Group-functionalized Multi-walled Carbon Nanotubes Research Articles

An ultra-sensitive ammonia sensor based on a quartz crystal microbalance using nanofibers overlaid with carboxylic group-functionalized MWCNTs.

Detecting ammonia at low concentrations is crucial in various fields, including environmental monitoring, industrial processes, and healthcare. This study explores the development and performance of an ultra-sensitive ammonia sensor using carboxylic group-functionalized multi-walled carbon nanotubes (f-MWCNTs) overlaid on polyvinyl acetate nanofibers coated on a quartz crystal microbalance (QCM). The sensor demonstrates high responsiveness, with a frequency shift response of over 120 Hz when exposed to 1.5 ppm ammonia, a sensitivity of 23.3 Hz ppm-1 over a concentration range of 1.5-7.5 ppm, and a detection limit of 50 ppb. Additionally, the sensor exhibits a rapid response time of only 14 s, excellent selectivity against other gases, such as acetic acid, formaldehyde, methanol, ethanol, propanol, benzene, toluene, and xylene, and good stability in daily use. These characteristics make the sensor a promising tool for real-time ammonia detection in diverse applications.

Electrochemical Sensing Platform Based on Functionalized Multi-Walled Carbon Nanotubes and Metal Oxide for the Detection and Degradation Studies of Orange II Dye.

Textile industry effluents are heavily contaminated with dyes. The discharge of these toxic dyes into waterbodies poses a serious threat to aquatic flora and fauna. The ultimate entrance of these toxins from thereon into the food chain affects the primary and secondary consumers. Therefore, the adoption of a sustainable solution for protection against the detrimental effects associated with adulterated water is an immediate need of the hour. To address the severity of the issue, the present work aims to design an electrochemical sensing platform by modifying the glassy carbon electrode (GCE) with zinc oxide nanoparticles and amino group-functionalized multi-walled carbon nanotubes (NH2-fMWCNTs) for the detection of Orange II, which is a toxic azo dye. Zinc oxide nanoparticles facilitate electron transfer between the transducer and the analyte. While, the positively charged NH2-fMWCNTs in acidic medium help in preconcentration of negatively charged analyte molecules at the electrode/electrolyte interface. The modification of the GCE catalyzed the oxidation of Orange II, as evidenced by the negative shift of the oxidation potential and enhancement in peak current intensity. Square wave voltammetry was used to optimize various experimental conditions, such as the supporting electrolyte, pH of the electrolyte, deposition potential, and deposition time for the best performance of the designed sensor. Under the optimized conditions, the detection limit and quantification of the designed sensor were found to be 0.57 and 1.92 nM, respectively. The catalytic degradation studies of Orange II was shown to be facilitated by titanium dioxide, which acted as a photocatalyst. The addition of hydrogen peroxide further promoted the extent and rate of degradation of dye. The breakdown of Orange II was probed by the designed sensing platform electrochemically and also by UV–visible spectroscopy. The dye degraded up to 92% by following pseudo-first-order kinetics.

Thermophysical Properties of IoNanofluids Composed of 1-ethyl-3-methylimidazolium Thiocyanate and Carboxyl-functionalized Long Multi-walled Carbon Nanotubes

The concept of IoNanofluids (INFs) as the stable dispersions of nanoparticles in ionic liquids was proposed in 2009 by Nieto de Castro’s group. INFs characterize exciting properties such as improved thermal conductivity, non-volatility, and non-flammability. This work is a continuation of our studies on the morphology and physicochemistry of carbon-based nanomaterials affecting thermal conductivity, viscosity, and density of INFs. We focus on the characterization of dispersions composed of long carboxylic group-functionalized multi-walled carbon nanotubes and 1-ethyl-3-methylimidazolium thiocyanate. The thermal conductivity of INFs was measured using KD2 Pro Thermal Properties Analyzer (Decagon Devices Inc., Pullman, WA, USA). The viscosity was investigated using rotary viscometer LV DV-II+Pro (Brookfield Engineering, Middleboro, MA, USA). The density of INFs was measured using a vibrating tube densimeter Anton Paar DMA 5000 (Graz, Austria). The maximum thermal conductivity enhancement of 22% was observed for INF composed of 1 wt% long carboxylic group-functionalized multi-walled carbon nanotubes.

Kinetic and isotherm studies on adsorption of methylene blue using polyacrylonitrile/hydroxyl group functionalized multiwall carbon nanotube multilayered nanofibrous composite

Nanofibrous composite mat was prepared using polyacrylonitrile hard yarn waste and hydroxyl group functionalized multiwall carbon nanotubes (MWCNTs-OH) by electrospinning technique and exploit for methylene blue dye adsorption from aqueous solution. The nanofibrous composite mat was characterized by Fourier transform (FT) infrared spectroscopy, FT-Raman, scanning electron microscopy, X-ray diffractometer and thermogravimetric analyser. The adsorption experiments were studied to investigate the effect of MWCNT-OH weight percentage, initial solution pH, contact time and initial dye concentration on the adsorption. The higher percentage of methylene blue adsorption was found to be 80.05% under optimal condition. The adsorption equilibrium data were studied with Langmuir and Freundlich isotherm models. The R 2 value was found to be higher in the Freundlich isotherm model which was clearly indicated that the Freundlich isotherm model is most suitable for the adsorption of methylene blue on nanofibrous composite mat. The kinetic study was carried out to explain the adsorption rate of methylene blue on nanofibrous composite. The kinetic study of methylene blue adsorption was favourable to the pseudo second-order equation.

Medium-chain-length poly-3-hydroxyalkanoates-carbon nanotubes composite as proton exchange membrane in microbial fuel cell

Medium-chain-length poly-3-hydroxyalkanoates (PHA) and carboxyl group-functionalized multiwalled carbon nanotubes (MC) were used to fabricate a composite membrane for application in a double-chambered microbial fuel cell (MFC). MC was composited into PHA at 5%, 10%, and 20% w/w via ultrasound dispersion blending method. PHA-MC composite was compared with Nafion 117 as proton exchange membrane in MFC operated with palm oil mill effluent (POME) wastewater. The composite exhibited prerequisite separator membrane characteristics. The dispersion of MC in the polymer matrix increased its interfacial surface area and water uptake properties. PHA-MC10% membrane in MFC showed maximum power density of 361 mW/m2, which was comparable with Nafion 117 (372 mW/m2). Internal resistance decrease, chemical oxygen demand (COD) removal, coulombic efficiency (CE), and conductivity of the PHA-MC10% were superior to Nafion 117. The environmental-friendly material could provide an alternative towards realizing practical MFC application.

Preliminary study on conjugation of formononetin with multiwalled carbon nanotubes for inducing apoptosis via ROS production in HeLa cells.

BackgroundThe present work was conducted to prepare and evaluate multiwalled carbon nanotube–formononetin (MWCNT-FMN) composite for sustained delivery and inducing apop-tosis via reactive oxygen species (ROS) production in HeLa cells.MethodsThe composite was prepared by solution mixing with short carboxylic group-functionalized multiwalled carbon nanotubes (MWCNT-COOH). Then the composite was characterized by laser particle size analysis, Fourier transform infrared spectrometry, X-ray diffractometry, differential scanning calorimetry, and scanning electron microscopy. Drug release rates in vitro were determined by dialysis method. The in vitro cytotoxicity study was performed using water soluble tetrazolium assay. The cellular apoptosis assay, ROS, and mitochondrial membrane potential (MMP) of HeLa cells were investigated by acridine orange and ethidium bromide double dye, 2′,7′-dichlorodihydrofluorescein diacetate, and 5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethyl-imidacarbocyanine iodide probe, respectively.ResultsThe entrapment efficiency was 28.77%±0.15%, and the loading capacity was 12.05%±0.20%. The release of MWCNT-FMN was sustained, and the cumulative release rate of formononetin (FMN) from MWCNT-COOH was higher at pH 7.4 than at pH 5.3. The in vitro cytotoxicity assay demonstrated that FMN, MWCNT-COOH, and MWCNT-FMN had no significant effects on the proliferation and viability of mouse fibroblast 3T3 cells over 48 hours, while the cell growth inhibition of the three samples showed concentration-dependent for HeLa cells. Biological assay suggested FMN and MWCNT-FMN could induce apoptosis in HeLa cells, meanwhile the cells exhibited stronger ROS signal and more depolarized MMP than that of the control group.ConclusionThese results preliminarily demonstrated that MWCNT-FMN exerted anticancer efficacy through cellular apoptosis induced by ROS-mediated mitochondrial dysfunctions in HeLa cells.

Chitosan based polymer matrix with silver nanoparticles decorated multiwalled carbon nanotubes for catalytic reduction of 4-nitrophenol

A novel catalyst for the reduction of 4-nitrophenol (4-NP) was prepared using carboxyl group-functionalized multiwalled carbon nanotubes (MWCNTs), polymer matrix, and silver nanoparticles (AgNPs). The AgNPs were prepared by the reduction of silver nitrate by trisodium citrate in the MWCNTs-polymer nanocomposite; the size of the synthesized AgNPs was found to be 3nm (average diameter). The synthesized nanocomposites were characterized using several analytical techniques. Ag@MWCNTs-polymer composite in the presence of sodium borohydride (NaBH4) in aqueous solution is an effective catalyst for the reduction of 4-NP. The apparent kinetics of reduction has a pseudo-first-order kinetics, and the rate constant and catalytic activity parameter were found to be respectively 7.88×10−3s−1and 11.64s−1g−1. The MWCNTs-polymer nanocomposite renders stability to AgNPs against the environment and the reaction medium, which means that the Ag@MWCNTs-polymer composite can be re-used for many catalytic cycles.

Functionalized Multi-Wall Carbon Nanotubes Enhance Transfection and Expression Efficiency of Plasmid DNA in Fish Cells.

DNA vaccines are considered to be the most promising method against infectious diseases in the aquaculture industry. In the present study, we investigated the potency of ammonium group-functionalized multi-walled carbon nanotubes (MWCNTs) in enhancing the transfection and expression efficiency of plasmid DNA (pEGFP-vp5) in Ctenopharyngodon idellus kidney (CIK) cells. Agarose gel shift assay results show that ammonium group-functionalized carbon nanotubes are able to condense DNA in varying degrees. Scanning electron microscope (SEM) images shows that CIK cells show a great affinity for MWCNTs-NH3+ and the CNTs covering the cell surface tend to orient their tips perpendicularly to the cell surface, and appear to be “needle-pricking the cells”. Transmission electron microscope (TEM) images confirmed that MWCNTs-NH3+ penetrate the cell membranes and are widely dispersed in the CIK cell. Real-time PCR was used to detect the transfection efficiency through the expression of the outer capsid protein (VP5). The results showed that the MWCNTs-NH3+:DNA complexes are able to transfect CIK cells effectively at different charge ratio than naked DNA. Subsequent studies confirmed that both functional groups and charge ratio are important factors that determine the transfection efficiency of plasmid DNA. All these results indicated that MWCNTs-NH3+:DNA complexes could be suitable for developing DNA vaccine for the control of virus infection in the aquaculture industry.

Multi-walled carbon nanotubes promote cementoblast differentiation and mineralization through the TGF-β/Smad signaling pathway.

Excretion of cementum by cementoblasts on the root surface is a process indispensable for the formation of a functional periodontal ligament. This study investigated whether carboxyl group-functionalized multi-walled carbon nanotubes (MWCNT-COOH) could enhance differentiation and mineralization of mammalian cementoblasts (OCCM-30) and the possible signaling pathway involved in this process. Cementoblasts were incubated with various doses of MWCNT-COOH suspension. Cell viability was detected, and a scanning electron microscopy (SEM) observed both the nanomaterials and the growth of cells cultured with the materials. Alizarin red staining was used to investigate the formation of calcium deposits. Real-time PCR and western blot were used to detect cementoblast differentiation and the underlying mechanisms through the expression of the osteogenic genes and the downstream effectors of the TGF-β/Smad signaling. The results showed that 5 µg/mL MWCNT-COOH had the most obvious effects on promoting differentiation without significant toxicity. Alp, Ocn, Bsp, Opn, Col1 and Runx2 gene expression was up-regulated. Smad2 and Smad3 mRNA was up-regulated, while Smad7 was first down-regulated on Day 3 and later up-regulated on Day 7. The elevated levels of phospho-Smad2/3 were also confirmed by western blot. In sum, the MWCNT-COOH promoted cementoblast differentiation and mineralization, at least partially, through interactions with the TGF-β/Smad pathway.

Mechanical reinforcement of polyethylene using n- alkyl group-functionalized multiwalled carbon nanotubes: Effect of alkyl group carbon chain length and density

Polyethylene (PE) is one of the most produced synthetic resins in the world. Functionalized multiwalled carbon nanotube (MWCNT) is a potential nanoscale filler to realize the next generation strong and multifunctional PE composites. We demonstrate that MWCNTs grafted with short n-alkyl groups are effective nanofillers for mechanical reinforcement of PE composites. At 1 wt% filler loading, the yield stress and Young’s modulus improve significantly up to 54 and 63% compared with neat PE, respectively. Among ductile properties, tensile strength increases up to 30%; ultimate strain is preserved; and toughness increases up to 33%. More important, we show that short n-alkyl groups can be grafted on MWCNTs much easier than long chain polymers. Further, we find that alkyl groups of C14‐C18 chains have the optimum length for reinforcement. The optimum density of grafted alkyl groups is around 0.390‐0.423 lmol/mg when the C14 alkyl groups are used. Overall, the results manifest that MWCNTs grafted with n-alkyl groups with suitable length and density are efficient nanoscale fillers for high-performance PE composites. POLYM. ENG. SCI., 54:336‐344, 2014. a 2013 Society of Plastics Engineers

Functionalized carbon nanotube-induced viscosity reduction of an ionic liquid and performance improvement of dye-sensitized solar cells

Ionic liquids are nonvolatile solvents and have high ionic conductivity. They can be used as stable electrolyte in many electrochemical systems. But their application is impeded by their high viscosity. This paper reports a novel method to reduce the viscosity of an ionic liquid, 1-propyl-3-methylimidazolium iodide (PMII) that is extensively used in dye-sensitized solar cells (DSSCs), by the addition of carboxylic group-functionalized multi-walled carbon nanotubes (oMWCNTs). The viscosity of PMII can decrease from 1380cP to 400cP at 25°C after the addition of 0.10wt% oMWCNTs. The viscosity reduction depends on the oMWCNT loading. Unfunctionalized MWCNTs hardly reduce the viscosity of PMII. The viscosity decrease is attributed to the reduction in the Coulombic attractions between the PMI+ cations and I− anions as a result of the hydrogen bond formation between PMI+ and carboxylic group of oMWCNTs. The presence of oMWCNTs gives rise to the increase in the size disparity of cations to anions of PMII and induces disordered structure. The addition of oMWCNTs does not affect the thermal stability of PMII. PMII–oMWCNT mixtures with reduced viscosity are used as the electrolyte of DSSCs. The addition oMWCNTs in the ionic liquid can significantly improve the photovoltiac efficiency of DSSCs. This is the first time to observe the viscosity reduction of ionic liquid by carbon nanotubes.

Thermogravimetric and resistivity study of Ex situ and In situ poly(methyl methacrylate)/carboxylic acid group functionalized multiwall carbon nanotubes composites

AbstractPolymer composites based on poly(methyl methacrylate) (PMMA)/carboxylic acid group functionalized multiwall carbon nanotubes (MWCNT) were prepared by the ex situ and in situ techniques with 0.05% loading by weight. Composite films were fabricated by solvent casting method. Electrical conductivity of the composites as well as of the neat PMMA polymer was measured in the temperature range 333 K to 423 K. Neat PMMA samples prepared by the same method showed complete insulating behavior. Ex situ technique leads to a lower value of percolation threshold. Infrared spectroscopy was used to analyze the effect of functionalization of MWCNT on the interfacial bonding of PMMA and MWCNT. Thermogravimetric analysis revealed that the maximum degradation temperature has been shifted to higher region for in situ composites compared to PMMA itself—and the ex situ composites indicated better thermal stability. X‐ray diffraction study of composites also indicates that in situ composites functionalization incorporated MWCNT particles in the polymer chain. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Simultaneous immobilization of glucose oxidase on the surface and cavity of hollow gold nanospheres as labels for highly sensitive electrochemical immunoassay of tumor marker

A novel tracer, glucose oxidase (GOD)-functionalized hollow gold nanospheres encapsulating glucose oxidase (Au shell@GOD), was designed to label the ferrocenemonocarboxylic-grafted secondary antibodies (Fc@Ab 2) for highly sensitive detection of tumor marker using carboxyl group functionalized multiwall carbon nanotubes as platform. Initially, Au shell@GOD was synthesized specially by reverse micelle approach, and then the labeling of antibody and the preparation of GOD-functionalized Au shell@GOD were performed by one-pot assembly of Fc@Ab 2 and GOD on the surface of Au shell@GOD. The ferrocene used to label antibodies acted as a mediator of electron transfer between GOD and electrode surface. The high-content glucose oxidase in the tracer (on the surface and in the cavity) could significantly amplify the amperometric signal for sandwich-type immunoassay. Using carcinoembryonic antigen (CEA) as model analyte, the designed tracer showed linear range from 0.02 to 5.0 ng mL −1 with the detection limit down to 6.7 pg mL −1. The assay results of serum samples with the proposed method were in an acceptable agreement with the reference values. The new protocol showed acceptable stability and reproducibility, high sensitivity, and good precision, which could provide a promising potential for clinical screening and diagnosis of tumor disease.

Electrical and Mechanical Properties of Poly(L-lactide)/Carbon Nanotubes/Clay Nanocomposites

An organoclay containing epoxy groups, twice-functionalized organoclay (TFC), was synthesized by reacting (glycidoxypropyl)trimethoxy silane with Cloisite25A (C25A), which had already been modified with an amine compound. The introduction of epoxy groups to the clay surface and carboxylic group-functionalized multiwalled carbon nanotubes (MWCNTs) improved the interfacial adhesion between the poly(L-lactide) (PLLA) and nano-sized fillers when melt-compounded. The PLLA/MWCNTs/TFC nanocomposites showed superior tensile properties to those of PLLA and PLLA/CNTs. The dispersion of MWCNTs in the PLLA matrix decreased the electrical resistivity of the composite substantially due to the higher MWCNT loading. However, the introduction of TFC to the PLLA/MWCNTs nanocomposites resulted in a slight increase in volume resistivity. This increase was attributed to the individual MWCNTs being blocked by the TFC. The clays in the PLLA/MWCNTs/TFC nanocomposites prevented direct contact between the neighboring MWCNTs, which increased the electrical resistivity of the nanocomposites.

Ultrathin Organically Modified Silica Layer Coated Carbon Nanotubes: Fabrication, Characterization and Electrical Insulating Properties

This paper describes the use of organically modified silica (ormosil) for the ultrathin nanoprecise coating of individual multiwall carbon nanotubes using a soft-chemistry approach. Hybrid organic/inorganic ormosil nanocoated carbon nanotubes were successfully prepared by in-situ deposition of 3-aminopropyltrimethoxysilane or N-methylaminopropyltrimethoxysilane in an aqueous suspension by means of their electrostatic interactions with carboxylic group functionalized multiwall carbon nanotubes. The coating layer was found to have a uniform thickness of about 3 nm. The products were characterized by high-angle annular dark field scanning transmission electron microscopy, high-resolution transmission electron microscopy (HR-TEM), TEM/energy-dispersive X-ray spectroscopy, TEM/electron energy loss spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and current-voltage measurements. The ormosil coatings demonstrated the favorable electrical insulating properties of individual multiwall carbon nanotubes. We also show that the resistance of the insulating thin layer can be tuned by altering the substituents of alkylmethoxysilanes.

Electrochemical impedance detection of DNA hybridization based on the formation of M-DNA on polypyrrole/carbon nanotube modified electrode

A new selective and sensitive biosensing strategy for electrochemical impedance spectroscopy (EIS) measurement of DNA hybridization is described. The detection approach relied on the doping of nucleic acid probes within electropolymerized polypyrrole (PPy) film onto a carboxylic group-functionalized multi-walled carbon nanotubes (MWNTs-COOH) modified electrode and monitoring the impedance changes provoked by the metallation of helix DNA after hybridization. Oligonucleotide probes served as the solo counter anions during the growth of conducting PPy film on the carbon nanotube modified electrode. As a consequence of hybridization and the formation of metallized double-stranded DNA (M-DNA), significant changes in electrochemical impedance values (both in real component Z re and imaginary component Z im) coming from the change of electronic transport resistance of the modified electrode were observed, especially a visible decrease in the Z re. Based on the unique response Δ Z re after hybridization and metallation at 5469 Hz, only the complementary DNA sequence had an obvious signal of the impedance decrease when compared with 1-base, 3-base mismatched and non-complementary sequences; hybridization amounts of 1-base, 3-base mismatched sequences were obtained only 35.7 and −5.8% responses. The protocol also offered high sensitivity with the detection limitation was 5×10 −11 M using 3 S.D., n=11. Results showed that Zn 2+-DNA had the best ability to transport electrons in M-DNA double-stranded chains when compared with Co 2+-DNA and Ni 2+-DNA on the same condition.