Activated carbon and Adsorption

GAS-liquid interfaces, ADSORPTION, ORGANIC chemistry, EMPIRICAL research, SURFACE chemistry, and ENVIRONMENTAL sciences

In this work, total smooth air-water interfacial areas were measured for a series of nine natural and model sandy porous media as a function of water saturation using synchrotron X-ray microtomography. lnterfacial areas decreased linearly with water saturation, while the estimated maximum interfacial area compared favorably to the media geometric surface areas. Importantly, relative interfacial area (i.e., normalized by geometric surface area) versus water saturation plots for all media collapsed into a single linear cluster (r² = 0.93), suggesting that geometric surface area is an important, and perhaps sufficient, descriptor of sandy media that governs total smooth interfacial area-water saturation relationships. Measured relationships were used to develop an empirical model for estimating interfacial area-water saturation relationships for sandy porous media. Model-based interfacial area estimates for independent media were generally slightly higher than interfacial areas measured using aqueous-phase interfacial tracer methods, which may indicate that microtomography captures regions of the air-water interface that are not accessible to aqueous-phase interfacial tracers. The empirical model presented here requires only average particle diameter and porosity as input parameters and can be used to readily estimate air-water interfacial area-water saturation relationships for sandy porous media. [ABSTRACT FROM AUTHOR]

ADSORPTION, HUMIC acid, FULVIC acids, ORGANIC acids, ABSORPTION, ORGANIC compounds, ORGANIC chemistry, LINEAR free energy relationship, LAND-water ecotones, and SORBENTS

In this work we present a dataset of more than 1000 natural organic matter (NOM)/air partition coefficients covering polar and nonpolar organic compounds measured in 10 different humic and fulvic acids (HAs/FAs) from terrestrial and aquatic origins. Differences of more than 1 order of magnitude in the sorption coefficients of a given compound measured in HAs and FAs from different origins were found. The terrestrial HAs exhibited substantially higher sorption coefficients compared to aquatic HAs and FAs. The difference between any two types of NOM is mainly reflected by a constant shift in the partition coefficients that applies to all compounds in the same way. This indicates that it is the number of available sorption sites per mass of sorbent rather than the types of intermolecular interactions between the sorbate and the sorbent that governs the major differences between the sorption properties of various types of NOM. The experimental partition coefficients measured in all HAs and FAs were successfully described by polyparameter linear free energy relationships (pp-LFERs) that explicitly account for van der Waals as well as H-donor/acceptor interactions between the sorbate and the sorbent. These pp-LFER equations provide for the first time a tool that allows including the variability of the sorption properties of NOM in environmental fate models. [ABSTRACT FROM AUTHOR]

ORGANIC compounds, HEATING, ORGANIC chemistry, ADSORPTION, SEPARATION (Technology), ELECTRON-stimulated desorption, THERMAL desorption, VAPORS, and CARBON compounds

A new method to achieve steady-state and dynamic-tracking desorption of organic compounds from activated carbon was developed and tested with a bench-scale system. Activated carbon fiber cloth (ACFC) was used to adsorb methyl ethyl ketone (MEK) from air streams. Direct electrothermal heating was then used to desorb the vapor to generate select vapor concentrations at 500 ppmv and 5000 ppmv in air. Dynamic-tracking desorption was also achieved with carefully controlled yet variable vapor concentrations between 250 ppmv and 5000 ppmv, while also allowing the flow rate of the carrier gas to change by 100%. These results were also compared to conditions when recovering MEK as a liquid, and using microwaves as the source of energy to regenerate the adsorbent to provide MEK as a vapor or a liquid. [ABSTRACT FROM AUTHOR]

ADSORPTION, ORGANIC compounds, ESCHERICHIA coli, ORGANIC chemistry, TETRACHLOROBENZENE, PHENANTHRENE, METAL ions, TRANSITION metals, and FUNCTIONAL groups

We observed that the presence of transition metal ion, Ag+, Cu2+, or Fe3+, at a concentration of 3 mg L-1 increases sorption of two nonpolar hydrophobic organic compounds (HOCs), phenanthrene (PHEN), and 1,2,4,5-tetrachlorobenzene (TeCB) by 1.5–4 times to Gram-negative bacteria Escherichia coli. Complexation of transition metals with the deprotonated functional groups (mainly carboxyl) of bacterial cell walls neutralizes the negative charge, making the bacterial surface less hydrophilic and enhancing hydrophobic partition of HOCs. This is evidenced by the fact that the zeta potential (ζ) value of bacteria becomes less negative when a transition metal is present. Furthermore, the observed higher sorption of PHEN than TeCB at low pH (3.8) cannot be fully explained by the pH-dependent hydrophobic effects. The results led us to propose two specific sorption mechanisms for π-donor compounds: cation-π interactions with protonated amines and π H-bonding with protonated carboxyls. The biosorption of PHEN was best described as π-donor compared to the biosorption of TeCB considered non-π-donor. Results of the present study highlight that the presence of coexisting transition metals and changes on pH have a major effect on the biosorption of nonpolar HOCs. [ABSTRACT FROM AUTHOR]

ADSORPTION, ABSORPTION, ENVIRONMENTAL protection, ENVIRONMENTAL management, ORGANIC compounds, EQUILIBRIUM, CONTAMINATION (Technology), ORGANIC chemistry, and ENVIRONMENTAL sciences

In a recent publication we presented experimental Leonardite humic acid/air partition coefficients for 188 polar and nonpolar organic compounds measured with one consistent method. In this paper these experimental data are evaluated with various model predictions. For the PcKocWlN model some major shortcomings become apparent. The octanol-based Karickhoff-model exhibits a good performance for the nonpolar compounds but not for the polar ones. A good description of the whole data set is achieved with a polyparameter linear free energy relationship (pp-LFER) that explicitly accounts for the nonpolar (van der Waals and cavity formation) and polar (electron donor/acceptor) interactions between the sorbate molecule and the sorbent phase. With this pp-LFER model, most of the humic acid/air partition coefficients could be predicted within a factor of 2. The pp-LFER model also successfully predicts organic-C/water partition coefficients (Kjoc) collected from the literature when it is combined with a pp-LFER for air/water partition coefficients. This supports our earlier conclusion thatthe thermodynamic cycle is applicable in the humic acid/water/air system. Based on our experimental data, we present a pp-LFER- model for humic acid/air and humic acid/water partitioning at any ambient temperatures. [ABSTRACT FROM AUTHOR]

ENVIRONMENTAL protection, ENVIRONMENTAL management, ORGANIC compounds, ADSORPTION, ABSORPTION, EQUILIBRIUM, CONTAMINATION (Technology), ORGANIC chemistry, and ENVIRONMENTAL sciences

The environmental fate of volatile and semivolatile organic compounds is determined by their partitioning between air and soil constituents, in particular soil organic matter (SUM). While there are many studies on the partitioning of nonpolar compounds between water and SUM, data on sorption of polar compounds and data for sorption from the gas phase are rather limited. In this study, Leonardite humic acid/air partition coefficients for 188 polar and nonpolar organic compounds at temperatures between 5 and 75°C and relative humidities between <0.01% and 98% have been determined using a dynamic flow-through technique. To the best of our knowledge, this is by far the largest and most diverse and consistent data set for sorption into humic material published so far. The major results are as follows: the relative humidity affected the experimental partition coefficients by up to a factor of 3; polar compounds generally sorbed more strongly than nonpolar compounds due to H-bonding (electron donor/acceptor interactions) with the humic acid; no glass transitions in the range of 5–75 °C that would be relevant with respect to the sorption behavior of hydrated Leonardite humic acid were observed; our experimental data agree well with experimental partition coefficients from various literature sources. [ABSTRACT FROM AUTHOR]

VOLATILE organic compounds, FORMALDEHYDE, ATMOSPHERIC deposition, HYDROXYAPATITE, SURFACE active agents, SURFACE tension, ORGANIC chemistry, ARTIFICIAL substrates (Aquatic biology), and ADSORPTION

Some harmful volatile organic compounds (VOCs), such as formaldehyde, are regulated atmospheric pollutants. Therefore, development of a material to remove these VOCs is required. We focused on hydroxyapatite, which had been biomimetically coated on a polyamide film, as an adsorbent and found that formaldehyde was successfully removed by this adsorbent. The amount of formaldehyde adsorbed increased with the area of the polyamide film occupied by hydroxyapatite. The amount of adsorbed formaldehyde and its rate of adsorption were larger for hydroxyapatite deposited on polyamide film than for the commercially available calcined hydroxyapatite powder. This high adsorption ability is achieved by the use of nanosized particles of hydroxyapatite with low crystallinity and containing a large number of active surface sites. Therefore, hydroxyapatite biomimetically coated on organic substrates can become a candidate material for removing harmful VOCs such as formaldehyde. [ABSTRACT FROM AUTHOR]

ORGANIC compounds, ACTIVATED carbon, ORGANIC chemistry, HERBICIDES, RATIONAL numbers, WATER purification, ADSORPTION, SEPARATION (Technology), and SURFACE chemistry

Natural organic matter (NOM) hinders adsorption of trace organic compounds on powdered activated carbon (PAC) via two dominant mechanisms: direct site competition and pore blockage. COMPSORB, a three-component model that incorporates these two competitive mechanisms, was developed in a previous study to describe the removal of trace contaminants in continuous-flow hybrid PAC adsorption/membrane filtration systems. Synthetic solutions containing two model compounds as surrogates for NOM were used in the original study to elucidate competitive effects and to verify the model. In the present study, a quantitative method to characterize the components of NOM that are responsible for competitive adsorption effects in natural water was developed to extend the application of COMPSORB to natural water systems. Using batch adsorption data, NOM was differentiated into two fictive fractions, representing the strongly competing and pore blocking components, and each was treated as a single compound. The equilibrium and kinetic parameters for these fictive compounds were calculated using simplified adsorption models. This parametrization procedure was carried out on two different natural waters, and the model was verified with experimental data obtained for atrazine removal from natural water in a PAC/membrane system. The model predicted the system performance reasonably well and highlighted the importance of considering both direct site competition and pore blockage effects of NOM in modeling these systems. [ABSTRACT FROM AUTHOR]

ADSORPTION, CARBON, SURFACE chemistry, ORGANIC chemistry, SURFACE tension, SORBENTS, THERMAL desorption, THERMOGRAVIMETRY, and HEAT treatment of metals

To understand the nature of H2S adsorption onto carbon surfaces under dry and anoxic conditions, the effects of carbon pore structure and surface chemistry were studied using activated carbon fibers (ACFs) with different pore structures and surface areas. Surface pretreatments, including oxidation and heat treatment, were conducted before adsorption/desorption tests in a fixed-bed reactor. Raw ACFs with higher surface area showed greater adsorption and retention of sulfur, and heat treatment further enhanced adsorption and retention of sulfur. The retained amount of hydrogen sulfide correlated well with the amount of basic functional groups on the carbon surface, while the desorbed amount reflected the effect of pore structure. Temperature-programmed desorption (TPD) and thermal gravimetric analysis (TGA) showed that the retained sulfurous compounds were strongly bonded to the carbon surface. In addition, surface chemistry of the sorbent might determine the predominant form of adsorbate on the surface. [ABSTRACT FROM AUTHOR]

SURFACE active agents, ADSORPTION, REFLECTANCE spectroscopy, HEAVY metals, ORGANIC chemistry, and WATER

The influence of interaction between mineral components in natural mixtures on the adsorption of organic and inorganic species on the mineral surfaces is recognized. However, the surface phenomena have been meagerly investigated. In this study the formation of different surface species of surfactant (amyl xanthate, C5H11,OC(S)S- adsorbed on FeS₂, PbS, and CuFeS₂ has been spectroscopically investigated in single-mineral and complex systems. The type and amount of adsorbed species were determined directly on each mineral surface by infrared external reflection spectroscopy. Galvanic interaction between grains of different minerals could have tremendous consequence on the adsorption of surfactants on each mineral component and their future reactivity. The detected changes are dramatic, from no adsorption to the formation of several layers of hydrophobic or hydrophilic surface products depending on which minerals are in contact It has been documented that even very short contact time between different mineral grains by collision is sufficient to produce dramatic modification of the surface composition and structure. The results obtained indicate clearly that the observations and conclusions about the surfactant adsorption made in a single mineral system cannot be simply extrapolated to describe the real situation in natural multicomponent mineral systems. The obtained information on sulfide mineral interaction in complex systems is indispensable to understand processes taking place in nature at mineral-water interfaces (dissolution of heavy metals). An additional benefit is the improved ability to design efficient separation processes of these minerals. [ABSTRACT FROM AUTHOR]

Organic compounds, Heating, Organic chemistry, Adsorption, Separation (Technology), Electron-stimulated desorption, Thermal desorption, Vapors, and Carbon compounds

A new method to achieve steady-state and dynamic-tracking desorption of organic compounds from activated carbon was developed and tested with a bench-scale system. Activated carbon fiber cloth (ACFC) was used to adsorb methyl ethyl ketone (MEK) from air streams. Direct electrothermal heating was then used to desorb the vapor to generate select vapor concentrations at 500 ppmv and 5000 ppmv in air. Dynamic-tracking desorption was also achieved with carefully controlled yet variable vapor concentrations between 250 ppmv and 5000 ppmv, while also allowing the flow rate of the carrier gas to change by 100%. These results were also compared to conditions when recovering MEK as a liquid, and using microwaves as the source of energy to regenerate the adsorbent to provide MEK as a vapor or a liquid. [ABSTRACT FROM AUTHOR]

Adsorption, Organic compounds, Escherichia coli, Organic chemistry, Tetrachlorobenzene, Phenanthrene, Metal ions, Transition metals, and Functional groups

We observed that the presence of transition metal ion, Ag+, Cu2+, or Fe3+, at a concentration of 3 mg L-1 increases sorption of two nonpolar hydrophobic organic compounds (HOCs), phenanthrene (PHEN), and 1,2,4,5-tetrachlorobenzene (TeCB) by 1.5–4 times to Gram-negative bacteria Escherichia coli. Complexation of transition metals with the deprotonated functional groups (mainly carboxyl) of bacterial cell walls neutralizes the negative charge, making the bacterial surface less hydrophilic and enhancing hydrophobic partition of HOCs. This is evidenced by the fact that the zeta potential (ζ) value of bacteria becomes less negative when a transition metal is present. Furthermore, the observed higher sorption of PHEN than TeCB at low pH (3.8) cannot be fully explained by the pH-dependent hydrophobic effects. The results led us to propose two specific sorption mechanisms for π-donor compounds: cation-π interactions with protonated amines and π H-bonding with protonated carboxyls. The biosorption of PHEN was best described as π-donor compared to the biosorption of TeCB considered non-π-donor. Results of the present study highlight that the presence of coexisting transition metals and changes on pH have a major effect on the biosorption of nonpolar HOCs. [ABSTRACT FROM AUTHOR]

Environmental protection, Environmental management, Contamination (Technology), Adsorption, Absorption, Organic compounds, Equilibrium, Organic chemistry, and Environmental sciences

In a recent publication we presented experimental Leonardite humic acid/air partition coefficients for 188 polar and nonpolar organic compounds measured with one consistent method. In this paper these experimental data are evaluated with various model predictions. For the PcKocWlN model some major shortcomings become apparent. The octanol-based Karickhoff-model exhibits a good performance for the nonpolar compounds but not for the polar ones. A good description of the whole data set is achieved with a polyparameter linear free energy relationship (pp-LFER) that explicitly accounts for the nonpolar (van der Waals and cavity formation) and polar (electron donor/acceptor) interactions between the sorbate molecule and the sorbent phase. With this pp-LFER model, most of the humic acid/air partition coefficients could be predicted within a factor of 2. The pp-LFER model also successfully predicts organic-C/water partition coefficients (Kjoc) collected from the literature when it is combined with a pp-LFER for air/water partition coefficients. This supports our earlier conclusion thatthe thermodynamic cycle is applicable in the humic acid/water/air system. Based on our experimental data, we present a pp-LFER- model for humic acid/air and humic acid/water partitioning at any ambient temperatures. [ABSTRACT FROM AUTHOR]

Environmental protection, Environmental management, Contamination (Technology), Organic compounds, Adsorption, Absorption, Equilibrium, Organic chemistry, and Environmental sciences

The environmental fate of volatile and semivolatile organic compounds is determined by their partitioning between air and soil constituents, in particular soil organic matter (SUM). While there are many studies on the partitioning of nonpolar compounds between water and SUM, data on sorption of polar compounds and data for sorption from the gas phase are rather limited. In this study, Leonardite humic acid/air partition coefficients for 188 polar and nonpolar organic compounds at temperatures between 5 and 75°C and relative humidities between <0.01% and 98% have been determined using a dynamic flow-through technique. To the best of our knowledge, this is by far the largest and most diverse and consistent data set for sorption into humic material published so far. The major results are as follows: the relative humidity affected the experimental partition coefficients by up to a factor of 3; polar compounds generally sorbed more strongly than nonpolar compounds due to H-bonding (electron donor/acceptor interactions) with the humic acid; no glass transitions in the range of 5–75 °C that would be relevant with respect to the sorption behavior of hydrated Leonardite humic acid were observed; our experimental data agree well with experimental partition coefficients from various literature sources. [ABSTRACT FROM AUTHOR]

Volatile organic compounds, Formaldehyde, Atmospheric deposition, Hydroxyapatite, Surface active agents, Surface tension, Organic chemistry, Artificial substrates (Aquatic biology), and Adsorption

Some harmful volatile organic compounds (VOCs), such as formaldehyde, are regulated atmospheric pollutants. Therefore, development of a material to remove these VOCs is required. We focused on hydroxyapatite, which had been biomimetically coated on a polyamide film, as an adsorbent and found that formaldehyde was successfully removed by this adsorbent. The amount of formaldehyde adsorbed increased with the area of the polyamide film occupied by hydroxyapatite. The amount of adsorbed formaldehyde and its rate of adsorption were larger for hydroxyapatite deposited on polyamide film than for the commercially available calcined hydroxyapatite powder. This high adsorption ability is achieved by the use of nanosized particles of hydroxyapatite with low crystallinity and containing a large number of active surface sites. Therefore, hydroxyapatite biomimetically coated on organic substrates can become a candidate material for removing harmful VOCs such as formaldehyde. [ABSTRACT FROM AUTHOR]

Organic compounds, Activated carbon, Organic chemistry, Herbicides, Rational numbers, Water purification, Adsorption, Separation (Technology), and Surface chemistry

Natural organic matter (NOM) hinders adsorption of trace organic compounds on powdered activated carbon (PAC) via two dominant mechanisms: direct site competition and pore blockage. COMPSORB, a three-component model that incorporates these two competitive mechanisms, was developed in a previous study to describe the removal of trace contaminants in continuous-flow hybrid PAC adsorption/membrane filtration systems. Synthetic solutions containing two model compounds as surrogates for NOM were used in the original study to elucidate competitive effects and to verify the model. In the present study, a quantitative method to characterize the components of NOM that are responsible for competitive adsorption effects in natural water was developed to extend the application of COMPSORB to natural water systems. Using batch adsorption data, NOM was differentiated into two fictive fractions, representing the strongly competing and pore blocking components, and each was treated as a single compound. The equilibrium and kinetic parameters for these fictive compounds were calculated using simplified adsorption models. This parametrization procedure was carried out on two different natural waters, and the model was verified with experimental data obtained for atrazine removal from natural water in a PAC/membrane system. The model predicted the system performance reasonably well and highlighted the importance of considering both direct site competition and pore blockage effects of NOM in modeling these systems. [ABSTRACT FROM AUTHOR]

Adsorption, Carbon, Surface chemistry, Organic chemistry, Surface tension, Sorbents, Thermal desorption, Thermogravimetry, and Heat treatment of metals

To understand the nature of H2S adsorption onto carbon surfaces under dry and anoxic conditions, the effects of carbon pore structure and surface chemistry were studied using activated carbon fibers (ACFs) with different pore structures and surface areas. Surface pretreatments, including oxidation and heat treatment, were conducted before adsorption/desorption tests in a fixed-bed reactor. Raw ACFs with higher surface area showed greater adsorption and retention of sulfur, and heat treatment further enhanced adsorption and retention of sulfur. The retained amount of hydrogen sulfide correlated well with the amount of basic functional groups on the carbon surface, while the desorbed amount reflected the effect of pore structure. Temperature-programmed desorption (TPD) and thermal gravimetric analysis (TGA) showed that the retained sulfurous compounds were strongly bonded to the carbon surface. In addition, surface chemistry of the sorbent might determine the predominant form of adsorbate on the surface. [ABSTRACT FROM AUTHOR]

Surface active agents, Adsorption, Reflectance spectroscopy, Heavy metals, Organic chemistry, and Water

The influence of interaction between mineral components in natural mixtures on the adsorption of organic and inorganic species on the mineral surfaces is recognized. However, the surface phenomena have been meagerly investigated. In this study the formation of different surface species of surfactant (amyl xanthate, C5H11,OC(S)S- adsorbed on FeS₂, PbS, and CuFeS₂ has been spectroscopically investigated in single-mineral and complex systems. The type and amount of adsorbed species were determined directly on each mineral surface by infrared external reflection spectroscopy. Galvanic interaction between grains of different minerals could have tremendous consequence on the adsorption of surfactants on each mineral component and their future reactivity. The detected changes are dramatic, from no adsorption to the formation of several layers of hydrophobic or hydrophilic surface products depending on which minerals are in contact It has been documented that even very short contact time between different mineral grains by collision is sufficient to produce dramatic modification of the surface composition and structure. The results obtained indicate clearly that the observations and conclusions about the surfactant adsorption made in a single mineral system cannot be simply extrapolated to describe the real situation in natural multicomponent mineral systems. The obtained information on sulfide mineral interaction in complex systems is indispensable to understand processes taking place in nature at mineral-water interfaces (dissolution of heavy metals). An additional benefit is the improved ability to design efficient separation processes of these minerals. [ABSTRACT FROM AUTHOR]