Electrochemical detection of 2-nitrophenol using a heterostructure ZnO/RuO2 nanoparticle modified glassy carbon electrode

Detection and treatment of mono and polycyclic aromatic hydrocarbon pollutants in aqueous environments based on electrochemical technology: recent advances

Mono and polycyclic aromatic hydrocarbons are widely distributed and severely pollute the aqueous environment due to natural and human activities, particularly human activity. It is crucial to identify and address them in order to reduce the dangers and threats they pose to biological processes and ecosystems. In the fields of sensor detection and water treatment, electrochemistry plays a crucial role as a trustworthy and environmentally friendly technology. In order to accomplish trace detection while enhancing detection accuracy and precision, researchers have created and studied sensors using a range of materials based on electrochemical processes, and their results have demonstrated good performance. One cannot overlook the challenges associated with treating aromatic pollutants, including mono and polycyclic. Much work has been done and good progress has been achieved in order to address these challenges. This study discusses the mono and polycyclic aromatic hydrocarbon sensor detection and electrochemical treatment technologies for contaminants in the aqueous environment. Additionally mentioned are the sources, distribution, risks, hazards, and problems in the removal of pollutants. The obstacles to be overcome and the future development plans of the field are then suggested by summarizing and assessing the research findings of the researchers.

Hybridized sulfated-carboxymethyl cellulose/MWNT nanocomposite as highly selective electrochemical probe for trace detection of arsenic in real environmental samples

A highly selective and ultra-sensitive electrochemical sensing probe was proposed by combining sulfated-carboxymethyl cellulose (CMC-S) and a functionalized-multiwalled carbon nanotube (f-MWNT) nano-composite with high conductivity and durability. The CMC-S/MWNT nanocomposite was impregnated on a glassy carbon electrode (GCE) to construct the non-enzymatic and mediator-free electrochemical sensing probe for trace detection of As(iii) ions. The fabricated CMC-S/MWNT nanocomposite was characterized by FTIR, SEM, TEM, and XPS. Under the optimized experimental conditions, the sensor exhibited the lowest detection limit of 0.024 nM, a high sensitivity (69.93 μA nM-1 cm-2) with a good linear relationship in the range of 0.2-90 nM As(iii) concentration. The sensor demonstrated strong repeatability, with the current response continuing at 84.52% after 28 days of use, in addition to good selectivity for the determination of As(iii). Additionally, with recovery ranging from 97.2% to 107.2%, the sensor demonstrated comparable sensing capability in tap water, sewage water, and mixed fruit juice. The electrochemical sensor for detecting trace levels of As(iii) in actual samples is anticipated to be produced by this effort and is expected to possess great selectivity, good stability, and sensitivity.

Quick and accurate determination of hazardous phenolic compounds using CaCu2O3 nanorods based electrochemical sensor

In the present work, we report the fabrication of a novel electrochemical sensor based on nanostructured CaCu₂O₃ as electrode material for the simultaneous determination of 2-Aminophenol (o-AP), 2-Chlorophenol (o-CP) and 2-Nitrophenol (o-NP). Nanorods-shaped CaCu₂O₃ have been synthesized by chemical precipitation method and characterized by powder X-ray diffraction (XRD), X-ray photo-electron microscopy (XPS), field emission electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM). Glassy carbon electrodes (3 mm diameter) have been modified using CaCu₂O₃ nanorods by drop-casting method. Cyclic voltammetry (CV) studies at CaCu₂O₃/GCE exhibited excellent electrochemical behaviours towards the oxidation of 2-AP, 2-CP and 2-NP at different potentials well separated from each other. The CaCu₂O₃/GCE displayed the lowest detection limits of 5.74 nM (0.626 ppb), 1.38 nM (0.177 ppb) and 1.03 nM (0.143 ppb) for 2-AP, 2-CP and 2-NP respectively over wide measurable linear ranges of 175 nM-68 μM (2-AP), 50 nM-90 μM (2-CP) and 25 nM-32 μM (2-NP). Cyclic stability studies showed a loss of 7%, 13% and 14% from initial current responses after conducting 100 cycles of CV for 2-AP, 2-CP and 2-NP in PBS (pH 7.0) which indicated the excellent stability of the fabricated electrode. Reproducibility studies of six different CaCu₂O₃/GCEs exhibited good recoveries in the order of 3.23% (2-AP), 3.54% (2-CP) and 2.46% (2-NP) respectively. The fabricated electrode with excellent sensitivity, stability and reproducibility has been successfully applied for the determination of 2-AP, 2-CP and 2-NP simultaneously in tap water and agricultural water samples. Selectivity studies carried out on CaCu₂O₃/GCE revealed its ability to detect 4-aminophenol and 4-nitorphenol at different oxidation potentials. High performance liquid chromatography (HPLC) studies have been carried out to validate the practical utility of the fabricated sensor.

Sensitive Electrochemical Detection of 4-Nitrophenol with PEDOT:PSS Modified Pt NPs-Embedded PPy-CB@ZnO Nanocomposites

In this study, a selective 4-nitrophenol (4-NP) sensor was developed onto a glassy carbon electrode (GCE) as an electron-sensing substrate, which decorated with sol-gel, prepared Pt nanoparticles- (NPs) embedded polypyrole-carbon black (PPy-CB)/ZnO nanocomposites (NCs) using differential pulse voltammetry. Characterizations of the NCs were performed using Field Emission Scanning Electron Microscopy (FESEM), Energy-Dispersive Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS), Ultraviolet-visible Spectroscopy (UV-vis), Fourier Transform Infrared Spectroscopy (FTIR), High Resolution Transmission Electron Microscopy (HRTEM), and X-ray Diffraction Analysis (XRD). The GCE modified by conducting coating binders [poly(3,4-ethylenedioxythiophene) polystyrene sulfonate; PEDOT:PSS] based on Pt NPs/PPy-CB/ZnO NCs functioned as the working electrode and showed selectivity toward 4-NP in a phosphate buffer medium at pH 7.0. Our analysis of 4-NP showed the linearity from 1.5 to 40.5 µM, which was identified as the linear detection range (LDR). A current versus concentration plot was formed and showed a regression co-efficient R² of 0.9917, which can be expressed by i_p(µA) = 0.2493C(µM) + 15.694. The 4-NP sensor sensitivity was calculated using the slope of the LDR, considering the surface area of the GCE (0.0316 cm²). The sensitivity was calculated as 7.8892 µAµM^-1cm^-2. The LOD (limit of detection) of the 4-NP was calculated as 1.25 ± 0.06 µM, which was calculated from 3xSD/σ (SD: Standard deviation of blank response; σ: Slope of the calibration curve). Limit of quantification (LOQ) is also calculated as 3.79 µM from LOQ = 10xLOD/3.3. Sensor parameters such as reproducibility, response time, and analyzing stability were outstanding. Therefore, this novel approach can be broadly used to safely fabricate selective 4-NP sensors based on nanoparticle-decorated nanocomposite materials in environmental measurement.

Review of the Design of Ruthenium-Based Nanomaterials and Their Sensing Applications in Electrochemistry

In this review, ruthenium nanoparticles (Ru NPs)-based functional nanomaterials have attractive electrocatalytic characteristics and they offer considerable potential in a number of fields. Ru-based binary or multimetallic NPs are widely utilized for electrode modification because of their unique electrocatalytic properties, enhanced surface-area-to-volume ratio, and synergistic effect between two metals provides as an effective improved electrode sensor. This perspective review suggests the current research and development of Ru-based nanomaterials as a platform for electrochemical (EC) sensing of harmful substances, biomolecules, insecticides, pharmaceuticals, and environmental pollutants. The advantages and limitations of mono-, bi-, and multimetallic Ru-based nanocomposites for EC sensors are discussed. Besides, the relevant EC properties and analyte sensing approaches are also presented. On the basis of these insights, we highlighted recent results for synthesizing techniques and EC environmental pollutant sensors from the perspectives of diverse supports, including graphene, carbon nanotubes, silica, semiconductors, metal sulfides, and polymers. Finally, this work overviews the modern improvements in the utilization of Ru-based nanocomposites on the basis for electroanalytical sensors as well as suggestions for the field's future development.

Enhancing the mediated electrochemical reduction process combined with developed liquid-gas electrochemical flow sensors for sustainable N2O removal at room temperature

New electrocatalysts with high reduction efficiency are needed to upgrade the mediated electrochemical reduction for real applications. In addition, automation is required to quantify active electrocatalysts in alkaline media and air pollution. In this study, N₂O was removed sustainably by electrogenerated low valent nickel(I) phthalocyanine tetrasulfonate [Ni(I)TSPc] in 1 M KOH using an electroscrubbing system. Ni(I)TSPc electro generation and N₂O removal were automated by two (liquid/gas) electrochemical flow sensors, respectively. The Ni(I)TSPc was generated electrochemically up to 95% in 1 M KOH, and high removal efficiency (100%) was observed for 5 ppm N₂O and 90% for 10 ppm N₂O. A limiting potential change in the in-situ LSV of the chemically synthesized Ni(I)TSPc was taken and derived from the calibration plot and validated by an ex-situ potentiometric titration using an oxygen reduction potential electrode. Using the obtained calibration plot, electrogenerated Ni(I)TSPc allowed a direct determination in a liquid flow cell. The gas flow sensor developed using a KOH/Ni(II)CN₄ (TCN (II))-fabricated silver solid amalgam electrode showed an excellent response to N₂O concentrations up to 32 ppm. A calibration plot with known concentration was derived and validated by gas chromatography. The response time and sensitivity obtained were approximately 500s and -0.012 mA ppm^-1 cm^-2, respectively. The sensor stability test confirmed its good stability. Finally, the developed in-situ electrochemical flow sensors were applied to the sustainable automation of N₂O pollutant removal.

Melamine functionalised multiwalled carbon nanotubes (M-MWCNTs) as a metal-free electrocatalyst for simultaneous determination of 4-nitrophenol and nitrofurantoin

An innovative melamine functionalised multiwalled carbon nanotube (M-MWCNTs) based electrochemical sensor has been developed for the determination of environmental nitro-aromatic pollutants, such as 4-nitrophenol (4-NP) and nitrofurantoin (NFT).

Assessment of anthropogenic pollution by monitoring occurrence and distribution of chemicals in the river Liffey in Dublin

This paper evaluates for the first time the spatial distribution of a wide group of organic (phthalates, nitro, aliphatic, halogen, aromatic, phenol and amino compounds) and inorganic pollutants along the Liffey river in Dublin city. The work takes into account the effect of short-term weather conditions on the occurrence of these contaminants. The results showed that rainfall conditions affect the levels of pollutants along the river in the days following a rainfall event. In addition, the tributaries entering the river Liffey were not found to impact its water quality. In relation to organic pollutants, 2,4,6-trichlorophenol, 2-nitrophenol and phthalate compounds were found in many water samples between concentrations of 0.21 and 2.17 μg L-1. On the other hand, dimethyl phthalate was present in certain samples at levels around 100 μg L-1. The levels of these contaminants in the river were lower than the toxicity values reported in the literature. Regarding inorganic pollutants, nitrates were detected from 0.59 to 6.81 mg L-1 increasing from upstream to downstream. Based on the chemical nature and applications of detected pollutants, the river contamination can be mainly related to agricultural, industrial activities as well as diffuse urban contributions. These vary with location within a short distance and have the potential to impact aquatic biodiversity as the chemical composition changes with rainfall events.

Simultaneous determination of nitrophenol isomers based on reduced graphene oxide modified with sulfobutylether-β-cyclodextrin

The present study reports the development of an electrochemical sensor based on sulfobutylether-β-cyclodextrin modified reduced graphene oxide hybrid (SBCD-rGO) for simultaneous detection of nitrophenol isomers. First, SBCD-rGO hybrid was synthesized and detailed characterized. Afterwards, a sensor was fabricated via the modification of glassy carbon electrode (GCE) with SBCD-rGO, and its electrochemical detection performances were also investigated. Then, the constructed electrochemical sensor was applied to detect nitrophenol isomers by voltammetry analysis. The results suggested that the sensitivities were 389.26, 280.88 and 217.19 μA/mM for p-nitrophenol (p-NP), m-nitrophenol (m-NP), and o-nitrophenol (o-NP), respectively, and their corresponding detection limits were all about 0.05 μM. Significantly, the combination of voltammetry analysis with the constructed sensor and data analysis by multiple linear regression realized the simultaneous detection of nitrophenol isomers.

Electrochemical Detection of 2-Nitrophenol Using a Glassy Carbon Electrode Modified with BaO Nanorods

Here, an electrochemical detection approach (differential pulse voltammetry) was employed to develop a 2-nitrophenol (2-NP) sensor probe using a glassy carbon electrode (GCE) coated by wet-chemically synthesized nanorods (NRs) of BaO. The prepared BaO NRs were characterized by field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and powder X-ray diffraction (XRD) analysis. The peak currents by differential pulse voltammetric (DPV) analysis of 2-NP are plotted against the concentration to obtain the calibration curve of the 2-NP detection. It was found to be linear from 1.5 to 9.0 μM, defined as the dynamic range (LDR) for 2-NP detection in phosphate buffer solution. The sensor sensitivity was calculated from the slope of LDR by considering the active surface area of NRs coated on GCE (0.0316 cm² ) and found as 17.6 μAμM^-1  cm^-2 . The limit of detection (LOD) was calculated as 0.50±0.025 μM from the signal/noise (S/N) ratio of 3. Moreover, the sensor analytical parameters such as reproducibility, long-term performing ability (stability), response time and validity in real environmental samples were found acceptable and to give satisfactory results. The development of a nanomaterial-based electrochemical chemical sensor might be an effective approach to sensor technology to detect carcinogenic and hazardous toxins for environmental safety and healthcare fields in a broad scale.

Recent advances in ZnO nanostructure-based electrochemical sensors and biosensors

Nanostructured metal oxides, such as zinc oxide (ZnO), are considered as excellent materials for the fabrication of highly sensitive and selective electrochemical sensors and biosensors due to their good properties, including a high specific surface area, high catalytic efficiency, strong adsorption ability, high isoelectric point (IEP, 9.5), wide band gap (3.2 eV), biocompatibility and high electron communication features. Thus, ZnO nanostructures are widely used to fabricate efficient electrochemical sensors and biosensors for the detection of various analytes. In this review, we have discussed the synthesis of ZnO nanostructures and the advances in various ZnO nanostructure-based electrochemical sensors and biosensors for medical diagnosis, pharmaceutical analysis, food safety, and environmental pollution monitoring.

2D alignment of zinc oxide@ZIF8 nanocrystals for photoelectrochemical water splitting

Thin films of zinc oxide nano-sheets loaded with Zeolitic Imidazole Framework 8 nanocrystals were synthesized using electrodeposition and chemical bath deposition for photoelectrochemical application.

Metal-free graphene-based nanoelectrodes for the electrochemical determination of ascorbic acid (AA) and p-nitrophenol (p-NP): implication towards biosensing and environmental monitoring

Herein, tyramine functionalized graphene oxide electrocatalyst is used for the electrochemical determination of ascorbic acid and p-nitrophenol in 1 M phosphate buffer solution at pH-7  with long term current/potential stability and reproducibility.

A novel highly selective electrochemical chlorobenzene sensor based on ternary oxide RuO2/ZnO/TiO2 nanocomposites

A novel electrochemical (EC) chlorobenzene (CBZ) sensor was fabricated using a ternary oxide RuO₂/ZnO/TiO₂ nanocomposite (NC)-decorated glassy carbon electrode (GCE). The nanoparticles (NPs) were synthesized by a wet-chemical method and characterized by X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), and ultraviolet-visible (UV-vis) spectroscopy. The synthesized RuO₂/ZnO/TiO₂ NC was layered as thin film on a GCE with Nafion (5% suspension in ethanol) adhesive, and the as-prepared sensor was subjected to CBZ analysis using an electrochemical approach. The calibration of the proposed CBZ sensor was executed with a linear relation of current versus concentration of CBZs known as the calibration curve. The sensitivity (32.02 μA μM⁻¹ cm⁻²) of the CBZ sensor was calculated from the slope of the calibration curve by considering the active surface area of the GCE (0.0316 cm²). The lower detection limit (LD; 98.70 ± 4.90 pM) was also calculated at a signal-to-noise ratio of 3. Besides these, the response current followed a linear relationship with the concentration of chlorobenzene and the linear dynamic range (LDR) was denoted in the range of 0.1 nM to 1.0 μM. Moreover, the CBZ sensor was found to exhibit good reproducibility, reliability, stability, and fast response time. Finally, the sensing mechanism was also discussed with the energy-band theory of ternary doped semiconductor materials. The sensing activity of the proposed sensor was significantly enhanced due to the combined result of depletion layer formation at the heterojunction of RuO₂/ZnO/TiO₂ NCs as well as the activity of RuO₂ NPs as oxidation catalysts. The proposed CBZ sensor probe based on ternary oxide RuO₂/ZnO/TiO₂ NCs was developed with significant analytical parameters for practical application in monitoring the environmental pollutants of CBZs for the safety of environmental fields on a large scale.

A novel electrochemical (EC) chlorobenzene (CBZ) sensor was fabricated using a ternary oxide RuO₂/ZnO/TiO₂ nanocomposite (NC)-decorated glassy carbon electrode (GCE).