固态离子选择性电极检测体系的构建及其在海水钾、钙分析中的 应用
曾现忠
学位类型博士
导师秦伟
2017
学位授予单位中国科学院大学
学位授予地点北京
关键词固态离子选择性电极 固态参比电极 海水
摘要
摘要
海洋中化学元素组分的定量分析检测是海洋化学研究的一个重要课题,一直为人们所广泛研究。以钾离子、钙离子为代表的海水中碱金属及碱土金属元素检测对促进海洋生物的生长发育及维持海洋生态环境的平衡具有重要意义。目前测定海水中钾离子、钙离子的常用方法有原子光谱法、分子光谱法以及质谱分析等等,然而上述检测手段存在设备复杂、操作繁琐、仪器价格昂贵等问题。离子选择性电极是存在时间较早的一类电化学传感器,能够将目标离子的活度转化为可以测量的电势信号。其作为一种常用的检测手段被广泛应用于医疗诊断、过程控制以及环境监测等领域。在传统的离子选择性电极检测体系中,由聚合物离子选择性膜、内充液及内参比电极所构成的液体接触式离子选择性电极与外接双液接盐桥的外参比电极共同构成检测回路。在上述检测体系中,液体接触式离子选择性电极中内充液、内参比电极的使用以及参比电极中盐桥及内充电解质的存在,导致传统离子选择性电极检测体系存在保养冗赘、体积大、不易携带等缺点,目前,开发基于固体导电基底的固态离子选择性电极检测体系已成为电位型传感器的研究热点。到目前为止,基于离子选择性电极进行海洋化学组分检测的报道较少。因此,进行固态离子选择性电极检测体系的构建,并用于海洋化学组分的检测分析,将为离子选择性电极在海洋分析化学领域的应用研究提供一定的指导意义。本论文从构建固态离子选择性电极检测体系出发,分别研究了新型固态离子选择性电极以及固态参比电极,并将其应用于海水样品中钾离子及钙离子的检测分析。研究内容包括以下五个部分:
1. 基于MoS2纳米花转导的固态离子选择性电极
涂丝电极作为最早的固态离子选择性电极,由于导电基底与离子选择性膜之间没有稳定的界面电位,所以该类电极的电位稳定性差。基于双电层电容转导机理的离子-电子转导层的引入能够保证聚合物膜与固体导电基底间界面电位的稳定。然而,该类转导层的使用主要以碳基、贵金属基两大类物质为主,到目前为止尚无基于非碳基、非贵金属基类双电层电容转导机理固体接触层的报道。我们以MoO3纳米带为前驱体,在水热条件下,通过调控反应条件合成了具有特定形貌的MoS2纳米花以及MoS2纳米颗粒,并探讨了反应的合成机理。同时,我们以MoS2纳米花为研究对象,将其作为一种碳基类似物,开发了一种新型的固态离子-电子转导层,并应用于固体接触式钾离子选择性电极的制备研究。我们考察了所制备的固体接触式钾离子选择性电极的性能,并将其成功应用于海水中钾离子的检测分析。
2. 基于MoO2微米球转导的固态离子选择性电极
受碳基类似物MoS2纳米花转导层的启发,我们以类金属的MoO2微米球为研究对象,进行了基于双电层电容转导机理新型离子-电子转导层的研发。在该体系中,我们以MoO3纳米带、MoO3微米棒为反应前驱体,通过调控反应条件,在异丙醇溶剂中,溶剂热合成了单分散MoO2微米球、连体MoO2微米球。我们对所合成的MoO2材料进行了表征,并探究了相应的合成机理。由于连体MoO2微米球的形貌不均一,我们以单分散的MoO2微米球为研究对象,制备了基于MoO2微米球转导的新型固体接触式钾离子选择性电极。研究表明,所制备的新型固体接触式钾离子选择性电极,在钾离子活度为10-5 - 10-3 M范围内呈现线性能斯特响应,响应斜率为55.0 mV/decade,检测下限为10-5.4 M;同时,MoO2微米球的引入使电极的稳定性增强、电容增加、电阻降低,有效降低了离子选择性电极中水层的存在。实验证明,MoO2微米球可以作为一种新型的类金属离子-电子转导层。
3. 基于Ag@AgCl/KCl转导的固态离子选择性电极
基于氧化还原电容转导机理的离子-电子转导层是固态离子选择性电极中研究最早的固体接触层材料。然而到目前为止,该类转导层材料的选择主要以有机类物质为主,对于无机材料的使用报道较少。基于无机材料的氧化还原电容转导层的应用,将为固态离子选择性电极中离子-电子转导层的开发提供一种新的思路。我们受Ag/AgCl参比电极的启发,设计了基于无机氧化还原材料Ag/AgCl/KCl的新型固态离子-电子转导层。我们以具有核壳结构的Ag@AgCl为无机氧化还原活性物质,通过添加无机盐KCl作为氯离子的来源,并借助于微体系中水分子的存在,构筑了新型的无机氧化还原转导体系。我们以该无机氧化还原转导层为研究对象,制备了新型的固态钙离子选择性电极,并考察了所制备电极的响应特性、选择性、稳定性以及无机氧化还原转导材料的引入对固态离子选择性电极电化学性能的影响。最后,我们采用制备的新型固态钙离子选择性电极成功进行了海水中钙离子浓度的检测分析。
4. 基于Ag@AgCl/离子液体转导的固态离子选择性电极
我们发现,上述基于无机氧化还原材料Ag@AgCl/KCl的离子-电子转导层,在使用过程中会存在因KCl的不断溶解,而发生亲水性离子(K+、Cl)从有机膜相到水溶液相渗漏现象,这在一定程度上会影响固态离子选择性电极的电位稳定性及使用寿命。为此,我们对上述无机氧化还原转导体系进行了优化,通过添加离子液体1-十四烷基-3-甲基咪唑氯盐(TMMCl)作为氯源,开发了基于Ag@AgCl/TMMCl转导的新型无机离子-电子转导层。我们以钙离子为检测对象,制备了新型的固体接触式钙离子选择性电极,并考察了电极的响应性能及稳定性。结果表明,固态钙离子选择性电极对钙离子的线性响应范围为10-6 - 10-2 M,响应斜率为28.3 mV/decade,检测限为10-6.5 M,且电极的电位响应稳定、电化学性能好。此外,考察了固态钙离子选择性电极的选择性系数,并将该固态离子选择性电极成功应用于海水中钙离子的检测分析。
5. 基于2,2,6,6-四甲基哌啶-1-氧基盐(TEMPO)的固态参比电极
传统的参比电极主要基于Ag/AgCl或Hg/Hg2Cl2的半电池,并通过盐桥与样品进行连接。盐桥中通常含有具有相近阴阳离子迁移率的盐溶液以降低盐桥与溶液界面间的液接电位。传统的参比电极虽然稳定、可靠,然而盐桥的存在使得该类参比电极在使用中存在诸多缺点,如经常保养、具有大的体积以及内充盐溶液与样品溶液产生的相互污染等问题。我们以廉价、易得的TEMPO为氧化还原活性物质,PVC为基底,o-NPOE为增塑剂,通过离子液体的添加,制备了新型的固态参比膜。另外,以石墨烯为转导层制备了新型固态参比电极。我们考察了该固态参比电极对盐溶液的响应、pH的效应以及抗干扰性,并同商品化参比电极对比,验证了新型固态参比电极在电流、电位分析的可靠性。同时以丝网印刷电极为基底,制备了微型化固态钙离子选择性电极检测体系,并用于海水中钙离子的检测分析。
 
其他摘要
Abstract
Determination of chemical components in seawater is of great importance. Potassium and calcium are the main elements of alkali and alkaline earth metals in seawater, which play important roles in marine organism systems and marine ecological environment. Nowadays, methods for the determination of potassium and calcium in seawater include atomic spectra, molecular spectrum, mass spectrum and so on, but these methods suffer from problems of complicated equipment, cumbersome operation and expensive apparatus. Ion-selective electrodes (ISEs) are electrochemical sensors that can convert the activity of a target ion into an electrical potential as the measurable signal. As routine analytical tools, ISEs have been widely applied in clinical diagnostics, process control, and environmental monitoring. In a traditional ISE measurement system, a liquid-contact ISE with a polymeric ion selective membrane, an inner solution, and an inner reference electrode is connected with the reference electrode coupled with a salt bridge through a sample solution. However, the presence of the inner solution and inner reference electrode in the liquid-contact ISE, and the usage of the salt bridge containing the aqueous solution in the outer reference electrode can cause problems of difficult maintenance, large volume and inconvenient handling of the ISE. Thus, it is highly desirable to develop all-solid-state ISE measuring systems. Untile now, very few papers for seawater analysis using ISEs have been reported. Fabrication of solid-state ISEs detection systems to analyze seawater components would provide instructive guidelines for marine chemistry. Herein, solid-state ion-selective electrode detection systems based on novel solid-state ISEs and solid-state reference electrodes have been developed and applied for the potentiometric analysis of potassium and calcium ions in seawater. Five ISE systems have been developed and investigated in detail:
1. Solid-state ion-selective electrodes with MoS2 nanoflowers as ion-to-electron transducer
Coated-wire electrodes are the earliest solid-state ISEs. However, such electrodes suffer from problems of potential instability, which is due to the lack of defined phase boundary potentials at the interface of the ISE membrane and the underlying solid substrate. Ion-to-electron transducers based on the double-layer capacitance transduction mechanism have been developed to improve the potential stability. However, solid-contact layers based on this transduction mechanism are mainly limited to carbon and noble metal materials. Until now, there are no solid-contact layers based on non-carbon and non-noble metal materials. Herein, MoO3 nanobelts are used as precusors to synthesize MoS2 with certain morphologies through a hydrothermal process. Under optimized conditions, MoS2 nanoflowers and MoS2 nanoparticles can be obtained, and the corresponding reaction mechanisms have been proposed. Additionally, MoS2 nanoflowers working as carbon analogues have been developed as novel ion-to-electron transducers to fabricate novel solid-contact K+-ISEs (SC-K+-ISE). The proposed SC-K+-ISE has been characterized and applied for the determination of K+ in seawater.   
2. Solid-state ISEs based on MoO2 microspheres as ion-to-electron transducer
Enlightened by the MoS2 nanoflower working as carbon analogue for the ion-to-electron transducer, we have developed the metal analogue (MoO2 microspheres) as novel ion-to-electron transducer for use in SC-ISEs based on the double-layer capacitance transduction mechanism. In this work, MoO3 nanobelts and MoO3 microrods have been applied as precursors to synthesize MoO2 in isopropanol via a solvothermal method. Under optimized conditions, mono-dispersed MoO2 microspheres and conjunctive MoO2 microspheres have been produced and characterized, respectively. The corresponding reaction mechanisms have been proposed. Due to the poor uniformity in diameter for the conjunctive MoO2 microspheres, monodispersed MoO2 microspheres have been used as solid-contact layer for the novel SC-K+-ISE. The ISE shows a Nernstian response of 55.0 mV/decade for potassium activity in the range from 10-5 to 10-3 M, and the limit of detection is 10-5.4 M. The electrode shows a fast and good potential response with excellent resistance to disturbances of light, O2 and CO2. The introduction of MoO2 microspheres has been found to improve the potential stability and capacitance, decrease the impedance, and reduce the water layer. As a result, MoO2 microspheres working as metal analogue can be used as a new ion-to-electron transducer for developing solid-state ISEs.
3. Solid-state ISEs based on Ag@AgCl/KCl transducer
Ion-to-electron transducers based on the redox capacitance transduction mechanism are the earliest solid-contact layers investigated. Those materials are mainly based on organic materials. Exploring inorganic materials as solid-contact layers, with the redox capacitance transduction mechanism, would pave a new avenue for the development of SC-ISEs. Enlightened by the Ag/AgCl reference electrode, we have developed a novel ion-to-electron transducer based on the inorganic redox material Ag@AgCl/KCl. Herein, Ag@AgCl with core-shell morphologies has been synthesized and applied as the inorganic redox active material. With the use of KCl as Cl- source, a novel redox system can be obtained. By using this inorganic redox transducer, a novel solid-state Ca2+ selective electrod has been developed. The potentiometric response, selectivity, stability and the electrochemical properties for the SC-Ca2+-ISE with the inorganic redox transducer have been extensively investigated. Experiments show that Ag@AgCl/KCl can be employed as a good ion-to-electron transducer. The proposed SC-Ca2+-ISE has been successfully applied for the determination of Ca2+ in seawater.
4. Solid-state Ca2+-ISE based on Ag@AgCl/ionic liquid transducer
It has been realized that the SC-ISE using Ag@AgCl/KCl as the transducer may suffer from problems of instability. With the dissolution of KCl, the hydrophilic ions such as K+ and Cl- would continuously diffuse from the polymeric membrane to the sample solution. This would affect the potential stability and life time of the ISE. To solve this problem, the ionic liquid in the redox system has been used to replace KCl, and a novel inorganic redox transducer Ag@AgCl/TMMCl has been proposed. With the Ca2+-ISE as a model, we have fabricated a SC-Ca2+-ISE and characterized the electrochemical properties. The developed SC-Ca2+-ISE shows a linear response to Ca2+ in the activity range of 10-6 to10-2 M with a detection limit of 10-6.5 M. The fabricated SC-Ca2+-ISE shows a good potential response and electrochemical properties. Additionally, we have evaluated the selectivity coefficients of this SC-Ca2+-ISE and applied it for the determination of Ca2+ in sea water.
5. Solid-state reference electrodes based on 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO)
Conventional reference electrodes are usually based on Ag/AgCl and Hg/Hg2Cl2 half cells,  which are connected to the sample through a salt bridge. An aqueous solution of an equitransferent salt is usually used as the salt bridge to minimize the liquid junction potential at the interface between the salt bridge and the sample solution. Although such reference electrodes are stable and reliable, the salt bridges may suffer from problems of difficult maintenance, large volume and mutual contamination between the bridge electrolyte and sample solution. In this work, the reference membrane has been fabricated by using TEMPO as redox active material, PVC as substrate, o-NPOE as plasterizer and ionic liquid as salt bridge. In order to reduce the presence of the water layer and to improve the potential stability, graphene is used as transducer to develop a novel solid-state reference electrode. The ionic potential responses to solutions, and the pH effect and resistances to disturbances have been tested for the solid state reference electrode. The reliability and accuracy of the novel solid-state reference electrode have been verified by the amperometric and potentiometric analyse, which are comparable with those of the commercial reference electrode. Additionally, with the screen printed electrode configuration, a miniturized potentiometric ISE measurement system for Ca2+-ISE has been fabricated and applied in the determination of Ca2+ in seawater.
 
文献类型学位论文
条目标识符http://ir.yic.ac.cn/handle/133337/22104
专题中国科学院烟台海岸带研究所知识产出_学位论文
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曾现忠. 固态离子选择性电极检测体系的构建及其在海水钾、钙分析中的 应用[D]. 北京. 中国科学院大学,2017.
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