Diameter controlled growth of single-walled carbon nanotubes from SiO2 nanoparticles

A rational approach is reported for the growth of single-walled carbon nanotubes (SWCNTs) with controlled diameters using SiO₂ nanoparticles in a chemical vapor deposition system. The SiO₂ nanoparticles with different sizes were prepared by thermal oxidation of 3-aminopropyltriethoxysilane (APTES) with different number of layers which were assembled on Si substrates. It was found that the size of SiO₂ nanoparticles increased with the number of assembled APTES layers. Using these SiO₂ nanoparticles as nucleation centers, the diameter distribution of as-grown SWCNTs were correlated with the size of SiO₂ particles. In addition, both the classical longitudinal optical or transverse optical bands of SiC in in situ Raman spectra during the whole growth process and the Si 2p peak of SiC in the X-ray photoelectron spectra were not observed, suggesting that the carbon sources did not react with the SiO₂ nanoparticles during the growth. Comparing to vapor–liquid–solid mechanism for metallic catalysts, vapor–solid mechanism is proposed which results in a lower growth rate when using SiO₂ nanoparticles as nucleation centers.     

荧光胺定量检测纳米SiO2表面氨基的含量

首先用3-氨丙基三乙氧基硅烷偶联剂(APTES)在一定条件下接枝于纳米二氧化硅表面,并采用傅里叶变换红外光谱仪(FI-IR)进行测试表征,建立了一种用荧光胺定量检测功能化纳米SiO2表面氨基的方法,并通过优化实验建立该检测方法的测试标准.最佳检测条件为:室温下,激发波长380 nm、发射波长480 nm,荧光胺的丙酮溶液与磷酸盐缓冲液体积比1:5,磷酸盐缓冲液pH值为10.0,反应时间为10 min等条件下,荧光信号最稳定.采用该最佳条件下制定的标准曲线对功能化纳米SiO2微球进行检测,结果符合预期,该方法检测灵敏度高、操作简单.     

An easy method for direct metal coordination reaction on unoxidized single-walled carbon nanotubes

The transition metal copper (II) ion (Cu²⁺) was effectively coordinated with a single-walled carbon nanotube (SWCNT) to produce a SWCNT–Cu²⁺ complex by a metal coordination reaction. Since the complex was very reactive towards the carboxylic acid group, the chemical functionalization of SWCNTs was easy to accomplish. This approach was used to functionalize the surface of the SWCNTs with stearic acid or ethylenediaminetetraacetic acid for tuning of the relative hydrophobicity and hydrophilicity of the surface, respectively. The mild reaction conditions used for metal coordination of the SWCNTs minimized the defects that result from chemical modification of SWCNT. Thus, the electrical properties of unmodified SWCNTs were preserved. Various analytical techniques, including Fourier transform infrared spectroscopy, thermal gravimetric analysis, ultraviolet–visible spectroscopy, and water sorption isotherm measurements, were used to characterize the surface properties of the functionalized SWCNTs. Functionalization of SWCNTs by metal coordination reaction effectively modified the SWCNT surface, while conserving the excellent physical properties of the SWCNTs. The surface properties of the SWCNTs were easily tuned by introduction of the functional groups required for specific applications.     

The influence of single-walled carbon nanotube functionalization on the electronic properties of their polyaniline composites

The “in situ” preparation and characterization of composites of polyaniline (PANI) and single-walled carbon nanotubes (SWCNTs) are reported. To improve the dispersion and compatibility with the polymer matrix the raw SWCNTs were modified following different routes. SWCNTs oxidized by chemical or thermal treatments (nitric acid and air oxidation, respectively) were subjected to covalent functionalization with octadecylamine (ODA). SWCNT/PANI composites were prepared either from just oxidized SWCNTs, or from ODA functionalized SWCNTs. Temperature-programmed desorption, elemental analyses, ultraviolet-visible (UV-vis), UV-vis with near infrared and Raman spectroscopy, X-ray diffraction, scanning and transmission electron microscopy and conductivity measurements were used to characterize the functionalized SWCNT materials, dispersions and composites. The PANI composite prepared from air oxidized SWCNTs showed the best electrical conductivity indicating a better interaction with polyaniline than ODA functionalised SWCNTs. The improvement of conductivity is attributed to the doping effect or charge transfer of quinoide rings from PANI to SWCNTs.     

Synthesis of high quality single-walled carbon nanotubes on natural sepiolite and their use for phenol absorption

Natural sepiolite mineral was used as a catalyst and catalyst support for the efficient growth of single-walled carbon nanotubes (SWCNTs). With the introduction of hydrogen, uniform active metal nanoparticles can be formed in the fibrous structure of sepiolite ore. High-quality SWCNTs with few defects and a large aspect ratio (over 10⁴) were synthesized. The structure of the CNTs was modified by controlling the catalyst composition with ion-exchange method and changing the growth conditions. The 1 wt.% Fe-based catalyst exhibited excellent activity for the growth of SWCNTs, while the Co/Mo-based catalyst preferred to grow small diameter SWCNTs. The reaction temperature showed a sensitive selectivity to the chirality and diameter distribution of the SWCNTs produced. Catalysts based on the sepiolite can also afford the effective growth of SWCNTs in a fluidized bed reactor. As-grown SWCNTs/calcined-sepiolite demonstrated excellent ability of phenol adsorption, with an adsorption capacity of 155.8 mg/g, which was much higher than that on natural sepiolite (12.7 mg/g).     

Layer-by-layer assembly of single-walled carbon nanotube-poly(viologen) derivative multilayers and their electrochemical properties

Layer-by-layer (LBL) multilayers of oxidized single-walled carbon nanotubes (SWCNTs) and poly(octylviologen) derivative (POV) have been assembled on gold electrode surfaces. The assembling process was characterized by quartz crystal microbalance (QCM) and electrochemical measurements. The average mass change was about 0.726 and 0.381 μg for each assembly of SWCNTs and POV, respectively. Cyclic voltammograms of the LBL multilayer modified electrodes showed well-reversible redox waves centered at about −640 mV vs Ag/AgCl, corresponding to the normal redox reaction of viologens. These LBL multilayers were very stable in the air and 1 mol/l KCl electrolyte solution. The results of QCM, cyclic voltammograms and chronocoulomograms of the multilayer modified Au electrodes indicated that the oxidized SWCNTs could not only support the formation of stable multilayers but also act as an electron mediator between viologens and electrodes.     

Effect of SWCNT dispersion on epoxy nanocomposite properties

In nanocomposites containing single wall carbon nanotubes (SWCNTs), the final properties strongly depend on the dispersion quality of these fillers. Various methods have been used to improve the dispersion of nanofillers; however, one of the most effective ways is to functionalize carbon nanotubes (CNTs) with covalent and noncovalent functional groups. In this work, the dispersion of SWCNTs in an epoxy system was studied by using surfactants, acid (COOH), and ester groups (PGE)‐modified CNTs. Rheological and scanning electron microscopy analysis showed that functionalization of CNTs helped in improving the dispersion of fillers in the epoxy matrix. Systems with surfactant modified SWCNTs (1 wt%) exhibited the highest storage modulus at low frequencies after 5‐min sonication. This behavior is associated to a stronger network of fillers as a result of a good dispersion. However, longer sonication times lowered the storage modulus, corresponding to a degradation of the tubes. The effect of the dispersion quality on mechanical properties was also studied using a three‐point bending set‐up. POLYM. COMPOS.,, 2012. © 2012 Society of Plastics Engineers     

氨基修饰复合型钠基吸收剂的脱碳特性

为弥补常规钠基吸收剂活性差、脱碳量低的不足,制备了多种表面氨基修饰的新型复合型钠基吸收剂并研究其脱碳特性。通过比较氨基流失率和实际脱碳量,选定二氧化硅的前驱物正硅酸乙酯为载体前驱物,以碳酸钠为活性成分,分别以3-氨基丙基三甲氧基硅烷(APS)、3-氨基丙基三乙氧基硅烷(APTES)、二乙烯三胺(DETA)、三乙烯四胺(TETA)为氨基前驱物,制备得到多种表面氨基修饰的复合型钠基吸收剂。探究各种吸收剂的孔隙结构与脱碳特性,结果表明,APS、APTES修饰后吸收剂孔隙特性较差,脱碳量较低,DETA、TETA修饰后吸收剂孔隙结构得到改善,脱碳量较高。     

Effect of functionalized SWCNTs on microstructure of PP‐g‐MA/OMMT/f‐SWCNTs nanocomposite

The aim of this work was to study the effect of functionalized single‐walled carbon nanotubes (f‐SWCNTs) on the microstructure of PP‐g‐MA/organic modified montmorillonite (OMMT)/f‐SWCNTs ternary nanocomposite. Pristine SWCNTs were chemically modified by maleic anhydride to improve the interaction between PP‐g‐MA and nanotubes. The dispersion states of OMMT in the different nanocomposites were investigated by wide angle X‐ray diffraction. The morphologies of the nanocomposites were characterized by scanning electron microscopy. Crystallization behaviors of nanocomposites were studied through differential scanning calorimetry and polarizing optical microscopy. Different than the PP‐g‐MA/OMMT binary nanocomposite, in which the OMMT is mainly in an exfoliated state, the ternary PP‐g‐MA/OMMT/f‐SWCNTs nanocomposite exhibits mostly intercalated OMMT. Furthermore, in the ternary nanocomposite, the crystallization of polymer is mainly induced by f‐SWCNTs rather than by OMMT. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation and characterisation of single-walled carbon nanotubes functionalised with amines

The amines octadecylamine, 2-aminoanthracene, 1-H,1-H-pentadecafluorooctylamine, 4-perfluorooctylaniline and 2,4-bis(perfluorooctyl)aniline, have been reacted with chemically modified single-walled carbon nanotubes (SWCNTs). The chemical modification consisted on a thermal treatment in air of arc discharge-grown SWCNTs with an optional purification with HNO₃. The selected amines have been allowed to interact with the obtained materials and with those resulting from an additional treatment with thionyl chloride. The resulting materials were characterised with different spectroscopic techniques such as X-ray photoelectron spectroscopy, attenuated total reflectance Fourier transform infrared spectroscopy, Raman spectroscopy, electron energy loss spectroscopy and fluorescence spectroscopy complemented with the thermogravimetric analysis and transmission electron microscopy. The chemically modified SWCNTs exhibit different solubility properties depending on the amines and the solvents used.     

Crystallization behavior and mechanical strength of poly(butylene succinate‐co‐ethylene glycol)‐based nanocomposites using functionalized multiwalled carbon nanotubes

Biodegradable poly(butylene succinate‐co‐ethylene glycol) (PBSG)/multiwalled carbon nanotube (MWCNT) nanocomposites were successfully prepared through physical blending and silication between PBSG and acyl aminopropyltriethoxysilane functionalized multiwalled carbon nanotube (MWCNT‐APTES). Nuclear magnetic resonance (NMR) spectra observations revealed that the PBSG chains were covalently attached to the MWCNT‐APTES by hydrolysis. PBSG/MWCNT‐APTES nanocomposites after hydrolysis showed excellent interfacial compatibility between PBSG and MWCNT‐APTES, which was helpful for the dispersion of MWCNT in the PBSG matrix. The incorporation of MWCNT‐APTES accelerated the crystallization of PBSG in the nanocomposites for both approaches of physical blending and hydrolysis due to the heterogeneous nucleation effect of MWCNT while the crystal structure of PBSG was remained. Furthermore, the crystallization rate of PBSG in PBSG/MWCNT‐APTES nanocomposites after hydrolysis was slower than that in the nanocomposite by physical blend. The tensile strength and modulus of the nanocomposites increased about 6% and 11% with the addition of only 1 wt% MWCNT‐APTES compared with that of neat PBSG, and was larger for the PBSG/MWCNT‐APTES nanocomposites after hydrolysis. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Novel organic–inorganic hybrid coatings prepared by the sol–gel process: corrosion and mechanical properties

(Hyperbranched polyurethane‐urea)/[(3‐aminopropyl)triethoxysilane]‐ZnO (HBPUU‐APTES‐ZnO) hybrid coatings were synthesized using an inexpensive mixing technique by varying the APTES‐modified ZnO concentration. The mechanical and surface properties of the hybrid coating films were studied and compared with unmodified and modified ZnO. The corrosion, solvent and abrasion resistance show significant enhancement in HBPUU‐APTES‐ZnO hybrids and their properties are increased with increasing APTES‐ZnO concentration. This hybrid coating has opened up an opportunity for automotive topcoat application. Copyright © 2012 Society of Chemical Industry     

Derivatization of SWCNTs with cobalt phthalocyanine residues and applications in screen printed electrodes for electrochemical detection of thiocholine

Single-walled carbon nanotubes (SWCNTs) derivatized with cobalt phthalocyanine (CoPh) were applied onto screen-printed graphite electrodes (SPEs) to be used for the low-potential electrochemical oxidation of thiocholine (TCh). Covalent attachment of CoPh to SWCNTs via stable sulfonamide bonds was confirmed by Raman/FT-IR spectroscopy and thermogravimetric analysis (TGA) coupled with FT-IR detection. The resulting modified SPE surfaces (CoPh-SWCNT-SPEs) were characterized by cyclic voltammetry and electrochemical impedance spectroscopy (EIS) with the redox probe [F₃(CN)₆]^3−/4−. Detection of TCh was accomplished using cyclic voltammetry and amperometry; a lower overpotential (100 mV vs. Ag/AgCl pseudoreference electrode) was obtained using CoPh-SWCNT-SPEs as compared to unmodified SPEs and SPEs modified with non-functionalized SWCNTs (SWCNT-SPEs). The linear range for TCh detection was 0.077–0.45 mM, with a sensitivity of 5.11 × 10⁻¹ μA mM⁻¹ and a limit of detection of 0.038 mM according to the 3 s/m definition.     

Modifying the electronic properties of single-walled carbon nanotubes using designed surfactant peptides

The electronic properties of carbon nanotubes can be altered significantly by modifying the nanotube surface. In this study, single-walled carbon nanotubes (SWCNTs) were functionalized noncovalently using designed surfactant peptides, and the resultant SWCNT electronic properties were investigated. These peptides have a common amino acid sequence of X(Valine)(5)(Lysine)(2), where X indicates an aromatic amino acid containing either an electron-donating or electron-withdrawing functional group (i.e. p-amino-phenylalanine or p-cyano-phenylalanine). Circular dichroism spectra showed that the surfactant peptides primarily have random coil structures in an aqueous medium, both alone and in the presence of SWCNTs, simplifying analysis of the peptide/SWCNT interaction. The ability of the surfactant peptides to disperse individual SWCNTs in solution was verified using atomic force microscopy and ultraviolet-visible-near-infrared spectroscopy. The electronic properties of the surfactant peptide/SWCNT composites were examined using the observed nanotube Raman tangential band shifts and the observed additional features near the Fermi level in the scanning tunneling spectroscopy dI/dV spectra. The results revealed that SWCNTs functionalized with surfactant peptides containing electron-donor or electron-acceptor functional groups showed n-doped or p-doped altered electronic properties, respectively. This work unveils a facile and versatile approach to modify the intrinsic electronic properties of SWCNTs using a simple peptide structure, which is easily adaptable to obtain peptide/SWCNT composites for the design of tunable nanoscale electronic devices.     

Enhanced field emission of an electric field assisted single-walled carbon nanotube assembly in colloid interstices

A novel method for fabrication of vertically aligned single-walled carbon nanotubes (SWCNTs) on indium-tin oxide glass substrates modified with self-assembly monolayer has been developed by using a supporting frame composed of a monolayer of monodispersed silica beads and an alternating current electric field. We have found that SWCNTs can be implanted into the interstices of the colloidal superlattices, which function as supporting scaffold to prevent the SWCNTs from falling down and maintain the SWCNTs at low density. As a result, this vertically aligned SWCNT assembly exhibits enhanced field emission.     

Modification of the wood-plastic composite for enhancement of formaldehyde clearance and the 3D printing application

As the formaldehyde is one of the main indoor pollutants, the purpose of this study is to effectively remove indoor formaldehyde pollution by using environmentally friendly 3D printing ornaments. The wood 3D printing filaments cellulose/polylactic acid composite (Cellu/P) was selected as the starting material, and 3-aminopropyltriethoxysilane (APTES) was used for chemical modification to obtain a series of cellulose composite materials with amino groups. The modified composite materials (APTES@Cellu/P) were characterized by Fourier transform infrared, X-ray diffraction, scanning electron microscope, energy dispersive spectroscopy, thermogravimetric analysis, and mechanical tests, and a formaldehyde removal experiment was performed. The feasibility of 3D printing was evaluated, and the process of 3D printing-functionalized customized ornaments was proposed, and then a school emblem was used for modeling, printing, and surface modification. Compared with the commercially traditional activated carbon, 3D printing-customized ornaments of APTES@Cellu/P material has a better formaldehyde removal effect, and can even avoid the secondary pollution that is common to the activated carbon.     

A method for the coating of silica spheres with an ultrathin layer of pristine single-walled carbon nanotubes

We describe a method to fabricate silica gel particles coated with a monolayer of pristine single-walled carbon nanotubes (SWCNTs). SWCNTs dissolved in 1-methyl-2-pyrrolidinone (NMP) are mixed with amino-functionalized silica gels having different diameters. Strong interaction between the amino group and the SWCNT surfaces induces the adsorption of the SWCNTs on the silica, while the stable solvation in NMP hampers further adsorption of the tubes. This approach enables the production of a homogeneous, nondestructive and high-yield coating of the SWCNTs onto the silica surfaces, especially for larger sphere with a diameter over 1 μm. The density and bundling degree of the SWCNTs on the silica gel surfaces are finely controlled by simply changing the ratios of the SWCNTs to the silica gels as well as the SWCNT concentrations. We also describe the coating of the silica gels with metallic SWCNTs. The SWCNT-coated silica gels are useful for a wide range of materials, such as the stationary phase for liquid chromatography and catalyst supporting materials.     

Grafting of 4-(2,4,6-Trimethylphenoxy)benzoyl onto Single-Walled Carbon Nanotubes in Poly(phosphoric acid) via Amide Function

Single-walled carbon nanotubes (SWCNTs), which were commercial grade containing 60–70 wt% impurity, were treated in a mild poly(phosphoric acid) (PPA). The purity of PPA treated SWCNTs was greatly improved with or without little damage to SWCNTs framework and stable crystalline carbon particles. An amide model compound, 4-(2,4,6-trimethylphenoxy)benzamide (TMPBA), was reacted with SWCNTs in PPA with additional phosphorous pentoxide as “direct” Friedel–Crafts acylation reaction to afford TMPBA functionalized SWCNTs. All evidences obtained from Fourier-transform infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, scanning electron microcopy, and transmission electron microscopy strongly supported that the functionalization of SWCNTs with benzamide was indeed feasible.     

Synthesis of single-walled carbon nanotube/metal nanoparticle hybrid materials from potassium-filled nanotubes

The reducing property of potassium-filled single-walled carbon nanotubes (SWCNTs) was used to synthesize single-walled carbon nanotube/metal nanoparticle hybrid materials. Electron transfer from potassium to SWCNTs gives rise to a substantial enhancement of the reducing ability of the carbon nanotubes. Metal ions with redox potentials lower than that of pristine SWCNTs can be reduced by potassium-filled SWCNTs. SWCNTs decorated with copper and zinc nanoparticles were synthesized through redox reactions between potassium-filled SWCNTs and metal ions. These redox reactions cannot take place if the potassium-filled SWCNTs have been exposed to air, because of oxidation of the carbon nanotubes which is shown by a shift of the G band frequency in Raman spectra.     

Studies of single-walled carbon nanotubes-induced hepatotoxicity by NMR-based metabonomics of rat blood plasma and liver extracts

The toxicological effects of single-walled carbon nanotubes (SWCNTs) were investigated after intratracheal instillation in male Wistar rats over a 15-day period using metabonomic analysis of ¹H (nuclear magnetic resonance) NMR spectra of blood plasma and liver tissue extracts. Concurrent liver histopathology examinations and plasma clinical chemistry analyses were also performed. Significant changes were observed in clinical chemistry features, including alkaline phosphatase, total protein, and total cholesterol, and in liver pathology, suggesting that SWCNTs clearly have hepatotoxicity in the rat. ¹H NMR spectra and pattern recognition analyses from nanomaterial-treated rats showed remarkable differences in the excretion of lactate, trimethylamine oxide, bilineurin, phosphocholine, amylaceum, and glycogen. Indications of amino acid metabolism impairment were supported by increased lactate concentrations and decreased alanine concentrations in plasma. The rise in plasma and liver tissue extract concentrations of choline and phosphocholine, together with decreased lipids and lipoproteins, after SWCNTs treatment indicated a disruption of membrane fluidity caused by lipid peroxidation. Energy, amino acid, and fat metabolism appeared to be affected by SWCNTs exposure. Clinical chemistry and metabonomic approaches clearly indicated liver injury, which might have been associated with an indirect mechanism involving nanomaterial-induced oxidative stress.