Aqueous Suspensions Of Carbon Nanotubes Research Articles

Surfactant Control of Coffee Ring Formation in Carbon Nanotube Suspensions.

The coffee ring effect regularly occurs during the evaporation of colloidal droplets and is often undesirable. Here we show that adding a specific concentration of a surfactant can mitigate this effect. We have conducted experiments on aqueous suspensions of carbon nanotubes that were prepared with cationic surfactant dodecyltrimethylammonium bromide added at 0.2, 0.5, 1, 2, 5, and 10 times the critical micelle concentration. Colloidal droplets were deposited on candidate substrates for printed electronics with varying wetting characteristics: glass, polyethylene terephthalate, fluoroethylene propylene copolymer, and polydimethylsiloxane. Following drying, four pattern types were observed in the final deposits: dot-like, uniform, coffee ring deposits, and combined patterns (coffee ring with a dot-like central deposit). Evaporation occurred predominantly in constant contact radius mode for most pattern types, except for some cases that led to uniform deposits in which early stage receding of the contact line occurred. Image analysis and profilometry yielded deposit thicknesses, allowing us to identify a coffee ring subfeature in all uniform deposits and to infer the percentage coverage in all cases. Importantly, a critical surfactant concentration was identified for the generation of highly uniform deposits across all substrates. This concentration resulted in visually uniform deposits consisting of a coffee ring subfeature with a densely packed center, generated from two distinct evaporative phases.

Solar-Thermal Conversion Characteristics of Surfactant-Free Gold Nanoparticles Produced By Plasma-Based Synthesis Method

Gold nanoparticles (Au NPs), with their unique plasmonic absorption in the visible spectrum, are promising candidates for the use as nanofluids for enhancing the solar-thermal conversion (STC) process in direct-absorption solar collectors (DASCs) [1-4]. Their absorption performance mainly depends on their size and morphology [5] controlled by the synthesis technique used [4], such as the widely-used wet chemistry-based methods. These chemical methods rely on the use of surfactants for controlling the nanoparticles size and shape, as well as achieving stability within the hosting fluid. However, utilizing chemical additives results in undesired by-products, which require washing, purification and recycling processes and also they eliminate the possibility of further functionalization of the produced Au NPs [6, 7]. Besides, surfactants increase the thermal resistance between the nanoparticle and the hosting fluid [8] and could also decompose and degrade over time, at operating temperatures as low as 70 °C [9].In the present work, the optical properties and STC characteristics of three types of Au NPs produced by different synthesis methods were experimentally investigated. The first type was produced using a plasma-induced non-equilibrium electrochemistry system, to form surfactant-free nanoparticles (sf-Au NPs). The second type was synthesized using Turkevich method to form PEGylated nanoparticles (p-Au NPs), while the third type is citrate-capped nanoparticles (c-Au NPs), supplied by Sigma. After washing and drying the Au NPs powder of each type, they were separately re-dispersed in ethylene glycol (EG) as a base fluid to give Au NPs concentration of 39.4 mg/L forming nanofluids of sf-Au NPs/EG, p-Au NPs/EG and c-Au NPs/EG.XPS results of the untreated and treated gold precursors, used for the synthesis process, showed that no gold ions were found in the treated sample, indicating the full reduction of the gold precursors. In addition, TEM images showed that all samples have the same average nanoparticle size of ~32 nm. However, the size and morphology of sf-Au NPs showed a broad range of sizes and shapes, while the other two samples have nanoparticles of fine spherical shapes and narrow size distribution. Furthermore, the optical properties results for a wavelength range of 280-900 nm, using UV-VIS spectroscopy, showed sf-Au NPs/EG nanofluid exhibited a broad plasmonic absorption peak over the visible spectrum, while the other two nanofluids have similar narrow peaks. Moreover, measurements from Zetasizer Nano ZS system showed that sf-Au NPs have a zeta potential of -25.8 mv, while the p-Au NPs and c-Au NPs have slightly higher values of -35.6 mV and -38.6 mV, respectively, which could be considered as good stabilization.A lab-scale DASC was built for investigating the STC performance of each nanofluid, under a uniform radiation intensity of ∼1000 W/m2 for 25 min, during which the nanofluids temperature change was recorded. Results revealed that sf-Au NPs/EG nanofluid achieved the highest solar-thermal conversion efficiency and specific absorption rate, compared to the other two surfactant-based Au NPs/EG nanofluids. The STC efficiency was enhanced to above 80%, compared to the efficiency of the base fluid, while 50-60% enhancement was reached by the surfactant-based nanofluids, highlighting the advantages of using plasm-liquid treatment method for the synthesis of sf-Au NPs for the use as nanofluids for solar energy harvesting in DASCs. References Zeiny, A., Jin, H., Bai, L., Lin, G. & Wen, D. 2018. A comparative study of direct absorption nanofluids for solar thermal applications. Solar Energy, 161, 74-82.Willets, K. A. & Van Duyne, R. P. 2007. Localized surface plasmon resonance spectroscopy and sensing. Rev. Phys. Chem., 58, 267-297.Lv, W. 2012. Plasmonic Nanoparticles and Their Suspensions for Solar Energy Conversion, Arizona State University.Xiong, Y., Long, R., Liu, D., Zhong, X., Wang, C., Li, Z.-Y. & Xie, Y. 2012. Solar energy conversion with tunable plasmonic nanostructures for thermoelectric devices. Nanoscale, 4, 4416-4420.Kamat, P. V., Flumiani, M. & Hartland, G. V. J. T. J. O. P. C. B. 1998. Picosecond dynamics of silver nanoclusters. Photoejection of electrons and fragmentation. 102, 3123-3128.Sakai, T., Enomoto, H., Torigoe, K., Sakai, H. & Abe, M. 2009. Surfactant-and reducer-free synthesis of gold nanoparticles in aqueous solutions. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 347, 18-26.Mariotti, D., Patel, J., Švrček, V. & Maguire, P. 2012. Plasma–liquid interactions at atmospheric pressure for nanomaterials synthesis and surface engineering. Plasma Processes and Polymers, 9, 1074-1085.Yu, W. & Xie, H. 2012. A review on nanofluids: preparation, stability mechanisms, and applications. Journal of nanomaterials, 2012, Wen, D. & Ding, Y. 2004. Effective thermal conductivity of aqueous suspensions of carbon nanotubes (carbon nanotube nanofluids). Journal of Thermophysics and Heat Transfer, 18, 481-485. Figure 1

Environmentally Induced Changes of Commercial Carbon Nanotubes in Aqueous Suspensions. Adaptive Behavior of Bacteria in Biofilms

The effects of environmental factors such as sunlight irradiation and the presence of humic acid (HA) on the physicochemical properties of commercial multiwall carbon nanotubes (MWCNT) suspended in a simulated inorganic matrix (SIM) and their impacts on bacteria growing in biofilms were evaluated. Both solar irradiation and the presence of HA lead to the dissolution of adsorbed metals on the MWCNT, which are residues of synthesis catalysts. Also, preferential adsorption of certain HA components on the MWCNT induces important modifications in the aliphatic/aromatic relationship of HA components in solution and the generation and release of new moieties. Results demonstrated that the variation of such physicochemical parameters strongly affects the interactions of MWCNT with Pseudomonas aeruginosa sessile bacteria. Thus, the number of attached bacteria increased, and stress responses such as decrease in bacterial size were found in the presence of sunlight-irradiated MWCNT with a particular distribution of extracellular polymeric substances (EPS) strands. A shielding effect was observed when HA was added. It was concluded that physicochemical alterations caused by environmental conditions (with/without irradiation, presence/absence of HA) on MWCNT-containing SIM trigger distinctive adaptive behavior of bacteria in biofilms. This information must be taken into account in the development of biologically assisted treatments for organic metal co-contamination of MWCNT-containing media since MWCNT discharge alters the physicochemical properties and composition of the aqueous environment and the response of the biofilms that interact with it.

Физико-химический анализ структуры и свойств нанокомпозитов полимер/углеродные нанотрубки, полученных из раствора

The structural (fractal) model, applied earlier for polymer solutions, was used for description of viscosity of aqueous suspensions of carbon nanotubes. The indicated model treates adequately the dependence of suspension viscosity on concentration of carbon nanotubes. At reaching of percolation theshold of this nanofiller a sharp growth of viscosity of aqueous suspensions is observed. The model reflects adequately also the dependence of viscosity on geometry of carbon nanotubes. A knowledge of nanofiller structure, characterizing by its fractal dimension, allows to predict reinforcement degree of solid-state polymer nanocomposites.

INCORPORATION OF MULTI-WALLED CARBON NANOTUBES INTO OXIDE LAYER FORMED ON AL ALLOY BY PLASMA ELECTROLYTIC OXIDATION

Plasma electrolytic oxidation (PEO) is an electrochemical-based surface modification technique that produces oxide layers on valve metals. The PEO process is performed in an electrolyte solution, which offers the possibility of particles’ incorporation into the growing oxide layer. In this study, we employed a PEO technique on a commercial Al alloy in an aqueous suspension of carbon nanotubes (CNTs) to fabricate CNT-incorporated oxide layer. The voltage–time response was recorded during the process. The surface of the resulting oxide layer was characterized by means of a scanning electron microscope (SEM), an energy-dispersive X-ray spectrometer (EDS), and X-ray diffraction (XRD). It was found from the SEM observation that the CNTs were successfully incorporated into the oxide layer. The PEO with the addition of CNTs led to a delay in time to breakdown (50[Formula: see text][Formula: see text][Formula: see text]s) and a decrease in breakdown voltage (442[Formula: see text][Formula: see text][Formula: see text]V) in the voltage–time curve. The microstructural feature was clearly distinguishable between the oxide layers produced with and without CNTs: a pancake-like structure for PEO without CNTs, and a doughnut-like structure for PEO with CNTs. However, neither the results of the structure analysis nor the elemental analysis provides a clear indication of carbon, even though the presence of CNTs in the oxide layer is evident, suggesting that further optimization of CNT concentration is required.

In English

This review analyses the authors’ recent and related works on electrokinetic properties and colloidal stability of aqueous suspension of multiwalled carbon nanotubes (CNTs) in the presence of surfactants and nanoparticles. Selected adsorptive properties of carbon nanotubes are also considered. The applicability of classical theories of electrophoresis for description of electrophoretic mobility of carbon nanotubes is discussed. Examples on the ζ-potential of CNTs in aqueous suspensions as a function of pH and concentration of electrolytes (KCl, CaCl 2 and AlCl 3 ) are given. Additions of cetyltrimethylammonium bromide (CTAB) cationic surfactant below the critical micelle formation concentration (CMC) values give a reduction and then an overcharging the CNT surface because of accumulation of the surfactant ions in the Stern layer. At concentrations above CMC the substantial drop in ζ is observed. It is due to the shift of the shear plane toward solution as a result of formation of hemi-micelles on the surface. An increase in the mass ratio of artificial mineral Laponite (Lap) in suspension (X) from 0 to 0.4 results in a monotonic decrease of the ζ-potential of CNT + Lap hybrids with reaching its plateau value ≈ –32 mV at X ≥ 0.4 that corresponds to the ζ of “pure” Lap platelets. This evidences the high surface coverage of nanotubes surface with Lap at X ≥ 0.4. The major methods to improve the dispersibility of carbon nanotubes, their colloidal stability and adsorptive properties are briefly discussed, namely: stabilization in mixtures of water and organic solvents; functionalization by chemical treatment; stabilization by additives of surfactants or polymers and hybridization by addition of supplementary stabilizing nanoparticles. CNTs can be significantly debundled in “good” solvents, such as 1-cyclohexyl-2-pyrrolidone, N,N-dimethylformamide, or N-methyl-2-pyrrolidone. It is demonstrated that the dispersibility of CNTs is a complex function of the type of surfactant, its concentration and the surfactant/CNTs ratio. The optimum concentration of CTAB to achieve homogeneous aqueous dispersion of carbon nanotubes was identified to be near the CMC. Additions of CTAB significantly modify the size distribution of CNTs and a sharp transition from small primary aggregates to large secondary aggregates at concentrations above CMC is observed. At optimal concentration of Lap the nanotube particles get well stabilized, and a stepwise increase of sedimentation stability is observed. We have shown also that CNT + Lap hybrids can be effectively used for removal of methylene blue dye from aqueous systems. The kinetics and mechanisms of adsorption are elucidated.

Entropy Generation and Heat Transfer Analysis in MHD Unsteady Rotating Flow for Aqueous Suspensions of Carbon Nanotubes with Nonlinear Thermal Radiation and Viscous Dissipation Effect.

The impact of nonlinear thermal radiations rotating with the augmentation of heat transfer flow of time-dependent single-walled carbon nanotubes is investigated. Nanofluid flow is induced by a shrinking sheet within the rotating system. The impact of viscous dissipation is taken into account. Nanofluid flow is assumed to be electrically conducting. Similarity transformations are applied to transform PDEs (partial differential equations) into ODEs (ordinary differential equations). Transformed equations are solved by the homotopy analysis method (HAM). The radiative source term is involved in the energy equation. For entropy generation, the second law of thermodynamics is applied. The Bejan number represents the current investigation of non-dimensional entropy generation due to heat transfer and fluid friction. The results obtained indicate that the thickness of the boundary layer decreases for greater values of the rotation parameter. Moreover, the unsteadiness parameter decreases the temperature profile and increases the velocity field. Skin friction and the Nusselt number are also physically and numerically analyzed.

Impact of surfactant and clay platelets on electrokinetic potential and size distribution in carbon nanotubes aqueous suspensions

Stabilization of aqueous suspensions of carbon nanotubes (CNTs) is an acute task for a number of technological processes. The effects of cationic surfactant (cetyltrimethyl-ammonium bromide, CTAB) and clay platelets (Laponite RD® (Lap)) on the electrokinetic potential and aggregation stability/size distribution of CNTs have been studied. The studies were performed at constant pH (4.5 ± 0.1), and at different values of the added amount of the reagent, mass ratio between Lap/CNTs, aging time as well as duration of the suspension ultrasonic treatment. In a CTAB concentration interval of Cs = 3.64.10−5 − 1.82.10-2 wt.% a narrow monomodal size distribution was found. The median size of aggregates was 21–24 μm that is two times larger than the length of individual CNTs (5–10 μm). At higher CTAB concentrations (above critical micelle concentrations (CMC)), formation of aggregates with median size of 140–150 μm takes place, with preserving the monomodal size distribution. Aggregation of CNTs in this case probably occurs by deposition of individual CNT on the surface of primary aggregates. Addition of Lap platelets in the range from X = 0 to 0.4 (where X is the mass ratio of Lap/CNTs) causes a monotonic decrease of the ζ-potential of the CNTs from −40 mV to −30 mV with reaching its plateau value at X = 0.4–1.0. This evidences the high surface coverage of CNTs by Lap platelets at which the CNT + Lap complex acquires the ζ-potential value of Lap. In mixed CNT + Lap suspensions (X = 1.0), a bimodal particle size distribution was registered, with appearance of big aggregates (≈150–300 μm), both in dilute (Cs = 3.64.10−5 – 3.64.10-3 wt.%) and concentrated (Cs > CsCMC) solutions. These big hybrid CNT + Lap aggregates were loose, rather unstable, and they could be easily destroyed by ultrasonic treatment.

Novel star-like surfactant as dispersant for multi-walled carbon nanotubes in aqueous suspensions at high concentration

A kind of novel surfactant with star-like molecular structure and terminated sulfonate was synthesized, and it was used as the dispersant for multi-walled carbon nanotubes (CNTs) in aqueous suspensions compared with a traditional single-chained surfactant. The star-like surfactant showed good dispersing ability for multi-walled CNTs in aqueous suspensions. Surface tension analysis, total organic carbon analysis, X-ray photoelectron spectroscopy, zeta potential, dynamic light scattering and transmission electron microscopy were performed to research the effect of star-like surfactant on the dispersion of multi-walled CNTs in aqueous suspensions. With the assistance of star-like surfactant, the CNTs could disperse well in aqueous suspension at high concentration of 50g/L for more than 30days, while the CNTs precipitated completely in aqueous suspension after 1day without any dispersant or after 10days with sodium 4-dodecylbenzenesulfonic acid as dispersant.

Increasing the Strength of Single Filaments and Yarns of a Paraaramid Fiber by Their Processing with an Aqueous Suspension of Carbon Nanoparticles

The paper presents the results of increasing the strength and modulus of single filaments and yarns of a paraaramid fiber by their processing with an aqueous suspension of carbon nanotubes in the production process

Application of carbon nanotubes to immobilize heavy metals in contaminated soils

The contamination of soils with heavy metals is a growing concern in modern societies. To avoid the spread of contamination, soil stabilization techniques can be applied mixing materials with the soil in order to partially immobilize heavy metals. Carbon nanotubes (CNTs) are nanomaterials known for its exceptional properties, like high surface area and adsorption capacity. Due to these unique properties, the potential use of CNTs in heavy metal contaminated water has been studied, with very satisfactory results; however, their application in contaminated soils is practically unexplored. This experimental work is focused on studying the potential of using CNTs in soil remediation, especially to immobilize the heavy metals ions: lead (Pb2+), copper (Cu2+), nickel (Ni2+), and zinc (Zn2+), commonly present in contaminated soils. In order to avoid CNT agglomeration, which originates the loss of their beneficial properties, an aqueous suspension of CNTs was prepared using a non-ionic surfactant combined with ultrasonic energy to promote CNTs dispersion. Then, the soil, with and without the addition of CNTs, was subjected to adsorption tests to evaluate the CNT capacity to improve heavy metal immobilization. To validate the adsorption test results, permeability tests were executed, simulating the conditions of a real-case scenario. The results obtained led to the conclusion that the addition of a small amount of dispersed CNTs can successfully increase the adsorption capacity of the soil and consequently improve the immobilization of heavy metals in the soil matrix. The immobilization percentage varies with the different heavy metals under study.

Combined effect of cetyltrimethylammonium bromide and laponite platelets on colloidal stability of carbon nanotubes in aqueous suspensions

The combined effect of cationic surfactant (cetyltrimethylammonium bromide, CTAB) and laponite platelets (laponite RD) on the stability of aqueous suspension of carbon nanotubes (NTs) has been investigated. The experimental methods include measurements of electrokinetic potential, radius of particles and aggregation stability. In individual suspensions the concentration of NTs was Cn=0.003% and concentration of laponite was Cl=0.5% and 2%. In hybrid NT+laponite suspensions the concentration of NTs was Cn=0.003% and 0.01% and the laponite/NT mass ratio, X=ml/mn, was varied within the range of X=0–1. For individual NTs and laponite species the increase of the CTAB concentration, Cs, changed the electrokinetic potential from negative to positive. However, the different effects of CTAB on stability of this species were observed: addition of CTAB stabilized the individual NTs and enhanced aggregation of laponite. The CTAB-induced overcharging was also typical for hybrid NT+laponite suspensions. Surprisingly, the minimum of a position of an isoelectric point Cs(IEP) (≈3·10−6M) at X≈0.1–0.3 was observed. This behavior can reflect the impact of CTAB on adhesion interactions between NTs and laponite platelets and adsorption of CTAB on individual NT and laponite species and their hybrids.

A study of the stability of aqueous suspensions of functionalized carbon nanotubes

The properties of aqueous suspensions of carbon nanotubes have been studied as depending on the conditions of their functionalization in a mixture of sulfuric and nitric acids. The elemental composition and contents of carboxyl, lactone, and hydroxyl groups in carbon nanotubes have been determined at different durations and temperatures of functionalization. The influence of functionalization conditions on the value of the electrokinetic potential of carbon nanotubes in aqueous suspensions and the nanotube solubility in water has been investigated. It has been found that the absolute value of the electrokinetic potential of nanotubes and their solubility in water increase with both the duration and temperature of functionalization due to a rise in the number of functional groups on their surface. The optimal regimes of functionalization of carbon nanotubes have been determined from the point of view of preserving their structure and stability in aqueous dispersions.

On the efficiency of UV–vis spectroscopy in assessing the dispersion quality in sonicated aqueous suspensions of carbon nanotubes

Abstract The present study evaluates carbon nanotube (CNT) dispersion quality in sonicated aqueous suspensions assisted by two types of dispersive agents, an ionic surfactant commonly used in nanocomposite development and a plasticizer-type dispersant relevant to cementitious matter. Dispersion quality is assessed by UV–vis spectroscopy and related to experimental parameters such as sonication duration/energy, dispersant type and concentration, and CNT loading. The results obtained from the versatile and straightforward methodology are compared to those obtained by the more complex and analytical Liquid Mode Laser Diffractometry (LMLD). The efficiency of UV–vis spectroscopy in effectively following the sonication process and in capturing its different stages is investigated and conclusions concerning the relation between surfactant concentration and sonication duration for achievement of monodisperse suspensions are drawn. The efficiency of the two assistive agents with regard to dispersion quality is compared and discussed in the text.

Aggregation and stabilization of multiwalled carbon nanotubes in aqueous suspensions: influences of carboxymethyl cellulose, starch and humic acid

Aggregation and stability of multiwalled carbon nanotubes in aqueous solutions were investigated with two polysaccharide stabilizers (carboxymethyl cellulose and a water soluble starch) and a natural organic matter (leonardite humic acid).

Carbon nanotubes enhanced cellulose nanocrystals films with tailorable electrical conductivity

Cellulose nanocrystals (CNCs) and commercial multi-walled carbon nanotubes (CNTs) are used to prepare CNT enhanced CNC films at various CNT weight fractions via an aqueous suspension vacuum filtration method with the purpose of studying potential synergistic effects between the CNTs and the CNCs in hybrid nanoparticle networks. The addition of CNTs even at very low concentrations allows the use of vacuum filtration for CNC films. The hybrid films show superior tensile and promising electrical properties by comparison with the CNC film. CNT enhanced CNC films prepared with micro-size CNT aggregates in the absence of surfactant exhibit improved tensile properties by comparison with the CNC films, suggesting that the CNCs could help disperse and stabilize the CNTs in aqueous suspensions. A maximum in tensile properties is obtained at a CNT concentration of around 10 wt.% with 6.26 GPa modulus and 179.7 MPa strength. Moreover the hybrid films are more ductile than the CNC film, resulting in improved tensile toughness. The surface electrical resistivity for the hybrid films can be tuned within a range from 102 to 1011 Ω/sq by manipulating the CNT weight fraction as well as the environmental humidity.

Study of geometric parameters of nonspherical nanoparticles by partially depolarized dynamic light scattering

An improved version of the depolarized dynamic light scattering method, which can be used for determining geometric parameters of nonspherical nanoparticles in liquids, has been proposed. Formulas are obtained that allow us to find the coefficients of translational and rotational diffusion of nanoparticles from autocorrelation functions of scattered light containing polarized and depolarized components in various ratios. This makes it possible to avoid the need to measure a completely depolarized component possessing an extremely low intensity. The proposed improvement presents the possibility of reducing the registration time and improving the signal-to-noise ratio and the accuracy of the results. Measurements of the parameters of multiwall carbon nanotubes in aqueous suspensions have been carried out. The values of the length and diameter of the tubes calculated by the coefficients of diffusion obtained with the help of the proposed method agree with the results of measurements on scanning and transmission electron microscopes.

Optimization of Sonication Parameters for Homogeneous Surfactant-Assisted Dispersion of Multiwalled Carbon Nanotubes in Aqueous Solutions

The current study provides answers to two critical open questions concerning homogeneity of aqueous suspensions of carbon nanotubes by ultrasonic processing. The first is the dependence of tube dispersion quality on sonication duration and intensity, and the second is the identification of the appropriate conditions for retaining the highly desirable initial aspect ratio of the free-standing tubes in the dispersed state. A straightforward methodology based on nanotube agglomerate size analysis by liquid mode laser diffraction is suggested for quantifying the effects of sonication parameters on tube length and sample polydispersity. The technique, which is superior to currently suggested methods in that analysis of larger representative volumes is allowed and tube sedimentation effects are avoided, was tested across surfactant-assisted aqueous suspensions of multiwalled carbon nanotubes, while no apparent factors limit application to other types of suspensions. A ruling rationale for distinguishing between...

Comparative studies of singlet oxygen generation by fullerenes and single- and multilayer carbon nanotubes in aqueous suspensions

Singlet oxygen generation is studied in three types of carbon nanoparticles (C60 fullerene and single- and multilayer carbon nanotubes in the form of aqueous suspensions obtained by sonication) upon their irradiation by continuous-wave broadband visible radiation of light-emitting diodes.

A Review of Spectral Methods for Dispersion Characterization of Carbon Nanotubes in Aqueous Suspensions

Characterization is a crucial step in the study of properties of nanomaterials to evaluate their full potential in applications. Carbon nanotube-based materials have properties that are sensitive to size, shape, concentration, and agglomeration state. It is therefore critical to quantitatively characterize these factors in situ, while the processing takes place. Traditional characterization techniques that rely on microscopy are often time consuming and in most cases provide qualitative results. Spectroscopy has been studied as an alternative tool for identifying, characterizing, and studying these materials in situ and in a quantitative way. In this paper, we provide a critical review of the spectroscopy techniques used to explore the surface properties (e.g., dispersion) characteristics of carbon nanotubes in aqueous suspensions during the sonication process.