Characterization of Carbon Nanomaterials Dispersions: Can Metal Decoration of MWCNTs Improve Their Physicochemical Properties?

A suitable dispersion of carbon materials (e.g., carbon nanotubes (CNTs)) in an appropriate dispersant media, is a prerequisite for many technological applications (e.g., additive purposes, functionalization, mechanical reinforced materials for electrolytes and electrodes for energy storage applications, etc.). Deep eutectic solvents (DES) have been considered as a promising “green” alternative, providing a versatile replacement to volatile organic solvents due to their unique physical-chemical properties, being recognized as low-volatility fluids with great dispersant ability. The present work aims to contribute to appraise the effect of the presence of MWCNTs and Ag-functionalized MWCNTs on the physicochemical properties (viscosity, density, conductivity, surface tension and refractive index) of glyceline (choline chloride and glycerol, 1:2), a Type III DES. To benefit from possible synergetic effects, AgMWCNTs were prepared through pulse reverse electrodeposition of Ag nanoparticles into MWCNTs. Pristine MWCNTs were used as reference material and water as reference dispersant media for comparison purposes. The effect of temperature (20 to 60 °C) and concentration on the physicochemical properties of the carbon dispersions (0.2–1.0 mg cm−3) were assessed. In all assessed physicochemical properties, AgMWCNTs outperformed pristine MWCNTs dispersions. A paradoxical effect was found in the viscosity trend in glyceline media, in which a marked decrease in the viscosity was found for the MWCNTs and AgMWCNTs materials at lower temperatures. All physicochemical parameters were statistically analyzed using a two-way analysis of variance (ANOVA), at a 5% level of significance.

Synthesis and Characterization of SiO2@CNTs Microparticles: Evaluation of Microwave-Induced Heat Production

This study was focused on the growth of multi-walled carbon nanotubes (MWCNTs) on iron chloride-functionalized silica microspheres. In addition, the microwave absorption potential and the subsequent heat production of the resulting structures were monitored by means of infrared thermometry and compared with pristine commercially available MWCNTs. The functionalized silica microparticle substrates produced MWCNTs without any amorphous carbon but with increased structural defects, whereas their heat production performance as microwave absorbents was comparable to that of the pristine MWCNTs. Two-minute microwave irradiation of the SiO2@CNTs structures resulted in an increase in the material’s temperature from ambient temperature up to 173 °C. This research puts forward a new idea of charge modulation of MWCNTs and sheds light on an investigation for the development of bifunctional materials with improved properties with respect to efficient microwave absorbance.

Effect of MWCNTs Functionalization on Thermal, Electrical, and Ammonia-Sensing Properties of MWCNTs/PMMA and PHB/MWCNTs/PMMA Thin Films Nanocomposites

Partially biodegradable polymer nanocomposites Poly(3-Hydroxybutyrate) (PHB)/MultiwalledCarbon Nanotubes (MWCNTs)/Poly(Methyl Methacrylate) (PMMA)and non-biodegradable nanocomposites (MWCNTs/PMMA) were synthesized, and their thermal, electrical, and ammonia-sensing properties were compared. MWCNTs were chemically modified to ensure effective dispersion in the polymeric matrix. Pristine MWCNTs (p-MWCNTs) were functionalized with –COOH (a-MWCNTs) and amine groups (f-MWCNTs). Then, PHB grafted multiwalled carbon nanotubes (g-MWNTs) were prepared by a ‘grafting to’ technique. The p-MWCNTs, a-MWCNTs, f-MWCNTs, and g-MWCNTs were incorporated into the PMMA matrix and PMMA/PHB blend system by solution mixing. The PHB/f-MWCNTs/PMMA blend system showed good thermal properties among all synthesized nanocomposites. Results from TGA and dTGA analysis for PHB/f-MWCNTs/PMMA showed delay in T5 (about 127 °C), T50 (up to 126 °C), and Tmax (up to 65 °C) as compared to neat PMMA. Higher values of frequency capacitance were observed in nanocomposites containing f-MWCNTs and g-MWCNTs as compared to nanocomposites containing p-MWCNTs and a-MWCNTs. This may be attributed to their excellent interaction and good dispersion in the polymeric blend. Analysis of ammonia gas-sensing data showed that PHB/g-MWCNTs/PMMA nanocomposites exhibited good sensitivity (≈100%) and excellent repeatability with a constant response. The calculated limit of detection (LOD) is 0.129 ppm for PHB/g-MWCNTs/PMMA, while that of all other nanocomposites is above 40 ppm.

MWCNT Decorated Rich N-Doped Porous Carbon with Tunable Porosity for CO2 Capture

Designing of porous carbon system for CO2 uptake has attracted a plenty of interest due to the ever-increasing concerns about climate change and global warming. Herein, a novel N rich porous carbon is prepared by in-situ chemical oxidation polyaniline (PANI) on a surface of multi-walled carbon nanotubes (MWCNTs), and then activated with KOH. The porosity of such carbon materials can be tuned by rational introduction of MWCNTs, adjusting the amount of KOH, and controlling the pyrolysis temperature. The obtained M/P-0.1-600-2 adsorbent possesses a high surface area of 1017 m2 g−1 and a high N content of 3.11 at%. Such M/P-0.1-600-2 adsorbent delivers an enhanced CO2 capture capability of 2.63 mmol g−1 at 298.15 K and five bars, which is 14 times higher than that of pristine MWCNTs (0.18 mmol g−1). In addition, such M/P-0.1-600-2 adsorbent performs with a good stability, with almost no decay in a successive five adsorption-desorption cycles.

Vapor Phase Modification for Selective Enrichment of Grafted Styrene/Acrylonitrile onto Carbon Nanotubes Via ATRP

Nitric acid vapor phase oxidation of multi-walled carbon nanotubes (MWCNTs) was proposed as a promising technique to fabricate poly styrene-co-acrylonitrile (SAN)-grafted-CNTs via atom transfer radical polymerization (ATRP). The in-situ ATRP grafting approach was successfully employed to graft polystyrene (PS), SAN and polyacrylonitrile (PAN), onto the convex surfaces of pristine MWCNTs (PCNT) and acid-functionalized MWCNTs (FCNT). Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H-NMR), and thermogravimetric analysis (TGA) confirmed the effectiveness of the modification via the ATRP grafting approach. The molar composition of acrylonitrile in the synthesized copolymer on the surface of CNTs for an FCNTs was calculated to be about 80% and 67.5% by 1H-NMR and TGA respectively, whereas the value is lower for PCNTs. Morphological studies showed that SAN-grafted FCNTs exhibit rougher surface morphology compared to the SAN-grafted PCNTs. Moreover, the higher diameter of the FCNTs indicated the higher polymer content, which was coated onto CNTs functionalized by vapor-phase oxidation. Therefore, the vapor phase oxidation strategy employed in this study could be utilized as a general method to prepare CNTs which can serve as an ATRP macroinitiator for the fabrication of various polymer grafted CNTs.

Improvement of photocatalytic decomposition of methyl orange by modified MWCNTs, prediction of degradation rate using statistical models

Multi-walled carbon nanotubes (MWCNTs) have been successfully modified with TiO2 nanoparticles via a two-step hydrolysis technique. Firstly, the pristine MWCNTs are functionalized in nitric acid (HNO3) to creation of oxygen containing groups. Secondly, TiO2 nanoparticles are synthesized on the surface of functionalized MWCNTs through hydrolysis method. The synthesized samples have been used as photocatalyst for decomposition of methyl orange (MO) as dye organic pollutant. The characterization of samples using x-ray diffraction pattern (XRD) confirm the presence of TiO2 nanoparticles with mixture of anatase and rutile phases. Regarding the photocatalytic performance of TiO2 nanoparticles and modified MWCNTs with TiO2 nanoparticles, it observed that the degradation rate of MO increases by increasing the irradiation time from 5 min to 35 min. The variation of degradation rate upon pH of suspension reveals that the maximum and minimum degradation rate are in acidic (pH=3) and neutral condition (pH=7). Meanwhile, the results show that the presence of MWCNTs leads to the enhancement of degradation rate. The analysis of variance (ANOVA) results confirm that both of main factors (irradiation time and pH) and their interaction have a significant influence on the degradation rate of MO. However, the effect of irradiation time is more than that of pH and their interaction. The graphical methods verify the quality and adequacy of the statistical models for prediction of the degradation rate.

Extraction of betacyanins from Hylocereus polyrhizus (dragon fruit) peel and further enrichment by adsorption

Mixtures of water and ethanol were tested for the extraction of betacyanins from Hylocereus polyrhizus peel to obtain natural colorants. In order to obtain betacyanins in a purified form, adsorption was carried out with two types of multi-walled carbon nanotubes (MWCNTs; pristine MWCNTs and carboxylated MWCNTs) and two macroporous resins (X-5 and AB-8). Carboxylated MWCNTs showed the highest adsorption capacity. On the basis of static adsorption test, carboxylated MWCNTs were selected for kinetic and isotherm studies. Langmuir and pseudo-first-order models could describe the process well. According to the Langmuir model, the maximum monolayer adsorption amount of carboxylated MWCNTs was 84.6 mg/g. After purification on a chromatographic column packed with carboxylated MWCNTs, the content of H. polyrhizus peel betacyanins in the pigment product was 4.62%.

Synthesis of Dihydromyricetin Coated Multi-Walled Carbon Nanotubes (MWCNTs) and Antibacterial Activities

The weak antimicrobial property of multi-walled carbon nanotubes (MWCNTs) hampers their use as an antimicrobial material. In the report, Dihydromyricetin (DMY) coated multi-walled carbon nanotubes (MWCNTs-DMY) were prepared with poly(ethylene glycol) (PEG1000) as a linker and evaluated for inactivating pathogenic bacteria. UV-visible spectra, FT-IR, transmission electron microscopy (TEM), and thermal gravimetric analysis (TGA) were used to characterize the MWCNTs-DMY. It has been shown that PEG and DMY are covalently attached to MWCNTs with excellent stability. Vibrio parahaemolyticus was employed as the target bacterium. Comparing with the raw and the functionalized MWCNTs (r-MWCNTs and f-MWCNTs), MWCNTs-DMY exhibited stronger antibacterial ability. The MWCNTs-DMY composite showed up to 10-fold higher antimicrobial property than pristine MWCNTs. The deposited DMY was suggested to play an important role in the bactericidal action of MWCNTs-DMY. The results of this study demonstrated that MWCNTs-DMY composite can serve as an effective and economical antimicrobial material.

RUBBER NANOCOMPOSITES REINFORCED WITH SINGLE-WALL AND MULTIWALL CARBON NANOTUBES FOR INDUSTRIAL APPLICATIONS

ABSTRACT Nanofillers of type carbon nanotubes (CNTs) were investigated as reinforcing agents in silicone rubber matrix. Two types of CNT, namely, single-wall CNTs (SWCNTs) and multiwall CNTs (MWCNTs), were tested as reinforcing agents in rubber matrix. These CNTs were characterized with different purity, morphology, and sonication treatment (MWCNTs). Rubber nanocomposites were prepared by mixing room temperature vulcanized (RTV) silicone rubber with CNTs. At a filler loading of 3 phr, the modulus increased by 190% for specimens with MWCNTs and 150% for specimens filled with SWCNTs. Sonication was used to de-bundle the MWCNT aggregates into individual particles and to improve filler dispersion in the rubber matrix. The resistance of the MWCNTs was almost 750 times lower than that of the SWCNTs at 3 phr. The sonicated MWCNTs (2.2 kΩ) show lower electrical resistance than the pristine MWCNTs (3 kΩ) at 2 phr. These improvements could be useful for new devices such as flexible electrodes or actuators.

Hemostatic Effect of Aminated Multiwalled Carbon Nanotubes/Oxidized Regenerated Cellulose Nanocomposites

We have investigated the covalent conjugation of aminated multiwalled carbon nanotubes (MWCNTNH2)s with Oxidized Regenerated Cellulose (ORC) in order to enhance the hemostatic effect. The MWCNT-NH2s were prepared by functionalization of pristine MWCNTs (pMWCNTs) using amine groups. Neat ORC gauze and MWCNT-NH2s were reacted using glutamic acid as cross linking bridge. We investigated an amination of pMWCNTs as well as the dispersion of MWCNT-NH2s in the ORC gauze as matrix and their interfacial interactions by SEM and FT-IR. The results revealed that relatively strong interaction exists between aminated MWCNTs and the ORC macromolecules. The hydrophilicity test results in the significant increment of water uptake of MWCNT-NH2s/ORC composites with increasing the concentration of MWCNT-NH2s in composite. The in-vitro procoagulation test shows that the MWCNT-NH2s/ORC gauzes have significant procoagulant activity. The hemostatic evaluation of MWCNT-NH2s/ORC composites on rabbits shows that the aminated MWCNTs increase the rate of blood stopping and hence they decrease the blood loosing from injured sites. Hemostatic evaluation indicates that the MWCNT-NH2s/ORC gauze has a valuable hemostatic performance. The products of platelets release reaction, activated platelets glycoprotein and activated clotting enzymes were increased simultaneously. The mechanism of the hemostasis for MWCNT-NH2s/ORC gauze is discussed.