Ferrocene In Solution Research Articles

Development of an in situ Mediator Dosing Concept for Scanning Electrochemical Microscopy in Lithium‐Ion Battery Research

AbstractIn scanning electrochemical microscopy (SECM), the addition of a redox active species plays an essential role. Those deliberately added mediators may alter results in SECM studies. In investigations of lithium‐ion battery (LIB) materials, especially of the positive electrode, the oxidation potentials of commonly used mediator substances such as ferrocene are located within the operation potential of the electrode. Thus, they possibly interfere with the regular charge/discharge processes. In situ studies are therefore in need of approaches reducing or eliminating the use of mediators. Within this publication, a novel mediator dosing (MD) concept is introduced. A capillary was closely positioned at the tip of the scanning probe. By gravity flow, stable flow rates of mediator solution of up to 32.4±0.6 μL h−1 were achieved. These low amounts were found to be sufficient to form a ferrocene zone at the probe tip enabling feedback mode SECM measurements with comparable quality to measurements directly in ferrocene solution. Proof of concept experiments were conducted by investigation of a thin‐film electrode with a micro‐structured surface. Furthermore, the MD concept was applied in imaging experiments of a commercially available LIB graphite electrode.

FERROCENE DISPROPORTIONATION REACTIONS IN A PLASMA-LIQUID SYSTEM WITH A ROTATING GLIDING DISCHARGE

A plasma-liquid system with the activation of H2O distillate and 0.1 M ferrocene solution in organic solvents (ethanol, acetonitrile) with a rotating gliding discharge plasma was studied. The research was conducted using various plasma-forming gases (air, Ar, N2, CO2). Determination of plasma parameters was performed by plasma emission spectroscopy methods. It was shown that the plasma of both the rotating gliding discharge and the plasma of the secondary discharge supported by the gliding discharge are non-isothermal. The study of the physicochemical properties of the synthesis products was performed by adsorption, luminescence analysis, polarimetry, chromatographymass spectrometry and NMR methods. It was found that cyclopentadiene ligands of ferrocene disproportionate into saturated cyclic hydrocarbons (cyclopentane and pentane). Also, as a result of plasma chemical synthesis, aromatic compounds (benzene and its derivatives) are formed.

A General Strategy for Increasing the Air Stability of Phosphines Including Primary Phosphines.

A general approach for increasing the air-stability of various primary phosphines in the absence of kinetic stabilization is presented that contrasts with previous interpretations, which were limited to specific phosphines. This contribution shows the synthesis of a series of air-stable primary phosphines Fc(CH2 )n PH2 , where n=0,1,2,3; and Fc=ferrocenyl, and their corresponding isolable primary phosphine oxides. It was demonstrated that the ferrocene moiety exerts an antioxidant effect on the primary phosphine group, which is intermolecular, solvent dependent and increases with the electron density on the ferrocene moiety. Furthermore, we demonstrated that the presence of ferrocene in solution also inhibits the oxidation of other secondary and tertiary phosphines in air. Together our findings suggest that quenching of singlet oxygen is the actual reason for the antioxidant effect; this was experimentally confirmed by using other established singlet oxygen quenchers, thus demonstrating a key role of singlet oxygen in the aerobic oxidation of phosphines.

Electron Transport through Nanoconfined Ferrocene Solution: Density Functional Theory─Nonequilibrium Green Function Approach

We investigate the transport of electrons in a ferrocene aqueous solution nanoconfined between two Pt electrodes using density functional theory and a nonequilibrium Green function method. The system consists of three characteristic phases: metal electrodes, the electrode–solution interface, and the nanoconfined solution phase. By performing the geometry optimization of such systems, it is found that the molecular configuration of water molecules at the Pt surface is adjusted due to the Pt–water interaction, and the charges at the Pt surface are redistributed. Next, by applying the external bias potential via the effective screening medium method during ab initio molecular dynamics simulations, it is revealed that water molecules are packed at the Pt–water interfacial region, and the electrostatic potential profile in the water phase is significantly changed due to aligned water layers. From the analysis of the electron transport characteristics, it is discovered that the ferrocene molecule generates a strong transmission function near the Fermi level and high electron density of states spatially connecting both electrodes through the water phase. These features explain the drastic enhancement in electrical current–voltage characteristics. Therefore, it is concluded that ferrocene enhances electron transport through nanoconfined solutions, indicating that it can be used as a signaling molecule in nanoscale systems for electrochemical sensor applications.

Insights into the formation of multiwall carbon nanotubes using simple flame pyrolysis method

Herein, we discuss the formation of multiwall carbon nanotubes (MWCNTs) during the simple and effective flame pyrolysis of ferrocene solution in ethanol with the help of alcohol lamp. The method is unique and simple one to prepare impure MWCNTs in the best possible way. Systematic investigations showed that the in-situ generated maghemite plays an important role in the formation and development of the MWCNTs. The growth of the maghemite impregnated MWCNTs were thoroughly studied using sophisticated instruments viz. XRD, BET, HR-SEM, and TEM analysis in details and on the basis of these, the growth mechanism is discussed.

Recognition of Heavy Metal Ions by Using E-5-((5-Isopropyl-3,8-Dimethylazulen-1-yl) Dyazenyl)-1H-Tetrazole Modified Electrodes

Chemically modified electrodes (CMEs) based on polymeric films of E-5-((5-isopropyl-3,8-dimethylazulen-1-yl) diazenyl)-1H-tetrazole (L) deposited on the surface of the glassy carbon electrode have been used for the recognition of heavy metal (Me) ions. The electrochemical study of L was done by three methods: differential pulse voltammetry (DPV), cyclic voltammetry (CV), and rotating disk electrode voltammetry (RDE). The CV, DPV, and RDE studies for L were performed at different concentrations in 0.1 M tetrabutylammonium perchlorate solutions in acetonitrile. The polymeric films were formed by successive cycling or by controlled potential electrolysis (CPE). The film formation was proven by recording the CV curves of the CMEs in ferrocene solution. The CMEs prepared at different charges or potentials were used for detection of heavy metal ions. Synthetic samples of heavy metal ions (Cd(II), Pb(II), Cu(II), Hg(II)) of concentrations between 10−8 and 10−4 M were analyzed. The most intense signal was obtained for Pb(II) ion (detection limit of about 10−8 M). Pb(II) ion can be detected by these CMEs in waters at such concentrations. The ability of the ligand L to form complexes with Pb(II) and Hg(II) ions was also tested by UV-Vis spectrometry. The obtained results showed the formation of Me(II)L2 complexes.

The ferrocenium/ferrocene couple: a versatile redox switch

Woodward and co-workers in 1952 characterised the unique structural features of ferrocene (the first sandwich compound), demonstrated its aromatic nature and observed that on treatment with mild oxidising agents (aqueous Ag2SO4, p-benzoquinone in organic solvents) the orange solution of ferrocene (Fc) turned blue due to the formation of ferrocenium (Fc+). A few months later, the one-electron Fc/Fc+ redox change was characterised polarographically by Page and Wilkinson with E1/2 = 0.31 V vs SCE (0.56 V vs NHE) in ethanol/water 9:1. Since then ferrocene has become an icon of organometallic electrochemistry. Owing to the stability of its molecular framework, to the ease of functionalisation at the cyclopentadienyl rings and to the fast, reversible and kinetically uncomplicated Fc/Fc+ redox change, ferrocene has been used as a building block for the design of switchable functional systems. In this review, we will consider (1) electrochemical sensors for metal ions, anions and metal–anion pairs operating through the Fc/Fc+ redox change, (2) ferrocene-based redox switches of fluorescence and (3) cross-transport of electrons and anions through a liquid membrane mediated by lipophilic ferrocene derivatives.Graphic abstract

Tapered Optical Fiber Detector for a Red Dye Concentration Measurement.

In this work, a detector based on optical fiber covered with Multi-Wall Carbon Nanotubes (MWCNTs) was used for sensing and removal of Alizarin from wastewaters. Alizarin is a strong anionic red dye that is part of the anthraquinone dye group. As a rule, this dye is used in the textile industry as a coloring agent. Experiments showed a good efficiency of wastewater treatment. This development could resolve the problem of water contamination with Alizarin red dye. We used a single-mode fiber SMF-28e with a core diameter of 8.2 μm and a cladding diameter of 125 μm as a base for the tapered optical fiber detector. An MWCNTs array was synthesized on the tapered optical fiber detector surface by spray pyrolysis Chemical Vapor Deposition (CVD) method at 800oC for 20 min inside a tubular furnace, using ferrocene solution in toluene as a catalyst precursor. The formed structure was applied for Alizarin detection in water. According to the patent studies, the nanotubes completely covered the optical fiber surface and the array had a high density with minimal distance between nearby nanotubes. Carbon nanotubes were oriented along the radius of the optical fiber. The average diameter of carbon nanotubes was 24 nm. The optical absorbance levels increased as the Alizarin concentration increased from 50 mg/L to 1000 mg/L. MWCNTs on the optical fiber tapered section adsorbed the dye molecules from aqueous solution. Three intensive absorption bands with the wavelength of the 700, 714 and 730 nm appeared and their intensity increased as the Alizarin concentration increased. The accumulated Alizarin can be recovered by multiple immersing clean water. This property may make tapered optical fiber detector reusable and increase the economic expediency of the sensor application. The study showed higher Alizarin adsorption efficiency of the tapered optical fiber detector compared with relative detectors. This structure can be reusable for dye detection. Removal efficiency for Alizarin reached 98.6%, which makes the tapered optical fiber detector promising for wastewater treatment and dye elimination.

Oxygenated Surface of Carbon Nanotube Sponges: Electroactivity and Magnetic Studies.

We report the synthesis of nitrogen-doped carbon nanotube sponges (N-CNSs) by pyrolysis of solutions of benzylamine, ferrocene, thiophene, and isopropanol-based mixture at 1020 °C for 4 h using an aerosol-assisted chemical vapor deposition system. The precursors were transported through a quartz tube using a dynamic flow of H2/Ar. We characterized the N-CNSs by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and thermogravimetric analysis. We found that isopropanol, isopropanol–ethanol, and isopropanol–acetone as precursors promote the formation of complex-entangled carbon fibers making knots and junctions. The N-CNSs displayed an outstanding oxygen concentration reaching a value of 9.2% for those synthesized with only isopropanol. We identified oxygen and nitrogen functional groups; in particular, the carbon fibers produced using only isopropanol exhibited a high concentration of ether groups (C–O bonds). This fact suggests the presence of phenols, carboxyl, methoxy, ethoxy, epoxy, and more complex functional groups. Usually, the functionalization of graphitic materials is carried out through aggressive acid treatments; here, we offer an alternative route to produce a superoxygenated surface. The understanding of the chemical surface of these novel materials represents a huge challenge and offers an opportunity to study complex oxygen functional groups different from the conventional quinone, carboxyl, phenols, carbonyl, methoxy, ethoxy, among others. The cyclic voltammetry measurements confirmed the importance of oxygen in N-CNSs, showing that with high oxygen concentration, the highest anodic and cathodic currents are displayed. N-CNSs displayed ferromagnetic behavior with an outstanding saturation magnetization. We envisage that our sponges are promising for anodes in lithium-ion batteries and magnetic sensor devices.

Spectroscopic Study of Large-Scale Synthesized, Nitrogen-doped carbon Nanotubes using Spray Pyrolysis Technique

Highly pure and aligned nitrogen-doped carbon nanotubes were synthesized by catalytic spray pyrolysis technique at 850°C using precursor; acetonitrile and ferrocene solution. Precursor solution with different concentrations of ferrocene in acetonitrile was introduced into the horizontally aligned reactor at a constant flow rate (∼1ml/min) with Ar gas serving as the carrier (∼50/500l/h). An optimum concentration of ferrocene in acetonitrile is 5mg/ ml. The structure of the synthesized N-CNTs was investigated by means of microscopic (SEM) as well as spectroscopic (FTIR, Raman, XRD, UV-Vis) techniques. The results show that the prepared N-doped CNTs have a uniform structure and high yield of N-CNTs is obtained.

Arrays of vertically aligned multi-walled carbon nanotubes grown on silicon and copper substrates by thermal decomposition of ferrocene-toluene aerosol

Arrays of multi-walled carbon nanotubes (MWCNTs) were grown vertically on the surfaces of SiO2/Si substrates using aerosol-assisted catalytic chemical vapour deposition (CCVD) method. Aerosol was produced by injecting a solution of ferrocene (catalyst source) in toluene (carbon source) into a hot zone of a horizontal CVD reactor. Dependences of the height and density of the MWCNT array on the synthesis temperature and ferrocene concentration were determined. The found optimal parameters were used for the MWCNT growth on copper substrates. For this purpose, a copper foil was covered by alumina layer and we showed that the thickness of this layer should be not less than 17 nm to provide the MWCNT growth over the entire foil surface. The vertically aligned MWCNT array tightly bonded with copper substrate can be used as a heat-exchange surface in various micro and nano heat-transfer devices.

Direct Phosphination of Ferrocenium Ion with Tertiary Phosphines by the Mechanism of Oxidative Nucleophilic Substitution

Ferrocenium salts [(C5H5)2Fe]X (X = BF4, PF6) (I+·) react with tertiary phosphines PR3 (PMe3, PEt3, PnBu3, PMe2Ph, and PMePh2) in dichloromethane at room temperature to form a mixture of the corresponding ferrocenylphosphonium salts [(C5H5)FeC5H4PR3]X (III), ferrocene (I), and phosphonium salts [HPR3]X. The same reaction was carried out in an electrochemical cell as the electrolysis of a solution of ferrocene and phosphine in dichloromethane at the oxidation potential of ferrocene. Possible reaction pathways for phosphination of ferrocenium ion were studied by DFT at the M06‐L/6‐311++G(d,p) theory level. The experimental and theoretical studies of this reaction suggest it to proceed according to the Scheme of oxidative nucleophilic substitution of hydrogen in I+· including the following steps: a) nucleophilic exo addition of a phosphine to the cyclopentadienyl ring of I+· to form the radical cation adduct [(η5‐C5H5)Fe·(η4‐C5H5–+PR3)]X (II+·); b) redox reaction of the initial adduct II+· with the starting ferrocenium salt I+· to result in ferrocene (C5H5)2Fe (I) and iron phosphoniocyclopentadiene dication [(η5‐C5H5)Fe+(η4‐C5H5–+PR3)](X)2 (II2+) where the Csp3–H bond is involved in the agostic interaction with the metal atom; and c) deprotonation of the Csp3–H bond in II2+ by the starting phosphine to form III. The relation between the data obtained and current concepts of C–H functionalization in transition metal arene and cyclopentadienyl complexes is discussed.

Fast and efficient removal of Toluene, Ethylbenzene and O-Xylene from aqueous phase by functionalized carbon micro/nano composites

In this work carbon nanotubes (LCNT) and carbon microspheres (LCM) were prepared by floating catalytic chemical vapor deposition method. 2% solution of ferrocene in benzene was used as the source of hydrocarbon. Further oxidation using nitric acid was carried out to obtain LCNT-OX and LCM-OX. Resultant carbon composites were characterized by various techniques. Adsorption properties of toluene(T), ethylbenzene(E) and o-xylene(X) as a function of equilibration time, pH, initial TEX concentrations were evaluated. Equilibrium of TEX for various carbon composites namely (LCNT, LCNT-OX, LCM, LCM-OX) was attained within 20 min in batch mode. The adsorption kinetics of TEX over various prepared carbon composites followed Pseudo Second Order Kinetics with regression coefficients >0.99. Langmuir and Freundlich isotherms were used to model the obtained equilibrium data and various isotherm constants were evaluated. Maximum adsorption capacity of LCNT, LCNT-OX, LCM and LCM-OX towards o-xylene were found to be 47.17, 72.46, 24.27 and 47.16 mg/g, respectively. It was found that using static adsorption test the TEX adsorption capacity for the carbon composites were in the order of LCNT-OX > LCNT, LCM-OX > LCM. Recyclability studies were demonstrated for 5 cycles without any decrease in the sorption capacity. Column studies revealed that 50 bed volumes of (950 ml) of 30 ppm toluene containing distilled water could be treated reducing the concentration from 30 ppm to below detection limit using 3 mg of LCNT. Finally, faster kinetic and its application to remove TEX from ground water demonstrated its applicability as pre-concentration cartridges and real waste water streams.

Oil-in-water microemulsion containing ferrocene: A new fire suppressant

This paper reports the preparation and fire-suppression efficiency of oil-in-water microemulsions containing ferrocene. In this work, oil-in-water emulsions containing 0–1000 ppm ferrocene and four surfactants (Surfynol 465, Olfin E1020, Triton X-100 (TX), and Noigen TDS-80 (NT)) were prepared by homogenizing n-octane solutions of ferrocene and aqueous surfactant solutions at ambient temperature. Four emulsion parameters were then characterized: emulsion stability, oil-droplet size in emulsion, flash point, and capability of extinguishing n-heptane pool fires. Emulsion stability experiments and droplet-size measurements clearly demonstrated that the oil-in-water emulsions containing ferrocene and TX/NT were thermodynamically stable microemulsions. Flash-point measurements confirmed that no oil-in-water microemulsions tested ignited below 93 °C. Suppression trials involving microemulsions containing 0–1000 ppm ferrocene and NT revealed the relationship between their fire suppression efficiency and the concentrations of ferrocene and NT, and also demonstrated that the microemulsions tested in this study have a higher ability to suppress pool fires compared with a conventional wet chemical agent.

Hopping mode SECM imaging of redox activity in ionic liquid with glass-coated inlaid platinum nanoelectrodes prepared using a heating coil puller

Major difficulties in nanoscale scanning electrochemical microscopy (SECM), resulting from the short tip-to-sample distance, are tilt misalignment and vertical thermal drift. This renders constant height mode nanoscale electrochemical imaging experimentally problematic. Nanoscale SECM also requires application of reliable nanoprobes. Although SECM nanotips are commercially available, they are rather disposable, fragile and their shelf-life is limited. Many SECM laboratories employ self-prepared nanoprobes, fabricated using advanced apparatus. In this paper, we employ a hopping mode approach to nanoscale electrochemical imaging, which resolves the mentioned common difficulties. The applied platinum nanoelectrodes, insulated with borosilicate glass, were prepared using affordable equipment and materials. They were applied for nanoscale mapping of redox mediator regeneration at a model interdigitated microsensor, composed of Pt microband electrodes, in a solution of ferrocene in viscous hydrophobic room temperature ionic liquid (RTIL) – 1-butyl-3-methylimidazoliumbis(trifluoro-methylsulfonyl)imide (C4mim N(Tf)2). The presented nanosensors were also characterized with cyclic voltammetry in aqueous electrolyte containing hexamineruthenium (III) chloride as redox mediator.

Electrochemical Characterization of Some Pyrrolo[1,2-c]Pyrimidine Derivatives

The electrochemical characterization of two pyrrolo[1,2-c]pyrimidine derivatives (I1 and I2) was realized by cyclic, differential pulse, and rotating disk electrode voltammetric methods. The character of redox processes was established by scanning on different domains and with different scan rates. The diffusion coefficients were determined. Modified electrodes have been obtained by cycling the potential or by controlled potential electrolysis at anodic potentials. The electrodes obtained with polyol1 and polyI2 films were characterized by cyclic voltammetry in ferrocene solution.

Two Sprayer CVD Synthesis of Nitrogen-doped Carbon Sponge-type Nanomaterials

Nitrogen-doped carbon sponge-type nanostructures (N-CSTNs) containing coaxial multiwalled carbon nanotubes are synthesized at 1020 °C by using a modified chemical vapor deposition (CVD) arrangement. Here, the CVD reactor is supplied by two flows coming from two independent sprayers (called sprayer A and sprayer B). The nebulized material in each sprayer is transported by two different gases with different flow velocities. The synthesis of carbon N-CSTNs is performed using different precursors: sprayer A contains a solution composed of ethanol, thiophene and ferrocene, whereas sprayer B contains a solution of benzylamine, thiophene and ferrocene. Samples are classified according to the position inside the reactor and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and thermogravimetric analysis (TGA). Samples collected at the beginning of the reactor contain curly structures with diameters of 10–100 nm. At the end of the reactor, the sample is mainly formed by one type of structure. A spongy-type material is mainly formed in the hottest zone of the tubular furnace. The N-CSTNs are highly hydrophobic with oil sorption properties, which could be used for adsorption of oil spills.

Tuning vertical alignment and field emission properties of multi-walled carbon nanotube bundles

We report the growth of vertically aligned carbon nanotube bundles on Si substrate by thermal chemical vapor deposition technique. Vertical alignment was achieved without any carrier gas or lithography-assisted deposition. Growth has been carried out at 850 °C for different quantities of solution of xylene and ferrocene ranging from 2.25 to 3.00 ml in steps of 0.25 ml at a fixed concentration of 0.02 gm (ferrocene) per ml. To understand the growth mechanism, deposition was carried out for different concentrations of the solution by changing only the ferrocene quantity, ranging from 0.01 to 0.03 gm/ml. A tunable vertical alignment of multi-walled carbon nanotubes (CNTs) has been achieved by this process and examined by scanning and transmission electron microscopic techniques. Micro-crystalline structural analysis has been done using Raman spectroscopy. A systematic variation in field emission (FE) current density has been observed. The highest FE current density is seen for the film grown with 0.02 gm/ml concentration, which is attributed to the better alignment of CNTs, less structural disorder and less entanglement of CNTs on the surface. The alignment of CNTs has been qualitatively understood on the basis of self-assembled catalytic particles.

A flow-through column electrolytic cell for supercritical fluid chromatography.

A novel flow-through column electrolytic cell was proposed as a detector to obtain current signals for supercritical fluid chromatography. The electrochemical cell consisted of two electrodes and its holder, and a working and a counter electrode were fabricated from 192 carbon strings, which were composed of 400 carbon fibers of 10μm in diameter filled into a heat-shrinkable tube. These electrodes were placed in the center of a holder made from polyether ether ketone blocks and they were separated by polytetrafluoroethylene membrane filters. To evaluate the sensitivity of this cell, a standard solution of ferrocene was injected into the supercritical fluid chromatography system connected to the electrolytic cell. The ferrocene was eluted through a silica gel column using a mixture of a mobile phase of supercritical CO2 and a modifier of methanol containing ammonium acetate. The current peak area of ferrocene correlated to the ferrocene concentration in the range of 10-400μmol/L (r=0.999). Moreover, the limit of detection on the column estimated from a signal-to-noise ratio of 3 was 9.8×10-13 mol.

Polyazulene based materials for heavy metal ions detection

Azulene is a special monomer used to functionalize electrodes, due to its spontaneous electron drift from the seven-membered ring to the five-membered ring. The seven-membered ring of the molecule may act as electron acceptor, while the five-membered ring – as electron donor. This leads to very attractive properties for the synthesis of functional advanced materials like: materials with nonlinear optical and photorefractive properties, cathode materials for lithium batteries, or light emitting diodes based on organic materials. Azulene derivatives have been used rarely to the metal ions electroanalysis. Our study concerns the synthesis and electrochemical characterization of a new azulene based monomer 4-(azulen-1-yl)-2,6-bis((E)-2-(thiophen-3-yl)vinyl)pyridine (L). L has been used to obtain modified electrodes by electrochemical polymerization. PolyL films modified electrodes have been characterized by cyclic voltammetry in ferrocene solutions. The complexing properties of polyL based functional materials have been investigated towards heavy metals (Pb, Cd Hg, Cu) by preconcentration – anodic stripping technique in order to analyze the content of these cations from water samples.