预阳极化超薄膜碳糊修饰镍铬合金电极测定尿酸

在0.2 mol/L的Na Cl溶液中对超薄膜碳糊修饰镍铬合金电极用循环伏安法进行预阳极化处理,所得电极对尿酸表现出较好的分离、富集和电催化氧化作用。结果显示,在最优的实验条件下,其氧化峰电流(Ip)与浓度在2.0×10-6mol/L~2.0×10-4mol/L内呈线性关系,检测限为1.1×10-8mol/L。此修饰电极制备简单,检测方便,可直接测定人体尿样中的尿酸含量。     

碳纳米管修饰阵列电极同时测定抗坏血酸和尿酸

本文建立了基于计时电流法的碳纳米管修饰阵列电极同时检测抗坏血酸和尿酸的方法。首先制作了由两个碳工作电极(1mm×2mm)、一个大面积碳对极(2mm×13mm)和一个厚膜Ag/AgCl参比电极构成的集成化碳阵列电极系统,然后以多壁碳纳米管修饰碳阵列电极,最后分别在CH1道电极电位为0.211V测定了抗坏血酸,在CH2道电极电位为0.428V测定了尿酸。实验结果表明,通过聚乙烯不干胶掩膜模板和手工丝网印刷碳技术制作的阵列电极电极面积一致,电活性好。CH1道氧化峰电流(I_(pCH1))与抗坏血酸浓度在4.0×10~(-6) mol/L～4.0×10~(-5)mol/L呈良好的线性关系,CH2道氧化峰电流(I_(pCH2))尿酸浓度在4.0×10~(-7) mol/L～4.0×10~(-6) mol/L呈良好的线性关系。本文设计的电极和建立的测定方法在多种生物样品的同时测定方面具有潜在的价值。     

多巴胺在石墨烯/多壁碳纳米管电极上的电化学行为

采用滴涂法在玻碳电极上修饰氧化石墨烯及多壁碳纳米管,通过电化学还原方法制备石墨烯/多壁碳纳米管复合材料及相应修饰电极(ERGO/MWCNTs/GCE)。运用循环伏安法研究多巴胺(DA)在修饰电极上的电化学行为。研究表明:与裸玻碳电极相比,多巴胺在修饰电极上氧化峰与还原峰电位差为70 m V,峰电流显著提高,表明该电极对多巴胺具有较好的催化氧化作用。高浓度抗坏血酸的存在不影响多巴胺的测定。在优化实验条件下,多巴胺在4.8×10~(-7)~1.1×10~(-5)mol/L和1.1×10~(-5)~2.93×10~(-4)mol/L范围内呈良好的线性关系,检出限为8.7×10~(-8)mol/L,RSD为4.3%。     

石墨烯修饰电极对去甲肾上腺素电分析性能的研究

制备了石墨烯修饰电极,研究了去甲肾上腺素(NE)在修饰电极上的电化学行为,实验结果表明,石墨烯修饰电极对去甲肾上腺素有明显的催化作用。在pH=5的柠檬酸-磷酸氢二钠的缓冲溶液中,NE的氧化峰电流与浓度在9.2×10-7～2.3×10-5mol/L范围内呈线性关系,检出限为4.6×10-8mol/L。修饰电极表现出良好的稳定性。     

Electrochemical determination of serotonin in oral fiquid of fructus hippophae

采用电化学沉积法制备咖啡酸膜修饰电极,研究了5-羟色胺(5-HT)在该修饰电极上的电化学行为.结果表明,高浓度的抗坏血酸(AA)和肾上腺素(EP)共存不干扰5-HT的检测,5-HT在0.41 V和-0.12 V出现一对灵敏的氧化还原峰,其氧化峰电流与浓度在2.0 ×10-6 ～6.0×10-5 mol/L范围内呈良好的线性关系,检测下限为8.0×10-7 mol/L.该修饰电极制备简单,可准确检测神兴沙棘欣之安口服液中5-HT的含量.     

银-亮氨酸复合膜修饰电极测定去甲肾上腺素

利用循环伏安法(CV)制备了银和亮氨酸聚合物膜修饰电极(Ag-Leu/GCE)。研究表明,电极对NE的电化学氧化具有明显的催化作用。氧化峰电流与去甲肾上腺素浓度在2.4×10-7~4.8×10-5mol/L范围内呈线性关系,检出限(3S/N)为1.2×10-8mol/L。修饰电极用于药物中去甲肾上腺素的测定,加标回收率在97.5%~101.3%之间。     

沙棘口服液中5-羟色胺的电化学检测

采用电化学沉积法制备咖啡酸膜修饰电极,研究了5-羟色胺(5-HT)在该修饰电极上的电化学行为。结果表明,高浓度的抗坏血酸(AA)和肾上腺素(EP)共存不干扰5-HT的检测,5-HT在0.41 V和-0.12 V出现一对灵敏的氧化还原峰,其氧化峰电流与浓度在2.0×10-6～6.0×10-5mol/L范围内呈良好的线性关系,检测下限为8.0×10-7mol/L。该修饰电极制备简单,可准确检测神兴沙棘欣之安口服液中5-HT的含量。     

利用聚罗丹明B薄膜修饰电极测定对乙酰氨基酚

利用循环伏安法(CV)将罗丹明B电聚合修饰于玻碳电极表面,制备出对对乙酰氨基酚(PRCT)具有良好电催化作用的聚罗丹明B薄膜修饰电极(PRhBE)。详细研究了PRhBE对PRCT电催化作用的最佳条件。结果表明,PRCT的浓度在3.31×10-7~6.62×10-5mol/L及7.94×10-4~3.31×10-2mol/L范围内与峰电流分段呈良好的线性关系;检测限可达1.65×10-7mol/L。相对标准偏差不大于1.5%,回收率在95.6%~105.4%之间,可用于实际样品中PRCT的定量分析。     

树枝状铜修饰电极同时测定酪氨酸和苏氨酸

采用电沉积的方法制备了树枝状铜修饰电极(Cu/Pt),研究了酪氨酸(Tyrosine)和苏氨酸(Threonine)在该修饰电极上的电化学行为。在0.05mol/L NaOH中,酪氨酸和苏氨酸分别在电位0.41V和0.62V处产生灵敏的氧化峰,表明树枝状铜修饰电极对二者的氧化反应具有良好的电催化活性。探讨了其作用机理,优化实验条件,建立了酪氨酸和苏氨酸的快速测定方法。在2.0×10-6 mol/L~5.0×10-3 mol/L范围内,酪氨酸和苏氨酸的氧化峰与浓度呈线性关系,二者的检出限均为6.0×10-7 mol/L。将本法用于氨基酸模拟样品的测定,回收率分别为96.0%~105.5%和96.3%~104.5%。     

纳米氧化亚铜修饰玻碳电极测定对硝基苯酚

采用恒电位沉积法制备了花状纳米氧化亚铜修饰玻碳电极,利用X射线衍射(XRD)、扫描电镜(SEM)对纳米氧化亚铜薄膜进行表征,探讨了花状氧化亚铜的形成机理,研究了修饰电极的电化学性能。在pH值为5.5,0.1mol/L HAc-NaAc溶液中,该修饰电极对对硝基苯酚(P-NP)的氧化还原表现出良好的电催化效果,通过测定P-NP的硝基还原峰电流,结合微分脉冲技术,建立了P-NP电化学快速检测方法。线性范围为6.6×10~(-7)~1.6×10~(-4) mol/L,检测限为2.1×10~(-7)mol/L,对模拟水样进行测定,回收率为98.8%~102.2%。     

Nanographite-reinforced carbon/carbon composites

Carbon/carbon composites (C/Cs) with nanographite platelets (NGP) filler in a matrix derived from phenolic resin were produced. Different weight concentration (0.5, 1.5, 3, 5 wt.%) NGP were introduced by spraying the NGP during the prepreg formation. The NGP-reinforced C/Cs were characterized for effect of NGP concentration on microstructure, porosity, interlaminar shear strength (ILSS), flexural, ultrasonic and vibration damping behavior. At 1.5 wt.% NGP C/C, the highest values of ILSS observed was 10.5 MPa (increased by 22%), flexure strength of 142.4 MPa (increased by 27%), flexural modulus of 59.2 GPa (increased by 68%) and porosity of 18.8% (reduced by 17.5%) in comparison to neat (without NGP) densified C/C. Ultrasonic testing revealed an average increase of 15% through the thickness Young’s modulus of NGP-C/C; (3.12 GPa at 1.5 wt.% NGP). A 20% average decrease in the damping ratio of the first four modes of vibration was observed in 1.5 wt.% NGP densified C/C. At low concentration (⩽1.5 wt.%) the NGP filled in the pores, cracks and debonded interface but at concentration higher than 1.5 wt.% NGP lost their effectiveness due to agglomeration. The required cycles for desired density/properties are projected to be less compared to neat C/C due to less porosity observed in ⩽1.5 wt.% NGP concentration C/C.     

Pulsed electrodeposition of carbon nanotubes-hydroxyapatite nanocomposites for carbon/carbon composites

Carbon nanotubes-hydroxyapatite (CNTs-HA) composite coatings, which behaved like single composites, were synthesized by a combined method composed of electrophoretic deposition and pulsed electrodeposition. The phase compositions and the microstructure of the composite coatings were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectrometry (FTIR). Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies showed that the CNTs-HA composite coatings protected the bare carbon/carbon composites from corrosion in simulated body fluid (SBF) solution. The adhesion strength of CNTs-HA composite coating prepared by the combined method is 14.57±1.06 MPa achieved at the CNTs EPD time of 10 min. Compared to the other CNTs-HA composite coatings with different content of CNTs, the CNT-HA composite coating with the electrophoretic deposition of 10 min showed the best corrosion resistance. The morphology of CNTs-HA composite coatings immersed in SBF solution rendered the formation of HA crystallites. In addition, in vitro cellular responses to the CNTs-HA composite coatings were assessed to investigate the proliferation and morphology of mouse cells 3T3 cell line.     

Single-walled carbon nanotube buckypaper and mesophase pitch carbon/carbon composites

Carbon/carbon composites consisting of single-walled carbon nanotube (SWCNT) buckypaper (BP) and mesophase pitch resin have been produced through impregnation of BP with pitch using toluene as a solvent. Drying, stabilization and carbonization processes were performed sequentially, and repeated to increase the pitch content. Voids in the carbon/carbon composite samples decreased with increasing impregnation process cycles. Electrical conductivity and density of the composites increased with carbonization by two to three times that of pristine BP. These results indicate that discontinuity and intertube contact barriers of SWCNTs in the BP are partially overcome by the carbonization process of pitch. The temperature dependence of the Raman shift shows that mechanical strain is increased since carbonized pitch matrix surrounds the nanotubes.     

Kinetics of pyrolytic carbon infiltration for the preparation of ceramic/carbon and carbon/carbon composites

Carbon/carbon and zeolite/carbon composites have been prepared by pyrolytic carbon infiltration of organic and inorganic substrates with different porous structures. The chemical vapour infiltration kinetics of these substrates has been studied in a thermogravimetric system at atmospheric pressure, using benzene as pyrolytic carbon precursor. The rate of pyrolytic carbon infiltration seems to depend on the porosity of the substrate available to the pyrolytic carbon precursor, irrespective of the nature of the substrate studied. Activation energy values of about 180 kJ/mol were found for the different substrates used in the temperature range of 700-800 °C, where the cracking reaction of benzene takes place, predominantly, in a heterogeneous form. At higher temperatures homogeneous reactions compete with heterogeneous ones and higher values of activation energies (280-380 kJ/mol) were obtained. The oxidation of the pyrolytic carbon deposited on the different substrates studied takes place in the same range of temperature, which suggests the presence of a similar pyrolytic carbon structure on substrates of different nature or a similar accessibility to the deposited layer.     

Mechanical behavior of two-dimensional carbon/carbon composites with interfacial carbon layers

Effect of interfacial carbon layers on the mechanical properties and fracture behavior of two-dimensional carbon fiber fabrics reinforced carbon matrix composites were investigated. Phenolic resin reinforced with two-dimensional plain woven carbon fiber fabrics was used as starting materials for carbon/carbon composites and was prepared using vacuum bag hot pressing technique. In order to study the effect of interfacial bonding, a carbon layer was applied to the carbon fabrics in advance. The carbon layers were prepared using petroleum pitch with different concentrations as precursors. The experimental results indicate that the carbon/carbon composites with interfacial carbon layers possess higher fracture energy than that without carbon layers after carbonization at 1000°C. For a pitch concentration of 0.15 g/ml, the carbon/carbon composites have both higher flexural strength and fracture energy than composites without carbon layers. Both flexural strength and fracture energy increased for composites with and without carbon layers after graphitization. The amount of increase in fracture energy was more significant for composites with interfacial carbon layers. Results indicate that a suitable pitch concentration should be used in order to tailor the mechanical behavior of carbon/carbon composites with interfacial carbon layers.     

Sharp indentation behavior of carbon/carbon composites and varieties of carbon

Sharp indentation tests on carbon fiber and carbon matrix composites (C/C composite) were carried out over a wide load range from 0 to 2 N on three different cross sections: normal, parallel and inclined to the fiber axis. For comparison purposes, a variety of carbons including HOPG, glassy C, and pyrocarbon films was also examined. Both the fibers and the matrices displayed first a purely elastic response and second crack-induced damage. A purely elastic behavior was also observed with most of the varieties of carbon considered. Young’s modulus was extracted from the indentation curves either at maximum or at various forces, using the Sneddon equation of elastic response on loading (elastic indentation) or a classical equation based on elastic recovery on unloading (elastoplastic indentation). Results are discussed with respect to features of structure and heterogeneity of material in the stressed volume.     

Porous carbon/carbon composites produced from carbon black and petroleum pitch

Granular porous carbon/carbon composites were prepared by mixing carbon black, petroleum pitch and a solvent, followed by granulating the mixture and carbonization of the resulting pellets in an inert atmosphere. The pore structure of this material is studied by mercury porosimetry and scanning electron microscopy. Based on the obtained results, a model for it is proposed. The effects of carbon black type used, filler/binder ratio, heat treatment temperature and mixing time on surface area, total pore volume and strength of the finished pellets were investigated. Comparison with activated carbons indicates that the investigated material can find industrial applications as a catalyst support and as an adsorbent for adsorption of large molecules due to the meso- and macroporous structure and low ash content.     

Friction behaviors of carbon/carbon composites with different pyrolytic carbon textures

Friction and wear properties of carbon/carbon (C/C) composites with a smooth laminar (SL), a medium textured rough laminar (RL) and a high textured RL pyrolytic carbon texture were investigated with a home-made laboratory scale dynamometer to simulate airplane normal landing (NL), over landing (OL) and rejected take-off (RTO) conditions. The morphology of worn surfaces at different braking levels was observed with scanning electron microscopy. The results show that C/C composites with RL have nearly constant friction coefficients, stable friction curves and proper wear loss at different braking levels, while friction coefficients of C/C composites with SL pyrolytic carbon decrease intensely and their oxidation losses increase greatly under OL and RTO conditions. Therefore, C/C composites with a high and medium textured RL pyrolytic carbon may satisfy the requirements of aircraft brakes. The good friction and wear properties of C/C composites with RL are due to the properties of RL, which leads to a uniform friction film forming on the friction surface.