Effects of Electroplating Variables on the Voltammetric Properties of Bismuth Deposits Plated Potentiostatically

Bismuth-coated screen-printed electrodes for the simple voltammetric determination of formaldehyde

For the first time, bismuth modified electrodes have been used for the voltammetric detection of formaldehyde (FM). The well-known method of forming formaldehyde hydrazone (FAH) in the presence of hydrazine sulphate was used to convert the hydrated form of FM into its electrochemically active derivative. Various experimental conditions for differential pulse voltammetry were studied to achieve the best analytical performance. The FAH reduction current (FM response) reaches its maximum value at a pH of a phosphate buffer solution of 5.2 ± 0.1 in the presence of 0.09-0.12 M hydrazine sulfate on a bismuth film preliminarily precipitated for 8-12 min from acidic Bi(III) acetate solutions at an electrolysis potential of -1.0 V on the surface of a screen-printed carbon electrode (SPCE). A dendritic-like film structure was created on the SPCE surface. Under the optimized conditions a linear calibration curve over the range of 0.01-5 mg L^-1 (0.33-167 μM) FM was achieved, with a detection limit of 0.002 mg L^-1 (0.06 μM). The determination of FM in waste water, melt water from snow within the city industrial zone, and a widely used pharmaceutical preparation "Endofalk®" with good results revealed the potential applicability of a bismuth modified SPCE (BiSPCE) for trace analysis.

The metal-organic framework supported gold nanoparticles as a highly sensitive platform for electrochemical detection of methyl mercury species in the aqueous environment

Mercury readily methylates to form extremely toxic methylmercury (CH₃Hg⁺) that seriously imparts central nervous systems' functionality in humans and animals. Therefore, the development of rapid CH₃Hg⁺ determination methods for the detection of environmentally relevant concentrations is a research priority. We developed an electrochemical technique to detect CH₃Hg⁺ with minimal sample preparations, cost-effectively. Gold nanoparticles (AuNPs) were synthesized on metal-organic frameworks (MOFs) in a facile way using potassium borohydride as a reductant. An electrochemical sensor was developed using Au nanoparticles and zeolitic imidazolate framework-67 (Au/ZIF67) modified glassy carbon electrode (Au/ZIF67 GCE) for the determination of CH₃Hg⁺. The linear stripping current responses were ranging from 1 µg/L to 25 µg/L [CH₃Hg⁺], with 0.571 µA/µgL^-1 sensitivity and 0.05 µg/L detection limit. The outstanding performance of Au/ZIF67 modified GCE for CH₃Hg⁺ detection might be attributed to the unique hollow structure and active Co sites of the ZIF67 skeleton and catalytic activity of AuNPs. The new electrochemical sensor shows good stability and no interference by metal ions in the matrix. The Au/ZIF67 modified GCE sensor shows a good promise in detecting CH₃Hg⁺ in natural water.

Bismuth/Porous Graphene Heterostructures for Ultrasensitive Detection of Cd (II)

Heavy metals pollution is one of the key problems of environment protection. Electrochemical methods, particularly anodic stripping voltammetry, have been proven a powerful tool for rapid detection of heavy metal ions. In the present work, a bismuth modified porous graphene (Bi@PG) electrode as an electrochemical sensor was adopted for the detection of heavy metal Cd2+ in an aqueous solution. Combining excellent electronic properties in sensitivity, peak resolution, and high hydrogen over-potential of bi-continuous porous Bi with the large surface-area and high conductivity on PG, the Bi@PG electrode exhibited excellent sensing ability. The square wave anodic stripping voltammetry response showed a perfect liner range of 10-9-10-8 M with a correlation coefficient of 0.9969. The limit of detection (LOD) and the limit of quantitation (LOQ) are calculated to be 0.1 and 0.34 nM with a sensitivity of 19.05 μA·nM-1, which is relatively excellent compared to other carbon-based electrodes. Meanwhile, the Bi@PG electrode showed tremendous potential in composite detection of multifold heavy metals (such as Pb2+ and Cd2+) and wider linear range.

The effective determination of Cd(ii) and Pb(ii) simultaneously based on an aluminum silicon carbide-reduced graphene oxide nanocomposite electrode

A platform for the simultaneous determination of Cd(ii) and Pb(ii) in aqueous solution has been applied based on an aluminum silicon carbide-reduced graphene oxide nanocomposite (Al₄SiC₄-RGO) modified bismuth film glassy carbon electrode (GCE) using square wave anodic stripping voltammetry (SWASV) for the first time. The Al₄SiC₄-RGO nanocomposite electrode was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Compared with the Al₄SiC₄ modified GCE and bare GCE, the electrochemical performance of the Al₄SiC₄-RGO nanocomposite electrode is obviously enhanced resulting from the synergistic effects of Al₄SiC₄, RGO and bismuth film. The chemical and electrochemical parameters that exert an influence on the deposition and stripping of metal ions, such as supporting electrolytes, pH values, concentrations of Bi³⁺, deposition potentials and deposition times, were carefully studied. Under optimal conditions, a linear relationship exists between the currents and the concentrations of Cd(ii) and Pb(ii) in the range of 50 to 2700 μg L^-1. The limits of detection (S/N = 3) are estimated to be 1.30 μg L^-1 for Pb(ii) and 2.15 μg L^-1 for Cd(ii). Compared with the related work reported in the literature, the analytical performance in this work has a lower determination limit and a wider detection linear range. In addition, this electrode also exhibits good stability and reproducibility. These results imply that the Al₄SiC₄-RGO nanocomposite might be a promising candidate for practical applications in the electrochemical detection of metal ions.

The Application of Nafion Metal Catalyst Free Carbon Nanotube Modified Gold Electrode: Voltammetric Zinc Detection in Serum

Metal catalyst free carbon nanotube (MCFCNT) whiskers were first used as an electrode modification material on a gold electrode surface for zinc voltammetric measurements. A composite film of Nafion and MCFCNT whiskers was applied to a gold electrode surface to form a mechanically stable sensor. The sensor was then used for zinc detection in both acetate buffer solution and extracted bovine serum solution. A limit of detection of 53 nM was achieved for a 120 s deposition time. The zinc in bovine serum was extracted via a double extraction procedure using dithizone in chloroform as a zinc chelating ligand. The modified electrode was found to be both reliable and sensitive for zinc measurements in both matrices.

Influence of Pb(II) concentration and pH of acetate buffer on the potential window of a lead film electrode: an Atomic Force Microscopy Study

Atomic force microscopy (AFM) studies on observations of lead films deposited from the solutions containing an acetate buffer and different concentration of Pb(II) are presented. AFM images show considerable variability in morphology of the deposited lead layer depending on experimental conditions. To investigate effects of the Pb(II) concentration and pH of the supporting electrolyte on the accessible potential window of the lead film electrode (PbFE), voltammetric techniques were used. It was found that the useful potential window of PbFE is affected by the pH and Pb(II) concentration. Additionally, it was found that the distribution and large size of Pb particles on the electrode surface shown by AFM corresponded well to the mass of Pb expected on the glassy carbon support with respect to the voltammetric data. Results reveal that PbFE is an attractive nonmercury metallic electrode suitable for electrochemical detection of metal ions and a lot of organic compounds in a wide potential window. The accessible potential window of the PbFE in an acetate buffer (pH = 5.0) was compared to those obtained at the bismuth film electrode and antimony film electrode.

Simultaneous determination of ultratrace lead and cadmium by square wave stripping voltammetry with in situ depositing bismuth at Nafion-medical stone doped disposable electrode

An ultrasensitive electrochemical method for simultaneous determination of lead and cadmium was first developed using the novel bismuth-Nafion-medical stone doped disposable electrode (an improved wax-impregnated graphite electrode). Through the synergistic sensitization effect of the resulting composite material, the disposable electrode showed remarkable electrochemical responses to lead and cadmium. The oxidation of the two metals produced two well-defined and separated square wave peaks at about -0.62 V for Pb(2+) and -0.85 V for Cd(2+), respectively. The effects of the amount of medical stone, concentration of Nafion, thickness of bismuth, pH of buffer solution, deposition potential, accumulation time, voltammetric measurement and possible interferences were investigated in detail. Under the optimal conditions, the fabricated electrode exhibited linear ranges from 2.0 to 12.0 μg L(-1) with detection limit of 0.07 μg L(-1) for lead and 2.0-12.0 μg L(-1) with detection limit of 0.47 μg L(-1) for cadmium. The assay results of heavy metals in wastewater with the proposed method were in acceptable agreement with the atomic absorption spectroscopy method.

Real-time in situ atomic force microscopy imaging of bismuth crystal growth

We have performed real-time atomic force microscopy (AFM) imaging of bismuth crystals that were grown under electrochemical control at low overpotentials to ensure a slow growth rate and allow in situ observation of the growth. A two step chronoamperometric potential was applied to a boron-doped diamond (BDD) working electrode with a short high overpotential, -0.4 V (2 s), to nucleate the bismuth, and then a long low overpotential for slow growth, -0.32 V (4.4 h). Growth rates of individual crystals and detailed growth mechanisms could be followed in real time because of the slow crystal growth. The close proximity of the AFM tip and tip holder to the working electrode appears to hinder the diffusion of bismuth to the BDD surface, as evidenced by the significantly lower density of crystals under the cantilever as compared to the rest of the electrode, therefore slowing down the growth process.