Sidewalls Of Multiwalled Carbon Nanotubes Research Articles

Catch and release: Gold adsorption and sorbent electrochemical regeneration

Wastewater generated from e-waste leaching is rich in precious metals including gold, silver and platinum. Conventional precipitation and solvent extraction are chemically intensive separations with concerning environmental externalities. Sorbents, in particular carbon nanotubes, have low chemical consumption, and have shown promise for gold adsorption due to their high specific surface area and chemical functionalization potential. However, regenerating sorbents used to adsorb Au is hazardous requiring strong acids. Herein, we delineate the effect of various functional groups on the sidewalls of multiwall carbon nanotubes (MWCNTs) on gold adsorption, and we introduced an acid-free electrochemical technique for Au elution from MWCNTs. Pristine MWCNTs (P-MWCNTs), carboxylic functionalised MWCNTs (COOH-MWCNTs) and amide functionalised MWCNTs (NH2-MWCNTs) were compared for their affinity for Au adsorption from acidic AuCl4−solutions mimicking acidic e-waste leachate. Au adsorption affinity onto MWCNTs followed the order of P-MWCNT > NH2-MWCNT > COOH-MWCNTs. Au elution from Au-saturated MWCNTs was subsequently achieved up to 65%, using acid-free electrochemical desorption in neutral aqueous brine. The Au electro-desorption was shown to have a direct relationship with both the applied current and the mass of the Au adsorbed on the MWCNTs. This study demonstrates enhanced adsorption-based preconcentration of gold and acid-free regeneration of sorbents.

Preparation and Statistical In-vitro Evaluation of Covalent Functionalized Multi Walled Carbon Nanotube 5-Fluorouracil Conjugates

In 21st century, carcinoma is predicted to be a remarkable health problem. The condition of the cancer patients will be critical when it comes to its remedy by chemotherapy using artificial anticancer molecules with various chemo side effects. In the field of nanotechnology, the nanomaterials are rapidly developing. Nanomaterials become admirable and necessary in lot of areas of human interest because of their exclusive size - dependent properties, chemical reactivity, conductivity, and enlarged strength. Carbon nanotubes (CNT) are referred to as nanomaterials. In this present world of medical research and the bio sensing technology has the capability to transform the CNT in the field of efficient medicine delivery, biosensor strategies for ailment treatment and for the health tracking. Our present work is an strive to probe the loading and release of 5- Fluorouracil from Multi Walled Carbon Nanotubes (MWCNTs) to cancer tissues. MWCNTs were subjected to covalent functionalization by using the strong acids, the oxidised MWCNTs are obtained in covalent functionalization process. Through this operation, carboxy (-COOH) groups are set up at the open sides (tips) and at the defects on the sidewalls of MWCNTs and then covalent functionalized MWCNTs were loaded with 5- Fluorouracil to prepare covalent functionalized MWCNTs-5-Flourouracil conjugate. Covalent functionalized MWCNTs-5-Flourouracil conjugate were subjected for SEM studies, TEM studies, particle size, zeta potential, drug entrapment efficiency and in vitro drug release. The release of drug shows longer than 40 h from covalent functionalized MWCNTs-5-Flourouracil conjugate and thus to manage the release of drug in controlled manner. The present research work presents esteemed, novel, and easy to prepare formulation of MWCNTs with superior drug entrapment efficiency with increased hydrophilic property of MWCNTs, and thus increases the bioavailability at selected site with narrow systemic toxicity.

Functionalizing Carbon Nanotubes with Bis(2,9-dialkyl-1,10-phenanthroline)copper(II) Complexes for the Oxygen Reduction Reaction.

A new ligand, namely, 2-(5-(pyren-1-yl)pentyl)-9-methyl-1,10-phenanthroline, as well as new bis(2,9-dialkyl-1,10-phenanthroline)copper(II) complexes were designed, which were immobilized on multiwalled carbon nanotube (MWCNT) electrodes. These complexes show a high tendency of autoreduction into their copper(I) form according to electrochemical and EPR experiments. These complexes exhibit strong interactions with MWCNT sidewalls either with or without anchor functions such as the pyrene moiety. The pyrene-modified derivative can be electropolymerized on glassy carbon and MWCNT electrodes to form a poly-[bis(2-(5-(pyren-1-yl)pentyl)-9-methyl-1,10-phenanthroline)copper(II)] metallopolymer film. Furthermore, these MWCNT-supported bis(2,9-dialkyl-1,10-phenanthroline)copper complexes demonstrate a low overpotential for a 4H+/4e- oxygen reduction reaction at pH 5 with an onset potential of 0.86 V versus RHE. Integration of these functionalized MWCNTs at gas-diffusion electrodes of H2/air fuel cells led to a high open-circuit voltage of 0.84 V and a maximum current density of 1.77 mW cm-2 using a Pt/C anode.

The hybrids of perylene tetracarboxylic acid functionalized multi-walled carbon nanotubes and chitosan for electrochemical chiral sensing of tryptophan enantiomers

To introduce abundant carboxyl (COOH) groups to the surface of multi-walled carbon nanotubes (MWCNTs) while maintaining the pristine structure of MWCNTs, 3,4,9,10-perylene tetracarboxylic acid (PTCA) was non-covalently grafted to the sidewalls of MWCNTs. The obtained PTCA functionalized MWCNTs (MWCNTs–PTCA) functioned as a scaffold for the further introduction of chitosan (CS) via electrostatic attractions and hydrogen-bonds. The resultant CS/MWCNTs–PTCA could be used for electrochemical chiral sensing of tryptophan (Trp) enantiomers due to the intrinsic chirality of CS and the high electrocatalytic activity of MWCNTs. Under optimized conditions, the Trp enantiomers could be effectively discriminated at the CS/MWCNTs–PTCA modified electrode by differential pulse voltammetry (DPV), demonstrating that the developed CS/MWCNTs–PTCA might be a potential candidate for the construction of electrochemical chiral sensors.

One-Dimensional Nanocomposites Based on Polypyrrole-Carbon Nanotubes and Their Thermoelectric Performance.

Conducting polymers have attracted significant attention due to their easy fabrication, morphology modification, and their electrical properties. Amongst them, polypyrrole (PPy) has attractive thermoelectric (TE) properties. Engineering of this polymer in one-dimensional (1D) nanostructured form is found to enhance its TE performance. This was achieved in the present work by using multi-walled carbon nanotubes (MWCNTs) as a core template to direct the self-assembly of PPy and also to further enhance its TE performance. The growth of PPy on the sidewalls of MWCNTs was performed in an acidic medium based oxidative in situ polymerization. Various concentrations of MWCNTs within the range 1.1–14.6 wt.% were used to form the MWCNTs/PPy nanocomposites in 1D core-shell structures. The morphology and microstructure results of the produced nanocomposite samples showed that this MWCNTs were successfully coated by thick and thin layers of PPy. At low concentrations of MWCNTs, thick layers of PPy are formed. While at high concentrations thin layers are coated. The formed 1D nanocomposites have enhanced TE performance, particularly those containing higher contents of MWCNTs. The power factor and figure of merit values for the formed 1D nanocomposites recorded around 0.77 µV/mK2 and 1 × 10−3 at room temperature (RT), respectively. This enhancement was attributed to the perfect coating and good interaction between PPy and MWCNT through π–π stacking between the polymer chains and these nanotubes. These results might be useful for developing future TE materials and devices.

Preliminary study on immobilization of plant esterase on functionalized multi-walled carbon nanotubes (MWCNTs) for biosensor application

The functionalization of multi-walled carbon nanotubes (MWCNTs) is extremely important to increase their solubility. This study reported the efficient functionalization of MWCNTs via acid treatment introducing carboxyl group at the side wall of MWCNTs by mixing the concentrated nitric and sulfuric acid. Plant esterase enzyme extracted from wheat flour called alpha naphthyl acetate esterase (ANAE) was immobilized onto functionalized MWCNTs via covalent attachment of amine group in ANAE and carboxyl group of functionalized MWCNTs. In order to characterize the functionalization of MWCNTs and immobilization of enzyme, Fourier transform infrared (FTIR) spectroscopy have been used to confirm the existence of these functional groups. The FTIR spectrums revealed that the several peaks formed at 1992.39, 2324.14, 2880.85 and 3029.51 cm−1 which can be assigned to the C=O symmetric stretching, O−H stretch from strongly hydrogen-bonded –COOH, H−C stretch modes of H−C=O in the carboxyl group, and O-H stretch from carboxyl groups (O=C−OH and C−OH) respectively. The immobilization of ANAE on functionalized MWCNTs confirmed by observation of the peak at 3646.81 cm−1 and 3850.91 cm−1 introduced the strong amide linkages between carboxylic acid groups and amine group on the MWCNTs. This proposed framework can be applied for fabrication of screen printed electrode as biosensor for detection of pesticide.

Effect of milling parameters on the dispersion characteristics of multi-walled carbon nanotubes in transition metal oxides

In this research investigation on milling parameters to achieve uniform dispersion of multi-walled carbon nanotubes (MWCNTs) was conducted. High-energy ball milling (HEBM) technique was adopted to disperse 1 wt. % MWCNTs in titanium and manganese oxides with ball to powder ratio (BPR) of 10:1 at 6 and 9 hours milling times. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to characterize the as-received MWCNTs and admixed composite powders. The results indicated that HEBM was an effective route to disperse MWCNTs in transition metal oxides. In addition, the characteristics of admixed powders evidently showed that the increase of milling time effectively dispersed the MWCNTs in titanium and manganese oxide respectively, however deformation of sidewalls of MWCNTs was observed due to harsh milling conditions that resulted on non-sp2 defects in the MWCNTs.

Sensitivity Enhancement of Benzene Sensor Using Ethyl Cellulose-Coated Surface-Functionalized Carbon Nanotubes

A hybrid sensor based on the integration of functionalized multiwalled carbon nanotubes (MWCNTs) with ethyl cellulose (EC) was fabricated for sensitivity enhancement of benzene detection. To functionalize the surface of MWCNTs, MWCNTs were treated with hydrochloric acid for 60 min (A60-MWCNTs), while other MWCNTs were treated with oxygen plasma for 30, 60, 90, and 120 min (P30-MWCNTs, P60-MWCNTs, P90-MWCNTs, and P120-MWCNTs, resp.). Pristine MWCNTs, A-MWCNTs, and P-MWCNTs were dispersed in 1,2-dichloroethane, then dropped onto a printed circuit board consisting of Cu/Au electrodes used as the sensor platform. Next, EC was separately spin coated on the pristine MWCNTs, A-MWCNTs, and P-MWCNTs (EC/MWCNTs, EC/A-MWCNTs, and EC/P-MWCNTs, resp.). All sensors responded to benzene vapor at room temperature by increasing their electrical resistance which was sensitive to benzene vapor. The EC/P90-MWCNTs enabled an approximately 11-fold improvement in benzene detection compared to EC/MWCNTs. The sensitivity of all sensors would be attributed to the swelling of EC, resulting in the loosening of the MWCNT network after benzene vapor exposure. The differences of the sensing responses of the EC/MWCNTs, EC/A-MWCNTs, and EC/P-MWCNTs would be ascribed to the differences in crystallinity and functionalization of MWCNT sidewalls, suggesting that acid and oxygen plasma treatments of MWCNTs would be promising techniques for the improvement of benzene detection.

Functionalized Carbon Nanotubes with Ni(II) Bipyridine Complexes as Efficient Catalysts for the Alkaline Oxygen Evolution Reaction

Among current technologies for hydrogen production as an environmentally friendly fuel, water splitting has attracted increasing attention. However, the efficiency of water electrolysis is severely limited by the large anodic overpotential and sluggish reaction rate of the oxygen evolution reaction (OER). To overcome this issue, the development of efficient electrocatalyst materials for the OER has drawn much attention. Here, we show that organometallic Ni(II) complexes immobilized on the sidewalls of multiwalled carbon nanotubes (MWNTs) serve as highly active and stable OER electrocatalysts. This class of electrocatalyst materials is synthesized by covalent functionalization of the MWNTs with organometallic Ni bipyridine (bipy) complexes. The Ni-bipy-MWNT catalyst generates a current density of 10 mA cm–2 at overpotentials of 310 and 290 mV in 0.1 and 1 M NaOH, respectively, with a low Tafel slope of ∼35 mV dec–1, placing the material among the most active OER electrocatalysts reported so far. Different ...

The Ultraviolet-Induced Functionalization of Multi-Walled Carbon Nanotubes with Polymer Radicals Generated from Polyvinyl Benzoate Derivatives

In order to develop a novel technique for the fabrication of hybrid materials containing polymers and nanocarbons, we examined the surface modification of pristine multi-walled carbon nanotubes (MWCNTs) with benzyl-type polymer side chain radicals generated through photolysis of 4-(chloromethyl)benzoate moieties. The polymer with a 4-(chloromethyl)benzoate side chain was prepared by the esterification of polyvinyl alcohol (PVA) with corresponding acid chloride. The synthesized polymer and MWCNTs were mixed in N-methylpyrrolidone and irradiated with ultraviolet (UV) light. Structural changes of the polymer and MWCNTs were observed by means of X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The XPS results revealed that scission of the C–Cl bonds of the chloromethyl groups and benzyl-type radical formation occurred. The incremental surface defects of the MWCNTs caused by UV irradiation were confirmed by means of Raman spectroscopy. These results support the covalent bond formation between the polymer side chain and MWCNT sidewalls by radical addition reaction. The photothermal conversion characteristics of the prepared materials were also evaluated.

Anti-Alzheimer's potential of berberine using surface decorated multi-walled carbon nanotubes: A preclinical evidence

Carbon nanotubes (CNTs), a sub-family of fullerenes, are nanosized seamless cylinders of graphene sheets with enormous drug loading potential. The current studies entail the systematic development of berberine (BRB)-loaded multiwalled carbon nanotubes (MWCNTs) with polysorbate and phospholipid coating for effective management of Alzheimer’s Disease (AD). For systematic optimization using design of experiment (DoE), a central composite design (FCCD) was employed and the optimized formulation was choosen using numerical desirability function. Optimized formulation exhibited particle size of 186nm, 68.6% drug adsorption and amount of drug released in 16h (Q16h) of 96%. Degree of carboxylation was observed to be 36%. FTIR and FESEM studies confirmed the coating of polysorbate and phospholipid onto the MWCNTs side walls. Confocal studies ratified the uptake potential of BRB-loaded MWCNT formulations on SH-SY5Y cell lines. In vivo pharmacokinetic studies in rats showed significant improvement in the rate and extent of drug absorption in the plasma and brain tissues, both, vis-a-vis pure drug. Behavioral assessment employing Morris Maze test demonstrated the enhanced performance efficiency of the formed MWCNT complexes. Moreover, the phospholipid-coated and the polysorbate-coated MWCNTs exhibited remarkable recovery in memory performance from 18th to 20th day vis-a-vis other groups. Maintenance of normal biochemical levels in brain tissue demonstrated the potential of these coated MWCNTs in reducing β-amyloid induced AD. The studies, in a nutshell, demonstrate significant potential of polysorbate/phospholipid coated MWCNTs of BRB in holistic management of AD.

Characteristics of hydrogen plasma treated carbon nanotubes and their influence on the mechanical properties of polyetherimide-based nanocomposites

The structural phase transformation and etching of the sidewalls of multi-walled carbon nanotubes (MWCNTs) by hydrogen plasma and the effect on the dispersion and mechanical properties of polyetherimide (PEI) composites was investigated. Surface-modified MWCNTs with various plasma treatment times were characterized using FESEM, HRTEM, Raman spectroscopy, FT-IR, and XPS. The results showed that plasma treatment facilitates the attachment of functional groups while damaging and detaching the sidewalls of the MWCNTs and modifying the crystallinity of the graphene layer. The mechanical properties of the PEI composites with the modified MWCNTs depended on the degree of damage to the surface and crystallinity modification of the MWCNTs. Hydrogen plasma treatment led to a significant improvement in the dispersion and mechanical properties of PEI/MWCNT composites due to the surface modification of the MWCNTs.

Highly Loaded Multi-Walled Carbon Nanotubes Non-Covalently Modified with a Bis-Imidazolium Salt and their Use as Catalyst Supports.

The surfaces of multi-walled carbon nanotubes (MWCNTs) were non-covalently modified using two bis-imidazolium dibromide derivatives having phenyl or pyrene groups. Due to the presence of the two pyrene groups the bis(pyren-1-ylmethylimidazolium) dibromide derivative was immobilised at a loading of about 15-16 wt %, whereas only <3 wt % of the phenyl derivative was immobilised. The presence of the two imidazolium cations helped the immobilisation of tetrachloropalladate ions after exchange with bromide ions. Tetrachloropalladate was used as pre-catalyst in several Suzuki-Miyaura carbon-carbon cross-coupling reactions in water or water/ethanol at 50 °C in only 0.1 mol % and compared with the non-supported pre-catalyst. The MWCNT-supported material was used in five consecutive cycles of the Suzuki-Miyaura reaction. Recycling using phenylboronic acid and 4-bromobenzaldehyde in water/ethanol was achieved with only a minor loss in activity. HRTEM images clearly showed the presence of the bis(pyren-1-ylmethylimidazolium) derivative on the sidewalls of MWCNTs.

Solvothermal synthesis of carbon nanotube-AgBiS2 hybrids and their optical limiting properties

AgBiS2 nanoparticles (NPs) have been loaded on multiwalled carbon nanotubes (MWCNTs) by the solvothermal treatment on a mixture of MWCNTs, AgNO3, Bi(NO3)3·5H2O and thiosemicarbazide in a mixed polyol solvent. The resulting MWCNT-AgBiS2 hybrid samples have been extensively characterized by a variety of microscopic and spectroscopic techniques. The AgBiS2 NPs can be uniformly deposited on the sidewalls of MWCNTs by appropriately regulating the reaction conditions including reaction temperature and reaction time. Optical limiting (OL) studies have been performed on typical MWCNT-AgBiS2 samples using the Z-scan and OL measurements at the laser wavelength of 532nm. The MWCNT-AgBiS2 hybrids with AgBiS2 NPs of ∼16nm in size uniformly coated on the nanotubes show a significantly enhanced OL effect in comparison to the purified MWCNTs.

Modified Sol-Gel Synthesis of Carbon Nanotubes Supported Titania Composites with Enhanced Visible Light Induced Photocatalytic Activity

Multiwalled carbon nanotube (MWCNT) enhanced MWCNT/TiO2nanocomposites were synthesized by surface coating of carbon nanotube with mixed phase of anatase and rutile TiO2through a modified sol-gel approach using tetrabutyl titanate as raw material. The morphological structures and physicochemical properties of the nanocomposites were characterized by FT-IR, XRD, DTA-TG, TEM, and UV-Vis spectra. The results show that TiO2nanoparticles with size of around 15 nm are closely attached on the sidewall of MWCNT. The nanocomposites possess good absorption properties not only in the ultraviolet but also in the visible light region. Under irradiation of ultraviolet lamp, the prepared composites have the highest photodegradation efficiency of 83% within 4 hours towards the degradation of Methyl Orange (MO) aqueous solution. The results indicate that the carbon nanotubes supported TiO2nanocomposites exhibit high photocatalytic activity and stability, showing great potentials in the treatment of wastewater.

Structural and optical properties of functionalized multi-walled carbon nanotubes

Herein, we report the functionalization of multiwalled carbon nanotubes (MWCNTs) using meta-Chloroperoxybenzoic acid (mCPBA) as an oxidizing agent. Epoxy groups are incorporated into the sidewall of MWCNTs and the prepared functionalized multiwalled carbon nanotubes (F-MWCNTs) were characterized using FT-IR spectroscopy, X-ray diffraction, Raman spectroscopy and UV–visible spectroscopy. Morphology of MWCNTs and F-MWCNTs was determined using Scanning electron microscopy (SEM) and transmission electron microscopy (TEM). TEM results clearly indicated that the diameter of F-MWCNTs is increased by 120% as compared to neat MWCNTs. From UV–visible spectroscopy data, band gap of F-MWCNTs was calculated using Tauc equation and it was found to be 3.9eV. Photo emission property of F-MWCNTs was analyzed using photoluminescence spectroscopy. F-MWCNTs showed nice emission in the visible region and it depended upon the excited wavelength. These functionalized carbon nanotubes could find use as tunable optoelectronic devices in future nanotechnology.

Solvothermal synthesis and characterization of carbon nanotube–CuInS2 hybrids

CuInS2 nanoparticles (NPs) have been decorated on the sidewalls of multiwalled carbon nanotubes (MWCNTs) by a solvothermal approach using copper diethyldithiocarbamate and indium diethyldithiocarbamate as precursors. The resulting MWCNT–CuInS2 hybrid samples have been extensively characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform IR spectra, ultraviolet–visible–near infrared spectra and X-ray photoelectron spectroscopy. The precursor concentration, reaction temperature and reaction time have a great influence on the size and morphology of the formed CuInS2 NPs. The open-aperture z-scan technique has been used to study the nonlinear optical properties of two typical MWCNT–CuInS2 samples, which show better optical limiting performance than purified MWCNTs.

Study on Effect of Acid and Heat Treatments of Multi-Walled Carbon Nanotubes on Benzene Detection

Effect of acid and heat treatments of multi-walled carbon nanotubes (MWCNTs) on benzene detection was investigated. For acid treatment, MWCNTs were treated by hydrochloric acid (HCl) for 1 h meanwhile other batches of MWCNTs were treated by heating under air ambient at 500°C for 1 h. Pristine, HCl-treated and heat-treated MWCNTs were separately coated with ethyl cellulose (EC) by spin-coating prior to fabrication of three different sensors named as EC/pristine MWCNTs, EC/HCl-MWCNTs and EC/heat-MWCNTs sensors, respectively. Each fabricated sensor was exposed to benzene vapor at room temperature for testing its sensing performance based on an increase in its electrical resistance which was sensitive to benzene vapor. Response of the sensors fabricated from EC/HCl-MWCNTs and EC/heat-MWCNTs were 3.66 and 1.92 times higher than that of EC/pristine MWCNTs, respectively. Sensitivity of all sensors would be attributed to swelling of EC, resulting in loosening of MWCNT network after benzene vapor exposure. In addition, the difference of sensing response of the EC/pristine MWCNTs when compared with those of EC/HCl-MWCNTs and EC/heat-MWCNTs would be ascribed to different crystallinity and functionalization of MWCNTs sidewalls, suggesting that acid and heat treatments of MWCNTs would be promising techniques for improvement of benzene detection.

Noncovalent compatibilization of polypropylene/MWCNT composites using an amino-pyridine grafted polypropylene matrix

Polypropylene (PP)/multiwalled carbon nanotube (MWCNT) composites are prepared by implementing noncovalent compatibilization. The compatibilization method involves PP matrix functionalization with pyridine (Py) aromatic moieties, which are capable of π–π interaction with MWCNT sidewalls. Imaging revealed that the addition of 25 wt% of PP-g-Py to neat PP is capable of drastically reducing nanotube aggregate size and amount, compared to a matrix containing the equivalent amount of a maleated PP (PP-g-MA). Raman spectroscopy confirms improved polymer/nanotube interaction with the PP-g-Py matrix. The electrical percolation threshold appears at a MWCNT loading of approximately 1.2 wt%, and the maximum value of the electrical conductivity achieved is 10−2 S/m, irrespective of the functionalization procedure. The modulus of the composites is improved with the addition of MWCNTs. Furthermore, composites functionalized with Py display significant improvements in composite ductility compared with their maleated counterparts because of the improved filler dispersion. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

Synthesis and Characterization of Co3O4/Multiwalled Carbon Nanotubes Nanocomposite for Amperometric Sensing of Hydrazine

AbstractCo3O4 nanoparticles (NPs) were synthesized and decorated on the multi‐walled carbon nanotubes (MWCNTs) through a simple hydrothermal procedure. The deposited Co3O4 NPs on the sidewalls of MWCNTs were found to be cubic crystal structure and homogenously dispersed with a narrow particle size distribution centered at around 6 nm. The Co3O4/MWCNTs nanocomposite was then utilized for the electrochemical detection of hydrazine, and exhibited a high sensitivity of 34.5 µA mM−1, a low detection limit of 0.8 µM (S/N=3), a wide linear range of 20 µM to 1.1 mM along with a short response time of less than 5 s.