Electrochemical Sensors Based On Vertically Ordered Nanoporous/Nanochannel Silica Film

Artificial solid-state nanoporous/nanochannel materials consist of a periodic and regular arrangement with well-defined nanopores and amorphous framework structures. Recently, they are usually used in DNA sequencing, drug loading, catalysis and analysis. Silica nanochannels vertically and regularly oriented to the surface of substrate (VOMS), possess large internal surface area, high specific pore volume, chemically stable and robust nanostructure and good biocompatibility. Due to the high density of silanol groups on the surface, VOMS can be modified with different chemical groups and functional biomolecules, and utilized in many field, such as adsorption, catalysis, analysis sensor and so on. Moreover, the nanochannels perpendicular to the electrode surface make it possible for the electron transfer between adsorbed MB and the underlying electrode, allowing the quantitative determination of analytes using voltammetry. In this thesis, indium tin oxide (ITO) electrodes modified with VOMS were prepared for preconcentration and determination of dye molecules and nitroaromatic explosives in aqueous solutions.In the first chapter, two kinds of nanoporous/nanochannel materials were introduced, including the biological and artificial solid-state ones. The latter was divided into six kinds according to the constitute, and their synthesis and applications were summarized. Apart from the preparation and characterization methods, the synthesis mechanism and applications of VOMS film were reviewed.In the second chapter, ITO electrodes modified with VOMS film were prepared and utilized for preconcentration and detection of methylene blue (MB) in aqueous solutions. The detailed UV-vis spectroscopic measurements suggested that the adsorption process followed the pseudo-first-order kinetic model and obeyed the Langmuir adsorption isotherm thermodynamically. The negative value of AG derived from the Langmuir adsorption isotherm indicated the thermodynamic feasibility of the adsorption and the spontaneous nature of the process. In addition, the adsorbed MB can undergo an electrochemical reaction on the ITO electrode at a suitable potential and be determined using voltammetry. A linear detection range from 10 nM to 1.0 μM and a detection limit of 4.10 nM were obtained.The third chapter presented a work on the extraction/preconcentration and simultaneously electrochemical analysis of common nitroaromatic compounds, using the ITO electrodes modified with the complex film of VOMS and surfactant micelles. As a result, each of five analytes, such as TNT, DNT, TNP, NP, NB, was determined in a wide dynamic range and a low LOD at the ppb level. A linear detection range from 10 ppb to 1000 ppb and a detection limit of 4.97 ppb were obtained for TNT. Additionally, the selectivity of the electrochemical sensor was assessed by measuring the mixture containing five compounds, and found that the TNT could be selectively determined in terms of its characteristic peak lies far from the current waves of others. The sensor was also utilized for TNT determination in real water samples, and a high recovery of 96.0% was obtained.In the last chapter, the work presented in this thesis was summarized. An attempt was also made to propose the future research trend of VOMS in eletrochemical sensor.