3,5-Diamino-1,2,4-triazole@electrochemically reduced graphene oxide film modified electrode for the electrochemical determination of 4-nitrophenol

Nitrophenols in the environment: An update on pretreatment and analysis techniques since 2017

Nitrophenols, a versatile intermediate, have been widely used in leather, medicine, chemical synthesis, and other fields. Because these components are widely applied, they can enter the environment through various routes, leading to many hazards and toxicities. There has been a recent surge in the development of simple, rapid, environmentally friendly, and effective techniques for determining these environmental pollutants. This review provides a comprehensive overview of the latest research progress on the pretreatment and analysis methods of nitrophenols since 2017, with a focus on environmental samples. Pretreatment methods include liquid-liquid extraction, solid-phase extraction, dispersive extraction, and microextraction methods. Analysis methods mainly include liquid chromatography-based methods, gas chromatography-based methods, supercritical fluid chromatography. In addition, this review also discusses and compares the advantages/disadvantages and development prospects of different pretreatment and analysis methods to provide a reference for further research.

Two-Dimensional Nickel Porphyrinic Metal-Organic Framework-Modified Electrode for Electrochemical Sensing

Due to their highly exposed active sites and high aspect ratio caused by their substantial lateral dimension and thin thickness, two-dimensional (2D) metal-organic framework (MOF) nanosheets are currently considered a potential hybrid material for electrochemical sensing. Herein, we present a nickel-based porphyrinic MOF nanosheet as a versatile and robust platform with an enhanced electrochemical detection performance. It is important to note that the nickel porphyrin ligand reacted with Cu(NO3)2·3H2O in a solvothermal process, with polyvinylpyrrolidone (PVP) acting as the surfactant to control the anisotropic development of creating a 2D Cu-TCPP(Ni) MOF nanosheet structure. To realize the exceptional selectivity, sensitivity, and stability of the synthesized 2D Cu-TCPP(Ni) MOF nanosheet, a laser-induced graphene electrode was modified with the MOF nanosheet and employed as a sensor for the detection of p-nitrophenol (p-NP). With a detection range of 0.5-200 μM for differential pulse voltammetry (DPV) and 0.9-300 μM for cyclic voltammetry (CV), the proposed sensor demonstrated enhanced electrochemical performance, with the limit of detection (LOD) for DPV and CV as 0.1 and 0.3 μM, respectively. The outstanding outcome of the sensor is attributed to the 2D Cu-TCPP(Ni) MOF nanosheet's substantial active surface area, innate catalytic activity, and superior adsorption capacity. Furthermore, it is anticipated that the proposed electrode sensor will make it possible to create high-performance electrochemical sensors for environmental point-of-care testing since it successfully detected p-NP in real sample analysis.

Electrochemical preparation and the characterizations of poly(3,5-diamino 1,2,4-triazole) film for the selective determination of pyridoxine in pharmaceutical formulations

This work describes the synthesis and characterization of a polymeric film of 3,5-diamino 1,2,4-triazole on a pencil graphite electrode for the selective sensing of pyridoxine (PY). The PGE was modified using the electropolymerization process by the potentiodynamic method. The polymerized electrode (PDAT/PGE) was characterized by IR, SEM, AFM, cyclic voltammetry, and electrochemical impedance spectroscopy. PY undergoes irreversible oxidation at 0.79 V on PDAT/PGE in phosphate buffer of pH 5. Using the differential pulse voltammetric technique (DPV), PY showed a linear range from 5 to 950 μM with a lower detection limit of 2.96 μM. The PDAT/PGE was applied for the analytical determination of PY in pharmaceutical tablets with good recovery.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s11696-023-02777-5.

Decoration of alkalization-intercalated Ti3C2 with ZIF-8@ZIF-67-derived N-doped carbon nanocage for detecting 4-nitrophenol

The highly effective alk-Ti₃C₂/bimetallic Co, Zn embedded N-doped carbon (Co-Zn-NC) composite was fabricated by a convenient self-assembled method strategy and applied to  the reduction of 4-nitrophenol(4-NP). Co-Zn-NC nanocage was synthesized by using designed core-shell ZIF-8@ZIF-67 as sacrificial template. The Co-Zn-NC was prepared by pyrolysis of ZIF-8@ZIF-67 at 900 °C with high-specific surface area and hollow structure, which facilitates the dispersion of Co species and produces abundant Co-Nx active sites. In addition, the electrochemical property and specific surface area of Ti₃C₂ were improved by alkaline treatment. As a result, compared with alk-Ti₃C₂ and Co-Zn-NC, the alk-Ti₃C₂/Co-Zn-NC sensor showed higher activity and stability in detecting 4-NP. The alk-Ti₃C₂/Co-Zn-NC sensor has a wide determination range of 2-500 μM and a low detection limit of 0.23 μM for 4-NP. In addition, the newly developed alk-Ti₃C₂/Co-Zn-NC sensor displayed satisfactory reproducibility and  good stability in detecting 4-NP in aqueous samples.

Electrocatalytic degradation of methyl orange and 4-nitrophenol on a Ti/TiO2-NTA/La-PbO2 electrode: electrode characterization and operating parameters

The anode material plays a crucial role in the process of electrochemical oxidation. Herein, a TiO₂ nanotube arrays (TiO₂-NTA) intermediate layer and La-PbO₂ catalytic layer were synthesized on a Ti surface by the electrochemical anodic oxidation and electrochemical deposition technology, respectively. The prepared Ti/TiO₂-NTA/La-PbO₂ electrode was used as an electrocatalytic oxidation anode for pollutant degradation. Scanning electron microscopy (SEM) analysis showed that the TiO₂-NTA layer possessed a highly ordered and well-aligned nanotube array morphology, and the La-PbO₂ layer with angular cone cluster was uniform and tightly bonded. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis indicated that the intermediate layer primarily consisted of the anatase crystal structure of TiO₂ and the catalyst layer was made of La-PbO₂. Electrochemical analysis revealed that Ti/TiO₂-NTA/La-PbO₂ electrode exhibited higher oxidation peak current, electrochemical active surface area, and oxygen evolution potential (OEP, 1.64 V). Using methyl orange and 4-nitrophenol as model pollutants, electrocatalytic properties of the prepared Ti/TiO₂-NTA/La-PbO₂ electrode were systematically investigated under different conditions, and the electrochemical degradation fitted well with the pseudo-first-order kinetics model. Efficient anodic oxidation of model pollutants was mainly attributed to the indirect oxidation mediated by hydroxyl radicals (•OH). The total organic carbon (TOC) removal efficiency of methyl orange and 4-nitrophenol was 70.2 and 72.8%, and low energy consumption (2.50 and 1.89 kWh g^-1) was achieved after 240 min of electrolysis under the conditions of initial concentration of model pollutant, electrode spacing, and electrolyte concentration were 50 mg L^-1, 2 cm, and 0.1 mol L^-1, respectively. This work provided a new strategy to develop the high-efficiency electrode for refractory pollutants degradation.

In situ electrochemical synthesis of graphene-poly(arginine) composite for p-nitrophenol monitoring

Para-Nitrophenol (p-nitrophenol) is a common industrial pollutant occurring widely in water bodies, yet actual monitoring methods are limited. Herein we proposed a fully electrochemically in situ synthesized graphene-polyarginine composite functionalized screen printed electrode, as a novel p-nitrophenol sensing platform. The electrode was characterized by morphologic, spectrometric and electrochemical techniques. p-nitrophenol in both pure aqueous solution and real water samples was tested. Results show a detection limit as low as the nanomolar level, and display a linear response and high selectivity in the range of 0.5-1250 μM. Molecular simulation reveals a detailed synergy between graphene and poly-arginine. The preferable orientation of nitrophenol molecules on the graphene interface in the presence of poly-arginine induces H- and ionic binding. This sensor is an ideal prototype for p-nitrophenol quantification in real waters.

Rapid electrochemical detection of domoic acid based on polydopamine/reduced graphene oxide coupled with in-situ imprinted polyacrylamide

Domoic acid, namely amnesic shellfish toxin, is a highly neurotoxic substance to marine animals and humankind. To reduce the incidence of poisoning accidents, the exploitation of specific and rapid detection method for domoic acid monitoring is highly required. Herein, an electrochemical molecularly imprinted polymer (MIP) sensor based on polydopamine-reduced graphene oxide/polyacrylamide composite (PDA-rGO/PAM) was constructed successfully to detect domoic acid. The domoic acid molecule could be recognized in imprinted cavities of PAM reversibly through hydrogen bonding. PDA-rGO promoted the loading capacity of PAM and improved the charge transfer rate, which amplified the electrical signal response of the MIP sensor. The screen-printed electrode (SPE) modified with PDA-rGO/PAM displayed satisfactory response toward toxin contaminated sample at a linear range from 1 to 600 nM and a low detection limit of 0.31 nM, demonstrating the prospective application of the transducer as a portable sensing platform for the on-site detection of hazardous marine biotoxin. Moreover, benefiting from the superior specificity and stability of MIP, the fabricated sensor could be utilized to detect the domoic acid content in mussel extracts directly without complex pretreatment operation.

NaYF4:Yb3+(58%),Tm3+@NaYF4@Au nanocomposite for 4-nitrophenol ultrasensitive quantitative detection and highly efficient catalytic reduction

NaYF4:Yb3+(58%),Tm3+@NaYF4@Au composite nanomaterials were designed and synthesized through condition optimization for the quantitative detection and catalytic reduction of 4-NP.

Sensing Methods for Hazardous Phenolic Compounds Based on Graphene and Conducting Polymers-Based Materials

It has been known for years that the phenolic compounds are able to exert harmful effects toward living organisms including humans due to their high toxicity. Living organisms were exposed to these phenolic compounds as they were released into the environment as waste products from several fast-growing industries. In this regard, tremendous efforts have been made by researchers to develop sensing methods for the detection of these phenolic compounds. Graphene and conducting polymers-based materials have arisen as a high potential sensing layer to improve the performance of the developed sensors. Henceforth, this paper reviews the existing investigations on graphene and conducting polymer-based materials incorporated with various sensors that aimed to detect hazardous phenolic compounds, i.e., phenol, 2-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, pentachlorophenol, 2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, and 2,4-dimethylphenol. The whole picture and up-to-date information on the graphene and conducting polymers-based sensors are arranged in systematic chronological order to provide a clearer insight in this research area. The future perspectives of this study are also included, and the development of sensing methods for hazardous phenolic compounds using graphene and conducting polymers-based materials is expected to grow more in the future.

Microwave-assisted assembly of Ag2O-ZnO composite nanocones for electrochemical detection of 4-Nitrophenol and assessment of their photocatalytic activity towards degradation of 4-Nitrophenol and Methylene blue dye

4-Nitrophenol (4-NP) is an extensively utilized industrial chemical and one of major toxic water pollutant. Therefore, there is an urgent need to monitor the levels of 4-NP from environmental samples as well as its eradication are extremely important. Keeping this as a motivation, this research for the first-time reports microwave-assisted cost-effective synthesis of silver oxide (Ag₂O)-zinc oxide (ZnO) composite nanocones (CNCs, 80-100 nm) for simultaneous electrochemical detection and photodegradation of 4-NP from aqueous solutions. The Ag₂O-ZnO CNCs modified gold electrode was fabricated for electrochemical detection of 4-NP. Such fabricated sensor exhibited a sensitivity of 1.6 µA µM^-1cm^-2, wide linear detection range of 0.4-26 µM & 28-326 µM, and a low limit of detection of 23 nM. The sensor also exhibited good selectivity in real water samples. Also, an outstanding photocatalytic performance of Ag₂O-ZnO CNCs was evaluated towards UV-assisted degradation of 4-NP and organic water pollutant dye, methylene blue. The Ag₂O-ZnO CNCs exhibited excellent electro- and photocatalytic activities due to the formation of p-n nano-heterojunction comprising of p-type Ag₂O and n-type ZnO semiconductor nanoparticles within the composite. Therefore, herein reported smart CNCs can be projected as applied nano-system for cost-effective and rapid simultaneous detection and removal of 4-NP from aqueous solutions. Such nano-system can be useful for industrial application where detection and removal of 4-NP is a key issue to resolve.

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 determination of 4-nitrophenol in environmental water samples using porous graphitic carbon nitride-coated screen-printed electrode

We demonstrate a facile preparation of novel oxidized graphitic carbon nitride (O-gC₃N₄) applied as an efficient electrocatalyst for highly sensitive electrochemical detection of 4-nitrophenol (4-NP) in environmental water samples. As-prepared O-gC₃N₄ were characterized by attenuated total reflection infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction methods for the confirmation of different functional groups and structural phase of O-gC₃N₄. The surface morphology of the O-gC₃N₄ was characterized using field emission scanning electron microscopy and high-resolution transmission electron microscopy. Results revealed that the synthesized gC₃N₄ possessed acid functional groups, nanosheet with porous in nature. The O-gC₃N₄ was drop cast on the screen-printed electrode (SPE), and it was applied for electrochemical determination of 4-NP using cyclic voltammetry and differential pulse voltammetry (DPV) techniques. The O-gC₃N₄/SPE exhibited excellent electrocatalytic activity towards 4-NP detection. Under the optimized experimental conditions, the DPV response of O-gC₃N₄/SPE showed good linear range from 0.0033 to 0.313 μM with a detection limit (S/N = 3) of 0.075 μM. The developed electrode has successfully applied for the determination of 4-NP in different environmental water samples, and the results have shown satisfied.

Insights into the role of an Fe–N active site in the oxygen reduction reaction on carbon-supported supramolecular catalysts

In this study, a nitrogen-containing ligand supramolecule named PPYTZ was successfully synthesized using 2,6-pyridinedicarboxylic acid chloride and 3,5-diamino-1,2,4-triazole in order to carry out oxygen reduction reaction (ORR). Such a polymer provides abundant coordination sites for iron ions, and the PPYTZ–Fe/C composite catalyst was formed with the PPYTZ–Fe complex loading on the surface of Vulcan XC-72 carbon. The physical characteristics and ORR performance of the composite catalysts were characterized systematically via various relevant techniques, and their catalytic activity and reaction mechanism were evaluated and compared. The results showed that the catalytic activities and the reaction mechanism of ORR were highly dependent on the formation of an Fe–N unit. Accordingly, the PPYTZ–Fe/C catalyst containing Fe–N active sites exhibited high ORR catalytic activity (an onset potential of +0.86 V vs. RHE) in 0.1 M KOH. Such an Fe–N catalyst can accelerate the adsorption of O₂ and increase the limiting current density (from 2.49 mA cm⁻² to 4.98 mA cm⁻²), optimizing the ORR catalytic process from a two-electron process to a four-electron process (an n value of 3.8).

The PPYTZ–Fe/C catalyst containing Fe–N active sites exhibited high ORR catalytic activity and stability in alkaline media with a four-electron pathway progress.

A dinuclear cobalt cluster as electrocatalyst for oxygen reduction reaction

Dinuclear metal clusters as metalloenzymes execute efficient catalytic activities in biological systems. Enlightened by this, a dinuclear {CoII 2} cluster was selected to survey its ORR (Oxygen Reduction Reaction) catalytic activities. The crystalline {CoII 2} possesses defined structure and potential catalytic active centers of {CoN4O2} sites, which was identified by X-ray single crystal diffraction, Raman and XPS. The appropriate supramolecular porosity combining abundant pyridinic-N and triazole-N sites of {CoII 2} catalyst synergistically benefit the ORR performance. As a result, this non-noble metal catalyst presents a nice ORR electrocatalytic activity and abides by a nearly 4-electron reduction pathway. Thus, this unpyrolyzed crystalline catalyst clearly provide precise active sites and the whole defined structural information, which can help researcher to design and fabricate efficient ORR catalysts to improve their activities. Considering the visible crystal structure, a single cobalt center-mediated catalytic mechanism was also proposed to elucidate the ORR process.

Impact of nano-morphology, lattice defects and conductivity on the performance of graphene based electrochemical biosensors

Diverse properties of graphenic materials have been extensively explored to determine properties that make good electrochemical nanomaterial-based biosensors. These are reviewed by critically examining the influence of graphene nano-morphology, lattice defects and conductivity. Stability, reproducibility and fabrication are discussed together with sensitivity and selectivity. We provide an outlook on future directions for building efficient electrochemical biosensors.

Facile and Ultrasensitive Determination of 4-Nitrophenol Based on Acetylene Black Paste and Graphene Hybrid Electrode

4-nitrophenol (4-NP) is a hazardous waste and a priority toxic pollutant identified by US Environmental Protection Agency (EPA). Hence, in this paper, a voltammetric sensor was proposed for the direct and sensitive detection of 4-nitrophenol (4-NP) at nanomolar level in complex matrices by using graphene and acetylene black paste hybridized electrode (GR/ABPE). Under optimal conditions, the calibration curve demonstrates a linear relationship for 4-NP in the range from 20 nM to 8.0 μM and 8.0 μM to 0.1 mM separately with the detection limit of 8.0 nM. In addition to it, the performance of the GR/ABPE in practical applications was evaluated by detecting 4-NP in various water samples, and satisfactory recoveries were realized. Therefore, GR/ABPE may have a great potential application for facile and sensitive detection of 4-NP in complex matrices at nanomolar level.

Simplistic synthesis of ultrafine CoMnO3 nanosheets: An excellent electrocatalyst for highly sensitive detection of toxic 4-nitrophenol in environmental water samples

Design and fabrication of cost effective analytical tools to monitor toxic organic emissions in eco system is of a great necessity. Nitrophenols are a class of widespread toxic organic pollutant lead to serious adverse effects in biosphere on its consumption. This article reports a high sensitive, cost effective, robust electrochemical sensor for 4-nitrophenol (4-NP) in environmental water samples. A novel sheet like CoMnO₃ (CMO Ns) nanocatalyst was synthesized via oxalic acid assisted co-precipitation technique and employed as electrocatalyst for the high sensitive detection of 4-NP. The physiochemical properties of CMO Ns are studied in detail via XRD, FTIR, TEM, TGA, and XPS. TEM results reviled the protocol is an excellent way for synthesis of a uniformly distributed CMO Ns with lathery surface. Evident to the surface and other physiochemical studies the CMO Ns based sensor holds superior electrocatalytic activity towards 4-NP detection with excellent sensitivity (2.458 μA μM^-1 cm^-2) coupled with nanomolar detection (10 nm) limits. Moreover, the constructed sensor holds reliable long-term durability, good reproducibility, and excellent working stability. The practical applicability of the developed sensor was evaluated by determination of 4-NP in samples acquired from water resources with RSD ± 3.3%.

Impedimetric sensor for tyramine based on gold nanoparticle doped-poly(8-anilino-1-naphthalene sulphonic acid) modified gold electrodes

A novel impedimetric sensor for the determination of tyramine (Tyr), a biogenic amine, on the surface of gold nanoparticle-poly-(8-anilino-1-napthalene sulphonic acid), AuNP-PANSA modified gold electrode (AuE) is presented for the first time. The AuNP were successfully synthesized by a green synthesis method. Their characterization and optimization were conducted using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, electrochemical impedance spectroscopy and cyclic voltammetry. Under optimal conditions, the impedimetric sensor revealed a relatively broad linear range from 0.8 to 80 µM similar to more complex architectures found in the literature and the limit of detection of 0.04 µM was the lowest achieved until now. In order to test the reliability of the proposed method, real sample application studies were conducted using dairy products and fermented drinks. It was found that the sensor presented a good selectivity and recovery. Furthermore, the impedimetric sensor shows good reproducibility, stability, selectivity and very small interferences which augur well for its application in food safety control processes.