京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第22508号 / 農博第2412号 / 新制||農||1078(附属図書館) / 学位論文||R2||N5288(農学部図書室) / 京都大学大学院農学研究科応用生命科学専攻 / (主査)教授 加納 健司, 教授 三芳 秀人, 教授 宮川 恒 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

Electrosorption-based capacitive deionization (CDI) has become a viable process for brackish water desalination and defluoridation. In this study, activated Douglas fir biochar is used as a low-cost electrode material with adsorption capacity comparable to activated carbon obtained from biomass precursors. Adding functional groups to the activated biochar enhanced salt removal capacity, providing cation and anion selectivity. The functionalized electrodes were prepared by Nafion, titanium isopropoxide, and p-phenylenediamine treatment, respectively, which introduced sulfonate, titanium dioxide and amine functional groups to the electrode surface. These modification methods are versatile and can be easily performed without sophisticated laboratory environment. Modified biochar electrodes were characterized by TEM, SEM-EDX, XRD, and XPS. Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were performed to analyze the electrochemical properties of the electrodes. The salt adsorption capacity (SAC) was evaluated in a 3D-printed capacitive deionization flow cell using a chloride and fluoride ion sensor. It was found that functionalized biochar electrodes had increased SAC and charge efficiency in asymmetrical setup due to reduced co-ion effect. For example, the asymmetrical CDI cell with Nafion cathode and amine biochar anode improved NaCl removal capacity by 54% over the activated biochar symmetrical cell (identical anode and cathode), with SAC 6.01 mg NaCl/g biochar at the symmetrical cell and 9.25 mg/g for the asymmetrical cell. The charge efficiency also increased by ≈ 67% from symmetric AcB cell to asymmetric TB-05 cathode and AmB anode. This work shows that biochar can be engineered and explored broadly as an inexpensive sustainable electrode material for asymmetrical capacitive deionization.

The presented dissertation encompasses three distinct investigations into novel complexes with diverse applications. Firstly, a Europium-based complex, K[Eu(hfa)4], exhibits remarkable potential for detecting dissolved CO2 in an ethylene glycol medium, offering a low limit of detection, rapid response times, and high signal-to-noise ratios. This complex demonstrates promise for quantifying CO2 concentrations and finds utility in sugar fermentation monitoring. Secondly, an innovative ratiometric optical sensor, Eu(tta)3([4,4'-(t-bu)2-2,2'-bpy)], showcases exceptional sensitivity and selectivity in detecting aluminum ions, making it suitable for environmental and biological applications. It exhibits reliable quantification in both methanol and aqueous samples, with remarkable accuracy validated by ICP-OES. Lastly, modifications to the Au3Pz3 complex synthesis enable the development of a silver ion sensor, paving the way for detecting silver ion leaching in real-life scenarios, such as silver nanoparticle-embedded bandages. The research extends to the synthesis of silver nanoparticles using various methods and foresees expanded in vitro and in vivo studies. These investigations collectively offer insights into the development of advanced sensing technologies with significant implications for a wide range of practical applications.

Ion sensing represents a grand research challenge. It finds a vast variety of applications in, e.g., gas sensing for domestic gases and ion detection in electrolytes for chemical-biological-medical monitoring. Semiconductor genome sequencing exemplifies a revolutionary application of the latter. For such sensing applications, the signal mostly spans in the low frequency regime. Therefore, low-frequency noise (LFN) present in the same frequency domain places a limit on the minimum detectable variation of the sensing signal and constitutes a major research and development objective of ion sensing devices. This thesis focuses on understanding LFN in ion sensing based on both experimental and theoretical studies. The thesis starts with demonstrating a novel device concept, i.e., ion-gated bipolar amplifier (IGBA), aiming at boosting the signal for mitigating the interference by external noise. An IGBA device consists of a modified ion-sensitive field-effect transistors (ISFET) intimately integrated with a bipolar junction transistor as the internal current amplifier with an achieved internal amplification of 70. The efficacy of IGBA in suppressing the external interference is clearly demonstrated by comparing its noise performance to that of the ISFET counterpart. Among the various noise sources of an ISFET, the solid/liquid interfacial noise is poorly studied. A differential microelectrode cell is developed for characterizing this noise component by employing potentiometry and electrochemical impedance spectroscopy. With the cell, the measured noise of the TiN/electrolyte interface is found to be of thermal nature. The interfacial noise is further found to be comparable or larger than that of the state-of-the-art MOSFETs. Therefore, its influence cannot be overlooked for design of future ion sensors. To understand the solid/liquid interfacial noise, an electrochemical impedance model is developed based on the dynamic site-binding reactions of surface hydrogen ions with surface OH groups. The model incorporates both thermodynamic and kinetic properties of the binding reactions. By considering the distributed nature of the reaction energy barriers, the model can interpret the interfacial impedance with a constant-phase-element behavior. Since the model directly correlates the interfacial noise to the properties of the sensing surface, the dependencies of noise on the reaction rate constants and binding site density are systematically investigated.