Low Equilibrium Concentrations Research Articles

Remediation of Groundwater Polluted by Aromatic Compounds by Means of Adsorption

In this work, an experimental and modeling analysis of the adsorption of four aromatic compounds (i.e., toluene, naphthalene, o-xylene and ethylbenzene) onto a commercial activated carbon is carried out. The aim is to assess the suitability of the adsorption process for the treatment of polluted groundwater, also when a multiple contamination is detected. Batch adsorption tests from simulated polluted groundwater are performed in single-compound systems and in two binary systems (i.e., toluene + naphthalene and o-xylene + ethylbenzene), at constant temperature (20 °C) and pH (7). Experimental results in single-compound systems reveal that all of the analytes are significantly adsorbed on the tested activated carbon. In particular, toluene and naphthalene adsorption capacities are the highest and of similar value, while for o-xylene and ethylbenzene, the performances are lower. The adsorption of these compounds seems to be influenced by a combined effect of several parameters, such as hydrophobicity, molecule size, structure of the molecule, etc. Experimental results in binary systems show a different behavior of the two systems, which confirms their complexity and explains the interest in these complex adsorption systems. In particular, toluene and naphthalene are mutually competitive, while in the case of o-xylene + ethylbenzene, only the former undergoes competitive effects. The analysis of the entire experimental data set is integrated with a dedicated modeling analysis using the extended Langmuir model. For both single-compound and binary systems, this model provides acceptable results, in particular for low equilibrium concentrations, like those more commonly found in groundwater, and for the compounds involved in adsorptive competitive effects.

Soil adsorption studies of a rice herbicide, cyhalofop-butyl, in two texturally different soils of India.

The ability of herbicides to be adsorbed by the soil and sediment and their tendency to be desorbed are some of the most important factors affecting soil and water contamination. Therefore, a sorption study was conducted to evaluate the adsorption of cyhalofop-butyl, butyl (2R)-2-[4-(4-cyano-2-fluorophenoxy) phenoxy] propanoate, in the sandy clay loam and clayey soils using a batch equilibrium method. The adsorption of cyhalofop-butyl was found positively related with the clay and organic carbon content. Freundlich constants (Kf) of cyhalofop-butyl in the clayey and sandy clay loam were found to be 13.39 and 2.21, respectively. Sorption coefficients (Koc) and distribution coefficients (Kd) were found to be 265.38 and 2,092.79, and 1.38 and 11.48, for sandy clay loam and clayey soils, respectively. The adsorption isotherm suggested a relatively higher affinity of cyhalofop-butyl to the adsorption sites at low equilibrium concentrations. The low value of the soil organic carbon partition coefficient (Koc) of cyhalofop-butyl in the sandy loam soil suggested its weaker adsorption in soil and thus increased its risk of mobility into water sources; hence, it should be used judiciously to prevent groundwater contamination.

Solvothermal synthesis and characterization of a layered silicate including a large quantity of Al atom and its mesoporous derivatives

A layered silicate K-LDS (K4H4Si8O20) analog including a large quantity of Al atom was synthesized by the solvothermal reaction of layered silicate H-RUB-18, potassium ethoxide, and aluminum isopropoxide. The overall Si/Al ratio of the layered compound (ca. 6) was much lower than other Al-substituted layered silicates (typically Si/Al>50). The presence of four- and six-coordinate Al nuclei was identified by 27Al MAS NMR spectra, and the relative ratio of AlO4:AlO6 was nearly 4:5. In contrast, the framework Si atoms presented only the Q3 (Si–OH) local structure. It was suggested that a large quantity of Al atoms was distributed over the crystal K-LDS surface as amorphous alumina. Mesoporous aluminosilicate derivatives were prepared by the treatment of Al-K-LDS with cationic surfactants (C16TMACl and C22TMACl). The products had foam-like mesopores with 2.4–3.7nm pore diameters and high Al contents with Si/Al=2–3. The mesoporous derivatives could be presumed as aluminosilicates because of their uniform Al distribution, and they exhibited high hydrophilicities owing to the presence of Al atoms or silanols. In addition, their ability to adsorb lysozyme into the mesopores was demonstrated under low equilibrium concentration conditions. The amount of lysozyme adsorbed and the adsorption velocity of these derivatives were considerably superior to those of typical mesoporous silica such as SBA-15, SBA-16, and FSM-16.

Effect of organic matter and calcium carbonate on behaviors of cadmium adsorption–desorption on/from purple paddy soils

Batch experiments and sequential extraction analysis were employed to investigate the effects of soil organic matter and CaCO3 on the adsorption and desorption of cadmium (Cd2+) onto and from two purple paddy soils, an acidic purple paddy soil (APPS) and a calcareous purple paddy soil (CPPS). The Cd2+ adsorption isotherms on both soils could be well-described by the Langmuir and Freundlich equations. CPPS had a higher capacity and a stronger affinity for Cd2+ adsorption compared with APPS. The adsorption process of Cd2+ on APPS was dominated by electrostatic attractions, whereas the adsorption mechanism varied depending on the Cd2+ concentrations in equilibrium solutions on CPPS. At low equilibrium concentrations, the adsorption process was primarily specific adsorption, but nonspecific adsorption dominated at high equilibrium concentrations. Removal of organic matter decreased the amount of Cd2+ adsorption on both of the soils, slightly affected the Cd2+ desorption rate and exchangeable Cd (EXC-Cd) in APPS and increased the desorption rate and EXC-Cd in CPPS, suggesting that the effect of organic matter on Cd2+ adsorption–desorption depends on the soils. CPPS and APPS containing CaCO3 exhibited higher adsorption amounts but lower desorption rates and lower proportions of EXC-Cd than those of their corresponding soils without CaCO3, demonstrating that CaCO3 played an important role in Cd2+ specific adsorption on soil. The changes in the thermodynamic parameters, including free energy (ΔG0), enthalpy (ΔH0) and entropy (ΔS0), as evaluated by the Van’t Hoff equations, indicated that the adsorption was a spontaneous and endothermic process with the primary interaction forces of dipole interactions and hydrogen bonds on APPS, whereas both physical and chemical interactions dominated the adsorption on CPPS.

Effect of heat treatment on copper removal onto manure-compost-activated carbons

The work was aimed to investigate the effect of heat treatment of manure-compost-based activated carbons on the adsorption of copper from aqueous solution. Activated carbons were characterized according to physical structures and surface functional groups. All equilibrium data of activated carbons formerly treated at different temperatures obeyed Langmuir model to linear approximation. Results showed that copper ions favorably adsorbed onto the mesopores at lower equilibrium concentrations and subsequently changed to the micropores at higher equilibrium concentrations. It was found that the increase in electron density upon heat treatment offered higher tendency for the uniform amount of protons to occupy the surface sites. Analysis of Scatchard plots suggested that the affinity driven by the mesopores toward copper ions was stronger than that of the micropores.

Renalase Is an α-NAD(P)H Oxidase/Anomerase

Renalase is a protein hormone secreted into the blood by the kidney that is reported to lower blood pressure and slow heart rate. Since its discovery in 2005, renalase has been the subject of conjecture pertaining to its catalytic function. While it has been widely reported that renalase is the third monoamine oxidase (monoamine oxidase C) that oxidizes circulating catecholamines such as epinephrine, there has been no convincing demonstration of this catalysis in vitro. Renalase is a flavoprotein whose structural topology is similar to known oxidases, lysine demethylases, and monooxygenases, but its active site bears no resemblance to that of any known flavoprotein. We have identified the catalytic activity of renalase as an α-NAD(P)H oxidase/anomerase, whereby low equilibrium concentrations of the α-anomer of NADPH and NADH initiate rapid reduction of the renalase flavin cofactor. The reduced cofactor then reacts with dioxygen to form hydrogen peroxide and releases nicotinamide dinucleotide product in the β-form. These processes yield an apparent turnover number (0.5 s(-1) in atmospheric dioxygen) that is at least 2 orders of magnitude more rapid than any reported activity with catechol neurotransmitters. This highly novel activity is the first demonstration of a role for naturally occurring α-NAD(P)H anomers in mammalian physiology and the first report of a flavoprotein catalyzing an epimerization reaction.

Sorption of aspartic and glutamic aminoacids on calcined hydrotalcite

Sorption of aspartic and glutamic aminoacids by regeneration of calcined hydrotalcite is reported. Hydrotalcite was synthesized by coprecipitation and calcined at 773 K. Sorption experiments were performed at 298 K and 310 K, and the results reveal that at low aminoacids equilibrium concentrations, intercalation of hydroxyl anions takes place while at high equilibrium concentrations, the sorption process occur by means re-hydration and aminoacids intercalation of hydrotalcite. The results also suggested that Asp and Glu sorption is a temperature dependent process. The amount of sorbed amino acid decreases as the temperature increase. The effect is more pronounced for Glu sorption probably due to its higher hydrophobic character, which makes the sorption more difficult in comparison with sorption of Asp at higher temperature.

Removal of TCEP from aqueous solutions by adsorption with zeolites

Emerging contaminants (ECs) and micropollutants are becoming a global environmental problem as there is increasing information linking them to environmental and human health hazards. One micropollutant of interest is tris-2-chloroethyl phosphate (TCEP), an organo-phosphate ester used as a plasticizer and flame retardant. TCEP is of special interest not only due to its potential toxicity and prevalence in the environment but it presents a difficulty in removal through conventional wastewater treatment operations such as adsorption by activated carbons. This paper presents exploratory results of identifying appropriate zeolite materials and assessing the removal of TCEP using microporous synthetic zeolite adsorbents. Two zeolites (of type β denoted BEA) one with a low (25:1) and one with high silica:alumina (300:1) ratio were tested. Equilibrium concentrations in the TCEP–zeolite systems evaluated ranged from 5μg/L to near 10,000μg/L, of which several points were within the range of environmental interest <100μg/L). Equilibrium adsorption isotherms of TCEP on the selected zeolites were obtained experimentally and the Langmuir and Redlich–Peterson isotherm models were fitted to the data. Both zeolites showed excellent removal (>99%) of TCEP from solution. Adsorption was determined to be a function of both solution pH and adsorbent type. Adsorption at an acidic initial solution pH exhibited the highest adsorption capacity compared to neutral or alkaline pH values. Maximum adsorption capacities of 77,000μg/g and 103,000μg/g were obtained for the 25:1 and 300:1 materials, respectively. However, at very low equilibrium concentrations (e.g., ce<100μg/L) which are in the range of environmental interest, the Henry's Law constant suggests that alkaline pH values support higher equilibrium adsorption (qe). The mechanism of adsorption is not completely understood but the testing suggests that it is a complex function of pH and hydrophobic/hydrophilic interaction between the adsorbent and adsorbate.

Biofiltration of the chlorophenol aqueous solution through the activated carbon bed

The efficiency of biofiltering the o-chlorophenol solution through the KAU-grade activated carbon is common and modified with iron oxide—was studied. Both sorbents showed high selective adsorption ability for the compound investigated. The activated carbon modified with iron oxides was found to have a positive effect on the adsorption of o-chlorophenol at low equilibrium concentrations and continuous filtration.

Tungsten species in natural ferromanganese oxides related to its different behavior from molybdenum in oxic ocean

The tungsten (W) species in marine ferromanganese oxides were investigated by wavelength dispersive XAFS method. We found that the W species are in distorted Oh symmetry in natural ferromanganese oxides. The host phase of W is suggested to be Mn oxides by μ-XRF mapping. We also found that the W species forms inner-sphere complexes in hexavalent state and distorted Oh symmetry on synthetic ferrihydrite, goethite, hematite, and δ-MnO2. The molecular-scale information of W indicates that the negatively-charged WO42− ion mainly adsorbs on the negatively-charged Mn oxides phase in natural ferromanganese oxides due to the strong chemical interaction. In addition, preferential adsorption of lighter W isotopes is expected based on the molecular symmetry of the adsorbed species, implying the potential significance of the W isotope systems similar to Mo.Adsorption experiments of W on synthetic ferrihydrite and δ-MnO2 were also conducted. At higher equilibrium concentration, W exhibits behaviors similar to Mo on δ-MnO2 due to their formations of inner-sphere complexes. On the other hand, W shows a much larger adsorption on ferrihydrite than Mo. This is due to the formation of the inner- and outer-sphere complexes for W and Mo on ferrihydrite, respectively. Considering the lower equilibrium concentration such as in oxic seawater, however, the enrichment of W into natural ferromanganese oxides larger than Mo may be controlled by the different stabilities of their inner-sphere complexes on the Mn oxides. These two factors, (i) the stability of inner-sphere complexes on the Mn oxides and (ii) the mode of attachment on ferrihydrite (inner- or outer-sphere complex), are the causes of the different behaviors of W and Mo on the surface of the Fe/Mn (oxyhydr)oxides.

Simultaneous improvements in power conversion efficiency and operational stability of polymer solar cells by interfacial engineering

This article addresses simultaneous improvements in the photovoltaic performance and operational stability of organic photovoltaic devices (OPVs) in the inverted configuration when nanostructured ZnO characterized by a lower density of localized surface atomic energy states is employed as an electron transport layer. Two sets of devices with the configuration ITO/ZnO/P3HT:PCBM/MoO3/Ag are employed in the present study. A difference in the density of localized energy states in the band gap of ZnO was produced by altering the crystallinity by annealing the ZnO at two temperatures, viz. 160 and 240 °C. The devices are characterized by scanning electron microscopy, X-ray diffractometry, current-voltage (I-V) measurements as functions of temperature and illumination intensity, incident photon to current conversion efficiency (IPCE) spectroscopy, and charge extraction by linearly increasing photovoltage (CELIV) spectroscopy. The devices fabricated using the ZnO nanostructures annealed at 240 °C have shown remarkably higher power conversion efficiency (PCE) and IPCE values than the other device. From I-V measured as a function of photon flux and temperature we show that the device with higher PCE is characterized by a lower depth of localized energy states by a factor of two than the other device. The implications of the lower trap depth was also evaluated using CELIV and the corresponding charge mobility obtained differed by a factor of three between the two sets of devices. The device with lower equilibrium concentration at the interface has three fold higher charge mobility and 40% enhanced photoconversion efficiency. The stability of the devices was evaluated with and without encapsulation under simulated sunlight (AM 1.5) following the ISOS-D-1 (shelf) and the ISOS-L-1 protocols; the device with higher PCE also showed higher operational stability. The findings in this study are expected to provide new directions in fabricating organic-inorganic heterojunction devices with high performance and stability.

Arsenic(III) removal from low-arsenic water by adsorption with amorphous mesoporous TiO2

The present study investigated the removal of As(III) from low-arsenic water through adsorption on amorphous mesoporous TiO2. The mesoporous TiO2 adsorbent size was 3.92nm as calculated by adsorption average pore width. The Brunauer–Emmett–Teller surface area was 205 m2/g. A 0.2g adsorbent treatment during five hours resulted in less than 4 μg/L remaining As(III) in the water, and nearly 84% of As(III) in the solution were removed in only 20 min. The As(III) adsorption kinetics data were well described by the pseudo-second-order model. The maximum adsorption pH value of 9.3 coincided with the first pK1 dissociation constant of H3AsO3 of 9.22. The Dubinin-Radushkevich and Langmuir isotherms provided maximum adsorption capacity of 4.57 and 4.79 mg/g, respectively, under low equilibrium concentration. These values possibly indicate the excellent capacity of amorphous mesoporous TiO2 on As(III) removal from low-arsenic water. Given by the b-value of Langmuir isotherm under different pH, the average standard Gibbs free energy changes (∆Go) was –11.6 kJ mol-1, which indicated spontaneous adsorption.

Bacillus cereus iron uptake protein fishes out an unstable ferric citrate trimer

Citrate is a common biomolecule that chelates Fe(III). Many bacteria and plants use ferric citrate to fulfill their nutritional requirement for iron. Only the Escherichia coli ferric citrate outer-membrane transport protein FecA has been characterized; little is known about other ferric citrate-binding proteins. Here we report a unique siderophore-binding protein from the gram-positive pathogenic bacterium Bacillus cereus that binds multinuclear ferric citrate complexes. We have demonstrated that B. cereus ATCC 14579 takes up (55)Fe radiolabeled ferric citrate and that a protein, BC_3466 [renamed FctC (ferric citrate-binding protein C)], binds ferric citrate. The dissociation constant (K(d)) of FctC at pH 7.4 with ferric citrate (molar ratio 1:50) is 2.6 nM. This is the tightest binding observed of any B. cereus siderophore-binding protein. Nano electrospray ionization-mass spectrometry (nano ESI-MS) analysis of FctC and ferric citrate complexes or citrate alone show that FctC binds diferric di-citrate, and triferric tricitrate, but does not bind ferric di-citrate, ferric monocitrate, or citrate alone. Significantly, the protein selectively binds triferric tricitrate even though this species is naturally present at very low equilibrium concentrations.

Study of current distribution and oxygen diffusion in the fuel cell cathode catalyst layer through electrochemical impedance spectroscopy

In this study, an analysis of the current distribution and oxygen diffusion in the Polymer Electrolyte Fuel Cell (PEFC) Cathode Catalyst Layer (CCL) has been carried out using Electrochemical Impedance Spectroscopy (EIS) measurements. Cathode EIS measurements obtained through a three-electrode configuration in the measurement system are compared with simulated EIS data from a previously validated numerical model, which subsequently allows the diagnostics of spatio-temporal electrochemical performance of the PEFC cathode. The results show that low frequency EIS measurements commonly related to mass transport limitations are attributed to the low oxygen equilibrium concentration in the CCL–Gas Diffusion Layer (GDL) interface and the low diffusivity of oxygen through the CCL. Once the electrochemical and diffusion mechanisms of the CCL are calculated from the EIS measurements, a further analysis of the current density and oxygen concentration distributions through the CCL thickness is carried out. The results show that high ionic resistance within the CCL electrolyte skews the current distribution towards the membrane interface. Therefore the same average current density has to be provided by few catalyst sites near the membrane. The increase in ionic resistance results in a poor catalyst utilization through the CCL thickness. The results also show that non-steady oxygen diffusion in the CCL allows equilibrium to be established between the equilibrium oxygen concentration supplied at the GDL boundary and the surface concentration of the oxygen within the CCL. Overall, the study newly demonstrates that the developed technique can be applied to estimate the factors that influence the nature of polarization curves and to reveal the effect of kinetic, ohmic and mass transport mechanisms on current distribution through the thickness of the CCL from experimental EIS measurements.

Competitive adsorption of the herbicide fluroxypyr and tannic acid from distilled and tap water on activated carbons and their thermal desorption

A study was conducted on batch and column competitive adsorption of fluroxypyr (FLX) and tannic acid (TA) from distilled (DW) and tap water (TW) on activated carbon cloth (ACC) and granular activated carbon (GAC). Thermal desorption of the adsorbates from the spent ACC was also studied. FLX adsorption was higher from TW than from DW at low FLX equilibrium concentrations, and the inverse was observed at high FLX concentrations. The presence of TA diminished the amount of FLX adsorbed from both solvents due to partial blocking of the microporosity, but the same trends as before were observed at low and high FLX concentrations. Carbon consumption, obtained from the breakthrough curves, was lower as a function of superficial contact time with ACC than with GAC. The presence of TA increased carbon consumption, which was related to the microporosity of the adsorbents. Thermal desorption profiles of the spent ACC showed two peaks and one peak after adsorption from DW and TW, respectively. Desorption peaks shifted to higher temperatures with an increase in the heating rate, allowing the apparent activation energies and pre-exponential factors of the desorption processes to be determined.

Arsenate and arsenite removal by FeCl3: Effects of pH, As/Fe ratio, initial As concentration and co-existing solutes

Coagulation is one of the most commonly used technologies for arsenic removal from water and wastewater. Jar tests were carried out to determine the influence of pH, initial As/Fe molar ratio, equilibrium As concentration and co-occurring solutes on the crossover pH, where As(V) removal was equivalent to As(III) by FeCl3 coagulation. As(V) was more effectively removed than As(III) at lower pH values in FeCl3 coagulation process but the opposite was true at higher pH level. Increasing As/Fe ratio from 0.12 to 0.50 progressively lowered the crossover pH from 8.5 to 7.4. The arsenic isotherms revealed that As(V) removal was favored at low pH and low equilibrium concentration yet the opposite was true for As(III). The co-existing solutes had different influences on the crossover pH, depending on their ability to compete for sorption sites and to hinder or facilitate the aggregation of ferric hydroxide flocs. The presence of sulfate broadened the pH range where As(III) removal was better than As(V) removal. However, As(V) removal was always superior to As(III) removal in the presence of Ca2+ and no crossover pH was observed. The results from this study revealed that arsenic speciation, arsenic loading, and pH should be considered when predicting and managing arsenic removal by coagulation.

Adsorption behavior of pesticide methomyl on activated carbon in a high gravity rotating packed bed reactor

High gravity rotating packed bed (HGRPB) reactor possesses the property of high mass transfer rate, which is expected to promote the adsorption rate for the process. In this study, HGRPB has been applied on adsorption removal of methomyl from solution, adopting the adsorbent of activated carbon F400. The influence of operating parameters of HGRPB on mass transfer such as the rotating speed (NR), the flow rate of solution (FL) and initial concentration of methomyl (Cb0) were examined. The traditionally internal mass transfer models combined with Freundlich isotherm were used to predict the surface and effective diffusion coefficients. In addition, the results have also been compared with those obtained from the traditional basket stirred batch reactor (BBR). The results showed that the larger values of NR and FL enhanced the effective intraparticle diffusion and provided more accessible adsorption sites so as to result in lower equilibrium concentration in HGRPB system when compared to SBR system. The results of adsorption kinetics demonstrated that surface and effective diffusions were both significantly greater in HGRPB system instead of BBR system. Furthermore, the values of BiS also manifested less internal mass transfer resistance in HGRPB system. The contribution ratio (RF) of the surface to pore diffusion mass transport showed that the larger contribution resulted from the surface diffusion in HGRPB system. Therefore, the results reasonably led to the conclusion that when the HGRPB system applied on the adsorption of methomyl on F400, the lower equilibrium concentration and faster internal mass transfer can be obtained so as to highly possess great potential to match the gradually stricter environmental standard.

Relationship between Helium Degassing of Cattle-Manure-Compost Adsorbents and Copper Ions Removal

This work was aimed to investigate the effect of helium degassing of cattle-manure-compost (CMC) based activated carbons on the adsorptive removal of copper ions from aqueous solution. Degassing temperatures were 500℃, 800℃ and 1000℃. Activated carbons were characterized according to surface chemistry and pore structures. Adsorption of copper ions was carried out using the conventional bottle-point technique to which the equilibrium data were correlated to Langmuir and Freundlich models. Results indicated that the uptake of copper ions could be well characterized by Langmuir model. It was found that the adsorption of copper ions decreased with significant decrease in surface area as a result of helium degassing at higher temperature. The increase of electron density on graphene layers offered higher affinity towards copper ions at lower equilibrium concentration. It was inferred that copper ions favorably adsorbed on mesopores at lower equilibrium concentration and switched to micropores at higher equilibrium concentration.

Sorption properties of porous spray-dried microspheres functionalized by phosphonic acid groups

We have shown that mesoporous silica microspheres with phosphonic groups ≡Si(СН2)2P(O)(ОН)2 in their pore surface layer have interesting properties for the sorption of neodymium(III) and dysprosium(III) from aqueous solutions, as well as for the adsorption of n-hexane, water, and triethylamine molecules from the gas phase. Such systems form the complexes LnL3 and LnL2+ in the surface layer in case of Lanthanide sorption. We found that at low equilibrium concentrations of metal ions in the solution the composition of the formed complexes is mainly LnL3, quickly reaching their saturation limit in the surface layer. Therefore, the further increase of sorption with the growing equilibrium concentration is observed due to the formation of complexes LnL2+. However, the ratio between these two types of complexes for neodymium(III) and dysprosium(III) are different probably because of the differences in Lanthanide radius. The mesoporous microspheric sorbents used are easily regenerated by hydrochloric acid, without substantial changes in their structure and in the composition of their surface layer. During sorption from the gas phase (in the absence of water molecules on the surface) phosphonic group could form hydrogen bonds among themselves or with silanol groups, which prevents their interaction with the electron-donor molecules (e.g. triethylamine).

Impact of carbon nanotube morphology on phenanthrene adsorption

The present study examined the roles of the specific surface area (SSA), diameter, and length of carbon nanotubes (CNT) on the adsorption of phenanthrene (PNT) by analyzing the adsorption isotherms obtained with several single-walled carbon nanotubes (SWNT) and multiwalled carbon nanotubes (MWNT). At low equilibrium concentrations (e.g., 1 ppb), MWNTs with larger outer diameters exhibited higher PNT adsorption capacity on an SSA basis than those with smaller diameters. With increasing equilibrium concentration, adsorption on an SSA basis became independent of MWNT diameter, and the total surface area controlled maximum adsorption capacity. A similar analysis for the adsorption of naphthalene, a planar molecule with one less benzene ring but 20 times higher solubility than PNT, showed no correlation with respect to MWNT outer diameter. The results indicated that the surface curvature of MWNT was more important on the adsorption of PNT than on the adsorption of naphthalene. Specific surface area normalized isotherms did not show a correlation between PNT adsorption and lengths of SWNTs and MWNTs. Characterization results indicated that the morphology of CNTs plays an important role on the SSA and pore volume. Data from the manufacturer may not always represent the characteristics of CNTs in a particular batch. Therefore, accurate characterization of CNTs is critical to systematically examine the behavior of CNTs, such as adsorption and transport, in environmental systems.