Carboxylic Acid-functionalized Multiwalled Carbon Nanotubes Research Articles

Redox-active cerium-based metal–organic layers coordinated on carbon nanotubes as materials for supercapacitors

In this work, the redox-active, two-dimensional (2D), and highly dispersible metal–organic layers (MOLs) constructed from hexa-cerium(IV) clusters, CeBTB (BTB = 1,3,5-benzenetribenzoate), were directly coordinated onto the surface of carboxylic acid-functionalized multi-walled carbon nanotubes (CNTs) by utilizing a post-synthetically grafting approach. Nanocomposites with various MOL-to-CNT ratios can be synthesized. Crystallinity, porosity, morphology, electrical conductivity, and electrochemical behaviors of CeBTB and all nanocomposites as well as the chemical interaction between CeBTB and CNT in the composite are investigated. Thin films of materials with the same mass loading are then fabricated for measuring their capacitive performances in neutral aqueous solutions of Na2SO4. With the electrical conductivity provided by carbon nanotubes and the redox activity of CeBTB between Ce(IV) and Ce(III), the optimal CeBTB-CNT nanocomposite can show a better capacitive performance compared to the pristine CeBTB, pristine CNT, and the physical mixture of both of them with the same MOL-to-CNT ratio. With such a simple post-synthetically grafting approach that can precisely control the ratio between the 2D MOLs and CNTs, the findings here open opportunities for designing numerous composites composed of MOLs and nanocarbons with tunable conductivity, redox activity, and functionality, which are potential candidates for a range of applications.

Carboxylic acid-functionalized multiwalled carbon nanotubes (COOH-MWCNTs) improved production of atropine in callus of Datura inoxia by influencing metabolism, gene regulation, and DNA cytosine methylation; an in vitro biological assessment

Atropine is a well-known tropane alkaloid commonly employed in medicine class called anticholinergics. This study intends to address biochemical and molecular responses of Datura inoxia calluses to fortifying culture medium with carboxylic acid-functionalized multi-walled carbon nanotubes (COOH-MWCNTs). The application of MWCNTs influenced callogenesis performance and biomass in a dose-dependent manner. The MWCNT at 5 mgL−1 resulted in the highest biomass of calluses by 57%. While, MWCNTs at high concentrations were accompanied by cytotoxicity. On the other hand, MWCNTs at concentrations above 100 mgL−1 exhibited cytotoxicity, decreased callogenesis performance, and reduced Atropine biosynthesis. The MWCNTs increased the activity of phenylalanine ammonia-lyase (PAL) and catalase enzymes. The concentrations of proline and soluble phenols displayed upward trends in response to using MWCNTs. According to the HPLC assessment, enriching culture medium with MWCNTs at 5 mgL−1 elicited Atropine production in calluses by 64%. The quantitative PCR assessment referred to the upregulation in the transcription of the PAL gene. The expression of ornithine decarboxylase (ODC) and putrescine N-methyltransferase 1 (PMT) genes were also upregulated in calluses cultured in a medium supplemented with MWCNTs. Methylation Sensitive Amplification Polymorphism (MSAP) technique indicated that employing MWCNTs altered the DNA methylation profile, reflecting epigenetic modification. Overall, engineering plant cells with MWCNTs as a nano-elicitor can be suggested for large-scale synthesis of industrially-valuable secondary metabolites.

In-situ growth of cerium-based metal organic framework on multi-walled carbon nanotubes for electrochemical detection of gallic acid

Gallic acid (GA) is a valuable polyphenolic compound. GA has a strong antioxidant effect, and its biological properties are anti-inflammatory, anti-histamine, anti-tumor, scavenging free radicals and protecting cardiovascular disease. Therefore, accurate and fast determination of gallic acid content is of great significance to human health. A simple and responsive electrochemical sensor for the detection of gallic acid was constructed by modifying glassy carbon electrodes with the CeMOF/MWCNTs composites synthesized by in situ growth of Ce metal organic framework (CeMOF) on carboxylic acid-functionalized multi-walled carbon nanotubes. The nanomaterials were characterized accurately by X-ray diffraction (XRD), X-ray photoelectron spectroscop (XPS) and scanning electron microscopy (SEM) and so on. Under the optimized conditions, the linear range of the sensor to detect gallic acid is 1.5 μM-200 μM, and the LOD is 0.14 μM (S/N = 3). The sensor can detect gallic acid in tea with good repeatability, stability and anti-interference.

Enhanced electrochemical hydrogen storage performance of organophosphonic carboxylic acid-modified multiwalled carbon nanotubes/Bi2S3 composite

Hydrogen energy, one of the recognized green energy sources, has many advantages, and electrochemical hydrogen storage has been regarded as one of the outstanding energy storage systems. The present research describes that the organophosphonic carboxylic acid-modified multiwalled carbon nanotubes/Bi2S3 composite (OPCAMCN/BS) has been produced successfully by a facile solution reaction method, and it has been characterized by Fourier transform infrared (FTIR), scanning electron microscope (SEM), energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), and porous structure analysis. Because of the efficient synergistic effect of organophosphonic carboxylic acid-functionalized multiwalled carbon nanotubes and bismuth sulfide, the composite displays excellent electrochemical hydrogen storage and stability performances. The electrochemical hydrogen storage performance of the OPCAMCN/BS electrodes has been measured, and its discharge capacity (950.9 mAh/g) greatly exceeds the relevant values of those two reference materials, and the cycle life of the OPCAMCN/BS electrodes is higher than that of Bi2S3 and MWCNTs/BS. Furthermore, the as-synthesized composite OPCAMCN/BS exhibits very low charge transfer resistance which signifies fast electron transfer. Therefore, OPCAMCN/BS is expected to be used as a kind of excellent electrochemical hydrogen storage material and can be applied in the areas of renewable energy to reduce the use of fossil fuels.

Facile preparation of water-soluble multiwalled carbon nanotubes bearing phosphorylcholine groups for heat generation under near-infrared irradiation

In the present study, water-soluble molecular complexes between carboxylic acid-functionalized multiwalled carbon nanotubes (MWCNTs) and biocompatible poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) were prepared by hand grinding. MWCNTs could be solubilized in phosphate-buffered saline using this simple method. The suspended concentration of MWCNTs was found to increase with increasing polymer concentration and pH of the solution. Heat generation from the complexes was studied upon irradiation with near-infrared (NIR) radiation at a wavelength of 808 nm. The results demonstrated that MWCNTs absorbed light and generated heat when the molecular complex was irradiated by NIR. The solution temperature increased with increasing MWCNT concentration and irradiation time. This study presents a facile method for preparation of water-soluble molecular complexes between carboxylic acid-functionalized multiwalled carbon nanotube and poly(2-methacryloyloxyethyl phosphorylcholine) (MWCNTs/PMPC) by hand grinding. MWCNTs could be solubilized in aqueous environment with higher suspended concentrations when increasing polymer concentration and pH of the solution. MWCNTs/PMPC adsorbed light and induced heat generation to reach the temperature required for photothermal therapy (PTT) when the complexes were irradiated by near-infrared (NIR) at a wavelength of 808 nm. The water-soluble MWCNT complex covered by biocompatible PMPC is a promising candidate for PTT application.

A Prussian Blue ZnO Carbon Nanotube Composite for Chronoamperometrically Assaying H2O2 in BT20 and 4T1 Breast Cancer Cells.

A Prussian Blue (PB) zinc oxide carbon nanotube sensing composite was developed for the rapid assaying of H2O2 generated from BT20 and 4T1 breast cancer cells, important for elucidating mechanisms governing apoptosis of these cell lines. The combination of H2O2's transient nature along with matrix effects makes monitoring this molecule in biological samples a challenge. The standard addition method (SAM) was coupled with chronoamperometric sensing (CA) to overcome these obstacles. An electrocatalyst composite consisting of refluxed zinc oxide nanoparticles (NPs) tethered to carboxylic acid-functionalized multiwalled carbon nanotubes (ZnO/COOH-MWNTs) was electrostatically attached to PB for signal enhancement. Optimization of the sensor was achieved via adjusting solution pH and stirring time to optimize PB electrostatic attachment to ZnO/COOH-MWNTs prior to its deposition onto the working glassy carbon electrode (GCE) surface. CA SAM showed the ability to accurately measure H2O2 within the 1-21 μM range, suitable for monitoring cancer cell line apoptosis resistance scenarios and offering analytical advantages over standard enzyme-linked immunosorbent assays (ELISA) for rapid, matrix-effect-free analysis.

Using carbon nanotubes to deliver genes to hard-to-transfect mammalian primary fibroblast cells

The insertion of DNA into primary mammalian cells is an important step towards gene therapy and production of transgenic animals. Recently, carbon nanotubes have been explored as an efficient novel non-viral system for delivering genes to cells due to their unique structure and properties. However, their potential for transfecting primary bovine cells in non-toxic concentrations has not been tested. The purpose of this study was to evaluate the cytotoxicity of carboxylic acid-functionalized multiwalled carbon nanotubes (COOH-MWCNTs) and their use to deliver plasmid DNA encoding the gene of green fluorescent protein to bovine primary fibroblast cells. Flow-cytometry cell viability results have shown the non-toxic nature of COOH-MWCNTs at low concentrations. The frequency shifts in Raman spectroscopy showed that the plasmid DNA connects to the nanomaterial. Fluorescence imaging, flow-cytometry and PCR analysis confirmed that the COOH-MWCNT nanovectors delivered pDNA into primary fibroblast cells successfully. The results show that COOH-MWCNTs can be attractive alternatives for delivery of DNA into hard-to-transfect primary bovine cells.

Enzyme-free uric acid electrochemical sensors using β-cyclodextrin-modified carboxylic acid-functionalized carbon nanotubes

Carboxylic acid-functionalized multi-walled carbon nanotubes (COOH-MWCNT) were modified via ultrasonication with β-cyclodextrin (β-CD) to obtain a COOH-MWCNT:β-CD nanocomposite material for the purpose of developing an enzyme-free electrochemical sensor for uric acid—a clinically relevant molecule implemented in pregnancy-induced hypertension diagnosis. The nanocomposite material is deposited onto glassy carbon electrodes and subsequently capped with layers of Nafion and Hydrothane polyurethane. The surface morphology and electronic structure of the nanocomposite material were characterized using UV–Vis, TEM, and FTIR. The performance of the electrochemical sensor was measured through direct injection of UA during amperometry. With the high surface area of the COOH-MWCNT in concert with the selectivity provided by β-CD, the composite system outperforms similar COOH-MWCNT systems, displaying enhanced UA sensitivity versus films with only COOH-MWCNT. With the improved sensitivity (4.28 ± 0.11 µA mM−1) and fast response time (4.0 ± 0.5 s), the sensors offer wide detection of UA across clinically relevant ranges (100–700 μM) as well as demonstrated selectivity against various interferents.

Interfacial charge transfer in functionalized multi-walled carbon nanotube@TiO2 nanofibres.

A new insight into photoinduced charge transfer processes across carbon nanotube@TiO2 interfaces has been gained based on experimental details from transient absorption spectroscopy. We show that photoinduced, interfacial hole transfer to carboxylic acid-functionalized multiwalled carbon nanotubes (oxMWCNTs) from TiO2 results in hole-doped oxMWCNTs and reduced TiO2. The latter is inferred from femto- and nanosecond transient absorption spectroscopy performed with oxMWCNT@TiO2 dispersions and complemented with investigations using methyl viologen and N,N,N',N'-tetramethyl-p-phenylenediamine as an electron scavenger and a hole scavenger, respectively. The results of ultraviolet photoemission spectroscopy (UPS) of the compounds corroborate the findings, highlighting the strong coupling between oxMWCNTs and TiO2 in these hybrids.

Electrochemiluminescence sensor for melamine based on a [formula omitted]-doped silica nanoparticles/carboxylic acid functionalized multi-walled carbon nanotubes/Nafion composite film modified electrode

In this work, a sensitive electrochemiluminescence (ECL) sensor for the determination of melamine (MEL) was developed based on a Ru(bpy)32+-doped silica nanoparticles (RUDS)/carboxylic acid functionalized multi-walled carbon nanotubes (CMWCNTs)/Nafion composite film modified electrode. The homogeneous spherical RUDS were synthesized by a reverse microemulsion method. As Ru(bpy)32+ were encapsulated in the RUDS, Ru(bpy)32+ dropping from the modified electrode can be greatly prevented, which is helpful for obtaining a stable ECL signal. Moreover, to improve the conductivity of the film and promote the electron transfer rate on electrode surface, CMWCNTs with excellent electrical conductivity and large surface area were applied in the construction of the sensing film. As CMWCNTs acted as electron bridges making more Ru(bpy)32+ participate in the reaction, the ECL intensity was greatly enhanced. Under the optimum conditions, the relative ECL signal (△IECL) was proportional to the logarithmic MEL concentration ranging from 5×10−13 to 1×10−7molL−1 with a detection limit of 1×10−13molL−1. To verify the reliability, the thus-fabricated ECL sensor was applied to determine the concentration of MEL in milk. Based on these investigations, the proposed ECL sensor exhibited good feasibility and high sensitivity for the determination of MEL, promising the applicability of this sensor in practical analysis.

The fabrication and characterization of nanocomposites containing new poly(amide–imide) based on 4,4-methylenebis(3-chloro-2,6-diethyl trimellitimidobenzene) and carboxylic acid-functionalized multiwalled carbon nanotubes

In this article, a nanostructure poly(amide–imide) (PAI) was prepared from the polymerization of 4,4′-methylenebis(3-chloro-2,6-diethyl trimellitimidobenzene) with 3,5-diamino- N-(4-hydroxyphenyl)benzamide using tetra- n-butylammonium bromide as a green media and triphenylphosphite as a condensing agent. This methodology is safe and green since toxic and volatile organic solvents were eliminated. To obtain a homogeneous dispersion of multiwalled carbon nanotubes (MWCNTs) in the PAI matrix, carboxyl-modified MWCNT (CA-MWCNT) was used. The resulting nanocomposites were characterized by Fourier transform infrared spectroscopy, powder X-ray diffraction, field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and thermogravimetric analysis. TEM and FESEM results confirm good dispersion of CA-MWCNTs in the polymer matrix.

Structure, electrical and mechanical properties of polyamide 66/acid-treated MWCNT composite films prepared by solution mixing in the presence of nonionic surfactant

Two different sets of polyamide 66(PA66)-based composite films containing 2.0-10.0 wt% acid-treated multiwalled carbon nanotubes (MWCNT) were manufactured by solution mixing and casting method in the presence or absence of a nonionic surfactant. For the improved dispersion and interfacial interaction of MWCNTs in the PA66 matrix, carboxylic acid-functionalized MWCNTs were prepared by the acid-treatment of pristine MWCNTs. The uniform dispersion of the acidtreated MWCNTs in the PA66 matrix was confirmed from FE-SEM images of the fractured composite film surfaces. DSC thermograms supported that the acid-treated MWCNTs served as nucleating agents for the melt-crystallization of PA66 in both composite films prepared with/without the addition of the surfactant. The electrical and tensile mechanical properties of the composite films prepared with the surfactant were ~20 % higher than those of the composite films manufactured without the surfactant. For both composite films, sheet resistivity and tensile mechanical properties were found to be highly decreased and increased, respectively, with the increment of the acid-treated MWCNT content.

Morphology evolution induced by carbon nanotubes on thermal and mechanical characters of semi-crystalline aromatic polyimide

A series of nanocomposites based on a new semi-crystalline polyimide (PI) and multi-walled carbon nanotubes (MWCNTs) were prepared by in situ polymerization. The TEM measurement reveals the improved dispersion of carboxylic acid-functionalized MWCNTs (COOH-MWCNTs) in semi-crystalline PI compared with pristine MWCNTs. The TGA analysis show that the concentration of carboxylic acid groups on the surface of nanotubes is about 4.34 wt%. The FT-IR spectroscopy analysis indicate that the imide rings of the PI interact non-covalently with nanotubes. The Polarized optical microscopy observation reveals significant morphology evolution in semi-crystalline PI induced by MWCNTs. The SEM micrographs suggest the strong interfacial interaction between COOH-MWCNTs and PI main chains, and significant changes in the fracture surfaces morphology. The WAXRD measurements reveal that COOH-MWCNTs promote the semi-crystalline PI crystallinity and structure change. COOH-MWCNTs can more efficiently improve the mechanical and thermal properties of resulting nanocomposites than pristine MWCNTs. COOH-MWCNT/PI nanocomposites show increases of Young’s modulus and yield strength, as high as 20–30 %, without sacrificing the elongation at break at loadings of 0.5 wt% nanotubes. Furthermore, with increasing the loadings of COOH-MWCNTs to 1.0 wt%, Young’s modulus and yield strength decrease due to nanotube aggregation, but elongation at break increase about 46 %. An abrupt increase of elongation at break in pristine MWCNT/PI nanocomposites was also registered at nanotubes loadings increasing from 0.5 to 1 wt%. These results indicate that the properties of semi-crystalline PI nanocomposites reinforced with carbon nanotubes are not only determined by the dispersion of nanotubes in the PI matrix and their interfacial interactions, but also by the crystalline phase morphology evolution in the PI matrix.

Dynamic Behavior of Nanocomposites Reinforced with Multi-Walled Carbon Nanotubes (MWCNTs).

The influence of multi-walled carbon nanotubes (MWCNT) on the structural dynamic behavior of MWCNT/epoxy nanocomposites was investigated. Two different types of MWCNTs, pristine MWCNT and functionalized MWCNT, were used in this study. Carboxylic acid-functionalized MWCNTs (MWCNT-COOH) were obtained by oxidation pristine MWCNTs via sonication in sulfuric-nitric acid and characterized by Fourier transform infrared spectroscopy (FTIR). Dynamic behaviors of the MWCNT reinforced nanocomposite including the natural frequency and damping ratio were determined using free vibration test. Experimental results showed that the damping ratio of the nanocomposite decreases with the increase of the MWCNT addition, while the natural frequency is increasing with the increase of the MWCNT addition. Functionalized MWCNTs improved the interfacial bonding between the nanotubes and epoxy resin resulting in the reduction of the interfacial energy dissipation ability and enhancement of the stiffness.

Surface Immobilization of Carbon Nanotubes by <I>β</I>-Cyclodextrins and Their Inclusion Ability

The surface immobilization of beta-cyclodextrins on the surface of multiwalled carbon nanotubes (MWNTs) in an aqueous medium was achieved by covalent-binding of diamino-functionalized beta-cyclodextrin with carboxylic acid-functionalized MWNTs via amide linkages using a water-soluble condensation agent at room temperature. The obtained product denoted as beta-cyclodextrin-modified MWNTs was highly dispersible in an aqueous medium. The covalent surface functionalization of MWNTs by beta-cyclodextrin was characterized by FTIR, TGA, EDS and TEM. The thermogravimetric analyses indicated that -70 wt% beta-cyclodextrin was attached on the surface of MWNTs. Furthermore, the fluorometric analysis for adsorption of rhodamine 6G dye suggested that the formation of beta-cyclodextrin-dye inclusion conjugate takes place prior to the adsorption of dyes on MWNTs and uniform dispersion of MWNTs after surface immobilization allows superior fluorescence quenching than the pristine and oxidized MWNTs.

Facile synthesis of poly(p-phenylenediamine)/MWCNT nanocomposites and characterization for investigation of structural effects of carbon nanotubes

Poly(p-phenylenediamine) (PpPD)/carboxylic acid-functionalized multiwalled carbon nanotubes (c-MWCNTs) nanocomposites were prepared by chemical oxidative polymerization using potassium persulfate (K2S2O8) as an oxidant. Field-emission scanning electron microscopy (FE–SEM) and field-emission transmission electron microscopy (FE–TEM) showed that a tubular layer of PpPD was coated on the surface of carbon nanotubes with a thickness of 10–20 nm. FT–IR analysis provided an evidence for the formation of nanocomposites. The thermal stability of nanocomposites was improved by addition of c-MWCNTs as confirmed by thermogravimetric analysis (TGA). XRD spectra showed that the crystalline nature of PpPD was not affected much by the addition of c-MWCNTs. As the content of c-MWCNTs was increased, the electrical conductivity of the nanocomposites increased due to the interaction between polymer and nanotubes that enhances electron delocalization.

Layer-by-Layer Assembly of Aqueous Dispersible, Highly Conductive Poly(aniline-co-o-anisidine)/Poly(sodium 4-styrenesulfonate)/MWNTs Core–Shell Nanocomposites

Poly(aniline-co- o-anisidine) (P(An-co- o-As)) ionomers and poly(sodium 4-styrenesulfonate) (PSS) were layer-by-layer (LbL) assembled on carboxylic acid-functionalized multiwalled carbon nanotubes (MWNTs). The multilayered polyelectrolyte greatly enhanced the dispersibility and stability of MWNTs in aqueous solutions. More importantly, the nanocomposites showed 3 orders of magnitude of conductivity increase, 4.2 S/cm, compared to that of neat ionomers, 0.004 S/cm. The deposition procedure was monitored with zeta (zeta) potential changes. Fourier transform infrared (FT-IR), ultraviolet-visible (UV-vis), and Raman spectra confirmed charge transfer from the quinoid units of the P(An-co- o-As) to MWNTs, which effectively delocalize the electrons. Further, we explored the pH response of the assembled P(An-co- o-As)/PSS/MWNTs multilayer nanocomposites. The sharp transition of the conductivity in the pH range of 2 to 6 makes the nanocomposites promising candidates for chemical-biological sensing.

Multiwalled Carbon Nanotubes with Chemically Grafted Polyetherimides

Covalent attachment of a non-fluorinated polyetherimide onto the surface of carboxylic acid-functionalized multiwalled carbon nanotubes (MWNTs) has been achieved via grafting reactions. This confirms for the first time that the grafting reaction occurs at the nanotube surface when the carboxylic acid-functionalized MWNTs react with the polyetherimide with amine-terminated groups, through both amide and imide linkages formed at the interface between the carbon nanotubes and the polyetherimide. Additionally, an increase in the average molecular weight is detected in gel permeation chromatography when the polyetherimide is chemically attached onto the nanotubes. More interestingly, the chemical bonding at the interface provides much better interfacial adhesion and mechanical stress transfer, evidenced by a significant improvement in mechanical properties. As a result of the chemical attachment, the carbon nanotube-reinforced polyetherimide composite films have enhanced electrical conductivity, thermal deformation temperatures, and mechanical properties.

Polyelectrolyte-functionalized multiwalled carbon nanotubes: preparation, characterization and layer-by-layer self-assembly

Two kinds of polyelectrolyte: polyacrylic acid (PAA) and poly(sodium 4-styrenesulfonate) (PSS), were grafted onto the convex surfaces of multiwalled carbon nanotubes (MWNTs) by surface-initiating ATRP (atom transfer radical polymerization) from the initiating sites previously anchored onto the convex surfaces of MWNTs. The grafted polyelectrolyte can be efficiently quantified by the feed ratio of monomer to MWNT-based macroinitiator, and the maximum amount of grafted polymer is higher than 55 wt%. The polyelectrolyte-coated MWNTs resembled core-shell structures justified by the TEM images of the samples obtained, which provided direct evidence for the covalent modification of MWNT. FTIR, 1H NMR and TGA were used to determine the chemical structure of the resulting products. Comparison of UV–Vis spectra demonstrated that the products were water-soluble, and that PSS was more effective for improving the water solubility of carbon nanotubes. Using the polyelectrolyte- and carboxylic acid-functionalized MWNTs as templates, and poly(2-( N, N-dimethylaminoethyl) methacrylate (PDMAEMA)/hyperbranched polysulfone amine (HPSA) and PSS as polycation and polyanion, respectively, layer-by-layer (LbL) electrostatic self-assembly was conducted in order to explore the application of the functionalized nanotubes. It was found that the functionalized MWNTs have a high efficiency for loading polyelectrolytes by the LbL approach (the adsorbed polymer quantity is higher than 10 wt% in one assembling step). TEM observations showed that the assembled polymer shell on the MWNT surfaces was very even and flat.