Bare Multi-walled Carbon Nanotubes Research Articles

Enhancing in vitro photothermal therapy using plasmonic gold nanorod decorated multiwalled carbon nanotubes.

Photothermal therapy (PTT) is a promising approach for cancer treatment that selectively heats malignant cells while sparing healthy cells. Here, the light-to-heat conversion efficiency of multiwalled carbon nanotubes (MWCNTs) within the near-infrared biological transmission window is enhanced by decorating them with plasmonic gold nanorods (GNRs). The results reveal a significant photothermal enhancement of hybrid MWCNTs-GNRs compared to bare MWCNTs, displaying a 4.9 enhancement factor per unit mass. The enhanced plasmonic PTT properties of MWCNTs-GNRs are also investigated in vitro using PC3 prostate cancer cell lines, demonstrating a potent ablation efficiency. These findings advance innovative hybrid plasmonic nanostructures for clinical applications.

Bi2Se3 nanoparticles anchored MWCNTs: Counter electrode in a dye-sensitized solar cell

Anchoring of Bi2Se3 nanoparticles over ‘dip and dry’ coated multiwalled carbon nanotubes (MWCNTs) has been accomplished using a room-temperature (27 °C), inexpensive, and convenient chemical route, namely, successive ionic layer adsorption and reaction (SILAR), to yield a nanohybrid composite electrode to serve as a counter electrode (CE) in dye-sensitized solar cell (DSSC) applications. The growth of Bi2Se3 on MWCNTs has been well-tuned through varying SILAR cycles (MBSe-series) and tested as counter electrodes (CEs) with reference to MWCNTs and Bi2Se3 in FTO/ZnO/Eosin-Y/Iodide-triiodide/Counter electrode/FTO assembly. Grown CEs have been validated through XRD, XPS, Raman, FTIR, and FESEM studies, while the assembled DSSCs have been assessed through JV, EQE, EIS, and electrochemical stability studies. Well-optimized Bi2Se3/MWCNTs nanohybrid composites have been used as CEs in DSSCs and showed superior device performance (0.52 %) compared to bare MWCNTs (0.14 %) and Bi2Se3 (0.09 %) due to the well-anchored Bi2Se3 over one-dimensional MWCNTs through a large number of synergistic electrochemical active sites. A DSSC fabricated with MBSe-12 as the CE exhibits enhanced stability compared to bare Bi2Se3 and MWCNTs. Also, it reveals a charge transfer resistance of 7.92 Ω/cm2 and an electron lifetime of 16 μs, yielding a maximum efficiency of 0.52 % and an external quantum efficiency of 28.20 %.

The Coupling of Dihydroxybenzene Derivatives to MWCNT and Electrochemical NADH Oxidation

3,4 and 2,5- dihydroxybenzene compounds were separately and covalently coupled to the multiwalled carbon nanotube (MWCNT) deposited on the surface of glassy carbon electrode through electrochemical reduction of diazonium compound of benzylamine bearing Boc protecting group (tert-butyloxycarbonyl). Following the removal of the Boc group, an amide bond was formed between the amine-terminated surface and the acyl group of the dihydroxybenzene derivatives. The electrochemical properties of dihydroxybenzene-modified MWCNT and the influence of the sweep rate on the voltammogram were elucidated by cyclic voltammetry (CV). Electron transfer kinetics of modified MWCNT by dihydroxybenzene derivatives was also studied using Laviron’s theory. As evidenced by an improvement in the anodic peak current and a negative shift in the overpotential of NADH oxidation when compared to the bare MWCNT, 3,4 and 2,5- dihydroxybenzene modified MWCNT electrodes were shown to possess catalytic activity toward NADH oxidation.

Electrochemical sensor of multiwalled carbon nanotube electrode modified by 1-phenyl-3-methyl-4-orthofluoro benzoyl-5-pyrazolone for sensing dopamine

ABSTRACT. This work explicates a simple, rapid, and sensitive method for the electrochemical detection of dopamine (DOP) utilising 1-phenyl-3-methyl-4-orthofluorobenzoyl-5-pyrazolone (HPMoFBP)/multiwalled carbon nanotube (MWCNT) carbon paste electrode (CPE). The electrochemical behaviour of DOP was performed through cyclic voltammetry and square wave voltammetry. HPMoFBP/MWCNT showed a higher current at the lower potential for the oxidation of DOP compared to bare MWCNT. The sensor's improved electrocatalytic activity was observed to detect in a 1.0 x 10-1 M phosphate buffer saline (PBS) solution at pH 8.0. A good linear regression analysis was observed between electrical response and the concentration of DOP in the range of 1 to 1000 µM. Under optimized experimental conditions, 1.0 x 10-7 M has been determined as the limit of detection (LOD). The sensor has expressed considerable sensitivity towards DOP detection without interference and is successfully used to determine DOP in dopamine hydrochloride injection.
 
 KEY WORDS: Electrochemical sensor, Dopamine, Pyrazolone, MWCNT, Voltammetry
 Bull. Chem. Soc. Ethiop. 2023, 37(4), 845-857. 
 DOI: https://dx.doi.org/10.4314/bcse.v37i4.4

Positive and Negative Changes in the Electrical Conductance Related to Hybrid Filler Distribution Gradient in Composite Flexible Thermoelectric Films Subjected to Bending

P-type multiwalled carbon nanotubes (MWCNTs), as well as heterostructures fabricated by direct deposition of inorganic thermoelectric materials as antimony and bismuth chalcogenides on MWCNT networks are known as perspective materials for application in flexible thermoelectric polymer-based composites. In this work, the electrical response of three types of Sb2Te3-MWCNT heterostructures-based flexible films-free standing on a flexible substrate, encapsulated in polydimethylsiloxane (PDMS), and mixed in polyvinyl alcohol (PVA) is studied in comparison with the flexible films prepared by the same methods using bare MWCNTs. The electrical conductance of these films when each side of it was subsequently subjected to compressive and tensile stress during the film bending down to a 3 mm radius is investigated in relation to the distribution gradient of Sb2Te3-MWCNT heterostructures or bare MWCNTs within the film. It is found that all investigated Sb2Te3-MWCNT films exhibit a reversible increase in the conductance in response to the compressive stress of the film side with the highest filler concentration and its decrease in response to the tensile stress. In contrast, free-standing and encapsulated bare MWCNT networks with uniform distribution of nanotubes showed a decrease in the conductance irrelevant to the bending direction. In turn, the samples with the gradient distribution of the MWCNTs, prepared by mixing the MWCNTs with PVA, revealed behavior that is similar to the Sb2Te3-MWCNT heterostructures-based films. The analysis of the processes impacting the changes in the conductance of the Sb2Te3-MWCNT heterostructures and bare MWCNTs is performed. The proposed in this work bending method can be applied for the control of the uniformity of distribution of components in heterostructures and fillers in polymer-based composites.

Plasma-enhanced atomic layer deposition of ruthenium metal on free-standing carbon nanotube forest for 3D flexible binder-less supercapacitor electrodes

Plasma-enhanced atomic layer deposition of ruthenium on functionalized free-standing multi-walled carbon nanotube (MWCNT) forest directly grown on a stainless steel mesh as a flexible supercapacitor electrode is done by a zero-oxidation state precursor and nitrogen plasma. Using this method for the fabrication of 3D flexible supercapacitor electrodes eliminates the need for any binder component and solution-based synthesis step as well as the production of any toxic by-products. Moreover, it enables the utilization of the entire high-surface-area MWCNTs and it alleviates the Ru agglomeration issue typically found in solution-based synthesis techniques. Accordingly, ruthenium is successfully deposited on the entire length of the carbon nanotubes in various process temperatures and plasma exposure durations with a thickness range of 15–60 nm. Electrochemical characterization of the electrodes shows a significant improvement in the capacitance of Ru coated MWCNT compared to bare MWCNT due to the additional surface faradaic redox reactions. Cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) are carried out to evaluate the electrochemical performance of the fabricated electrodes. The capability of the 3D flexible electrode is evaluated in different bending angles of 60, 80, and 180° and twisting conditions. Capacitance as high as 1834.5 mF.cm−2 (393 F.g−1) with a very low charge transfer resistance of 5.49 Ω.cm−2 is achieved that shows >400 % improvement in capacitance compared to bare MWCNTs. A capacitance retention of 92 % after 1000 CV cycles is achieved.

Is It Possible to Restrain OER on Simple Carbon Electrodes to Efficiently Electrooxidize Organic Pollutants?

This paper presents a comparative analysis of three carbon-based electrodes: bare multiwalled carbon nanotubes (MWCNT), SnO2/MWCNT, and PbO2/graphene-nanoribbons (PbO2/GNR) composites, as anodes for the electrooxidative degradation of Rhodamine B as a model organic pollutant. Anodic electrooxidation of Rhodamine B was performed on all three electrodes, and the decolorization efficiency was found to increase in the order MWCNT < PbO2/GNR < SnO2/MWCNT. The electrodes were characterized by X-ray photoelectron spectroscopy (XPS) and linear sweep voltammetry (LSV). It was proposed that, in the 0.1 M Na2SO4 applied as electrolyte, observed decolorization mainly occurs in the interaction of Rhodamine B with OH radical adsorbed on the anode. Finally, the obtained results were complemented with Density Functional Theory (DFT) calculations of OH-radical interaction with appropriate model surfaces: graphene(0001), SnO2(001), and PbO2(001). It was found that the stabilization of adsorbed OH-radical on metal oxide spots (SnO2 or PbO2) compared to carbon is responsible for the improved efficiency of composites in the degradation of Rhodamine B. The observed ability of metal oxides to improve the electrooxidative potential of carbon towards organic compounds can be useful in the future design of appropriate anodes.

Dry Synthesis of Binder-Free Ruthenium Nitride-Coated Carbon Nanotubes as a Flexible Supercapacitor Electrode.

Ruthenium nitride was successfully deposited on a multiwalled carbon nanotube (MWCNT) forest grown on a stainless-steel mesh substrate by radiofrequency plasma-assisted pulsed laser deposition. This novel dry fabrication method for flexible supercapacitor electrodes eliminates toxic byproducts and the need for any binder component. Experimental results show a successful thin film coating of the individual MWCNTs with RuNx under various synthesis conditions. The electrochemical characterization demonstrates a significant improvement in capacitance of the synthesized RuNx-MWCNT electrode compared to the bare MWCNT forest, with a large potential window of 1.2 V. Capacitance values as high as 818.2 F g-1 (37.9 mF cm-2) have been achieved.

Comparing Commercial Metal-Coated AFM Tips and Home-Made Bulk Gold Tips for Tip-Enhanced Raman Spectroscopy of Polymer Functionalized Multiwalled Carbon Nanotubes.

Tip-enhanced Raman spectroscopy (TERS) combines the high specificity and sensitivity of plasmon-enhanced Raman spectroscopy with the high spatial resolution of scanning probe microscopy. TERS has gained a lot of attention from many nanoscience fields, since this technique can provide chemical and structural information of surfaces and interfaces with nanometric spatial resolution. Multiwalled carbon nanotubes (MWCNTs) are very versatile nanostructures that can be dispersed in organic solvents or polymeric matrices, giving rise to new nanocomposite materials, showing improved mechanical, electrical and thermal properties. Moreover, MWCNTs can be easily functionalized with polymers in order to be employed as specific chemical sensors. In this context, TERS is strategic, since it can provide useful information on the cooperation of the two components at the nanoscale for the optimization of the macroscopic properties of the hybrid material. Nevertheless, efficient TERS characterization relies on the geometrical features and material composition of the plasmonic tip used. In this work, after comparing the TERS performance of commercial Ag coated nanotips and home-made bulk Au tips on bare MWCNTs, we show how TERS can be exploited for characterizing MWCNTs mixed with conjugated fluorene copolymers, thus contributing to the understanding of the polymer/CNT interaction process at the local scale.

Vanadium telluride nanoparticles on MWCNTs prepared by successive ionic layer adsorption and reaction for solid-state supercapacitor

Anchoring of vanadium telluride (VxTey) nanoparticles onto the exterior layer of multi-walled carbon nanotubes (MWCNTs) has been successfully employed at room temperature (300 K) as first report by using successive ionic layer adsorption and reaction (SILAR) to yield VxTey/MWCNTs surface architecture. Mutualistic contribution from ion insertion/extraction introduced non-stoichiometric vanadium telluride with electric double-layer involved MWCNTs have been unified to enrich excellent electrochemical performance. Three-electrode system configured VxTey/MWCNTs electrode yields 16-fold enhancement in specific capacitance compared to the bare MWCNTs electrode. Achieved performance forced us to construct flexible solid-state supercapacitor device (FSS-SC). Symmetric electrode embedded with PVA-LiClO4 gel mediator harvests remarkable 2 V voltage window to gain 34.5 Wh/kg energy density and 0.7 kW/kg power density. Cycling over 10000 replications confirms the pronounced (82.5 %) stability of designed device and growing LED enables practical evidence; demonstrating its capacity as efficient energy storage device. Correlated density functional theory (DFT) has been manifested to confirm synergistic interactions between the VxTey and MWCNTs, and a corresponding enhancement in the electron density at the Fermi level of VxTey/MWCNTs describes the insight origin for enhanced supercapacitance.

Poly (DL-valine) electro-polymerized carbon nanotube paste sensor for determination of antihistamine drug cetirizine

Poly (DL-valine) modified multiwalled carbon nanotube paste sensor (PVLMCNTPS) was prepared by electro-polymerization route. PVLMCNTPS and bare multiwalled carbon nanotube paste sensor (BMCNTPS) morphologies and sensing properties for cetirizine (CTZ) were confirmed through a field emission scanning electron microscope (FE-SEM) and electrochemical studies, respectively. In contrast to BMCNTPS, PVLMCNTPS surface composite creates an electrocatalytic impact on the oxidation of CTZ. PVLMCNTPS properties were optimized using parameters such as accumulation time, number of polymerization cycles, solution pH, and scan rate. The optimized PVLMCNTPS was applied for the determination of cetirizine in 0.1 M phosphate buffer solution (PBS) of pH 7.0, using cyclic voltammetry (CV). It is shown that PVLMCNTPS provided analytical linearity from 2.0 to 80 µM, with a detection limit of 0.11 µM for CTZ determination. PVLMCNTPS is found highly selective for CTZ in presence of some interfering organic molecules. The stable and selective PVLMCNTPS was applied for CTZ determination in pharmaceutical pills with satisfactory results.

Microwave-assisted ultrafast in-situ growth of N-doped carbon quantum dots on multiwalled carbon nanotubes as an efficient electrocatalyst for photovoltaics

Multiwalled carbon nanotubes (MWCNTs) are at the forefront of metal-free electrocatalysts, however, the performance is still limited due to lack of functionality and dispersion. Coupling of MWCNTs with nitrogen doped carbon quantum dots (NCQDs) can impart the required active sites and dispersion. For the purpose, NCQDs are generally attached to MWCNTs by multistep processing, such as NCQDs synthesis, followed by their complex purification, surface activation, and crosslinking with MWCNT. The scalability of such a multistep process is limited, which is addressed by direct microwave-assisted growth of NCQDs on MWCNT. The concentration of reactants of NCQDs synthesis was optimized (with respect to MWCNTs), to achieve controlled direct growth of NCQDs on MWCNTs. The proposed strategy significantly reduced time and energy consumption, along with providing an overlapped interface for the fast charge transfer. Moreover, NCQDs' growth effectively modulated the surface reactivity and internal band structure of the MWCNTs. In response, dye-sensitized solar cells employing NCQDs modified MWCNT as a counter electrode showed 50% higher photovoltaic performance as compared to bare MWCNTs.

Preparation of 3D network CNTs-modified nickel foam with enhanced microwave absorptivity and application potential in wastewater treatment

Multi-walled carbon nanotubes (MWCNTs) modified nickel foams (MWCNTs-NF) were developed with an electrophoretic deposition methodology for microwave (MW) assisted catalysis and processing enhancement. A nickel foam (NF) was selected to serve the dual purpose both as the MW absorbing catalytic materials and the matrix for MWCNTs loading in order to maximize the recyclability of the catalysts. The effects of electrophoretic voltage and concentration of electrophoretic fluid on the morphology and deposition characteristics of MWCNTs on the NF matrix were investigated. It was found that the MWCNTs-NF composite material resulted in strong enhancement of MW absorptivity with synergistic heat-generating effects that were not observed when MWCNTs or NF was exposed to MW alone. The combination of NF and MWCNTs brought a catalytic total organic carbon removal efficiency of 97% in wastewater treatment, while that using bare MWCNTs and NF were only 65.2% and 79.3%, respectively. The coupling of NF with MWCNTs led to the formation of additional MW-absorbing channels and focal sites with strong MW absorptivity, which in turn gave rise to the synergistic MW heating effects. This research highlights the great prospect of the MW-assisted reaction enhancement using the MWCNTs-NF composite material as the catalyst in wastewater treatment and other similar engineering applications.

Modeling and optimization of heterogeneous Fenton-like and photo-Fenton processes using reusable Fe3O4-MWCNTs

In this work, iron (II, III) oxide (Fe3O4) was synthesized and incorporated onto multi-walled carbon nanotubes (MWCNTs) to prepare Fe3O4-MWCNTs composite in a quest for evaluating its performance and reusability in both Fenton-like and photo-Fenton processes. The characterization of Fe3O4-MWCNTs by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared (FTIR) spectroscopy, and energy dispersive X-ray (EDX) spectroscopy showed that the prepared catalyst can behave as a composite. Methylene blue (MB) was used as a substrate for evaluation of Fenton-like and photo-Fenton processes. The reusability of the catalyst and the influence of operation parameters such as pH, H2O2 dosage, and catalyst loading were investigated. Complete degradation of MB was attained by Fe3O4-MWCNTs in the aforementioned processes, whereas the removal efficiency of MB by using bare MWCNTs under the same conditions was 52%, which suggests that the generated oxidant species due to the reactions between H2O2 and leached iron contribute to the degradation of MB. A degradation pathway was proposed based on the oxidation intermediates that have been detected by mass spectrometry. The reusability of Fe3O4-MWCNTs has been examined in four consecutive cycles. The final removal of MB in the fourth cycle was 94%. The optimization of MB removal was investigated by response surface methodology (RSM) based on central composite design (CCD). Moreover, an artificial neural network (ANN) of type feed-forward back propagation was employed to model the influence of operating conditions. The ANN model revealed a high correlation in the prediction of the removal efficiency (R2=0.9934).

Low-Energy Electrocatalytic CO2 Reduction in Water over Mn-Complex Catalyst Electrode Aided by a Nanocarbon Support and K+ Cations

Electrocatalytic CO2 reduction over a Mn-complex catalyst in an aqueous solution was achieved at very low energy with a combination of multiwalled carbon nanotubes (MWCNTs) and K+ cations. Although the bare Mn-complex did not function as a catalyst in an aqueous solution, the combined Mn-complex/MWCNT cathode promoted electrocatalytic CO2 reduction at an overpotential of 100 mV where neither the bare MWCNTs nor bare Mn-complex were catalytically active. The Mn-complex/MWCNT produced CO at a constant rate for 48 h with a current density of greater than 2.0 mA cm–2 at −0.39 V (vs RHE). The MWCNTs with electron accumulation properties, together with surface adsorbed K+ ions, provided an environment to stabilize CO2 adjacent to the Mn-complex and significantly lowered the overpotential for CO2 reduction in an aqueous solution, and these results were consistent with density functional theory (DFT) calculations. Experiments clarified that the synergetic effect of the MWCNTs and K+ ions was also applicable to Co...

Floating liquid crystalline molecularly imprinted polymer coated carbon nanotubes for levofloxacin delivery

Liquid crystalline molecularly imprinted polymers (LC-MIPs) were low cross-linking MIPs (5–20 mol%) by introducing a LC monomer into the MIP polymerization system to keep the shape of the imprinted cavities due to additional interactions between the mesogenic groups. The multiwalled carbon nanotubes (MWCNTs) coated LC-MIP (MWCNT@LC-MIP) was the first fabricated as a novel floating interaction-controlled DDS. The synthesis was achieved by adding 9-vinylanthracene to obtain the high-density vinyl group functionalized MWCNTs firstly, and then polymerization of LC MIPs was performed on the surface of MWCNTs using a mixture of methacrylic acid, ethylene glycol dimethacrylate, and 4-methyl phenyl dicyclohexyl ethylene (LC monomer) with levofloxacin (LVF) as model template drug. Both template/functional monomer ratio and levels of crosslinker were optimized to obtain the best imprinting factor. Characterizations of polymer were investigated by the transmission electron microscope, nitrogen adsorption, thermogravimetric analysis, Fourier transform infrared spectra and floating behavior studies. The imprinting effect was confirmed by the adsorption isotherms, adsorption kinetics and effect of selectivity. In vitro release studies were examined by the LVF-loaded MWCNT@LC-MIP and the control samples, MWCNT@LC-NIP, MWCNT@MIP, MWCNT@NIP and the bare MWCNT using acetonitrile as the dissolute medium. The release profiles showed an obvious zero-order release of LVF from MWCNT@LC-MIP, which exhibited 3.8 μg/h of the release rate with duration of about 20 h. In vivo pharmacokinetic study displayed the relative bioavailability of the gastro-floating MWCNT@LC-MIP was 578.9%, whereas only 58.0% of MWCNT@MIP and 11.7% of the bared MWCNT. As a conclusion, MWCNT@LC-MIP showed potentials for oral administration by the innovative combination of floating and controlled release properties.

Transport of multi-walled carbon nanotubes stabilized by carboxymethyl cellulose and starch in saturated porous media: Influences of electrolyte, clay and humic acid

This study investigated the transport behaviors of carboxymethyl cellulose (CMC) and starch stabilized multi-walled carbon nanotubes (MWNTs) through a saturated quartz sand column in the presence of electrolytes, model clays, and natural organic matter (humic acid) through column breakthrough experiments and model simulations. Both stabilizers, CMC and starch, greatly enhanced the breakthrough of MWNTs, with a full breakthrough plateau (C/C0) ranging from 0.69 to 0.90 at ionic strength from 0.3 to 10mM. Between the two stabilizers, CMC was more effective in resisting particle deposition, and thus CMC-stabilized MWNTs were more transportable through the medium. While non-stabilized MWNTs were much less transportable and were vulnerable to electrolyte effects (especially Ca2+), the stabilized counterparts were much more resistant to the coagulation effects of electrolytes. The presence of colloidal clay particles showed contrasting effects on the transport of bare and stabilized MWNTs. The full breakthrough C/C0 of bare MWNTs was suppressed by kaolinite and montmorillonite particles from 0.33 to <0.15 with 5mg/L clay, indicating that the presence of both clays enhanced the aggregation and deposition of MWNTs. However, kaolinite particles facilitated the transport of stabilized-MWNTs, while montmorillonite weakened the breakthrough of stabilized MWNTs. Humic acid had less effect on the mobility of stabilized-MWNTs than that of bare MWNTs. The advection-dispersion transport model incorporated with the filtration theory was able to simulate the breakthrough curves and quantitatively interpret the particle deposition. The results can facilitate our understanding of fate and transport of stabilized carbon nanotubes in the environment.

Synthesis, characterization and gas sensing properties of ZnO-decorated MWCNTs

In this work, ZnO-decorated multi-walled carbon nanotube (MWCNT) nanocomposites prepared using an in-situ method involving the thermal evaporation of Zn powders in the presence of MWCNTs. The gas sensing characteristics of the MWCNT/ZnO nanocomposites are studied, and results for the material characterizations for the synthesized nanocomposites confirm the formation of well-distributed ZnO nanoparticles onto MWCNTs, creating MWCNT/ZnO nanocomposites. The gas sensing properties of the MWCNT/ZnO nanocomposite gas sensor, such as response, cross-sensitivity, and response-recovery time, are investigated and compared with a bare MWCNT sensor. The decoration of ZnO nanoparticles greatly improves the gas sensing properties of bare MWCNTs. We discussed the possible mechanisms for the enhancement of sensing capabilities. The results suggest that decoration of n-type semiconducting oxide materials, such as ZnO in the form of nanoparticles, is a promising strategy for improvement of gas sensing properties of p-MWCNTs.

A self-assembled flavin protective coating enhances the oxidative thermal stability of multi-walled carbon nanotubes

Multi-walled carbon nanotube (MWNT) has many commercial applications. However, its broad use is limited by the surface-bound oxygen lowering its thermal stability. Here, we developed a facile method to enhance the oxidative thermal resistance of MWNTs that involves molecular coating promoted surface passivation. In the approach, ball milling is employed to self assemble flavin mononucleotide (FMN) helically around MWNTs through non-covalent interactions with no increased defects in MWNT. Upon high temperature oxidation, the ribityl phosphate side chain of FMN in the nanoconstruct undergoes partial decomposition to generate a corresponding isoalloxazine derivative on the surface of the MWNTs. Transmission electron microscopy reveals that the oxidatively annealed material is comprised of a tight isoalloxazine coating stacked on the sidewalls of the MWNT. The results of thermal gravimetric analysis studies show that the coating further elevates long-term stability and the energy barrier for oxidation of the MWNT by 28 kJ/mol from 113 kJ/mol for the bare MWNT. The role of the isoalloxazine coating is proposed to be surface passivation from molecular oxygen. As a consequence of the passivation, the maximum oxidative temperature of the MWNT is raised to 938 K as compared to that of 843 K for bare MWNT.

Selective glycerol oxidation using platinum nanoparticles supported on multi-walled carbon nanotubes and nitrogen-doped graphene hybrid

Selective oxidation of glycerol is a hot topic. Increased biodiesel production has led to glycerol oxidation over Au- and Pt-based catalysts being widely studied. However, Pt catalysts suffer from deactivation because of weak metal-support interactions. In this study, multi-walled carbon nanotube (MWCNTs)-pillared nitrogen-doped graphene (NG) was prepared by direct pyrolysis of melamine on MWCNTs, and the synthesized NG-MWCNT composite was used as the support for Pt. Characterization results showed that the surface area (173 m2/g) and pore volume of the NG-MWCNT composite were greater than those of bare MWCNTs and the separated melamine pyrolysis product (CNx). Pt (1.4 ± 0.4 nm) dispersion on the NG-MWCNTs was favorable and the Pt/NG-MWCNT catalyst was highly active and selective in the oxidation of glycerol to glyceric acid (GLYA) in base-free aqueous solution. For example, the conversion of glycerol reached 64.4% with a GLYA selectivity of 81.0%, whereas the conversions of glycerol over Pt/MWCNTs and Pt/CNx were 29.0% and 31.6%, respectively. The unique catalytic activity of the Pt/NG-MWCNTs is attributed to well-dispersed Pt clusters on the NG-MWCNTs and the electron-donating effect of the nitrogen dopant in the NG-MWCNTs.