An In Situ Copper Plated Boron-Doped Diamond Microelectrode Array for the Sensitive Electrochemical Detection of Nitrate

A non-enzymatic highly stable electrochemical sensing platform based on allylamine capped copper nanoparticles for the detection of the soil nitrate content

Nitrate (NO3-) ion contamination of water is a major issue that affects many parts of the world due to excessive usage of nitrogen containing fertilizers in the soil. Hence, quantification of NO3- ions in the soil is of utmost importance. In the present research work, we have developed an efficient and highly stable non-enzymatic electrochemical sensor for NO3- ion detection based on allylamine capped copper nanoparticles (Alym@CuNPs) decorated on exfoliated multi-walled carbon nanotubes (Exf-CNTs). Herein, we have addressed the sensor surface storage stability issue of copper nanoparticle based electrochemical sensors for the first time and confirmed the superior storage stability of the Alym@CuNPs modified glassy carbon electrode (GCE) over uncapped copper nanoparticles (uCuNPs) and electrodeposited copper nanoparticles (eCuNPs) modified GCEs. In comparison to the bare GCE, Exf-CNT/GCE and Alym@CuNPs/Exf-CNT/GCE, the proposed Alym@CuNPs-Nafion (NF)/Exf-CNT/GCE demonstrated enhanced catalytic activity towards the electro-reduction of NO3- ions (pH = 2) under optimal experimental conditions, with a considerable increase in cathodic peak currents. Along with that, no inert gas was purged into the electrolyte medium prior to the detection of NO3- ions which makes the sensor more reliable under real environmental conditions. The sensor displayed broad linear ranges from 10 to 1000 μM (R2 = 0.997), with a limit of detection (LOD) of 5.28 μM (n = 3) for NO3- ion detection. The sensor surface shows excellent storage stability even up to 45 days with 97.8% retention in current value which is much higher compared to the previously reported works. Additionally, the sensor surface shows promising reproducibility and repeatability results with RSD values of 1.78% and 0.91%, respectively. Moreover, the proposed sensor is successfully utilized to detect NO3- ions in real soil samples.

A combined experimental and computational approach to unravel degradation mechanisms in electrochemical wastewater treatment

Electrochemical wastewater treatment is a promising technique to remove recalcitrant pollutants from wastewater. However, the complexity of elucidating the underlying degradation mechanisms hinders its optimisation not only from a techno-economic perspective, as it is desirable to maximise removal efficiencies at low energy and chemical requirements, but also in environmental terms, as the generation of toxic by-products is an ongoing challenge. In this work, we propose a novel combined experimental and computational approach to (i) estimate the contribution of radical and non-radical mechanisms as well as their synergistic effects during electrochemical oxidation and (ii) identify the optimal conditions that promote specific degradation pathways. As a case study, the distribution of the degradation mechanisms involved in the removal of benzoic acid (BA) via boron-doped diamond (BDD) anodes was elucidated and analysed as a function of several operating parameters, i.e., the initial sulfate and nitrate content of the wastewater and the current applied. Subsequently, a multivariate optimisation study was conducted, where the influence of the electrode nature was investigated for two commercial BDD electrodes and a customised silver-decorated BDD electrode. Optimal conditions were identified for each degradation mechanism as well as for the overall BA degradation rate constant. BDD selection was found to be the most influential factor favouring any mechanism (i.e., 52-85% contribution), given that properties such as its boron doping and the presence of electrodeposited silver could dramatically affect the reactions taking place. In particular, decorating the BDD surface with silver microparticles significantly enhanced BA degradation via sulfate radicals, whereas direct oxidation, reactive oxygen species and radical synergistic effects were promoted when using a commercial BDD material with higher boron content and on a silicon substrate. Consequently, by simplifying the identification and quantification of underlying mechanisms, our approach facilitates the elucidation of the most suitable degradation route for a given electrochemical wastewater treatment together with its optimal operating conditions.

Chemical analysis in saliva and the search for salivary biomarkers – a tutorial review

A review of the uses of saliva biomarkers, detection methods and requirements for new biomarkers.

A Palladium-Tin Modified Microband Electrode Array for Nitrate Determination

A microband electrode array modified with palladium-tin bimetallic composite has been developed for nitrate determination. The microband electrode array was fabricated by Micro Electro-Mechanical System (MEMS) technique. Palladium and tin were electrodeposited successively on the electrode, forming a double-layer structure. The effect of the Pd-Sn composite was investigated and its enhancement of catalytic activity and lifetime was revealed. The Pd-Sn modified electrode showed good linearity (R² = 0.998) from 1 mg/L to 20 mg/L for nitrate determination with a sensitivity of 398 μA/(mg∙L⁻¹∙cm²). The electrode exhibited a satisfying analytical performance after 60 days of storage, indicating a long lifetime. Good repeatability was also displayed by the Pd-Sn modified electrodes. The results provided an option for nitrate determination in water.

Electrocatalytic Sensing of Nitrate at Cu Nanosheets Electrodeposited on WO3/Polyaniline Modified Electrode

A porous copper/tungsten oxide (WO3)/polyaniline (PANI) composite modified electrode CuWP was fabricated by electrochemical deposition of copper nanosheets on WO3/PANI composite. The CuWP exhibited higher electrocatalytic activity for nitrate reduction than the similarly prepared copper modified electrode due to the larger surface area of CuWP and the synergistic catalytic effect of copper and WO3/PANI. The linear scan voltammetry results showed a good linear relationship between nitrate reduction current and concentration of nitrate from 40 to 276 μM, with a sensitivity of 4.5 μA/μM and detection limit (S/N=3) of 1.2 μM. The CuWP modified electrode was tried to be employed in determination of nitrate in drinking water.

Investigation of a Cu/Pd Bimetallic System Electrodeposited on Boron-Doped Diamond Films for Application in Electrocatalytic Reduction of Nitrate

The Cu/Pd bimetallic system electrodeposited on boron-doped diamond (BDD) films for application, as electrode material in the electrochemical reduction of nitrate was studied. The electrochemical behavior of Cu, Pd, and Cu/Pd bimetallic system was evaluated by cyclic voltammetry. From these results, the formation of the Cu/Pd composite was verified. In addition, Cu with different phases and a Cu/Pd phase in the composite were obtained. Morphological analysis by scanning electron microscopy (SEM) revealed a homogeneous distribution of Cu/Pd bimetallic particles with intermediary dimensions compared to those observed in Cu or Pd electrodeposits separately. These composites were tested as electrocatalysts for nitrate reduction in Britton-Robinson buffer solution (pH 9). Electrochemical measurements showed that composites with higher Cu content displayed the best electrocatalytic activity for nitrate reduction, and the Cu/Pd phase in the bimetallic system served to improve the Cu adherence on BDD electrode.

Microelectrode arrays for electrochemistry: approaches to fabrication

Microelectrode arrays have unique electrochemical properties such as small capacitive-charging currents, reduced iR drop, and steady-state diffusion currents. These properties enable the use of microelectrode arrays and have captured much interest in the field of electrochemistry. Techniques for the fabrication of such arrays are reviewed. The relative features and merits of different techniques are also discussed.

General Theory of Cathodic and Anodic Stripping Voltammetry at Solid Electrodes: Mathematical Modeling and Numerical Simulations

Theory is presented to describe the voltammetric signals associated with the stripping phase of stripping voltammetry at solid electrodes. Three mathematical models are considered, and the importance of the hemispherical diffusion associated with electrochemical dissolution of particles in the micrometer range is investigated. Model A considers a "monolayer" system where the coverage at a specific point cannot exceed a maximum value. Model B considers a thin layer of metal or metal oxide, but in contrast to model A, the maximum surface coverage is not restricted. Model C represents the stripping of a "thick layer" where the deposition is also unrestricted.

The use of nanoparticles in electroanalysis: a review

Nanoparticles can display four unique advantages over macroelectrodes when used for electroanalysis: enhancement of mass transport, catalysis, high effective surface area and control over electrode microenvironment. Therefore, much work has been carried out into their formation, characterisation and employment for the detection of many electroactive species. This paper aims to give an overview of the investigations carried out in this field. Particular attention is paid to examples of the advantages and disadvantages nanoparticles show when compared to macroelectrodes and the advantages of one nanoparticle modification over another. Most work has been carried out using gold, silver and platinum metals. However, iron, nickel and copper are also reviewed with some examples of other metals such as iridium, ruthenium, cobalt, chromium and palladium. Some bimetallic nanoparticle modifications are also mentioned because they can cause unique catalysis through the mixing of the properties of both metals.