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The work herein describes the electrochemical detection of heavy metal ions, specifically cadmium and lead. The introduction and modification of functional groups such as Schiff bases leads to an enhanced sensitivity of the electrode to analytes. In this study, a platinum electrode has, for the first time, been modified with poly(3,4-ethylenedioxythiophene) (PEDOT/Schiff base) in CH2Cl2 containing Bu4NPF6 to detect cadmium(II) and lead(II) ions. The structures and morphologies of the polymer coatings were characterised via Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. The electrochemical synthesis and redox state response in monomer-free synthesised films have been studied via cyclic voltammetry. Moreover, the effect of scan rate on the electrochemical behaviour of the modified electrodes was also studied. The voltammetric findings have been used to calculate the surface coverage required for the polymer films and the stability of polymer electrodes in the monomer-free solutions. Square wave voltammetry was applied for the determination of cadmium(II) and lead(II) ion concentrations and to assess the effects of pH on aqueous samples. The limits of detection for the modified electrode for cadmium(II) and lead(II) were found to be 0.95 μg L−1 and 1.84 μg L−1, respectively. These findings revealed that modified films can be considered good candidates for application in electrochemical detection devices.

In this study, a new type of multifunctional material PANI/NiO/MnO2 nanocomposite was first time prepared by chemical polymerisation from aniline monomer in the presence of metal oxides (NiO and MnO2) and an oxidant (ammonium persulfate) in acidic aqueous solution for the elimination of methyl orange (MO) dye from water. Herein, the PANI/NiO/MnO2 nanocomposite was found to be a favourable adsorbent for wastewater treatment due to its high adsorption and efficiency, self-regeneration, low cost and easy synthesis. Fourier transform infrared spectroscopy, X-ray diffraction, thermo-gravimetric analysis, transmission electron microscopy, scanning electron microscopy, Brunauer–Emmett–Teller analysis and Zeta potential were employed to characterise the synthesised nanocomposites. The data revealed that PANI nanocomposites doped with NiO and MnO2 nanoparticles had a higher adsorption efficiency (~ 97%) than that found in pure PANI (~ 53%). The adsorption conditions, such as pH of the medium, initial dye concentration, adsorbent dosage, and adsorption time were investigated. Various kinetic and isotherm models were used to analyse the results of the kinetics and the equilibrium adsorption and to interpret the interaction between the dye and nanocomposite adsorbents. The adsorption kinetics data for MO dye on the PANI/NiO/MnO2 were well explained based on a pseudo-second-order model while adsorption isotherm results were analysed based upon the Langmuir isotherm model. In addition, the adsorption process was an endothermic, favourable and spontaneous reaction according to thermodynamic studies. Also, the influence of matrix synthetic waste on MO dye removal was studied and found to show good results with matrix synthetic waste for both PANI/NiO/MnO2 and PANI adsorbents. The experimental adsorption capacity of the PANI/NiO/MnO2 nanocomposite (248.4 mg/g) was considerably greater than that of PANI (57.5 mg/g). The PANI/NiO/MnO2 adsorbent can be recycled up to four times and maintains a good adsorption capacity throughout.

The electrodeposition of cobalt from alternative electrolytes, including ionic liquids and deep eutectic solvents (DES), has become a topic of great interest to the scientific community, with a significant impact in both academic circles and in the development of commercial industrial electrochemical processes. However, very few studies have considered the effects of water on the electrodeposition of metals from deep eutectic solvents. In this work, the electrodeposition of Co from a choline chloride (ChCl) ethylene glycol (EG)-based deep eutectic solvent (DES) containing 10%, 20% and 30% water has been studied, and for the first time a uniform and bright Co deposit has been obtained when the deposition was achieved from an electrolyte containing 20% water. The speciation of Co in a mixed 1:2 ChCl:EG-based liquid (Ethaline 200) has been studied in both the absence and presence of water. The conductivities of the Co electrolyte were increased with increasing amounts of water. The electrochemical properties of the Co electrolytes have been studied using cyclic voltammetry, where it was found that the redox peak current gets larger and shifts in a positive direction when water was included in the Co solution. The resultant surface morphologies, topography, and roughness of the Co deposits were revealed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), which demonstrated that a highly uniform and smooth cobalt coating had been produced when the deposition occurred in Ethaline 200 containing 20% water.

The use of additives to modulate metal electrodeposition from deep eutectic solvents has, to date, apparently been of little interest given the dearth of such studies in the literature. Here, we have actively investigated the effects of nicotinic acid (NA) on the electrodeposition of copper in a choline chloride (ChCl)-ethylene glycol (EG)-based deep eutectic solvent (DES), (1ChCl:2EG), considered a “green solvent” due to its physiochemical properties. Bright copper deposits were formed when NA was added to the Cu electrolyte, while a dull Cu deposit was produced in its absence. New Cu species were found to have formed in the 1ChCl:2EG-based liquid when NA was added to the electrolyte. A number of analytical techniques, in this instance cyclic voltammetry, chronoamperometry, and chronocoulometery, have been employed to determine the various electrochemical properties, nucleation mechanisms, and kinetics of the Cu species reported herein. The diffusion coefficient for the Ethaline-Cu system was found to be affected by the concentration of NA. An electrochemical quartz crystal microbalance (EQCM) was used to monitor the current efficiency of the copper deposition in both systems. The morphologies, thicknesses, roughnesses, and crystal structures of the copper electrodeposited from the NA-modified electrolyte were characterised via scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD), which between them demonstrate that the NA introduced into this system acts as a highly effective brightener, producing highly uniform and smooth copper deposits.

We report herein the electrochemical polymerisation of aniline from a choline chloride (ChCl)-based deep eutectic solvent (DES) at room temperature in both the presence and absence of deionised water in the solvent. The current study used Propeline as the DES electrolyte, which we found to be rich in protons (i.e. similar to protic ionic liquids) and which allowed the polymerisation of aniline in this system. The morphology of films was characterised by scanning electron microscopy (SEM) and atomic force microscopy (AFM), which showed the polymer film to have a compact structure and rough surface. The electrochemical quartz crystal microbalance (EQCM) was used for the first time to investigate the mass changes that occur during the electrochemical deposition of polyaniline (PANI) in situ, and was used to monitor cation, anion, and solvent transport when PANI films were immersed in pure Propeline and 0.5 M H2SO4 solution (monomer free) at 25 °C and 50 °C. In the case of the PANI exposed to pure Propeline at room temperature, the mass change increased continuously in both oxidation and reduction switching due to anion transfer dominating the mass change, while the PANI exposed to pure Propeline at 50 °C was found to form due to a two-step combined mechanism, showing excellent redox switching stability with changing mass. These variations in mass tend to be dominated by cation expulsion in the first oxidative process (the later reductive process being cation insertion) and by anion insertion in the second oxidative stage (the early reductive process being anion expulsion). In aqueous systems, the mechanism of mass change was dominated by anion movement associated with solvent transfer. The movement of neutral species in Propeline and water is in the reverse direction to those of cation or anion transfer.

The work herein concentrates on the electrochemical detection of heavy metal ions, specifically cadmium and lead ions. The introduction and modification of functional groups such as Schiff bases had led to an enhanced sensitivity of the electrode to analytes. In this study, a platinum electrode has for the first time been modified with poly(3,4- ethylenedioxythiophene) (PEDOT/Schiff base) in CH2Cl2 containing Bu4NPF6 for use to detection cadmium (II) and lead (II) ions. The structure and morphology of the polymer coatings were characterised by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM), respectively. The electrochemical synthesis and redox state response in monomer-free synthesised films have been studied by cyclic voltammetry. Moreover, the effect of scan rate on the electrochemical behaviour of the modified electrodes was also studied. The voltammetric findings have been used to calculate the surface coverage required for the polymer films and the stability of polymer electrodes in the monomer-free solutions. Square wave voltammetry (SWV) was applied for the determination of cadmium (II) and lead (II) ion concentrations and to assess the effects of pH on aqueous samples. The limits of detection for the modified electrode for cadmium (II) and lead (II) were found to be 0.95 μg L-1 and 1.84 μg L-1, respectively. These findings revealed that modified films can be considered good candidates for application in electrochemical detection devices

Electroactive polymers such as polyaniline and its derivatives have many potential applications, but the nature of the dopants can have an adverse effect on their properties. Polyaniline (PANI), poly(o-methoxyaniline) (POMA) and poly(o-toluidine) (POT) have been synthesised using appropriate organic acid dopants (2-naphthalenesulfonic acid and 1,5-naphthalenedisulfonic acid) via electrochemical and chemical polymerisation methods, where the later was achieved at pH (1–2) in the presence of ammonium persulfate as an oxidant. The effects of the monomers and organic dopants on the physiochemical properties and morphological surface of the polymers were studied by means of Fourier transform infrared spectroscopy, electrical conductivity measurements, thermogravimetric analysis and scanning electron microscopy (SEM). The above films were also synthesised electrochemically whilst varying conditions such as scan rate, scan number and in aqueous solution of organic acids using cyclic voltammetry techniques. Cyclic voltammetry experiments have been employed to analyse the growth behaviour and electrochemical stability of films in the background electrolytes (monomer-free). It was found that PANI salts displayed higher doping levels and conductivity while POMA and POT salts were found to show lower conductivity and doping levels, respectively. Furthermore the electrochemical response of films was different in the stability and this may be because of the methoxy (–OCH3) and methyl (–CH3) groups located at the ortho position of the aromatic ring structure of the monomers (o-methoxyaniline and o-toluidine). The –OCH3 and–CH3 groups have significant steric effects and can reduce to form long chains of polymers and also decrease conductivity. The SEM showed that the morphologies of the prepared conducting polymers were different, which was associated with the nature and size of the dopant and monomer present in the bath solution.

This work will show, for the first time, the effect of nicotinic acid (NA) and 2-methylnicotinic acid (MNA)on the synthesis and properties of conducting polyaniline (PANI). The work investigates the effects of sulphuric acid (H2SO4), nicotinic acid (NA), and 2-methylnicotinic acid (MNA) on the synthesis and properties of polyaniline. The results show that the preparation of polyaniline from a sulphuric acid electrolyte is faster than the preparation from nicotinic acid and 2- methylnicotinic acid electrolytes. Moreover, the electrical conductivity and thermal stability of PANI/H2SO4 were greater than PANI/NA and PANI/MNA. All the polymers prepared in this study were identified using FT-IR. Scanning electron microscopy (SEM) was used to examine the morphologies of the PANI samples, from which it was determined that PANI/H2SO4 has a fibrous and open structure with a higher porosity morphology compared to PANI/NA and PANI/MNA. The electrical conductivities of the PANI samples were measured as 1.09 S cm-1, 0.65 S cm-1 and 0.089 S cm-1 for PANI/H2SO4, PANI/NA and PANI/MNA, respectively. The thermal stability of PANI was examined using the Thermogravimetric Analysis (TGA) technique. PANI/H2SO4 was found to degrade between 450-500°C, while PANI/NA and PANI/MNA decomposed at temperatures between 300-400°C.

Electroactive films based on conducting polymers have numerous potential applications, but practical devices frequently require a combination of properties not met by a single component. This has prompted an extension to composite materials, notably those in which particulates are immobilised within a polymer film. Irrespective of the polymer and the intended application, film wetting is important: by various means, it facilitates transport processes – of electronic charge, charge-balancing counter ions (“dopant”) and analyte/reactant molecules – and motion of polymer segments. While film solvent content and transfer have been widely studied for pristine polymer films exposed to molecular solvents, extension to non-conventional solvents (such as ionic liquids) or to composite films has been given much less attention. Here we consider such cases based on polyaniline films. We explore two factors, the nature of the electrolyte (solvent and film-permeating ions) and the effect of introducing particulate species into the film. In the first instance, we compare film behaviours when exposed to a conventional protic solvent (water) with an aprotic ionic liquid (Ethaline) and the intermediate case of a protic ionic liquid (Oxaline). Secondly, we explore the effect of inclusion of physically diverse particulates: multi-walled carbon nanotubes, graphite or molybdenum dioxide. We use electrochemistry to control and monitor the film redox state and change therein, and acoustic wave measurements to diagnose rheologicallyvs.gravimetrically determined response. The outcomes provide insights of relevance to future practical applications, including charge/discharge rates and cycle life for energy storage devices, “salt” transfer in water purification technologies, and the extent of film “memory” of previous environments when sequentially exposed to different media.

Novel polyaniline (Pani) and/or graphite (Gr)/molybdenum dioxide (MoO2) composites have been successfully synthesised via an in situ chemical polymerisation method using a Deep Eutectic Solvent (DES) as the electrolyte. The chemical structure and properties of the Pani composites were characterised using various analytical techniques such as Raman, FTIR and UV–Vis spectroscopies, Thermo-Gravimetric Analysis (TGA), X-ray diffraction (XRD) and conductivity measurements, confirming its semi-crystalline nature. The results show shifts in the Raman, XRD and FTIR spectral features associated with the Pani composites, indicating that a matrix of metal oxide and/or graphite had formed in the polymer. Higher electrical conductivity was observed for the Pani/Gr (5.58 S cm−1) and Pani/Gr/MoO2 (9.87 S cm−1) composites compared to pure Pani (1.25 S cm−1). The homogenous growth of Pani chains on the graphite and MoO2 network were clearly observed by Scanning Electron Microscopy (SEM) and Energy Dispersive Analysis by X-ray (EDAX). A larger surface area and greater porosity were achieved in the Pani/MoO2, Pani/Gr/MoO2 and Pani/Gr samples, while a more compact structure was obtained for the Pani sample. These findings support that the idea that the polymer/graphite composites would be more useful for electrochemical charge transport, supercapacitance and energy storage applications compared to those using the pure polymer alone.

This work presents an efficient and facile electrodeposited nickel using an organic additive, namely hydantoin (HD) from choline chloride and ethylene glycol in 1:2 mol ratio. It has also been shown that a relatively high brightness of the nickel deposits. The electrochemical properties of the Ni electrolyte in the absence and presence of HD have been examined via cyclic voltammetry, chronocoulometry, and chronoamperometry. The inclusion of HD causes the deposition potential of nickel to shift to more negative overpotentials. From the UV-spectra, it has been confirmed that the speciation of the nickel solution remained unchanged even over a wide range of temperature and coordination environments around the nickel centre. The presence of HD participates in interfacial region, in other words, acts an effective species in the nucleation and growth mechanisms of Ni deposition. A mirror-like and shiny nickel layers free of crystal grain have been achieved in the presence of HD when hydantoin was utilized as an effective additive. From the x-ray diffraction (XRD), the impact of the HD additive on the crystal growth along the [2 0 0] and [2 2 0] orientations during bulk deposition has been proved.

A number of studies have reported the effects of additives on metal coatings electrochemically deposited from deep eutectic solvents (DESs). However, no previous study has investigated the influences of methyl nicotinate (MN) as an additive on the electrodeposition of zinc on a copper substrate from a DES. The results of this investigation show that MN significantly develops the Zn deposition in this system compared to the corresponding system in its absence. This is the first study to date to show that a mirror zinc coating can be obtained on a copper substrate using such a mechanism. Various electrochemical methods such as cyclic voltammetry, chronocoulometry, and chronoamperometry have been used to understand the electrochemical properties of Zn electrolytes in the absence and presence of MN. These experiments found that the redox reaction currents decline when the additive was included in the Zn electrolyte, and that Zn deposition followed an instantaneous nucleation mechanism in the absence of the additive while in its presence the mechanism was closer to that of progressive growth. Further, the current efficiency decreased from 98.99% in the absence of additive to approximately 82% as a result of including the additive in the Zn plating bath, according to electrochemical quartz crystal microbalance (EQCM) data. The resultant roughness, thickness and surface morphology of the deposited zinc were characterised using atomic force microscopy, scanning electron microscopy, and X-ray diffraction, indicating that methyl nicotinate, as an additive, functions as a highly influential brightener that allows the formation of highly homogeneous and flat zinc deposits.

The effects of additives on the electrodeposition of Zn Sn alloy from aqueous electrolyte have been the subject of considerable interest in the literature; however, to date there has been little consideration of their effects on alloy electrodeposition from Deep Eutectic Solvents (DESs). This work will show, for the first time, the effects of boric acid, ammonium chloride and nicotinic acid on the electrodeposition of Zn Sn alloys on copper from a DES consisting of a stoichiometric 1:2 mix of choline chloride and ethylene glycol (Ethaline 200). Cyclic voltammetry has been used to study the electrochemical properties of the Zn Sn electrolyte, and the resultant surface morphologies, composition and roughness of the Zn Sn coating were revealed via SEM/EDX and AFM, demonstrating that boric acid and nicotinic acid function as very effective brighteners, producing highly uniform and smooth Zn Sn deposits. It was found that these additives strongly affect the morphology, composition, and roughness of the Zn Sn coating. XRD was also used to examine the crystal structure of Zn Sn coatings, where it was found that the phase composition of the deposits depends on the additive(s) used. In addition, corrosion of the Zn Sn alloy in salty media was measured using the Tafel method.

The electropolymerisation of aniline is a well-studied and often used technology. While the mechanism has been investigated in a variety of media these have all concentrated on understanding the process on a molecular level. Anomalies in the electropolymerisation of aniline in four deep eutectic solvents, DESs, using urea, ethylene glycol, glycerol and oxalic acids as hydrogen bond donors with choline chloride led to an investigation of the aniline phase behaviour. It was only with oxalic acid that polymerisation was achieved and adjusting the pH of the other DESs using sulphuric acid did not enable polymer formation suggesting that pH was not the only factor enabling polymer growth. When 10 wt% water was added, polymers could be grown in all the DESs despite negligible change in solution pH. Dynamic light scattering showed that polymer only formed in systems where aniline formed an emulsion. Scanning electron microscopy, SEM and atomic force microscopy, AFM showed that the polyaniline films were formed of an agglomeration of small particles of the same dimensions as the dispersed monomer phase in solution. This suggests that the droplets of the monomer arrive at the electrode surface where they polymerise. This provides the first evidence that polyaniline grows by an emulsion polymerisation mechanism even in aqueous solutions.

Electroactive polymer films derived from aniline and substituted derivatives have attracted huge interest, as a consequence of their electronic, optical, chemical and charge storage properties. Surprisingly, there has been limited translation of these characteristics into practical devices. Two factors that have impeded progress here are an inability to deliver and optimise multiple characteristics in a single material and the absence of control of internal film structure. The latter is particularly difficult to maintain for soft matter, whose molecular geometry and spatial disposition at the mesoscopic scale necessarily changes in response to solvent influx/efflux during redox switching. These solvation phenomena have been variously described in terms of activity (thermodynamic) effects, volume constraints (polymer mechanical properties) and mobility (kinetic) effects. Quite generally, the dominant factor depends on the timescale, a feature of the experiments reported here. In this presentation, we explore strategies aimed at understanding and controlling internal film structure and solvation for polymer films based on aniline-type monomers. From a chemical perspective, we explore the effects of three factors: the nature of the solvent / electrolyte, extension from homopolymers to co-polymers, and the inclusion of geometrically distinct particulate species to generate hybrid organic/inorganic materials. In the first instance, we compare film deposition and subsequent redox chemistry when exposed to a conventional protic solvent (water) or to the aprotic ionic liquid Ethaline (a mixture of choline chloride and ethylene glycol). As an intermediate case, we consider film deposition and redox chemistry in the protic ionic liquid Oxaline (a mixture of choline chloride and oxalic acid). Quantitative nanogravimetric (QCM) measurements during deposition from ionic liquid reveal that the polymer film has substantially greater solvent content than if deposited from aqueous medium. A recognised phenomenon for electroactive polymer films is an anomalous response for the first redox cycle; this is generally attributed to solvation effects. This phenomenon is manifested quite differently for polyaniline films in water and Ethaline. In water, film evolution occurs over a number of cycles, while in Ethaline (in which the film is more highly solvated) the transition is complete with a single cycle. In the second instance, we consider copolymerization of aniline with o-toluidine or with o-aminophenol. Counter ion coordination by the hydrogen bond donors results in substantive differences in the effectively transferred entity. In the cases of Ethaline and Oxaline, the counter ion is no longer a small, mobile chloride ion, but rather a large hydrogen bond donor-coordinated species. In pursuit of possible environmental applications, we consider the extreme case of fluoride as a counter ion. Surprisingly, the relatively small changes in polymer composition effected by co-polymerisation with o-toluidine or o-aminophenol result in substantial changes in fluoride uptake. Finally, we explore the effect of inclusion of particulates, chosen so as to influence different aspects of film behaviour. Specifically, we chose multi-walled carbon nanotubes (MWCNT), graphite flakes and molybdenum oxide particles as examples of 1D, 2D and 3D entities, respectively. Electrochemical and imaging data will be presented to demonstrate their substantive effects on film structure and dynamics. The outcomes of these studies provide insights relevant to practical applications. A particular case is that of medium transfer experiments, in which a film is deposited from one medium (aqueous or ionic liquid), redox cycled in the second and then returned to the first. We discuss the responses in terms of a “nature vs nurture” competition, in which the “nature” of a film is dictated by the conditions (medium) of deposition, and “nurture” is represented by the conditions to which it is exposed. Nanogravimetric (EQCM) responses of films subjected to water / ionic liquid / water and ionic liquid / water / ionic liquid transfer experiments reveal that films do retain some memory of their deposition conditions, but that extended redox cycling results in slow evolution that reflects the immediate medium of exposure. We discuss this in terms of slow polymer structural relaxation.