Covalent Functionalization Of Carbon Nanotubes Research Articles

Synthesis of a Poly(3-dodecylthiophene) Bearing Aniline Groups for the Covalent Functionalization of Carbon Nanotubes

The functionalization of carbon nanotubes by polymers necessitates two steps, first their modification by oxidizing them or by covalently attaching small compounds to them, then the growth of the polymer chains from these anchors or their grafting onto them. In order to better control the process and the rate of functionalization, we develop polymers able to covalently react with the carbon nanotubes by their side chains in one step. We describe the synthesis of a copolymer of dodecylthiophene and its analogue bearing an aniline group at the end of the dodecyl side chain. This copolymer can functionalize single-walled carbon nanotubes (SWNTs) non-covalently and disperse more SWNTs than its hexyl analogues. UV-Vis and fluorescence spectroscopies show that in these non-covalent hybrids, the polymer forms p-stacked aggregates on the SWNTs. The non-covalent hybrids can be transformed into covalent ones by diazonium coupling. In these covalent hybrids the polymer is no longer p-stacked. According to Raman spectroscopy, the conformation of the poly(3-hexylthiophene) backbone is more ordered in the non-covalent hybrids than in the covalent ones.

Quantum Defects As a Toolbox for the Covalent Functionalization of Carbon Nanotubes with Peptides and Proteins

Single‐walled carbon nanotubes (SWCNTs) are a 1D nanomaterial that shows fluorescence in the near‐infrared (NIR, >800 nm). In the past, covalent chemistry was less explored to functionalize SWCNTs as it impairs NIR emission. However, certain sp3 defects (quantum defects) in the carbon lattice have emerged that preserve NIR fluorescence and even introduce a new, red‐shifted emission peak. Here, we report on quantum defects, introduced using light‐driven diazonium chemistry, that serve as anchor points for peptides and proteins. We show that maleimide anchors allow conjugation of cysteine‐containing proteins such as a GFP‐binding nanobody. In addition, an Fmoc‐protected phenylalanine defect serves as a starting point for conjugation of visible fluorophores to create multicolor SWCNTs and in situ peptide synthesis directly on the nanotube. Therefore, these quantum defects are a versatile platform to tailor both the nanotube's photophysical properties as well as their surface chemistry.

Hybrid Plasma-Liquid Treatment of Carbon Nanotubes for Application in Direct Absorption Solar Thermal Collectors

Covalent functionalization of carbon nanotubes (CNTs) with oxygen-based or nitrogen-based functional groups is one of the most popular techniques to modify the surface energy and inherent properties of the CNTs.1 This functionalization generates interest for a broad range of applications including mechanically superior advanced composites,2 more sensitive gas sensors,3 enhanced energy storage materials4 or ultra-conductive fibers.5 As an alternative to the harsh chemicals used by traditional chemical functionalization, plasma-based surface treatments can be used with great efficacy and reduced reaction times, providing an array of application-specific benefits.Awareness of the environmental pollution caused by fossil fuels and the ever-increasing demand for energy has driven research focussed on zero-carbon renewable energy sources. Conscious of this, direct absorption solar thermal collectors are gaining prominence, both for domestic heating and steam generation. CNTs have been investigated as an additive to take advantage of the near blackbody absorption and high thermal conductivity to improve system efficiency. Critical to the success of the additive nanoparticles is the stability in the fluid, however, due to their high surface energy CNTs tend to agglomerate which can limit the efficacy of their integration into real-world products.In this work, macroscopic ribbon-like assemblies of carbon nanotubes are functionalized by plasma-induced non-equilibrium electrochemistry (PiNE) implemented through a simple direct current-based plasma-liquid system. This system utilizes the plasma-generated species in an electrolyte of 10 %vol ethanol in water, with or without a nitrogen precursor, for the oxygen and/or nitrogen functionalization of the carbon nanotube assembly. For this treatment, a ribbon-like piece of CNT was used as the anode and a helium plasma discharge triggered by applying 10 mA and 1 - 1.6 kV to act as the cathode. The plasma-generated species are then expected to migrate towards the CNTs and functionalize the sidewalls.The oxygen content is shown to be increased by between 70 % and 300 % when the treatment solution of 10 %vol ethanol is used in the ribbon electrode configuration. When ethylenediamine is added as a nitrogen precursor, the atomic concentration of nitrogen reaches 23 %, with amine groups, pyrrolic groups and graphitic nitrogen observed in the x-ray photoelectron spectra. This nitrogen content is unmatched in quantity when compared to either a simple soaking procedure or an electrolysis process with a platinum foil replacing the plasma as the counter-electrode. This demonstrates that the plasma either directly or indirectly, through plasma-generated species, facilitates and enhances the availability of nitrogen from the ethylenediamine precursor. The potential plasma-induced chemical pathways which lead to the functionalization of the CNTs are also investigated and discussed.In the application of a direct absorption solar collector system, it is found that the covalent functionalization provided by the plasma-liquid system enhances the stability of the CNT-ethylene glycol nanofluid, with the oxygen-functionalized samples producing the most stable nanofluids. This is explained through the lower value for contact angle measurements, suggesting greater hydrophobicity of the CNTs.References(1) Mallakpour, S.; Soltanian, S. Surface Functionalization of Carbon Nanotubes: Fabrication and Applications. RSC Adv. 2016, 6 (111), 109916–109935. https://doi.org/10.1039/c6ra24522f.(2) Williams, J.; Broughton, W.; Koukoulas, T.; Rahatekar, S. S. Plasma Treatment as a Method for Functionalising and Improving Dispersion of Carbon Nanotubes in Epoxy Resins. J. Mater. Sci. 2013, 48 (3), 1005–1013. https://doi.org/10.1007/s10853-012-6830-3.(3) Ham, S. W.; Hong, H. P.; Kim, J. H.; Min, S. J.; Min, N. K. Effect of Oxygen Plasma Treatment on Carbon Nanotube-Based Sensors. J. Nanosci. Nanotechnol. 2014, 14 (11), 8476–8481. https://doi.org/10.1166/jnn.2014.10007.(4) Hulicova-Jurcakova, D.; Seredych, M.; Lu, G. Q.; Bandosz, T. J. Combined Effect of Nitrogen- and Oxygen-Containing Functional Groups of Microporous Activated Carbon on Its Electrochemical Performance in Supercapacitors. Adv. Funct. Mater. 2009, 19 (3), 438–447. https://doi.org/10.1002/adfm.200801236.(5) Li, L.; Liu, E.; Shen, H.; Yang, Y.; Huang, Z.; Xiang, X.; Tian, Y. Charge Storage Performance of Doped Carbons Prepared from Polyaniline for Supercapacitors. J. Solid State Electrochem. 2011, 15 (1), 175–182. https://doi.org/10.1007/s10008-010-1087-8. Figure 1

Inside Cover: Quantum Defects as a Toolbox for the Covalent Functionalization of Carbon Nanotubes with Peptides and Proteins (Angew. Chem. Int. Ed. 40/2020)

Inside Cover: Quantum Defects as a Toolbox for the Covalent Functionalization of Carbon Nanotubes with Peptides and Proteins (Angew. Chem. Int. Ed. 40/2020)

Quantum Defects as a Toolbox for the Covalent Functionalization of Carbon Nanotubes with Peptides and Proteins.

Single‐walled carbon nanotubes (SWCNTs) are a 1D nanomaterial that shows fluorescence in the near‐infrared (NIR, >800 nm). In the past, covalent chemistry was less explored to functionalize SWCNTs as it impairs NIR emission. However, certain sp3 defects (quantum defects) in the carbon lattice have emerged that preserve NIR fluorescence and even introduce a new, red‐shifted emission peak. Here, we report on quantum defects, introduced using light‐driven diazonium chemistry, that serve as anchor points for peptides and proteins. We show that maleimide anchors allow conjugation of cysteine‐containing proteins such as a GFP‐binding nanobody. In addition, an Fmoc‐protected phenylalanine defect serves as a starting point for conjugation of visible fluorophores to create multicolor SWCNTs and in situ peptide synthesis directly on the nanotube. Therefore, these quantum defects are a versatile platform to tailor both the nanotube's photophysical properties as well as their surface chemistry.

Design and synthesis of aniline-appended P3HT for single step covalent functionalisation of carbon nanotubes

Aniline-appended P3HT copolymer allows covalent functionalization of carbon nanotubes in a single step. Both copolymer synthesis and the resulting nanohybrid characterisations are reported.

Covalent functionalization of carbon nanotubes with hydroxyl-terminated polydimethylsiloxane to enhance filler dispersion, interfacial adhesion and performance of poly(methylphenylsiloxane) composites

Surface modification of carbon nanotubes (CNTs) were performed by grafting of hydroxyl-terminated polydimethylsiloxane (HPDMS) covalently. The results of dissolution experiments revealed that long-time stable dispersions of HPDMS-functionalized CNTs (CNTs-HPDMS) were achieved in a range of solvents including ethanol, ethyl acetate, dimethylbenzene and cyclohexane, even after being placed for 3 months. Subsequently, CNTs-HPDMS were incorporated into poly(methylphenylsiloxane) (PMPS) matrix to prepare composites. Scanning electron microscopy analysis showed that CNTs-HPDMS had homogeneous dispersion and strong interfacial adhesion in PMPS, which led to much better mechanical properties of composites compared to those filled with untreated CNTs. Furthermore, the incorporation of CNTs-HPDMS significantly enhanced the thermal stability of PMPS composites both under nitrogen and air. The improved barrier effect of CNTs-HPDMS resulted from the better filler dispersion was considered to play a crucial role, which on the one hand suppressed the depolymerization of PMPS under nitrogen and on the other hand inhibited the oxygen diffusion in matrix under air. Besides, the hydroxyl groups of HPDMS could react with PMPS to form additional crosslinking during heating, and thus delayed the degradation of PMPS to some extent.

Facile covalent functionalization of carbon nanotubes via Diels-Alder reaction in deep eutectic solvents

Deep eutectic solvents (DESs), a new type of cost-effective ionic liquid analogues, were employed to develop a novel and efficient method for direct functionalization of multiwalled carbon nanotubes (MWNTs) via Diels-Alder (DA) click reaction. Poly(ionic liquid)s featuring furfuryl moieties (P(F-ILs)) and butyl moieties (P(B-ILs)) were synthesized by the functionalization of poly(chloromethylstyrene-alt-maleic anhydride) with 1-methylimidazole and furfuryl amine or butylamine. Then, the polymer was directly grafted on the surface of untreated MWNTs in choline:ethylene glycol (ChCl:EG) based DES without any catalyst. The successful functionalization of the polymer on MWNTs was confirmed by Raman spectroscopy, TGA, and XPS analysis. It was shown that the reaction proceeded in a very rapid fashion (less than an hour) and the use of DESs significantly improved the grafting density (more than double) as compared with the reaction in water.

2,2′-bipyridine-functionalized single-walled carbon nanotubes: The formation of transition metal complexes and their charge transfer effects

There is presently a great interest in the development of versatile nanohybrid systems that are based on the covalent functionalization of carbon nanotubes. Covalent functionalization of the single walled carbon nanotubes (SWCNTs) enhances their processability and functionality, allowing them to be further used in different applications. However, at the same time this leads to a disturbance of the nanotube π-network, thus reducing its intrinsically distinct physical and chemical properties of nanotubes. In the optimal situation, covalently functionalized SWCNT nanohybrid materials could be formed in a way where both of these wanted properties would exist; Good processability and the electronic properties nanotubes had before the functionalization. In this work, we describe the formation of nanohybrid materials by covalently grafting bipyridyl ligands directly onto the sidewall of the SWCNT. This is followed by addition of several different transition metals to form organometallic complexes. The systems we describe here does not utilize linker molecules between the ligands and the nanotubes allowing a better electronic communication between them. The covalent addition of the ligand onto the sidewall first causes p-type doping which is reversed to n-type doping after the addition of a transition metal. This technique offers a possibility to tune the electronic properties through reversing doping in charge transport between substrates and SWCNT. All new nanotube hybrids were fully characterized with the help of FTIR, XPS, Raman spectroscopy and HRTEM.

Covalent Functionalization of Carbon Nanomaterials with Iodonium Salts

Covalent functionalization significantly enhances the utility of carbon nanomaterials for many applications. Herein, we report an efficient method for the covalent functionalization of carbon nanotubes (CNTs) and graphite. This reaction involves the reduction of carbon nanomaterials with sodium naphthalide, followed by the addition of diaryliodonium salts. CNTs, including single-walled, double-walled, and multi-walled variants (SWCNTs, DWCNTs, and MWCNTs, respectively), as well as graphite, can be efficiently functionalized with substituted arene and heteroarene iodonium salts. The preferential transfer of phenyl groups containing electron-withdrawing groups was demonstrated by reactions with unsymmetrical iodonium salts. The lower reactivity of iodonium salts, relative to the more commonly used diazonium ions, presents opportunities for greater diversity in the selective functionalization of carbon nanomaterials.

Double-walled carbon nanotube/zirconia composites: Preparation by spark plasma sintering, electrical conductivity and mechanical properties

Double-walled carbon nanotube/yttria-stabilized zirconia composite powders with carbon contents up to 6.3wt% are prepared by soft covalent functionalization of carbon nanotubes (CNTs) followed by mixing with a nanometric yttria-stabilized zirconia (YSZ) powder. Composites are densified by spark plasma sintering (SPS). The composites present an electrical conductivity (0.09–0.88Scm−1) which is among the highest values reported in the literature. Both the fracture strength (σf) and the single-edged notched beam fracture toughness (KIc) are measured for the first time on CNT/YSZ composites. The best mechanical properties (σf=694MPa; KIc=7MPam1/2), obtained for low carbon contents (up to 1.2wt%), are among the highest reported up to now. However, the fracture toughness is lower than that of the YSZ ceramic (KIc=10.3MPam1/2) whose mechanical properties are outstanding, taking into account its very fine microstructure.

(Invited) Photoluminescence Carrier Dynamics and Photon Statistics of Covalent Dopant-Induced Trap States in Single Wall Carbon Nanotubes

Recent advances in low level covalent functionalization of carbon nanotubes are receiving significant attention due to new emitting states being introduced by chemically stable oxygen1,2 and aryl diazonium dopants3 that increase photoluminescence quantum yields. Recent low-temperature studies have further elucidated the associated chemical and electronic structure.4 We report here photoluminescence studies of dynamic behaviors of the dopant sites. Relevant to their potential uses in imaging and as novel photon sources, we demonstrate blinking behaviors and discuss a range of response as a function of dopant species. We also report across a range of dopants photoluminescence decay dynamics obtained at the ensemble and single tube levels. We find that localization of excitons at dopant sites dramatically increases photoluminescence lifetimes, indicating the importance of exciton trapping as a route to limiting non-radiative decay pathways arising from exciton mobility. Relevant to interest in these new emitting states as single photon emitters for quantum information processing, we also demonstrate an approach to stabilizing emission output while also introducing solitary dopant sites. Finally, lifetime and photon correlation studies enabled by superconducting nanowire single-photon detectors will be presented. Evolution of behaviors as a function of temperature will be discussed in the context of realizing room-temperature photon antibunching. 1. S. Ghosh, et al., Science, 330, 1656 (2010). 2. Y. Piao, et al., Nature Chem., 5, 840 (2013). 3. Y. Miyauchi, et al., Nature Photon., 7, 715 (2013). 4. X. Ma, et al., ACS Nano, 8, 10782 (2014).

Nondestructive covalent functionalization of carbon nanotubes by selective oxidation of the original defects with K2FeO4

Chemical oxidation is still the major approach to the covalent functionalization of carbon nanotubes (CNTs). Theoretically, the defects on CNTs are more reactive than skeletal hexagons and should be preferentially oxidized, but conventional oxidation methods, e.g., HNO3/H2SO4 treatment, have poor reaction selectivity and inevitably consume the CC bonds in the hexagonal lattices, leading to structural damage, π-electrons loss and weight decrease. In this work, we realized the nondestructive covalent functionalization of CNTs by selective oxidation of the defects. In our method, potassium ferrate K2FeVIO4 was employed as an oxidant for CNTs in H2SO4 medium. The CNT samples, before and after K2FeO4/H2SO4 treatment, were characterized with colloid dispersibility, IR, Raman spectroscopy, FESEM and XPS. The results indicated that (i) CNTs could be effectively oxidized by Fe (VI) under mild condition (60°C, 3h), and hydrophilic CNTs with abundant surface COOH groups were produced; and (ii) Fe (VI) oxidation of CNTs followed a defect-specific oxidation process, that is, only the sp3-hybridized carbon atoms on CNT surface were oxidized while the CC bonds remained unaffected. This selective/nondestructive oxidation afforded oxidized CNTs in yields of above 100wt%. This paper shows that K2FeO4/H2SO4 is an effective, nondestructive and green oxidation system for oxidative functionalization of CNTs and probably other carbon materials as well.

Covalent Functionalization of Carbon Nanotubes with Xanthates and Peroxides

AbstractThe covalent grafting of xanthates onto carbon nanotubes (CNTs) by using peroxides as radical initiators was studied. Carbon nanotubes were functionalized with seven different xanthates by employing dilauroyl peroxide as a radical initiator. This allowed for the concomitant double functionalization by both xanthate and peroxide moieties. This one‐step double functionalization was demonstrated by the use of a heteroatom‐containing peroxide, and optimization reactions were performed to determine the maximum grafting yields of each component. The maximum grafting yield of the xanthate occurred when the xanthate and peroxide were introduced in stoichiometric amounts, whereas the grafting yield of the peroxide was simply a function of the quantity of peroxide introduced to the reaction. On the basis of these results, a mechanism for this double functionalization is proposed. Finally, some postfunctionalization reactions of the grafted moieties were performed as proof that their chemical integrity was retained after being anchored to the CNT surface.

Effects of functionalization of carbon nanotubes on their dispersion in an ethylene glycol-water binary mixture--a molecular dynamics and ONIOM investigation.

The present work utilizes classical molecular dynamics simulations to investigate the covalent functionalization of carbon nanotubes (CNTs) and their interaction with ethylene glycol (EG) and water molecules. The MD simulation reveals the dispersion of functionalized carbon nanotubes and the prevention of aggregation in aqueous medium. Further, residue-wise radial distribution function (RRDF) and atomic radial distribution function (ARDF) calculations illustrate the extent of interaction of -OH and -COOH functionalized CNTs with water molecules and the non-functionalized CNT surface with EG. As the presence of the number of functionalized nanotubes increases, enhancement in the propensity for the interaction with water molecules can be observed. However, the same trend decreases for the interaction of EG molecules. In addition, the ONIOM (M06-2X/6-31+G**:AM1) calculations have also been carried out on model systems to quantitatively determine the interaction energy (IE). It is found from these calculations that the relative enhancement in the interaction of water molecules with functionalized CNTs is highly favorable when compared to the interaction of EG.

Invited Presentation: Covalent Functionalization of Carbon Nanotubes and Graphene: Chemistry, Electronic Structure and Physical Properties

We have demonstrated the covalent functionalization of carbon nanotubes and graphene with a variety of chemistries including the use of nitrophenyl groups, Diels-Alder reactions and organometallic derivatization. The chemical formation of covalent carbon-carbon bonds involving the basal plane carbon atoms modifies the electronic properties of graphene; the transformation of the carbon centers from sp2 to sp3 introduces a barrier to electron flow by saturating the carbon atoms and opening a band gap which potentially allows the generation of insulating and semiconducting regions in graphene wafers. In this talk I will discuss our recent results on the electronic and magnetic properties of chemically modified graphene, the observation of ferromagnetism, and the application of organometallic chemistry to facilitate the interconnection of single-walled carbon nanotubes.

Preparation and Supercapacitive Performance of Polyaniline Covalently Grafted Carbon Nanotubes Composite Material

Rencently, covalent functionalization carbon nanotubes have been received special attention because of the expansive application prospect in the areas of nanoscience and nanotechnology. Moreover, covalent functionalization of carbon nanotubes can readily deal with fundamental issues of purification, solubilization, and processing. In particular, polyaniline, due to its high electronic conductivity, good environmental stability, easy preparation and reversible acid-base doping-dedoping chemistry, has been one of the most studied conducting polymers. Recently, CNTs-PANI composites were investigated widely, such as supercapacitor, optoelectronic devices, sensing and catalysis as well. In this work, we perform in situ polymerization method at low temperatures obtaining uniform structures PANI grafted on CNTs (which has been covalently functionalization with -NH2 groups on its surface) composites. Concerning CNTs-NH-PANI composites, PANI could be covalently grafted onto CNTs through -NH2 groups. Due to the fact that CNTs-NH-PANI composites have abundant -NH2 groups on their surface, serving as anchor centers for polymerization of aniline monomer. Introduction of-NH2 groups can not only increase the dispersion of carbon nanotubes itself, but also can be as growth sites to form PANI uniform grafted to the core-shell structure of carbon nanotubes in the growth process of PANI. More importantly, PANI uniformly grafted on CNTs is prone to disperse the bundle of CNTs into separated lines and improve water dispersibility of obtained CNTs-NH-PANI composites. Potential application of the composite material as high performance supercapacitor has been explored. Composite material samples were characterized by transmission electron microscopy (TEM), X-ray diffraction(XRD) and electrochemical methods and so on. TEM results showed that the hierarchical CNTs-PANI composites with uniform morphology have been successfully prepared due to hydrophilic groups -OH and -NH2 are successfully covalently functionalization on the surface of CNTs. Moreover, the electrochemical measurement show that CNTs-NH-PANI composites have high specific capacitance as supercapacitor material. At the current density of 0.1A/g, the specific capacity can reach 251.2F/g. For PANI, the capacitance contribution is higher in covalently grafted CNTs-g-PANI composites than PANI-c-CNTs. At the Charge-Discharge test, at the current density of 1A/g, the composite material capacity retention stability rate at 64% after 5000 charge discharge test, higher than that of PANI-c-CNTs 48% significantly.

Surface functional groups of carbon nanotubes to manipulate capacitive behaviors

The covalent functionalization of carbon nanotubes (CNTs) is a basic but important chemistry that can modify their physicochemical properties, resolve their poor dispersion capability, and improve their capacitance to enable their use as high-energy supercapacitors. However, the relationship between functional groups on the CNT surface and their capacitive characteristics has not yet been explored. Here, we demonstrate the influence of carboxylic, sulfonic, and amine groups tethered to CNTs (Cf-CNTs, Sf-CNTs, and Nf-CNTs, respectively) on capacitor performance in an organic electrolyte. The Cf-CNTs show the highest specific capacitance of 129.4 F g(-1), four-fold greater than 31.2 F g(-1) of pristine CNTs, but they reveal the lowest rate capability of 57%. In contrast, the Sf- and Nf-CNTs exhibit specific capacitances of 70.9 F g(-1) and 83.6 F g(-1), two-fold greater than that of pristine CNTs, along with a good rate capability greater than 80%. Despite their pseudocapacitive nature, all functionalized CNTs show a cyclic stability of more than 80% after 500 cycles due to the electrochemical stability of the functional groups. As demonstrated by spectroscopic analysis, the supercapacitive behaviors of the functionalized CNTs originate from specific interactions between functional groups and lithium ions and the alteration of the electronic structure arising from covalent functionalization.

Preparation of Polyaniline Covalently Grafted Carbon Nanotubes Supported Pt Catalysts and Its Electrocatalytic Performance for Methanol

Recently, covalently functionalization carbon nanotubes have been received special attention because of the ex- pansive application prospect in the areas of nanoscience and nanotechnology. Moreover, covalent functionalization of carbon nanotubes can readily deal with fundamental issues of purification, solubilization, and processing. In particular, polyaniline, due to its high electronic conductivity, good environmental stability, easy preparation and reversible acid-base dop- ing-dedoping chemistry, has been one of the most studied conducting polymers. Recently, CNTs-PANI composites were in- vestigated widely, such as supercapacitor, optoelectronic devices, sensing and catalysis as well. In this work, uniform struc- tures PANI covalently grafted onto CNTs functionalization with -NH2 groups composites have been obtained by using liq- uid/liquid(L/L) interfacial polymerization method. The interfacial system was established by using CNTs, FeCl3, HCl as top aqueous phase and aniline, CH2Cl2 as bottom organic phase, which effective suppress second growth of PANI and obtain uniform CNTs-NH-PANI composites. Concerning CNTs-NH-PANI composites, PANI can covalently be grafted on CNTs with -NH2 groups. The resulted CNTs-NH-PANI composites have abundant -NH2 groups on their surface, serving as anchor centers for achieving high Pt dispersion. More important, PANI uniformly grafted on CNTs is prone to disperse the bundle of CNTs into separated lines and improve water dispersibility of obtained CNTs-NH-PANI composites. Subsequently, PtNPs were successfully deposited on the CNTs-PANI to form ternary hybrids. Potential application of the ternary hybrids as high performance catalysts for direct methanol fuel cells has been explored. The catalyst samples were characterized by transmis- sion electron microscopy (TEM), X-ray diffraction (XRD) and electrochemical methods. TEM results showed that the hier- archical CNTs-PANI composites with uniform morphology have been successfully prepared due to hydrophilic -OH and -NH2 groups covalently functionalized onto the surface of CNTs. Moreover, the electrochemical measurement show that the Pt/CNTs-NH-PANI hybrid have better stabilities compared with commercial JM (Pt/C) catalyst. The long-term durability test of the Pt/CNTs-CO-PANI, Pt/CNTs-NH-PANI and Pt/C catalysts shows that PANI grafted on CNTs as catalyst supports have better stabilities and more tolerant toward poisoning. Moreover, PANI covalently grafted on CNTs as catalyst supports has more excellent performance. The If/Ib of Pt/CNTs-NH-PANI catalyst for electrocatalytic methanol oxidation is 1.65 which is nearly 1.6 and 1.2 times than that of the commercial JM(Pt/C) and Pt/CNTs-CO-PANI catalysts, respectively. The results show that carbon nanotubes covalently grafting polyaniline as support can effectively improve the catalyst stability, increas- ing the service life of the catalyst. Keywords carbon nanotube; polyaniline; covalently; catalyst; methanol oxidation; CO-tolerance

Radical Addition of Xanthates on Carbon Nanotubes as an Efficient Covalent Functionalization Method

Radical-initiated support: Xanthates were used as chemical reagents for the sidewall covalent functionalization of carbon nanotubes (see figure). The best grafting yields were obtained with stoichiometric ratios of xanthate and the radical initiator lauroyl peroxide. One grafted function was used as a tether for bimetallic cluster compounds, which were converted into very small (1-2 nm) supported nanoparticles upon heating.