Effect of different microwave-based treatments on multi-walled carbon nanotubes

Three new methods for the functionalization of multi-walled carbon nanotubes (MWCNTs) are reported using microwave (MW) energy and water as a mild chemical agent. In the first method we reported the effect of MW irradiation on a dispersion of MWCNTs in deionized water, in the second method we studied the exposing of MWCNT to microwave irradiation in the presence of steam, and in the third method we used microwave oven-generated plasma for the functionalization of MWCNTs. We also performed thermal oxidation and acid treatment as two conventional methods for oxidative functionalization of carbon nanotubes, to compare their effect with our results. Transmission electron microscopy (TEM) and Raman spectroscopy results showed that although these microwave methods introduced some defects to the carbon nanotubes, the damage was less severe than conventional treatments. X-ray photoelectron spectroscopy (XPS) measurements confirmed that the functionalization of carbon nanotubes by these methods favored hydroxyl groups, which are useful when further functionalization is required.     

Deposition of silver nanoparticles on carbon nanotube by chemical reduction method: Evaluation of surface,thermal and optical properties

Silver was stabilized on multi-walled carbon nanotubes (MWCNTs) by chemical-reduction technique using N,N-dimethylformamide (DMF) as a reducing agent. The influence of silver on the performance of carbon nanotubes (CNTs) was investigated by employing Fourier-transform infrared spectra (FTIR), Raman spectroscopy (RAS), thermal gravimetric analysis (TGA), zeta potential measurement, scanning electron microscope (SEM), electron dispersive X-ray spectrometer (EDX), transmission electron microscopy (TEM), and reflectance spectroscopy (RS). FTIR as well as RS methods evidenced the synthesis procedure using chemical reduction method was successful. Performing TGA of the samples under oxygen atmosphere demonstrated that the silver nanoparticles (Ag NPs) generated on MWCNTs surface can decrease the thermal stability of the particles by the catalytic oxidation of CNTs. In contrary, the thermal stability of the MWCNTs has improved under nitrogen atmosphere. EDX results showed the presence of Ag, Au and Co on the surface of deposited sample. The synthesised silver multi-walled carbon nanotubes (Ag–MWCNTs) were found to have higher UV reflection activity compared with untreated particles. The Ag–CNTs can be used in producing anti-UV composites.     

Effect of carbon nanotubes dispersion on morphology, internal structure and thermal stability of electrospun poly(vinyl alcohol)/carbon nanotubes nanofibers

The current work reports the effect of multi walled carbon nanotubes and single walled carbon nanotubes dispersion on morphological, structural and thermal degradation of electrospun poly(vinyl alcohol) (PVA)/carbon nanotubes (CNTs) dispersed in sodium dodecyl sulfate (SDS) (PVA/CNTs–SDS) composites nanofibers. (PVA/CNTs–SDS) nanocomposites fibers were elaborated using the traditional electrospinning process to disperse and align CNTs into the fibers, especially for low CNTs loading fraction: 0.3 and 0.7 wt%. The morphology of the electrospun fibers was studied using the scanning electronic microscopy. The average diameter of the fibers changes significantly after the incorporation of the CNTs in the PVA. Furthermore, Fourier transform infrared spectroscopy elucidated the effect of CNTs on the crystallization of the PVA which was confirmed by X-ray diffraction analysis. Thermogravimetric analysis showed that the thermal stability of the composite fibers depends on the loading fraction and on the type of carbon nanotubes.     

Loading carbon nanotubes with viscous fluids and nanoparticles – a simpler approach

Carbon nanotubes have demonstrated exceptional properties enabling them to be considered for applications in drug delivery and other biologically important fields. The emphasis of the current drug delivery research with carbon nanotubes focuses on surface functionalization of the nanotubes and attachment of biomolecules, while leaving the inner void unmodified and mostly empty. Here, we report a simple, cost effective, and scalable method for filling and sealing carbon nanotubes with viscous solutions of biomaterials and nanoparticles (10 to 100 nm). The loading of nanotubes was achieved by optimal centrifugation in the presence of the viscous solution containing nanoparticles. This novel method was found to be effective for loading nanoparticles from 10 nm up to 40 nm in diameter, while increased sedimentation of particles larger than 40 nm resulted in reduced loading efficiency. Scanning electron microscopy and confocal laser scanning microscopy were used to analyze to confirm and image the loading of carbon nanotubes. This method could have immediate exciting applications in drug delivery especially for subcutaneous and slow release formulations. PACS 61.46.Df; 61.46.Fg; 83.50.Uv; 47.61.Jd     

Influence of the electronic distribution of polymers in the spatial conformation of polymer grafted carbon nanotube composites

In this work we report the covalent functionalization of multiwalled carbon nanotubes (MWCNTs) with polyacrylonitrile (PAN) and polyvinylpyridine (PVP) by the graft from method. Differences in the electronic distribution of both polymers resulted in different interaction between polymers and the nanotubes. It was found that PVP chains wrapped the nanotubes while nanotubes functionalized with PAN presented PAN chains forming amorphous entanglements on the nanoscale linked to the MWCNTs. Differences in the conformation between both polymers and the MWCNTs can be attributed to interactions between the aromatic groups in PVP and the MWCNTs through π–π stacking. The absence of aromatic groups in the case of the PAN chains favours the interaction between them. The functionalization efficiency was characterized using Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and UV–vis spectroscopy, while morphological changes were characterized by high resolution transmission electron microscopy.     

An efficient route towards the covalent functionalization of single walled carbon nanotubes

A simple and efficient method of chemical functionalization of both single and multiwalled carbon nanotubes has been discussed to give enhanced water solubility by rapidly and efficiently generating an appreciable amount of hydrophilic functional groups using microwave radiation. Surface functionalization containing more than 30 wt% of oxygen has been achieved, resulting into solubility of 2–5 mg/mL. Further covalent functionalization of such soluble SWNTs provides a remarkable degree of aniline functionalization through amidation, where the formation of polyaniline has been avoided. Functionalization of SWNTs is confirmed by techniques like electron microscopy, Fourier transform infrared spectroscopy, thermogravimetry, Raman spectroscopy, cyclic voltammetry and impedance spectroscopy. Electrochemical analysis suggests an enhanced double layer capacitance (110 F/g) of nanotubes after microwave treatment. Aniline functionalization of SWNTs shows possible variations on the nanotube topography with concomitant formation of a dynamic polymer layer on the nanotube surface.     

碳纳米管的表面修饰及FTIR,Raman和XPS光谱表征

用红外、拉曼光谱、X射线光电子能谱（XPS）研究了水热条件下碳纳米管在不同氧化剂中的表面修饰过程。结果表明水热条件下可以成功地实现碳纳米管的表面修饰,而且,通过控制反应条件可以改变反应产物中官能团的种类和数量。     

Surface chemical functionalized single-walled carbon nanotube with anchored phenol structures: Physical and chemical characterization

Surface functionalization of single-walled carbon nanotube was carried out by introducing ylides groups containing anchored phenol structures. The functionalized nanotube is characterized using elemental analysis, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis, Raman spectroscopy and zeta potential measurements. Elemental and FT-IR analysis reveal the successful functionalization of azomethine ylides. Raman spectroscopic studies corroborates that the surface functionalization does not affect the basic crystal domain size of the nanotubes. Functionalized carbon nanotubes exhibit higher zeta potential values showing its higher dispersant ability in water and acetone solvent in comparison to pure carbon nanotube.     

One-pot, efficient functionalization of multi-walled carbon nanotubes with diamines by microwave method

Diamines are known to act as a medium to bind miscellaneous compounds to carbon nanotubes (CNT). However, they are commonly applied in a tedious manner. Here, multi-walled carbon nanotubes (MWCNTs) were functionalized by a series of diamine molecules (ethylenediamine, 1,6-hexamethylenediamine and 1,4-diaminobenzen) in a one-pot, rapid microwave-assisted method. Surface functionality groups and morphology of MWCNTs were analyzed by infrared spectroscopy, thermogravimetric analysis, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. The results consistently confirmed the formation of diamines functionalities on MWCNTs, while the structure of MWCNT has remained relatively intact. This simple and efficient process may play an important role for realizing miscellaneous functionalization of CNTs.     

Thermal treatment of the carbon nanotubes and their functionalization with styrene

In this work we studied the functionalization of commercially available multiwalled carbon nanotubes (MWCNT) (Nanocyl 3100) with polystyrene by the method so called “grafting from”. The nanotubes were used as received and oxidized in air at 400 °C. The functionalization was started using thionyl chloride under reflux, followed by a reaction with ethylene glycol which allowed the inclusion of hydroxyl groups. The reaction of those with 2-chloropropionyl chloride led to the generation of the polymerization initiator. Last, the radical polymerization of the functionalized nanotubes, using styrene as the monomer, led to new materials which were studied with thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM) and ultraviolet–visible (UV–vis) spectroscopy.     

Effect of PVA functionalization on hydrophilicity of Y-junction single wall carbon nanotubes

Hydrophilic surface of carbon nanotubes (CNTs) are of great interest for various applications including chemical and biological sensing. Surface functionalization of single wall carbon nanotubes (SWNTs) mats with a biocompatible polymer polyvinyl alcohol (PVA) was studied. PVA modification induced a drastic change in water wettability of the SWNT surface transforming it from hydrophobic to highly hydrophilic. These PVA modified SWNTs mats have also demonstrated increasing impedance variation in relative humidity compared to the pristine nanotubes. An appreciable change in conductivity of Y-junction SWNT mats as a function of relative humidity indicates its potential application as humidity sensor. This higher sensitivity for humidity variation shown in Y-junction SWNT mats could be attributed to the greater portion of semiconducting nanotubes in these mats revealed by Raman analysis. A possible conductance changing mechanism of surface modified SWNTs mats is discussed.     

Study the effect of acetic acid on structural,optical and mechanical properties of PVA/chitosan/MWCNT films

Polyvinyl alcohol (PVA)/chitosan/multiwalled carbon nanotube (MWCNT) films were successfully prepared by using solution-casting method. Structural properties were studied using Fourier transform infrared (FTIR) and X-ray diffraction (XRD) spectroscopies. The effect of acetic acid (AA) concentration on the films optical parameters was studied by using absorbance and transmittance data recorded during ultraviolet-visible (UV–Vis) spectroscopy. The results indicated that increasing the AA concentration in MWCNT-reinforced PVA films caused an increase in their optical capability. We also evaluated mechanical properties such as stress-strain behavior, Young's modulus, tensile strength, elongation at break, etc. Mechanical indices have been modified by introducing carbon nanotubes, even though enhancing the AA concentration meets significant restrictions on higher percentages of AA concentration, which needs to be delicately considered. The porous structure of the films, such as porous pattern, materials’ diameter, and shape was examined by field emission electron microscopy (FESEM). Engineering analyses showed that the films reinforced with MWCNTs exhibited an interconnected homogenous structure in various acid concentrations.     

Preparation and property of polyvinyl alcohol-based film embedded with gold nanoparticles

Gold nanoparticles were prepared by a simple heat-treated method using polyvinyl alcohol (PVA) as reducing and stabilizing agent in this article. UV/Vis spectroscopy was used to monitor the preparation. The formation of a sharp band at ~530 nm in the UV/Vis spectra and morphological characters revealed by transmission electron microscopy indicated the generation of Au nanoparticles. The PVA film embedded with Au nanoparticles was prepared by flow casting method and characterized by thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, Fourier transform infrared spectra, and X-ray photoelectron spectroscopy. The results showed that Au nanoparticles embedded in PVA film can improve the thermal stability of the film under investigation, leading to interesting technological applications.     

The use of calcination in exposing the entrapped Fe particles from multi-walled carbon nanotubes grown by chemical vapour deposition

Multi-walled carbon nanotubes (MWCNTs) were synthesized a by chemical vapour deposition method. The effect of calcination at temperatures ranging from 300 to 550°C in exposing the metal nanoparticles within the nanotube bundles was studied. The degree of degradation of the structural integrity of the MWCNTs during the thermal process was studied by Raman spectroscopy, X-ray diffraction analysis, field-emission scanning electron microscopy, and transmission electron microscopy. The thermal behaviour of the as-prepared and calcined samples was investigated by thermogravimetric analysis. Calcination in air, at 400°C for 1 h, was found to be an efficient and simple method to extract metallic impurities from the amorphous carbon shells with minimal damage to the tube walls and lengths. The nanotubes were observed to be damaged at temperatures higher than 450°C.     

Structural,thermal and optical behavior of laser irradiation-induced PVA–PEG–Ag nanocomposites

Polyvinyl alcohol?polyethylene glycol?silver (PVA–PEG–Ag) nanocomposites were prepared by adding Ag nanoparticles with 5?wt.% to the (PVA–PEG) blend. The films of 0.05?mm thickness were prepared by the casting method. Samples from these films were irradiated with infrared (IR) laser fluences ranging from 1.7 to 15?J/cm². The effect of IR laser radiation on the structural properties of PVA–PEG–Ag has been investigated using X-ray diffraction and Fourier transform infrared spectroscopy. The results indicate that the crosslinking dominates due to laser exposure at the fluence range 1.7–15?J/cm², reducing the ordering character of the nanocomposite samples. Also, the variation of transition temperatures with the laser fluence has been determined using differential thermal analysis. The nanocomposite thermograms were characterized by the appearance of an endothermic peak due to melting, and were found to be dependent on the laser fluence. In addition, the color changes due to laser irradiation were computed using the transmission data. It is found that the color difference is largely dependent on the proportions of the red color component.     

Visible-light photocatalytic degradation of methylene blue with laser-induced Ag/ZnO nanoparticles

The preparation of Ag doped ZnO nanoparticles conducted through the method of laser-induction is presented in this work. The Ag/ZnO nanoparticles attained from various weight percentages of added AgNO₃ relative to ZnO were applied under visible-light irradiation for evaluating the heterogeneous photocatalytic degradations of methylene blue (MB) solutions. It was shown that the catalytic behavior of Ag/ZnO nanoparticles in the visible-light range is notably improved through the Ag deposition onto ZnO nanoparticles by the method of laser-induction with a maximum effectiveness of 92% degradation. The properties of the nanoparticles were characterized by the employments of UV-vis spectroscopy (UV-vis), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), and selected-area electron diffraction (SAED).     

Thermal and Tensile Properties of Epoxy Nanocomposites Reinforced by Silane-functionalized Multiwalled Carbon Nanotubes

Epoxy nanocomposites with unmodified multiwalled carbon nanotubes (u-MWCNTs) and silanized multiwalled carbon nanotubes (si-MWCNTs) were prepared by a cast molding method. The effects of 3-aminopropyltriethoxysilane functionalization of MWCNTs on thermal, tensile, and morphological properties of the nanocomposites were examined. The nanocomposites were characterized by thermogravimetric analysis, dynamic mechanical thermal analysis, and tensile testing. The results showed that epoxy composites based on si-MWCNTs showed better thermal stability, glass transition temperature, and tensile properties than the composites based on u-MWCNTs. These results prove the effect of silane functionalization on the interfacial adhesion between epoxy and MWCNTs. This was further confirmed by morphology study of fractured surfaces of nanocomposites by field emission scanning electron microscopy.     

Characterization of thiol-functionalized carbon nanotubes on gold surfaces

Multi-walled carbon nanotubes were functionalized with thiol groups by chemical route. Exploiting the chemical affinity between thiol and gold an assembly of carbon nanotubes was obtained by spontaneous chemical adsorption to gold using Au–S bonds. The multi-walled carbon nanotubes were first chemically cut by acid treatment and then functionalized with short chain thiol (2-aminoethanethiol). Substrate dipping in a suspension of functionalized carbon nanotubes allows them to bond to the gold surface. The resultant products, as well as the intermediate were characterized by means of X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, visible spectroscopy, scanning electron microscopy and atomic force microscopy.     

Microwave-assisted functionalization of single-walled carbon nanotubes with 3-chloropropene

We have reported a highly efficient approach to functionalize single-walled carbon nanotubes by electrophilic addition polymerization of 3-chloropropene under microwave irradiation. Using Lewis acids as catalysts, 3-chloropropene can undergo polymerization followed by hydrolysis with alkaline methanol, and thus the reaction results in the attachment of polymer chains and hydroxyl groups to the surface of the nanotubes. The resulting nanotubes were characterized with Fourier transform infrared spectroscopy, thermogravimetric analysis, Raman spectroscopy, high-resolution transmission electron microscopy, and atomic force microscopy. The result shows that 30 min of irradiation time is enough to bring the reaction to the end and a longer time did not improve the degree of functionalization.     

Field emission characteristics study for ZnO/Ag and ZnO/CNTs composites produced by DC electrophoresis

A simple controllable method is reported for the coating of ZnO nanowires with Ag nanoparticles and ZnO/carbon nanotubes (CNTs) composite. It has been achieved through DC electrophoresis AgNO₃ electrolyte and CNTs in the presence of isopropanol dispersion of ZnO nanowires. In the present work, the influence of Ag nanoparticles and CNTs on the field emission properties of the composite materials is studied. The results of this research demonstrate a remarkable enhancement of field emission current of ZnO nanowires in case of CNTs mixture and Ag nanoparticles coating.