Adsorption Of Multi-walled Carbon Nanotubes Research Articles

Fabrication and Evaluation of Multiwalled Carbon Nanotube-Containing Bijels and Bijels-Derived Porous Nanocomposites

Structures having continuous porous networks are of great interest for applications in areas such as separation, energy storage, and tissue engineering. Bicontinuous interfacially jammed emulsion gels ("bijels") have been actively investigated as templates for fabricating useful structures for such applications. However, the fabrication of bijels-templated porous nanocomposites incorporated with reinforcing or functional nanoparticles (or nanofibers) to provide specific, targeted functions is still a challenge, stemming from the difficulties of fabricating functional nanoparticle-containing bijels. In this study, bijels-derived porous nanocomposites incorporated with multiwalled carbon nanotubes (MWCNTs), which possessed interconnected channels inside the structures, were made via a facile phase inversion technique for bijels fabrication. For the composite manufacture, in the first step of bijels fabrication, MWCNT adsorption into the oil phase of bijels was observed. It was revealed that MWCNTs were physically absorbed into the oil-rich phase without disrupting the bicontinuous structure of bijels. The successful fabrication of non-crosslinked and crosslinked porous structures containing MWCNTs was evidenced through imaging by confocal laser scanning microscopy and scanning electron microscopy, respectively. For potential controlled release applications, an anticancer drug, doxorubicin hydrochloride (DOX), was incorporated into bijels-derived structures and nanocomposites. The in vitro DOX release profiles from drug delivery systems based on bijels-derived MWCNT-containing nanocomposites suggested that the photothermal effect of MWCNTs initiated by near-infrared irradiation could modulate the drug release behavior. Overall, this study has developed a facile approach to fabricate bijels-templated bicontinuous porous structures incorporated with functional nanoparticles (or nanofibers) and opened an avenue for making MWCNT-containing porous nanocomposites for controlled drug release applications.

A composite material with controllable electromagnetic characteristics for the terahertz frequency range

In this study, a new method is proposed for producing polymer composites via the adsorption of multiwalled carbon nanotubes (MWCNTs) on the surface of polystyrene spheres (PS) to provide a cellular distribution of MWCNTs in the composite. The method makes it possible to control the cell size down to the submicron level and the conductivity of the composite in a wide range. The effect of the MWCNT concentration on the surface of PS on the structure of the resulting composites and their electrophysical properties are studied in the frequency range of 115 GHz–1.4 THz. The percolation nature of the composite conductivity was established. It was shown that the obtained composite is a regularly chaotic medium, and its regularity scale corresponds to the sizes of the PS. MWCNTs on the PS surface form two subsystems: the first is a pseudo-regular subsystem on the edges of cuboid-like PS, while the second subsystem consists of chaotically scattered MWCNTs with unclosed ends on the faces of PS. The first subsystem belongs to the regular part of the structure and mainly determines the properties of the medium at frequencies above 500 GHz. The second subsystem of nanotubes is characterized by a small electrodynamic scale comparable with the size of one PS cell and determines the effective properties of the composites at frequencies below 500 GHz.

Comparing the morphologies and adsorption behavior of electrospun polystyrene composite fibers with 0D fullerenes, 1D multiwalled carbon nanotubes and 2D graphene oxides

Nanoscale adsorbents with unique engineered morphologies give them properties that can be transformative for water treatment. Unlike bulk-scale and top-down sorbents such as activated carbon, bottom-up nanoscale adsorbents dispersed into water are difficult to recover from water unless enmeshed in macro-scale architectures. Electrospinning is a facile and scalable method of immobilizing nanomaterials (NM) including fullerenes (C60), multi-walled carbon nanotubes (MWCNT) and graphene oxide (GO) into non-woven, flexible polymeric fabric architectures. In this study, electrospinning was used to compare three types of NM-polystyrene (PS) composites. The integration of NMs into electrospun fibers created pores, increased fiber diameter, decreased polymer beading and maintained fibers’ surface pore size distribution for all composites. The scanning electron microscopy inspection indicated that GO in electrospun PS coated the surface of the fibers. This was attributed to the 2D sheet like structure of GO that was pushed outside by the evaporating organic solvent during electrospinning. Phenanthrene adsorption experiments indicated that GO preserved adsorptive properties when incorporated into PS whereas MWCNT and C60 did not. The restricted adsorption of MWCNT and C60 was caused by the concealing of NMs within the PS filaments. On the other hand, partial exposure of GO surfaces enabled adsorption of phenanthrene by GO. Despite the similarities in pore formation and increased diameter when NMs are incorporated into electrospun PS, the type, and morphological properties of the NMs played a critical role on their application potential as an adsorbent for water treatment. Further advances in fiber synthesis are needed such as higher NM loadings in fibers, partial exposure without compromising the composite integrity and continuous pores that allow pollutant access to NM surfaces where adsorption occurs.

Thermodynamics of multi-walled carbon nanotube biofunctionalization using nisin: The effect of peptide structure

A detailed adsorption thermodynamic study of two nisin variants (nisA and nisZ) on multi-walled carbon nanotubes (MWCNT) was conducted, and the antimicrobial properties of biofunctionalized MWCNT were evaluated. The MWCNT adsorption capacity for peptides (qp) increased with pH increase, with greater values for nisZ (qp up to 250 mg g−1) than for nisA (qp up to 180 mg g−1) for all studied conditions. Zeta potential measurements (ζ) showed that the electrostatic repulsion between the MWCNT-peptide complexes determined the dispersion features that were stable at pH 2.0 and 3.0, with ζ reaching 45.0 mV at the lowest pH. Despite the similar ζ values for both peptides, slightly greater stabilization of MWCNT dispersions was exhibited in presence of nisZ at pH 3. At pH 4 and 5, peptide adsorption was not able to promote MWCNT dispersibility. Isothermal titration calorimetry revealed that the adsorption process was driven by enthalpy for both peptides, as the adsorption enthalpy changes (ΔHads) were less negative than −99.7 kJ mol−1. Despite the large dependence of ΔHads on the pH andqp values, indicating the important role of electrostatic interactions on the adsorption process, a change in only one amino acid residue in the nisin structure promoted intense changes in the adsorption thermodynamic parameters. We have suggested that the more hydrophobic character of nisZ at the lower pH values caused this peptide to interact with the MWCNT surface through its two domains. Interesting, the antimicrobial properties of both peptides were not damaged, and the functionalized MWCNT showed antibacterial activity against the indicator micro-organism Lactococcus lactis in the agar diffusion and solution assays.

Graphene oxide-assisted dispersion of multi-walled carbon nanotubes in biodegradable Poly(ε-caprolactone) for mechanical and electrically conductive enhancement

Multi-walled carbon nanotubes (MWCNTs) are known for improving the mechanical and electrical properties of polymers. The dispersion state of MWCNTs in the polymer matrix is critical for the fabrication of high-performance nanocomposites. Here, we show a simple strategy for tuning the dispersion state of MWCNTs in poly(ε-caprolactone) (PCL) via graphene oxide (GO) nanosheets and to further balance electrical and mechanical properties of the PCL/MWCNT nanocomposites. The strong π-π interactions between MWCNTs and GO nanosheets lead to easy adsorption of MWCNTs on GO nanosheet surfaces to form GO/MWCNT hybrids that retard the aggregation of MWCNTs in PCL. Furthermore, the GO/MWCNT ratio could also affect the dispersion of GO/MWCNT hybrids in PCL. Three different dispersion states of MWCNTs were found in the PCL matrix, i.e. PCL/MWCNT, PCL/GO/MWCNT (1/4) and PCL/GO/MWCNT (2/1) nanocomposites that represented severe, low and almost no aggregation of MWCNTs, respectively. The GO/MWCNT hybrids with a 2/1 ratio showed better dispersion in PCL matrix than the hybrids with a 1/4 ratio and pristine MWCNTs. The PCL/GO/MWCNT nanocomposites with almost no aggregation of GO/MWCNT (2/1) hybrids exhibited the highest tensile strength and elongation at break in comparison to the PCL/GO/MWCNT (1/4) nanocomposites and PCL/MWCNT nanocomposites. However, the best electrical conductivity was achieved in the PCL/GO/MWCNT (1/4) nanocomposites due to the low aggregation of MWCNTs.

A multi-walled carbon nanotube electrode based on porous Graphite-RuO2 in electrochemical filter for pyrrole degradation

A novel electrochemical filter has been prepared for the effective adsorption and electrochemical oxidation of aqueous organic pollutants. The adsorptive electrode utilized in the electrochemical filter was a porous Graphite-RuO2 electrode decorated with multi-walled carbon nanotubes (MWCNTs) adsorption layer, which was prepared by sol–gel coating, thermal decomposition, and vacuum filtration synthesis. The morphology and composition of adsorptive electrode characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) revealed a uniform distribution of RuO2 active coating and MWCNTs adsorption layer. Electrochemical measurements indicated that the adsorptive electrode possessed a favorable oxygen evolution potential (OEP) of 1.42V and inner voltammetric charge 170.05mC·cm−2, which were higher than that of non-MWCNTs electrode. Furthermore, the mass transfer of adsorptive electrode was enhanced as high as 4.6-fold in the electrochemical filter. The optimal operation parameters obtained was 3mA·cm−2 and 7g·L−1 Na2SO4. Under this condition, the electrochemical filter can remove>97% of pyrrole and>75% of total organic carbon. The pyrrole oxidation mechanism of electrochemical filter was also investigated, revealed three dominant reaction stages: adsorption (≤0.3V), direct oxidation (0.3–1.2V) and indirect oxidation (>1.2V). In general, the high electrochemical performance of Graphite-RuO2-MWCNTs filter on pyrrole removal resulted from the enhanced mass transfer, which attributed to the synergistic effect of adsorption from MWCNTs, electrochemical oxidation and convection by filtration.

Electrochemical reduction of nalidixic acid at glassy carbon electrode modified with multi-walled carbon nanotubes

The aqueous phase electrochemical degradation of nalidixic acid (NAL) is studied in this work, using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) as instrumental techniques. The promotional effect of multi-walled carbon nanotubes (MWCNT) on the performance of glassy carbon electrodes is demonstrated, being observed that these materials catalyze the NAL reduction. The effect of surface functional groups on MWCNT −MWCNT-COOH and MWCNT-NH2–was also studied. The modification of glassy carbon electrode (GCE) with MWCNT leads to an improved performance for NAL reduction following the order of MWCNT>MWCNT-NH2>MWCNT-COOH. The best behavior at MWCNT-GCE is mainly due to both the increased electrode active area and the enhanced MWCNT adsorption properties.The NAL degradation was carried out under optimal conditions (pH=5.0, deposition time=20s and volume of MWCNT=10μL) using MWCNT-GCE obtaining an irreversible reduction of NAL to less toxic products. Paramaters as the number of DPV cycles and the volume/area (V/A) ratio were optimized for maximize pollutant degradation. It was observed that after 15 DPV scans and V/A=8, a complete reduction was obtained, obtaining two sub-products identified by liquid chromatography-mass spectrometry (LC–MS).

Enhancing Adsorption of Multi-Walled Carbon Nanotubes for Dye Removal

Enhancing Adsorption of Multi-Walled Carbon Nanotubes for Dye Removal

Using Titanium Dioxide/carbon Nanotubes To Remove Humic Acids In Water

This study used multi-walled carbon nanotubes (MWCNTs), TiO2 and their mixture (TiO2/CNT) to remove humic acids (HA) in water. The thermodynamic parameters with respect to the adsorption of MWCNTs, including free energy of adsorption (ΔG 0 ), enthalpy (ΔH 0 ), and entropy (ΔS 0 ) changes, are further calculated in the study. The ΔH 0 data showed the adsorption of HA onto MWCNTs is an endothermic physisorption. The ΔG 0 data indicates the adsorption of HA onto MWCNTs was spontaneous and thermodynamically favorable. Photocatalytic experiments showed 60 mgl -1 of HAs were completely degraded and mineralized as CO2 after 5 h UV irradiation by 0.8 gl -1 of TiO2, indicating the efficiency of TiO2 for the removal of HA is better than CNTs. The experiments of TiO2/CNT indicated the photocatalytic efficiency of TiO2 in the presence of CNTs was not improved, even worse than TiO2 alone. However, the photocatalytic efficiency of TiO2/CNT mixture became better than TiO2 alone due to the supply of oxygen by aeration, ascribing to the reason that the provided oxygen might be adsorbed on the

DNA-Assisted Solubilization of Carbon Nanotubes and Construction of DNA-MWCNT Cross-Linked Hybrid Hydrogels.

A simple method for preparation of DNA-carbon nanotubes hybrid hydrogel based on a two-step procedure including: (i) solubilization of multi-walled carbon nanotubes (MWCNT) in aqueous solution of DNA, and (ii) chemical cross-linking between solubilized MWCNT via adsorbed DNA and free DNA by ethylene glycol diglycidyl ether is reported. We show that there exists a critical concentration of MWCNT below which a homogeneous dispersion of MWCNT in hybrid hydrogel can be achieved, while at higher concentrations of MWCNT the aggregation of MWCNT inside hydrogel occurs. The strengthening effect of carbon nanotube in the process of hydrogel shrinking in solutions with high salt concentration was demonstrated and significant passivation of MWCNT adsorption properties towards low-molecular-weight aromatic binders due to DNA adsorption on MWCNT surface was revealed.

Carbon nanoparticles pillared multi-walled carbon nanotubes for adsorption of 1-naphthol: Thermodynamics, kinetics and isotherms

Abstract Carbon nanotubes (CNTs) have emerged as efficient adsorbents since their first discovery in 1991. However, due to their huge specific surface areas and strong van der Waals binding energies, CNTs are prone to aggregate. Therefore, controlled dispersion of CNTs in solution or composite matrix remains a challenge so far. Herein, novel pillared CNT composites—2c-G-MWCNTs, with increased specific surface area and less agglomeration, were prepared and applied as efficient adsorbents for removal of 1-naphthol from aqueous solution. The maximum adsorption capacity for 1-naphthol onto 2c-G-MWCNTs is 37.74 mg/g at 25 °C, which is about 2.5 times as much as that onto pristine MWCNTs. And the influences of preparation methods, carbon sources, calcination temperature, and the amount of carbonized glucose particles were examined. The MWCNTs-based adsorbents were characterized by scanning electron microscopy (SEM) and Fourier transform-infrared (FT-IR) spectroscopy. The adsorption thermodynamics, adsorption kinetics and adsorption isotherms of these CNT materials were investigated systematically.

Self-assembled photonic-plasmonic nanotweezers for directed self-assembly of hybrid nanostructures

We demonstrate a technique for assembling photonic-plasmonic nanotweezers by optically driving the adsorption of multi-walled carbon nanotubes onto a silicon waveguide. The nanotweezers are then used to trap and release individual polystyrene beads. Additionally, we demonstrate the ability to localize the deposition of metallic nanoparticles to the intersection points between multiple carbon nanotubes with the goal of forming more complex hybrid nanostructures.

Electrochemically enhanced adsorption of nonylphenol on carbon nanotubes: Kinetics and isotherms study

Removal of nonylphenol (NP) from aqueous solution has attracted widely attention due to its aquatic toxicity and potential to disrupt the endocrine system. In an effort to develop the effective and environment-friendly treatment method for NP, adsorption of 4-n-nonylphenol (4-NP) on multi-walled carbon nanotubes (MWCNTs) under electrochemical assistance was studied. The adsorption kinetics and isotherms were investigated at different polarization potentials and compared with those of open circuit (OC) and powder MWCNTs adsorption. The adsorption kinetics was simulated by the model including pseudo-first-order model, pseudo-second-order model and intraparticle diffusion model. The isotherm was simulated with Langmuir model and Freudlich model, respectively. Experimental results indicated that 4-NP is able to be efficiently removed at a potential of −0.6V. Comparing with that of powder MWCNTs adsorption, the initial adsorption rate υ0 at −0.6V increased 7.9-fold according to pseudo-second-order model and the maximum adsorption capacity qm improved 1.7-fold according to Langmuir model. The improved adsorption effect at negative potential was ascribed to enhanced π–π electron-donor–acceptor (EDA) interaction between 4-NP and MWCNTs under electrochemical assistance.

Tuning the adsorption capability of multi-walled carbon nanotubes to polar and non-polar organic compounds by surface oxidation

This current study addresses the inter-relationship between the surface oxidation of multi-walled carbon nanotubes (MWCNTs) and the polarity of organic solutes and its effect on the adsorption reaction between them. Results indicated that pristine MWCNTs exhibited a stronger affinity toward non-polar compounds such as phenanthrene compared to that of ozone-oxidized MWCNTs (O-MWCNTs). On the contrary, the adsorption of polar compounds, such as phenol, on MWCNTs occurred to a much less extent compared to that on O-MWCNTs as indicated by a smaller Freundlich affinity coefficient. The adsorption capability of various organic compounds on MWCNTs could be tuned. It was found that the stability of MWCNTs did not control the adsorption capacity. The solution chemistry only had minimal influence on the adsorption of phenanthrene on MWCNTs. Results demonstrated the importance of surface chemistry and the properties of adsorbates on the adsorption process. Overlooking either aspect might lead to a misinterpretation of the adsorption reaction. Understanding the interactive nature of MWCNTs adsorption provides information on the preparation of green and “smart” adsorbents according to the nature of adsorbates.

Influence of polar functional groups introduced by COOH+ implantation on cell growth and anticoagulation of MWCNTs.

Though multiwalled carbon nanotubes (MWCNTs) have shown great promise in biomedical applications, our understanding about their biocompatibility is limited. Here, COOH+ implantation was performed for MWCNTs in order to gain insight into how COOH+ implantation affected the cell growth and blood adsorption of MWCNTs. The extensive measurements demonstrated that carboxyl groups were successfully introduced onto the surface of MWCNTs, inducing more hydrophilicity compared with pristine MWCNTs. Two kinds of cells, mouse fibroblast cells (L929) and human endothelial cells (EAhy926), were used to assess the cell growth of MWCNTs before and after COOH+ implantation. COOH+ implantation led to a significant improvement in cell proliferation and adhesion, indicating superior cell adhesion over pristine MWCNTs. As the ion dose increased, the platelet adhesion assays of COOH+ implantation-MWCNTs (COOH/MWCNTs) displayed a significant enhancement, which implied COOH/MWCNTs could be used as anticoagulant and nonhemolytic material. The results were helpful to design modified surfaces of nanomaterials for improving their biocompatibility.

Removal of heavy metal ions from aqueous solutions with multi-walled carbon nanotubes: Kinetic and thermodynamic studies

Multi-walled carbon nanotubes were used successfully for the removal of Copper(II), Lead(II), Cadmium(II), and Zinc(II) from aqueous solution. The results showed that the % adsorption increased by raising the solution temperature due to the endothermic nature of the adsorption process. The kinetics of Cadmium(II), Lead(II), Copper(II), and Zinc(II) adsorption on Multi-walled carbon nanotubes were analyzed using the fraction power function model, Lagergren pseudo-first-order, pseudo-second-order, and Elovich models, and the results showed that the adsorption of heavy metal ions was a pseudo-second-order process, and the adsorption capacity increased with increasing solution temperature. The binding of the metal ions by the carbon nanotubes was evaluated from the adsorption capacities and was found to follow the following order: Copper(II) > Lead(II) > Zinc(II) > Cadmium(II). The thermodynamics parameters were calculated, and the results showed that the values of the free energies were negative for all metals ions, which indicated the spontaneity of the adsorption process, and this spontaneity increased by raising the solution temperature. The change in entropy values were positives, indicating the increase in randomness due to the physical adsorption of heavy metal ions from the aqueous solution to the carbon nanotubes’ surface. Although the enthalpy values were positive for all metal ions, the free energies were negative, and the adsorption was spontaneous, which indicates that the heavy metal adsorption of Multi-walled carbon nanotubes was an entropy-driving process.

Application of polyaniline and multiwalled carbon nanotube magnetic composites for removal of Pb(II)

Aniline molecules were polymerized and formed polyaniline (PANI) on multiwalled carbon nanotubes (MWCNTs) by using plasma induced polymerization technique. The PANI modified MWCNTs (PANI/MWCNTs) composites were characterized by using ultraviolet–visible spectrophotometry, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis–differential thermal analysis (TGA–DTA), field-emission scanning electron microscopy (FE-SEM), and vibrating sample magnetometer (VSM). The results indicated that the PANI/MWCNTs magnetic composites were synthesized. The application of PANI/MWCNTs magnetic composites for the removal of Pb(II) from aqueous solutions was investigated under ambient conditions. The modified PANI on MWCNT surfaces contributed to the enhancement of MWCNT adsorption capacity because the amine and imine functional groups of PANI have strong affinity with Pb(II) ions. PANI/MWCNTs magnetic composites can be separated and recovered from aqueous solution by simple magnetic separation. The results show that PANI/MWCNTs magnetic composites are promising magnetic materials for the preconcentration and separation of heavy metal contaminants from large volumes of aqueous solutions in environmental pollution cleanup.

Preparation of graphene/multi-walled carbon nanotube hybrid and its use as photoanodes of dye-sensitized solar cells

This study employed a solution-based method to prepare a 3-D hybrid material comprising graphene and acid-treated multi-walled carbon nanotubes (MWCNTs). The adsorption of MWCNTs on graphene reduces the π– π interaction between graphene sheets resulting from steric hindrance, providing a subsequent reduction in aggregation. Optimal proportions of MWCNTs to graphene (2:1) enabled the even distribution of individual MWCNTs deposited on the surface of the graphene. The hybrid 3-D material was incorporated within a TiO 2 matrix and used as a working electrode in dye-sensitized solar cells (DSSCs). The hybrid material provides a number of advantages over electrodes formed of either MWCNTs or graphene alone, including a greater degree of dye adsorption and lower levels of charge recombination. In this study, DSSCs incorporating 3-D structured hybrid materials demonstrated a conversion efficiency of 6.11%, which is 31% higher than that of conventional TiO 2-based devices.

Multi-walled Carbon Nanotubes Penetrate into Plant Cells and Affect the Growth of Onobrychis arenaria Seedlings

Engineered nanoparticles (ENPs) are now being used in many sectors of industry; however, the impact of ENPs on the environment still requires further study, since their use, recycling, and accidental spill can result in the accumulation of nanoparticles in the atmosphere, soil, and water. Plants are an integral part of ecosystems; hence their interaction with ENPs is inevitable. It is important to understand the consequences of this interaction and assess its potential effects. The present research is focused on studying the effects of the industrial material Taunit, containing multi-walled carbon nanotubes (MWNTs), on plants, and testing of its ability to penetrate into plant cells and tissues. Taunit has been found to stimulate the growth of roots and stems and cause an increase in peroxidase activity inOnobrychis arenariaseedlings. Peroxidase activity increases with decreasing concentration of Taunit from 1,000 to 100mg/l. MWNTs from Taunit were detected in the cells and tissues of seedling roots and leaves, implying the ability of MWNTs to penetrate into roots and accumulate there, as well as their ability to be transported into seedling leaves. Thus, the changes in the physiological parameters of plants are associated not only with MWNT adsorption on the root surface, as previously believed, but also with their penetration, uptake and accumulation in the plant cells and tissues.

Preconcentration of Pb 2+ from aqueous solution using poly(acrylamide) and poly(N,N-dimethylacrylamide) grafted multiwalled carbon nanotubes

Multiwalled carbon nanotubes (MWCNTs) were grafted with poly(acrylamide) (PAAM) and with poly(N,N-dimethylacrylamide) (PDMA) at same grafting percentage by using N 2 plasma technique. The PAAM grafted MWCNTs (MWCNT- g-PAAM) and PDMA grafted MWCNTs (MWCNT- g-PDMA) were characterized by using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), thermo gravimetric analysis-differential thermal analysis (TGA–DTA), scanning electron microscopy (SEM), and potentiometric titration. The results indicated that the grafting processes occurred on the surfaces of MWCNTs without destroying the framework of MWCNTs. The application of MWCNTs, MWCNT- g-PAAM, and MWCNT- g-PDMA in the removal of Pb 2+ from aqueous solution was investigated under ambient conditions. The grafted PAAM and PDMA improved MWCNT adsorption capacity in the removal of Pb 2+ from large volumes of aqueous solutions. MWCNT- g-PAAM had much higher adsorption capacity than MWCNT- g-PDMA, which was attributed to higher amide group content in acrylamide than that in N,N-dimethylacrylamide.