Multi-walled Carbon Nanotubes In Water Research Articles

Impact of length and radius of carbon nanotubes on flow and heat transfer in converging and diverging channels with entropy generation

This research examines the complex interplay between the carbon nanotubes' length and radius and how that affects flow patterns, heat transfer properties, and entropy creation in both convergent and divergent channels. Our research elucidates the mechanisms at play by revealing a crucial link between carbon nanotube dimensions and the efficacy of heat transfer processes. In particular, carbon nanotubes with a longer length have better heat transmission properties, while carbon nanotubes with a smaller radius generate less entropy. From microfluidics to energy-efficient materials, these results show significant promise for optimizing thermal systems and improving performance. This research looks on the differences between the thermal transports of single- and multi-walled carbon nanotubes in water. Thermo physical characteristics of carbon nanoparticles are one of a kind and essential for this purpose. The fluid is assumed to be incompressible and to flow steadily a two-dimensional plane. The effects of thermal radiation on the heat transfer of a water-based fluid in convergent and divergent channels with decreasing and expanding walls have been studied. In order to quickly sketch the equations, the RK-4 method with shooting approach is used, and similarity transformation is employed to reduce their dimensionality. The key factors influencing hydrothermal performance have been visualized through the use of graphs. The production numbers of entropy are also shown and explained at length. The obtained data supports the reliability of the approach used. Surface heat transport was found to be negatively impacted by elongation. Colloidal single-walled carbon nanotube (SWCNT) suspensions in water had higher thermal conductivity than water itself.

Thermal and exergy analysis of Pin-finned heatsinks for nanofluid cooled high concentrated photovoltaic thermal (HCPV/T) hybrid systems

• Cooling performance of HCPV/T is systematically investigated. • Different shaped pin-finned heat sinks (inline and staggered) are examined. • Thermal performance is determined for MWCNT nanofluids. • Exergy efficiencies of pin-fin heat sinks in HCPV/T are evaluated. • 2% MWCNT nanoparticle concentration is found to be the optimum. Cooling of High Concentrated Photovoltaic (HCPV) cells is a major concern among researchers due to higher heat generation in the cells from highly concentrated solar radiation. In the present investigation, a numerical study of the High Concentrated Photovoltaic Thermal (HCPV/T) system is conducted for the combined effect of nanofluids and pin-finned heatsinks on the cooling performance. The investigation is carried out for AZUR SPACE solar cell (Model: 3C44C) for 1000 Concentration Ratio (CR) and the Reynolds number ( Re ) varies within the laminar range (600 ≤ R e ≤ 2200). Different shapes of pin-fins and their orientations are systematically investigated for the effect of Multi-walled Carbon Nanotube (MWCNT) nanoparticles in a base fluid. The results show a significant reduction in the temperature (up to 18K) of the solar cells for the MWCNT nanofluid compared to its base fluid counterpart. A higher heat transfer characteristics (Nusselt numbers) and lower average temperature of top surface of HCPV cells are found to occur for the staggered arrangements of pin-fins. It is also noticed that the volume concentration of MWCNT in water affects heat transfer characteristics and reduction in temperature takes place up to the volume concentration of 2%. About 1.3% reduction in temperature is predicted for adding MWCNT nanoparticle concentration from 0.5% to 2%. However, in terms of exergy efficiency, maximum overall exergy (about 67% for water flow rate of 0.00167 kg/s) is found for square pin-fins with inline arrangements. The average increase in Nusselt number from inline to staggered arrangement are around 11%, 74%, and 22% respectively for circular, square and triangular fins. The maximum electrical efficiency reaches to 42.2% for both 2% and 4% MWCNT with staggered circular pin-fins for a mass flow rate of 0.0058kg/s. Finally, it appears that a combination of nanofluids and pin-finned heatsinks gives a better cooling rate in the HCPV/T system and could be a promising alternative along with other cooling techniques.

Effect of sodium dodecyl sulfate on CO2 and H2S absorption enhancement of functionalized multiwall carbon nanotubes in water: Experimental study and empirical model

A single bubble absorption column was used to examine the effect of hydrodynamic on carbon dioxide (CO2) and hydrogen sulfide (H2S) absorption in pure water and water-based nanofluids dispersed with neat, and OH and NH2 functionalized multiwall carbon nanotubes (MWCNTs). Sodium dodecyl sulfate (SDS) was used as a surfactant and stabilizer. The maximum absorption of CO2 and H2S were found to be 0.0038 mmol/m2·s and 0.056 mmol/m2·s using NH2-MWCNTs /nanofluid with 0.5 wt% content, respectively. The diffusion coefficients of gases into the nanofluids were computed by using an equation attained based on Dankwert’s theory. A last, an empirical correlation was proposed to determine the Sherwood number for the absorption of the aforementioned gases into the nanofluids.

Compositing prevulcanized natural rubber with multiwalled carbon nanotubes to make antistatic films

AbstractNatural rubber was prevulcanized using ultraviolet (UV) light and the resulting prevulcanized natural rubber (PVNR) was composited with multiwalled carbon nanotubes (MWCNT) as a conductive filler, to make films suitable for antistatic gloves. These films were characterized in terms of mechanical properties and electrical resistivity. Effects of type of UV radiation and other specifics of the production process, on mechanical properties of neat PVNR were first investigated. This was followed by an investigation of the effects of surfactant type on the dispersion of MWCNT in water and the PVNR matrix. Four surfactants with different headgroups were used in preparing MWCNT dispersions that were then mixed with the PVNR latex to form the different films. As a consequence of its milk‐like turbidity, the natural rubber latex was found to require deeply penetrating UVA light for satisfactory prevulcanization. Sodium dodecyl sulfate (SDS) was the best surfactant for dispersing MWCNT both in water and in PVNR matrix. SDS resulted in MWCNT–PVNR composite films with the least electrical resistivity and good mechanical properties for making antistatic gloves. SDS did not interfere with stress transfer at NR–MWCNT interface. SDS was superior to the other surfactants because its head group had a charge opposite to that on the NR surface and lacked a benzene ring that would have interacted strongly with the hydrophobic surface of MWCNT.

Electrochemical determination of Saccharomyces cerevisiae sp using glassy carbon electrodes modified with oxidized multi-walled carbon nanotubes dispersed in water –Nafion®

The electrochemical behavior of Saccharomyces cerevisiae sp was studied using a glassy carbon electrode (GCE) modified with Nafion-dispersed oxidized multi-walled carbon nanotubes (OMWCNT). The morphology was studied using scanning electron microscopy (SEM), showing that the yeast sticks to the carbon nanotube surface instead of the glassy carbon surface. The redox couple Fe(CN)64−/Fe(CN)63− was used to determine the electroactive area and the heterogeneous transfer constant, which increased 80.5% and 108% respectively by the presence of nanotubes. The studies of the pH effect showed that the anodic potential decreases at alkaline pH and that the highest current intensity occurs at a pH value of 7.00. Studies of the scan rate effect have shown that yeast oxidation is an irreversible mixed control process in which two electrons participate. The relationship between yeast concentration and the anodic current density was studied using different electrochemical techniques obtaining the best analytical parameters through chronoamperometry. The linear range was between 3.36 and 6.52 g L−1, the limit of detection (LOD) and the limit of quantification (LOQ) were 0.98 g L−1 and 3.36 g L−1 respectively, and the sensibility obtained was 0.086 μA L g−1 mm−2. These results show that the multi-walled carbon nanotubes in water and Nafion® allow obtaining an anodic signal corresponding to the yeast, which facilitates its quantification through electrochemical methodologies, favoring the reduction of analysis times and costs compared with other techniques.

Deep-Ultraviolet Transparent Conductive MWCNT/SiO2 Composite Thin Film Fabricated by UV Irradiation at Ambient Temperature onto Spin-Coated Molecular Precursor Film.

Deep-ultraviolet (DUV) light-transparent conductive composite thin films, consisting of dispersed multiwalled carbon nanotubes (MWCNTs) and SiO2 matrix composites, were fabricated on a quartz glass substrate. Transparent and well-adhered amorphous thin films, with a thickness of 220 nm, were obtained by weak ultraviolet (UV) irradiation (4 mW cm−2 at 254 nm) for more than 6 h at 20−40 °C onto the precursor films, which were obtained by spin coating with a mixed solution of MWCNT in water and Si(IV) complex in ethanol. The electrical resistivity of MWCNT/SiO2 composite thin film is 0.7 Ω·cm, and transmittance in the wavelength region from DUV to visible light is higher than 80%. The MWCNT/SiO2 composite thin film showed scratch resistance at pencil hardness of 8H. Importantly, the resistivity of the MWCNT/SiO2 composite thin film was maintained at the original level even after heat treatment at 500 °C for 1 h. It was observed that the heat treatment of the composite thin film improved durability against both aqueous solutions involving a strong acid (HCl) and a strong base (NaOH).

Unsteady free convection flow of water-based carbon nanotubes due to non-coaxial rotations of moving disk

ABSTRACT Nanofluid is one of the significant developments for having an efficient heat transport process. Its implementation in a non-coaxial rotating system has benefited from designing a mixer machine with two stirrer blades, cooling fan, and jet engines. This study analytically investigates the free convection of unsteady non-coaxial rotating nanofluid flow through a moving disk. The suspension of single-wall or multi-wall carbon nanotubes in water is known as the nanofluid in this study. The fluid motion is affected by the effects of rotation and buoyancy forces. Using suitable dimensionless variables, the dimensional coupled partial differential of momentum and energy equations along with their initial and moving boundary conditions are converted into the dimensionless form. The expressions for temperature and velocity profiles are obtained by solving governing equations using Laplace transform method. The validity of obtained solution is confirmed by having a good agreement when comparing present results with the published result. The results show that the insertion of CNTs particles into the rotating water causes the temperature and velocity profiles to increase. The amount of heat transferred by SWCNTs is greater than MWCNTs. Increasing CNTs particles has descended both primary and secondary skin friction but increase Nusselt number. Further analysis with the help of pictorial discussion for the fluid flows and heat transfer under the influences of nanoparticle volume fraction, Grashof number, the amplitude of disk, and time is carried out.

Sonication-driven dispersion of multiwalled carbon nanotubes in water with the aid of Na+-montmorillonite

The poor dispersibility of multiwalled carbon nanotubes (MWNTs) in aqueous solvents is a serious obstacle to give full play to the excellent properties of MWNTs. How to effectively disperse MWNTs has become an urgent problem to be solved. Therefore, the addition of tertiary phase became necessary to promote such dispersion. In the present work, the sonication-driven dispersion of multi-wall carbon nanotubes (MWNTs) in aqueous Na+-montmorillonite (MMT) solution has been investigated with the help of UV-vis spectroscopy, particle agglomeration size and Transmission Electron Microscopy (TEM). The impact of ultrasonic power and time as well as MMT/MWNTs ratio on the dispersion of MWNTs was discussed. It was observed that sonication at 240 W for 40 min at MMT/MWNTs weight ratio of 2 resulted in efficient dispersion and formation of stabilized suspensions of individual nanotubes. The ultrasound provided high local shears to overcome the van der Waals interactions between tubes and lead to MWNTs debundling, which facilitate adsorption and immobilization of MMT on the surface of the MWNTs, preventing re-aggregation of MWNTs.

Non-covalent and covalent immobilization of Candida antarctica lipase B on chemically modified multiwalled carbon nanotubes for a green acylation process in supercritical CO2

• Efficient immobilization of Candida antarctica B lipase on modified MWCNTs. • Enzyme loading reaching as high as 21 wt.% for non-covalent immobilization. • Active O-acylation of geraniol into geranyl acetate by CAL-B in supercritical CO 2 . • Reaction regioselectivity unchanged through immobilization. • Development of a fully green enzymatic process. Candida antarctica B lipase (CAL-B) was immobilized on purified and functionalized multiwalled carbon nanotubes (MWCNTs). Both immobilization routes, physical adsorption and covalent bonding, were investigated. MWCNT functionalization by a non-aggressive oxidation by potassium permanganate led to an interesting balance between the hydrophilic and the hydrophobic areas of the MWCNT surface; the former being responsible of the good dispersion of MWCNTs in water and the latter having a favorable affinity with CAL-B. The enzyme loadings reached were significant: around 16 wt. % and 21 wt.% for non-covalent and covalent immobilization, respectively. The enzymatic activity was studied with the reaction of O-acylation of geraniol into geranyl acetate by CAL-B in supercritical CO 2 . Even if a decay in synthesis of geranyl acetate was observed over cycling for both CAL-B@MWCNT catalysts, it was demonstrated that the regioselectivity of CAL-B was unchanged through immobilization on the MWCNT surface for both routes. Interestingly, it was shown that a fully green enzymatic process can be achieved with these prepared CAL-B@MWCNT biocatalyst. Such approach could be transferred to other support/enzyme systems for developing new eco-friendly synthesis processes.

Carbon nanotubes grafted with sulfonated polyacrylamide as a heterogeneous catalyst for the preparation of bis(indolyl)methanes

Multiwalled carbon nanotubes (MWCNTs) were grafted with poly(AMPS–co–AM) by free-radical polymerization of acrylamide (AM) and 2–acrylamido–2-methylpropane sulfonic acid (AMPS) monomers initiated by benzoyl peroxide (BPO). MWCNT–poly(AMPS–co–AM) was characterized by Fourier transform–infrared spectroscopy (FT–IR), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS). Observation showed that grafting of poly(AMPS–co–AM) to MWCNTs improves solubility of MWCNTs in water, ethanol, and dichloromethane. MWCNT–poly(AMPS–co–AM) also showed good catalytic performance for the preparation of bis(indolyl)methanes and 1,8-dioxo-octahydroxanthenes through the condensation of an aldehyde with indole and 5,5-dimethyl-1,3-cycloheanedione (dimedone), respectively. MWCNT–poly(AMPS–co–AM) catalyst can be reusable for at least up to eight times without significant loss of activity.

Study on the behaviors of multi-walled carbon nanotubes modified by gemini sulfonate dispersant and their reinforced magnesium matrix composite

The dispersion behaviors of multi-walled carbon nanotubes (MWCNTs) in water, using an ionic-gemini type molecule, 4, 4′-di (n-alkyl) diphenylmethane disulfate salt (Cn-DSDM, n = 12, 14, 16) as the dispersant, were investigated. The MWCNTs reinforced magnesium (Mg) matrix composite was fabricated successfully by using the MWCNTs dispersed by DSDM. The effects of hydrophobic chain length, sonication time and pH on the dispersibility of MWCNTs were characterized by UV-vis spectrophotometer, dynamic light scattering, Raman spectroscopy, transmission electron microscopy and zeta potential measurements. Results show that the Cn-DSDM can effectively disperse MWCNTs in water through a noncovalent functionalizing mechanism, and the dispersion is enhanced with reducing in the hydrophobic chain length, i.e. the C12-DSDM shows the best dispersibility among the three kinds of Cn-DSDM. The pH value of water for the most effective dispersion is 7, and the dispersibility is improved with the increase in sonication time. The tensile test result of the C12-DSDM dispersed MWCNTs reinforced Mg matrix composite demonstrates that the mechanical properties especially the elongation are outstandingly enhanced, i.e. by addition of 0.1 wt% C12-DSDM dispersed MWCNTs, the ultimate tensile strength (UTS) and elongation (E) of pure Mg are improved by about 12.5% and 50.7%, respectively. The strengthening mechanism of C12-DSDM-MWCNTs/Mg composite was discussed in detail.

Dispersion and stability of multi-walled carbon nanotubes in water as affected by humic acids

The effects of two different humic acids (HAs), commercial Aldrich HA (AHA) and HA extracted from forest soils (FHA), on the dispersion and stability of three multi-walled carbon nanotubes (MWCNTs) in water were investigated. The amount of MWCNTs suspended in pure water increased with increases in the MWCNT surface oxygen content and solution pH, and the amount decreased as the ionic strength increased. These results indicated that electrostatic repulsion drove the dispersion of MWCNTs. Adsorbed HA greatly enhanced the dispersion and stability of MWCNTs due to the increased steric hindrance and electrostatic repulsion between individual MWCNTs. Suspended MWCNT concentrations and HA adsorption to MWCNTs were positively correlated with low ionic strengths (0–40 mM) and/or pH values between 3 and 7, which were independent of the change in electrostatic repulsion, suggesting that the dispersion of MWCNTs was primarily controlled by steric hindrance. At higher ionic strengths, MWCNTs rapidly precipitated due to the reduction of the electrostatic repulsion between individual MWCNTs. AHA could suspend more MWCNTs than FHA, which was ascribed to the higher molecular weight and aromatic carbon content of AHA that led to greater steric hindrance between individual MWCNTs. This result verified that steric hindrance was the dominant mechanism by which HAs disperse MWCNTs.

Optimization of Carbon Nanotube Dispersions in Water Using Response Surface Methodology.

The aim of this work was to demonstrate an optimization methodology to reliably obtain stable macrodispersions (i.e., for ≥24 h) of carbon nanotubes in water using sonication. Response surface methodology (RSM) was utilized to assess and optimize the sonication parameters for the process. The studied input parameters were (i) sonication time (duration), (ii) amplitude (of vibration), and (iii) pulse-on/off (duration) of the sonicator. The analyzed responses were mean diameter and size distribution of multiwalled carbon nanotube (MWNT) aggregates in water, which were measured by the dynamic light scattering technique. A semiempirical model was developed and statistically tested to estimate the magnitude of sonicator parameters required to obtain specified MWNT macrodispersions (i.e., aggregates’ mean diameter and distribution) in water. The results showed that MWNT aggregates of 2 ± 0.5 μm can be obtained by optimizing sonicator parameters to a sonication time of 89 s, amplitude of 144 μm, and pulse-on/off cycle of 44/30 s. These process settings for 100 mg/L MWNTs in a 30 mL aliquot of deionized water would consume 863 J/mL of sonication energy. Contrary to the popular belief, “sonication time” and/or “sonication energy input” were not found to be proportional to the degree of dispersion of MWNTs in water. This might be the reason for the frequent disparity and nonreproducibility of sonication results reported in scientific literature, especially for dispersing nanomaterials in a number of different systems. The amplitude of vibration was noted to be the most sensitive parameter affecting MWNT aggregates’ diameter and distribution in water. The characterization of MWNTs was performed using electron microscopy, surface area analyzer, thermogravimetric analyzer, and zeta potential analyzer. This study can be helpful in evaluating sonication dispersion of particulate matter in other incompressible fluids such as graphene dispersion in organic solvents.

Sulfonitric Treatment of Multiwalled Carbon Nanotubes and Their Dispersibility in Water.

In this study, Multiwalled carbon nanotubes (MWCNTs) were oxidized by a mixture of sulfuric acid and nitric acid (V:V = 3:1) at 70 °C for 1, 2, and 4 h, respectively. The oxidized MWCNTs were characterized by N2 adsorption, Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA), and Raman spectroscopy to determine the oxidation degree. The dispersion of the MWCNTs was investigated by UV-vis-NIR, SEM, and dynamic light scattering measurements. Results show that sulfonitric treatment increased the surface area and total pore volume and reduced the average pore diameter of MWCNTs. The treatment promoted the formation of oxidized species on the surface MWCNTs, as identified by FT-IR, TGA, and X-ray photoelectron spectroscopy measurements, and more oxygen-containing functional groups were generated when treatment time was extended. Moreover, a general relationship between oxidation degree and dispersibility of MWCNTs in water was established. UV-vis-NIR and dynamic light scattering measurements and SEM images revealed that MWCNTs with higher oxidation degree showed better dispersibility in water.

Electrochemical Performance of Nano-SnO2 Anode with Carbonized Carbon Nanotubes Paper as Host

A 3-dimensional carbonized multi-walled carbon nanotube (MWCNT) paper was used as the host of nano-tin oxide (SnO2) for lithium-ion batteries (LIBs). The cellulose fibers were fully mixed with MWCNTs in water. Then, the paper was obtained via vacuum filtration. Carbonization was carried out in a vacuum furnace at 1460°C. SnO2 slurry was coated on the carbonized MWCNT paper (CMP). Scanning electron microscopy (SEM) was utilized to observe the anode electrode. The images of SEM indicated that the nano-SnO2 was embedded into the holes of the porous CMP collector. This contributed the increase of contact interface area of the nano-SnO2 and the collector and the significantly reduced interface resistance. Electrochemical tests showed that the initial discharge capacity reached 1745 mAh g−1 with a coulumbic efficiency (CE) of 70.39% at a current density of 50 mA g−1. The composite electrode still maintained a reversible capacity of 753 mAh g−1 with a CE of 98% at a current density of 200 mA g−1 after 100 cycles. These marvelous composite electrodes exhibited a promising future for the next generation of LIBs.

Fuel-Driven Dissipative Self-Assembly of a Supra-Amphiphile in Batch Reactor.

Dissipative self-assembly is an intriguing but challenging research topic in chemistry, materials science, physics, and biology because most functional self-assembly in nature, such as the organization and operation of cells, is actually an out-of-equilibrium system driven by energy dissipation. In this article, we successfully fabricated an I2-responsive supra-amphiphile by a PEGylated poly(amino acid) and realize its dissipative self-assembly in batch reactor by coupling it with the redox reaction between NaIO3 and thiourea, in which I2 is an intermediate product. The formation and dissipative self-assembly of the supra-amphiphile can be repeatedly initiated by adding the mixture of NaIO3 and thiourea, which herein acts as "chemical fuel", while the lifetime of the transient nanostructures formed by the dissipative self-assembly is easily tuned by altering thiourea concentration in the "chemical fuel". Furthermore, as an application demo, the dissipative self-assembly of the supra-amphiphile is examined to control dispersion of multiwalled carbon nanotubes in water, exhibiting a good performance of organic pollutant removal.

Rapid and sensitive detection of the phenoxy acid herbicides in environmental water samples by magnetic solid-phase extraction combined with liquid chromatography-tandem mass spectrometry.

Phenoxy acid herbicides are widely used herbicides that play an important role in improving the yield and quality of crops. However, some research has shown that this kind of herbicide is poisonous to human and animals. In this study, a rapid and sensitive method was developed for the detection of seven phenoxy acid herbicides in water samples based on magnetic solid-phase extraction followed by liquid chromatography and tandem mass spectrometry. Magnetic amino-functionalized multiwalled carbon nanotubes were prepared by mixing bare magnetic Fe3 O4 nanoparticles with commercial amino-functionalized multiwalled carbon nanotubes in water. Then the amino-functionalized multiwalled carbon nanotubes were used to enrich phenoxy acid herbicides from water samples based on hydrophobic and ionic interactions. The effects of experimental variables on the extraction efficiency have been studied in detail. Under the optimized conditions, the method validation was performed. Good linearities for seven phenoxy acid herbicides were obtained with squared regression coefficients ranging from 0.9971 to 0.9989. The limits of detection ranged from 0.01 to 0.02μg/L. The method recoveries of seven phenoxy acid herbicides spiked at three concentration levels in a blank sample were from 92.3 to 103.2%, with inter- and intraday relative standard deviations less than 12.6%.

In-vitro Study of Photothermal Anticancer Activity of Carboxylated Multiwalled Carbon Nanotubes.

Multi-walled Carbon Nano Tubes (MWCNTs) as an important element of nanosciences have a remarkable absorption in the region of NIR window (650-900 nm) which can overcome the limitations of deep treatment in photothermal therapy. To disperse MWCNTs in water, it is proposed to attach carboxylated functional group (-COOH) to MWCNTs in order to increase dispersivity in water. A stable suspension of MWCNTs-COOH with different concentrations (from 2.5 to 500 μg/ml) was prepared. Then, they were compared for their ability to increase temperature in the presence of 810 nm laser irradiation and through a wide range of radiation time (from 20 to 600 s) and three laser powers (1.5, 2 and 2.5 w). The temperature rise was recorded real time every 20 seconds by a precise thermometer. Absorption spectrum of MWCNTs-COOH suspension was remarkably higher than water in a wavelength range of 200 to 1100 nm. For example, using the concentrations of 2.5 and 80 μg/ml of MWCNTs-COOH suspension caused a temperature elevation 2.35 and 9.23 times compared to water, respectively, upon 10 min laser irradiation and 2.5 w. Moreover, this predominance can be observed for 1.5 and 2 w radiation powers, too. Our findings show that the maximum of temperature increase was obtained at 80 μg/ml concentration of MWCNT-COOH suspension for three powers and through all periods of exposure time. Our results show that the minimum required parameters for a 5°C temperature increase (a 5°C temperature increase causes cell death) were achieved through 2.5 w, 28 μg/ml concentration and 20 second irradiation time in which both concentration and radiation times were relatively low. Our results showed that MWCNTs-COOH can be considered as a potent photothermal agent in targeted therapies. New strategies must be developed to minimize the concentration, irradiation time and radiation power used in experiments.

Photothermal therapy of melanoma tumor using multiwalled carbon nanotubes.

Photothermal therapy (PTT) is a therapeutic method in which photon energy is transformed into heat rapidly via different operations to extirpate cancer. Nanoparticles, such as carbon nanotubes (CNTs) have exceptional optical absorbance in visible and near infrared spectra. Therefore, they could be a good converter to induce hyperthermia in PTT technique. In our study, for improving the dispersibility of multiwalled CNTs in water, the CNTs were oxidized (O-CNTs) and then polyethylene glycol (PEG) was used for wrapping the surface of nanotubes. The formation of a thin layer of PEG around the nanotubes was confirmed through Fourier transform infrared, thermogravimetric analysis, and field emission scanning electron microscopy techniques. Results of thermogravimetric analysis showed that the amount of PEG component in the O-CNT-PEG was approximately 80% (w/w). Cell cytotoxicity study showed that O-CNT was less cytotoxic than pristine multiwalled nanotubes, and O-CNT-PEG had the lowest toxicity against HeLa and HepG2 cell lines. The effect of O-CNT-PEG in reduction of melanoma tumor size after PTT was evaluated. Cancerous mice were exposed to a continuous-wave near infrared laser diode (λ=808 nm, P=2 W and I=8 W/cm2) for 10 minutes once in the period of the treatment. The average size of tumor in mice receiving O-CNT-PEG decreased sharply in comparison with those that received laser therapy alone. Results of animal studies indicate that O-CNT-PEG is a powerful candidate for eradicating solid tumors in PTT technique.

Dispersion of Water Proton Spin–Lattice Relaxation Rates in Aqueous Solutions of Multiwall Carbon Nanotubes (MWCNTs) Stabilized via Alkyloxymethylimidazolium Surfactants

Carbon nanotubes and a number of other carbon nanomaterials have a tendency to aggregate, which often resulted in difficulties of dispersion of these nanomaterials in aqueous solutions. The ability of dicationic (gemini) surfactants to disperse multiwall carbon nanotubes in water and the dynamic processes taking place at the water–multiwall carbon nanotubes (MWCTs) interface are studied. Stable dispersions of multiwall carbon nanotubes with selected gemini surfactants (1,1′-(1,6-hexanediyl)bis(3-alkyloxymethylimidazolium) dichlorides) were prepared and characterized by nuclear magnetic relaxation dispersion (NMRD), NMR diffusometry, scanning and transmission electron microscopy, and Fourier transform infrared spectroscopy. The addition of multiwall carbon nanotubes to aqueous solutions of studied gemini surfactants leads to significant paramagnetic enhancement of the spin–lattice relaxation processes, which gets more pronounced with increasing concentration of well-dispersed MWNTs in water. The dominant role of outer sphere (OS) relaxation mechanism in total observed R1, governed by two-dimensional diffusion of water on the carbon nanotube surface in the vicinity of paramagnetic centers incorporated in the MWCNTs’ sidewalls (mainly of iron origin), was assumed to explain NMRD data. The NMR diffusion experiments confirm the existence of restricted water diffusion in the studied supernatants. The NMR diffusion results are consistent with the FTIR and NMR proton spin–lattice relaxation dispersion in which the more effective R1 dispersion noticed for the sample with IMIC6C12 was ascribed to the better accessibility of water molecules to the surface of the MWCNTs.