Acid-oxidized Carbon Nanotubes Research Articles

Synthesis and characterization of multiwalled carbon nanotubes functionalized with chlorophyll-derivatives compounds extracted from Hibiscus tiliaceus

In this work, we are presenting the synthesis and characterization of compound materials based on multiwalled carbon nanotubes and chlorophyll-derivatives as chlorophyllide-a and pheophorbide-a, extracted from the plant Hibiscus tiliaceus. Three types of multiwalled carbon nanotubes were used: i) pristine carbon nanotubes (diameter < 10 nm); ii) acid-oxidized carbon nanotubes (diameter < 10 nm), and iii) nitrogen doped multiwalled carbon nanotubes (20 nm diameter). Materials were characterized by ultraviolet-visible spectroscopy, Raman spectroscopy, fluorescence spectroscopy, dynamic light scattering, and field effect scanning electron microscopy. The method we have used for the synthesis was straightforward and easy, and also, we have found evidence of interactions between carbon nanotubes and chlorophyll-derivatives. The interaction between both compounds was confirmed by the significant quenching of signals measured by optical techniques as ultraviolet-visible spectroscopy, Raman spectroscopy, and fluorescence spectroscopy. In addition, we found that interaction increased as the time went on. We also found evidence of the formation of covalent bonds because of the shifting of the absorbance peaks, showing the formation of J or H aggregates. Complementary information about the morphology, revealed a significant increase in the nanotubes thickness, in the range from 80 to 160% for nanotubes with diameters < 10 nm, while nitrogen doped nanotubes showed a lower increase (25–40%). In this way, we have synthesized and characterized compound materials based on multiwalled nanotubes and chlorophyll-derivatives compounds, extracted from natural sources. We synthesized compounds with different coatings that can be used in fields as gas sensing or water remediation.

Aptamer-based sensor for diclofenac quantification using carbon nanotubes and graphene oxide decorated with magnetic nanomaterials

In this contribution, a novel label-free electrochemical biosensor for diclofenac (DCF) detection was developed using the unique properties of acid-oxidized carbon nanotubes (CNT), graphene oxide (GO), and Fe3O4 magnetic nanomaterials. The GO sheets and CNT were interlinked by ultrafine Fe3O4 nanoparticles forming three-dimensional (3D) architectures. The characterization of the nanocomposite was studied by scanning electron microscopy (SEM), energy-dispersive X-ray (EDS), and wavelength-dispersive X-ray (WDX) spectroscopy. Initially, aminated detection probe (aptamer) was surface-confined on the CNT/GO/Fe3O4 nanocomposite via the covalent amide bonds formed by the carboxyl groups on the CNT/GO and the amino groups on the oligonucleotides at the 5′ end. Our constructed folding-based electrochemical sensor was used for detection of target molecule utilizing structure-switching aptamers. Signaling arose from changes in electron transfer efficiency upon target-induced changes in the conformation of the aptamer probe. These changes were readily monitored using differential pulse voltammetry technique. This sensor exhibited binding affinities ranging from 100 to 1300 pM with a low detection limit of 33 pM.

Impedimetric biosensor based on bimetallic AgPt nanoparticle-decorated carbon nanotubes as highly conductive film surface

In the present study, an ultrasensitive impedimetric aptasensor for the quantitative detection of diclofenac (DCF) was fabricated based on a novel signal amplification strategy. As a transducer material, acid-oxidized carbon nanotubes (CNT-COOH) and Pt and Ag nanoparticles (PtAgNPs) were used for promoting electron transfer between the electroactive probe and electrode. It is worth noting that the proposed nanocomposite revealed significant properties through the synergistic effects of the nanocomponent materials. In this strategy, aminated capture probe (ssDNA1) and DCF aptamer (ssDNA2) as a detection probe were attached at the surface of a modified electrode via the formation of covalent amide bond and hybridization, respectively. The proposed nanoaptasensor combined the advantages of the deposition of neatly arranged PtAgNPs and the covalent attachment of the capture probe at the surface of the modified electrode. The change of interfacial charge transfer resistance (R ct ) recorded by [Fe(CN)6]3−/4− as a redox probe was monitored for sensitive quantitative detection of DCF. Addition of DCF resulted in the increase of the value of R ct due to suppression of the electron exchange between [Fe(CN)6]3−/4− in the surface layer. Under optimized conditions, the proposed aptasensor showed good detection range from 10 pM to 800 nM with unprecedented detection limit of 2.8 pM. More importantly, the developed strategy showed highly sensitive responses to DCF, responses that are more sensitive than those of previously reported methods.

Aptamer-based electrochemical biosensor by using Au-Pt nanoparticles, carbon nanotubes and acriflavine platform

Herein, an ultrasensitive electrochemical aptasensor for quantitative detection of bisphenol A (BPA) was fabricated based on a novel signal amplification strategy. This aptasensor was developed by electrodeposition of gold-platinum nanoparticles (Au-PtNPs) on glassy carbon (GC) electrode modified with acid-oxidized carbon nanotubes (CNTs-COOH). In this protocol, acriflavine (ACF) was covalently immobilized at the surface of glassy carbon electrode modified with Au-PtNPs/CNTs-COOH nanocomposite. Attachment of BPA-aptamer at the surface of modified electrode was performed through the formation of phosphoramidate bonds between the amino group of ACF and phosphate group of the aptamer at 5′end. By interaction of BPA with the aptamer, the conformational of aptamer was changed which lead to retarding the interfacial electron transfer of ACF as a probe. Sensitive quantitative detection of BPA was carried out by monitoring the decrease of differential pulse voltammetric (DPV) responses of ACF peak current with increasing the BPA concentration. The resultant aptasensor exhibited good specificity, stability and reproducibility, indicating that the present strategy was promising for broad potential application.

Design of ultrasensitive bisphenol A–aptamer based on platinum nanoparticles loading to polyethyleneimine-functionalized carbon nanotubes

Here, a highly sensitive electrochemical aptasensor based on a novel signal amplification strategy for the determination of bisphenol A (BPA) was developed. Construction of the aptasensor began with the deposition of highly dispersed platinum nanoparticles (PtNPs)/acid-oxidized carbon nanotubes (CNTs–COOH) functionalized with polyethyleneimine (PEI) at the surface of glassy carbon (PtNPs/PEI/CNTs–COOH/GC) electrode. After immobilizing the amine-capped capture probe (ssDNA1) through the covalent amide bonds formed by the carboxyl groups on the nanotubes and the amino groups on the oligonucleotides, we employed a designed complementary BPA–aptamer (ssDNA2) as a detection probe to hybridize with the ssDNA1. By adding BPA as a target, the aptamer specifically bound to BPA and its end folded into a BPA-binding junction. Because of steric/conformational restrictions caused by aptamer–BPA complex formation at the surface of modified electrode, the interfacial electron transfer of [Fe(CN)6]3−/4− as a probe was blocked. Sensitive quantitative detection of BPA was carried out by monitoring the decrease of differential pulse voltammetric responses of [Fe(CN)6]3−/4− peak current with increasing BPA concentrations. The newly developed aptasensor embraced a number of attractive features such as ease of fabrication, low detection limit, excellent selectivity, good stability and a wide linear range with respect to BPA.

A label-free aptasensor based on polyethyleneimine wrapped carbon nanotubes in situ formed gold nanoparticles as signal probe for highly sensitive detection of dopamine

Herein, a highly sensitive and selective aptamer biosensor for quantitative detection of a model target, dopamine (DA), was developed by using a gold (Au) electrode modified with highly dispersed gold nanoparticles (AuNPs) and acid-oxidized carbon nanotubes (CNTs-COOH) functionalized with polyethyleneimine (PEI). Amine-terminated12-mercaptureprobe (ssDNA1) as a capture probe and specific DA-aptamer (ssDNA2) as a detection probe was immobilized on the surface of a modified electrode via the formation of covalent amide bond and hybridization, respectively. Methylene blue (MB) was used as the redox probe, which was intercalated into the aptamer through the specific interaction with its guanine bases. In the presence of DA, the interaction between aptamer and DA displaced the MB from the electrode surface, rendering a lowered electrochemical signal attributed to decreased amount of adsorbed MB. The developed electrochemical DA aptasensor showed a good linear response to DA from 5 to 300nM with detection limit of 2.1nM. The biosensor also exhibited satisfactory selectivity and could be successfully used to detect DA in blood serum sample.

Design and characterization of electrochemical dopamine–aptamer as convenient and integrated sensing platform

Here, an ultrasensitive label-free electrochemical aptasensor was developed for dopamine (DA) detection. Construction of the aptasensor was carried out by electrodeposition of gold–platinum nanoparticles (Au–PtNPs) on glassy carbon (GC) electrode modified with acid-oxidized carbon nanotubes (CNTs–COOH). A designed complementary amine-capped capture probe (ssDNA1) was immobilized at the surface of PtNPs/CNTs–COOH/GC electrode through the covalent amide bonds formed by the carboxyl groups on the nanotubes and the amino groups on the oligonucleotides. DA-specific aptamer was attached onto the electrode surface through hybridization with the ssDNA1. Methylene blue (MB) was used as an electrochemical indicator that was intercalated into the aptamer through the specific interaction with its guanine bases. In the presence of DA, the interaction between aptamer and DA displaced the MB from the electrode surface, rendering a lowered electrochemical signal attributed to a decreased amount of adsorbed MB. This phenomenon can be applied for DA detection. The peak current of probe (MB) linearly decreased over a DA concentration range of 1–30 nM with a detection limit of 0.22 nM.

Directing carbon nanotubes from aqueous phase to o/w interface for heavy metal uptaking.

Separation and reuse of dispersed nanoparticles are major obstacles to the extensive application of nano-sized absorbents in wastewater treatment. Herein, we demonstrate the capability of directing acid-oxidized carbon nanotubes (CNTs) as the transfer vehicles of heavy metal ions from simulated wastewater. The heavy metal-loaded CNTs can be readily separated from the aqueous phase via the aggregation process at an oil/water (o/w) interface. The minimum surfactant amount to achieve 99 % transfer ratio (Tr) of 100 mg/L CNTs from water phase to o/w interface was ∼0.01 mM. The adsorption experiments showed that the removal efficiency of the divalent lead ions increased with an increase in CNT mass, and the subsequent addition of cetyltrimethylammonium bromide (CTAB) surfactant did not negatively impact the removal of soluble divalent lead species (Pb(II)). In a wide region of pH and ionic strength, both the decontamination of Pb(II) and the transfer of CNTs from water phase to o/w interface can be accomplished successively. The method presented in this study may be developed as a generic one for collecting or recycling the pollutant-loaded nano-sized absorbents.

Electropolymerization of PEDOT on CNTs conductive network assembled at water/oil interface

We demonstrate an interfacial electrochemical process for the preparation of composite film of poly(3,4-ethylenedioxythiophene) (PEDOT) and carbon nanotubes (CNTs) at a water/oil (w/o) interface. The 3,4-ethylenedioxythiophene (EDOT) monomer and lithium perchlorate electrolyte were supplied from the oil phase (dichloromethane) and water phase, respectively. Firstly, acid-oxidized carbon nanotubes were assembled at the w/o interface with the assistance of a trace dosage of cationic surfactant, forming a CNTs network. And then the CNTs network acted as a “working electrode” and “reinforcement bars” for the electropolymerization of PEDOT, resulting in the production of PEDOT@CNTs composite film. Higher CNTs areal density (μg/mm2 CNTs) caused a faster radial growth of PEDOT at the CNTs network, namely a faster growth of “apparent area” of the composite film. The current-time curves of the electropolymerization demonstrated that there was an optimal areal density of CNTs network (0.40μg/mm2) to achieve the largest amount of polymerized PEDOT. These observations suggested that the assembled CNTs network and the formed PEDOT@CNTs composite film not only functioned as an electrical conductor for the electrochemical process, but also affected the mass transfer of the reactants. The prepared PEDOT@CNTs composite film showed heterogeneous structures with a capacitance of 0.148 F/C. The pre-assembled nano-particles network involved liquid-liquid interfacial eletropolymerization may be developed for the preparation of a series of conductive polymer@nanoparticle composite film.

Improved mechanical and crystallization characteristics of polymer nanocomposites reinforced with carbon nanotube oxidized via wet mechanochemical method

In the present study, a novel approach of wet mechanochemical oxidation of carbon nanotubes (CNTs) has been established in order to improve the uniformity in nanodispersion of the CNTs. This approach was found to be more efficient for CNT oxidation as compared to the acid oxidation method as observed from the Fourier transform infrared spectroscopy and titrometric analyses. From the x-ray diffraction and Raman spectroscopic analyses, it was also noticed that the damage to the surface of CNTs caused by acid can be prevented using wet mechanochemical process for oxidation. The transmission electron microscopic micrographs also revealed lesser degree of entanglement of the CNT fibrils. The polymer nanocomposites reinforced with wet mechanochemically oxidized CNT (McCNT) revealed considerably higher mechanical properties as compared to that of acid-oxidized CNTs. Also, the much higher uniformity in dispersion and nucleating effect of the McCNT was observed from the Raman spectroscopy and differential scanning calorimetry analysis, respectively.

Effects of carbon dioxide and acidic carbon compounds on the analysis of Boehm titration curves

In the characterization of the surface functionality of acid-oxidized carbon nanotubes (CNTs) using the Boehm titration method, dissolution of acidic carbon compounds (ACCs) fragmented from the acid-oxidized CNTs and atmospheric carbon dioxide (CO 2) in the reaction base results in a somewhat over-estimation of the surface functionality of the CNTs. We developed a modified Henderson–Hasselbalch equation to show that the influence of the carboxylic and phenolic groups of ACCs and atmospheric CO 2 on the resultant titration curve can be identified and quantitatively measured, which makes it possible to determine the true surface functionality of acid-oxidized CNTs and ACCs.

Enhanced Nucleation Rate of Polylactide in Composites Assisted by Surface Acid Oxidized Carbon Nanotubes of Different Aspect Ratios

Biodegradable polylactide (PLA) composites added with acid oxidized multiwalled carbon nanotubes (A-MWCNTs) of two different aspect ratios (length to diameter) were prepared by coagulation. The aspect ratios and surface structures of A-MWCNTs were characterized by TGA, Raman, and SEM measurements. The percolation thresholds for gelation in the PLA composites with A-MWCNTs of large and small aspect ratios are 2.5 and 4.0 wt %, respectively, which were determined by a rheological method, and in turn, the rheological result confirms the aspect ratio differences for the added two types of A-MWCNTs in the composites. Isothermal crystallization kinetics of neat PLA and its composites were further investigated by using polarized optical microscope (POM) and differential scanning calorimetry (DSC) to clarify the effects of A-MWCNTs of different aspect ratios and concentrations. The different aspect ratio A-MWCNTs with the same carboxyl group mass percent show substantial effects on PLA crystallization kinetics. Those with smaller aspect ratios enhance nucleation rate for PLA spherulites much more than those with larger aspect ratios. This phenomenon can be attributed to fewer sidewall carboxyl groups on the surfaces of A-MWCNTs with smaller aspect ratios, which provides more nucleation sites for PLA crystallization than those with larger aspect ratios at the same concentration, resulting in faster PLA nucleation rates for the former one.

Soluble P3HT-Grafted Carbon Nanotubes: Synthesis and Photovoltaic Application

CH2OH-terminated regioregular poly(3-hexylthiophene) (P3HT) was grafted onto carboxylic groups of acid-oxidized carbon nanotubes (CNTs) via esterification reaction. The P3HT-attached CNTs (P3CNTs) are soluble in common organic solvents, facilitating an intimate mixing with free P3HT chains for strong electronic interactions. The optical and electrochemical properties of the resultant nanocomposite were found to be different from the conventional composite, in which the pristine CNT and P3HT were physically mixed together (P3HT/CNT). Electrochemical measurements on the onset oxidation and reduction potentials of the P3CNT showed positive shifts by 0.06 and 0.1 eV, respectively, with respect to the corresponding values of pure P3HT, indicating that P3CNT has a lower highest occupied molecular orbital (HOMO) energy level and a lower lowest unoccupied molecular orbital (LUMO) energy level than those of pure P3HT. Bilayer photovoltaic devices with a thin film of pure P3CNT as the electron-donor and C60 as the ...

Interfacial Energy Level Alignment at Acid Oxidized Carbon Nanotube - Triphenyldiamine Contacts

AbstractWe report an ultraviolet photoelectron spectroscopy study of the energetics at the interface between acid oxidised carbon nanotubes and the archetypical molecular N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'biphenyl-4,4'diamine(TPD). Electrical equilibrium is achieved across both interfaces within the experiment time frame due to the formation of an interfacial dipole layer which abruptly shifts the vacuum level at the interface. To the authors knowledge this is the first reported measurement of the electronic structure of a carbon nanotube / organic semiconductor interface; a system in which the magnitude of the dipole layer formed at the interface upon contact formation is proportional to the difference in work function between the substrate and organic semiconductor overlayer.

Aqueous stability of oxidized carbon nanotubes and the precipitation by salts

The stability of nitric acid oxidized carbon nanotubes (CNTs) and the precipitation of oxidized CNTs in water by salts were investigated. Stability investigation shows that during an aging time of 30 days, oxidized CNTs dispersion shows characteristic UV–vis absorbance peak of individual CNTs at 252 nm and CNTs concentration in the dispersion after 30 d aging is 85% of the initial concentration. The precipitation value of salts were measured and the precipitation value follows the order of NaCl > KCl > 1/2(MgCl 2) > 1/2(CaCl 2) > 1/3(FeCl 3) > 1/3(AlCl 3). The nature of anions investigated has little effect on precipitation values of salts.

Surface Adsorption and Replacement of Acid-Oxidized Single-Walled Carbon Nanotubes and Poly(vinyl pyrrolidone) Chains

Quartz crystal microbalance (QCM) was used to investigate the adsorption of acid-oxidized single-walled carbon nanotubes (Ox-SWNTs) and poly(vinyl pyrrolidone), PVP. It was found for the first time that Ox-SWNTs adsorbed onto the QCM electrode can be effectively replaced by PVP chains in an aqueous solution. This replacement process was also investigated by atomic force miscroscopic (AFM) imaging, which shows good agreement with the QCM measurements. This study provides powerful tools for fundamental investigation of polymer-nanotube interactions and for controlled design/fabrication of functional polymer-nanotube surfaces for potential applications.

Lithium insertion into the composites of acid-oxidized carbon nanotubes and tin oxide

Lithium intercalation into the composites of acid-oxidized carbon nanotubes and tin oxide was studied in an electrolyte system, 1 M solution of LiPF 6 dissolved in a 50:50 mixture by volume of ethylene carbonate (EC) and dimethyl carbonate (DMC). The electrochemical method that is constant current charge–discharge test was used for electrochemical properties of the acid-oxidized carbon nanotubes and tin oxide. The nanocomposites show higher specific capacities than the acid-oxidized carbon nanotubes and better cyclability than SnO 2, and the improvement is believed to be due to the improved maintainability of high dispersion of SnO 2 in the carbon nanotubes. The second cycle de-lithiation capacity of 255 mAh/g from the nanocomposites was nevertheless reduced to 250 mAh/g after 50 deep charge and discharge cycles, and the nanocomposites of acid-oxidized carbon nanotubes and SnO 2 may be considered as a candidate anode material for Li-ion batteries.

DNA-modified Carbon Nanotubes for Self-assembling and Biosensing Applications

We have demonstrated that specific DNA sequences could be covalently immobilized onto acid-oxidized and plasma-activated carbon nanotubes. While various functional supramolecular structures could be prepared by self-assembling of the acid-oxidized carbon nanotubes attached with DNA chains of complementary sequences, the DNA-immobilized aligned carbon nanobues have been demonstrated to be significant for sensing complementary DNA and/or target DNA chains of specific sequences with a high sensitivity and selectivity.

Electrochemical impedance study of Li-ion insertion into the raw acid-oxidized carbon nanotubes

Electrochemical impedance spectroscopy (EIS) was applied for the raw acid-oxidized multiwall carbon nanotubes during Li-ion insertion with the electrolyte of 1M LiPF 6 in EC and DMC. Impedance spectroscopy consists of two separated arcs in the high and intermediate range frequency. The high frequency arc is attributed to Li migration within the surface films and the medium frequency arc is associated with the charge transfer. Obtained spectra were analyzed with an equivalent circuit model. Kinetic parameters such as the charge transfer resistance, film resistance, diffusion coefficient and exchange current were evaluated. The contribution of the film to the measured impedance response is discussed.

Effects of doped copper on electrochemical performance of the raw carbon nanotubes anode

The raw carbon nanotubes pre-doped with copper are used as anode materials for lithium ion batteries. Constant current discharge and charge tests using the raw carbon nanotubes pre-doped with copper as Li + storage compounds show lower specific capacities than that of the acid-oxidized carbon nanotubes. The acids play an important role; H 2SO 4 and HNO 3 can easily permeate through the graphene sheets, then they will make the defects or pores in the graphene sheets, and this reaction can make the expansion of the graphite. Meanwhile, Cu 2+ will diffuse into the pores and onto the outer surfaces of the carbon nanotubes. Cu 2+ can be easily turned into Cu at high temperature in the presence of the carbon nanomaterial. So parts of the pores and the surfaces of the carbon nanotubes will be filled with the Cu atom. Once the space positions of the nanotubes were occupied, lithium cannot intercalate into the pores and onto the outer surface of the carbon nanotubes, thus the doped carbon nanotubes will have a low specific capacity.