy of treated Shorea dasyphylla bark for Cu(II) and Cr(VI) adsorption was assessed in a batch adsorption system as a function of pH, agitation period, and initial metal concentration. The equilibrium nature of Cu(II) and Cr(VI) adsorption was described by the Freundlich, Langmuir, and Dubinin-Radushkevich isotherms. The maximum monolayer capacities of treated Shorea dasyphylla bark, estimated from the Langmuir equation were 184.66 and 42.72 mg/g for Cu(II) and Cr(VI), respectively. The experimental results were fitted using pseudo-first order, pseudo-second order and intraparticle diffusion kinetic models; the pseudo-second order showed the best conformity to the kinetic data. Thermodynamic parameters such as enthalpy change (ΔH°), free energy change (ΔG°) and entropy change (ΔS°) were determined by applying the Van't Hoff equation. The adsorption of Cu(II) and Cr(VI) onto treated Shorea dasyphylla bark was found to be spontaneous and exothermic. The adsorption mechanism was confirmed by means of Fourier transform infrared (FTIR) and Energy dispersive X-ray (EDX) spectroscopy. The dimensionless constant separation factor (RL), indicated that treated Shorea dasyphylla bark was favorable for Cu(II) and Cr(VI) adsorption. [ABSTRACT FROM AUTHOR]

In this study, Cd(II) ions adsorption from synthetic wastewater was investigated in batch mode using locally available maple sawdust. The equilibrium adsorption quantity was determined to be a function of the solution pH, initial concentration, contact time, and sawdust dose. The equilibrium adsorption results closely followed both the Langmuir and the Freundlich isotherms, but somehow it was well fitted to the Langmuir isotherms. According to the parameters of the Langmuir isotherm, the maximum Cd(II) ions adsorption capacity (qe) onto maple sawdust was found to be 7.429 mg/g that was very close to other adsorbents. [ABSTRACT FROM AUTHOR]

In this work, calcined and uncalcined mixed clays containing kaolin, ball clay, feldspar, pyrophyllite, and quartz are examined as a potential adsorbent for the removal of crystal violet dye from aqueous solution. These clays are characterized by nitrogen adsorption/desorption isotherms, X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and thermo gravimetric analysis (TGA). The kinetics and thermodynamic parameters as well as the effects of the pH, the temperature, and the adsorbent dosage have also been investigated. The experimental results indicate that the Langmuir model expresses the adsorption isotherm better than the Freundlich model. The obtained result showed a tremendous increase in the crystal violet adsorption capacity (1.9 × 10-3 mol g-1) after calcination, which is one order greater than that of the uncalcined mixed clay. The mechanism of the adsorption process is elucidated on the basis of experimental data. The percentage removal of crystal violet dye increases with increasing the pH, the temperature, and the adsorbent dosage. The investigation of kinetic studies indicates that the adsorption of crystal violet on calcined and uncalcined mixed clays could be described by the pseudo-second-order model. The negative ΔG0 values obtained from the thermodynamic investigation confirm that the adsorption is spontaneous in nature. The adsorption results suggest that the calcined and uncalcined mixed clays can also be used as low cost alternatives to the expensive activated carbon for the removal of dyes from aqueous solution. [ABSTRACT FROM AUTHOR]

The chelating ion exchange resin - Dowex M 4195 was used in palladium(II) complexes adsorption from the acidic solutions. This study discusses the sorption kinetics, and more specifically the interparticle diffusion behavior of palladium(II) onto Dowex M 4195. The adsorption studies were used to determine the amount of palladium(II) complexes uptake (resin loading), the distribution coefficients, and the recovery efficiency of Pd(II) complexes. The influence of the agitation speed, the beads size (mean radius of swollen particles), the palladium concentrations, as well as acid concentrations (ionic strength of solutions), the macrocomponent addition (sodium chloride), and the phases contact time was also discussed. Moreover, the effect of temperature was taken into account during the determination of the isotherms. The experimental data obtained at 100 µg/cm3 Pd(II) initial concentration were applied to the kinetic models, and the sorption parameters as well as the normal standard deviation were calculated. Moreover, the Langmuir, Freundlich, and Tempkin-Pyzhev isotherm models were applied and the isotherms parameters were calculated. [ABSTRACT FROM AUTHOR]

Periwinkle shell, an abundant and inexpensive natural resource, was used to prepare activated carbon by physicochemical activation with potassium hydroxide (KOH) and carbon dioxide (CO2) as the activating agents at 850 °C for 2 h. The adsorption equilibrium and kinetics of methylene blue dye on such carbon were then examined at 25 °C. Adsorption isotherm of the methylene blue (MB) on the activated carbon was determined and correlated with common isotherm equations. The equilibrium data for methylene blue adsorption well fitted to the Langmuir equation, with maximum monolayer adsorption capacity of 500.00 mg/g. Two simplified kinetic models including pseudo-first-order and pseudo-second-order equation were selected to follow the adsorption processes. The adsorption of methylene blue on activated carbon derived from periwinkle shell could best be described by the pseudo-second-order equation. The kinetic parameters of this best-fit model were calculated and discussed. [ABSTRACT FROM AUTHOR]

Biosorption studies of Cr(VI) were carried out using waste weed, Salvinia cucullata. Various adsorption parameters were studied, such as agitation speed, contact time, pH, particle size, and concentrations of adsorbent and adsorbate. The equilibrium was achieved in 12 h. A lower pH favoured adsorption of Cr(VI). The kinetics followed pseudo-second-order rate equations. The adsorption isotherm obeyed both the Langmuir and Freundlich models. The calculated activation energy (1.1 kJ mol-1) suggested that the adsorption followed a diffusion-controlled mechanism. Various thermodynamic parameters such as Δ G°, Δ H°, and Δ S° were also calculated. The positive values of enthalpy indicated the endothermic nature of the reaction, and Δ S° showed the increasing randomness at the solid liquid interface of Cr(VI) on the adsorbent, which revealed the ease of adsorption reaction. These thermo-dynamic parameters showed the spontaneity of the reaction. The maximum adsorption of uptake (232 mg g-1) compared well with reported values of similar adsorbents. The rate-determining step was observed to follow an intra-particle diffusion model. [ABSTRACT FROM AUTHOR]

This work focuses on the fundamental studies of heterogeneous adsorption characteristics of mesoporous adsorbent. MCM‐48 was synthesized to investigate the adsorption properties of eight different volatile organic compounds (benzene, cyclohexane, n‐hexane, toluene, methanol, acetone, methyl ethyl ketone (MEK), and trichloroethylene (TCE)). The gravimetric method was used to measure the adsorption equilibrium amount. Several simple and reliable methods such as isosteric enthalpy of adsorption, thermodynamic properties, condensation pressure, organophilicity, and adsorption energy distribution were evaluated to understand the surface heterogeneity of the VOCs+MCM‐48 adsorption system. This work shows that the unique features of the VOCs+MCM‐48 adsorption system are highly dependent on the adsorption step, ionization potential, and Debye dipole moment of VOCs.W. G. Shim and J. W. Lee contributed equally to this work. [ABSTRACT FROM AUTHOR]

The interaction of fluorescein‐5‐isothiocyanate (F5ITC) with gold surfaces—either uncoated or pre‐coated with passivating layers of either sodium citrate (citrate), bis(p‐sulfonatophenyl)phenylphosphine dihydrate dipotassium (BSPP), Pluronic P123 (EO 20 PO 70 EO 20 ), or Pluronic F127 (EO 100 PO 70 EO 100 )—was studied using quartz crystal microbalance (QCM) measurements in order to determine the surface coverage of F5ITC in each case. Adsorption isotherms of the polymers (P123 and F127) binding to a gold surface were also obtained. Binding of F5ITC to the gold surfaces was found to be highly dependent on the passivating layer. The surface coverage Γ F5ITC of F5ITC on gold surfaces can be listed in decreasing order as Γ F5ITC, Au >Γ F5ITC, citrate >Γ F5ITC, P123 >Γ F5ITC, BSPP >Γ F5ITC, F127 . Mechanisms for binding of F5ITC to the gold surfaces are also discussed. [ABSTRACT FROM AUTHOR]

The adsorption of some heavy metals onto the walls of harvested, washed, and dried non-living biomass cells of different Pseudomonas strains was studied at optimum experimental conditions using a simplified single component system. The Langmuir adsorption model was found to be a suitable approach to describe the system via multi-step processes. Isotherms measured at 30.0°C and pH 5.5 with [M] total &ThickSpace;=&ThickSpace;10–100 mM for tight, reversible Cr 6+ (aq), Ni 2+ (aq), Cu 2+ (aq) and Cd 2+ (aq) binding by the cell walls of the investigated biomass fit the Langmuir model and give the pH-independent stoichiometric site capacities ν i and equilibrium constants K i for metal binding at specific biomass sites i &ThickSpace;=&ThickSpace;A, B, C, and D. Tight binding sites A, B, and D of the non-living biomass are occupied by Cr VI , sites A and C by Ni II , sites A and D by Cd II , and only site B by Cu II . It is concluded that ν i is a stoichiometric parameter that is independent of the magnitude of K i for binding site i and that the studied heavy metals selectively and tightly bind at different biomass sites. [ABSTRACT FROM AUTHOR]

The effects of the initial pH and buffer on the adsorption isotherms for cupric and cadmium ions by corncob particles were investigated. The uptakes of the two ions on corncob particles increased with the initial pH. A modified Langmuir model, which considers the effect of pH on the isotherm, has been developed and was used to fit the experimental equilibrium data. The pH at zero-charge point of corncob particles was measured (pH zcp 4.97) by applying the primary equilibrium method of H + and OH - . A method to determine the chemical free energy in the James-Healy model has been proposed in which the pH zcp is used to distinguish the chemical free energy from the solvation and coulombic free energies in that model. The calculated results indicate that the chemical and solvation free energies contribute much to the adsorption free energy. The chemical free energy is constant, while the solvation free energy increases with increasing pH; their effects are opposite. The adsorption free energy increases with the pH value during the adsorption processes of cupric and cadmium ions on corncob particles. [ABSTRACT FROM AUTHOR]