Carboxylic Acid-functionalized Carbon Nanotubes Research Articles

Green functionalization for chelating ligand-like and π-conjugated active sites on carbon nanotubes and its use for vanadium redox flow batteries

An imide bond-based functional group is proposed for the catalyst's active site in vanadium redox flow batteries (VRFBs). Based on the functional group's inherent property produced by the optimized process, the catalytic activity toward vanadium ion redox reaction (VIRR) on both sides was increased sixfold without adversely affecting VIRR reversibility in comparison to the raw material, carboxylic acid-functionalized carbon nanotubes. These advantages were attributed to the imide bond-based functional groups acting as a chelating ligand to form strong interactions with vanadium redox couples while also inducing facile electron transfer by the π-conjugated bonds, resulting in increased catalytic activity and reversibility. Moreover, the treatment used an eco-friendly process comprising low-cost precursors (citric acid and urea) and mild conditions (80 °C, 2 h), thereby improving the commercial availability of VRFBs. In VRFB driving tests, the fabricated electrode outperformed the electrode with a polymer-like structure in terms of catalytic activity and long-term stability due to leaching of the active sites from the latter. Overall, the proposed catalyst could be a practical option for enhancing VRFB performance based on a low-cost and eco-friendly treatment method.

Integrated carbon nanotube and triazine-based covalent organic framework composites for high capacitance performance.

As a rising class of crystallographic organic polymers, covalent-organic frameworks (COFs) have high specific surface areas, ordered pore structures, and designability, which exhibit broad application prospects in the energy storage sector. However, their low electrical conductivity hinders their potential use in supercapacitors. To improve the electrical conductivity, we introduced carboxylated multi-walled carbon nanotubes to obtain a series of carbon nanotube@COF composites by a facile one-pot method, in which 2D TFA-COFs are in situ grown on the surface of carboxylated multi-walled carbon nanotubes. Among them, the CNT@TFA-COF-3 composite exhibits good crystallinity, regular pores, excellent stability and a specific surface area of 1034 m2 g-1. As expected, as a capacitive electrode material, the CNT@TFA-COF composite shows improved electrochemical performance. Notably, the value of specific capacitance of the CNT@TFA-COF-3 composite (338 F g-1) is about 8.5, 4.9, and 7.5 times higher than those of TFA-COFs, CNTs, and the CNT/TFA-COF physically mixed complex at a current density of 1.0 A g-1, respectively. Furthermore, the CNT@TFA-COF-3 supercapacitor exhibits long-term cycle chemical stability and splendid rate capability even after 7000 charge-discharge cycles. The successful preparation of the CNT@TFA-COF-3 composite can provide new ideas for the construction of new COF-based composites and the development of new materials for energy storage.

A Rapid Label-Free Disposable Electrochemical Salivary Point-of-Care Sensor for SARS-CoV-2 Detection and Quantification.

The coronavirus disease 2019 (COVID-19) pandemic has created an urgent need for accurate early diagnosis and monitoring. A label-free rapid electrochemical point-of-care (POC) biosensor for SARS-CoV-2 detection in human saliva is reported here to help address the shortcomings of traditional nucleic acid amplification methods and give a quantitative assessment of the viral load to track infection status anywhere, using disposable electrochemical sensor chips. A new chemical construct of gold nanoparticles (GNp) and thionine (Th) are immobilized on carboxylic acid functionalized carbon nanotubes (SWCNT-COOH) for high-performance biosensing. The sensor uses saliva with a one-step pretreatment and simple testing procedure as an analytical medium due to the user-friendly and non-invasive nature of its procurement from patients. The sensor has a response time of 5 min with a limit of detection (LOD) reaching 200 and 500 pM for the freely suspended spike (S) protein in phosphate buffer saline (PBS) and human saliva, respectively. The sensor's performance was also proven for detecting a COVID-19 pseudovirus in an electrolyte solution with a LOD of 106 copies/mL. The results demonstrate that the optimized POC sensor developed in this work is a promising device for the label-free electrochemical biosensing detection of SARS-CoV-2 and different species of viruses.

Alkaline aqueous redox flow batteries using 2,5‐dihydroxy‐1,4‐benzoquinone and ferrocyanide adopting bismuth and carboxylic acid functionalized carbon nanotube catalyst

Alkaline aqueous redox flow batteries using 2,5‐dihydroxy‐1,4‐benzoquinone and ferrocyanide adopting bismuth and carboxylic acid functionalized carbon nanotube catalyst

Theoretical and experimental investigations of a gold nanosensor based on rhodamine-modified carbon nanotubes

A high selective nanosensor for metal ion sensing of rhodamine functionalized carbon nanotubes (CNT-RB) was successfully designed and synthesized. The complexation abilities of CNT-RB with metal ions including Cu2+, Hg2+, Al3+, and Au3+ ions were investigated using DFT calculations. The interactions between metal ions and CNT-RB were also investigated. The calculated results point out that CNT-RB displays the strongest complexation ability with Au3+ ion compared with Cu2+, Hg2+, and Al3+ ions. The electronic properties reveal that after CNT-RB forms complexes with Au3+, the energy gap of CNT-RB is clearly modified. Subsequently, the CNT-RB was synthesized via an amidation reaction of carboxylic acid functionalized carbon nanotubes (CNT-COOH) and rhodamine B-ethylenediamine (RB) in the addition of N-hydroxysuccinimide/1-ethyl-3-(3-dimethylaminopropyl)carbodiimide as coupling reagents. The sensitivity and selectivity of CNT-RB nanosensor to metal ions, i.e., Na+, Ag+, Mg2+, Ca2+, Pb2+, Co2+, Ni2+, Cu2+, Zn2+, Pt2+, Hg2+, Cd2+, Al3+, Cr3+, Fe3+, Au3+, and Ru3+ ions were studied using the absorption and emission techniques. Experimental results are in good agreement with the computed results in which CNT-RB nanosensor displays high selectivity and sensitivity for Au3+ ion over the other metal ions. Therefore CNT-RB nanosensor could be applied as a naked-eye and fluorometric nanosensor for Au3+ ion detections.

Aqueous organic redox flow batteries using naphthoquinone and iodide maintaining pH of electrolytes desirably by adoption of carboxylic acid functionalized carbon nanotube catalyst

Aqueous organic redox flow batteries using naphthoquinone and iodide maintaining pH of electrolytes desirably by adoption of carboxylic acid functionalized carbon nanotube catalyst

Impact of Surface Hydrophilicity of Gas-Diffusion-Type Biocathodes on Their Oxygen Reduction Ability for Biofuel Cells

The surface hydrophilicity of a gas-diffusion-type biocathode, in which bilirubin oxidase was immobilized, was regulated by varying the polymer binder hygroscopicity and UV-ozone treatment time of carbon composite electrodes. The surface hydrophilicity was found to influence its oxygen reduction activity by affecting the penetration of the electrolyte and O2 gas into the electrode layer. The oxygen reduction activity was maximized at an intermediate surface hydrophilicity because of the trade-off between enzyme utilization and oxygen diffusion. A glucose/O2 biofuel cell was fabricated by combining the optimal biocathode with a suitable bioanode fabricated with carboxylic acid-functionalized carbon nanotubes. We demonstrated that the glucose/O2 gas-diffusion-type biofuel cell exhibited a maximum current density of 3.0 mA cm−2 and a maximum power density of 0.66 mW cm−2.

Cerium-Based Metal-Organic Framework Nanocrystals Interconnected by Carbon Nanotubes for Boosting Electrochemical Capacitor Performance.

In this study, nanocrystals of a cerium-based metal-organic framework (Ce-MOF), Ce-MOF-808, are directly grown on the surface of carboxylic acid-functionalized carbon nanotubes (CNTs) by a facile one-step solvothermal synthesis method. Ce-MOF-CNT nanocomposites with various Ce-MOF-to-CNT ratios are synthesized, and their crystallinity, morphology, porosity, and electrical conductivity are examined. The redox-hopping and electrochemical behaviors of the pristine Ce-MOF in aqueous electrolytes are investigated, suggesting that the pristine Ce-MOF is electrochemically active but possesses a limited charge-transport behavior. As a demonstration, all the Ce-MOF, CNT, and nanocomposites are used as active materials for application in aqueous-based supercapacitors. The capacitive performance of the CNT can be significantly boosted with the help of redox-active Ce-MOF-808 nanocrystals.

Vanadium redox flow battery working even at a high current density by the adoption of tris(hydroxymethyl) aminomethane functionalized acidified carbon nanotube catalyst

Tris(hydroxymethyl) aminomethane (Tris) functionalized carbon nanotube (Tris-CNT) is newly suggested as a catalyst promoting the redox reactivity of vanadium ions in vanadium redox flow battery (VRFB). This Tris-CNT is synthesized by a condensation reaction between the carboxyl group of carboxylic acid functionalized carbon nanotube (CA-CNT) and the amine group of Tris. Since one Tris molecule has three hydroxyl groups, the surface of Tris-CNT consists of abundant oxygen functional groups that play a key role in facilitating the redox reaction of vanadium ions. To confirm the viability of Tris-CNT as a catalyst for VRFB, its chemical and electrochemical properties are evaluated. As a result, the reactivity of Tris-CNT increases by 136 and 159% for V2+/V3+ and VO2+/VO2+ reactions when compared to those of CA-CNT. Besides, at a high current density of 250 mA cm−2, VRFB using Tris-CNT shows a capacity of 19.1 Ah L−1 and energy efficiency of 69%, while those of VRFB using CA-CNT are 13.0 Ah L−1 and 63%. The above results show that the use of the new Tris-CNT catalyst has a strong influence on the improvement in the performance of VRFB.

A highly-sensitive and selective antibody-like sensor based on molecularly imprinted poly(L-arginine) on COOH-MWCNTs for electrochemical recognition and detection of deoxynivalenol

A new strategy to mimic antibody for electrochemical recognition and detection of deoxynivalenol (DON) using a highly-sensitive and selective antibody-like sensor based on molecularly imprinted poly(l-arginine) (P-Arg-MIP) on carboxylic acid functionalized carbon nanotubes (COOH-MWCNTs) was proposed. l-arginine as functional monomer was screened to prepare imprinted electrode via its electro-polymerization in the presence of DON onto the surface of COOH-MWCNTs electrode coupled with theoretical calculation. Surface morphology, structural characteristics, and electrochemical properties of P-Arg-MIP/COOH-MWCNTs were characterized by SEM, EDS, FTIR, and CV, respectively. P-Arg-MIP/COOH-MWCNTs displayed relatively high conductivity, high effective surface area, antibody-like molecular recognition and affinity, and a good response towards DON in a linear range from 0.1 to 70 μM with LOD of 0.07 μM in wheat flour samples with satisfactory recovery and feasible practicability in comparison with HPLC. This method provides a promising biomimetic sensing platform for the determination of mycotoxins in food and agro-products.

Heat-treated multi-walled carbon nanotubes-supported (Fe,Co,Ni)-coordinated polyporphyrin: A robust air cathode catalyst for rechargeable zinc-air batteries

Developing robust dual-function oxygen electrode reaction catalysts is vital toward renewable/rechargeable energy systems but remains challenging. In this work, novel electrocatalytically active hybrid materials comprising Fe0.5Co0.4Ni0.1 alloy nanoparticles-embedded N-doped carbon nanotubes, named CNTs@(Fe,Co,Ni)PP-T (where T denotes the pyrolysis temperature employed to prepare them), are developed by pyrolyzing the mixture of hyperbranched tri-metal (Fe, Co, Ni)-coordinated polyporphyrin-encapsulated carboxylic acid-functionalized carbon nanotubes and melamine. The materials are demonstrated to act as effective bifunctional oxygen electrode catalysts. Especially, the one generated at 800 °C, termed as CNTs@(Fe,Co,Ni)PP-800, has larger specific surface area, larger active surface area and better electrical conductivity than other as-obtained contrast materials. Undoubtedly, this material displays superior reactive activity for O2-associated electrochemical reactions in alkaline media, delivering more positive onset (0.988 V vs. RHE) and half-wave (0.837 V vs. RHE) potentials for the reduction of oxygen and a smaller overpotential (355 mV) at 10 mA cm−2 for the evolution of oxygen than its counterparts. In practical application, the CNTs@(Fe,Co,Ni)PP-800 based zinc-air battery (ZAB) achieves a small initial charge-discharge voltage gap of 0.69 V at 2 mA cm−2 and an outstanding cycling durability in 300 cycles of charge-discharge (in over 50 h), superior to the benchmark Pt/C+RuO2 based ZAB under the identical testing conditions.

αVβ3-Targeted Delivery of Camptothecin-Encapsulated Carbon Nanotube-Cyclic RGD in 2D and 3D Cancer Cell Culture

Integrin αvβ3 is widely expressed in various types of human cancer lines and plays a key role in angiogenesis for tumor growth and metastasis. Delivery of therapeutics to αvβ3-expressing tumors can thus be a promising approach for treating cancer. For targeted delivery of anticancer therapeutics to αvβ3-expressing tumor cells, cyclic arginylglycylaspartic acid (RGD) peptide was covalently conjugated to the surface of carboxylic acid–functionalized carbon nanotubes (fCNTs), and the topoisomerase I inhibitor camptothecin (CPT) was encapsulated in the fCNTs (CPT@fCNT-RGD). CPT@fCNT-RGD was successfully delivered to αvβ3-expressing A375 cells, and compared with nontargeted CPT@fCNT, it provided 3.78- and 3.02-fold increases in the anticancer effect in 2D and 3D culture. Analysis of apoptosis-related gene expression shows that the expression levels of Bax, cleaved caspase-3, and nuclear factor kappa-light-chain-enhancer of activated B cells were significantly increased in A375 cells incubated with CPT@fCNT-RGD compared with those incubated with CPT@fCNT. These results suggest that cyclic RGD-conjugated CNTs encapsulating an anticancer therapeutic can be a promising platform for treating cancer.

Effect of the redox reactivity of vanadium ions enhanced by phosphorylethanolamine based catalyst on the performance of vanadium redox flow battery

Phosphorylethanolamine (PHOS) doped carbon nanotube (CNT) is newly suggested as a catalyst for enhancing the redox reactions of vanadium ions and vanadium redox flow battery (VRFB) performance. For synthesizing the catalyst, CNT is linked to the phosphate group of the PHOS, forming phosphate functionalized carbon nanotube (POH-CNT). Its catalytic activity is then compared with those of pure CNT and carboxylic acid functionalized CNT (CA-CNT) catalysts. Regarding the redox reactivity of vanadium ions, POH-CNT exhibits superior catalytic activity and reaction reversibility for VO2+/VO2+ reaction to CNT and CA-CNT because of (i) the chelation ability of phosphate group, (ii) its low electron delocalization capability and (iii) its high acid dissociation constant. By the role as chelating agent of phosphate group, the density of active sites for reaction of VO2+ and VO2+ ions in POH-CNT increase. Also, the low electron delocalization and high acid dissociation constant induce effective adsorption and desorption of VO2+ and VO2+ ions. Such effects facilitate the VO2+/VO2+ reaction. In contrast, regarding V2+/V3+ reaction, POH-CNT shows equivalent reactivity to CA-CNT because phosphate and carboxyl groups form similar active sites for the V2+/V3+ reaction. The above results are supported by calculating kinetic parameters, such as charge transfer resistance and diffusion coefficient, while chemical bonding of the catalysts is examined by XPS. Finally, as the POH-CNT is used as catalyst for positive electrode prompting the VO2+/VO2+ reaction, performance of VRFB single cell is improved.

Antishear Stress Bionic Carbon Nanotube Mesh Coating with Intracellular Controlled Drug Delivery Constructing Small-Diameter Tissue-Engineered Vascular Grafts.

Small-diameter (<6 mm) tissue-engineered blood vessels (TEBVs) have a low patency rate due to chronic inflammation mediated intimal hyperplasia. Functional coating with drug release is a promising solution, but preventing the released drug from being rushed away by blood flow remains a great challenge. A single-walled carboxylic acid functionalized carbon nanotube (C-SWCNT) is used to build an irregular mesh for TEBV coating. However, an interaction between the released drug and the cells is still insufficient due to the blood flow. Thus, an intracellular drug delivery system mediated by macrophage cellular uptake is designed. Resveratrol (RSV) modified CNT is used for macrophage uptake. M1 macrophage uptakes CNT-RSV and then converts to the M2 phenotype upon intracellular RSV release. Prohealing M2 macrophage inhibits the chronic inflammation thus maintains the contractile phenotype of the vascular smooth muscle cell (VSMC), which reduces intimal hyperplasia. Additionally, RSV released from the mesh coating also directly protects the contractile VSMCs from being converted to a secretory phenotype. Through antishear stress coating and macrophage-based intracellular drug delivery, CNT-RSV TEBVs exhibit a long-term anti-intimal hyperplasia function. Animal transplantation studies show that the patency rate remains high until day 90 after grafting in rat carotid arteries.

Role of single‐source‐precursor structure on microstructure and electromagnetic properties of CNTs‐SiCN nanocomposites

AbstractNovel single‐source‐precursors (SSPs), namely carbon nanotube modified poly (methylvinyl) silazane (CNTs‐HTT 1800), were synthesized via amidation reaction of poly (methylvinyl) silazane (HTT 1800) with carboxylic acid functionalized carbon nanotubes (CNTs‐COOH) at the assistance of ZnCl2 catalyst, which was confirmed by means of Fourier transform infrared spectra (FT IR) and transmission electron microscopy (TEM). Besides, the TEM results unambiguously show the homogeneous distribution of the CNTs in the matrix of SSPs while serious aggregation of the CNTs in the matrix of physically‐blended‐precursor. Crack‐free monolithic silicon carbonitride modified by carbon nanotubes ceramic nanocomposites (CNTs‐SiCN) were prepared through pyrolysis of the obtained SSP green bodies at 1000°C. Due to the strong influence of polymer structure on the microstructure of final ceramics, the SSP‐derived CNTs‐SiCN nanocomposites clearly show the homogeneous distribution of the CNTs in the SiCN matrix while the physically‐blended‐precursor derived CNTs‐SiCN nanocomposites exhibit serious aggregation and entangling of the CNTs in the SiCN matrix. With the same CNT content in the feed, the SSP‐derived CNTs‐SiCN nanocomposites possess significant improvements of electromagnetic (EM) absorbing properties compared to those from physically‐blended‐precursors, due to the quality of the dispersion of CNTs in the ceramic matrices.

Iron oxide on carbon‐based supports as efficient catalysts for organic compounds oxidation

For the first time, iron oxide on carbon aerogel, amine functionalized carbon nanotube, black carbon and carboxylic acid functionalized carbon nanotube in the presence of H2O2 was reported as an efficient and stable catalyst for the selective oxidation of sulfides and alcohols. The catalysts were characterized by scanning electron microscopy, energy‐dispersive spectroscopy, transmission electron microscopy, X‐ray photoelectron spectroscopy, X‐ray diffraction, Fourier transform infrared spectroscopy and atomic absorption spectroscopy. In the next step, catalytic reactivity toward sulfide to sulfoxide and alcohol to aldehyde/ketone oxidation in the presence of H2O2 was studied and discussed.

Carbon Nanotubes Covalently Attached to Functionalized Surfaces Directly through the Carbon Cage.

The covalent attachment of nonfunctionalized and carboxylic acid-functionalized carbon nanotubes to amine-terminated organic monolayers on gold and silicon surfaces is investigated. It is well established that the condensation reaction between a carboxylic acid and an amine is a viable method to anchor carbon nanotubes to solid substrates. The work presented here shows that the presence of the carboxylic group on the nanotube is not required for attachment to occur, as direct attachment via the substrate amine and the nanotube cage can take place. Scanning and transmission electron microscopy and atomic force microscopy confirm the presence of carbon nanotubes in intimate contact with the surface. X-ray photoelectron spectroscopy is utilized to compare the surface chemistry of the functionalized and nonfunctionalized carbon nanotubes and is supported by a computational investigation. Ion fragments attributed to the direct attachment between the surface and carbon nanotube cage are detected by time-of-flight secondary ion mass spectrometry. The overall attachment scheme is evaluated and can be further used on multiple carbonaceous materials attached to solid substrates.

Adsorption of anionic and cationic dyes from aqueous solution using gelatin-based magnetic nanocomposite beads comprising carboxylic acid functionalized carbon nanotube

Significant efforts have been made to develop adsorbents capable of removing pollutant from aqueous solutions, making it possible to easily and rapidly separate from the treated solution via the magnetic field. In the current study, a novel magnetic adsorbent based on gelatin (Gel), which is entrapped carboxylic acid functionalized multi-walled carbon nanotube (CNT) and embedded magnetic nanoparticles of iron oxide (MNPs) was successfully synthesized. The synthesized magnetic nanocomposite beads were used as an adsorbent for removal of anionic direct red 80 (DR) dye and cationic methylene blue (MB) dye from aqueous solutions. To confirm the synthesis of the nanocomposite beads, the following studies were performed: Fourier transform infrared (FTIR) spectra and X-ray diffraction (XRD), differential scanning calorimetry (DSC), and scanning electron microscope (SEM) and transmission electron microscope (TEM) analyses. In addition, the magnetic properties of the nanocomposite beads were determined using vibrating sample magnetometer (VSM). The adsorption process, kinetics, isotherm, and thermodynamics of the adsorption were studied. Notably, the magnetic biosorbent removed 96.1% of DR and 76.3% of MB in a second order kinetic model. The high adsorption efficiency and strong magnetic properties of the nanocomposite beads suggest that they may be a promising adsorbent in the water treatment industry.

Direct DNA Immobilization onto a Carbon Nanotube Modified Electrode: Study on the Influence of pH and Ionic Strength

Over the past years, DNA biosensors have been developed to analyze DNA interaction and damage that have important applications in biotechnological researches. The immobilization of DNA onto a substrate is one key step for construction of DNA electrochemical biosensors. In this report, a direct approach has been described for immobilization of single strand DNA onto carboxylic acid-functionalized carbon nanotubes modified glassy carbon electrode. To do this, we first modified the glassy carbon electrode surface with MWCNT-COOH. The immersion of MWCNT-COOH/GCE in ss-DNA probe solution, with different pH and ionic strength, was followed by suitable interaction between amine group of ss-DNA bases and carboxylic groups of MWCNT-COOH. This interaction leads to successful ss-DNA immobilization on MWCNT-COOH that was confirmed by cyclic voltammetry, electrochemical impedance spectroscopy and atomic force microscopy. Immobilization of ss-DNA on the modified electrode increased the charge transfer resistant but decreased the peak current of redox probe ([Fe(CN)6]3-/4-). The result of cyclic voltammograms implicates that enhancements in the DNA immobilization are possible by adroit choice of low pH and high ionic strength. The standard free-energy of adsorption (ΔG°ads) was calculated from electrochemical impedance spectroscopy data (-47.75 kJ mol-1) and was confirmed covalent bond formation. atomic force microscopy topographic images demonstrate increased surface roughness after ss-DNA immobilization. Results offer a simple, rapid and low-cost of DNA immobilization strategy can be opportunities to design of novel nucleic acid biosensors.

Synergistic effects of carboxylic acid-functionalized carbon nanotube and nafion/silica nanofiber on electrical actuation efficiency of shape memory polymer nanocomposite

Synergistic effects of self-assembled carboxylic acid-functionalized carbon nanotube (CNT) and nafion/silica nanofiber on the electro-activated shape recovery behavior of shape memory polymer (SMP) nanocomposite were investigated. Carboxylic acid-functionalized CNTs were self-assembled onto the carbon fiber mat to enhance their bonding reliability and achieve efficient electrical actuation for SMP matrix. Nafion/silica nanofibers were electrospun onto surfaces of the carbon fiber mat to prevent electrically resistive heat dissipation. The combination of electrically/thermally conductive CNTs and thermally resistive nafion/silica nanofibers results in improvement for both electrically induced shape recovery and actuation efficiency in the SMP nanocomposite.