Transport Of Multi-walled Carbon Nanotubes Research Articles

Significance of Non-DLVO Interactions on the Co-Transport of Functionalized Multiwalled Carbon Nanotubes and Soil Nanoparticles in Porous Media.

Derjaguin-Landau-Verwey-Overbeek (DLVO) theory is typically used to quantify surface interactions between engineered nanoparticles (ENPs), soil nanoparticles (SNPs), and/or porous media, which are used to assess environmental risk and fate of ENPs. This study investigates the co-transport behavior of functionalized multiwalled carbon nanotubes (MWCNTs) with positively (goethite nanoparticles, GNPs) and negatively (bentonite nanoparticles, BNPs) charged SNPs in quartz sand (QS). The presence of BNPs increased the transport of MWCNTs, but GNPs inhibited the transport of MWCNTs. In addition, we, for the first time, observed that the transport of negatively (BNPs) and positively (GNPs) charged SNPs was facilitated by the presence of MWCNTs. Traditional mechanisms associated with competitive blocking, heteroaggregation, and classic DLVO calculations cannot explain such phenomena. Direct examination using batch experiments and Fourier transform infrared (FTIR) spectroscopy, asymmetric flow field flow fractionation (AF4) coupled to UV and inductively coupled plasma mass spectrometry (AF4-UV-ICP-MS), and molecular dynamics (MD) simulations demonstrated that MWCNTs-BNPs or MWCNT-GNPs complexes or aggregates can be formed during co-transport. Non-DLVO interactions (e.g., H-bonding and Lewis acid-base interaction) helped to explain observed MWCNT deposition, associations between MWCNTs and both SNPs (positively or negatively), and co-transport. This research sheds novel insight into the transport of MWCNTs and SNPs in porous media and suggests that (i) mutual effects between colloids (e.g., heteroaggregation, co-transport, and competitive blocking) need to be considered in natural soil; and (ii) non-DLVO interactions should be comprehensively considered when evaluating the environmental risk and fate of ENPs.

Transport of surface-modified multi-walled carbon nanotubes in saturated porous media.

Carbon nanotubes (CNTs) are widely used and may pose potential environmental risks to soil and groundwater systems. Therefore, it is important to improve current understanding of the fate and transport of CNTs in porous media. In this study, the transport behavior of multi-walled carbon nanotubes (MWCNTs) with different surface modifications were examined in water-saturated sand columns under different pH (5 and 7) and ionic strength (0.1, 1, and 5mM) conditions. COOH-MWCNTs have the strongest mobility among the five types of MWCNTs, followed by pristine MWCNTs. NH2-MWCNTs, Cu-MWCNTs, and Fe-MWCNTs have the weaker mobility. The transport of five types of MWCNTs decreased with the increase of ionic strength, while increased with the increase of pH value. The results suggested that the transport of MWCNTs can be affected by the electrostatic attraction between the functional groups on the surface of MWCNTs and quartz sand. Moreover, the pH and ionic strength of the solution also played an important role in enhancing the transport of MWCNTs, which have great significance for evaluating the transport and fate of MWCNTs in natural environment.

Non-monotonic contribution of nonionic surfactant on the retention of functionalized multi-walled carbon nanotubes in porous media

The concentration of nonionic surfactants like Triton X-100 (TX100) can influence the transport and fate of emerging contaminants (e.g., carbon nanotubes) in porous media, but limited research has previously addressed this issue. This study investigates the co-transport of functionalized multi-walled carbon nanotubes (MWCNTs) and various concentrations of TX100 in saturated quartz sand (QS). Batch experiments and molecular dynamics simulations were conducted to investigate the interactions between TX100 and MWCNTs. Results indicated that the concentration ratio of MWCNTs and TX100 strongly influences the dispersion of MWCNTs and interaction forces between MWCNTs and QS during the transport. Breakthrough curves of MWCNTs and TX100 and retention profiles of MWCNTs were determined and simulated in column studies. MWCNTs strongly enhanced the retention of TX100 in QS due to the high affinity of TX100 for MWCNTs. Conversely, the concentration of TX100 had a non-monotonic impact on MWCNT retention. The maximum transport of MWCNTs in the QS occurred at an input concentration of TX100 that was lower than the critical micelle concentration. This suggests that the relative importance of factors influencing MWCNTs changed with TX100 sorption. Results from interaction energy calculations and modeling of competitive blocking indicate that the predictive ability of interaction energy calculations and colloid filtration theory may be lost because TX100 mainly altered intermolecular forces between the MWCNT and porous media. This study provides new insights into the co-transport of surfactants and MWCNTs in porous media, which can be useful for environmental applications and risk management.

Co-transport of multi-walled carbon nanotubes and sodium dodecylbenzenesulfonate in chemically heterogeneous porous media

Multi-walled carbon nanotubes (MWCNTs) are increasing used in commercial applications and may be released into the environment with anionic surfactants, such as sodium dodecylbenzenesulfonate (SDBS), in sewer discharge. Little research has examined the transport, retention, and remobilization of MWCNTs in the presence or absence of SDBS in porous media with controlled chemical heterogeneity, and batch and column scale studies were therefore undertaken to address this gap in knowledge. The adsorption isotherms of SDBS on quartz sand (QS), goethite coated quartz sand (GQS), and MWCNTs were determined. Adsorption of SDBS (MWCNTs » GQS > QS) decreased zeta potentials for these materials, and produced a charge reversal for goethite. Transport of MWCNTs (5 mg L−1) dramatically decreased with an increase in the fraction of GQS from 0 to 0.1 in the absence of SDBS. Conversely, co-injection of SDBS (10 and 50 mg L−1) and MWCNTs radically increased the transport of MWCNTs when the GQS fraction was 0, 0.1, and 0.3, especially at a higher SDBS concentration, and altered the shape of retention profile. Mathematical modeling revealed that competitive blocking was not the dominant mechanism for the SDBS enhancement of MWCNT transport. Rather, SDBS sorption increased MWCNT transport by increasing electrostatic and/or steric interactions, or creating reversible interactions on rough surfaces. Sequential injection of pulses of MWCNTs and SDBS in sand (0.1 GQS fraction) indicated that SDBS could mobilize some of retained MWCNTs from the top to deeper sand layers, but only a small amount of released MWCNTs were recovered in the effluent. SDBS therefore had a much smaller influence on MWCNT transport in sequential injection than in co-injection, presumably because of a greater energy barrier to MWCNT release than retention. This research sheds novel insight on the roles of competitive blocking, chemical heterogeneity and nanoscale roughness, and injection sequence on MWCNT retention and release.

Plasmonic heating induced by Au nanoparticles for quasi-ballistic thermal transport in multi-walled carbon nanotubes.

The plasmon resonances of nanostructures enable wide applications from highly sensitive sensing to high-resolution imaging, through the improvement of photogeneration rate stimulated by the local field enhancement. However, quantitative experimental studies on the localized heating and the thermal transport process in the vicinity of plasmonics are still lacking because of the diffraction limit in conventional optothermal methodologies. In this work, we demonstrate an approach based on Raman thermometry to probe the near-field heating caused by plasmonics. An array of Au nanoparticles (AuNPs) fabricated by the template-assisted method is used to generate the near field effect. Multi-walled carbon nanotubes (MWCNTs) dispersed on the AuNPs are employed to quantify the near-field heating from their Raman peak shifts. Results show that the temperature rise in MWCNTs on AuNPs is much higher than that in a control group under the same laser irradiation. Further analysis indicates that the enhanced photon absorption of MWCNTs attributed to plasmon resonances is partially responsible for the different heating effect. The nonuniform thermal hot spots at the nanoscale can result in the quasi-ballistic thermal transport of phonons in MWCNTs, which is another reason for the temperature rise. Our results can be used to understand plasmonic heating effects as well as to explore quasi-ballistic thermal transport in carbon-based low-dimensional materials by tailoring the geometry or size of plasmonic nanostructures.

Environmental fate of multiwalled carbon nanotubes and graphene oxide across different aquatic ecosystems

The industrial use and widespread application of carbon-based nanomaterials have caused a rapid increase in their production over the last decades. However, toxicity of these materials is not fully known and is still being investigated for potential human and ecological health risks. Detecting carbon-based nanomaterials in the environment using current analytical methods is problematic, making environmental fate and transport modeling a practical way to estimate environmental concentrations and assess potential ecological risks. The Water Quality Analysis Simulation Program 8 (WASP8) is a dynamic, spatially resolved fate and transport model for simulating exposure concentrations in surface waters and sediments. Recently, WASP has been updated to incorporate processes for simulating the fate and transport of nanomaterials including heteroaggregation and phototransformation. This study examines the fate and transport of multiwalled carbon nanotubes (MWCNT), graphene oxide (GO) and reduced graphene oxide (rGO) in four aquatic ecosystems in the southeastern United States. Sites include a seepage lake, a coastal plains river, a piedmont river and an unstratified, wetland lake. A hypothetical 50-year release is simulated for each site-nanomaterial pair to analyze nanomaterial distribution between the water column and sediments. For all nanomaterials, 99% of the mass loaded moves though systems of high and low residence times without being heteroaggregated and deposited in the sediments. However, significant accumulation in the sediments does occur over longer periods of time. Results show that GO and rGO had the highest mass fraction in the water column of all four sites. MWCNT were found predominantly in the sediments of the piedmont river and seepage lake but were almost entirely contained in the water column of the coastal plains river and wetland lake. Simulated recovery periods following the release estimate 37+ years for lakes and 1–4 years for rivers to reduce sediment nanomaterial concentrations by 50% suggesting that carbon-based nanomaterials have the potential for long-term ecological effects.

Transport of multi-walled carbon nanotubes stabilized by carboxymethyl cellulose and starch in saturated porous media: Influences of electrolyte, clay and humic acid

This study investigated the transport behaviors of carboxymethyl cellulose (CMC) and starch stabilized multi-walled carbon nanotubes (MWNTs) through a saturated quartz sand column in the presence of electrolytes, model clays, and natural organic matter (humic acid) through column breakthrough experiments and model simulations. Both stabilizers, CMC and starch, greatly enhanced the breakthrough of MWNTs, with a full breakthrough plateau (C/C0) ranging from 0.69 to 0.90 at ionic strength from 0.3 to 10mM. Between the two stabilizers, CMC was more effective in resisting particle deposition, and thus CMC-stabilized MWNTs were more transportable through the medium. While non-stabilized MWNTs were much less transportable and were vulnerable to electrolyte effects (especially Ca2+), the stabilized counterparts were much more resistant to the coagulation effects of electrolytes. The presence of colloidal clay particles showed contrasting effects on the transport of bare and stabilized MWNTs. The full breakthrough C/C0 of bare MWNTs was suppressed by kaolinite and montmorillonite particles from 0.33 to <0.15 with 5mg/L clay, indicating that the presence of both clays enhanced the aggregation and deposition of MWNTs. However, kaolinite particles facilitated the transport of stabilized-MWNTs, while montmorillonite weakened the breakthrough of stabilized MWNTs. Humic acid had less effect on the mobility of stabilized-MWNTs than that of bare MWNTs. The advection-dispersion transport model incorporated with the filtration theory was able to simulate the breakthrough curves and quantitatively interpret the particle deposition. The results can facilitate our understanding of fate and transport of stabilized carbon nanotubes in the environment.

Thermal Transport in Multi-Walled Carbon Nanotubes

Studies on heat conduction in nano-dimensional structures have raised numerous interests not only because of geometry dependent thermal transport but also apparently controllable heat dissipation in confined regions including the role of defects and impurity atoms. On reducing the structural size from bulk-to-nanoscale dimension, there will be significant alteration of specific heat capacity. So, thermal conductivity goes different in different temperature regimes approaching to a maximal value at 300 K for carbon nanotubes (CNTs). It may be noted that, unlike electronic contribution to the specific heat capacity, the lattice contribution in a 1D system varies as ~T (as compared to ~T3 trend for a 3D system). Though theoretically and practically thermal conductivity measurements have been carried out for SWCNT but no such theoretical works have been performed for double and triple wall carbon nanotube. We first established the theoretical calculation of thermal conductivity of DWCNT and TWCNT which matches with the experimental observations. The novelty of our work lies with the fact that we first found that as the no of walls increase in CNT from single to double to triple, thermal conductivity values decreases due to van der Waals interaction between the atoms of different walls. We see that thermal conductivity of single-wall CNT is very high (~3500 WmK-1), but it gets reduced to ~700 WmK-1 for a double-wall CNT. This drop is ascribed to incoherent heat dissipation owing significantly to the van der Waals interaction among the atoms of different co-axial walls

Roles of cation valance and exchange on the retention and colloid-facilitated transport of functionalized multi-walled carbon nanotubes in a natural soil

Saturated soil column experiments were conducted to investigate the transport, retention, and release behavior of a low concentration (1 mg L−1) of functionalized 14C-labeled multi-walled carbon nanotubes (MWCNTs) in a natural soil under various solution chemistries. Breakthrough curves (BTCs) for MWCNTS exhibited greater amounts of retardation and retention with increasing solution ionic strength (IS) or in the presence of Ca2+ in comparison to K+, and retention profiles (RPs) for MWCNTs were hyper-exponential in shape. These BTCs and RPs were well described using the advection-dispersion equation with a term for time- and depth-dependent retention. Fitted values of the retention rate coefficient and the maximum retained concentration of MWCNTs were higher with increasing IS and in the presence of Ca2+ in comparison to K+. Significant amounts of MWCNT and soil colloid release was observed with a reduction of IS due to expansion of the electrical double layer, especially following cation exchange (when K+ displaced Ca2+) that reduced the zeta potential of MWCNTs and the soil. Analysis of MWCNT concentrations in different soil size fractions revealed that >23.6% of the retained MWCNT mass was associated with water-dispersible colloids (WDCs), even though this fraction was only a minor portion of the total soil mass (2.38%). More MWCNTs were retained on the WDC fraction in the presence of Ca2+ than K+. These findings indicated that some of the released MWCNTs by IS reduction and cation exchange were associated with the released clay fraction, and suggests the potential for facilitated transport of MWCNT by WDCs.

Deposition and mobilization of functionalized multiwall carbon nanotubes in saturated porous media: effect of grain size, flow velocity and solution chemistry

Carbon nanotubes (CNTs) are widely manufactured nanoparticles which are utilized in a number of consumer products, such as sporting goods, electronics and biomedical applications. Due to their accelerating production and use, CNTs constitute a potential environmental risk if they are released to soil and groundwater systems. It is, therefore, essential to improve the current understanding of environmental fate and transport of CNTs. The current study systematically investigated the effect of solution chemistry (pH and ionic strength) and physical conditions (collector grain size and flow rate) on the deposition and mobilization of functionalized multiwall carbon nanotubes (MWCNTs) using a series of column experiments under fully saturated conditions. A one-dimensional convection–dispersion model including collector efficiency for cylindrical nanoparticles was used to simulate the transport of MWCNTs in porous media. It was observed that an increase in pH resulted in increased mobility of MWCNTs. However, the transport of MWCNTs was strongly dependent on ionic strength of the background solution and a critical deposition concentration was observed between 3 and 4 mM NaCl concentration, with more than 99 % filtration of MWCNTs at 4 mM. The finer sand grains were able to filter a significant amount of MWCNTs (15 % more than coarse sand) from the inflow solution; this was likely caused by grain-to-grain straining mechanisms in the finer sand. A decrease in pore water velocity also led to more deposition of MWCNTs due to lowering of the kinetic energy of the particles. The results from this study indicated that a weak secondary minimum existed under unfavorable conditions for deposition, but the particles were trapped at both primary and secondary minimum.

Effect of primary particle size on colloidal stability of multiwall carbon nanotubes

Multiwall carbon nanotubes (MWCNTs) are one type of nanoparticles that have various special properties and potential applications. Due to their increasing production and potential toxicological effects, the environmental behavior and transport of MWCNTs have become important research topics. Particle size is one of the important properties of nanoparticles, yet its effects on MWCNT environmental behaviors have not been fully investigated. In this study, we tested how the length of MWCNTs influenced their settling in the presence of Na(+) and/or natural organic matter (NOM), and postulated the governing mechanisms. The results showed that when adding Na(+) the shorter MWCNTs exhibited preferential aggregation and settling. One possible reason could be that shorter MWCNTs possess larger specific surface area and consequently stronger attraction forces. However, NOM strongly mitigated such aggregation, and helps to disperse MWCNTs regardless of their length and aqueous conditions.

The effects of surfactants and solution chemistry on the transport of multiwalled carbon nanotubes in quartz sand-packed columns

The effect of different surfactants on the transport of multiwalled carbon nanotubes (MWCNTs) in quartz sand-packed columns was firstly investigated under various conditions. The stable plateau values (Cmax) of the breakthrough curves (BTCs), critical PVs (the number of pore volumes of infusions needed to reach the Cmax), maximum transport distances (Lmax), deposition rate coefficients (kd) and retention rates were calculated to compare the transport and retention of MWCNTs under various conditions. Stability of the MWCNT suspensions as a function of the influencing factors was examined to reveal the underlying mechanism of the MWCNT retention. Results showed that MWCNTs suspended by different surfactants presented different BTCs; the MWCNT transport increased with increasing sand size and MWCNT concentration; high flow velocity was favorable for the MWCNT transport, while high Ca2+ concentration and low pH were unfavorable for the transport; hetero-aggregation, straining and site blocking occurred during the transport.

Limited transport of functionalized multi-walled carbon nanotubes in two natural soils

Column experiments were conducted in undisturbed and in repacked soil columns at water contents close to saturation (85–96%) to investigate the transport and retention of functionalized 14C-labeled multi-walled carbon nanotubes (MWCNT) in two natural soils. Additionally, a field lysimeter experiment was performed to provide long-term information at a larger scale. In all experiments, no breakthrough of MWCNTs was detectable and more than 85% of the applied radioactivity was recovered in the soil profiles. The retention profiles exhibited a hyper-exponential shape with greater retention near the column or lysimeter inlet and were successfully simulated using a numerical model that accounted for depth-dependent retention. In conclusion, results indicated that the soils acted as a strong sink for MWCNTs. Little transport of MWCNTs is therefore likely to occur in the vadose zone, and this implies limited potential for groundwater contamination in the investigated soils.

Giant Enhancement and Anomalous Thermal Hysteresis of Saturation Moment in Magnetic Nanoparticles Embedded in Multiwalled Carbon Nanotubes

We report high-energy synchrotron X-ray diffraction spectrum and high-temperature magnetic data for multiwalled carbon nanotubes (MWCNTs) embedded with Fe and Fe3O4 nanoparticles. We unambiguously show that the saturation moments of the embedded Fe and Fe3O4 nanoparticles are enhanced by a factor of about 3.0 compared with what would be expected if they would be unembedded. More intriguingly the enhanced moments were completely lost when the sample was heated up to 1120 K, and the lost moments were completely recovered through two more thermal cycles below 1020 K. These novel results cannot be explained by the magnetism of the Fe and Fe3O4 impurity phases, the magnetic proximity effect between magnetic nanoparticles and carbon, and the ballistic transport of MWCNTs.

Extrapulmonary transport of MWCNT following inhalation exposure

BackgroundInhalation exposure studies of mice were conducted to determine if multi-walled carbon nanotubes (MWCNT) distribute to the tracheobronchial lymphatics, parietal pleura, respiratory musculature and/or extrapulmonary organs. Male C57BL/6 J mice were exposed in a whole-body inhalation system to a 5 mg/m3 MWCNT aerosol for 5 hours/day for 12 days (4 times/week for 3 weeks, lung burden 28.1 ug/lung). At 1 day and 336 days after the 12 day exposure period, mice were anesthetized and lungs, lymph nodes and extrapulmonary tissues were preserved by whole body vascular perfusion of paraformaldehyde while the lungs were inflated with air. Separate, clean-air control groups were studied at 1 day and 336 days post-exposure. Sirius Red stained sections from lung, tracheobronchial lymph nodes, diaphragm, chest wall, heart, brain, kidney and liver were analyzed. Enhanced darkfield microscopy and morphometric methods were used to detect and count MWCNT in tissue sections. Counts in tissue sections were expressed as number of MWCNT per g of tissue and as a percentage of total lung burden (Mean ± S.E., N = 8 mice per group). MWCNT burden in tracheobronchial lymph nodes was determined separately based on the volume density in the lymph nodes relative to the volume density in the lungs. Field emission scanning electron microscopy (FESEM) was used to examine MWCNT structure in the various tissues.ResultsTracheobronchial lymph nodes were found to contain 1.08 and 7.34 percent of the lung burden at 1 day and 336 days post-exposure, respectively. Although agglomerates account for approximately 54% of lung burden, only singlet MWCNT were observed in the diaphragm, chest wall, liver, kidney, heart and brain. At one day post exposure, the average length of singlet MWCNT in liver and kidney, was comparable to that of singlet MWCNT in the lungs 8.2 ± 0.3 versus 7.5 ± 0.4 um, respectively. On average, there were 15,371 and 109,885 fibers per gram in liver, kidney, heart and brain at 1 day and 336 days post-exposure, respectively. The burden of singlet MWCNT in the lymph nodes, diaphragm, chest wall and extrapulmonary organs at 336 days post-exposure was significantly higher than at 1 day post-exposure.ConclusionsInhaled MWCNT, which deposit in the lungs, are transported to the parietal pleura, the respiratory musculature, liver, kidney, heart and brain in a singlet form and accumulate with time following exposure. The tracheobronchial lymph nodes contain high levels of MWCNT following exposure and further accumulate over nearly a year to levels that are a significant fraction of the lung burden 1 day post-exposure.

Transport and retention of multi-walled carbon nanotubes in saturated porous media: Effects of input concentration and grain size

Water-saturated column experiments were conducted to investigate the effect of input concentration (Co) and sand grain size on the transport and retention of low concentrations (1, 0.01, and 0.005 mg L−1) of functionalized 14C-labeled multi-walled carbon nanotubes (MWCNT) under repulsive electrostatic conditions that were unfavorable for attachment. The breakthrough curves (BTCs) for MWCNT typically did not reach a plateau, but had an asymmetric shape that slowly increased during breakthrough. The retention profiles (RPs) were not exponential with distance, but rather exhibited a hyper-exponential shape with greater retention near the column inlet. The collected BTCs and RPs were simulated using a numerical model that accounted for both time- and depth-dependent blocking functions on the retention coefficient. For a given Co, the depth-dependent retention coefficient and the maximum solid phase concentration of MWCNT were both found to increase with decreasing grain size. These trends reflect greater MWCNT retention rates and a greater number of retention locations in the finer textured sand. The fraction of the injected MWCNT mass that was recovered in the effluent increased and the RPs became less hyper-exponential in shape with higher Co due to enhanced blocking/filling of retention locations. This concentration dependency of MWCNT transport increased with smaller grain size because of the effect of pore structure and MWCNT shape on MWCNT retention. In particular, MWCNT have a high aspect ratio and we hypothesize that solid phase MWCNT may create a porous network with enhanced ability to retain particles in smaller grain sized sand, especially at higher Co. Results demonstrate that model simulations of MWCNT transport and fate need to accurately account for observed behavior of both BTCs and RPs.

Impact of Porous Media Grain Size on the Transport of Multi-walled Carbon Nanotubes

Nanoparticles possess unique physical, electrical, and chemical properties which make them attractive for use in a wide range of consumer products. Through their manufacturing, usage, and eventual disposal, nanoparticles are expected to ultimately be released to the environment after which point they may pose environmental and human health risks. One critical component of understanding and modeling those potential risks is their transport in the subsurface environment. This study investigates the mobility of one important nanoparticle (multi-walled carbon nanotubes or MWCNTs) through porous media, and makes the first measurements on the impact of mean collector grain size (d(50)) on MWCNT retention. Results from one-dimensional column experiments conducted under various physical and chemical conditions coupled with results of numerical modeling assessed the suitability of traditional transport models to predict MWCNT mobility. Findings suggest that a dual deposition model coupled with site blocking greatly improves model fits compared to traditional colloid filtration theory. Of particular note is that the MWCNTs traveled through porous media ranging in size from fine sand to silt resulting in normalized concentrations of MWCNTs in the effluent in excess of 60% of the influent concentration.

Probing the inter-tube transport in aligned and random multiwall carbon nanotubes

The temperature and magnetic field dependence of conductivity has been used to probe the inter-tube transport in multiwall carbon nanotubes (MWNTs). The scanning electron microscopy images show highly aligned and random distribution of MWNTs. The conductivity in aligned carbon nanotube (ACNT) and random carbon nanotube (RCNT) samples at low temperature follows T1/2 (at T &amp;lt; 8 K) and T3/4 (at T &amp;gt; 8 K) dependence in accordance with the weak localization and electron-electron (e-e) interaction model. The values of diffusion coefficient in ACNT and RCNT are 0.25 × 10−2 and 0.71 × 10−2 cm2 s−1, respectively, indicating that larger number of inter-tube junctions in later enhances the bulk transport. The positive magnetoconductance (MC) data in both samples show that the weak localization contribution is dominant. However, the saturation of MC at higher fields and lower temperatures indicate that e-e interaction is quite significant in RCNT. The T−3/4 and T−1/2 dependence of inelastic scattering length (lin) in ACNT and RCNT samples show that the inelastic e-e scattering is more important in aligned tubes.

Morphology and Dopant Influence Electrical Properties and Stability of Multiwalled Carbon Nanotube-Polyaniline Composites

In situ chemical polymerization is used to prepare composites of multiwalled carbon nanotubes (MWCNTs) that are either wrapped with polyaniline (PANI) (MWP), or with perpendicular aligned PANI (MAP). Systematic study of morphology, composition, structure, thermal stability, and electrical properties is performed as a function of temperature to understand the composite formation. Orientation of PANI chains and the direction of electron transport in MWCNTs and PANI play an important role in conductivity. At room temperature (RT), MWP, wherein PANI and MWCNTs are aligned parallel, exhibits high conductivity, which decreases gradually above RT. Contrary in MAP, the conductivity at RT is lower because of the perpendicular alignment of PANI on the MWCNTs. However, it increases with the increase in temperature, as short chains of PANI switchover and get adsorbed onto the MWCNTs forming a near parallel orientation, in which, aromatic amines of PANI graft to the MWCNTs. Eventually, morphology becomes a dominating factor which influences the conductivity and thermoelectric properties of the composites, above 150 °C. The results show that the morphology, interfacial contact, and the dopant concentration are the key factors in governing the conductivity of MWP and MAP composites at RT and above. These observations are supported by X-ray diffraction, X-ray photoelectron spectroscopy, and time of flight-secondary ionization mass spectrometry study. Keywords: Multiwalled carbon nanotube/polyaniline composites, PANI structures, thermal analysis, electron microscopy, characterization, electrical properties

Mobility of Multiwalled Carbon Nanotubes in Porous Media

Engineered multiwalled carbon nanotubes (MWCNTs) are the subject of intense research and are expected to gain widespread usage in a broad variety of commercial products. However, concerns have been raised regarding potential environmental and human health risks. The mobility of MWCNTs in porous media is examined in this study using one-dimensional flow-through column experiments under conditions representative of subsurface and drinking water treatment systems. Results demonstrate that pore water velocity strongly influenced MWCNT transport, with high MWCNT mobility at pore water velocities greater than 4.0 m/d. A numerical simulator, which incorporated a newly developed theoretical collector efficiency relationship for MWCNTs in spherical porous media, was developed to model observed column results. The model, which incorporated traditional colloid filtration theory in conjunction with a site-blocking term, yielded good agreement with observed results in quartz sand-packed column experiments. Experiments were also conducted in glass bead-packed columns with the same mean grain size as the quartz sand-packed columns. MWCNTs were more mobile in the glass bead-packed columns.