Multiwalled Carbon Nanotube Deposition on Model Environmental

Article pubs.acs.org/est

Multiwalled Carbon Nanotube Deposition on Model Environmental Surfaces Xiaojun Chang† and Dermont C. Bouchard‡,* †

U.S. Environmental Protection Agency, Athens, Georgia 30605, United States U.S. Environmental Protection Agency, Office of Research and Development, National Exposure Research Laboratory , 960 College Station Road, Athens, Georgia 30605, United States

‡

S Supporting Information *

ABSTRACT: Deposition of multiwalled carbon nanotubes (MWNTs) on model environmental surfaces was investigated using a quartz crystal microbalance with dissipation monitoring (QCMD). Deposition behaviors of MWNTs on positively and negatively charged surfaces were in good agreement with Derjaguin−Landau−Verwey−Overbeek (DLVO) theory, although hydrophobic interactions dominated MWNTs deposition on a hydrophobic polystyrene surface. Initial deposition rates (rf) and deposition attachment efficiencies (αD) depended on solution ionic strengths (IS) and surface electrostatic properties. Identical rf and αD values at constant IS on similar surfaces suggested that deposition was insensitive to surface morphology (i.e., bare crystal surface vs coated surface). The dissipation unit (D) was used with frequency ( f) to investigate nanoparticle deposition: |ΔD/Δf | values varied for deposition on different surfaces, indicating that the nature of MWNT association with surfaces varied despite constant rf and αD values.

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INTRODUCTION Since their discovery in 19911 carbon nanotubes (CNTs) have attracted attention due to their unique properties.2−4 CNTs have been utilized in various fields, including polymer composites,5 drug delivery,6 energy storage,7 and construction.8 Due to increased applications and production,9 it is inevitable that CNTs will be released to the environment incidentally or intentionally.10 Recent studies revealed that CNTs exhibit toxic effects,11,12 therefore, a complete understanding of CNTs transport and fate in the environment is necessary. Although pristine CNTs exist mainly as parallel bundles due to strong van der Waals interaction energies of ca. 500 eV/μm of tube−tube contact,13 techniques have been developed to facilitate their dispersion in aqueous media: chemical modifications via covalent bonding14 and dispersion via ultrasonication in the presence of stabilizing agents.15−19 Compared to covalent bonding which alters electrical and optical properties of CNTs,20 ultrasonication in surfactants preserves the integrity of CNTs’ electronic structure. Ultrasonication introduces mechanical energy overcoming the van der Waals forces between CNTs and results in debundling. Surfactant molecules adsorb onto the surfaces of debundled CNTs and stabilize them through electrostatic, steric, or electrosteric interactions. CNTs dispersed in solutions with low surfactant concentrations (i.e., below their critical micelle concentrations, CMCs) are environmentally relevant since surfactant concentrations are expected to decrease with dispersal in the environment. Most previous studies on CNTs’ behavior in the environment have been conducted with CNTs dispersed in solutions with surfactant concentrations above CMCs21 or with chemically modified CNTs,22 © XXXX American Chemical Society

and limited information is available on CNTs dispersed at low surfactant concentrations.16 Quartz crystal microbalance (QCM) has been used extensively in biological studies23,24 and more recently to evaluate stability and mobility of nanomaterials in aqueous systems.22,25−30 The use of QCM to monitor the adsorption and deposition of CNTs has been reported by Yi and Chen22 who studied oxidized multiwalled carbon nanotubes (MWNTs) deposition onto silica surfaces. However, there are no studies investigating deposition behaviors of MWNTs dispersed in solutions with environmentally relevant surfactant concentrations. To fill this gap, we examined the deposition of MWNTs dispersed in solutions with a low surfactant level on different environmental surfaces using QCM with dissipation monitoring (QCM-D). This study provides information on aqueous MWNTs stability and deposition behaviors that will support more accurate prediction of the environmental fate of these nanomaterials.

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MATERIALS AND METHODS Materials. MWNTs were purchased from CheapTubes Inc. (Brattleboro, VT) with a reported >95% wt. purity, an outside diameter of 20−30 nm, and a length of 10−30 μm. The polystyrene nanosphere (PS-NP) size standards (NIST-traceable materials) with a certified diameter of 59 ± 2 nm,

Received: May 16, 2013 Revised: August 8, 2013 Accepted: August 19, 2013

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dx.doi.org/10.1021/es402200h | Environ. Sci. Technol. XXXX, XXX, XXX−XXX

Environmental Science & Technology

Article

The flow rate through QCM−D modules was 0.1 mL/min and the temperature was 25 ± 0.2 °C. Details of the deposition protocol are listed in Table 1. Deposition onto bare sensor

analytical grade sodium chloride (NaCl) and sodium dodecyl sulfate (SDS) were purchased from Thermo-Fisher (Fremont, CA). N-(2-hydroxyethyl)-piperazine-N′-(2-ethanesulfonic acid) (HEPES, 99%) was purchased from Arcos Organics. Poly-Llysine hydrobromide (PLL, molecular weight 70 000−150 000 by viscosity) was purchased from Sigma-Aldrich. Suwannee River humic acid (SRHA, Standard II) was purchased from the International Humic Substances Society. All solutions were prepared with deionized water (resistivity = 18.2 mΩ·cm). The PLL and SHRA solution were filtered through a 0.45 μm cellulose acetate filter. Preparation of Nanoparticle Suspensions. A 40-mL mixture of MWNTs and 0.001% w/v SDS solution was ultrasonicated with a probe sonicator (Sonic & Materials, Newton, CT) in an ice−water bath for 10 min at an average energy level of ∼32 W. The resulting mixture was centrifuged at 50 000 RCF at 4 °C (Beckman Coulter, Brea, CA) for 1 h and 30 mL of the supernatant was transferred to a clean container as the stock MWNTs suspension. The PS-NPs were included in the present study because they are commonly available in environmental nanotechnology laboratories and therefore will offer a reliable interlab comparison. In addition, the comparison between the results on MWNTs and PS-NPs may help us to understand the shape effects on nanoparticle QCM-D deposition. The working PS-NPs suspension had a concentration of 50 mg/L at an ionic strength of 10 mM (NaCl). Characterization of Nanoparticle Suspensions. Concentration of the stock MWNTs suspension was determined using UV−vis absorbance measured by an Enspire Multimode Reader 2300 (PerkinElmer, MA) and a predetermined calibration curve (Supporting Information (SI) Figures S1 and S2). Using a Nano ZetaSizer (Malvern Instruments, Worcestershire, U.K.) equipped with a helium/neon laser, nanoparticles electrophoretic mobility (EPM) was determined using phase analysis light scattering and intensity averaged hydrodynamic diameter (Zave) and polydispersity index (PDI) determined using dynamic light scattering (DLS).16,31 Time-Resolved DLS. Time-resolved dynamic light scattering was employed to study nanoparticle aggregation kinetics using the following equation:

ka ∝

1 ⎛ dZave(t ) ⎞ ⎜ ⎟ N0 ⎝ dt ⎠t → 0

Table 1. QCM-D Deposition Experiment Solution/ Suspension Introduction function stabilization PLL coating

humic acid coating

αA =

ka ,fast

=

( (

) )

dZave(t ) dt

1 N0,fast

dZave(t ) dt

C1

Da

electrolyte solution stabilization

D1 D2

deposition

E

rinsing

F

solution/suspension introduced DI water 10 mM HEPES + 100 mM NaCl 10 mM HEPES + 100 mM NaCl + 0.1 g/L PLLs 10 mM HEPES + 100 mM NaCl 1 mM NaCl humic acid in 1 mM NaCl (30 mg/L TOC) 1 mM NaCl DI water + electrolyte solution (V: V = 1:4) 0.001% SDS + electrolyte solution (V:V = 1:4) MWNTsb + electrolyte solution (V: V = 1:4)

F1 F2

electrolyte solution of low concentration DI water

a

For PS-NPs deposition, electrolyte solution stabilization, Stage D included only one step: 10 mM NaCl: electrolyte solution (V:V = 1:4). b For PS-NPs deposition experiments, the MWNTs suspension was replaced by PS-NPs.

surfaces are described by Stages A, D, E, and F. For deposition onto PLL-coated silica surfaces, Stage B was introduced before Stage D to produce a positively charged PLL layer. To study nanoparticle deposition on an SRHA-coated suace, Stage C was included between Stage B and Stage D. Since the deposited nanoparticles do not form a homogeneous rigid layer, the changes in deposited mass and frequency do not follow the Sauerbrey equation.32,33 However, data from QCM-D can be used to evaluate nanoparticle deposition behaviors by calculating deposition rate and deposition attachment efficiency based upon the decrease in frequency.26,28,30 In the present study, we monitored shifts in frequency and dissipation at the third overtone. Initial deposition rates rf is defined as rates of frequency change in a time period t: ⎛ dΔf(3) ⎞ ⎟⎟ r f = ⎜⎜ ⎝ dt ⎠ t → 0

t→0

t → 0,fast

C

C2

(1)

1 N0

B1 B2 B3 B4

where ka is the initial aggregation rate during the initial aggregation period t0, which is defined as the period from experiment initiation to when the Zave reaches 1.50Zave, initial,16 and N0 is the initial particle concentration. The aggregation attachment efficiency (αA) was defined as ka normalized by the aggregation rate under diffusion-limited (fast) conditions:26 ka

stage A B

(2)

(3)

where Δf(3) is the shift in the third overtone efficiency. The deposition attachment efficiency αD is calculated from deposition rates:

QCM-D Deposition. Nanoparticle deposition was investigated using a Q-Sense E4 (Västra Frölunda, Sweden). Crystal sensors with different surfaces, including silicon dioxide (SiO2/ silica, QSX303), aluminum oxide (Al2O3, QSX306), iron oxide (Fe3O4, QSX326), polystyrene (QSX309), and PLL- and SRHA-coated silica sensors were employed in the present study. Crystal sensors were cleaned via protocols modified from those recommended by Q-Sense (SI) before use.

dΔf(3)

αD =

rf

( ) = ( ) dt

(r f )fav

dt

B

t→0

dΔf(3)

fav, t → 0

(4)



Article

Figure 1. (A) Electrophoretic mobilities (EPM) of MWNTs as a function of ionic strength. Each data point represents the average of three measurements for one sample. Error bars represent the standard deviation. (B) Aggregation attachment efficiencies of MWNTs as a function of ionic strength. AFM images of MWNTs on PLL-coated silica sensors in the presence of (C)20, (D)30, (E)40, and (F)60 mM NaCl.

∼30 nm to ∼1 μm, are much shorter than the manufacturer’s reported values of 10−30 μm and likely due to ultrasonication dispersal. The average size for 269 MWNTs from a 3.3 × 3.3 μm2 region in the middle of the crystal sensor is 81.8 ± 42.5 nm (SI Figure S5), which is smaller than the Zave. The discrepancy is due to different mechanisms of measurements: the former calculates the size of a particle as the diameter of a sphere, which covers the same area as the target particle; the latter is determined as the diameter of a spherical particle with the same diffusivity. Effect of Ionic Strength on MWNTs Surface Charges. The EPM values of MWNTs as a function of solution ionic strength (IS) are shown in Figure 1A. MWNTs exhibited negatively charged surfaces over the tested [NaCl] range. Consistent with classic colloidal theory and commonly found in various nanoparticles,22,26,29 EPM of MWNTs became less negative with IS. The mechanisms by which CNTs obtain negative surface charges are not fully understood,34 however, defects on the sidewalls and tube-ends of CNTs35 are enhanced by ultrasonication and prone to being oxidized to carboxyl and hydroxyl functional groups. Dissociation of these functional groups could be an origin of CNTs negative charges, and adsorption of anionic surfactants like SDS on CNTs surfaces also contributes to negative charge.36 MWNTs Aggregation. MWNTs aggregation experiments were conducted in solutions with [NaCl] ranging from 10 to 160 mM. Representative MWNTs aggregation profiles are presented in SI Figure S6. When [NaCl] > 120 mM, the initial aggregation rates were stable at ∼1.0 nm/s, indicating that diffusion-limited (fast) aggregation was achieved. The aggregation attachment efficiency (αA) calculated from the initial

In eq 4 the denominator represents the rate of frequency change obtained under model favorable conditions (PLLcoated silica surface). Atomic Force Microscopy. MWNTs morphology was characterized using a Veeco Multimode Atomic Force Microscopy (AFM) with a Nanoscope V controller and an EScanner (Bruker AXC Inc., Madison, WI). MWNTs deposited on PLL-coated surfaces obtained from QCM-D were gently dried with nitrogen, then mounted on 12 mm stainless steel discs. Images were taken under tapping mode with silicon TappingMode cantilevers at the speed of 1.0 Hz and a resolution of 512 × 512 pixels.

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RESULTS AND DISCUSSION

Characteristics of MWNTs. Although the SDS concentration used here (0.001% w/v) was 3 orders of magnitude lower than its CMC, it was capable of dispersing and stabilizing MWNTs: stock suspension concentration was 6.07 ± 0.08 mg/ L and the pH was stable around 6.9 as monitored weekly over the four-month experimental period. Zave and EPM were measured prior to each aggregation and deposition experiment (Zave = 175.9 ± 2.5 nm, PDI = 0.276 ± 0.015, and EPM = (−4.311 ± 0.150) × 10−8 m2/V-s). Size distribution of MWNTs, determined by DLS (SI Figure S3), indicates that this suspension is polydisperse, with size ranging from ∼20 nm to several hundred nanometers. SI Table S2 contains the key physicochemical parameters of the PS-NP suspensions. AFM imaging (SI Figure S4) shows that the MWNTs were debundled as indicated by diameters of the dispersed MWNTs on the crystal (20−30 nm), which are consistent with that reported by the manufacturer. MWNTs lengths, varying from C



Article

Figure 2. Representative deposition profiles of MWNTs on (A) an Al2O3 surface and (B) a SRHA-coated silica sensor in the presence of 20 mM NaCl.

Figure 3. Deposition rate |rf | of MWNTs deposition on different surfaces: (A) under favorable conditions; (B) under unfavorable conditions. Each data point represents the average of four replicate QCM-D deposition experiments; the error bar represents their standard deviation.

sensor surface, was observed; this is also supported by the lack of nonlinear decrease in f(3) during deposition stage in the QCM experiments (discussed later). Similar to the salt-free MWNTs observed in SI Figure S4, singlets of MWNTs were observed in solutions with low IS (Figure 1C and D). With increasing IS, large aggregates of a number of MWNTs singlets were observed (Figure 1E and F). Deposition under Favorable Conditions. Since metal oxide surfaces exist as coating patches on natural sands and are positively charged at neutral pH,39,40 Al2O3 and Fe3O4 sensors were also chosen for favorable deposition. Deposition was conducted on positively charged PLL-coated silica surfaces.22 A representative deposition profile of MWNTs onto an Al2O3 surface is presented in Figure 2A. DI water was introduced to attain stable baselines (Stage A). After 20 mM NaCl solution was introduced (Stage D1), a small decrease in f(3) and a corresponding small increase in D(3) were observed due to increased solution density and viscosity41 (|Δf(3)| and ΔD(3) increase linearly with [NaCl], SI Figure S8). After stabilizing f(3) and D(3) with 20 mM NaCl, a solution containing 0.001% SDS and 20 mM NaCl was introduced (Stage D2); there were no noticeable shifts in f(3) or D(3), suggesting the SDS did not

aggregation rate using eq 2 is plotted as a function of IS in Figure 1B. There was no aggregation in NaCl solutions ≤10 mM due to the strongly negatively charged MWNTs surfaces (Figure 1A). Two distinct aggregation regimes were observed: the reaction-limited regime ([NaCl] < 120 mM, αa < 1.0), in which reduction in the energy barrier due to electrolyte screening leads to faster aggregation; and the diffusion-limited regime ([NaCl] ≥ 120 mM, αa ≈ 1.0), in which aggregation rate is independent of IS and solely dependent on particle diffusion rates. These observations are in agreement with the classic Derjaguin−Landau−Verwey−Overbeek (DLVO) theory,37 and consistent with previous aggregation studies of CNTs suspensions prepared with longer ultrasonication periods38 and oxidized CNTs.22 The critical coagulation concentration (CCC), determined by the intersection of extrapolations of reaction-limited and diffusion-limited regimes, is 120 mM NaCl. AFM images of MWNTs. Representative AFM images of MWNTs in the presence of NaCl are presented in Figures 1C− F. Deposited MWNTs covered only a small portion of the sensor surface. No ripening phenomenon,25 where nanoparticles attach to nanoparticles previously deposited to the D



Article

Figure 4. Deposition attachment efficiency (αD) as a function of [NaCl]: (A) favorable conditions and (B) unfavorable conditions. Each data point represents the average of four replicate QCM-D deposition experiments; the error bar represents their standard deviation.

pH, the silica crystal surface is negatively charged42,43 and MWNT deposition onto silica is thus unfavorable. A representative deposition profile is presented in SI Figure S9A. |rf | on silica surfaces as a function of [NaCl] is presented in Figure 3B. There was no deposition on silica surfaces in the absence of NaCl. The lack of deposition indicates that strong repulsive electrostatic forces between the negatively charged MWNTs and silica surfaces40 inhibit deposition. As the MWNTs’ electrical double-layer is compressed due to more effective counterion screening, deposition rates increased with [NaCl] at low IS levels ( 20 mM. The MWNTs Zave increased from 175 nm to >800 nm within 60 min in the presence of 60 mM NaCl, while it remained stable around 175 nm during this time period in the presence of 20 mM NaCl (SI Figure S6). At a constant IS there was no noticeable difference among deposition rates for the three surfaces. This identity was also observed for deposition of PS-NP onto the three positively charged surfaces (SI Figure S11) suggesting that PS-NP deposition on positively charged surfaces is also independent of surface chemistry and that particle concentration and size are predominant factors controlling deposition rates under favorable conditions. Deposition under Unfavorable Conditions. The pHs of MWNTs suspensions at varying NaCl concentrations and all other solutions used in the present study were near 6.5; at this E



Article

Figure 5. The ratio of dissipation unit to frequency at the third overtone (|ΔD(3)/Δf(3)|) for PS-NPs deposition as a function of NaCl concentration for different depositions: (A) favorable conditions; (B) unfavorable conditions. Insets: |ΔD(3)/Δf(3)| for MWNTs deposition. Each data point represents the average of four replicate QCM-D deposition experiments; the error bar represents their standard deviation.

surfaces, and 43.4 ± 5.2 mM NaCl for SRHA-coated surfaces. In addition to CDCs that were not significantly different, αD values on SRHA-coated surfaces were not lower than corresponding values on silica surfaces in the unfavorable regime. This is inconsistent with Chen and Elimelech’s study on nC6027 which reported that the deposition of nC60 particles is depressed on SRHA-coated surfaces and explained this observation by steric repulsion of the SRHA layer. In contrast, the constant D measurements (Figure 2B) during Stage C1 indicate a rigid SRHA-coated surface. Comparison of QCM-D results for negatively charged silica and SRHA-coated surfaces suggests that despite their different chemical properties, MWNTs deposition behaviors on the two surfaces are essentially identical. Unlike deposition on negatively charged surfaces, there are no distinct unfavorable and favorable regimes in the MWNTs deposition profile on polystyrene surfaces (Figure 4B). The discrepancy with classic DLVO colloidal theory may be caused by the hydrophobic nature of the polystyrene surface; MWNTs deposition may be dominated by hydrophobic interactions rather than electrostatic and van der Waals attractions. PS-NPs Deposition Attachment Efficiency. PS-NPs had similar deposition behaviors onto the three positively charged surfaces (SI Figure S13A): their deposition attachment efficiencies were near 1.0 and independent of IS for all surface types. Similarly to MWNTs, PS-NPs did not demonstrate increasing attachment efficiency with IS on the polystyrene surface, indicating that hydrophobic interactions are the possible origin of PS-NPs deposition onto this surface. Differences were observed for PS-NPs deposition on the two negatively charged surfaces: on silica surfaces, αD increased with IS until IS ≥ 240 mM and then was stable around 1.0, which is consistent with classic colloid deposition theory. αD on SRHAcoated surfaces were higher than those on the silica surface and kept increasing with IS over the whole test [NaCl] range. αD > 1.0 on the SRHA-coated surface when IS > 200 mM, which may be due to a combination of electrostatic and hydrophobic interactions: Favorable conditions are defined by electrostatic

formation of a homogeneous, rigid SRHA layer onto the crystal surface.45 The changing pattern of |rf | with IS on SRHA coated surfaces is similar to that on silica (Figure 3B). Polystyrene sensors were chosen as representative hydrophobic surfaces.45 Compared to the two negatively charged surfaces discussed before, deposition onto polystyrene surfaces did not show an obvious increasing trend in the range of 10 ≤ [NaCl] ≤ 40 mM (Figure 3B). Such independence of electrolyte concentration suggests that MWNTs deposition on polystyrene surface is probably not due to DLVO interactions. We conjecture that hydrophobic properties of polystyrene are the reasons for unique MWNTs deposition on this surface. For QCM-D deposition experiments on all surfaces, there was no increase in f and its corresponding decrease in D in Stages F1 and F2, indicating no release of MWNTs during rinsing stages. The lack of reversibility on hydrophilic surfaces observed here, which is consistent with previous QCM-D studies on nC6026 and TiO2 nanoparticles,28 suggests there will be no release of MWNTs after deposition if there is no drastic change in solution chemistry. MWNTs Deposition Attachment Efficiency. To eliminate effects of aggregation, attachment efficiencies αD are calculated by normalizing initial deposition rates rf obtained on different types of surfaces by the corresponding rates obtained under model favorable conditions PLL-coated surfaces at the same [NaCl]. Under favorable conditions, deposition attachment efficiencies are close to 1.0 and independent of [NaCl] and surface type (Figure 4A). MWNTs αD profiles on negatively charged silica and SRHA-coated surfaces (Figure 4B) are consistent with classical deposition behaviors of colloids and nanoparticles.46 There are two regimes in these profiles: the unfavorable zone where αD < 1.0 and increases with [NaCl] and the favorable zone where αD ≈ 1.0 and independent of IS. The critical deposition concentration (CDC) is the minimum electrolyte concentration that allows favorable deposition to take place. The CDC value is 39.3 ± 9.3 mM NaCl on silica F



Article

Figure 6. Schematic figures of nanoparticle deposition onto crystal sensor surfaces: (A) PS-NPs onto metal oxide surfaces; (B) aggregated PS-NPs onto metal oxide surfaces; (C) PS-NPs onto PLL coated silica surface; and (D) MWNTs onto silica surface.

uncoated surfaces. This slight increase can also be explained by the association of MWNTs with SRHA coating instead of their association with solid silica surfaces similar to the schematic in Figure 6C. Compared to |ΔD(3)/Δf(3)| under favorable conditions, |ΔD(3)/Δf(3)| on these three unfavorable conditions are slightly higher which indicates deposition via electrostatic interactions forms more rigid, less dissipative deposited layer/ particles. MWNTs |ΔD(3)/Δf(3)| values under favorable and unfavorable conditions (Figure 5 insets) increased with IS due to aggregation. For MWNTs deposition onto polystyrene, |ΔD(3)/ Δf(3)| ≈ 0.5 when IS ≤ 30 mM (no significant aggregation in this IS range) and |ΔD(3)/Δf(3)| ≈ 1.0 when IS ≥ 40 mM IS. The relatively stable |ΔD(3)/Δf(3)| at low IS levels correspond to the statistically unchanged rf and αD in this range and indicate that dissipative properties of deposited MWNTs onto polystyrene surfaces are not sensitive to IS. The significantly high |ΔD(3)/Δf(3)| at IS = 40 and 50 mM are likely due to large aggregate deposition via hydrophobic interactions. In general, |ΔD(3)/Δf(3)| for MWNTs were much higher than those for PSNPs. This dissimilarity may be related to differences in particle shape and heterogeneity. The PS-NP standard is much more monodisperse than the MWNTs (PDI = 0.025 and 0.276, respectively); the small, uniform PS-NP spheres are more readily packed on the sensor surface than the more heterogeneous MWNTs. Deposited MWNTs are also prone to protrude into the bulk solution and enhancing the crystal sensor’s ability to dissipate energy due to high aspect ratios (Figure 6D). Environmental Implications. After the release of CNTs in the environment, their transport and fate will be governed by their aggregation and deposition behaviors. The present study reports the deposition of MWNTs on various environmental surfaces. Data from the present study suggest that electrostatic surface properties are the most important surface characteristics governing MWNTs deposition in the presence of monovalent sodium cation. In addition, MWNTs deposition behaviors on hydrophobic polystyrene surface were first investigated here, and data indicate that hydrophobic interactions can result in significant MWNTs deposition which is irreversible when IS decreases. To our knowledge, this is the first environmentally

interactions and do not consider hydrophobic interactions which could be crucial for hydrophobic particle deposition. |ΔD/Δf | Values for Deposition Study. In addition to decreased f, the increase in total mass of the crystal sensor due to deposition also enhances the crystal’s ability to dissipate energy.28 This corresponding increase in dissipation unit D has been observed in QCM-D deposition of nanoparticles,25,28,47,48 bacteria,49 and viruses,50 as well as for the PS-NPs and MWNTs investigated here. Combined with Δf, ΔD reveals dissipative properties and structure of the deposited nanoparticles.51 The slope of D vs f (i.e., |ΔD/Δf |) is an estimation of the induced energy dissipation per coupled mass change:45 a lower value of |ΔD/Δf| suggests the formation of a rigid layer, while an elevated slope indicates a ‘soft’ and dissipative layer.52 In the present study, the D and f for each deposition experiment exhibited a clear linear relationship (R2 ≥ 0.99) during deposition Stage E. |ΔD/Δf| therefore is calculated using all D and f data from this stage. |ΔD(3)/Δf(3)| of PS-NPs deposition are presented as a function of [NaCl] in Figure 5. Under favorable conditions, |ΔD(3)/Δf(3)| increased with IS, indicating that deposited PS-NPs became more dissipative. This can be explained by the aggregation of PS-NPs with [NaCl]: at low IS levels, PS-NPs exist in aqueous suspension as individual particles and deposit individually onto positively charged surfaces via electrostatic interactions (Figure 6A). When PSNPs aggregate into large clusters at high IS levels, the deposited clusters are only partially associated with sensor surfaces and the rest of the cluster mass protrudes into the bulk solution (Figure 6B); enhancing the crystal’s ability to dissipate energy. Interestingly, although |rf | and αD were statistically the same for PS-NPs on the three positively charged surfaces (SI Figure S11), |ΔD(3)/Δf(3)| of PS-NPs deposition onto PLL-coated surfaces were noticeably higher than those for their deposition onto bare metal oxide surfaces, especially at low IS levels. This increase is likely the result of PS-NPs on the PLL surface being less fully coupled to the sensor (Figure 6C) than those deposited directly onto metal oxide surfaces (Figure 6A). The increase in |ΔD(3)/Δf(3)| with IS was also observed in PS-NPs deposition onto other surfaces (Figure 5B). |ΔD(3)/Δf(3)| values on silica and polystyrene surfaces were quite similar, while |ΔD(3)/Δf(3)| for SRHA-coated surface was slightly higher than G



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(7) Che, G.; Lakshmi, B. B.; Fisher, E. R.; Martin, C. R. Carbon nanotubule membranes for electrochemical energy storage and production. Nature 1998, 393, 346−349. (8) Lee, J.; Mahendra, S.; Alvarez, P. J. J. Nanomaterials in the construction industry: A review of their applications and environmental health and safety considerations. Acs Nano 2010, 4, 3580− 3590. (9) Mueller, N. C.; Nowack, B. Exposure modeling of engineered nanoparticles in the environment. Environ. Sci. Technol. 2008, 42, 4447−4453. (10) Petersen, E. J.; Zhang, L.; Mattison, N. T.; O’Carroll, D. M.; Whelton, A. J.; Uddin, N.; Tinh, N.; Huang, Q.; Henry, T. B.; Holbrook, R. D.; Chen, K. L. Potential release pathways, environmental fate, And ecological risks of carbon nanotubes. Environ. Sci. Technol. 2011, 45, 9837−9856. (11) Long, Z. F.; Ji, J.; Yang, K.; Lin, D. H.; Wu, F. C. Systematic and quantitative investigation of the mechanism of carbon nanotubes’ toxicity toward algae. Environ. Sci. Technol. 2012, 46, 8458−8466. (12) Shi, X. H.; von dem Bussche, A.; Hurt, R. H.; Kane, A. B.; Gao, H. J. Cell entry of one-dimensional nanomaterials occurs by tip recognition and rotation. Nat. Nanotechnol. 2011, 6, 714−719. (13) Girifalco, L. A.; Hodak, M.; Lee, R. S. Carbon nanotubes, buckyballs, ropes, and a universal graphitic potential. Phys. Rev. B 2000, 62, 13104−13110. (14) Banerjee, S.; Hemraj-Benny, T.; Wong, S. S. Covalent surface chemistry of single-walled carbon nanotubes. Adv. Mater. 2005, 17, 17−29. (15) Rastogi, R.; Kaushal, R.; Tripathi, S. K.; Sharma, A. L.; Kaur, I.; Bharadwaj, L. M. Comparative study of carbon nanotube dispersion using surfactants. J. Colloid Interface Sci. 2008, 328, 421−428. (16) Bouchard, D.; Zhang, W.; Powell, T.; Rattanaudompol, U. Aggregation kinetics and transport of single-walled carbon nanotubes at low surfactant concentrations. Environ. Sci. Technol. 2012, 46, 4458− 4465. (17) Tian, Y. A.; Gao, B.; Ziegler, K. J. High mobility of SDBSdispersed single-walled carbon nanotubes in saturated and unsaturated porous media. J. Hazard. Mater. 2011, 186, 1766−1772. (18) Wang, J. Y.; Li, Y. Selective band structure modulation of singlewalled carbon nanotubes in ionic liquids. J. Am. Chem. Soc. 2009, 131, 5364−+. (19) Manivannan, S.; Jeong, I. O.; Ryu, J. H.; Lee, C. S.; Kim, K. S.; Jang, J.; Park, K. C. Dispersion of single-walled carbon nanotubes in aqueous and organic solvents through a polymer wrapping functionalization. J. Mater. Sci.: Mater. Electron. 2009, 20, 223−229. (20) Cognet, L.; Tsyboulski, D. A.; Rocha, J. R.; Doyle, C. D.; Tour, J. M.; Weisman, R. B. Stepwise quenching of exciton fluorescence in carbon nanotubes by single-molecule reactions. Science 2007, 316, 1465−1468. (21) Tian, Y.; Gao, B.; Silvera-Batista, C.; Ziegler, K. J. Transport of engineered nanoparticles in saturated porous media. J. Nanopart. Res. 2010, 12, 2371−2380. (22) Yi, P.; Chen, K. L. Influence of surface oxidation on the aggregation and deposition kinetics of multiwalled carbon nanotubes in monovalent and divalent electrolytes. Langmuir 2011, 27, 3588− 3599. (23) Tymchenko, N.; Nileback, E.; Voinova, M. V.; Gold, J.; Kasemo, B.; Svedhem, S., Reversible changes in cell morphology due to cytoskeletal rearrangements measured in real-time by QCM-D. Biointerphases 2012, 7. (24) Goda, T.; Miyahara, Y. Interpretation of protein adsorption through its intrinsic electric charges: A comparative study using a fieldeffect transistor, surface plasmon resonance, and quartz crystal microbalance. Langmuir 2012, 28, 14730−14738. (25) Fatisson, J.; Ghoshal, S.; Tufenkji, N. Deposition of carboxymethylcellulose-coated zero-valent iron nanoparticles onto silica: Roles of Solution Chemistry and Organic Molecules. Langmuir 2010, 26, 12832−12840. (26) Chen, K. L.; Elimelech, M. Aggregation and deposition kinetics of fullerene (C60) nanoparticles. Langmuir 2006, 22, 10994−11001.

related study with QCM-D, reporting the slope of the dissipation unit vs the frequency (|ΔD/Δf |) to facilitate the understanding of nanoparticle deposition on various surfaces. In general, |ΔD/Δf | increased with aggregate size, which is controlled by IS. Although deposition kinetics (rf and αD) were not sensitive to surface types, |ΔD/Δf | was surface dependent. Although the rate of frequency shift (rf) and dissipation shift (rD) have been reported as reliable parameters for quantifying nanoparticle deposition28,49 and several previous studies24,51 have shown that deposition attachment efficiencies obtained by rf and rD are quite similar, our results on size-, IS-, and surfacedependent |ΔD/Δf| suggest that rD cannot be a simple replacement of rf without taking these factors into consideration.

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ASSOCIATED CONTENT

* Supporting Information S

MWNTs concentration determination. QCM-D crystal sensors cleaning protocols. Size distribution of MWNTs stock suspension determined by DLS. Key physicochemical properties of MWNTs and PS-NPs suspensions. AFM images and particle size distribution determined by AFM. Aggregation profiles of MWNTs in the presence of NaCl. Initial deposition rate of MWNTs as a function of salt concentration. Changes in frequency and dissipation unit as a function of [NaCl] due to changes in density and viscosity. Representative MWNTs deposition profiles on various surfaces. Initial deposition rates of PS-NPs on various surfaces. PS-NPs deposition attachment efficiency as a function of [NaCl]. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Phone: 706-355-8333; fax: 706-355-8007; e-mail: Bouchard. [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This paper has been reviewed in accordance with the USEPA’s peer and administrative review policies and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

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REFERENCES

(1) Iijima, S. Helical microtubules of graphitic carbon. Nature 1991, 354, 56−58. (2) Poncharal, P.; Wang, Z. L.; Ugarte, D.; de Heer, W. A. Electrostatic deflections and electromechanical resonances of carbon nanotubes. Science 1999, 283, 1513−1516. (3) Liu, J.; Rinzler, A. G.; Dai, H.; Hafner, J. H.; Bradley, R. K.; Boul, P. J.; Lu, A.; Iverson, T.; Shelimov, K.; Huffman, C. B.; RodriguezMacias, F.; Shon, Y.-S.; Lee, T. R.; Colbert, D. T.; Smalley, R. E. Fullerene pipes. Science 1998, 280, 1253−1256. (4) Tans, S. J.; Verschueren, A. R. M.; Dekker, C. Room-temperature transistor based on a single carbon nanotube. Nature 1998, 393, 49− 52. (5) Clayton, L. M.; Sikder, A. K.; Kumar, A.; Cinke, M.; Meyyappan, M.; Gerasimov, T. G.; Harmon, J. P. Transparent poly(methyl methacrylate)/single-walled carbon nanotube (PMMA/SWNT) composite films with increased dielectric constants. Adv. Funct. Mater. 2005, 15, 101−106. (6) Bianco, A.; Kostarelos, K.; Prato, M. Applications of carbon nanotubes in drug delivery. Curr. Opin. Chem. Biol. 2005, 9, 674−679. H



Article

(46) Elimelech, M.; Gregory, J.; Jia, X.; Willams, R. A. Particle Deposition and Aggregatuion - Measurement, Modelling and Simulation; Butterworth-Heinemann: Oxford, England, 1995. (47) Xu, D.; Hodges, C.; Ding, Y. L.; Biggs, S.; Brooker, A.; York, D. A QCM study on the adsorption of colloidal laponite at the solid/ liquid interface. Langmuir 2010, 26, 8366−8372. (48) Sirk, K. M.; Saleh, N. B.; Phenrat, T.; Kim, H.; Dufour, B.; Ok, J.; Golas, P. L.; Matyjaszewski, K.; Lowry, G. V.; Tilton, R. D. Effect of adsorbed polyelectrolytes on nanoscale zero valent iron particle attachment to soil surface models. Environ. Sci. Technol. 2009, 43, 3803−3808. (49) Poitras, C.; Tufenkji, N. A QCM-D-based biosensor for E. coli O157:H7 highlighting the relevance of the dissipation slope as a transduction signal. Biosens. Bioelectron. 2009, 24, 2137−2142. (50) Steinmetz, N. F.; Bock, E.; Richter, R. P.; Spatz, J. P.; Lomonossoff, G. P.; Evans, D. J. Assembly of multilayer arrays of viral nanoparticles via biospecific recognition: A quartz crystal microbalance with dissipation monitoring study. Biomacromolecules 2008, 9, 456− 462. (51) Rodahl, M.; Hook, F.; Fredriksson, C.; A. Keller, C.; Krozer, A.; Brzezinski, P.; Voinova, M. V.; Kasemo, B. Simultaneous frequency and dissipation factor QCM measurements of biomolecular adsorption and cell adhesion. Farad. Discuss. 1997, 107, 229−246. (52) Gall, I.; Herzberg, M.; Oren, Y. The effect of electric fields on bacterial attachment to conductive surfaces. Soft Matter 2013, 9, 2443−2452.

(27) Chen, K. L.; Elimelech, M. Interaction of fullerene (C60) nanoparticles with humic acid and alginate coated silica surfaces: Measurements, mechanisms, and environmental implications. Environ. Sci. Technol. 2008, 42, 7607−7614. (28) Fatisson, J.; Domingos, R. F.; Wilkinson, K. J.; Tufenkji, N. Deposition of TiO2 nanoparticles onto silica measured using a quartz crystal microbalance with dissipation monitoring. Langmuir 2009, 25, 6062−6069. (29) Quevedo, I. R.; Tufenkji, N. Influence of solution chemistry on the deposition and detachment kinetics of a CdTe quantum dot examined using a quartz crystal microbalance. Environ. Sci. Technol. 2009, 43, 3176−3182. (30) Liu, X.; Chen, G.; Su, C. Influence of collector surface composition and water chemistry on the deposition of cerium dioxide nanoparticles: QCM-D and column experiment approaches. Environ. Sci. Technol. 2012, 46, 6681−6688. (31) Bouchard, D.; Zhang, W.; Chang, X. A rapid screening technique for estimating nanoparticle transport in porous media. Water Res. 2013, 47 (12), 4086−4094. (32) Reviakine, I.; Johannsmann, D.; Richter, R. P. Hearing what you cannot see and visualizing what you hear: Interpreting quartz crystal microbalance data from solvated interfaces. Anal. Chem. 2011, 83, 8838−8848. (33) Sauerbrey, G. Verwendung von Schwingquarzen zur Wagung dunner schichten und zur mikrowagung. Z. Fur Physik 1959, 155, 206−222. (34) Smith, B.; Wepasnick, K.; Schrote, K. E.; Cho, H. H.; Ball, W. P.; Fairbrother, D. H. Influence of surface oxides on the colloidal stability of multi-walled carbon nanotubes: A structure-property relationship. Langmuir 2009, 25, 9767−9776. (35) Müller, T. J. J.; Bunz, U. H. F. Functional Organic Materials: Syntheses, Strategies and Applications; Wiley-VCH, 2007. (36) White, B.; Banerjee, S.; O’Brien, S.; Turro, N. J.; Herman, I. P. Zeta-potential measurements of surfactant-wrapped individual singlewalled carbon nanotubes. J. Phys. Chem. C 2007, 111, 13684−13690. (37) Vold, M. J. Van der Waals’ attraction between anisometric particles. J. Colloid Sci. 1954, 9, 451−459. (38) Saleh, N. B.; Pfefferle, L. D.; Elimelech, M. Influence of biomacromolecules and humic acid on the aggregation kinetics of single-walled carbon nanotubes. Environ. Sci. Technol. 2010, 44, 2412− 2418. (39) Tamura, H.; Katayama, N.; Furuichi, R. Modeling o fionexchange reactions on metal oxides with the frumkin isotherm. 1. Acid−base and charge characteristics of MnO2, TiO2, Fe3O4, and Al2O3 surfaces and adsorption fffinity of alkali metal ions. Environ. Sci. Technol. 1996, 30, 1198−1204. (40) Zhang, W.; Isaacson, C. W.; Rattanaudompol, U.; Powell, T. B.; Bouchard, D. Fullerene nanoparticles exhibit greater retention in freshwater sediment than in model porous media. Water Res. 2012, 46, 2992−3004. (41) Martin, S. J.; Granstaff, V. E.; Frye, G. C. Characterization of a quartz crystal microbalance with simultaneous mass and liquid loading. Anal. Chem. 1991, 63, 2272−2281. (42) Bergna, H. E.; Roberts, W. O. Colloidal Silica: Fundamentals and Applications; CRC, 2005; Vol. 131. (43) Yuan, B. L.; Pham, M.; Nguyen, T. H. Deposition kinetics of bacteriophage MS2 on a silica surface coated with natural organic matter in a radial stagnation point flow cell. Environ. Sci. Technol. 2008, 42, 7628−7633. (44) Hyung, H.; Kim, J. H. Natural organic matter (NOM) adsorption to multi-walled carbon nanotubes: Effect of NOM characteristics and water quality parameters. Environ. Sci. Technol. 2008, 42, 4416−4421. (45) Feiler, A. A.; Sahlholm, A.; Sandberg, T.; Caldwell, K. D. Adsorption and viscoelastic properties of fractionated mucin (BSM) and bovine serum albumin (BSA) studied with quartz crystal microbalance (QCM-D). J. Colloid Interface Sci. 2007, 315, 475−481. I


Multiwalled Carbon Nanotube Deposition on Model Environmental

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