Effects of poly(oxyethylene)-block structure in polyetheramines on the modified carbon nanotube/poly(lactic acid) composites

The hybrids of multi-walled carbon nanotube and poly(lactic acid) (MWCNT/PLA) were prepared by a melt-blending method. In order to enhance the compatibility between the PLA and MWCNTs, the surface of the MWCNTs was covalently modified by Jeffamine® polyetheramines by functionalizing MWCNTs with carboxylic groups. Different molecular weights and hydrophilicity of the polyethermaines were grafted onto MWCNTs with the assistance of a dehydrating agent. The results showed that low-molecular-weight Jeffamine® polyetheramine modified MWCNTs can effectively improve the thermal properties of PLA composites. On the other hand, high-molecular-weight and poly(oxyethylene)-segmented polyetheramine could render the modified MWCNTs of well dispersion in PLA, and consequently affecting the improvements of mechanical properties and conductivity of composite materials. With the addition of 3.0 wt% MWCNTs, the increment of E′ of the composite at 40 °C was 79%. For conductivity, the surface resistivity decreased from 1.27 × 10¹² Ω/sq for neat PLA to 8.30 × 10⁻³ Ω/sq for the composites.     

An investigation of electrochemical behavior of nanofluids containing MWCNT on the corrosion rate of carbon steel

In this research, the corrosion rate of carbon steel in nanosuspensions containing multi-walled carbon nanotubes (MWCNT) is investigated by using potentiodynamic polarization measurements. It was observed that functionalized MWCNTs prevent carbon steel corrosion to some extent in comparison with the distillated water, but by adding MWCNTs to the SDS and SDBS water solution, the corrosion current increased. On the other hand, after adding acid-based commercial inhibitor to the functionalized sample, in the range of 12–100 ppm, polarization measurements indicated an increase in the corrosion rate of carbon steel from 0.538 to 4.26 mpy. This increase is believed to be due to the enhanced mass transfer of species to and from the metal, as well as the partial destruction of functional groups on CNTs by the protective layer adsorbed (such as SDS) on the carbon steel surface. Also by using a basic CSI inhibitor (nitrite based), corrosion rate decreased to 0.499 mpy.     

Synthesis of multi-walled carbon nanotubes using Co–Fe–Mo/Al2O3 catalytic powders in a fluidized bed reactor

The effects of the metal loading (30–70 wt.%), metal molar ratio (Co/Fe, 1–5) and mass ratio of citric acid to the catalyst (0–0.6) on the productivity and mean diameter of the multi-walled carbon nanotubes (MWCNTs) in a gas–solid fluidized bed reactor (with an inner diameter of 0.056 m and a height of 1.0 m) were determined. Liquefied petroleum gas (LPG) was used as the carbon source. X-ray diffraction (XRD) was used to characterize the catalysts synthesized using a combustion method. MWCNTs synthesized in the fluidized bed reactor were characterized by field emission scanning electron microscopy (FE-SEM) to observe their morphologies and measure their diameters. Productivity was increased by increasing both the metal loading and the mass ratio of citric acid to the catalyst. A high productivity, up to 2000%, was obtained. The catalyst transition metal particle grain size decreased in the range of 8–17 nm with an increasing citric acid mass ratio to the catalyst and the mean diameter of the MWCNTs decreased with increasing the metal molar ratio, however the correlation between the grain size in the catalyst and the mean diameter of MWCNTs remains unclear.     

Methoxypolyethylene glycol functionalized carbon nanotube composites with high permittivity and low dielectric loss

High relative permittivity and low dielectric loss were simultaneously achieved in the percolative nanocomposites with methoxypolyethylene glycol (mPEG) modified multi-walled carbon nanotubes (MWCNTs). The dense mPEG layer with a thickness of approximately 1.7 nm was continuously coated on the surface of MWCNTs. MWCNTs exhibited excellent dispersibility after being functionalized by mPEG (mPEG@MWCNTs), the mPEG@MWCNTs/ethanol suspension was still turbid even when the suspension was deposited for two months. A high permittivity of 69.7 and a low dielectric loss of 0.042 were simultaneously achieved in the poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) nanocomposite with 4.02 vol% mPEG@MWCNTs at 1 kHz. The improved dielectric properties in the nanocomposite is mainly ascribed to the following reasons: (i) the increased microcapacitors formed by MWCNTs and insulated dielectric composite; (ii) the enhanced interfacial polarization due to the homogeneous dispersion of mPEG@MWCNTs in the nanocomposites and tight adhesion between mPEG@MWCNTs and P(VDF-HFP) matrix.     

Mechanical properties of nanostructured Al2024–MWCNT composite prepared by optimized mechanical milling and hot pressing methods

Nanostructured Al2024–multiwall carbon nanotubes (MWCNTs) composites were produced using optimized mechanical milling and hot pressing methods. Nanostructured Al2024 powder was first prepared through 30 h mechanical milling of the alloy powder. MWCNTs up to 3 vol.% were added to the milled Al2024 powder and milled for different times. Differential thermal analysis (DTA) and X-ray diffraction (XRD) were used to assess the structural changes and thermal behavior during mechanical milling and hot pressing. Hardness and compression tests were applied on bulk samples to evaluate their mechanical properties. Mechanical milling applied on Al2024 powders for 30 h resulted in the grain refinement to ～30 nm. DTA analysis showed an endothermic peak at ～632 °C due to Al2024 melting and an exothermic peak between 645 and 658 °C related to Al and MWCNTs reaction. Mechanical milling of nanocomposite powder for 4 h and following hot pressing at 500 °C under a pressure of 250 MPa for 0.5 h were selected as optimized conditions for bulk nanocomposite preparation. With MWCNTs addition up to 2 vol.%, relative density remained at 98%, and hardness increased to 245 HV. Compressive strength of nanocomposites found a maximum value of 810 MPa at 2 vol.% MWCNTs addition which is 78%, 34% and 12% greater than that for Al2024–O, Al2024–T6 and nanostructured Al2024, respectively.     

Highly porous ZnS microspheres for superior photoactivity after Au and Pt deposition and thermal treatment

This work highlights the enhanced photocatalytic activity of porous ZnS microspheres after Au and Pt deposition and heat treatment at 500 °C for 2 h. Microporous ZnS particles of size 2–5 μm with large surface area 173.14 m² g⁻¹ and pore volume 0.0212 cm³ g⁻¹ were prepared by refluxing under an alkaline medium. Photoluminescence of ZnS at 437 nm attributed to sulfur or zinc vacancies were quenched to 30% and 49%, respectively, after 1 wt% Au and Pt loading. SEM images revealed that each ZnS microparticle consist of several smaller ZnS spheres of size 2.13 nm as calculated by Scherrer's equation. The rate of photooxidation of 4-nitrophenol (10 μM) under UV (125 W Hg arc–10.4 mW/cm²) irradiation has been significantly improved by Au and Pt deposition followed by sintering due to better electron capturing capacity of deposited metals and growth of crystalline ZnS phase with less surface defects.     

Effect of amino-functionalization on the interfacial adhesion of multi-walled carbon nanotubes/epoxy nanocomposites

Two types of multi-walled carbon nanotubes (MWCNTs) functionalized with different amino-organics, dicyanodiamide and phenylbiguanide, respectively, were achieved in this paper. The physico-chemical properties of MWCNTs before and after amino group modification were characterized by thermogravimetric analysis (TGA), Raman spectroscopy and inverse gas chromatography (IGC). The results showed that amino-functionalization changed evidently the surface properties of MWCNTs, such as the dispersive surface energy (decreased from 122.95 mJ/m² to 18.65 mJ/m² and 25.69 mJ/m², respectively) and specific surface energy (decreased from 8.84 mJ/m² to 0.56 mJ/m² and 4.60 mJ/m², respectively) for two functionalized MWCNTs. And then, the interfacial adhesion states of the functionalized MWCNTs/epoxy nanocomposites were investigated using scanning electron microscope (SEM) and dynamic mechanical analysis (DMA). The results also indicated that the dispersion of MWCNTs in epoxy resin and the interfacial adhesion of MWCNTs/epoxy nanocomposites were both strongly dependent on the surface physico-chemical properties of functionalized MWCNTs, and the effect of MWCNTs functionalized by phenylbiguanide with slightly higher polarity was better.     

A highly-sensitive l-lactate biosensor based on sol-gel film combined with multi-walled carbon nanotubes (MWCNTs) modified electrode

A new type of amperometric l-lactate biosensor based on silica sol-gel and multi-walled carbon nanotubes (MWCNTs) organic–inorganic hybrid composite material was developed. The sol-gel film was used to immobilize l-lactate oxidase on the surface of glassy carbon electrode (GCE). MWCNTs were used to increase the current response and improve the performance of biosensor. The sol-gel film fabrication process parameters such as H₂O : TEOS and pH were optimized, Effects of some experimental variables such as applied potential, temperature, and pH on the current response of the biosensor were investigated. Analytical characteristics and dynamic parameters of the biosensors with and without MWCNTs in the hybrid film were compared, and the results showed that analytical performance of the biosensor could be improved greatly after introduction of the MWCNTs. Sensitivity, linear range, limit of detection (S / N = 3) were 2.097 μA mM^− 1, 0.3 to 1.5 mM, 0.8 × 10^− 3 mM for the biosensor without MWCNTs and 6.031 μA mM^− 1, 0.2 to 2.0 mM, 0.3 × 10^− 3 mM for the biosensor with MWCNTs, respectively. This method has been used to determine the l-lactate concentration in real human blood samples.     

Preparation of carbon supported binary Pt–M alloy catalysts (M = first row transition metals) by low/medium temperature methods

Carbon supported Pt alloyed with first row transition elements (Pt–M/C) is being used as improved cathode catalyst for low temperature fuel cells. These catalysts have been usually prepared by deposition of the non-precious metal onto pre-formed carbon supported platinum, followed by alloying at temperatures of the order or above 700 °C. As the thermal treatment at high temperature gives rise to an undesired metal particle growth, synthetic methods based on the simultaneous deposition of Pt and M on the carbon substrate, followed by thermal treatment at lower temperature have been developed. In this paper the formation of Pt–M/C by low/intermediate temperature methods is reviewed.Moreover, to investigate the effect of the conditions used in the synthesis on the Pt:M atomic ratio, the degree of alloying and the particle size, carbon supported Pt–Co electrocatalysts with nominal Pt:Co atomic ratio 75:25 were prepared by a low temperature chemical reduction of the precursors with sodium borohydride at two different temperatures and NaBH₄ concentrations. The physical characterization of these electrocatalysts was performed by energy dispersive X-ray analysis and X-ray diffraction.     

Amperometric choline biosensors based on multi-wall carbon nanotubes and layer-by-layer assembly of multilayer films composed of Poly(diallyldimethylammonium chloride) and choline oxidase

A layer-by-layer deposition technique combined with Multi-wall carbon nanotubes (MWCNTs) was employed for fabricating choline sensors. The terminals and side-walls were linked with oxygen-containing groups when MWCNTs were treated with concentrated acid mixtures. A film of MWCNTs was initially prepared on the platinum electrode surface. Based on the electrostatic interaction between positively charged polyallylamine (PAA) and negatively charged MWCNTs and poly(vinyl sulfate) (PVS), a polymer film of (PVS/PAA)₃ was alternately adsorbed on the modified electrode continuously to be used as a permselective layer. Then poly(diallyldimethylammonium) (PDDA) and choline oxidase(ChOx) multilayer films were assembled layer-by-layer on the pretreated electrode, so an amplified biosensor toward choline was constructed. The choline sensor showed a linear response range of 5 × 10^? 7 to 1 × 10^? 4 M with a detection limit of 2 × 10^? 7 M estimated at a signal-to-noise ratio of 3, and a sensitivity of 12.53 μA/mM with a response time of 7.6 s in the presence of MWCNTs. Moreover, it exhibited excellent reproducibility, long-term stability as well as good suppression of interference. This protocol could be used to immobilize other enzymes for biosensor fabrication.     

Magnetically-sensitive shape memory polyurethane composites crosslinked with multi-walled carbon nanotubes

Magnetically-sensitive polyurethane composites, which were crosslinked with multi-walled carbon nanotubes (MWCNTs) and were filled with Fe₃O₄ nanoparticles, were synthesized via in situ polymerization method. MWCNTs pretreated with nitric acid were used as crosslinking agents. Because of the crosslinking of MWCNTs with polyurethane prepolymer, the properties of the composites with a high content of Fe₃O₄ nanoparticles, especially the mechanical properties, were significantly improved. The composites showed excellent shape memory properties in both 45 °C hot water and an alternating magnetic field (f = 45 kHz, H = 29.7 kA m⁻¹). The shape recovery time was less than one minute and the shape recovery rate was over 95% in the alternating magnetic field.     

Preparation and characterization of multi-walled carbon nanotube/hydroxyapatite nanocomposite film dip coated on Ti–6Al–4V by sol–gel method for biomedical applications: An in vitro study

In the present research, the introduction of multi-walled carbon nanotubes (MWCNTs) into the hydroxyapatite (HA) matrix and dip coating of nanocomposite on titanium alloy (Ti–6Al–4V) plate was conducted in order to improve the performance of the HA-coated implant via the sol–gel method. The structural characterization and electron microscopy results confirmed well crystallized HA–MWCNT coating and homogenous dispersion of carbon nanotubes in the ceramic matrix at temperatures as low as 500 °C. The evaluation of the mechanical properties of HA and HA/MWCNT composite coatings with different weight percentages of MWCNTs showed that the addition of low concentrations of MWCNTs (0.5 and 1 wt.%) had improved effect on the mechanical properties of nanocomposite coatings. Moreover, this in vitro study ascertained the biocompatibility of the prepared sol–gel-derived HA/MWCNT composite coatings.     

Preparation and characterization of carbon nanotube/polyetherimide nanocomposite films

Multi-walled carbon nanotube (MWCNT)/polyetherimide (PEI) nanocomposite films have been prepared by casting and imidization. A homogeneous dispersion of MWCNTs throughout the PEI matrix is observed by scanning electron microscopy of fracture surfaces, which shows not only a fine dispersion of MWCNTs but also strong interfacial adhesion with the matrix, as evidenced by the presence of many broken but strongly embedded carbon nanotubes (CNTs) in the matrix and by the absence of debonding of CNTs from the matrix. Differential scanning calorimetry and dynamic mechanical analysis show that the glass transition temperature of PEI increases by about 10 °C by the addition of 1 wt% MWCNTs. Mechanical testing shows that for the addition of 1 wt% MWCNTs, the elastic moduli of the nanocomposites are significantly improved by about 250% while the tensile strength is comparable to that of the matrix. This improvement is due to the strong interfacial interaction between the MWCNTs and the PEI matrix which favors stress transfer from the polymer to the CNTs.     

Pt nanoparticles modified by rare earth oxides: Electronic effect and influence to catalytic hydrogenation of 3-phenoxybenzaldehyde

The rare earth elements (La, Ce, Nd, Sm, Pr, and Gd) modified Pt/Al₂O₃ catalysts were prepared by the colloidal deposition and chemical reduction methods, respectively. Pt nanoparticles with average size 3 ± 0.5 nm were uniformly dispersed on the surface of Al₂O₃ for the samples prepared by the colloidal deposition method, which exhibited higher activities in the hydrogenation of 3-phenoxybenzadehyde than the corresponding samples prepared by chemical reduction method. Moreover, except Gd, the catalysts modified by rare earth elements showed better catalytic performance than unmodified Pt/Al₂O₃. For Pt–Ce/Al₂O₃ catalyst, when the weight percent of Pt and Ce was 0.5 and 0.25, respectively, the hydrogenation conversion of 3-phenoxybenzaldehyde was 97.3% after 6 h reaction. This activity improvement is due to the electronic interaction between Pt and rare earth elements, which was investigated by X-ray photoelectron spectroscopy.     

Preparation,morphology and properties of acid and amine modified multiwalled carbon nanotube/polyimide composite

The precursor of polyimide, polyamic acid, was prepared by reacting 4,4′-oxydianiline (ODA) with 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA). Unmodified, acid-modified and amine-modified multiwall carbon nanotubes (MWCNT) were separately added to the polyamic acid and heated to 300 °C to produce polyimide/carbon nanotube composite. Scanning electron microscopic (SEM) and transmission electron microscopic (TEM) microphotographs reveal that acid-modified MWCNT and amine-modified MWCNT were dispersed uniformly in the polyimide matrix. The effect of the acid and amine-modified MWCNTs on the surface and volume electrical resistivities of MWCNT/polyimide composites were investigated . The surface electrical resistivity of the nanocomposites decreased from 1.28 × 10¹⁵ Ω/cm² (neat polyimide) to 7.59 × 10⁶ Ω/cm² (6.98 wt% unmodified MWCNT content). Adding MWCNTs influenced the glass transition temperatures of the nanocomposites. Modified MWCNTs significance enhanced the mechanical properties of the nanocomposites. The tensile strength of the MWCNT/polyimide composite was increased from 102 MPa (neat polyimide) 134 MPa (6.98 wt% acid modified MWCNT/polyimide composites).     

Effect of chemical functionalization of multi-walled carbon nanotubes with 3-aminopropyltriethoxysilane on mechanical and morphological properties of epoxy nanocomposites

Nanocomposites based on epoxy resin and different weight percentages of unmodified, oxidized, and silanized multi-walled carbon nanotubes (MWCNTs) were prepared by cast molding method. Effects of MWCNTs content on the flexural properties were examined. The results showed that as the loading of the MWCNTs increased, improved flexural strength and flexural modulus were observed. The mechanical properties decreased when the MWCNTs content exceeded 0.2 wt.% due to agglomeration of MWCNTs. These results prove the effect of functionalization on the interfacial adhesion between epoxy and MWCNTs. This was further confirmed by morphology study of fractured surfaces of nanocomposites by SEM and TEM.     

Microstructural and optical properties of nanocrystalline ZnO deposited onto vertically aligned carbon nanotubes by physical vapor deposition

Nanocrystalline ZnO films with thicknesses of 5 nm, 10 nm, 20 nm, and 50 nm were deposited via magnetron sputtering onto the surface of vertically aligned multi-walled carbon nanotubes (MWCNTs). The ZnO/CNTs heterostructures were characterized by scanning electron microscopy, high resolution transmission electron microscopy, and X-ray diffraction studies. No structural degradation of the CNTs was observed and photoluminescence (PL) measurements of the nanostructured ZnO layers show that the optical properties of these films are typical of ZnO deposited at low temperatures. The results indicate that magnetron sputtering is a viable technique for growing heterostructures and depositing functional layers onto CNTs.     

Flexible and high thermal conductivity thin films based on polymer: Aminated multi-walled carbon nanotubes/micro-aluminum nitride hybrid composites

Multi-walled carbon nanotubes functionalized with amino groups (MWCNT-NH₂) were prepared via the chemical modification of the carboxyl groups introduced on the surface of MWCNT. The synthesized materials and untreated micro-aluminum nitride (micro-AlN) particles were embedded in a polymer resin, viz. epoxy-terminated dimethyl siloxane. The thermal diffusivity and conductivity of all of the composites continuously improved with increasing the content of fillers. A thermal conductivity of 3.81 W/mK was achieved at an MWCNT-NH₂ loading of 3 wt% and micro-AlN loading of 70 wt% while their flexibility was maintained. This result is due to the high aspect ratio of the MWCNT-NH₂ which allows a heat conductive percolation network to be established between the micro-AlN particles. Also, all of the composites fabricated by the optimized process endured about 200,000 bending cycles without rupturing or losing their thermal conductivity.     

Synergetic effect of thermal conductive properties of epoxy composites containing functionalized multi-walled carbon nanotubes and aluminum nitride

This study investigates the thermal conductivity of epoxy composites containing two hybrid fillers which are multi-walled carbon nanotubes (MWCNTs) and aluminum nitride (AlN). To form a covalent bonds between the fillers and the epoxy resin, poly(glycidyl methacrylate) (PGMA) were grafted onto the surface of nano-sized MWCNTs via free radical polymerization and micro-sized AlN was modified by zirconate coupling agent. Results show that functionalized fillers improve thermal conductivity of epoxy composites, due to the good dispersion and interfacial adhesion, which is confirmed by scanning electron microscope. Furthermore, the hybrid fillers provide synergetic effect on heat conductive networks. The thermal conductivity of epoxy composites containing 25 vol.% modified AlN and 1 vol.% functionalized MWCNTs is 1.21 W/mK, comparable to that of epoxy composites containing 50 vol.% untreated AlN (1.25 W/mK), which can reduce the half quantity of AlN filler used.     

Characteristics of multi-walled carbon nanotubes and background aerosols by carbon analysis; particle size and oxidation temperature

Novel carbonaceous nanomaterials such as carbon nanotubes and fullerenes have many beneficial characteristics as industrial materials, but exposure to these nanomaterials also poses health risks. As part of an exposure assessment, we characterized the following carbonaceous nanomaterials, using an aerosol carbon monitor: nine samples of multi-walled carbon nanotubes (MWCNTs), a sample of single-walled carbon nanotubes (SWCNTs), a standard sample of diesel exhaust particles (DEPs), and an ambient particulate matter (APM). The amounts of elemental carbon (EC) determined by the monitor coincided with the mass of MWCNTs calibrated by a microbalance. The carbonaceous nanomaterials were oxidized in three steps of oven temperatures (550, 700 and 920 °C) in this method. The portion of oxidized carbon at each temperature depended on the sample characteristic. We used the monitor to analyze the aerosol samples collected in five stages by a Sioutas cascade impactor (SCI), which collects size-segregated airborne particles having aerodynamic diameters from 6.6 μm to less than 0.25 μm. As MWCNTs aggregate/agglomerate easily, the size was of a good parameter to distinguish the MWCNTs from other materials. Two-dimensional mapping by size and oxidized temperature suggested the origin of the carbonaceous aerosol samples. Based on the results, we reanalyzed our previous data obtained at a factory manufacturing MWCNTs. The characteristics of workplace samples by particle size and carbon analysis were similar to those of MWCNT aerosol particles.