Faraday Discussions最新文献

The development of chemical sensors has advanced due to an increase in demand; however, the potential of chemical sensors as devices to monitor organic reactions has not been revealed yet. Thus, we aim to propose a chemical sensor platform for facile monitoring of chemical reactions, especially at a solid–liquid interface. In this study, an extended-gate-type organic field-effect transistor (OFET) has been employed as a platform to detect chemical reactions at an interface between the extended-gate electrode and an aqueous solution. The OFET device functionalized with 4,4′-thiobisbenzenthiol has shown time- and concentration-dependent shifts in transistor characteristics upon adding H₂O₂. In a selectivity test using seven oxidant agents, the transistor responses depended on the oxidation of the organic sulfur compound (i.e., 4,4′-thiobisbenzenthiol) stemming from the ability of the oxidant agents. Therefore, the observed changes in the transistor characteristics have suggested the generation of sulfur-oxidized products at the interface. In this regard, the observed responses were caused by disulfide formation accompanied by changes in the charges under neutral pH conditions. Meanwhile, weak transistor responses derived from the generation of oxygen adducts have also been observed, which were caused by changes in the dipole moments. Indeed, the yields of the oxygen adducts have been revealed by X-ray photoelectron spectroscopy. The monitoring of gradual changes originating from the decrease in the disulfide formation and the increase in the oxygen adducts implied a novel aspect of the OFET device as a platform to simultaneously detect reversible and irreversible reactions at interfaces without using large-sized analytical instruments. Sulfur oxidation by H₂O₂ on the OFET device has been further applied to the indirect monitoring of an enzymatic reaction in solution. The OFET-based chemical sensor has shown continuous changes with an increase in a substance (i.e., lactate) in the presence of an enzyme (i.e., lactate oxidase), which indicates that the OFET response depends on the H₂O₂ generated through the enzymatic reaction in the solution. In this study, we have clarified the versatility of organic devices as platforms to monitor different chemical reactions using a single detection method.

In aprotic lithium–oxygen (Li–O₂) batteries, solvent properties are crucial in the charge/discharge processes. Therefore, a thorough understanding of the solvent stability at the cathode surface during the oxygen reduction/evolution reactions (ORR/OER) is essential for the rational design of high-performance electrolytes. In this study, the stability of typical solvents, a series of glyme solvents with different chain lengths, has been investigated during the ORR/OER by in situ vibrational spectroscopy measurements of sum frequency generation (SFG) spectroscopy and infrared reflection absorption spectroscopy (IRRAS). The structural evolution and decomposition mechanism of the solvents during ORR/OER have been discussed based on the observations. Our results demonstrate that superoxide (O₂⁻) generated during the ORR plays a critical role in the stability of the solvents.

Condensation and arrangement of ions at water–solid interfaces are of great importance in the formation of electrical double layers (EDL) and the transport of ions under a confined geometry. So far, the microscopic understanding of interfacial ion configurations is still far from complete, especially when the local ion concentration is high and ion–ion interactions become prominent. In this study, we directly visualized alkali metal cations within the hydrogen-bonding network of water on graphite and Cu(111)-supported graphene surfaces, using qPlus-based noncontact atomic force microscopy (NC-AFM). We found that the codeposition of the alkali cations and water molecules on the hydrophobic graphite surface leads to the formation of an ion-doped bilayer hexagonal ice (BHI) structure, where the ions are repelled from each other and scattered in a disordered distribution. In contrast, the hydrated alkali cations aggregate in one dimension on the more hydrophilic graphene/Cu(111) surface, forming a nematic state with a long-range order. Such a nematic state arises from the delicate interplay between water–ion and water–water interactions under surface confinement. These results reveal the high sensitivity of ion–ion interactions and ionic ordering to the surface hydrophobicity and hydrophilicity.

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