Unmodified Multi-walled Carbon Nanotubes Research Articles

Enhancing thermal energy storage in buildings with novel functionalised MWCNTs-enhanced phase change materials: Towards efficient and stable solutions

Phase change materials (PCMs) are a promising panacea to tackle the intermittency of renewable energy sources, but their thermal performance is limited by low thermal conductivity (TC). This pioneering work investigates the potential of organic PCM-enriched surface-modified and un-modified multi-walled carbon nanotubes (MWCNTs) for low-temperature thermal energy storage (TES) applications. The functionalised and un-functionalised MWCNTs enhanced PCM have demonstrated a TC enhancement of 158 % and 147 %, respectively, at 25 °C. However, the TC value of the unmodified MWCNTs-based PCM dropped by 52.5 % after 48 h at 25 °C, while that of the functionalised MWCNTs-based PCM remained stable. A DSC analysis of up to 200 thermal cycles confirmed that the surface-modified and un-modified MWCNTs had no major effect on the peak melting and cooling temperatures of the nano-enhanced PCMs although a minor decrease of 7.5 % and 7.7 % in the melting and crystallisation enthalpies, respectively, was noticed with the inclusion of functionalised MWCNTs. Moreover, functionalised MWCNTs incorporated PCMs have led to increases in specific heat capacity by 23 % with an optimal melting enthalpy value of 229.7 J/g. In addition, no super-cooling, no phase segregation, and a small phase change temperature were noticed with these nano-enhanced PCMs. Finally, no chemical interaction from nano-PCMs was seen in the FT-IR spectra with the incorporation of both functionalised and un-treated MWCNTs. It is evident that the functionalised MWCNT-based PCM has better thermal stability and it offers a promising alternative for improving thermal storage and management capabilities in buildings, contributing to a sustainable and energy-efficient building design.

Synthesis of highly grafted MWCNTs with epoxy silane to improve curing, thermal and mechanical performances of epoxy nanocomposites

Hydrophobic CNTs have weak interfacial interactions to epoxy matrix which causes their agglomeration and significant decline in the thermal/electrical/mechanical of epoxy nanocomposites. In this research, multi walled carbon nanotubes (MWCNTs) were acid treated at three different times to prepare nanotubes with the highest functional groups on surface. Thereafter, the best functionalized nanotubes were surface modified using 3-glycidyloxypropyltriethoxysilane (GPTES) at different concentrations to prepare GPTES@MWCNTs nanoparticles with the highest silane grafting content. The unmodified, acid treated and GPTES@MWCNTs were characterized carefully. The pure, functionalized and silane modified nanotubes were then applied to epoxy resin at 0.5 to 2 wt% and the mechanical, curing, thermo-mechanical and morphological features of the nanocomposites were assessed. It was declared that the unmodified MWCNTs (at 0.5 wt%) caused about 35 % decline in enthalpy of curing and 24 °C decrement in decomposition temperature of the epoxy polymer. However, the modified nanotubes enhanced the curing enthalpy and decomposition temperature of the polymer by 95 % and 31 °C compared to the unmodified nanocomposites, respectively. It was also found that the GPTES@MWCNT containing nanocomposite (at 0.5 wt%) showed enhanced tensile, flexural and compressive strengths by 69, 106 and 34 % compared to the pristine epoxy sample and 47, 73 and 25 % compared to the unmodified nanocomposite, respectively. It also caused 54 % and 13 °C improvement in the storage modulus and Tg compared to the unmodified nanocomposite.

Electrophoretic Deposition of Multi-Walled Carbon Nanotube Coatings on CoCrMo Alloy for Biomedical Applications.

Carbon nanotubes are a promising material for use in innovative biomedical solutions due to their unique chemical, mechanical, electrical, and magnetic properties. This work provides a method for the development of ultrasonically assisted electrophoretic deposition of multi-walled carbon nanotubes on a CoCrMo dental alloy. Functionalization of multi-walled carbon nanotubes was carried out by chemical oxidation in a mixture of nitric and sulfuric acids. The modified and unmodified multi-walled carbon nanotubes were anaphoretically deposited on the CoCrMo alloy in an aqueous solution. Chemical composition was studied by Fourier transform infrared spectroscopy. Surface morphology was examined by scanning electron microscopy. The mechanism and kinetics of the electrochemical corrosion of the obtained coatings in artificial saliva at 37 °C were determined using the open-circuit potential method, electrochemical impedance spectroscopy, and anodic polarization curves. The capacitive behavior and high corrosion resistance of the tested electrodes were revealed. It was found that the kinetics of electrochemical corrosion of the CoCrMo electrode significantly decreased in the presence of the functionalized multi-walled carbon nanotube coating. Electrophoretic deposition was shown to be an effective, low-cost, and fast method of producing nanotubes with controlled thickness, homogeneity, and packing density.

Supported ionic liquids for effective ruthenium olefin metathesis

Supported olefin metathesis catalysts have attracted considerable interest for over two decades, regarding their facile separation, reusability and decreased product contamination. In this study two strategies toward synthesis of heterogeneous ruthenium-catalyst were explored using supported ionic liquid phase (SILP) and supported ionic liquid-like phase (SILLP) with multi-walled carbon nanotubes (MWCNTs) as a support. The structure of ionic liquids used for the construction of catalysts was varied regarding length of alkyl chain and anion in terms of providing influence on catalytic activity and stability as well as reaction product contamination. The activity of prepared catalysts was tested in ring-closing metathesis (RCM). The Ru-based SILLP catalyst demonstrated high performance (conversions >90 % in five reaction cycles), compared to SILP and Ru@MWCNTs catalyst synthesized using unmodified MWCNTs, additionally decreasing the product contamination with Ru (14 ppm).

A low seepage threshold and super‐toughness of polybutylene succinate‐based composites with double percolation structure: Synergy of multi‐wall carbon nanotubes and polyvinyl butyral

AbstractTo obtain a super‐toughness and low seepage threshold for the conductivity of biodegradable soft polymer material, biodegradable polybutylene succinate (PBS)‐based composites with different contents of polyvinyl butyral (PVB) and multi‐wall carbon nanotubes (MWCNTs) were prepared by melt‐blending method. Synergy effects of different modified MWCNTs and PVB on the morphology, crystallization, and electrical and mechanical properties of MWCNTs/PVB/PBS composites were examined by Fourier Transform Infrared Spectroscopy (FTIR), scanning electron microscope (SEM), transmission electron microscopy (TEM), wide angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), polarizing microscope (POM), resistance tester, and universal testing machine. Compared with pure PBS, with increasing MWCNT content, the electrical conductivity of the MWCNTs/PBS composites showed an upward trend, and the percolation threshold for electrical conductivity of the MWCNTs/PBS composites reached 0.47%. The electrical conductivity of the PBS composite mixed with 1.0 wt% of surface modified MWCNTs slightly increased by one order of magnitude compared with that of pure PBS. By adding 20 wt% of the PVB and 1 wt% of the unmodified MWCNTs, the electrical conductivity of the MWCNTs/PVB/PBS composite increased by seven orders of magnitude compared with that of pure PBS. The percolation threshold for electrical conductivity of the MWCNTs/PVB/PBS composites decreased to 0.049% owing to the formation of double percolation structure. Furthermore, compared with pure PBS, when the PVB content was 20 wt%, and the MWCNTs was 1 wt%, the elongation at break and V‐notch impact strength of PBS‐based composite dramatically increased by approximately 300% and 12‐fold, respectively.

Influences of Unmodified and Carboxylated Carbon Nanotubes on Lipid Profiles in THP-1 Macrophages: A Lipidomics Study.

Since the possible roles of surface modifications in determining multi-walled carbon nanotube (MWCNT)-promoted endoplasmic reticulum (ER) stress-mediated lipid-laden macrophage foam cell formation are still in debate, we compared unmodified and carboxylated MWCNT-induced cytotoxicity, lipid profile changes, and expression of ER stress genes in THP-1 macrophages. Particularly, we focused on lipid profile changes by using lipidomics approaches. We found that unmodified and carboxylated MWCNTs significantly decreased cellular viability and appeared to damage the cellular membrane to a similar extent. Likewise, the results from Oil Red O staining showed that both types of MWCNTs slightly but significantly induced lipid accumulation. In keeping with Oil Red O staining results, lipidomics data showed that both types of MWCNTs up-regulated most of the lipid classes. Interestingly, almost all lipid classes were relatively higher in carboxylated MWCNT-exposed THP-1 macrophages compared with unmodified MWCNT-exposed cells, indicating that carboxylated MWCNTs more effectively changed lipid profiles. But in contrast to our expectation, none of the MWCNTs significantly induced the expression of ER stress genes. Even, compared with carboxylated MWCNTs, unmodified MWCNTs induced higher expression of lipid genes, including macrophage scavenger receptor 1 and fatty acid synthase. Combined, our results suggested that even though carboxylation did not significantly affect MWCNT-induced lipid accumulation, carboxylated MWCNTs were more potent to alter lipid profiles in THP-1 macrophages, indicating the need to use omics techniques to understand the exact nanotoxicological effects of MWCNTs. However, the differential effects of unmodified and carboxylated MWCNTs on lipid profiles might not be related with the induction of ER stress.

Carbon nanotubes, activated carbon and Oasis HLB as sorbents of passive samplers for extraction of selected micropollutants — Comparison of sampling rates and extraction efficiency

Currently, the POCIS (passive organic chemical integrative samplers) are promising tools for future regular monitoring of the aquatic environment. As the commercially available POCIS has its limitations, innovative solutions, and modifications of conventionally used samplers are sought. For this reason, this study compares the sampling rates (Rs) and extraction efficiencies (EE) of ketoprofen, naproxen, flurbiprofen, diclofenac, imipramine, desipramine, carbamazepine, methotrexate, bisphenol A, 17-β-estradiol, 17-α-ethinylestradiol, p-nitrophenol and 3,5-dichlorophenol by kinetic passive samplers containing various types of sorbents. Five types of multi-walled carbon nanotubes, activated carbon and Oasis HLB were used as receiving phases. Additionally, the influence of environmental factors such as: water salinity, water pH, dissolved humic acids and the real water matrix (treated and untreated sewage) on the Rs and EE values was investigated. The advantage of using unmodified multi-walled carbon nanotubes with an outer diameter < 8 nm in passive sampling devices (8-CNTs-PSD) compared to other used sorbents was demonstrated. Using 8-CNTs, sampling rates in the range of 0.037–0.132 L d−1 and extraction efficiencies in the range of 46–105% (excluding methotrexate) were obtained, which were independent of environmental factors. The collected results show that 8-CNTs-PSDs are the best choice for the future monitoring of the target analytes in the aquatic environment compared to the other tested samplers.

Polymer Composites Based on Polycarbonate (PC) Applied to Additive Manufacturing Using Melted and Extruded Manufacturing (MEM) Technology.

As part of the present work, polymer composites used in 3D printing technology, especially in Melted and Extruded Manufacturing (MEM) technology, were obtained. The influence of modified fillers such as alumina modified silica, quaternary ammonium bentonite, lignin/silicon dioxide hybrid filler and unmodified multiwalled carbon nanotubes on the properties of polycarbonate (PC) composites was investigated. In the first part of the work, the polymer and its composites containing 0.5–3 wt.% filler were used to obtain a filament using the proprietary technological line. The moldings for testing functional properties were obtained with the use of 3D printing and injection molding techniques. In the next part of the work, the rheological properties—mass flow rate (MFR) and mechanical properties—Rockwell hardness, Charpy impact strength and static tensile strength with Young’s modulus were examined. The structure of the obtained composites was also described and determined using scanning electron microscopy (SEM). The porosity, roughness and dimensional stability of samples obtained by 3D printing were also determined. On the other hand, the physicochemical properties were presented on the basis of the research results using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), wide angle X-ray scattering analysis (WAXS) and Fourier Transform infrared spectroscopy (FT-IR). Additionally, the electrical conductivity of the obtained composites was investigated. On the basis of the obtained results, it was found that both the amount and the type of filler significantly affected the functional properties of the composites tested in the study.

Carbon nanotubes interaction with amorphous and semi‐crystalline domains of polypropylene in melt‐mixed composites: Influence of multiwall carbon nanotubes agglomerate and their modifications

AbstractPolypropylene (PP) and multi‐walled carbon nanotubes (MWCNTs) composites were prepared by melt‐mixing with two types of MWCNTs of varying agglomerate size. Agglomerate dominated dispersion was observed in the PP matrix, wherein N‐MWCNTs exhibit a finer dispersion as compared to D‐MWCNTs. Further, MWCNTs were encapsulated by Li‐salt of 6‐amino caproic acid in various proportions along with PP‐g‐maleic anhydride in order to achieve finer MWCNTs dispersion. Thermogravimetric analysis exhibited an increase in onset of degradation temperature and higher residual weight (%) at 500 °C of PP with increased MWCNTs concentration, which suggests the formation of a thicker “interphase.” Glass transition temperature of the PP phase was increased monotonically as a function of unmodified MWCNTs concentration, which suggests a strong interfacial interaction between PP and MWCNTs. An extensive analysis was carried out with modified MWCNTs based PP composites. Moreover, MWCNTs act as a strong hetero‐nucleating agent manifesting in smaller spherulite size of PP, wherein bulk crystallization temperature is increased to ~130 °C of the PP phase at 5 wt% MWCNTs content. The influence of unmodified and modified MWCNTs on the interaction between the PP chains and MWCNTs in the amorphous phase as well as in the crystalline domains are analyzed in PP/MWCNTs composites.

Preparation of multi-walled carbon nanotubes/high density polyethylene composites with enhanced properties by using a master batch method

Multi-walled carbon nanotubes (MWCNTs)/high density polyethylene (HDPE) composites were prepared by a masterbatch method (mPEC) in which a commercial HDPE was blended with a MWCNTs/HDPE masterbatch obtained from in situ polymerization. Owing to the interfacial interaction, a 13 cm−1up-shift of the G band for the MWCNTs was observed in the Raman spectrum of the MWCNTs/HDPE masterbatch and the homogeneous distribution of MWCNTs in the mPEC was realized. Compared to the pure HDPE and the MWCNTs/HDPE composites prepared by a direct melt-blending method (dPEC), the mPEC had better electrical, mechanical and rheological properties, suggesting that the in situ polymerized HDPE covering on the MWCNTs surfaces played an important role in the reinforcing effects as an interfacial modifier. The tensile yield strength and the Young’s modulus of the mPEC containing 3 wt% MWCNTs (mPEC3), and the flexural strength and the flexural modulus of the mPEC containing 1 wt% MWCNTs were improved by 38.3%, 41.7%, 24.4%, and 42.9%, respectively, compared to those of the pure HDPE. For, the electrical resistivity of mPEC3 was decreased by about three orders of magnitude relative to that of the pure HDPE. The | η*|, G′, and G″ of the mPEC were obviously higher than those of pure HDPE. Moreover, the polyethylene-modified MWCNTs obtained from in situ polymerization could facilitate the crystallization of the HDPE macromolecular chains more effectively compared to the unmodified MWCNTs.

The Effect of Multiwalled Carbon Nanotubes on the Thermal Conductivity and Cellular Size of Polyurethane Foam

Polyurethane (PU) foam is known as the popular material for the applications in many fields of industry and life. To improve the mechanical and thermal properties of this material, in this research, PU foam was reinforced with aniline-modified multiwalled carbon nanotubes (MWCNTs). Fourier transform infrared FTIR spectrum of modified MWCNTs showed the aniline was grafted on the surface of MWCNTs through the appearance of –NH2 stretches. The effect of MWCNTs with and without modification on the density, porosity, compressive strength, and heat conductivity of PU/MWCNT foam nanocomposites was investigated. The dispersibility of MWCNTs in the PU matrix was enhanced after modification with aniline. Compressive strength of PU nanocomposite reached the highest value after adding 3 wt.% of modified MWCNTs into PU foam. Besides, the water uptake of PU nanocomposites using 3 wt.% of MWCNTs was decreased to 13.4% as compared to that using unmodified MWCNTs. The improvement in thermal conductivity of PU/aniline-modified MWCNT nanocomposite was observed due to the change in the cellular size of PU foam in the presence of MWCNTs as shown by SEM images.

Physical motion forms and properties of biopolymers based on nanotubes

In order to prepare nanotube-modified biomaterials from a certain amount of unmodified multiwalled carbon nanotubes (MWCNTs), the physical movement and properties of biopolymers based on nanotubes were studied. The tribophysical movement of biopolymers based on nanotubes was simulated by using the corresponding instruments and software packages. The experimental potential and tight-binding potential of the NON7 software package were used to simulate the physical movement of biopolymers based on nanotubes. X-ray diffraction, scanning electron microscopy and a DMA 242 C instrument were used to study the thermal transformation and perform dynamic mechanical thermal analysis of the modified biopolymers. The results show that the biopolymer based on MWCNTs vibrates only slightly in the process of molecular adhesion, and its structural characteristics have no obvious deformation. The biopolymers based on MWCNTs have good lubricity, while the crystallinity of the biopolymers based on MWCNTs is positively correlated with temperature. When the optimum ratio is exceeded, there is a significant negative correlation between the tensile strength and the number of nanotubes.

Influence of preparation methods on the activity of macro-structured ball-milled MWCNT catalysts in the ozonation of organic pollutants

A series of macro-structured catalysts consisting of nanostructured layers of mechanically processed multiwalled carbon nanotubes (MWCNT) coated onto cordierite monoliths were prepared using a novel methodology and assessed as catalysts in the ozonation of a model organic pollutant. The often used chemical vapor deposition method for formation of nanostructured layers of carbon materials is, by nature, incompatible with ball-milling or other methods for mechanical or mechano-chemical modification of MWCNT. The preparation method here described was designed to translate the positive effect observed in the performance of ball-milled MWCNT as ozonation catalysts when compared with unmodified MWCNT to macro-structured catalytic systems. The performance of such macro-structured catalysts in the ozonation of organic pollutants is reported and analyzed for the first time. The effect of the preparation methodology, which includes physical functionalization of the MWCNT with a non-ionic surfactant (Triton X-100®), in the performance of the powder catalysts was evaluated. It was found that, for the coated nanostructured layers, the decrease in the expected activity is related to the packing of the materials. Nevertheless, the catalytic nanostructured coated layers were found to compare favorably with a reference sample. Thus, the beneficial effect of ball-milling MWCNT is still retained upon coating, even with a decrease in the intrinsic activity of the powder material. The increase in MWCNT mass in the coated samples introduces diffusion limitations, suggesting that creating a macroporous system in the MWCNT layers might be desirable. The introduction of oxygen-containing surface functionalities improved the long-term stability of the nanostructured catalytic layers.

Dispersion and Localization Behavior of Modified MWCNTs in Immiscible Polymer Blends of Polystyrene and Polybutadiene and in Corresponding Nanostructured Block Copolymers

The influence of carbon nanotube (CNT) modification on the dispersion and localization behavior of the CNTs in immiscible blends of polystyrene (PS) and polybutadiene (PB), and in the nanostructured morphology of a star-shaped styrene-butadiene based block copolymer (BCP), was studied to form a basis for the development of functional materials with defined electrical property profiles. Unmodified multi-walled CNTs (MWCNTs) were dispersed in PS, PB and PS/PB blends by solution mixing. Additionally, MWCNTs were functionalized with n-octadecylamine and monoamino-terminated polystyrene to increase the compatibility between the homopolymers and the nanofiller. The MWCNT dispersion and the blend morphology formation were studied using transmission light microscopy and scanning electron microscopy. The MWCNT dispersion could be significantly improved by the modification of the MWCNTs. All MWCNT types were found to preferably localize in the PS phase of the PS/PB blend. However, only blends containing unmodified MWCNTs were electrically conductive. Similar effects were found in BCP/MWCNT composites. The BCP was already electrically conductive with a filler content of 0.1 wt % of unmodified MWCNTs. The stress–strain behavior of the BCP was slightly influenced by MWCNT addition and CNT modification. The dispersability of MWCNTs was significantly improved by CNT functionalization, which indicates a strong polymer-filler interaction.

The effect of debris on the adsorption and electron-transfer capacity at the interface of oxidized carbon nanotubes

The functionalization of carbon nanotubes has become a common approach to modify the surface properties of these materials for different applications such as in the formulation of polymeric composites, as electrodes of electrochemical devices and, mainly, in the removal of organic contaminants. On the other hand, these functionalization procedures generates oxidized polyaromatic fragments known as debris, which impacts the material properties. Unfortunately, most papers published in the literature disregard these effects or do not cite experimental procedures for debris removal, which are strongly adsorbed onto the surface of nanotubes. In this study, we evaluated the effects of debris – generated on multiwalled carbon nanotubes (MWCNT) subjected to acid oxidation – on the capacities, kinetics and adsorption mechanism. For this, three different MWCNTs were employed: a pristine unmodified MWCNT; an oxidized MWCNT (obtained by common procedure and without the removal of debris); and an oxidized MWCNT without debris (obtained after reflux in alkaline medium). In addition, methylene blue (MB) has been used as model adsorbate in these experiments. As a second goal, the effects of debris on MB faradic electron transfer at the MWCNT interface were also investigated using cyclic voltammetry and cyclic chronopotenciometry techniques. Finally, we have shown that debris impacts the adsorption capacity, kinetics and limits the performance of MWCNTs as electrodes.

Electrochemical Reaction Assisted 2D π-Stacking of Benzene on a MWCNT Surface and its Unique Redox and Electrocatalytic Properties.

Turning the π-structure and electronic properties of carbon nanotubes (CNTs) is a cutting-edge research topic in interdisciplinary areas of material chemistry. In general, chemical functionalization of CNT has been adopted for this purpose, which has resulted in a few monolayer thickness increment of CNT diameter size. Herein, we report an interesting observation of >10-fold increment in the apparent diameter of multiwalled carbon nanotubes (MWCNTs) brought about by a process of self-assembly of the BZ moiety on MWCNT, which is formed by electrochemical oxidation of a surface-adsorbed benzene-water cluster, {BZ-nH2O}. From physicochemical characterizations by transmission electron microscopy (TEM) and Raman and IR spectroscopic techniques and electrochemical characterizations by several radical scavenger species, it has been revealed that benzene radical moieties as a series of π-stacked layers ([BZ]-π-stack) were self-assembled on the MWCNT surface. A possible mechanism for their formation was proposed to be electrochemical oxidation of H2O from the MWCNT@{BZ-nH2O}ads layer to oxygen gas via hydroxyl radical formation and benzene cationic radical species at 1.2 V vs Ag/AgCl followed by its self-assembly into a unique MWCNT@[BZ]-π-stack network. The scanning electrochemical microscopic (SECM) technique was used to identify the in situ •OH radical formation. The electrochemical studies of a glassy-carbon-modified MWCNT@[BZ]-π-stack system showed a well-defined and highly symmetrical redox peak at an equilibrium potential E1/2 = 0.2 V vs Ag/AgCl (pH 2 HCl/KCl), with a peak-to-peak potential separation of 0 V, highlighting the ideal-surface-confined electron-transfer nature of the redox couple. Furthermore, enhanced electrical conductivity over the unmodified MWCNT was observed when testing the surface-sensitive redox couple Fe3+/Fe2+ with the modified electrode. This new redox material showed a specific electrocatalytic reduction of hydrogen peroxide at neutral pH (pH 7 phosphate buffer solution) unlike the quinone and other organic redox mediators, which show the reduction signal only in the presence of horseradish peroxidase enzyme.

CO oxidation and the inhibition effects of carboxyl-modification and copper clusters on multi-walled carbon nanotubes

An inhibition of CO oxidation on catalytically active pristine multi-walled carbon nanotubes (MWCNT) in the presence of selected pollutant constituents in flue gas streams was studied. We simulated an interaction between the active MWCNT and the contaminants in CO oxidation atmosphere of: (i) an acidic wet flue gas environment modelled by using MWCNT grafted with carboxyl (COOH) groups; and (ii) a polluted environment formed by trace metal copper particles and other contaminant constituents (e.g. PAHs, VOCs and P) by using a copper cluster of chemical formulae [(PPh3)CuH]6·0.75THF as a model pollutant, doped on the MWCNT. The pristine, unmodified MWCNT were catalytically active from ∼150 °C, whilst the carboxyl-modified MWCNT behaved as an adsorbent of CO molecules without converting them into CO2. The copper cluster was found to have formed CuCO3 during the CO oxidation reaction at temperatures below 330 °C but decomposed above 400 °C to release CO2 product.

A novel modification of carbon nanotubes for improving the electrical and mechanical properties of polyethylene composites

A simple and effective method, modifying MWCNTs with cationic waterborne epoxy emulsion, was developed to improve the dispersion of multi-walled carbon nanotubes (MWCNTs) and enhance the interfacial interaction between matrix and the filler. The dispersion of mMWCNTs in polymer was characterized by Scanning Electron Microscope and Transmission Electron Microscope. Rheological analysis revealed that better mMWCNTs network in PE matrix was developed at a lower content of MWCNTs as compared with that of unmodified MWCNTs, which resulting in a lower percolation threshold and improved electrical conductivity of mMWCNTs/PE. Moreover, the PE nanocomposite with uniformly dispersed mMWCNTs has better mechanical properties than those of MWCNTs/PE.

CE with multi-walled carbon nanotubes (MWCNTs). Part I. Functionalized and SDS coated MWCNTs as pseudo-stationary phases in nanoparticle EKC – Studies on retention energetics

In this study, multi-walled carbon nanotubes (MWCNTs) in either unmodified, hydroxylated (MWCNT-OH), carboxylated (MWCNT-COOH) or sulfonated (MWCNT-SO3H) forms were incorporated into the running electrolytes in capillary electrophoresis (CE) to play the role of pseudo-stationary phases (PSPs) and perform nanoparticle electrokinetic capillary chromatography (NPEKC). MWCNT-COOH and MWCNT-SO3H were derived from MWCNTs via their treatment with concentrated strong acids. These functionalized MWCNTs were characterized by Raman and FTIR spectroscopies to demonstrate their covalent functionalization. The study of MWCNT-SO3H and MWCNT-OH as PSPs were introduced in this research report for the first time in NPEKC. The results obtained with functionalized MWCNTs were compared to those obtained using unmodified MWCNTs for better understanding the electrophoretic behavior of these functionalized MWCNTs. While only MWCNT-COOH allowed the separation of some nucleic acid bases and nucleosides, neutral solutes such as alkylbenzenes (ABs), phenyl alkyl alcohols (PAAs) and aniline derivatives in neutral forms (i.e., at basic pH) were not resolved in the presence of neither MWCNT-COOH nor MWCNT-SO3H in the running electrolytes, indicating that these functionalized MWCNTs do not have enough surface charge density to function as effective PSPs in NPEKC. This necessitated the coating of the functionalized MWCNTs under investigation with sodium dodecyl sulfate (SDS) to bring about the separation of neutral solutes by NPEKC. The SDS coated MWCNTs whether unmodified or functionalized were characterized with two homologous series namely ABs and PAAs in order to evaluate their relative retention energetics under the same electrolyte composition. The results showed that the systems pairs SDS-MWCNT-COOH/SDS-MWCNTs and SDS-MWCNT-OH/SDS-MWCNTs were homoenergetics (i.e., same energetics) while the system pair SDS-MWCNT-SO3H/SDS-MWCNTs was homeoenergetics (i.e., similar energetics). On the other hand, all the systems pairs SDS coated MWCNTs/SDS were homeoenergetics. Homoenergetics means that the solute retention has an identical physico-chemical basis and the differences observed in the magnitude of solute retention on the various PSPs are attributed to differences in the nonpolar phase ratios of the PSPs under otherwise the same electrolyte composition. Conversely, homeoenergetics signifies that the solute retention has a similar physico-chemical basis in the PSPs systems under investigation, which also differ in their phase ratios.

Synthesis and characterization of maghemite nanocrystals decorated multi-wall carbon nanotubes for methylene blue dye removal

Maghemite nanocrystals decorated multi-wall carbon nanotubes (MWCNTs) magnetic and electronic properties enhanced nanocomposites are synthesized using infrared (IR) irradiation and diazonium chemistry. The present method is simple and very effective as it overcomes the problem faced in the past decade for the decoration of carbon nanotubes (CNTs) with maghemite nanoparticles. The resulting materials are characterized using different techniques such as XPS, TEM, PXRD, STEM, EDX, HRTEM, and UV–Vis spectrophotometry. Firstly, sodium hydroxide treatment leads to the purification of MWCNTs (p-MWCNTs). The p-MWCNTs functionalization with tricarboxylic aryl diazonium salts generated in situ (p-MWCNTs-D3) followed by its impregnation with iron (II) ethylenediammonium sulfate (p-MWCNTs-D3/IEDS) utilizing IR radiation is the key step in homogeneously impregnating functionalized MWCNTs. Calcination of p-MWCNTs-D3/IEDS at 500 °C under argon atmosphere results in a controlled decoration of p-MWCNTs with maghemite nanocrystals (p-MWCNTs/MC). A homogeneous distribution of maghemite nanocrystals (cubic crystal system) on MWCNTs is observed in the size range of 1–6 nm, with a Gaussian mean diameter of ∼ 1.9 nm. To illustrate the applications of p-MWCNTs/MC for the decontamination of pollutants in water, methylene blue (MB), a model pollutant, is used and the performances are compared with the unmodified MWCNTs, Fe2O3 nanopowder and a mixture of MWCNTs and Fe2O3 nanopowder (1:1). Successful integration of properties of both constituents (MWCNTs and maghemite nanocrystals) in the new nanocomposite with superior characteristics is proved. The present method is valid for large-scale preparations which also opens very interesting perspectives in nanotechnology.