以多孔碳毡为工作电极的流动注射库仑检测器的研究及应用

本文设计了一个以多孔碳毡为工作电极的库化检测器并将其于用流动注射分析,以抗坏血酸、氢醌,没食子酸及二氧化硫为电活性物质检验该检测器的电化学特性。详细地研究了该检测器的库仑转换效率,选择性,线性范围,检测限及质量转移系数,并将该检测器作为双检测器流动注射分析系统中的“清除”电解池,用于酒中二氧化硫的测定,其结果与常规的吹气－氧化法非常吻合。     

基于多孔碳固载离子液体修饰电极的叔丁基对苯二酚的检测研究

制备了多孔碳固载离子液体纳米材料修饰玻碳电极(GCE),用于抗氧化剂叔丁基对苯二酚(TBHQ)的检测研究。不同电极上的交流阻抗结果表明,经过多孔碳固载离子液体修饰后的玻碳电极阻抗显著减小。多孔碳固载离子液体修饰后电极的氧化峰电流为41.93μA,比修饰前增大约5.5倍,说明多孔碳固载离子液体可显著提高电极的导电性,促进电极表面的电子转移,提高检测灵敏度。用时间~电流曲线测得TBHQ的线性范围为1.00~120.00μg/mL,检出限为0.16μg/mL。     

碳毡电极研究(Ⅰ)——碳毡电极的特征密度

本文提出碳毡电极特征密度新概念,即碳毡电极对溶液中镉离子富集时,当碳毡在电极管中的密度为0.040—0.120g/cm~3时,富集效率随密度增加而增大。当密度大于0.120g/[cm]~3时,富集效率几乎不变。并由浓度为1×10~(-8)—1×10~(-5)g/ml的古镉离子溶液富集实验数据得到证明。     

碳毡电极的表面改性——Ⅲ.碳毡表面热氧化改性对电极性能的影响

碳毡电极材料经高温热氧化改性后,表面结构和性质发生明显变化。随热氧化温度上升,碳毡石墨结构更趋有序定向排列,石墨化程度提高。这不仅明显提高了其导电性能,同时也使表面含氧官能团的含量或O/C原子比下降。由于碳毡金属杂质含量减少以及表面担载的催化剂颗粒变大且分布更为不均匀,高温热氧化碳毡表面对析氢副反应具有较高的过电位,放氢电流大幅度降低,但提高热氧化温度使碳毡电极的电化学反应活性有所下降。为使碳毡电极上放氢电流降低的同时又保证电极具有较高的Fe~(3+)/Fe~(2+)及Cr~(3+)/Cr~(2+)反应的电化学活性,热氧化温度1700℃为宜。     

银离子在碳毡电极上的富集与洗脱

本文报道富集银后的碳毡电极用四种方法进行洗脱处理的结果。实验表明,当银离子浓度在1×10~(-1)—1×10~(-7)g/mL,范围内,被碳毡电极系统电化学富集后,用1mol/L硝酸作为洗脱剂,用活化加热法能使富集在碳毡电极表面的银获得最好的洗脱效率,平均洗脱率为95±2%。对于1×10~(-7)g/mL的原始待富集液与浓集液体积之比为270:1左右,每克碳毡可富集银1. 67×10~(-3)g。     

酸功能化碳纳米管对多孔碳材料储能活性及稳定性的增强作用

采用球磨法将酸功能化碳纳米管（AMWCNTs）与环糊精均匀混合。 酸功能化有利于增强碳管和环糊精间的相互作用,从而使二者形成均匀、有效的复合。 在N2气保护下碳化并经后续的ZnCl2活化处理,最终获得酸功能化碳纳米管/多孔碳(PC)复合体材料。 采用透射电子显微镜、X射线衍射和拉曼光谱等方法对材料结构进行了表征。 结果表明,碳纳米管在多孔碳骨架内均匀分布,并且复合体同时具有较高的比表面积和良好的导电性。 循环伏安及恒流充放电等电化学测试表明,由于二者的协同作用及碳纳米管在多孔碳骨架内均匀、有效的复合,材料具有较好的电化学储能性能和良好的电化学稳定性。 电流密度为0.5 A/g时,AMWCNTs/PC12-4（其中12代表β-环糊精和AMWCNTs的质量比,4代表酸化碳纳米管/β-环糊精碳与氯化锌的质量比）复合材料的质量比电容为156 F/g,远远高于AMWCNTs（43 F/g）和PC-4（87 F/g）。 经5000次循环后,电极比电容无明显衰减,而且每次恒流充放电的库仑效率均大于99.9%,说明复合材料具有良好的稳定性,是非常有前景的超级电容器电极材料。     

锂离子电池用多孔硅/石墨/碳复合负极材料的研究

在两步高能球磨和酸蚀条件下制得了多孔硅/石墨复合材料，并对其进行碳包覆制成多孔硅/石墨/碳复合材料。通过TEM，SEM等测试手段研究了多孔硅材料的结构。作为锂离子电池负极材料，电化学测试结果表明多孔硅/石墨/碳复合材料相比纳米硅/石墨/碳复合材料有更好的循环稳定性。同时，改变复合体配比、热解碳前驱物、粘结剂种类和用量也会对材料的电化学性能产生较大的影响。其中使用质量分数为10％的LA132粘结剂的电极200次循环以后充电容量保持在649.9 mAh·g^-1，几乎没有衰减。良好的电化学性能主要归因于主活性体-多孔硅颗粒中的纳米孔隙很好地抑制了嵌锂过程中自身的体积膨胀，而且亚微米石墨颗粒和碳的复合也减轻了电极材料的体积效应并改善了其导电性。     

碳毡电极对痕量金属离子的富集

在前文基础上,提出用碳毡电极对多种痕量金属离子进行富集,然后进行光谱分析。1975年日本高田芳矩等人用碳面做工作电极组成流动电解槽,对原子吸收分析试样做前处理。1977年Lund等提出对痕量金属经铂电极电化学富集后,用火焰原子吸收法分析。还有人进行过类似的工作。我们使用碳毡作为富集工作电极,对七种痕量金属离子进行富集。富集效率达98％左右。并用原子吸收进行分析,数据重现性良好。     

抗坏血酸自加速的圆二色谱电化学研究

以现场长光程薄层圆二色光谱电化学方法研究了抗坏血酸在玻碳电极上的电极反应过程,通过双对数法和非线性回归的方法处理了薄层圆二色光谱电化学实验数据,结果表明抗坏血酸在ＰＨ７．０的缓冲溶液中玻碳电极上为２个电子转移的不可逆电化学氧化,氧化产物在电极上发生了强吸附,吸附层对抗坏血酸的电化学氧化反应有自加速作用,并获得了抗坏血酸在裸电极和在吸附电极上的式电位分别为Ｅ＝０．０９Ｖ,Ｅｎ＝０．２６Ｖ;电子转移数     

碳毡电极的表面改性——Ⅱ.碳毡表面HNO_3化学改性对电极性能影响

对碳毡表面HNO_3化学改性引起电极性能的变化进行较详细研究。物理分析数据表明,由于HNO_3氧化处理,碳毡表面亲水性含氧官能团含量增加及HNO_3分子易嵌入并吸引高温碳毡石墨层状结构中的电子使空穴增多,电极表面浸润性和导电性明显提高。碳毡比表面也因HNO_3腐蚀作用有所增加。另外,循环伏安分析结果指出,在表面改性电极上Cr~(3+)/Cr~(2+)及Fe~(3+)/Fe~(2+)反应电化学活性增强,不仅峰值电流I_(pa)、I_(pa)随HNO_3氧化时间增长明显加大,而且峰电位差△Ep(=E_(pa)-E_(pc))变小,反应更趋可逆。还因为催化剂Pb沉积量增加而提高了其催化活性,经HNO_3氧化处理后的碳毡表面更利于Cr~(3+)/Cr_(2+)反应进行,其I_(pa)、I_(pc)值的增加明显高于Fe~(3+)/Fe~(2+)反应。     

Coulometric detector based on porous carbon felt working electrode for flow injection analysis

A coulometric detector based on carbon felt as working electrode has been designed. Ascorbic acid, hydroquinone, gallic acid and sulfur dioxide were used as electroactive compounds to determine the electrochemical characteristics of this detector. The coulometric conversion efficiency, selectivity, linear response range, detection limit and mass transfer coefficient were investigated in order to use the detector as a cleanup device in a flow injection system with dual-detector. This system has been used for determination of sulfur dioxide in wine, and the results are compared to those from the aspiration-oxidation method.     

Electrical Control of Urease Activity Immobilized to the Conducting Polymer on the Carbon Felt Electrode

The activity of urease varies by its redox reaction. Active urease has an SH group that is essential to exhibit its activity, however, oxidation agents such as quinone compounds can oxidize the SH group in urease and a S–S bond is produced, resulting in the loss of enzyme activity. The reduction potential of cystine was almost the same as that of the recovery of urease activity. In this work, it has been found that the SH group of urease can be oxidized by not only chemical reaction but also by the direct electrode oxidation of urease and the produced S–S bond can be reduced to SH group by chemical and electrode reactions, and the original enzyme activity is recovered. This research shows that the regulation of urease activity is easily possible by changing the electrode potential of the porous carbon felt immobilized urease. The variation of urease activity was monitored by ammonia or carbon dioxide electrode equipped with the urease immobilized carbon felt, and the ammonia or carbon oxide generated from urea can transfer through the carbon felt to reach the each gas permeable membrane. The combination of gas electrode with porous conducting material such as carbon can supply the novel device for the electrochemical investigation of enzyme activity.     

Mathematical models for estimating effective diffusion parameters of spherical drug delivery devices

Mathematical modeling of drug delivery is of increasing academic and industrial importance in many aspects. In this paper, we propose an optimization approach for the estimation of the parameters characterizing the diffusion process of a drug from a spherical porous polymer device to an external finite volume. The approach is based on a nonlinear least-squares method and a novel mathematical model which takes into consideration both boundary layer effect and initial burst phenomenon. An analytical solution to the model is derived and a formula for the ratio of the mass released in a given time interval and the total mass released in infinite time is also obtained. The approach has been tested using experimental data of the diffusion of prednisolone 21-hemisuccinate sodium salt from spherical devices made of porous poly(2-hydroxyethyl methacrylate) hydrogels. The effectiveness and accuracy of the method are well demonstrated by the numerical results. The model was used to determine the diffusion parameters including the effective diffusion coefficient of the drug from a series of devices that vary in both the porous structure and the drug loading levels. The computed diffusion parameters are discussed in relation to the physical properties of the devices.     

Mathematical modeling of gas–liquid membrane contactors using random distribution of fibers

This work presents a mathematical model for gas absorption in microporous hollow fiber membrane contactors by using a random distribution of fibers. The chemical absorption of carbon dioxide into aqueous amine solutions and sulfur dioxide into water were simulated by this model. The nonlinear mathematical expressions of the component material balance for the liquid, membrane, and gas were solved simultaneously by using a numerical method. The results from the model were compared with four sets of different experimental data in the literature. In addition, the contactors were modeled based on the assumption of regular arrangement of fibers in the shell side by using Happel's free surface as well as plug flow models. The plug flow model was employed to compare the various available equations in the literature for the shell side mass transfer coefficient. The results indicate that the channeling of gas in the shell side decreases the efficiency of contactor significantly. It was found that the random distribution of fibers is a suitable method to simulate the commercial modules. The results also indicate that, the regular Happel's free surface model and the plug flow model are more suitable for handmade modules. The influence of shell side channeling on the contactor performance were investigated in different fiber packing densities, and in various gas and liquid flow rates.     

Treated carbon felt as electrode material in vanadium redox flow batteries: a study of the use of carbon nanotubes as electrocatalyst

Electrodes for large-scale usage in vanadium redox flow battery are usually fabricated without any electrocatalyst due to the lack of good, viable options. The best performance is achieved of carbon-based materials. Recently, some researchers have been reported regarding the use of carbon nanotube as the electrocatalyst in the vanadium redox flow batteries. However, these researches have been carried out without making any comparison between the performance of the traditional method and the carbon nanotube electrocatalyst. In the present study, the loading of multi-walled carbon nanotube, the acid–heat treatment, and their combination were used to modify the carbon felt electrode to be applied in the vanadium redox flow battery. The obtained results showed better electrochemical properties for acid–heat-treated carbon felt electrode compared to the carbon nanotube-loaded one. The best electrode was obtained for using in a vanadium redox flow battery in terms of electrochemical and surface properties after applying a combination of two modification strategies. Applying this proposed method in modification of the carbon felt electrode increased its hydrophilicity more than 17 times and its capability to absorb VOSO₄ solution more than eight times. Also, the charge transfer resistance of a modified electrode, by the combination of the carbon nanotube and the acid–heat treatment, significantly decreased in both positive and negative poles of vanadium redox flow battery. Consequently, the exchange current density enhanced more than 100- and 175-fold in positive and negative poles, respectively, in comparison with carbon felt electrode.     

Applicability of Alginate Film Entrapped Yeast for Microbial Fuel Cell

New strategies are proposed for modification of the anode of a Microbial Fuel Cell (MFC). Immobilization of yeast cells as electrogenic microorganism in MFC was reported using alginate. Yeast cells entrapment within alginate matrices was done through films deposited at the surface of a carbon felt electrode and the resulting anodes were characterized by chronoamperometry. Yeast entrapped within alginate films on carbon felt oxidized glucose and generates a current by direct and mediated electrons transfer from yeast cells to the carbon electrode. The result substantiated that immobilization of yeast for MFC could be a promising method to product green electricity.

     

Hydrothermal Synthesis of Porous Al2O3/Al Metal Ceramics: II. Mechanism of Formation of a Porous Al(OH)3/Al Composite

The formation of a porous layer of aluminum hydroxide on the surface of aluminum particles and the aggregation of Al(OH)₃/Al composite particles were analyzed theoretically. It was found that the diffusion mass transfer of the hydroxo complexes of aluminum through the porous structure of a growing layer of aluminum hydroxide to the outer surface is a rate-limiting step in the synthesis of the porous composite. A model mechanism of formation of the porous composite was developed, and rate equations were derived for describing the growth of an aluminum hydroxide layer on the surface of an aluminum particle and changes in the degree of aluminum conversion and the contact radius between composite particles. Based on the developed mathematical model and experimental data, the diffusion coefficient of the hydroxo complexes of aluminum in the porous structure of aluminum hydroxide was calculated.     

Dynamic calibration and dissolved gas analysis using membrane inlet mass spectrometry for the quantification of cell respiration

A membrane inlet mass spectrometer connected to a miniaturized reactor was applied for dynamic dissolved gas analysis. Cell samples were taken from 7 mL shake flask cultures of Corynebacterium glutamicum ATCC 13032, and transferred to the 12 mL miniaturized reactor. There, oxygen uptake and carbon dioxide and its mass isotopomer production rates were determined using a new experimental procedure and applying nonlinear model equations. A novel dynamic method for the calibration of the membrane inlet mass spectrometer using first-order dynamics was developed. To derive total dissolved concentration of all carbon dioxide species (C(T)) from dissolved carbon dioxide concentration ([CO(2)](aq)), the ratio of C(T) to [CO(2)](aq) was determined by nonlinear parameter estimation, whereas the mass transfer coefficient of CO(2) was determined by the Wilke-Chang correlation. Subsequently, the suitability of the model equations for respiration measurements was examined using residual analysis and the Jarque-Bera hypothesis test. The resulting residuals were found to be random with normal distribution, which proved the adequacy of the application of the model for cell respiration analysis. Hence, dynamic changes in respiration activities could be accurately analyzed using membrane inlet mass spectrometry with the novel calibration method.     

Electroactive porous films of myoglobin within calcium alginate

In this work, a novel two-step construction strategy for protein assembly films was proposed. The first step was the preparation of porous calcium alginate (CA) films by spraying calcium chloride (CaCl₂) solution over the mixture surface of sodium alginate and polyethylene glycol on various solid substrates. The second step involved the cast of myoglobin (Mb) onto the porous CA films and then formed the electroactive porous Mb-CA films. The nitrogen adsorption desorption isotherm, scanning electron microscope, alternating current impendence and cyclic voltammetry were used to characterize the porous films. Fully hydrated porous CA films had nearly 90 wt% water contents and UV–vis showed that Mb in the porous films retained its near native conformation at medium pH. The stable films modified on glassy carbon electrode demonstrated good electroactivity in protein-free buffer, which was originated from protein heme Fe(III)/Fe(II) redox couples. The electrochemical parameters such as apparent heterogeneous electron transfer rate constant (k _s) and formal potential (E ^o′) were estimated by fitting the data of square-wave voltammetry with nonlinear regression analysis. It was observed that the formal potential of the Mb Fe(III)/Fe(II) couple in porous CA films shifted linearly between pH 4.0 and 11.0 with a slope of −52.7 mV/pH, suggesting that one proton transfer was coupled to each electron transfer in the electrochemical reaction. The porous Mb-CA films showed the electrocatalytic activity toward dioxygen, hydrogen peroxide, and nitrite with significant decreases in the electrode potential required, and exhibited good operational and storage stability, reproducibility and fast response time for H₂O₂ detection. It is showing the possible future application of the films for biosensors and biocatalysis.