Use of x-ray microtomography to visualise dynamic adsorption of organic vapour and water vapour on activated carbon

X-ray microtomography coupled with image analysis was used to quantify the adsorption of vapours on activated carbon beds. This technique was tested using three different challenges: CCl₄, water vapour and a mixture of water- and organic vapour. It is shown that the used technique allows determining the adsorption front progress in the case of organic vapour and mixture of water and organic vapour whereas the existence of this front was not so obvious in the case of water vapour. Experimental results obtained for organic vapours were interpreted on the basis of the Wheeler-Jonas equation: a good agreement was found between experimental and theoretical breakthrough times.     

Molecular dynamics study of selective adsorption of PCB on activated carbon

The selectivity of PCB adsorption from fish oil onto activated carbon (AC) was investigated by means of molecular dynamics to determine the importance of molecular planarity. PCB congeners 77 and 118 were selected for comparison purposes due to pronounced differences in mean adsorption efficiency and molecular geometry; triolein, a triacylglycerol of oleic acid (C18:1), was used as the representative fish oil component. Graphitic carbon structure was set up to serve as activated carbon model. Molecular force fields employed in the simulations combined short-range parameters from the OPLS with partial atomic charges obtained via quantum chemical calculations using DFT/B3LYP/6-31**G+ and Solvation Model 6. We modified the dihedral angle potential between the PCB aromatic rings and applied Schrödinger's Jaguar package to evaluate the required force field constants. Our complete system comprised a number of PCB molecules dissolved in triacylglycerol that overlaid and filled the pores of an AC structure. The production run of 4 ns provided strong indications that smaller pores will be conductive to better selectivity though also resulted in certain doubts concerning the estimation and assignment of partial atomic charges on the activated carbon. The majority of PCB molecules trapped in pores were attached via cl-AC “bonding”, leaving the main part of the PCB molecule free to interact with triolein. The cl-AC adsorption energy was found to surpass the energy criteria conventionally used for hydrogen bonds. Planar orientation assumed by a PCB molecule in a very energetically favored position on top of the graphite sheet clearly supported the π-cloud overlap hypothesis.     

Chromium adsorption in olive stone activated carbon

In this work, Cr(III) adsorption on activated carbon obtained from olive stones in an upflow fixed-bed column at 30^∘C was studied. The flow rate influence on the breakthrough curves at a feed concentration of 0.87 meq/L was investigated in an attempt to minimize the diffusional resistances. Breakthrough curves for a flow range of 2–8 mL/min were obtained at 10.5 cm bed height and inlet diameter of 0.9 cm. The mass transfer parameters indicated that the bed minimal resistance was attained at 2 mL/min. Therefore, the data equilibrium was carried out until the bed was saturated at 2 mL/min. The dynamic system generated a favorable isotherm with a maximum chromium uptake of 0.45 meq/g. A column sorption mathematical model was created considering the axial dispersion in the column and the intraparticle diffusion rate-controlling steps. The isotherm was successfully modeled by the Langmuir equation and the mathematical model described the experimental dynamic data adequately for feed concentrations from 0.26 to 3.29 meq/L.     

Removal of copper from aqueous solutions by adsorption on activated carbons

The adsorption isotherms of Cu(II) ions from aqueous solutions in the concentration range 40–1000 mg l⁻¹ on two samples of granulated and two samples of activated carbon fibres containing varying amounts of associated oxygen have been reported. The adsorption isotherms are type I of BET classification showing initially a rapid adsorption tending to be asymptotic at higher concentrations. The amounts of oxygen associated with the carbon surface has been enhanced by oxidation with nitric acid and ammonium persulphate in the solution phase and with oxygen gas at 350°C and decreased by degassing of the oxidized carbon samples at 400, 650 and 950°C. The adsorption of Cu(II) ions increases on oxidation and decreases on degassing. The increase in adsorption on oxidation depends on the nature of the oxidative treatment while the decrease in adsorption on degassing depends on the temperature of degassing. This has been attributed to the increase in the carbon–oxygen acidic surface groups on oxidation and their decrease on degassing. Suitable mechanisms consistent with the results have been proposed.     

Kinetics of adsorption and desorption of Pb(II) in aqueous solution on activated carbon by two-site adsorption model

The adsorption and desorption equilibrium and kinetics of lead ions from aqueous solutions on a granular activated carbon (GAC) were examined. Rapid increase followed by slow increase in Pb(II) amount on the GAC was observed as a function of time for the adsorption, while rapid decrease and consecutive very slow decrease was observed in desorption. Based on the experimental results, a two-site adsorption model was proposed for the adsorption and the desorption of Pb(II) under the study conditions. The Pb(II) adsorption on the GAC was estimated to have simultaneously occurred on the strong and the weak adsorption sites. Conventional Langmuir-type kinetic equations were introduced to quantitatively predict the adsorption and desorption with the two-site model by optimizing the parameters to fit the equilibrium and the kinetic experimental results. The equilibrium and kinetic experimental results could be represented by the equations by using one set of the common Langmuir parameters. Resultant kinetic parameters revealed that the adsorption equilibrium constant was two orders of magnitude greater for strong adsorption site than for weak adsorption site, though the maximum number of weak adsorption site was 1.5 times as great as that of strong adsorption site. The strong adsorption equilibrium constant resulted from a small desorption rate constant for the site. The equations were demonstrated to be applicable for predicting other desorption performances as well.     

活性炭吸附-石墨炉原子吸收光谱法测定环境水样中痕量铊

采用以活性炭吸附分离, 石墨炉原子吸收光谱法测定环境水样中的痕量铊. 活性碳吸附后, 用热的(NH4)2C2O4溶液进行淋洗分离, 以0.06 μg/L PdCl2溶液作为基体改进剂. 检出限为2.65 ng/L, 线性范围0.00265～200 μg/L, 回收率为 92.7%～99.0%. 方法可用于环境水样中痕量铊的测定.     

Simultaneous adsorption of copper ions and humic acid onto an activated carbon

In this study, simultaneous adsorption of copper ions and humic acid (HA) from Aldrich onto an activated carbon is investigated. It is found that the HA adsorption in the absence of copper decreases as the pH is increased. It leads to a reduction of 34.7% in the specific surface area of carbon. There exists a critical concentration (CC) of HA for copper adsorption. At HA concentrations < CC, a decrease in copper adsorption is observed; however, the HA improves the adsorption at HA concentrations > CC. An increase in ionic strength can enhance the copper uptake; however, zinc and/or cobalt ions have an insignificant influence on copper adsorption. The adsorption is significantly increased by citric acid, whereas addition of EDTA slightly decreases the uptake. An intraparticle diffusion model is successfully used to describe the copper adsorption kinetics.     

Chemical production of activated carbon from green coffee with adsorption isotherm support by Taguchi model

In this study, the aim was to produce the activated carbon from green coffee for use in liquid phase applications with adding zinc borate which was a boron chemical. Phosporic acid was chosen as the chemical activation material and different reaction parameters (percent of phosporic acid, amount of zinc borate) were tested during the process of chemical activation. The experimental sets were determined by using Taguchi optimization method and optimal conditions were obtained. Taguchi optimization method was preferred to reach optimum process parameters by using time and material in the most beneficial way. The effects of the process parameters (microwave drying time, temperature of carbonization and duration of carbonization) were investigated to determine the optimal sample. The characteristic properties of the obtained activated carbons were determined with Fourier transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller surface area analysis (BET), Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The samples of activated carbon produced were used for determination of the iodine number and the adsorption of heavy metal Cr (VI) ions from solution. Analysis and studies of adsorption showed that activated carbon was produced successfully. The activated carbon was evaluated in liquids phase applications and Langmuir isotherm was found more applicable and experimental data was proper with the second-order kinetic model.     

Effect of doping activated carbon based Ricinodendron Heudelotti shells with AgNPs on the adsorption of indigo carmine and its antibacterial properties

Two adsorbents samples namely ZnCl₂ Activated carbon (ACZ); and a composite from ACZ doped with silver nanoparticles (ACZ/AgNP) made by successful precipitation loading onto ACZ and silver nanoparticles of the Recinodendron heudelotti shells aqueouse extract (RHSNP) were prepared. The ACZ and ACZ/AgNP materials were characterised by scanning electron microscopy (SEM), Energy dispersive X-ray (EDX), Fourier Transform Infra-Red (FTIR) spectroscopy, X-ray diffraction (XRD) and particle size by Zeta sizer. The antibacterial activities of ACZ, ACZ/AgNP the RHSNP and the RHS extract was done by the broth microdilution test on Shigella flexneri, Salmonella typhi and Escherichia coli species. Futhermore, the adsorption capacities of the ACZ and the ACZ/AgNP was investigated using the hazardous Indigo Carmine (IC) dye. The SEM results shows spongy rock-like surface on both adsorbents (ACZ and ACZ/AgNP) with the presence of pores, EDX and XRD shows the presence of crystalline zincite on ACZ and Ag on the ACZ/AgNP. The FTIR spectral for both adsorbents preseumes a composite material while the zeta sizer shows that all the materials samples prepared were in the nano-range. The extract and ACZ showed no antimicrobial activities while the antimicrobial properties were proven to be very interesting for the nanoparticles and the ACZ/AgNP but higher for the ACZ/AgNP (7.812 ≤ MIC ≤ 31.25 µg/ml). The adsorption capacities of IC were found to decrease by 33.15% respectively using the maximum concentration at equilibrium. RHS is therefore a good and promising precursor for the preparation of activated carbon and nanoparticles for bacterial containing water purification and for the treatment of bacterial infections.     

Competitive adsorption and desorption of a bi-solute mixture: effect of activated carbon type

This study aims to clarify the effects of carbon activation type and physical form on the extent of adsorption capacity and desorption capacity of a bi-solute mixture of phenol and 2-chlorophenol (2-CP). For this purpose, two different PACs; thermally activated Norit SA4 and chemically activated Norit CA1, and their granular countertypes with similar physical characteristics, thermally activated Norit PKDA and chemically activated Norit CAgran, were used. The thermally activated carbons were better adsorbers for phenol and 2-CP compared with chemically activated carbons, but adsorption was more reversible in the latter case. 2-CP was adsorbed preferentially by each type of activated carbon, but adsorption of phenol was strongly suppressed in the presence of 2-CP. The simplified ideal adsorbed solution (SIAS) model underestimated the 2-CP loadings and overestimated the phenol loadings. However, the improved and modified forms of the SIAS model could better predict the competitive adsorption. The type of carbon activation was decisive in the application of these models. For each activated carbon type, phenol was desorbed more readily in the bi-solute case, but desorption of 2-CP was less compared with single-solute. This was attributed to higher energies of 2-CP adsorption.     

Influence of surface heterogeneity on hydrogen adsorption on activated carbons

This study presents an experimental and theoretical analysis of the effect of surface heterogeneity on the capacity of 20 commercial activated carbons to adsorb hydrogen at 77 and 258 K and for maximum pressures of 20 bar. Some of the samples have been subjected to surface modification by impregnation or by surface oxidation prior to the hydrogen adsorption measurements. All the activated carbons have been analyzed by N₂ adsorption at 77 K using the thermodynamic isotherm presented in a previous study. The hydrogen adsorption capacity of the activated carbons has been well correlated to the micropore volume and the characteristic m₂ parameter of the thermodynamic isotherm accounting for the energy heterogeneity of the material. On the basis of the model presented here, we discuss how surface heterogeneity, in addition to the adsorption strength, might affect the ability of activated carbons and related materials to adsorb hydrogen.     

Adsorption of anthracene using activated carbon and Posidonia oceanica

The aim of this work was to examine the static capacity of adsorption of anthracene by Posidonia oceanica and activated carbon. The effect of experimental parameters pH and contact time on the anthracene adsorption onto cited materials was investigated in detail. The results showed that the anthracene removal on both P. oceanica and activated carbon was unaffected in the pH range of 2–12. The equilibrium data fit well to the Langmuir model with a maximum adsorption capacity of 8.35 mg/g and 0.14 mg/g, respectively with activated carbon and P. oceanica.     

Atenolol sequestration using activated carbon derived from gasified Glyricidia sepium

Activated carbon (AC) derived from gasified Glyricidia sepium woodchip (GGSWAC) was prepared using KOH and CO₂ activation via microwave radiation technique to remove atenolol (ATN) from aqueous solution. The surface area (S_BET) and total pore volume (TPV) of GGSWAC were 483.07 m²/g and 0.255 cm³, respectively. The n-BET model fits well with the isothermal data indicating a multilayer adsorption with the saturation capacity of 121, 143 and 163 mg/g at 30, 45 and 60 °C, respectively. The kinetic study showed that ATN adsorption followed Avrami model equation (R² ≅ 0.99). Based on the thermodynamic parameters, the adsorption of ATN onto GGSWAC was endothermic (ΔH_S = 234.17 kJ/mol) in the first layer of adsorption and exothermic in the subsequent layer (ΔH_L = −165.62 kJ/mol). The ATN adsorption was controlled by both diffusion and chemisorption. In continuous operation, the Thomas (R² = 0.9822) and Yoon–Nelson (R² = 0.9817) models successfully predicted the ATN adsorption.     

Removal of ionic liquids and ibuprofen by adsorption on a microporous activated carbon: Kinetics,isotherms, and pore sites

Ionic liquids (ILs) are considered as emergent pollutants as their synthesis and further use at a large scale might generate environmental problems. The adsorption on activated carbons represents one of the most effective methods to remove ionic liquids and other micropollutants from wastewater. In this work, the adsorption properties on an activated carbon cloth of two pyridinium ionic liquids (4-tert-butyl-1-propylpyridinium bromide (IL1) and 4-tert-butyl-1-(2-carboxyethyl)pyridinium bromide (IL2)) newly synthesized, were compared with the ones of ibuprofen. The adsorption kinetics and isotherms were studied at pH 3 and 7.5. The adsorption thermodynamic parameters calculated from the isotherms indicate an exothermic process, typical of physisorption. The adsorption kinetics of a mixture of the molecules show a competition between ibuprofen and IL2. The location of each adsorbed ionic liquid and ibuprofen into the porosity of the activated carbon cloth was determined from N₂ (at 77 K) and CO₂ adsorption isotherms (at 273 K). The purification process of an effluent containing the ionic liquids and the ibuprofen in mixture or in single solute could be workable by adsorption on an activated cloth.     

Prediction of adsorption of organic component and water vapour mixture onto activated carbon

A simple isotherm equation is derived for the adsorption of an organic component onto activated carbon in presence of water vapour. The theoretical results are compared with experimental data for toluene-water vapour-activated carbon, which were published byRipperger andGermerdonk [10].

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Vorhersage der Adsorption einer organischen Komponente und Wasserdampf an Aktivkohle

Zusammenfassung Es wird eine einfache Adsorptionsisotherme abgeleitet, welche die gleichzeitige Adsorption eines organischen Stoffes und Wasser an Aktivkohle beschreibt. Die theoretischen Ergebnisse werden mit experimentellen Resultaten vonRipperger undGermerdonk [10] für Toluol-Wasser-Aktivkohle verglichen.

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Symbols a _i adsorbate concentration in adsorbent, kg/kg of carbon - a _0i monolayer capacity, kg/kg of carbon - b _i kinetic parameter of theLangmuir equation - E _j adsorption energy in thej-th layer - i i-th component (1 — water vapour, 2 — organic compound) - j j-th layer - m number of layers - n number of adsorbed components - p partial pressure, Pa - p* saturation partial pressure, Pa - p _C water vapour partial pressure at begining of capillary condensation, Pa - surface coverage     

Application of the LBET class models to describe the structure of microporous activated carbons on the basis of argon and benzene adsorption isotherms

The reported research is concerned with the properties of the new LBET class models designed to describe the heterogeneous adsorption on microporous carbonaceous materials. In particular, the new adsorption models were applied to a computer analysis of the microporous structure of two active carbons on the basis of argon and benzene adsorption isotherms. This paper provides for more thorough information on the properties of the proposed models and identification technique presented in the earlier papers.     

Electrochemically assisted adsorption/desorption of bentazone on activated carbon cloth

This paper investigates the use of electrochemical techniques for the removal of a common herbicide, bentazone, from water streams using a carbon-based electrode. Activated carbon cloth with high surface area and narrow micropores was used as electrode. For a better understanding of the process, adsorption was investigated under both open circuit and controlled polarization conditions, the latter in anodic and cathodic directions. It was found that anodic polarization enhances the kinetics of adsorption of the herbicide on the carbon cloth, the extent of which is strongly related to the applied current value. At converse, cathodic polarization induces the reversible desorption of the compound. Moreover, in-situ UV spectra recording on the solution did not show any structural change of the herbicide upon polarization, demonstrating the reversibility of the process for the regeneration of the adsorbent and the recovery of the compound. Based on these experiments, a mechanism is proposed to interpret the reversible sorption of bentazone under polarization.     

Activated carbon/MOFs composite: AC/NH2-MIL-101(Cr), synthesis and application in high performance adsorption of p-nitrophenol

P-nitrophenol (PNP), a hazardous phenolic material, should be eliminated from water in order to prevent damage to the marine ecosystem, animals as well as humans. Although adsorption seems to become the most widely used strategy, an effective and strong-capacity adsorbent to minimize PNP under the approved concentration is essential to discovering. In this study, a class of porous adsorbents composite was developed for the PNP removal from water. AC-NH₂-MIL-101(Cr) has chosen to boost the removal of PNP from water owing to extremely porous and stable in water. The fabricated composite has 2049 m².g⁻¹ large surface area and 0.93 cm³.g⁻¹ pore volume. The adsorption kinetics and isotherms were investigated. AC-NH₂-MIL-101(Cr) was found to exhibit an adsorption capacity of ~ 18.3 mg g⁻¹. The mechanism for this strong adsorption performance was suggested and related to affinity NO₂ groups of PNP and the unsaturated chromium site of AC-NH₂-MIL-101(Cr), the coulombic interaction via the hydrogen bond between the PNP and AC-NH₂-MIL-101(Cr) and π-π stacking interaction. AC-NH₂-MIL-101(Cr) composite also displayed exceptional stability and reusability after a successive PNP removal processes. This study provides new insight into developing and synthesizing extremely effective nanoporous material for organic contaminants disinfection from waste water based on MOFs.     

Kinetic and equilibrium studies of urea adsorption onto activated carbon: Adsorption mechanism

We found that activated carbon effectively removed urea from solution and that urea adsorption onto activated carbon followed a pseudo-second-order kinetic model. We classified the urea adsorption on activated carbon as physical adsorption and found that it was best described by the Halsey adsorption isotherm, suggesting that the multilayer adsorption of urea molecules on the adsorption sites of activated carbon best characterized the adsorption system. The mechanism of adsorption of urea by activated carbon involved two steps. First, an amino (–NH₂) group of urea interacted with a carbonyl (–C?O) group and a hydroxyl (?OH) group on the surface of activated carbon via dipole–dipole interactions. Next, the –C?O group of the urea molecule adsorbed to the activated carbon interacted with another –NH₂ group from a second urea molecule, leading to multilayer adsorption.     

Adsorption of organics on activated carbon cloth at zero surface coverage

Summary Adsorption properties of activated carbon cloth were investigated by gas-solid chromatography. Retention of several organic compounds was measured in the temperature range from 200 to 250°C. The gas/solid distribution coefficients and the related thermodynamic function of adsorption at zero surface coverage were determined. The obtained experimental data were used to explain the adsorbent-adsorbate interaction.