Functionalized Carbon Nanotubes Research Articles

Insights into Selective Removal by Dye Adsorption on Hydrophobic vs Multivalent Hydrophilic Functionalized MWCNTs.

Hydrophilic functionalized carbon nanotubes (MWCNT-COOH) were developed via hydrothermal glucose-coated carbonization, mixing MWCNTs with glucose in different weight ratios. Methyl violet (MV), methylene blue (MB), alizarin yellow (AY), and methyl orange (MO) were used as dye models for adsorption studies. Comparative dye adsorption capacity onto the pristine (MWCNT-raw) and functionalized (MWCNT-COOH-11) CNTs was evaluated in aqueous solution. These results revealed that MWCNT-raw is capable of adsorbing either anionic or cationic dyes. In contrast, an induced selective cation dye adsorption capacity is significantly enhanced on multivalent hydrophilic MWCNT-COOH, in comparison to a pristine surface. This ability can be tuned to the selective adsorption of cations over anionic dyes or between anionic mixtures from binary systems. An insight into adsorbate-adsorbent interactions shows that hierarchical supramolecular interactions dominate the adsorption processes, which is ascribed to the chemical modification by switching from a hydrophobic to a hydrophilic surface, dye charge, temperature, and potential matching multivalent acceptor/donor capacity between chemical groups in the adsorbent interface. The dye adsorption isotherm and thermodynamics on both surfaces were also studied. Changes in the Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) were evaluated. Thermodynamic parameters were endothermic on MWCNT-raw, whereas the adsorption process on MWCNT-COOH-11 revealed that adsorption processes were spontaneous and exothermic, accompanied by a significant reduction of entropy values as a consequence of a multivalent effect. This approach provides an eco-friendly, low-cost alternative for the preparation of supramolecular nanoadsorbents with unprecedented properties to achieve remarkable selective adsorption independent of the presence of intrinsic porosity.

Nanoparticle-Enhanced PVDF Flat-Sheet Membranes for Seawater Desalination in Direct Contact Membrane Distillation

In this study, hydrophobic functionalized carbon nanotubes (fCNTs) and silica nanoparticles (fSiO2NPs) were incorporated into polyvinylidene fluoride (PVDF) flat-sheet membranes to improve their performance in membrane distillation (MD). The performance of the as-synthesized membranes was evaluated against commercial reference polytetrafluoroethylene (PTFE) flat-sheet membranes. The water contact angle (WCA) and liquid entry pressure (LEP) of the PVDF membrane were compromised after incorporation of hydrophilic pore forming polyvinylpyrrolidone (PVP). These parameters were key in ensuring high salt rejections in MD processes. Upon incorporation of fCNTS and fSiO2NPs, WCA and LEP improved to 103.61° and 590 kPa, respectively. Moreover, the NP additives enhanced membrane surface roughness. Thus, an increase in membrane roughness improved WCA and resistance to membrane wetting. High salt rejection (>99%) and stable fluxes (39.77 kg m-2 h-1) were recorded throughout a 3 h process evaluation where 3.5 wt% NaCl solution was used as feed. These findings were recorded at feed temperature of 60 ℃. Evidently, this study substantiated the necessity of high feed temperatures towards high rates of water recovery.

Highly sensitive detection of thyroglobulin based on sandwich-type electrochemical immunoassay.

As a dimeric protein, thyroglobulin (Tg) is an important biomarker for different thyroid cancer (DTC), so designing effective method to detect Tg is of great significance. In this work, by preparing β-cyclodextrin (CD) functionalized carbon nanotubes (CNTs) nanohybrid (CD-CNTs) as carrier to immobilize primary antibody (Ab1) of Tg, assembling sulfydryl ferrocene (Fc) and secondary antibody (Ab2) on the surface of nanogold (Au) as signaling amplifier (Ab2-Au-Fc), a simple and sensitive sandwich-type electrochemical immunoassay (STEM) of Tg was designed herein for the first time. In brief, CNTs show large surface area and conductivity, while CD offers superior host-guest recognition capability that can bound with Ab1; meanwhile, Fc probe can offer stable electrochemical signal that is proportionable to the concentration of Tg. Under the optimum conditions, the proposed STEM platform shows excellent sensing results for Tg detection: a considerable low analytical detection (0.5ngmL-1) and wide linearity (2 to 200ngmL-1), suggesting the designed STEM platform offers potential real applications for detect Tg.

Functionalized carbon nanotubes/polyimide nanocomposites with high energy density for high‐temperature dielectric materials

AbstractPolymer‐based dielectric capacitors have attracted much attention because of their good flexibility, lightness, and high‐power density. However, the current polymer dielectric capacitors usually have too low energy density and cannot be used in high temperature environments, which limits the further development. Therefore, it has become increasingly important to develop high‐temperature dielectric materials with high energy density and low dielectric loss. In this study, long‐chain functionalized carbon nanotubes (CNTF) were introduced in Polyimide (PI) to obtained CNTF/PI composite film. CNTF have good compatibility with polymer and can solve the dispersion problem. The CNTF/PI composite film exhibits good dielectric property and an ultralow dielectric loss of 0.015. Especially, the discharged energy density of 3.77 J/cm3 of CNTF/PI composite film is the highest discharged energy density of reported polyimide‐based dielectric films at 300 MV/m. Therefore, these polyimide‐based dielectric materials are promising in the high temperature field of novel high‐performance film dielectric capacitor.

RECENT MODIFICATIONS OF CARBON NANOTUBES FOR BIOMEDICAL APPLICATIONS

Recent advances in the field of biomedical have been remarkably achieved in the last few years, especially in the fabrication of nanomaterials that have various applications. Carbon nanotubes (CNTs) are carbon-based materials with cylindrical shapes that have an average diameter of less than 2 nanometre (nm) for single-walled CNTs (SWCNTs) and multi-walled CNTs (MWCNTs) with average diameters up to 100 nm. CNTs demonstrate various outstanding and excellent mechanical, electrical, conductivity, thermal properties, high surface area, and high biocompatibility. These remarkable properties have led to the development of CNTs-based materials in the biomedical field. For the past decades, the functionalization of CNTs has been actively researched in order to increase their biocompatibility for application in antibacterial materials, dentistry, drug delivery, and biosensing. The surface functionalization enhances the capabilities, features, and properties by modifying the surface chemistry of CNTs to improve their biocompatibility. The functionalization of CNTs will enable the biomolecule loading on the surface of CNTs, and thus can be used for drug delivery for targeted cells or immobilization support. In this review, we discuss the related literatures on biomedical applications of CNTs such as antibacterial, dental materials, cancer therapy and biosensors from 2007 – 2022. We also review the antibacterial properties between SWCNTs and MWCNTs, functionalized CNTs-reinforced nanocomposite for dental applications, and the ability of CNTs to work as nanocarriers to deliver drugs directly to cancer cells. Moreover, the applications of CNTs-based biosensors in detecting biological and biomedical compounds are also discussed.

A Damped Double Dipole Antenna for UHF RFID Sensing in the Frequency Domain

Ultrahigh frequency (UHF) radio frequency identification (RFID) tags provide an inexpensive framework for distributed sensing, yet for the most cost-effective implementation, it is necessary to consider antenna design in concert with the capabilities of responsive materials that can be coupled to the tag response. Materials, such as functionalized carbon nanotubes (CNTs), have been engineered to change in resistance when exposed to a variety of analytes and have been incorporated in RFID tags to create low-cost sensors that work at a fixed reader–tag separation distance. This article presents a damped double dipole antenna design enabling UHF RFID tags that are able to sense changes in resistance of a sensing element (with a conductivity similar to that of printed CNT networks) regardless of reader–tag distance within the far-field read range. Simulations of the proposed design show two methods of operation, either by comparing the damping between two resonant peaks or by shifting the resonant frequency of the RFID tag. The first method is validated experimentally with surface mount resistors, showing a relative change in the effective antenna transmission coefficient, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\tau _{e}$ </tex-math></inline-formula> , of 0.2 for a 35% change in resistance of the sensing element.

Synthesis of poly(methacrylic acid)/functionalized carbon nanotubes nanocomposite modified electrode for electrochemical sensitive determination of acrylamide in food sample

Poly(methacrylic acid) and functionalized carbon nanotubes nanocomposite modified glassy carbon electrodes (PMAA, f-CNTs, and GCE) have been synthesized for electrochemically sensitive determination of acrylamide (AA) in food samples. A study of the structure and morphology of modified electrodes using XRD and FE-SEM analyses showed that the f-CNTs were completely covered by PMAA molecules in the nanocomposite. Electrochemical studies on the determination of AA by PMAA/f-CNTs/GCE sensors using CV and DPV techniques showed that PMAA/f-CNTs nanocomposite enhanced the sensitivity and selectivity of an electrochemical sensor due to the synergetic effect of f-CNTs and PMAA. Results indicated a sensitivity of 0.0171 µA/μM, detection limit of 15 μM and a linear range of 0–2400 μM. Results of the study on the applicability and verification of the PMAA/f-CNTs/GCE as an AA sensor in prepared real samples of potato crisps indicated a notable conformity between the results of DPV and ELISA assays, and the relatively small values of RSD (3.41–5.11 %) and recovery (97.50–99.00 %) values for DPV analysis were acceptable which corroborated the appropriate applicability and validation of the results of PMAA/f-CNTs/GCE for determination of AA content in food samples.

Superior electro-optical switching properties in polymer dispersed liquid crystals prepared with functionalized carbon nanotube nanocomposites of LC for switchable window applications

In this work, we are reporting the results on electro-optical switching properties of polymer dispersed liquid crystal (PDLC) devices for switchable window related applications. The PDLC cells are prepared by mixing octadecylamine functionalized single-walled carbon nanotubes (ODA-SWCNT) nanocomposites of liquid crystals (LC) and acrylate-based monomer by polymerization induced phase separation method. The important switchable device parameters such as threshold voltage, switching voltage, response time, contrast ratio and effective refractive index are investigated. The PDLC cells prepared with 0.05 wt% ODA-SWCNT nanocomposites of the LC, 7CB show almost zero threshold field and 36% less driving field compared to PDLC prepared with pure 7CB. A distinct optical response (frequency doubling) phenomenon is observed for PDLC prepared with 0.03 and 0.05 wt% ODA-SWCNT nanocomposites of 7CB compared to PDLC cells prepared with pure 7CB and lower concentrations (<0.03 wt%) of ODA-SWCNT. The relaxation of optical transmittance is observed at low frequency even when the applied electric field (Eapp) is ON which is due to the strong induced internal electric field (due to free ions) which nullifies the Eapp. The physical mechanism of this unique optical behavior is discussed in detail. The PDLC prepared with 0.01 wt% ODA-SWCNT show 84% faster response time compared to PDLC prepared with pure 7CB. The working of prototype PDLC devices for use in switchable window related applications is reported. The results indicate that, the PDLC prepared with 0.05 wt% ODA-SWCNT nanocomposites of 7CB show high ON state clarity and high OFF state opacity compared to PDLC prepared with pure LC and lower concentrations of ODA-SWCNT.

Interfacial engineering of Copper(I) oxide nanocubes wrapped with functionalized carbon nanotubes toward carbon dioxide electroreduction to ethylene

Copper(I) oxide (Cu2O)-based nanomaterial is considered to be a highly attractive electrocatalyst for the carbon dioxide (CO2) reduction to ethylene (C2H4), while the selectivity of C2H4 still faces challenges. Herein, a unique nanocomposite consisted of Cu2O nanocubes trapped with oxygen-containing groups functionalized carbon nanotubes (O-CNTs) through a facile wet chemical method is reported. Benefiting from the novel structure and robust interface, the nanocomposite (Cu2O/O-CNTs) electrocatalyst exhibits an enhanced C2H4 selectivity (Faradic efficiency = 40.3%) at –1.3 V vs. RHE, a current density of 13.6 mA/cm2, and long-term durability (over 8 h) in KHCO3 electrolyte. The O-CNTs trapping around Cu2O nanocubes with an intimately interface ensures highly conductive network and uniform dispersion of active sites in the electrochemical CO2 reduction reaction (ECO2RR). The improved performance of Cu2O/O-CNTs can be attributed to the rapid mass transport, increased local concentration of *CO intermediates, and stable heterointerface. This study presents a new route to increase the performance and cyclic lifetime of Cu-based catalyst for CO2 electroreduction to C2H4 by the trapping interfacial engineering.

Electrochemistry of Carbon Materials: Progress in Raman Spectroscopy, Optical Absorption Spectroscopy, and Applications.

This paper is dedicated to the discussion of applications of carbon material in electrochemistry. The paper starts with a general discussion on electrochemical doping. Then, investigations by spectroelectrochemistry are discussed. The Raman spectroscopy experiments in different electrolyte solutions are considered. This includes aqueous solutions and acetonitrile and ionic fluids. The investigation of carbon nanotubes on different substrates is considered. The optical absorption experiments in different electrolyte solutions and substrate materials are discussed. The chemical functionalization of carbon nanotubes is considered. Finally, the application of carbon materials and chemically functionalized carbon nanotubes in batteries, supercapacitors, sensors, and nanoelectronic devices is presented.

Selective Label-Free Electrochemical Aptasensor Based on Carbon Nanotubes for Carbendazim Detection

One of the most widely used pesticides in Chile is carbendazim (CBZ), which in agriculture is used to protect crops from fungal diseases that commonly occur in rice, vegetable, and fruit crops. However, prolonged exposure to it, and its high persistence, can cause adverse health effects. Therefore, it is necessary to determine the presence of CBZ through rapid detection methods in food samples to prevent ingestion and exposure to this pesticide at risk concentrations. In this work, a label-free electrochemical aptasensor based on functionalized carbon nanotubes was prepared for CBZ detection. The carbodiimide reaction between the amino-terminated aptamer and the carboxylic groups of carbon nanotubes achieved the covalent immobilization of the aptamer. The immobilized aptamer changed its conformation when it detected CBZ and blocked access to the redox mediator on the electrode surface, resulting in a measurable decrease in the voltammetric response. Under the optimal conditions, the aptasensor featured a linear detection range between 1.0 and 50.0 nM, with a detection limit of 4.35 nM. Moreover, the aptasensor exhibited good selectivity for CBZ, among other pesticides, and good repeatability. For CBZ detection in tomatoes, the aptasensor accurately measured CBZ content in a sample prepared using the standard addition method. This work provides a simple, rapid, sensitive, and selective biosensor for CBZ detection and quantification in food samples.

Folic acid functionalized carbon nanotubes as pH controlled carriers of fluorouracil: Molecular dynamics simulations

This study deals with molecular dynamics simulations of the folic acid (FA) functionalized carbon nanotube (CNT) as a pH-responsive carrier of fluorouracil (5-FU) drug. We chose FA as a targeting agent, as the folate receptor is considerably upregulated by a broad spectrum of cancer cells. Thus, it may facilitate the targeted delivery of chemotherapeutic agents. The results showed that the FA does not affect the loading capacity of CNT at neutral pH so both CNT and CNTFA can load 51 drug molecules. Unmodified CNT behaves in the same manner at different pH conditions, and so cannot be used as a pH-selective nanocarrier. However, the maximum loading capacity of CNTFA is decreased to 45 by decreasing the environmental pH. The molecular mechanics Poisson-Boltzmann surface area analysis showed that the hydrophobic and π-π stacking interactions are the main forces behind the complex stability. The least value of △Gbind belongs to the CNTFA:5-FU at low pH, which is favorable for drug release from a thermochemical viewpoint. The lowest and highest values of diffusion coefficients are those of CNTFA:5-FU at neutral and low pH, respectively. This means that CNTFA holds the drug molecules tightly at physiological pH, but releases them at low pH environments. Also, the reduction of the number of hydrogen bonds between CNTFA and 5-FU molecules as well as a decrease in height of the radial distribution function profile at low pH propose the CNTFA as a pH-sensitive nanocarrier for 5-FU. The simulation results show the important effect of the FA on the controlled release of 5-FU from CNT, which is suitable for targeted drug delivery applications.

Highly efficient synthesis of benzyl benzoate directly from self-coupling of benzyl alcohol in water

Benzyl benzoate (BB), an important ester, still demands for green synthesis routes. In this work, by size regulation and proper functionalization of carbon nanotubes (CNTs) as the support of gold catalyst, this ester can be synthesized very efficiently directly from benzyl alcohol via oxidative coupling. More attractively, the reaction is performed using water as green solvent and molecular oxygen as green oxidant. Simultaneously, very high selectivity to BB can be obtained near full conversion within very short reaction time (just 0.5 h), while the low-value benzoic acid byproduct is negligible. This is very different from many reported gold catalysts that yield much benzoic acid and/or benzaldehyde in water. The results show that, besides the size of CNTs (length and diameter), the functionalization of CNTs is also critical for improving both conversion and the selectivity to BB. In addition, the reaction mechanism for forming BB ester is put forward as well.

Investigation of the effect of functionalized carbon nanotube and graphene oxide in guar gum‐based mixed matrix membrane for gas separation application

AbstractThe present study deals with preparing mixed matrix membranes (MMMs), a new polysaccharide‐based natural polymer used as a matrix with functionalized carbon nanotubes (FCNTs) and graphene oxide (GO) used as an inorganic filler. This work identified the effect of the inorganic fillers (FCNTs or GO) with naturally occurring polymer for gas separation. The incorporation of fillers improves the gas separation performance of MMMs. In GG/FCNTs MMMs, the selectivities of CO2/N2 and CO2/H2 were enhanced by 55.24% and 57.89%, respectively. Moreover, in GG/GO MMMs, the selectivities of CO2/N2 and CO2/H2 were improved by 99.50% and 50%, respectively. The membrane was characterized by scanning electron microscopy (SEM) and Fourier‐transform infrared spectroscopy (FTIR). The SEM analysis of GG/GO MMMs reveals layered structure, and GG/FCNTs MMMs create passages to transport gases. The Universal testing machine (UTM) is used to analyze the mechanical properties of pristine and modified membranes.

Removal of ciprofloxacin and indigo carmine from water by carbon nanotubes fabricated from a low-cost precursor: Solution parameters and recyclability

Water contamination is one of humanity's threatening problems. This study synthesized pristine carbon nanotubes (PCNTs) from commercial gasoline (CG) as a relatively low-cost precursor. 200 mL of CG yielded an average CNTs mass of 26.23 ± 0.97 g. The functionalized carbon nanotubes (FCNTs) were produced by acid-treatment of PCNTs, and the yield was 93.3%. The surface area of PCNTs and FCNTs was 29.69 and 66.16 m 2 g −1 . The FTIR and EDX indicated an introduction of oxygenated groups on the FCNTs. The FCNTs removed ciprofloxacin (CIP) and indigo carmine (IC) from water with an adsorption capacity of 95.5 and 93.0 mg g −1 , respectively, while the PCNTs showed 78.9 and 63.7 mg g −1 , respectively. The pH 4.0 and 6.0 suited the adsorption of CIP and IC on both sorbents. The adsorption processes for all sorbent-sorbate systems were spontaneous and exothermic. The FCNTs and PCNTs recyclability showed an average efficiency of 90.0%.

Synthesis of a Functionalized Carbon Nanotube Graphene Composite Enabling pH-Responsive Electrochemical Sensing for Biomedical Applications

Sensing of pH value plays an important role in many fields of studies including biology, chemistry, and biomedicine. In recent years, nanomaterials have emerged as a promising sensing element for a variety of applications. In this study, we report a high-sensitivity pH sensor synthesized by a functionalized single-wall carbon nanotube graphene (FSWCNT/G) composite. This sensor was constructed with Cr/Au electrodes and FSWCNT/G sealed in a PDMS microchannel on a glass substrate. The experiments of a field-effect transistor (FET), linear sweep voltammetry (LSV), and response time measurement all proved the superiority of the fabricated composite sensor over a pristine graphene sensor. A high potentiometric gradient of 98.75 mV/pH within the operating pH range of 4–10 was obtained in direct potentiometric measurements. The composite nanosensor can be used to monitor the pH value in cancer cell solution. Moreover, the composite nanosensor was tested for cancer cell detection, and the range of the concentration detection was from 5 × 106 to 2.5 × 105 cells/mL, showing a potential way to achieve label-free cell detection.

Non-toxic CuInS2 quantum dot sensitized solar cell with functionalized thermoplast polyurethane gel electrolytes

Functionalization of multi-walled carbon nanotubes (CNTs) was carried out through ultrasonication in acidic medium followed by chemical attachment of thermoplastic polyurethane and subsequent chain extension using butane-diol to obtain CNT-tagged polyurethane (PU-CNT). PU-CNT was functionalized by using propane sultone as a sulfonating agent to attach the pendent sulfonate moiety on urethane linkage. The functionalization of CNTs, tagging of CNTs with polymer chain, chain extension and subsequent functionalization of polymer have been confirmed though through spectroscopic techniques such as NMR, FTIR, UV–vis, and Raman spectroscopy. Thermal stability and the nature of interaction is explored through thermal measurements to understand the effect of CNT functionalization. Electrical conduction has been improved by the chemical attachment of CNTs with polymer (1.61 × 10−6 S/cm) which further increases through functionalization (1.37 × 10−4 S/cm) and thereby make them suitable for gel electrolyte. Quantum dot of CuInS2 has been synthesized using DDT as capping agent and its characteristic properties and the dimension are worked out for their suitability as active materials in solar cell. Optical band gap of quantum dots and HOMO/LUMO band structure of functionalized polyurethanes have been measured through UV–vis and cyclic voltametry, and thereby, draw the overall energy diagrams of possible combination of materials. Solar cell devices have been fabricated using the appropriate materials and found improved power conversion efficiency of 0.81% with Au (gold) as counter electrode. The reason behind the better efficiency is understood from the lesser energy gap between HOMO energy level of prepared gel electrolyte (SPU-CNT) and Au (gold) counter electrode, better conductivity and higher rate of hole transportation, to reduce the electron-hole pair recombination.

Multi-length scale strengthening and cytocompatibility of ultra high molecular weight polyethylene bio-composites by functionalized carbon nanotube and hydroxyapatite reinforcement

The mechanical properties, such as hardness and elastic modulus, of ultra-high molecular weight polyethylene (UHMWPE) composites for acetabular cup liner are improved by adding hydroxyapatite (HAp) and carbon nanotubes (CNT). However, the weak adhesion of HAp (H) and CNT (C) with UHMWPE (U) limits the enhancement of mechanical properties. Thus, the surface of these reinforcements is silane-treated to improve the adhesion with polymer via Si–O and C=O bonds, as evidenced from spectroscopy techniques. An increased dispersion and interfacial adhesion of functionalized HAp (fH) and CNT (fC) with the polymer matrix is confirmed by nearly two-fold increased reinforcement fraction (Rf: 0.55) of U-10 wt% fHAp-2 wt.% fCNT (U10fH2fC) in comparison to U-10 wt% HAp-2 wt.% CNT (U10H2C). Additionally, Voronoi Tessellation (VT) on SEM micrographs of U10H2C and U10fH2fC revealed the dispersion of functionalized CNTs in U10fH2fC with a center-to-center distance of 0.076 μm, which is 74% higher for unfunctionalized CNT in U10H2C. The multilength scale strengthening of the UHMWPE matrix is confirmed from atomic level modification via functionalization of fillers which effectively adhered to the polymer chain on a micro-scale level. A uniform distribution of CNTs rendered increased crystallinity (+28%) of U10fH2fC, which in turn resulted in significant improvement in bulk mechanical properties (18%, 49%, and 12% increased hardness (148.1 MPa), elastic modulus (3.51 GPa) and tensile elastic modulus (219.8 MPa), respectively) in comparison to that of U10H2C. Functionalized-HAp/CNT reinforced UHMWPE composites maintained its cytocompatibility in the MTT test and fluorescence microscopy, affirming their potential employment as acetabular cup liners for hip joint arthroplasty.

Synthesis of Highly Dispersible Functionalized Carbon Nanotubes as Conductive Material through a Facile Drying Process for High-Power Lithium-ion Batteries.

Herein, surface-functionalized carbon nanotubes (CNTs) were successfully synthesized by dry ball milling that facilitates industrial application. The optimal conditions were determined by analyzing the physicochemical characteristics of CNTs, including the content of the carboxyl group (-COOH) induced on the surface of CNTs by co-existing dry ice based on the ball milling time. Among them, 30 s ball milling (CNTs-30s) showed a high dispersibility in N-methyl-2-pyrrolidone (NMP) while retaining most carboxyl groups and maintaining the intrinsic high conductivity. In the evaluation of rate capability and 5 C/5 C cyclability applied to the Li1+x (Ni1-y-z Coy Mnz )1-x O2 with 60 % Ni (NCM622) cathode, CNTs-30s showed excellent performance based on a well-formed conductive network. Regarding improved dispersion properties and electrochemical performance, the optimal surface functionalization conditions, dispersibility, and electrode properties according to the processing time were analyzed; based on these, the correlation with electrochemical performance was confirmed.

Aligned silver nanoparticles anchored on pyrrolic and pyridinic-nitrogen induced carbon nanotubes for enhanced oxygen reduction reaction

Comprehension of the metal-nanostructure arrays is of great significance for the rational design of the cathode catalyst for the oxygen reduction reaction (ORR). Therefore, we fabricated a cathode catalyst consisting of the small-size, aligned silver nanoparticles (Ag NPs) embedded into the pyrrolic and pyridinic-Nitrogen functionalized carbon nanotubes. The N-defected structure was prepared by acidification of carbon nanotubes (CNTs) to avoid inherited stacking of its layers followed by the introduction of 2,7 diaminophenazine (DPA) using a hydrothermal process, while small-size Ag NPs were aligned through electrodeposition onto the N-defected carbon nanotube (CNT-DPA-Ag). The individual role of pyrrolic and pyridinic -N in the electrocatalytic ORR performance, synthesis of small size, and distribution behavior of Ag NPs were evaluated. To maximize the ORR performance of the catalyst, the advantage was taken from the presence of carbon atoms next to the pyridinic-N which is a Lewis base and acts as an adsorption and protonation site for the oxygen (O2) molecule and eventually ensures a direct 4e− transfer route for the electrochemical conversion of O2 into water (H2O). Transmission electron microscopy (TEM) analysis of CNT-DPA-Ag revealed a small size, aligned Ag NPs (average size 2 nm) resulting in a large surface area and rich electroactive sites for adsorption of O2. The CNT-DPA-Ag showed a remarkable ORR performance in terms of positive onset potential (-0.052 V), high diffusion-limiting current density (-5.54 mAcm−2), and noteworthy methanol tolerance, and long-term durability in comparison to the commercial 20 wt% Pt/C.