Random nucleation and growth of Pt nanoparticles at the polarised interface between two immiscible electrolyte solutions

Au Nanofiber/CNT 1D/1D Composites Formed Via Redox Reaction at the Ionic Liquid/Water Interface

Au nanofiber/carbon nanotube (CNT) 1D/1D composites and Janus-type Au/CNT composites have been prepared by utilizing the liquid/liquid interface between water (W) and a hydrophobic ionic liquid (IL) as a redox reaction site. AuCl₄^- in W is reduced at the IL/W interface where CNTs are adsorbed, by a reducing agent in the IL, leading to the formation of the Au/CNT composites. The Au/CNT composites are Janus-type in which Au microurchins and Au nanofibers are deposited on the W side and the IL side of the CNTs on the IL/W interface, respectively. Reversing the order of the CNT adsorption and AuCl₄^- reduction results in the formation of the Au nanofiber/CNT composites, which are 1D/1D metal/carbon composites.

Polystyrene-coated Interdigitated Microelectrode Array to Detect Free Chlorine towards IoT Applications

We apply interdigitated microelectrode array (IDA) sensors for water quality monitoring. IDA sensors with an ion-sensitive coating show higher sensitivity of about 600 mV with the hypochlorite ion concentration increasing from 0 to 10 ppm more than the traditional sensing method. The response mechanism and selectivity have been studied. Several material components that affect the sensing process were explored. Coupling agents and plasticizer were introduced into the coating material to improve the coating material quality and its adhesion to the electrodes. The stability/repeatability and linearity have been significantly improved.

Janus-Type Gold/Polythiophene Composites Formed via Redox Reaction at the Ionic Liquid|Water Interface

Janus-type Au/polythiophene (PT) composites have been prepared by utilizing the liquid/liquid interface between water (W) and a hydrophobic ionic liquid (IL) as the redox reaction site. AuCl₄^- is reductively deposited, and terthiophene is oxidatively polymerized spacio-selectively at the IL|W interface, leading to the formation of the Au/PT composites. The composites are Janus-type Au-attached PT plates with two surface morphologies, flat surface and flowerlike surface at the W and IL sides of the plates at the IL|W interface, respectively. Not only surface morphologies but also attached Au structures are different at the two surfaces; Au microurchins on the flat surface and dendritic Au nanofibers on the flowerlike surface. Optical and scanning electron microscopic observations have revealed that nanofibers and microurchins are formed at the early and later stage of the reaction, respectively. Electrochemistry at the IL|W interface has illustrated that electron transfer across the IL|W interface during the formation of the Janus-type Au/PT composites is coupled with ion transfer of AuCl₄^- to compensate for the charge unbalance in the two liquid phases. AuCl₄^- transferred into IL is found to be the source of the dendritic Au nanofibers formed at the IL side of the PT plates.

The significance of bromide in the Brust-Schiffrin synthesis of thiol protected gold nanoparticles

The mechanism of the two-phase Brust-Schiffrin synthesis of alkane thiol protected metal nanoparticles is known to be highly sensitive to the precursor species and reactant conditions. In this work X-ray absorption spectroscopy is used in conjunction with liquid/liquid electrochemistry to highlight the significance of Br^- in the reaction mechanism. The species [AuBr₄]^- is shown to be a preferable precursor in the Brust-Schiffrin method as it is more resistant to the formation of Au(i) thiolate species than [AuCl₄]^-. Previous literature has demonstrated that avoidance of the Au(i) thiolate is critical to achieving a good yield of nanoparticles, as [Au(i)X₂]^- species are more readily reduced by NaBH₄. We propose that the observed behavior of [AuBr₄]^- species described herein explains the discrepancies in reported behavior present in the literature to date. This new mechanistic understanding should enable nanoparticle synthesis with a higher yield and reduce particle size polydispersity.

Detection and characterisation of sub-critical nuclei during reactive Pd metal nucleation by X-ray absorption spectroscopy

The interfacial reduction of aqueous [PdCl₄]²⁻ at the interface with an organic solution of ferrocene has been characterised by X-ray absorption fine structure (XAFS) spectroscopy.

Amperometric Ion Sensing Approaches at Liquid/Liquid Interfaces for Inorganic, Organic and Biological Ions

Electrochemistry at the interface between two immiscible electrolyte solutions (ITIES) has become an invaluable tool for the selective and sensitive detection of cationic and anionic species, including charged drug molecules and proteins. In addition, neutral molecules can also be detected at the ITIES via enzymatic reactions. This chapter highlights recent developments towards creating a wide spectrum of sensing platforms involving ion transfer across the ITIES. As well as outlining the basic principles needed for performing these sensing applications, the development of ITIES-based detection strategies for inorganic, organic, and biological ions is discussed.

Dendritic nanofibers of gold formed by the electron transfer at the interface between water and a highly hydrophobic ionic liquid

Novel nanostructures, dendritic nanofibers of gold, have been found to be formedviaan electron-transfer reaction at the ionic liquid–water interface, instead of the more conventional oil–water interface.

Composite PET membrane with nanostructured Ag/AgTCNQ Schottky junctions: electrochemical nanofabrication and charge-transfer properties

Large-area nanostructured Ag/Ag-tetracyanoquinodimethane (TCNQ) Schottky junctions are fabricated electrochemically on a mesoporous polyethylene terephthalate (PET) membrane-supported water/1, 2-dichloroethane (DCE) interface. When the interface is polarized, Ag(+) ions transfer across the PET membrane from the aqueous phase and are reduced to form metallic Ag on the PET membrane, which reacts further with tetracyanoquinodimethane (TCNQ) in the DCE phase to form nanostructured Ag/AgTCNQ Schottky junctions. Once the mesoporous membrane is blocked by metallic Ag, a bipolar mechanism is proposed to explain the successive growth of AgTCNQ nanorods and Ag film on each side of the PET membrane. Due to the well-formed nanostructure of Ag/AgTCNQ Schottky junctions, the direct electrochemical behavior is observed, which is essential to explain the physicochemical mechanism of its electric performance. Moreover, the composite PET membrane with nanostructured Ag/AgTCNQ Schottky junctions is tailorable and can be assembled directly into electric devices without any pretreatment.

Simple Ion Transfer at Liquid|Liquid Interfaces

The main aspects related to the charge transfer reactions occurring at the interface between two immiscible electrolyte solutions (ITIES) are described. The particular topics to be discussed involve simple ion transfer. Focus is given on theoretical approaches, numerical simulations, and experimental methodologies. Concerning the theoretical procedures, different computational simulations related to simple ion transfer are reviewed. The main conclusions drawn from the most accepted models are described and analyzed in regard to their relevance for explaining different aspects of ion transfer. We describe numerical simulations implementing different approaches for solving the differential equations associated with the mass transport and charge transfer. These numerical simulations are correlated with selected experimental results; their usefulness in designing new experiments is summarized. Finally, many practical applications can be envisaged regarding the determination of physicochemical properties, electroanalysis, drug lipophilicity, and phase-transfer catalysis.

Strategies for the fabrication of porous platinum electrodes

Porous platinum is of high technological importance due to its various applications in fuel cells, sensors, stimulation electrodes, mechanical actuators and catalysis in general. Based on a discussion of the general principles behind the reduction of platinum salts and corresponding deposition processes this article discusses techniques available for platinum electrode fabrication. The numerous, different strategies available to fabricate platinum electrodes are reviewed and discussed in the context of their tuning parameters, strengths and weaknesses. These strategies comprise bottom-up approaches as well as top-down approaches. In bottom-up approaches nanoparticles are synthesized in a fi rst step by chemical, photochemical or sonochemical means followed by an electrode formation step by e.g. thin fi lm technology or network formation to create a contiguous and conducting solid electrode structure. In top-down approaches fabrication starts with an already conductive electrode substrate. Corresponding strategies enable the fabrication of substrate-based electrodes by e.g. electrodeposition or the fabrication of self-supporting electrodes by dealloying. As a further top-down strategy, this review describes methods to decorate porous metals other than platinum with a surface layer of platinum. This way, fabrication methods not performable with platinum can be applied to the fabrication of platinum electrodes with the special benefit of low platinum consumption.

Hydrogen evolution catalyzed by electrodeposited nanoparticles at the liquid/liquid interface

Hydrogen evolution by decamethylferrocene in 1,2-dichloroethane can be catalyzed efficiently by platinum and palladium nanoparticles electrogenerated in situ at the liquid–liquid interface.

Potentiometric Sensor for Heparin Polyion: Transient Behavior and Response Mechanism

Chronopotentiometry and electrochemical impedance spectroscopy were used to study the transient behavior and the potentiometric response mechanism of the polymer membrane-based sensor for heparin. Membrane with a composition of 66 wt % poly(vinyl chloride), 33 wt % o-nitrophenyl octyl ether (plasticizer), and 0.05 M tridodecylmethylammonium chloride (ion exchanger) was deposited on the surface of a silver or a glassy carbon (GC) electrode. In the latter case, the membrane contained also 0.1 M 1,1'-dimethylferrocene/1,1'-dimethylferricenium+ couple ensuring the electronic contact between the membrane and GC. The sensor was dipped in an aqueous solution of 0.1 M LiCl, which was stirred with a magnetic stirrer (2-18.2 Hz), and eventually spiked with heparin (0.05-5 U mL-1). Chronopotentiometric measurements were carried out using either the Ag supported membrane with a thickness>100 microm or the GC supported membrane with a defined thickness of 2-30 microm, which was also used in impedance measurements. Remarkable features of the potentiometric response include the linear dependence of the initial slope of the potential transient on the heparin concentration in the aqueous phase and on the square root of the stirring frequency, and the absence of the effect of the membrane thickness. Impedance measurements (0.1 Hz-10 kHz) made it possible to identify and to evaluate the geometric capacitance and the capacitance of the electric double layer at the membrane/solution interface, the bulk membrane and charge-transfer resistances, and the Warburg impedance of the chloride transport. Changes in the membrane bulk and charge-transfer resistances and the Warburg impedance upon spiking the aqueous solution with heparin were found to be consistent with the steady-state response of approximately -25 mV, indicating that the bulk chloride concentration in the membrane decreased to about half of its initial value. A novel theoretical model of the transient behavior was developed based on the balance of the charging and the faradic currents of chloride and heparin, in accordance with the ion-exchange mechanism that has been proposed previously. It was concluded that the initial slope of the potential transient is linked to the charging of the double layer coupled to the chloride ion transfer across the membrane/solution interface and to the diffusion-limited transport of heparin in the solution. The potentiometric assay of heparin could be based on measurements of the initial slope of the potential transient or the potential at a fixed time shortly after the heparin injection.