The influence of activated carbon surface chemical composition on the adsorption of acetaminophen (paracetamol) in vitro

Linking the effect of temperature on adsorption from aqueous solution with solute dissociation

Imperative decarbonization of water purification processes entails alternative regeneration methods for activated carbon. Regeneration based on changing dissociation equilibria, i.e. a major influencing factor on adsorption, usually requires the addition of acids/bases, but may also be triggered by temperature swing. Although adsorption and dissociation are both temperature-dependent phenomena, their conjunction has received little attention regarding trace organic compounds (TrOCs) and large temperature intervals, in particular above ΔT ≥ 50 ^∘C. Therefore, we studied the adsorption equilibria of 16 TrOCs onto one granular activated carbon at temperatures ranging from 20 to 95 ^∘C. The majority of compounds (12/16) exhibited an exothermic apparent adsorption enthalpy, while 3 out of 16 exhibited an endothermic apparent enthalpy. The range spanned from - 46 to + 50 kJ mol^-1 (median at - 17 kJ mol^-1). The possible origins of endothermic adsorption were discussed. A rationale of shifting pK_a and thus changing dissociation of TrOCs was introduced and traded off against existing rationales, i.e. changing solute solubility, changing adsorption heat capacity, and saturation effects of the adsorbates. This knowledge may allow designing temperature swing adsorption processes that unlock the dissociation switch. The augmented process efficiency can thus provide the foundation for low-carbon emission, circular water purification processes.

Synthesis and characterisation of acid/basic modified adsorbents. Application for chlorophenols removal

A commercial activated carbon was modified with acid and basic reagents -an acidic one via treatment with sulphuric acid and a basic via treatment with pentaethylenehexamine- to yield adsorbents with different surface acid/base character. These modified adsorbents were characterised by elemental and immediate analysis, N₂ adsorption, XPS and point zero charge measurements. The new adsorbents were tested for chlorophenols removal in water (4-chlorophenol, 3,5-dichlorophenol, 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol and pentachlorophenol) at different temperatures. Although the calculated process enthalpy was positive for all cases, indicating an endothermic process, the entropy was positive, resulting in a negative Gibbs free energy and spontaneous process. The adsorption capacity increases with temperature and decreases when the phenols' number of substituents increases. The modified acid-activated carbon demonstrated an exciting higher adsorbing capacity from 426.9 to 742.3 mg g^-1 for 2,4,6-trichlorophenol, whereas the adsorption capacity for the basic ranged between 142.9 and 238.0 mg g^-1. The Langmuir model satisfactorily fitted the adsorption equilibrium data for all chlorophenol contaminants.

Low-temperature sintering of silver patterns on polyimide substrate printed with particle-free ink

In this study, a transparent particle-free reactive silver ink was used to fabricate conductive patterns on a flexible substrate. Thermal annealing and plasma irradiation at low temperature were utilized to improve the conductivity of the as-printed patterns. The effects of sintering process parameters on the microstructure and resistivity of the patterns were investigated. Under the optimized processing conditions, the resistivity of the pattern reached 1.2 × 10 ^-7 Ω · m by thermal sintering, while it was 8 × 10 ^-8 Ω · m after plasma sintering. Combined with these two sintering techniques, the resistivity was reduced to 6 × 10^-8 Ω · m, close to that of bulk silver. This work provides an alternative solution for the fabrication of highly conductive feature patterns on common flexible substrates.

Aqueous-Phase Temperature Swing Adsorption for Pesticide Removal

Recently, activated carbon adsorption for water treatment regained substantial attention due to the emerging task to remove trace organic compounds such as pesticides. In many applications, especially in decentralized water treatment, one major drawback of adsorbents is their limited recyclability due to inadequate logistics or uneconomical reactivation. In this lab-scale study, we present the temperature swing adsorption in the aqueous phase that allows the in situ regeneration of fixed-bed adsorbers, and prove its technical feasibility. Complying with circular water economy principles, we eliminated the pivotal need for regular replacement and consumables by employing only clean water instead of dedicated regeneration solutions. Adsorption of the herbicide amitrole in aqueous solution on granular activated carbon was exothermic (Δ H = -14.4 ± 3.2 kJ mol^-1 for T = 20-94 °C) and followed the Freundlich model. The proposed method consisting of a short counterflow flush with liquid water at 125 °C effectively regenerated the adsorbent. Hence, we obtained a cyclic steady state operation with breakthrough after 122 ± 14 bed volumes (at c_out/ c_in = 0.2), cycle-average rejection of 90 ± 1%, and water recovery of up to 78 ± 4%. No thermal aging of adsorbent was observed over the investigated 17 cycles.

In Vitro Study of Adsorption Kinetics of Dextromethorphan Syrup onto Activated Charcoal in Simulated Gastric and Intestinal Fluids

Adsorption kinetics of dextromethorphan (DXM) syrup in simulated gastric and intestinal fluids onto activated charcoal (AC) were investigated in an in vitro model. The adsorption studies were performed as a function of time, initial concentration, and temperature. The quantification of DXM adsorbed onto AC was obtained from the Langmuir adsorption isotherms using HPLC. The maximum adsorption capacities (at 95% confidence limits) of AC for DXM were 111.615 [106.38; 126.85] mg in simulated intestinal environment (pH 6.8) and 78.314 [86.206; 70.422] mg in simulated gastric environment (pH 1.2). The adsorption capacity of AC for DXM in simulated gastric fluid (pH 1.2) was not significantly different from the adoption capacity of AC for DXM in simulated intestinal fluid (pH 6.8). Moreover, the adsorption kinetics behavior of dextromethorphan onto AC followed pseudo-second-order kinetics. Our results show that AC in therapeutically acceptable doses can be beneficial in the majority of oral overdose of DXM.

Adsorption of Biologically Active Compounds from Aqueous Solutions on to Commercial Unmodified Activated Carbons. Part IV. Do the Properties of Amphoteric Carbon Surface Layers Influence the Adsorption of Paracetamol at Acidic pH Levels?

Three previously characterised, unmodified commercial activated carbons (D43/1, WD and AHD), differing in porosity and surface layer composition, were further examined using some additional methods of surface chemical description (electrochemical studies, acid–base site distribution, pHPZC and resistance measurements). Paracetamol adsorption isotherms (as well as kinetic curves) were measured on these carbons at acidic pH (1.5) and three temperatures, i.e. 300, 310 and 320 K. Measurements of the enthalpies of immersion in HCl and paracetamol solutions were also performed at 310 K, and diffusion coefficients and energies calculated.

The results of measurements at acidic pH were compared with those obtained under neutral pH conditions. Some new correlations between the properties of the carbon surface and the constants characterising the process of paracetamol adsorption suggested recently were extended from data measured initially for six carbons. The mechanism of adsorption at both pH values was elaborated with the importance of surface carbonyls and basic groups being emphasised. The adsorption of the polymerisation product of paracetamol at acidic pH was determined using FT-IR and UV–vis spectroscopic measurements.

Adsorption of Biologically Active Compounds from Aqueous Solutions on to Commercial Unmodified Activated Carbons. Part III. Theoretical Description of Paracetamol Adsorption Data at Neutral pH

A theoretical description of recently published paracetamol adsorption data on a series of non-modified commercial activated carbons is presented. Nineteen of the most widespread adsorption isotherm equations are analysed and the resulting maximum adsorption values compared. The equations proposed by Weber and Vliet, by O'Brien and Myers as well as by Dubinin and Astakhov led to the highest values of the average correlation coefficient describing the fit of the theoretical data to those obtained experimentally. On the basis of the results obtained as well as those published previously, the importance of carbon surface basic groups and carbonyl groups in the mechanism of paracetamol adsorption is emphasised.

Influence of activated carbon porosity and surface oxygen functionalities' presence on adsorption of acetonitrile as a simple polar volatile organic compound

Based on series of porous carbon models, systematic Monte Carlo studies on the adsorption of acetonitrile (as a simple representative of polar volatile organic compounds) were performed. The influence of porosity and chemical composition of the carbon surface on CH3CN adsorption was studied and it was shown that both the factors influenced the adsorption mechanism. A decrease in the pore size and the introduction of oxygen surface groups led to a rise in adsorption energy and to an increase in the filling of accessible volume in the low-pressure part of the isotherm. However, from a practical point of view, it is easier to increase the adsorption by introducing polar groups on the carbon surface than by modifying the porosity.

The influence of the textural properties of activated carbons on acetaminophen adsorption at different temperatures

Positive effect of temperature on acetaminophen adsorption is observed for carbons with non-continuous micropore size distribution centered at widths close to the critical dimension of acetaminophen planar form.

Effect of calcium on adsorption capacity of powdered activated carbon

We investigated the effect of calcium ion on the adsorption of humic acid (HA) (as a target pollutant) by powered activated carbon. The HA adsorption isotherms at different pH and kinetics of two different solutions including HA alone and HA doped Ca(2+), were performed. It was showed that the adsorption capacity of powdered activated carbon (PAC) for HA was markedly enhanced when Ca(2+) was doped into HA. Also, HA and Ca(2+) taken as nitrate were tested on the uptake of each other respectively and it was showed that the adsorbed amounts of both of them were significantly promoted when HA and calcium co-existed. Furthermore, the adsorbed amount of HA slightly decreased with the increasing of Ca(2+) concentration, whereas the amount of calcium increased with the increasing of HA concentration, but all above the amounts without addition. Finally, the change of pH before and after adsorption process is studied. In the two different solutions including HA alone and HA doped Ca(2+), pH had a small rise, but the extent of pH of later solution was bigger.

Photo-regenerable multi-walled carbon nanotube membranes for the removal of pharmaceutical micropollutants from water

Pharmaceutical micropollutants fall in the category of "emerging contaminants" in water because of their prevalence and persistence in the aqueous environment, and because of a poor understanding of their low-dose exposure effects on human and animal populations. In this study, photo-regenerable multiwalled carbon nanotube membranes with variable water permeabilities were produced by embedding hierarchical TiO2 structures (having porous, spherical morphology) onto a pre-deposited bed of multi-walled carbon nanotubes (MWNTs) using a modified sol-gel technique. These MWNT-TiO2 composites and their constituent materials were characterized by analytical electron microscopy, surface charge measurement, thermogravimetric analysis, and hydrophobicity determination. The adsorption removal potential of MWNT-TiO2 membranes was demonstrated for three representative pharmaceuticals: acetaminophen, carbamazepine and ibuprofen. The peak initial removal percentages of the pharmaceuticals by the MWNT-TiO2 membranes were 80%, 45%, and 24% for carbamazepine, ibuprofen, and acetaminophen, respectively. The ability of the membranes to be regenerated, once they were saturated with the pharmaceutical compounds, was verified by repeating the adsorption removal experiment on the same membranes after exposure to UV light at 254 nm. Peak removal efficiencies after regeneration were 55%, 32%, and 19% for carbamazepine, ibuprofen, and acetaminophen, respectively, indicating some loss in sorptive capacity upon regeneration. Furthermore, the effect of pH on adsorption of ibuprofen, the pharmaceutical that attained the highest mass loading on the sorbent at equilibrium saturation, was studied and its mechanism of adsorption was proposed at pH below pKa.

Temperature dependence of herbicide adsorption from aqueous solutions on activated carbon fiber and cloth

Diuron and amitrole adsorption from aqueous solution on an activated carbon fiber and an activated carbon cloth were studied as a function of temperature. Diuron adsorption was greater than that of amitrole and increased with rising temperature, whereas amitrole adsorption decreased when the temperature increased. Endothermicity of diuron adsorption was due to an increase in the planarity and diffusion of diuron molecules with higher temperatures. However, the exothermicity found for amitrole was due to the increase in amitrole solubility and in vibrational energy of adsorbed molecules with higher temperature. External mass transfer resistance was also found to play an important role in diuron adsorption on activated carbon cloth.

Changes of the porous structure of activated carbons applied in a filter bed pilot operation

The paper investigates the changes in porosity (i.e., in the accessible adsorption capacity of carbonaceous adsorbents for pollutants during filter bed maturation) of three activated carbons applied in a filter bed pilot operation. The results of this investigation may help to reduce operating costs, increase granular activated carbon bed life, maximize the useful life of biofilters, and understand the mechanism of water purification by carbon adsorbents. The analysis of the pore structure was limited to the first year of service of the beds, since this was when the largest decrease in the available pore capacity occurred. Low-temperature nitrogen adsorption isotherms were used to evaluate the structural parameters and pore size distributions (PSDs) of carbon samples (virgin (reference) and mature adsorbents for different periods of water treatment) on the basis of the Nguyen and Do (ND) method and density functional theory (DFT). These results were compared with small-angle X-ray scattering (SAXS) investigations (PSDs calculated by Glatter's indirect transformation method (ITP)). The results show that in general, the ND and ITP methods lead to almost the same qualitative distribution curve behavior. Moreover, the enthalpy of immersion in water, mercury porosimetry, densities (true and apparent), and the analysis of ash are reported and compared to explain the decrease in adsorptive capacity of the carbons investigated. On the other hand, the efficacy of TOC (total organic carbon, i.e., a quantity describing the complex matrix of organic material present in natural waters) removal and the bacteria count were analyzed to explain the role of adsorption in the elimination of contaminants from water. Finally, a mechanism of organic matter removal was suggested on the basis of the above-mentioned experimental data and compared with mechanisms reported by other authors.

Effect of the carbon surface layer chemistry on benzene adsorption from the vapor phase and from dilute aqueous solutions

We present a complex study of benzene adsorption on chemically modified commercial activated carbons. The porosity of studied carbons is almost the same, whereas the chemical composition and the acid-base properties of surface layers differ drastically from amphoteric (initial de-ashed carbon D43/1, Carbo-Tech, Essen, Germany) and acidic (carbon modified with concentrated HNO3 and fuming H2SO4) to strongly basic (carbon modified with gaseous NH3). Benzene adsorption isotherms measured from aqueous solution at three temperatures (298, 313, and 323 K) and at the neutral pH level are reported. They are supported by studies of water and benzene adsorption from the gaseous phase (volumetric and calorimetric data) and the data of benzene temperature-programmed desorption (TPD). Moreover, the data of the enthalpy of immersion in water and benzene are also presented. Obtained data of benzene adsorption from the gaseous phase are approximated by applying the method of Nguyen and Do (ND) and the Dubinin-Astakhov (DA) equation. The data of adsorption from solution are described by the hybrid DA-Freundlich (DA-F) model. We show that there are similarities in the mechanisms of benzene adsorption from the gaseous phase and from aqueous solutions and that the pore-blocking effect is the main stage of the adsorption mechanism. This effect strongly depends on the polarity of the carbon surface. The larger the ratio of the enthalpy of carbon immersion in water to the enthalpy of immersion in benzene, the larger the reduction in adsorption from solution, compared to that in the gaseous phase, that is observed.

Further insights into the role of carbon surface functionalities in the mechanism of phenol adsorption

The presented study describes the temperature as well as pH dependence of phenol adsorption (and adsorption kinetics) on four carbons with different chemical compositions of the surface layer but almost identical porosity. In the first part, it is shown, applying the most sophisticated method of carbon porosity characterization (i.e., the method of Do and co-workers-ND method), that the porosity does not change much after the chemical modification of carbons. Then it is shown that the ND method leads to the same results as the DFT (density functional theory) does. Next, the TPD results for D43/1 carbons (initial, modified with HNO(3), fuming H(2)SO(4), and with NH(3)) are described. The TPD results for carbon modified with fuming sulphuric acid has not been reported yet by others. The deconvolution of peaks is performed. The obtained results, together with those already published, lead to the chemical structures of surface functionalities for all studied carbons. The thermogravimetric analysis of phenol adsorption shows that the amount of chemically bonded molecules is small. Then it is shown that the adsorption at the acidic pH (1.5) level is lower for all studied carbons than that at the neutral one. The description of the isotherms applying adsorbability, quasi-Freundlich and DA models, together with enthalpy measurements, lead to the mechanism of phenol adsorption at both pH values. The mechanism is, furthermore, confirmed by some empirical correlations. The analysis of the average hysteresis on adsorption-desorption isotherms as well as the comparison of phenol adsorption in oxic and anoxic conditions leads to the mechanism of irreversible phenol adsorption. It is suggested that the irreversibility is caused by two effects: the creation of strong complexes between phenol and surface carbonyl and lactones as well as by the polymerization. The last effect is due to the ability of carbon to adsorb the oxygen from solution and form superoxo ions. Finally, the kinetics is considered. The analytical solution of Fick's law of diffusion for adsorption in cylindrical particles is applied, the diffusion coefficients are calculated. It is shown that phenol diffusion is mixed between a surface process and a pore one. The obtained energy of diffusion is correlated with the values of the physicochemical parameters of studied carbons. As a final point, it is concluded that the mechanism of phenol adsorption is not only determined by so called "pi-pi interactions" and "donor-acceptor complex formation" but also by (strongly depending on temperature) the "solvent effect" balancing the influence of the two mentioned factors on this mechanism.

Molecular properties and intermolecular forces—factors balancing the effect of carbon surface chemistry in adsorption of organics from dilute aqueous solutions

Presented paper recapitulates the results of 6 years' study concerning the effect of carbon surface chemical composition on adsorption of paracetamol, phenol, acetanilide, and aniline from dilute aqueous solutions on carbons. Adsorption-desorption isotherms, enthalpy, and kinetics of adsorption data are shown for the measurements performed at three temperatures (300, 310, and 320 K) at two pH levels (1.5 and 7) on commercial activated carbons. The data were obtained for four carbons: the initial carbon D43/1 and forms modified by applying concentrated HNO3, fuming H2SO4, and gaseous NH3. The modification procedures do not change the porosity in a drastic way, but lead to drastic changes of the composition of carbon surface layer. By applying MOPAC (a general-purpose semiempirical molecular orbital package), the physicochemical constants characterizing the molecules of adsorbates are calculated, including the distribution of the Mulliken charges, the dipole moments and ionization potentials, and the energies of interaction with the unique positive and negative charges. They are correlated with the parameters characterizing the adsorption (and kinetics) process of studied molecules on the mentioned above carbons. The mechanisms proposed in the literature for the description of adsorption from dilute aqueous solutions are verified, and a general mechanism of adsorption is proposed.

The effect of carbon surface chemical composition on the adsorption of acetanilide

The study of acetanilide adsorption-desorption performed at three temperatures (300, 310, and 320 K) and at two pH levels (7.0 and 1.5) on the series of D43/1 carbons (initial and modified with HNO3, fuming H2SO4, and gaseous NH3) is reported. Sorption data are additionally supplemented with the results of thermal analysis and calorimetric and kinetic measurements. It is shown that, generally, acetanilide adsorption at the neutral pH level is reversible (only on the more acidic carbons and at the lowest temperature does hysteresis occur due to the formation of hydrogen bonds with surface OH groups), and it decreases for the chemically modified carbons. In contrast, at the acidic pH level acetanilide adsorption is irreversible. A mechanism of irreversibility is proposed and it is shown that hysteresis is caused by the chemical reaction between the nucleophile (carbon) and the protonized acetanilide molecules. For all studied carbons, at the acidic pH level, adsorption increases and this is caused by the weakly basic character of acetanilide molecule. Adsorption results are described applying adsorbability and Dubinin-Astakhov, quasi-Freundlich and solution analogue of the Toth adsorption isotherm equations. Using the kinetic data, the effective diffusion coefficients and the energy of diffusion are calculated. It is shown that the diffusion is mainly a surface process, and the contribution of the pore diffusion increases with the rise in temperature. By applying different correlations between the parameters obtained from the theoretical description of experimental data and those characterizing the chemical composition of the studied carbons, the role of the latter in the adsorption and kinetics of acetanilide adsorption is determined.

Structural characteristics of activated carbons and ibuprofen adsorption affected by bovine serum albumin

Structural characteristics of a series of MAST carbons were studied using scanning electron microscopy images and the nitrogen adsorption isotherms analyzed with several models of pores and different adsorption equations. A developed model of pores as a mixture of gaps between spherical nanoparticles and slitlike pores was found appropriate for MAST carbons. Adsorption of ibuprofen [2-(4-isobutylphenyl)propionic acid] on activated carbons possessing different pore size distributions in protein-free and bovine serum albumin (BSA)-containing aqueous solutions reveals the importance of the contribution of mesopores to the total porosity of adsorbents. The influence of the mesoporosity increases when considering the removal of the drug from the protein-containing solution. Cellulose-coated microporous carbon Norit RBX adsorbs significantly smaller amounts of ibuprofen than uncoated micro/mesoporous MAST carbons whose adsorption capability increases with increasing mesoporosity and specific surface area, burnoff dependent variable. A similar effect of broad pores is observed on adsorption of fibrinogen on the same carbons. Analysis of the ibuprofen adsorption data using Langmuir and D'Arcy-Watt equations as the kernel of the Fredholm integral equation shows that the nonuniformity of ibuprofen adsorption complexes diminishes with the presence of BSA. This effect may be explained by a partial adsorption of ibuprofen onto protein molecules immobilized on carbon particles and blocking of a portion of narrow pores.

Developing the solution analogue of the Toth adsorption isotherm equation

The well-known Toth adsorption isotherm equation developed formerly for adsorption of vapors is converted into its solution analogue. It is shown that this equation can be successfully applied to the description of adsorption data of organics on activated carbons.

The Simple Procedure of the Calculation of Diffusion Coefficient for Adsorption on Spherical and Cylindrical Adsorbent Particles—Experimental Verification

A recently proposed simplified procedure for calculating the effective diffusion coefficient (D(e)) for adsorption on spherical and cylindrical adsorbent particles is now experimentally verified for adsorption systems: paracetamol-activated carbon. Adsorption kinetics was measured on nine carbons; for seven of them, measurements were taken at three temperatures. Since for adsorption on spherical adsorbent particles the approximate methods of D(e) calculation are already available in literature, only two systems have been studied, and the results of the new procedure are compared with those calculated from previously published methods. However, for cylinders the proposed method is the first simplification of this kind available in literature, thus, we focus our attention on the comparison of the results of the analytical approach with the simplified approaches for the systems where an adsorbent possesses cylindrically shaped granules. It is shown that for adsorption on spherical as well as on cylindrical adsorbent granules the proposed simplification leads to satisfactory results that, taking into account an experimental error, are practically the same as those obtained from exact time-consuming and mathematically advanced numerical fitting procedure. It is also shown that, for the studied carbons, the surface diffusion process dominates, and this explains the recently obtained correlation between the effective diffusion coefficient and the enthalpy of carbon immersion in water.

Describing Adsorption of Paracetamol from Aqueous Solution on Carbons While Utilizing the Most Widespread Isotherm Models—The Impact of Surface Carbonyl and Basic Groups

The 15 most widespread adsorption isotherm equations are applied for describing recently published paracetamol adsorption data from aqueous solutions (pH 7). Twelve adsorption isotherms, measured at 300, 310, and 320 K, on the series of chemically modified carbons D43/1 (Carbo-Tech, Essen, Germany) differing in surface properties (from basic to strongly acidic) but possessing almost the same porosity, are analyzed. The results of fitting theoretical models to experimental data are arranged according to a decrease in the average value of the determination coefficient. From the models studied the best fit is obtained for Weber-Vliet, Dubinin-Astakhov, and the model published by Jossens. The most important conclusion is that at the lowest temperature studied, where the effect of carbon surface composition on adsorption properties is the most strongly marked, the value of paracetamol maximal adsorption decreases as the amount of surface basic groups and carbonyls increases.

The Impact of Carbon Surface Composition on the Diffusion and Adsorption of Paracetamol at Different Temperatures and at Neutral pH

Commercial activated carbon D43/1 (Carbo-Tech, Essen, Germany) was deashed and modified chemically to increase surface acidity and basicity, as well as to introduce metal cations onto the surface and yet conserve the porosity. The five carbons obtained were applied as adsorbents. Based on the results of batch-reactor test kinetic measurements of the adsorption of 4-hydroxyacetanilide (paracetamol) from aqueous solution at the neutral pH and at three temperatures (300, 310, and 320 K), the values of the effective diffusion coefficient (D(e)) were calculated. It is shown that D(e) increases (up to the relative adsorption equal to approximately 0.6) with rise in the magnitude of the enthalpy of immersion of carbons in water. Based on the obtained results as well as those published previously, the role of surface composition in the mechanism of paracetamol adsorption and in the kinetics of this process is discussed. Copyright 2000 Academic Press.