Decorating multi-walled carbon nanotubes with nickel nanoparticles for selective hydrogenation of citral

The nanocomposites of multi-walled carbon nanotubes (MWNTs) decorated with nickel nanoparticles were conveniently prepared by a chemical reduction of nickel salt in the present of poly(acrylic acid) grafted MWNTs (PAA-g-MWNTs). Due to the strong interaction between Ni²⁺ and –COOH, PAA-g-MWNTs became an excellent supporting material for Ni nanoparticles. The morphology and distribution of Ni nanoparticles on the surface of MWNTs were greatly influenced by the reduction temperatures, the experimental results also showed that the distribution of Ni nanoparticles was greatly improved while the MWNTs were modified by poly(acrylic acid) (PAA). The hydrogenation activity and selectivity of MWNTs decorated with Ni nanoparticles (Ni-MWNTs) for α, β-unsaturated aldehyde (citral) were also studied, and the experimental results showed that the citronellal, an important raw material for flavoring and perfumery industries, is the favorable product with a percentage as high as 86.9%, which is 7 times higher than that of catalyst by Ni-supported active carbon (Ni-AC).     

Synthesis and high electrochemical performance of polyaniline/MnO2-coated multi-walled carbon nanotube-based hybrid electrodes

Multi-layered electrodes which consist of polyaniline (PANI)/manganese dioxide (MnO₂)-multi-walled carbon nanotubes (MWNTs) are prepared as the electrode materials for supercapacitors. MnO₂-MWNTs are made by the in situ direct coating method to deposit MnO₂ onto MWNTs; the core/shell structure of multi-layered fibrous electrodes can also be obtained by PANI coating onto the MnO₂-MWNTs. The effect of PANI coating on the electrochemical performance and cyclic stability of MnO₂-MWNTs is investigated. From the cyclic voltammograms, the PANI/MnO₂-MWNTs show remarkably enhanced specific capacitance and cycle stability compared to MnO₂-MWNTs, where the highest specific capacitance (350 F/g) is obtained at a current density of 0.2 A/g for the PANI/MnO₂-MWNTs as compared to 92 F/g for pristine MWNTs and 306 F/g for MnO₂-MWNTs. This indicates that the improved electrochemical performance of PANI/MnO₂-MWNTs is due to the enhanced electrical properties by nano-scale-coated MnO₂ onto MWNTs and the PANI coating that leads to the increased cycle stability by delaying the dissolution of MnO₂ during charge/discharge tests.     

Synthesis and self‐assembly of polystyrene‐grafted multiwalled carbon nanotubes with a hairy‐rod nanostructure

Polystyrene‐grafted multiwalled carbon nanotubes (PS‐g‐MWNTs) with a hairy‐rod nanostructure were synthesized by the in situ free‐radical polymerization of styrene in the presence of multiwalled carbon nanotubes (MWNTs) terminated with vinyl groups. To quantitatively study the molecular weight and composition of polystyrene (PS) chains in PS‐g‐MWNTs, PS‐g‐MWNTs were fully defunctionalized by hydrolysis. The results showed that 1 of every 100 carbon atoms in MWNTs was functionalized at the tips and outer walls of the carbon nanotubes and grafted by PS with a weight‐average molecular weight of 9800 g/mol; therefore, a uniform thin layer (ca. 8–10 nm) of a PS shell was formed on the outer wall of MWNTs. PS‐g‐MWNTs were soluble in dimethylformamide and tetrahydrofuran. The thermal stability and glass‐transition temperature of PS in PS‐g‐MWNTs were obviously increased. Nanopins were formed on the glass substrates by the self‐assembly of PS‐g‐MWNTs, and the dewetting effect between the glass substrate and PS chains covered MWNTs during the evaporation of the solution. Both the length and diameter of the nanopins increased with the solution concentration. When PS‐g‐MWNTs were compression‐molded, MWNTs were dispersed uniformly in the PS matrix and formed good networks, such as circlelike and starlike structures, because of the entanglements of hairy PS chains on MWNTs. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3869–3881, 2006     

Nanocomposites derived from in situ grafting of linear and hyperbranched poly(ether‐ketone)s containing flexible oxyethylene spacers onto the surface of multiwalled carbon nanotubes

Linear and hyperbranched poly(ether‐ketone)s (PEKs) containing flexible oxyethylene spacers grafted multiwalled carbon nanotube (PEK‐g‐MWNT) nanocomposites were prepared by direct Friedel‐Crafts acylation as the polymer forming and grafting reaction. To achieve the composites, in situ polycondensations of AB monomers 3‐(2‐phenoxyethoxy)benzoic acid (3‐PEBA) and 4‐(2‐phenoxyethoxy)benzoic acid (4‐PEBA), and AB₂ monomer 3,5‐bis(2‐phenoxyethoxy)benzoic acid (3,5‐BPEBA) were carried out in the presence of multiwalled carbon nanotubes (MWNTs). The reaction conditions, polyphosphoric acid (PPA) with additional phosphorous phentoxide (P₂O₅) in the temperature range of 110–120 °C, were previously optimized. The conditions were used as the polymerization and grafting medium that were indeed benign not to damage MWNTs but strong enough to promote the covalent attachment of PEKs onto the surface of the electron‐deficient MWNTs. From scanning electron microscopy (SEM) and transmission electron microscopy studies, the polymers were uniformly grafted onto the MWNTs. The resultant nanocomposites are soluble in most strong acids such as trifluoroacetic acid, methanesulfonic acid, and sulfuric acid. Both isothermal and dynamic TGA studies in air showed that nanocomposites displayed improved thermo‐oxidative stability when compared with those of corresponding PEK homopolymers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3471–3481, 2008     

Biobased Polymers via Radical Homopolymerization and Copolymerization of a Series of Terpenoid-Derived Conjugated Dienes with exo-Methylene and 6-Membered Ring

A series of exo-methylene 6-membered ring conjugated dienes, which are directly or indirectly obtained from terpenoids, such as β-phellandrene, carvone, piperitone, and verbenone, were radically polymerized. Although their radical homopolymerizations were very slow, radical copolymerizations proceeded well with various common vinyl monomers, such as methyl acrylate (MA), acrylonitrile (AN), methyl methacrylate (MMA), and styrene (St), resulting in copolymers with comparable incorporation ratios of bio-based cyclic conjugated monomer units ranging from 40 to 60 mol% at a 1:1 feed ratio. The monomer reactivity ratios when using AN as a comonomer were close to 0, whereas those with St were approximately 0.5 to 1, indicating that these diene monomers can be considered electron-rich monomers. Reversible addition fragmentation chain-transfer (RAFT) copolymerizations with MA, AN, MMA, and St were all successful when using S-cumyl-S’-butyl trithiocarbonate (CBTC) as the RAFT agent resulting in copolymers with controlled molecular weights. The copolymers obtained with AN, MMA, or St showed glass transition temperatures (T_g) similar to those of common vinyl polymers (T_g ~ 100 °C), indicating that biobased cyclic structures were successfully incorporated into commodity polymers without losing good thermal properties.     

Electrocatalytic Oxidation of Glucose at Carbon Nanotubes Supported PtRu Nanoparticles and Its Detection

PtRu nanoparticles were supported on multiwall carbon nanotubes (MWNTs), which were further fabricated as an electrode for nonenzymatic glucose sensing. Transmission electron microscope and X‐ray diffraction patterns were used for characterization of the PtRu nanoparticles on MWNTs. Cyclic voltammetry and chronopotentiometry were applied to investigate the performance of the PtRu/MWNTs nanocomposite electrode for nonenzymatic oxidation of glucose. The PtRu/MWNTs electrode shows high electrocatalytic activity towards the oxidation of glucose in 0.1 M NaOH solution and thus can be used to selectively detect glucose. Under the optimal potential (+0.55 V vs. Ag/AgCl), the biosensor effectively performs a selective electrochemical analysis of glucose in the presence of common interferents, such as ascorbic acid (AA), dopamine (DP) and uric acid (UA). Wide linear calibration ranging from 1 mM to 15 mM, high sensitivity of 28.26 μA cm^?2 mM^?1, low detection limit of 2.5×10^?5 M, and fast response time of 10 s were achieved for the detection of glucose at the PtRu/MWNTs electrode.     

An enzyme-free highly glucose-specific assay using self-assembled aminobenzene boronic acid upon polyelectrolytes electrospun nanofibers-mat

A highly selective enzyme-free amperometric glucose sensor based on electrostatic self-assembling of 3-aminobenzene boronic acid (ABBA) onto a poly(styrene-co-acrylamide)/polystyrene sulfonic acid (PSA/PSSA) electrospun nanofibers-mat was investigated. Emerging ability of phenylboronic acid to bind with the diols of sugars has been extended for rapid response of glucose with a pH-sensitive redox mediator, hematein natural dye. ABBA was adsorbed on the PSA/PSSA nanofibers-mat/Pt-disc electrode that resulted in an ABBA/PSA/PSSA glucose active electrode. The interaction of ABBA onto the PSA/PSSA nanofibers-mat/Pt-disc electrode was characterized with Fourier transform infrared spectroscopy (FT-IR), ζ-potential, scanning electron microscopy (SEM), contact angle and cyclic voltammetry (CV) measurements. The prepared enzyme-free sensor exhibited a fast amperometric response, i.e., about 4 s and linearity ranging from 0.75 to 14 mM to glucose with a sensitivity of 0.987 μA mM⁻¹ cm⁻². Compared to other types of glucose biosensors viz. use glucose oxidase as sensing elements, present glucose sensor offers basic advantages including ease of fabrication, high affinity-selectivity to the glucose upon the electrode surface and quick response.     

Preparation of carbon nanotubes supported platinum nanoparticles by an organic colloidal process for nonenzymatic glucose sensing

Multi-walled carbon nanotubes (MWNTs) supported platinum nanoparticles with narrow size distribution were prepared by an organic colloidal process with sodium citrate as the coordination reagent and stabilizer, and ethylene glycol as the reduction reagent. A nonenzymatic glucose sensor with high sensitivity based on the Pt/MWNTs electrode was demonstrated. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were employed to investigate the size distributions and the crystal structure of Pt nanoparticles on the MWNTs. The TEM images show that the Pt nanoparticles with about 2–4 nm in diameter are well dispersed on the MWNTs. The Pt/MWNTs shows high electrocatalytic activity towards the oxidation of glucose in 0.1 M NaOH solution. At +0.5 V, the Pt/MWNTs nanocomposite electrode exhibits linearity in the range of 1 mM to 23 mM (R > 0.998) glucose with a response time of 11.6 s. The detection limit is 50 μM (S/N = 3). It was demonstrated that the Pt/MWNTs electrode with high electrocatalytic activity to glucose oxidation could find application in nonenzymatic detection of glucose.     

Synthesis and characterization of poly(phenylene oxide) graft copolymers by atom transfer radical polymerizations

A series of comb-like poly(phenylene oxide)s (PPO) graft copolymers with controlled grafting density and length of grafts were synthesized by atom transfer radical polymerization (ATRP). The α-bromo-poly(2,6-dimethyl-1,4-phenylene oxide)s (BPPO) were used as macroinitiators to polymerize vinyl monomers and the graft copolymers carrying polystyrene (PS), poly(p-acetoxystyrene) (PAS), and poly(methyl methacrylate) (PMMA) as side chains were synthesized and characterized by NMR, FTIR, GPC, DSC and TGA. The composition-dependent glass-transition temperatures (T_g) of PPO-g-PS exhibited good correlation with theoretical curve in Couchman equations except for the cases of low PS content (<40 mol%) copolymers in which a positive deviation was observed due to enhanced molecular interactions. The increase in monomer/initiator ratio led to the increase of degree of polymerization and the decrease of polydispersity. Despite the immiscibility nature between PPO and PMMA, the PPO-g-PMMA exhibited enhanced compatibilization as apparent single T_g in a wide temperature window throughout various compositions revealing an efficient segmental mixing on a molecular scale due to grafting structure.     

Tribological and Mechanical Properties of Poly[(R)-3-hydroxybutyric acid] Grafted with Vinyl Compounds: Insight into Possible Application

Biodegradable graft copolymers were prepared by gamma radiation-induced graft polymerization of two vinyl monomers, vinyl acetate and vinyl alcohol, onto poly[(R)-3-hydroxybutyric acid]. Success of the grafting reaction was verified by Fourier-transform infrared and nuclear magnetic resonance spectroscopy. Thermal remolding was used to create membranes from the copolymers. We determined tribological and mechanical properties of the membranes obtained. The lowest elongation at break in tensile testing is seen for P(3HB) and the highest for P(3HB-g-VA). Up to 5 N or so, the highest scratch resistance is exhibited by P(3HB-g-VA). Piezoelectric behavior is seen for P(3HB-g-VA) while P(3HB-g-VAc) and plain P(3HB) showed no electric response. Explanation of the piezoelectric behavior in terms of molecular structures is provided.     

Grafting Efficiency of Hydroxy‐Terminated Poly(methyl methacrylate) with Multiwalled Carbon Nanotubes

Summary: Poly(methyl methacrylate)s (PMMAs) containing a terminal hydroxy group or multiple hydroxy groups as pendants were grafted to multiwalled carbon nanotubes (MWNTs) by esterification in toluene at 100 °C. The recovered polymer with a low level of MWNTs and the PMMA‐g‐MWNTs with up to 12 wt.‐% grafted polymer were characterized using spectroscopic, microscopic, and thermogravimetric analyses. The percentage of polymer present in the PMMA‐g‐MWNT samples is very low based upon the concentration of the acid groups in the tubes.

The grafting of hydroxy‐terminated PMMA to MWNTs by esterification.     

Preparation,structure, and property of polyoxymethylene/carbon nanotubes thermal conducive composites

Polyoxymethylene (POM)/multiwalled carbon nanotubes (MWNTs) nanocomposites were prepared through a simple solution‐evaporation method assisted by ultrasonic irradiation. To enhance the dispersion of MWNTs in POM, MWNTs were chemically functionalized with PEG‐substituted amine (MWNT‐g‐PEG), which exhibited strong affinity with POM due to their similar molecular structure. The thermal conductivity and the mechanical properties of the composites were investigated, which showed that the thermal conductive properties of POM were improved remarkably in the presence of MWNTs, whereas reduced by using MWNT‐g‐PEG due to the heat transport barrier of the grafted‐PEG‐substituted amine chain. A nonlinear increase of the thermal conductivity was observed with increasing MWNTs content, and the Maxwell‐Eucken model and the Agari model were used for theoretical evaluation. The relatively high effective length factor of the composite predicted with mixture equation indicated that there were few entangles of MWNTs for the samples of MWNT‐g‐PEG in the composites. The mechanical strength of the composites can be improved remarkably by using suitable content of such functionalized MWNTs, and with the increase of the aliphatic chain length of PEG‐substituted amine, the toughness of the composites can be enhanced. Transmission electron microscope result indicated that MWNT‐g‐PEG exhibited strong affinity with POM and a good dispersion of MWNTs was achieved in POM matrix. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 905–912, 2010     

Synthesis of ion exchange membranes from ozonized high density polyethylene

The synthesis and the characterization of graft copolymers prepared from ozonized high density polyethylene (HDPE) are described. The powder of HDPE was treated with ozone in well defined conditions and then copolymerized with monomers, such as, acrylic acid (AA), N,N-dimethylamino-2 ethylmethacrylate (MADAME) and vinyl phosphonic acid (VPA). Cationic exchange membranes were prepared from the grafted copolymers of AA and VPA and anionic exchange membrane from the grafted copolymer of MADAME. The obtained copolymers were characterized by the grafting rate, FTIR spectroscopy, scaning electronic microscopy, thickness, exchange capacity and electrical resistance.     

Surface functionalization of multiwalled carbon nanotubes with poly(3,4-propylenedioxythiophene) and preparation of its random copolymers: new hybrid materials

Multiwalled carbon nanotubes (MWNTs) were functionalized with poly(3,4-propylenedioxythiophene) (PProDOT) using a simple “chemical grafting” approach. After the conventional acid oxidation (AO) process, the MWNT-COOH was converted to the acyl chloride functionalized MWNTs (MWNT-COCl) by treating them with thionyl chloride. The MWNT-COCl were further reacted with a functionalized monomer based on 3,4-propylenedioxythiophene (ProDOT-OH), followed by oxidative polymerization to prepare the MWNT-g-PProDOT hybrid. The monomer-functionalized MWNTs was further copolymerized with thiophene to prepare conducting copolymers on carbon nanotubes (CNTs). Fourier-transformed infrared spectrophotometry was employed to characterize the change in surface functionalities, which revealed that the PProDOT was covalently grafted to the MWNTs, while TGA was used to study the weight gain due to the functionalization. UV–Vis absorption spectra revealed the functionalization of the conjugated polymer by showing the typical absorption band. The morphology micrographs of the grafted PProDOT on MWNTs as evidenced by field emission scanning electron microscopy and transmission electron microscopy showed apparent effect on the structure and appearance of the MWNTs by growing thicker as expected from surface modification. Using the facile route developed in this study, CNTs can be easily fabricated with other types of polymers for several applications.     

Sugar end-capped polyethylene: Ceric ammonium nitrate initiated oxidation and melt phase grafting of glucose onto polyethylene and its microbial degradation

Low density polyethylene (LDPE) was modified to introduce biodegradability by grafting highly hydrophilic monomers (which can act as nutrients for microorganisms) such as glucose by a novel melt phase reaction using Brabender plasti-corder in the presence of ceric ammonium nitrate (CAN) to obtain 4-O-hydroxymethyl d-arabinose (sugar) end-capped LDPE (Su-g-LDPE) at a maximum grafting of 16%. The grafted polymers were characterized by FTIR, thermal analysis, WAXD and mechanical property measurements. The biodegradability of Su-g-LDPE was carried out by soil-burial test and by optical density measurements in presence of an aerobic bacterium Pseudomonas sp. The degraded polymer shows changes in weight, crystallinity and inherent viscosity. Optical density of the medium registered an increase with degradation. FTIR spectra of the degraded samples showed 70% decrease in the ketone carbonyl index (ν₁₇₁₉/ν₁₄₆₅) of Su-g-LDPE indicating microbial degradation of LDPE matrix, which was further confirmed by SEM micrographs. The present data support a microbial oxidation process involving β-oxidation whereby the carbonyl is further oxidized to carboxylic acid and affects cleavage of the LDPE chain at the ends.     

Nonenzymatic electrochemical glucose sensor based on MnO2/MWNTs nanocomposite

In this communication, an amperometric glucose biosensor based on MnO₂/MWNTs electrode was reported. MnO₂ was homogeneously coated on vertically aligned MWNTs by electrodeposition. The MnO₂/MWNTs electrode displayed high electrocatalytic activity towards the oxidation of glucose in alkaline solution, showing about 0.30 V negative shift in peak potential with oxidation starting at ca. −0.20 V (vs. 3 M KCl–Ag/AgCl) as compared with bare MWNTs electrode. At an applied potential of +0.30 V, the MnO₂/MWNTs electrode gives a linear dependence (R = 0.995) in the glucose concentration up to 28 mM with a sensitivity of 33.19 μA mM⁻¹. Meanwhile, the MnO₂/MWNTs electrode is also highly resistant toward poisoning by chloride ions. In addition, interference from the oxidation of common interfering species such as ascorbic acid, dopamine, and uric acid is effectively avoided. The MnO₂/MWNTs electrode allows highly sensitive, low-potential, stable, and fast amperometric sensing of glucose, which is promising for the development of nonenzymatic glucose sensor.     

Novel cyano-containing copolymers of vinyl esters for piezoelectric materials

The synthesis of a series of novel cyano-containing copolymers is described. Alternating copolymers of acrylonitrile with vinyl esters are obtained by increasing the electrophilic character of the nitrile monomers by complexation with zinc chloride. Copolymers of methyl and ethyl α-cyanoacrylates with vinyl esters are prepared using radical initiators in the presence of 7% acetic acid as inhibitor for anionic polymerization. The copolymers of methyl α-cyanoacrylate with the vinyl esters have T_g's above 140°C. Methyl vinylidene cyanide (MVCN) copolymerizes spontaneously with para-substituted styrenes to yield copolymers with high inherent viscosities and high T_g (160°C) and the copolymer of MVCN with vinyl acetate is also synthesized. The pyroelectric constants p for these polymers were measured and the values of p for the copolymers of vinyl acetate with methyl β,β-dicyanoacrylate, methyl α-cyanoacrylate, or MVCN were in the same range as the well-studied vinylidene cyanide/vinyl acetate copolymer. A higher concentration of dipoles generally results in higher T_g's and higher pyroelectric coefficients. © 1992 John Wiley & Sons, Inc.     

Preparation and electrocatalytic activities of platinum nanoclusters deposited on modified multi-walled carbon nanotubes supports

Multi-walled carbon nanotubes (MWNTs) were modified by oxyfluorination treatment at several different temperatures of 20, 100, 200, and 300 °C. The changes of surface properties of oxyfluorinated MWNTs were investigated using X-ray photoelectron spectroscopy (XPS) method. As a result, it was found that surface fluorine contents were varied with changing an oxyfluorination temperature and showed a maximum value at 100 °C. By changing the treatment temperature in the process of oxyfluorination for carbon supports, the surface characteristics of MWNTs had been modified, resulting that the size and loading content of deposited Pt on the modified carbon supports could be changed. Consequently, Pt deposited MWNTs that were treated at 100 °C (Pt/100-MWNTs) showed the best electroactivity among samples. The enhanced electroactivity was dependent on the higher surface area of electrochemical reaction for metal catalyst, which was related to the particle size and the morphology of the deposited particle catalysts.     

Functionalization of carbon nanotubes with biodegradable supramolecular polypseudorotaxanes from grafted-poly(ε-caprolactone) and α-cyclodextrins

Functionalization of multiwalled carbon nanotubes (MWNTs) with biodegradable supramolecular polypseudorotaxanes has been successfully performed by utilizing surface-initiated ring-opening polymerization of ε-caprolactone (CL) to yield poly(ε-caprolactone)-grafted MWNTs (MWNT-g-PCL), followed by forming inclusion complexes between grafted-PCL chains and α-cyclodextrins (α-CDs) to give α-CD-NTPCL hybrids. There are significant differences in the morphology and solubility of MWNTs before and after introduction of α-CD. Some protuberances are clearly observed for α-CD-NTPCL as compared with MWNT-g-PCL. Furthermore, the host-guest stoichiometry (monomeric unit of CL/α-CD molar ratio) for α-CD-NTPCL is much higher than that of polypseudorotaxanes consisted of linear PCL and α-CDs. This observation can be explained by a combination of several reasons including the steric hindrance of grafted-PCL, the competitive exclusion between adjacent PCL chains toward α-CD, and the addition order of α-CD as well as the host-guest feed ratio. The present methodology may open up a new opportunity toward the application of supramolecular chemistry for the chemical manipulation and processing of CNTs. Moreover, such novel supramolecular hybrids provide an entry to extend the applications of CNTs to medicine and biology fields through embedding the functional polymers and heterogeneous components.     

Synthesis and characterization of multiwall carbon nanotubes/alumina nanohybrid-supported cobalt catalyst in Fischer-Tropsch synthesis

Multiwall carbon nanotubes (MWNTs) and alumina are combined to give a new type of nanohybrid for Fisher-Tropsch synthesis (FTS) catalyst support. Alumina nano-particles (10 wt%) were introduced directly on functionalized MWNTs by a modified sol-gel method. Microstructure observations show that alumina particles were homogeneously dispersed on the inside and outside of modified MWNTs surfaces. 15 wt% cobalt loading catalysts were prepared with this nanohybrid and γ-alumina as a reference, using a sol-gel technique and wet impregnation method respectively. These catalysts were characterized by TEM, XRD, N₂-adsorption, H₂ chemisorption and TPR. The deposition of cobalt nanoparticles synthesized by sol-gel technique on the MWNTs nanohybrid shift the reduction peaks to a low temperature, indicating higher reducibility for uniform cobalt particles. Nanohybrid also aided in high dispersion of metal clusters and high stability and performance of catalyst. The proposed MWNTs nanohybrid-supported cobalt catalysts showed the improved FTS rate (g_HC/(g_cat·min)), CO conversion (%), and water gas shift rate (WGS)(g_CO2/(g_cat·h)) of 0.012, 52, and 30E-3, respectively, as compared to those of 0.007, 25, and 18E-3, respectively, on the γ-alumina-supported cobalt catalysts with the same Co loading.