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.     

Electrochemical biosensor based on multi-walled carbon nanotubes and Au nanoparticles synthesized in chitosan

A new biosensor is prepared by cross-linking glucose oxidase (GOD) with glutaradehyde at the electrode combining Au nanoparticles (AuNP) with multi-walled carbon nanotubes (MWCNTs). Au nanoparticles-doped chitosan (CS) solution (AuNP-CS) is prepared by treating the CS solution followed by chemical reduction of Au (III) with NaBH4. MWCNTs are then dispersed in AuNP-CS solution. TEM, FT-IR, and UV-Vis show that the AuNP-CS solution is highly dispersed and stable. The synergistic effect between AuNP and CNTs of the AuNP-CNTs-CS material has been investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and amperometric methods. The modified glassy carbon electrode (GCE) allows low-potential detection of H2O2 with high sensitivity and fast response time. With the immobilization of GOD, a biosensor has been constructed. In phosphate buffer solutions (PBS, pH 7.0), nearly free interference determination of glucose has been realized at 0.4 V(vs. Ag/AgCl/3.0 M KCI) with a wide linear range from 2.0 x 10(-5) to 1.5 x 10(-2) M and a fast response time within 5s. The biosensor has been used to determine glucose in human serum samples and the results are satisfactory.     

The poly(urethane-ionic liquid)/multi-walled carbon nanotubes composites

In the paper, a novel kind of imidazolium based poly(urethane-ionic liquid)/multi-walled carbon nanotubes (PUIL/MWCNT) composites was facilely prepared by uncovalent ways. The imidazolium based ionic liquid (IL) greatly improved the dispersion of pristine MWCNTs in PUIL by the π-cation interaction formed between the imidazolium cation and the π-electron of MWCNTs. The PUIL/MWCNT composites showed obviously increased modulus, glass transition temperature and tensile strength in comparison with PU/MWCNT composites. The thermal and mechanical properties of the PUIL/MWCNT composites presented significant increase with low load of the MWCNTs. It indicated the interactions between PUIL and MWCNTs played an important role to enhance the performances of the composites.     

Mechanical properties of porous Al2O3 composite with surface modified multi-walled carbon nanotubes (MWCNTs)

Multi-walled carbon nanotubes (MWCNTs) have been reinforced in alumina (Al2O3) matrix to overcome the inherent brittleness of the Al2O3 matrix. In this work, MWCNTs were treated by acid to provide hydrophilicity to hydrophobic MWCNTs, inducing the homogeneous dispersion of MWCNTs in an aqueous solution. Aluminum hydroxide (Al(OH)3) as a Al2O3 precursor was added in the solution with the modified MWCNTs, and then this mixture solution was filtered at room temperature. The prepared powders were calcinated at 800-1000 degrees C to reduce the gas pocket in the matrix by decomposition of Al(OH)3. Then the calcinated powders were formed, and heat-treated. The porous MWCNTs-Al2O3 composites show higher mechanical properties in flexure strength and hardness than the porous Al2O3 without the reinforcement phase, which is attributed to the high mechanical properties of MWCNTs. However, higher MWCNTs contents in the composites decrease the mechanical properties due to the aggregation of MWCNTs in the composites. Therefore, control of the MWCNTs content and its dispersibility in the matrix are key factors to be considered for the fabrication of the porous MWCNT-Al2O3 composites.     

Biomimetic mineralization of electrospun poly(lactic-co-glycolic acid)/multi-walled carbon nanotubes composite scaffolds in vitro

Biomimetic mineralization is an effective method to improve the biocompatibility and bone inductivity of certain materials. In this study, composite scaffolds composed of poly(lactic-co-glycolic acid) (PLGA) and multi-walled carbon nanotubes (MWNTs) were prepared by electrospinning. Subsequently, the scaffolds were immersed in a simulated body fluid (1.5 × SBF) at 37 °C for 7, 14 and 21 days for biomimetic mineralization. Scanning electron microscopy, Raman spectroscopy, and X-ray diffraction were used for characterization. It was found that the electrospun scaffolds had extremely resemblant structural morphology to the natural extracellular matrix. After mineralization, apatite crystals were deposited on the PLGA/MWNTs composite scaffolds. The mineralized PLGA/MWNTs composites may be potentially useful in tissue engineering applications, particularly as scaffolds for bone tissue regeneration.     

Study on morphology and characterization of poly(mphenylene isophtalamide)/multi-walled carbon nanotubes composite nanofibers by electrospinning

Electrospinning technique is the main method of preparing polymer nanofiber simply, directly and continuously at present. In this work, electrospinning blend solution was prepared by in-situ polymerization using acid-modified multi-walled carbon nanotubes (MWNTs), m-phenylenediamine (MPD) and isophthaloyl chloride (IPC). And then composite nanofibers were prepared by electrospinning. MWNTs played an important role in nanofiber's properties. The effects of MWNTs on the morphology and characterization of the MWNTs/PMIA composite nanofibers were investigated. Scanning electron microscopy (SEM), thermal gravimetric analyzer (TGA), and X-ray diffraction (XRD) were utilized to characterize the MWNTs/PMIA nanofibers morphology and properties. The experimental results indicated that the nanofibers diameter decreased and solution dynamic viscosity increased with increasing MWNTs contents. XRD data demonstrated that PMIA composite nanofibers had the same crystal type as the pure PMIA nanofiber, and crystallinity was improved with increasing MWNTs loading. Transmission electron microscopy (TEM) was used to confirm MWNTs aligned along the axis of composite nanofibers.     

磺化聚醚醚酮/多壁碳纳米管复合质子交换膜的制备与性能

合成了表面接枝磺酸基团的改性多壁碳纳米管(S-MWNTs),通过溶液共混法制备了用于直接甲醇燃料电池的磺化聚醚醚酮(SPEEK)/S-MWNTs复合膜.扫描电镜显示,SMWNTs在掺杂量比较少时,能够在SPEEK基体中均匀分散;热重分析证明,复合膜具有优异的热稳定性.当掺杂量为1%时,复合膜的机械性能,尺寸稳定性及电导率均提高,这有效解决了纯SPEEK膜中质子电导率与机械性能、尺寸稳定性等相矛盾的问题.     

Novel fabrication of silica nanotubes using multi-walled carbon nanotubes as template

Silica nanotubes were synthesized using multi-walled carbon nanotubes (MWCNTs) as template. The as-obtained samples were characterized by infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscope (FE-SEM) and photoluminescent (PL) spectroscopy. The results indicate that the thickness of the outer walls is about 10 nm and the inner diameter is completely dependent on the size of MWCNTs. The as-fabricated silica nanotubes emit a strong violet light under excitation of 250 nm.     

碳纳米管的表面修饰对Co-Mo催化剂HDS性能影响的研究

采用程序升温脱附(TPD)、Boehm滴定以及质量滴定(Masstitration)等方法分析了多壁碳纳米管(MWCNT)经过浓硝酸改性处理前后的表面酸性和酸性分布;同时运用XRD技术研究了碳纳米管负载Co Mo催化剂的表面物种和活性组分的分散;并在高压微型反应器中,以二苯并噻吩(DBT)为模型化合物,对碳纳米管负载的Co Mo催化剂体系进行了加氢脱硫(HDS)活性评价,以期揭示碳纳米管的表面修饰对其负载Co Mo催化剂HDS性能的影响。研究结果表明:MWCNT表面呈一定的碱性,通过浓硝酸化学修饰以后,反而呈现较强的酸性,并且随着酸处理时间的延长,表面的酸性进一步增加。如,M MWCNT 6(酸化6h)表面总酸量为1.29×10-3mol/g,M MWCNT 24(酸化24h)表面总酸量为2.46×10-3mol/g。酸改性提高了Co Mo催化剂在MWCNT表面的分散程度,以致Co Mo/MWCNT催化剂的HDS活性和选择性明显高于Co Mo/γ Al2O3催化体系。然而,Co Mo/M MWC NT 6的HDS活性以及选择性与Co Mo/MWCNT相差不多,略有降低,但是仍比Co Mo/γ Al2O3催化体系的HDS活性高。Co Mo/M MWCNT 24催化剂的HDS活性降低很多,并且催化性能发生了很大改变,产物中出现了大量的副产物1,2 二苯基乙烷。表明,深度酸化改性反而不利于提高碳纳米管负载Co Mo催化体系的HDS活性。     

Determination of Pb2+ ions by a modified carbon paste electrode based on multi-walled carbon nanotubes (MWCNTs) and nanosilica

A novel carbon paste ion selective electrode for determination of trace amount of lead was prepared. Multi-walled carbon nanotubes (MWCNTs) and nanosilica were used for improvement of a lead carbon paste sensor response. MWCNTs have a good conductivity which helps the transduction of the signal in carbon paste electrode. The electrode composition of 20 wt% paraffin oil, 57% graphite powder, 15% ionophore (thiram), 5% MWCNTs, and 3% nanosilica showed the stable potential response to Pb²⁺ ions with the Nernstian slope of 29.8 (±0.2) mV decade^?1 over a wide linear concentration range of 10^?7–10^?2 mol L^?1. The electrode has fast response time, and long term stability (more than 2 months). The proposed electrode was used to determine the concentration of lead ions in waste water and black tea samples.     

Determination of Cu2+ using poly(2-aminothiazole)/ multi-walled carbon nanotubes composite film modified glassy carbon electrodes

2-Aminothiazole was electropolymerized by cyclic voltammetry (CV) on the multi-walled carbon nanotubes (MWCNTs) modified glassy carbon electrode (GCE) surface. Poly(2-aminothiazole)/MWCNTs/GCE was used for determination of copper ions. The anodic peak currents of copper ions evaluated by differential pulse stripping voltammetry (DPSV) are linear with the concentrations in the range from 1.0 x 10(-7) M to 2.0 x 10(-5) M with a linear coefficiency of 0.9985. The detection limit is 2.0 x 10(-9) M calculated for a signal-to-noise ratio of 3 (S/N = 3). The proposed method was applied successfully to the determination of copper ions in drinking water, and the recovery was 96%.     

Crystallization behavior of poly (vinylidene fluoride)/multi-walled carbon nanotubes nanocomposites

The non-isothermal and isothermal crystallization of poly (vinylidene fluoride) (PVDF)/multiple-walled carbon nanotubes (MWNTs) composites containing pristine (MWNT1) and carboxyl group (–COOH) functionalized MWNT (MWNT2) were investigated. The effects of MWNT on the crystallization behavior of PVDF were dependent on the dispersion state of MWNT. Pristine MWNT could increase the nucleation due to better dispersion, and thus, PVDF/MWNT1 composites exhibited higher crystallization peak temperatures (T _cps) and crystallinities (X _cs) compared with PVDF/MWNT2 composites. Meanwhile, the formation of MWNT network confined the growth of crystals. For the isothermal crystallization, MWNT acted as nucleating agents, and the crystallization rate constant k was increased with the addition of MWNT. Besides, the half crystallization time, t _0.5, was remarkably shortened with the increase of MWNT content, especially for the pristine MWNT.     

Photoactive multi-walled carbon nanotubes: synthesis and utilization of benzoin functional MWCNTs

This study describes a facile method for the synthesis of functionalized multi-walled carbon nanotubes (MWCNTs) carrying photoactive group. The synthesis of MWCNTs-based macro-photoinitiator was achieved by the esterification reaction between benzoin moiety and acyl chloride functional MWCNTs. Synthesized MWCNT-based photoinitiator (MWCNTs–benzoin) was used in the photopolymerization of styrene to yield polystyrene (PS)-grafted MWCNTs (MWCNTs–PS) by “grafting from” method. The efficiency of MWCNTs–benzoin photoinitiator was determined by evaluating the effect of initiator to monomer ratio and reaction period on photopolymerization of styrene. Fourier transform infrared spectroscopy, Raman and X-ray photoelectron spectroscopy analyses confirmed the covalent bonding for functionalization of MWCNTs and determined the final structures. Thermogravimetric analysis, gel permeation chromatography and UV spectroscopy were performed to evaluate the grafting efficiency of PS that covalently grafted to MWCNTs, and high efficiency of MWCNTs–benzoin as a macro-photoinitiator was also confirmed. Scanning electron microscopy was used to determine the surface morphology of functionalized MWCNTs and MWCNTs–PS.     

Synthesis of composite material of cobalt oxide (Co3O4) with hydroxide functionalized multi-walled carbon nanotubes (MWCNTs) for electrochemical determination of uric acid

The gout is mainly found due to accumulation of uric acid crystals into the joints which produces the inflammatory symptoms. Thus, it is highly demanded to detect uric acid from our body. Herein, we prepare a composite material of cobalt oxide (Co₃O₄) with hydroxide functionalized multi-walled carbon nanotubes (MWCNTs) by hydrothermal method. The composite material is used for the modification of glassy carbon electrode (GCE) and investigated for the electrochemical determination of uric acid (UA). The analytical techniques such as scanning electron microscopy (SEM), powder X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and Fourier Infra-red spectroscopy (FTIR) are used to characterize the composite material. The Co₃O₄ exhibits a dendrite morphology and very well chemically coupled with MWCNTs. The elemental analysis confirms the presence of cobalt (Co), oxygen (O) and carbon (C) as main constituent of the composite material. The Co₃O₄ exhibitsa cubic unit cell crystallography in the composite system. The FTIR study reveals the characteristic bands of Co–O bands in the composite material. The cyclic voltammetry isused to study the electrochemical properties of prepared materials. The composite sample with highest percentage of MWCNTs shows an excellent electrochemical activity towards the oxidation of uric acid in phosphate buffer solution pH 7.3. The enzyme free uric acid sensor possesses a linear range of 0.1 mM to 3 mM with a quantified limit of detection of 0.005?±?0.0023 mM. The modified electrode is stable, selective, and very sensitive towards uric acid, therefore it may be used for the monitoring of uric acid from clinical samples. The proposed composite material can be of great interest for energy and biomedical fields.

     

基于溶胶-凝胶技术结合多壁纳米碳管化学修饰电极的方法制备高灵敏葡萄糖生物传感器的研究

基于多壁纳米碳管修饰铂电极与二氧化硅溶胶-凝胶(sol-gel)固定化酶相结合的技术制备了葡萄糖氧化酶传感器,充分利用了溶胶-凝胶固定化酶稳定的优点和纳米碳管的高灵敏电催化作用,优化了该酶传感器的制备过程,提高了传感器的电流响应和反应线性.结果表明,sol-gel构建的优化条件是:H2O:TEOS为2.5～3.5,TritonX-100浓度为5%,pH值为5.5.在本实验条件下,多壁纳米碳管的最适固定量为5μl(0.25g/L),溶胶-凝胶与酶的优化体积比为3:2.工作电位 0.55V、pH 6.5、25℃为制备传感器的最适工作条件.该传感器对葡萄糖在0.5～6 mmol/L呈线性响应,响应时间为20 s,检出限为0.05mmol/L,45天时的响应值仍保持90%.     

Studies on preparation and properties of the multi-walled carbon nanotubes (MWNTs)/epoxy nanocomposites

The MWNTs were coated with polyaniline (PANI) by in situ chemical oxidation polymerization method. FTIR spectroscopy, scanning electron microscope (SEM) and X-ray diffraction (XRD) indicated that the MWNTs were coated with PANI. The MWNTs/epoxy nanocomposites were fabricated by using the solution blending method. Differential scanning calorimetry (DSC), tensile testing, HP 4294A impedance analyzer and SEM were used to investigate the properties of the nanocomposites. The results showed that the modified carbon nanotubes were well dispersed in the polymer matrix. The nanocomposites have enhancements in mechanical, thermal and dielectric properties compare with the neat epoxy resin. The nanocomposites were proven to be a good polymer dielectric material.     

Dispersion characteristics and properties of poly(methyl methacrylate)/multi-walled carbon nanotubes nanocomposites

The preparation, characterization, and properties of poly(methyl methacrylate) (PMMA)/multi-walled carbon nanotubes (MWCNTs) nanocomposites are described. Nanocomposites have been prepared by melt-blending in a batch mixer. Both unmodified and surface modified MWCNTs have been used for the nanocomposites preparation. Using both unmodified and modified MWCNTs, the effect of surface modification in nanocomposites is investigated by focusing on three major aspects: dispersion characteristics, mechanical properties, and electrical conductivity measurements. Dispersion of the MWCNTs in the PMMA matrix is examined by scanning and transmission electron microscopy that revealed a homogeneous distribution-dispersion of MWCNTs in the PMMA matrix for both unmodified and modified MWCNTs. Thermomechanical behavior is studied by dynamic mechanical analyzer and results showed a substantial improvement in the mechanical properties of PMMA in conjunction to an increase in the elastic behavior. The tensile properties of neat PMMA moderately improved after nanocomposites preparation with both modified and unmodified MWCNTs, however, electrical conductivity of neat PMMA significantly improved after nanocomposites preparation with 2 wt% unmodified MWCNTs. For example, the through plane conductivity increased from 3.6 x 10(-12) S x cm(-1) for neat PMMA to 3.6 x 10(-9) S x cm(-1) for nanocomposite. The various property measurements have been conducted and results have shown that, in overall, surface modifications have very little or no effect on final properties of neat PMMA.     

Fabrication of novel sol-gel silica coatings reinforced with multi-walled carbon nanotubes

Novel sol-gel silica coatings reinforced with multi-walled carbon nanotubes (MWCNTs) have been prepared using the organic sol-gel route and the dip-coating technique on magnesium alloy substrates. Homogeneous and dense composite coatings with good reinforcement dispersion were fabricated using low temperature and atmospheric pressure fabrication conditions. The presence of nanotubes caused a substantial enhancement of silica coating fracture toughness on coatings deposited on grounded substrates but it was not as effective on polished substrates because of the low adhesion of the coating to the substrate. Bridging phenomena caused by the MWCNTs was observed, indicating that an effective load transfer between the silica matrix and the nanotube reinforcement was also achieved.     

Capillary effect of multi-walled carbon nanotubes suspension in composite processing

Carbon nanotubes (CNTs) do have the potential to improve the interlaminar shear strength (ILSS) of composites if they can be successfully integrated into the matrix as it infuses into the fiber preform. The infusion under capillary action of Multi-Walled Carbon Nanotubes (MWNT)/Epoxy suspension with tubes of length 0.3 approximately 1 microm in glass fiber bundles containing pores of the order of 5 nm approximately100 microm was investigated. The influence of parameters such as suspension concentration, viscosity, porous media architecture, surface tension and contact angle were explored. It was found that filtering of the suspension is a major challenge for uniform infusion for concentrations beyond 0.5% MWNT by weight. This is even truer for fiber bundles that are compacted. Hence for successful manufacturing, new infusion techniques that rely on fabrics of high permeability will have to be developed to fabricate such nanocomposites.