Acid-functionalized Carbon Nanotubes Research Articles

Preparation and catalytic performance of perfluorosulfonic acid-functionalized carbon nanotubes

Perfluorosulfonic acid-functionalized carbon nanotubes were prepared by liquid deposition of the perfluorosulfonic acid-polytetrafluoroethylene copolymer and characterized by N2 adsorption, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and acid-base titration. The effects of reaction temperature and the type of solvent were investigated. The results showed that these solid acids are very stable in both polar and non-polar solvents and can maintain their acidity up to 300 °C. Higher activity and better stability were observed over these materials in the alkylation of hydroquinone compared with poly(styrene sulfonic acid)-grafted carbon nanotubes.

Effect of multiwalled carbon nanotube loading on the properties of Nafion® membranes

Abstract

Adsorption of Zinc and Lead Ions from Aqueous Solutions Using Chitosan/Polyvinyl Alcohol Membrane Incorporated via Acid-Functionalized Carbon Nanotubes

Carbon nanotubes were synthesized via the chemical vapor deposition method using cyclohexanol and ferrocene as carbon precursor and catalyst, respectively, and then they are functionalized with acid treatment. Chitosan/polyvinyl alcohol adsorptive membrane incorporated with carbon nanotubes (CS/PVA-CNTs membrane) was prepared via the solution casting method. The CS/PVA-CNTs membrane was employed for adsorption of lead and zinc ions from aqueous solutions. Various isotherms and kinetic models were applied to fit the experimental data. It was found out that adsorption behavior of the heavy metal ions using CS/PVA-CNTs membrane match well with the Freundlich isotherm and the pseudo-first-order kinetic models.

The effect of hyaluronic acid functionalized carbon nanotubes loaded with salinomycin on gastric cancer stem cells

Gastric cancer stem cells (CSCs) play a crucial role in the initiation, development, relapse and metastasis of gastric cancer because they are resistant to a standard chemotherapy and the residual CSCs are able to proliferate indefinitely. Therefore, eradication of this cell population is a primary objective in gastric cancer therapy. Here, we report a gastric CSCs-specifically targeting drug delivery system (SAL-SWNT-CHI-HA complexes) based on chitosan(CHI) coated single wall carbon nanotubes (SWNTs) loaded with salinomycin (SAL) functionalized with hyaluronic acid (HA) can selectively eliminate gastric CSCs. Gastric CSCs were identified as CD44+ cells and cultured in serum-free medium. SAL-SWNT-CHI-HA complexes were capable of inhibiting the self-renewal capacity of CD44+ population, and decrease mammosphere- and colon-formation of CSCs. In addition, the migration and invasion of gastric CSCs were significantly blocked by SAL-SWNT-CHI-HA complexes. Quantitative and qualitative analysis of cellular uptake demonstrated that HA functionalization facilitated the uptake of SWNTs in gastric CSCs while free HA competitively inhibited cellular uptake of SAL-SWNT-CHI-HA delivery system, revealing the mechanism of CD44 receptor-mediated endocytosis. The SAL-SWNT-CHI-HA complexes showed the strongest antitumor efficacy in gastric CSCs by inducing apoptosis, and in CSCs mammospheres by penetrating deeply into the core. Taken altogether, our studies demonstrated that this gastric CSCs-targeted SAL-SWNT-CHI-HA complexes would provide a potential strategy to selectively target and efficiently eradicate gastric CSCs, which is promising to overcome the recurrence and metastasis of gastric cancer and improve gastric cancer treatment.

Phosphinic acid functionalized carbon nanotubes for sensitive and selective sensing of chromium(VI)

Single-walled carbon nanotubes (SWCNTs) have been functionalized with a phosphinic acid derivative ‘bis(2,4,4-trimethylpentyl) phosphinic acid’ (PA/d). It has been achieved by treating the chlorinated SWCNTs with PA/d at 80°C. Successful functionalization and different nanomaterial properties have been investigated by UV–vis–NIR, FTIR, Raman spectroscopy, AFM and FE-SEM. PA/d conjugated SWCNTs (CNT–PA) are dispersible in some common organic solvents, e.g. CH2Cl2, DMF, CHCl3, and THF. The ‘CNT–PA’ complex was spin-casted on boron doped silicon wafer. Thus fabricated sensing electrode is demonstrated for sensitive and selective electrochemical sensing of chromium(VI) ions. A linear response is obtained over a wide range of Cr(VI) concentration (0.01–10ppb). The sensor's sensitivity and the limit of detection are observed to be 35±4nA/ppb and 0.01ppb, respectively. The practical utility of the proposed sensor is demonstrated by determining the Cr(VI) concentration in an industrial effluent sample and an underground water sample.

Carbon nanotube-gelatin-hydroxyapatite nanohybrids with multilayer core–shell structure for mimicking natural bone

We attempted to mimic collagen fibrils bearing apatite crystals in natural bone, using gelatin, carboxylic acid functionalized carbon nanotubes (f-CNTs), and hydroxyapatite (HA). Gelatin molecules were covalently grafted on the surface of f-CNTs by the formation of amide linkages. HA crystals were then assembled onto the gelatin-grafted f-CNTs in a highly concentrated CaP solution, resulting a multilayered core–shell structure, consisting of a f-CNT core and gelatin-HA shells (as a fibrous multilayered f-CNT/Gel/HA nanohybrid), and in a similar formation to the collagen fibers of natural bone. The tensile strength, elastic modulus, and elongation rate of the new hybrid material were significantly improved compared to both pure (f-CNT free) gelatin and a mixture of f-CNT and gelatin, by 4.6–8.8, 9–10, and 28–42 times, respectively. Cell viability studies of the f-CNT/Gel/HA nanohybrid also suggest a higher degree of biocompatibility compared to pure gelatin.

Immobilization of Glucose Oxidase on 4-(pyrrole-1-yl) Benzoic Acid Functionalized Carbon Nanotubes for Direct Electrochemistry and Glucose Sensing

In recent years, carbon nanotubes (CNT) have gained considerable attention, because of their remarkable electronic and mechanical properties, which have made them extremely attractive for a wide range of sensing applications from structural materials to nanoelectronic components. The ability of CNT-modified electrodes to promote electron transfer reactions has been documented in connection with important biomolecules [1]. Our goal is to explore new applications of CNT as an electrode material in facilitating the electron transfer between enzyme molecule and electrode in the bioelectrocatalytic system for glucose oxidation that is of potential utility for bioelectronic devices such as biosensors and biofuel cells.Our research focuses on the direct electrochemical performance of glucose oxidase (GOx) immobilized on 4-(pyrrole-1-yl) benzoic acid (PyBA) modified multi-walled carbon nanotubes (CNTs). GOx is a homodimer containing two tightly bound flavin adenine dinucleotide (FAD) redox centers embedded deeply in the enzyme [2]. Modification of carbon nanostructures allow to obtain thin and organized films, causing a rapid and effective transfer of electrons between the active center of the biocatalyst (GOx) and the electrode surface. The presence of PyBA in our composite film significantly improves their stability and introduces new functional groups that have great importance in the enzyme immobilization process onto the CNTs-modified electrode [3].In this work stable immobilization and direct electron transfer of glucose oxidase were achieved on the composite film modified glassy carbon electrode. The resulting electrode gave a well-defined redox peaks with a formal potential of about −440 mV (vs. Ag/AgCl) in 0.1 phosphate buffer solution pH=7.0. The electron transfer rate constant was estimated to be 3.15 s-1, due to the combined contribution of CNTs/PyBA and GOx. Furthermore, the method for detecting of glucose was proposed based on the decrease of oxygen caused by the enzyme-catalyzed reaction between GOx and glucose. The low calculated apparent Michaelis–Menten constant (KM app) was 10.2 mM, implying the high enzymatic activity and affinity of immobilized enzyme for glucose. It can reasonably be expected that this observation might hold true for other noble carbon nanostructure-electroactive protein systems, providing a promising platform for the development of biosensors and biofuel cells.

Hybrid carbon nanotube—silica/ polyvinyl alcohol nanocomposites films: preparation and characterisation

Composites of carbon nanotubes (CNT) in polymeric matrices have attracted considerable attention in the research and industrial communities due to their interesting and unique properties. However, the main intrinsic problem of CNT is their insolubility or very poor solubility in either water or organic solvents. Therefore, the dispersion of CNT has become the focus of many researches. In this study, a simple method based on a chemical process was developed in order to improve the dispersion of CNT. Our method consists in grafting carboxylic acid-functionalized carbon nanotubes (CNT-COOH) onto an amino-functionalized silica particles (SiO2-NH2) surface. Prior to assembly, CNT-COOH were prepared by using a mixture of concentrated nitric and sulfuric acids, while SiO2-NH2 were prepared by a silanization with 3-aminopropyltriethoxysilane (APTES). The hybrid carbon nanotube-silica (CNT/SiO2) was dispersed in polyvinyl alcohol (PVA) with 1, 3 and 5 wt% (by weight). Techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) measurement have been employed to study the dispersion state in the polymer matrix. The results indicated a good and uniform dispersion of hybrid fillers. Indeed, it was shown that the silica particles play the role of dispersing agents. In addition, a decrease of the resistivity of the composite films was observed as the concentration of CNT-silica fillers in the PVA increases, reaching 3.4 × 103 Ω.m when the hybrid fillers concentration is equal to 5 %.

Effect of Chloride Ions and Water Chemistry on Copper(II) Adsorption on Functionalized and Pristine Carbon Nanotubes Compared to Activated Carbon F-400

The objective of this study was to investigate the effect of chloride ions (Cl−) on Cu2+ adsorption to carbon nanotubes (CNT). The isotherms showed a significant decrease in adsorption capacity on F-400, pristine, and acid-functionalized CNT in the presence of Cl−, but had little effect on alcohol-functionalized CNT. Several inductively coupled plasma (ICP) analyses measured the impurities concentration of (1) aqueous-phase isotherm solute, (2) as-received, and (3) acid-washed CNT solutions. Chemical-equilibrium-modeling software MINEQL+ calculations were applied to compare ICP results to complexes formation. The model suggested that some solid-phase residual-catalytic metals, such as Cr2+, after released in water from as-received CNT, formed aqueous-phase complexes and were readsorbed. The 18-metal ICP results were more than two orders of magnitude lower ( 5.1, when less Cu2+ ions are present in solution. scanning electron microscopy–energy dispersive X-ray spectroscopy analysis showed impurities on as-received F-400 and positively charged surface at pH 5.1 (pHpzc 7.1) explaining possible electrostatic attraction of Cl− ions, blocking adsorptive sites, reducing its adsorptive capacity for Cu2+.

Highly-selective electrochemical determination of catechol based on 3-aminophenylboronic acid-3,4,9,10-perylene tetracarboxylic acid functionalized carbon nanotubes modified electrode

In this paper, a new electrochemical method for the highly-selective determination of catechol (CC) has been fabricated based on the 3-aminophenylboronic acid-3,4,9,10-perylene tetracarboxylic acid functionalized carbon nanotubes (3-APBA–PTCA–CNTs) modified glassy carbon (GC) electrode. The 3-APBA–PTCA–CNTs hybrids and the related electrode were characterized by Fourier transform infrared spectroscopy, differential pulse voltammetry and electrochemical impedance spectroscopy. Due to the highly-selective bonding of 3-APBA with 1,2-diols to form a pinacol ester, the 3-APBA–PTCA–CNTs/GC electrode showed high selectivity for the determination of CC from dihydroxybenzene isomers with a linear response range of 0.5 to 30 μM and a detection limit of 0.1 μM (S/N = 3). Furthermore, the developed 3-APBA–PTCA–CNTs/GC electrode was successfully applied to selectively detect CC in local river water samples with the co-existence of hydroquinone (HQ), CC and resorcinol (RE).

Effect of Short Carbon Fibers and Carbon Nanotubes Dispersed by Utilizing Hollow Glass Beads as Carriers on the Tensile and Curing Properties of Epoxy Resin

The effects of the combination of silane functionalized hollow glass beads (silanized HGBs), acid functionalized carbon nanotubes (oxidized CNTs), and short carbon fibers (SCFs) on the tensile properties of epoxy (EP) resin were investigated. The combined utilization of silanized HGBs, oxidized CNTs and SCFs led to a pronounced synergy in the tensile properties of the SCF/HGB/CNT/EP composites. The composites exhibited greater tensile strength and Young's modulus than the neat EP, clearly. The mechanism of such synergetic effect was analyzed by tensile fracture studies using SEM. In addition, by analyzing the DSC curves, the curing temperatures of the composites were obtained.

Voltammetric behavior of uric acid on carbon paste electrode modified with salmon sperm dsDNA and its application as label-free electrochemical sensor

A simple and sensitive label-free electrochemical DNA biosensor was proposed for the rapid determination of uric acid (UA) using a carbon nano tube paste electrode (CNTPE) modified with salmon sperm dsDNA. At first, the interaction between UA and the DNA was studied using differential pulse voltammetry (DPV). The addition of the DNA to UA solution resulted in a decrease in the peak current of UA and at the same time, a positive shift in the peak potential indicating an intercalative interaction. Then, the voltammetric response of a DNA-immobilized CNTPE was investigated for the determination of UA. The immobilization of the DNA was carried out using acid-functionalized carbon nanotubes and studied using Fe(CN)63−/Fe(CN)64− redox indicator. Compared with unmodified CNTPE, the oxidation signal of UA showed a significant increase at the DNA-coated electrode, and shifted to more positive potentials attributed to the pre-concentration of UA at the electrode surface due to interaction with the surface-confined DNA layer. This interaction was used for the fabrication of a simple and sensitive biosensor for determining UA. After the optimization of operational parameters, a linear dependence of the peak current on the UA concentration was observed in the range of 7.0×10−7 to 1.1×10−4molL−1, with the detection and quantification limits of 1.8×10−7 and 5.8×10−7molL−1, respectively. The proposed biosensor was successfully applied to validate its capability for the analysis of UA in human serum and urine samples.

Enhanced Activity and Stability of Porous Carbon for Storage Energy by Acid Functionalized-Carbon Nanotubes

In this paper,the acid-functionalized multi-wall carbon nanotubes /porous carbon(AMWCNTs /PC) composites were prepared by an effective method,and the application of the composites for electrochemical energy storage was also studied.In the synthesis,the AMWCNTs were mixed with cyclodextrin by a milling method.The acid treatment was favorable for the formation of a uniform and effective composite due to the enhancement of the interaction of AMWCNTs with cyclodextrin.After carbonization under N 2 protection and activation with ZnCl 2,the AMWCNTs/PC composites could be obtained.The materials were characterized by transmission electron microscopy,X-ray diffraction and Raman spectroscopy.The results indicate that the CNTs are uniformly distributed into the framework of the porous carbon,and the materials have a high BET specific surface area and good conductivity.Cyclic voltammetry(CV) and galvanostatic charge-discharge(GCD) measurements indicate that the composites have good performances for electrochemical energy storage and a high stability.The AMWCNTs / PC-12-4(numbers 12 and 4 represent the mass ratios of cyclodextrin to AMWCNTs and AMWCNTs / PC to ZnCl 2,respectively) exhibits a high specific capacitance of 156 F/g,much higher than the AMWCNTs(43 F / g) and PC-4(87 F / g) at 0.5 A / g.Also,the AMWCNTs / PC-12-4 shows superior cycle durability and columbic efficiency over 99.9% after 5000 cycles in KOH,indicating a promising potential for AMWCNTs / PC-12-4 to be used as electrodes materials in supercapacitor.

Influence of rare-earth-functionalized carbon nanotubes on thermal and mechanical properties of polytetrafluoroethylene nanocomposites

Mixed acid and rare-earth (RE) solution were used as the surface modifiers to functionalize multi-walled carbon nanotubes (CNTs). Fourier transform infrared spectra reveal that the carboxylic groups were induced on the surface of acid-functionalized and RE-functionalized CNTs, and the presence of C–N bond suggests that the ethylenediamine tetraacetic acid molecules were successfully grafted on the surface of RE-functionalized CNTs. Raman analysis indicates that acid-treatment and RE-treatment did not significantly change the structure of pristine CNTs. X-ray photoelectron spectroscopy analysis shows that both acid-treatment and RE-treatment improved the number of carboxylic groups on treated CNTs surfaces compared to pristine CNTs, and RE-treatment is superior to acid-treatment to improve the oxygen to carbon ratio on the CNTs surfaces. Transmission electron microscope and scanning electron microscope observations indicate that RE-functionalized CNTs have better dispersion in solvent and in polytetrafluoroethylene (PTFE) matrix than acid-functionalized CNTs, respectively. Thermal stability analysis and mechanical tests display that RE-functionalized CNTs/PTFE nanocomposite has the highest thermal stability and mechanical properties than acid-functionalized CNTs/PTFE nanocomposite and pristine CNTs/PTFE nanocomposite.

PtNi supported on oxygen functionalized carbon nanotubes: In depth structural characterization and activity for methanol electrooxidation

Mild-condition nitric acid functionalized carbon nanotubes were used as support for PtNi electrocatalysts with variation of Pt to Ni atomic ratio prepared by a polyol method in which ethylene glycol was used as solvent and reducing agent under conventional reflux conditions. TPD, TGA, N2 adsorption and cyclic voltammetry confirmed the presence of functional groups in the functionalized carbon nanotubes. Supported PtNi nanocatalysts were characterized with ICP-OES, TEM, XRD, XPS and XAFS. Well dispersed particles on the supporting material with particle sizes in the range of 2–3nm were obtained. PtNi alloy formation was concluded from XRD, XPS and XAFS results, while the latter two methods point to the formation of Ni oxides as well. The elemental distribution within the catalyst nanoparticles is inhomogeneous with Ni enrichment close to the support. Heat treatment in inert gas up to 400°C results in restructuring of the catalysts surface which changes the active sites arrangements. CV and CO stripping measurements showed that the PtNi catalysts have a higher electrocatalytic activity toward methanol oxidation in comparison to a commercial Pt/C E-TEK catalyst and the highest activity was found for a Pt to Ni atomic ratio of 3. The prepared catalysts show highly stable mass specific activity over 200 potential cycles. The catalysts treated at higher temperature (400°C) show a surface enriched in Pt and exhibit lower activity for methanol oxidation reaction but higher stability over 200 cycles. The high catalytic activity and durability of the prepared PtNi electrocatalysts render them possible candidate catalysts for methanol oxidation in direct methanol fuel cells (DMFCs).

Synergistic effect of self-assembled carboxylic acid-functionalized carbon nanotubes and carbon fiber for improved electro-activated polymeric shape-memory nanocomposite

The present work studies the synergistic effect of self-assembled carboxylic acid-functionalized carbon nanotube (CNT) and carbon fiber on the electrical property and electro-activated recovery behavior of shape memory polymer (SMP) nanocomposites. The combination of CNT and carbon fiber results in improved electrical conductivity in the SMP nanocomposites. Carboxylic acid-functionalized CNTs are grafted onto the carbon fibers and then self-assembled by deposition to significantly enhance the reliability of the bonding between carbon fiber and SMP via van der Waals and covalent crosslink. Furthermore, the self-assembled carboxylic acid-functionalized CNTs and carbon fibers enable the SMP nanocomposites for Joule heating triggered shape recovery.

Cubic spinel cobalt oxide/multi-walled carbon nanotube composites as an efficient bifunctionalelectrocatalyst for oxygen reaction

A facile hydrothermal route has been adopted to fabricate cubic spinel cobalt oxide/multi-walled carbon nanotube composite using acid-functionalized carbon nanotubes as structure directing/oxidizing agents. The composite material demonstrated excellent bifunctionality before and after long periods of cyclic voltammetry cycling. After cycling, the oxygen reduction current density of the composite shows about 4, 34 and 3 times improvements in comparison to multi-walled carbon nanotube, cubic spinel cobalt oxide and their physical mixture, respectively. The oxygen evolution current density of the composite was 49% higher than the physical mixture and even greater than each component alone after 500 CV cycles. The cause of high performance is presumably contributed to the synergistic coupling effects between the multi-walled carbon nanotubes and the cubic spinel cobalt oxide.

Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) composite electrode as sensing platform for the simultaneous electrochemical determination of dihydroxybenzene isomers

Dihydroxybenzene isomers catechol (CC), resorcinol (RC), and hydroquinone (HQ) were simultaneously determined using a simple, inexpensive, water-stable, and conducting poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) composite sensing electrode by linear sweep voltammetry. The sensing electrode was prepared by dip-coating a mixture of PEDOT:PSS, Nafion, and carboxylic acid-functionalized single-walled carbon nanotubes on a gold electrode, then modifying by electrochemical doping in a hydrophobic ionic liquid. Nafion was selected as a binding agent to improve the adhesion and binding force between films and electrode interface, and ionic liquid was employed to improve the conductivity and water resistance of the composite electrode. The as-proposed sensing electrode displayed excellent electrochemical catalytic activities towards CC, RC, and HQ. Large peak separations were obtained between HQ and CC as well as CC and RC, i.e., up to 109 and 496 mV, respectively. The calibration curves for CC, RC, and HQ were obtained in the ranges of 0.56–70, 0.18–50, and 0.56–50 μM, with detection limits (S/N = 3) of 0.19, 0.08, and 0.20 μM, respectively. Finally, the sensing electrode was applied to river water sample analysis with reliable recovery. Satisfactory results revealed that the PEDOT:PSS composite can provide a promising platform for the design and application of sensing devices.

Scalable, non-invasive glucose sensor based on boronic acid functionalized carbon nanotube transistors

We developed a scalable, label-free all-electronic sensor for D-glucose based on a carbon nanotube transistor functionalized with pyrene-1-boronic acid. This sensor responds to glucose in the range 1 μM–100 mM, which includes typical glucose concentrations in human blood and saliva. Control experiments establish that functionalization with the boronic acid provides high sensitivity and selectivity for glucose. The devices show better sensitivity than commercial blood glucose meters and could represent a general strategy to bloodless glucose monitoring by detecting low concentrations of glucose in saliva.

Deoxyribonucleic Acid Functionalized Carbon Nanotube Network as Humidity Sensors

In this paper, deoxyribonucleic acid functionalized carbon nanotube (DFC) network has been used to develop field effect transistor (FET)-based humidity sensor. The sensor works on the principle of variation of conductance of the DFC network with change in relative humidity. Since the output signal current of the sensor increases exponentially with increase in RH, the device offers higher sensitivity especially at higher RH. The response and recovery times of this zero gate biased FET-based humidity sensor are measured to be 4 and 8 s, respectively, and offers no baseline shift during recovery, which indicates that the sensing mechanism is governed by charge transfer between the DFC and water molecules. The device is highly selective to atmospheric humidity, having no response to nitrogen and oxygen. The effect of temperature on the performance of the sensor is also studied and reported in this paper.