Simultaneous voltammetric determination of nitrophenol isomers at ordered mesoporous carbon modified electrode

A Multifunctional CaII-EuIII Heterometallic Organic Framework with Sensing and Selective Adsorption in Water

With increasing global industrialization, it is urgent and challenging to develop multifunctional species for detection and adsorption in the environment. For this purpose, a novel anionic heterometallic organic framework, [(CH3)2NH2][CaEu(CAM)2(H2O)2]·4H2O·4DMF (CaEuCAM), is hydrothermally synthesized based on chelidamic acid (H3CAM). Single crystal analysis shows that CaEuCAM features two different oxygen-rich channels along the c-axis in which one CAM3- bridges two sextuple-coordinated Ca2+ and two octuple-coordinated Eu3+ with a μ4-η1: η1: η1: η1: η1: η1 new chelating and bridging mode. The characteristic bright red emission and superior hydrostability of CaEuCAM under harsh acidic and basic conditions benefit it by acting as a highly sensitive sensor for Fe3+ and 3-nitrophenol (3-NP) with extremely low LODs through remarkable quenching. The combination of experiments and theoretical calculations for sensing mechanisms shows that the competitive absorption and interaction are responsible for Fe3+-induced selective emission quenching, while that for 3-NP is the result of the synergism of host-guest chemistry and the inner filter effect. Meanwhile, the assimilation of negative charge plus channels renders CaEuCAM a highly selective adsorbent for methylene blue (MB) due to a synergy of electrostatic affinity, ion-dipole interaction, and size matching. Of note is the reusability of CaEuCAM toward Fe3+/3-NP sensing and MB adsorption besides its fast response. These findings could be very useful in guiding the development of multifunctional Ln-MOFs for sensing and adsorption applications in water media.

Alzahrani K, Althomali RH, Althobaiti SA. Electrochemical Detection of 4-Nitrophenol Using a Novel SrTiO3/Ag/rGO Composite

In this study, an eco-friendly strategy was used to prepare a novel SrTiO3/Ag/rGO composite. A SrTiO3/Ag/rGO composite-modified screen-printed carbon electrode (SPCE) was applied for the electrochemical detection of 4-nitrophenol. A simple ultrasonic method with an ultrasonic frequency of 20 kHz was used for the synthesis of SrTiO3/Ag/rGO composite material. The obtained SrTiO3/Ag/rGO composite was characterized by X-ray diffraction, Fourier transform infrared, Raman spectroscopy, field emission electron microscopy, and UV-visible spectroscopy. Electrochemical impedance spectroscopy was used to determine the electrical conductivity of the SrTiO3/Ag/rGO composite. The electrochemical properties of the modified electrode were studied using cyclic voltammetry as well as linear sweep voltammetry techniques. In comparison to SrTiO3/SPCE, SrTiO3/Ag/SPCE, and SrTiO3/rGO/SPCE electrodes, SrTiO3/Ag/rGO/SPCE demonstrates a considerable increase in 4-nitrophenol redox peak current. At optimum conditions, a large linear response range of 0.1-1000 M, with a relatively low limit of detection (0.03 M), outperforms the previously published modified electrode for 4-nitrophenol. Moreover, the SrTiO3/Ag/rGO/SPCE electrode-based 4-nitrophenol sensor is distinguished by good selectivity, high stability, and repeatability. Furthermore, SrTiO3/Ag/rGO/SPCE contributed to the detection of 4-nitrophenol in river water and drinking water with the recovery range from 97.5 to 98.7%. The experimental finding was supported by density functional theory calculation.

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.

Nickel/nitrogen-doped carbon nanocomposites: Synthesis and electrochemical sensor for determination of p-nitrophenol in local environment

A novel electrochemical sensor was prepared using N-doped carbon mesoporous materials supported with nickel nanoparticles (Ni-NCs) for environmental p-nitrophenol (p-NP) detection in a specific geographical area. These as-prepared Ni-NCs were dispersed in polyethyleneimine (PEI) solution and modified onto a glassy carbon electrode (GCE) for electrocatalytic reduction of p-NP. The Ni-NCs-PEI/GCE showed a high Faraday current at -0.302 V during p-NP reduction, because of the synergistic effect between Ni-NCs and PEI. Under ideal conditions, the Ni-NCs-PEI/GCE was used in the voltametric determination of p-NP, with high sensitivity. The linear ranges for p-NP are 0.06-10 μM and 10-100 μM with low detection limit (4.0 nM) and high sensitivity (1.465 μA μM^-1 cm^-2). In the presence of other phenolic compounds, this sensor showed good selectivity for p-NP detection. The Ni-NCs-PEI/GCE was also used to determine p-NP in environmental water samples of a specific geographical area, with recoveries ranging from 95.9% to 109.4%, and an RSD of less than 3.6%. Therefore, this novel Ni-NCs-PEI/GCE provides a good example for the design of other carbon-based nanocomposite materials, for electrochemical detection of trace p-NP in a specific geographical area.

Cr-MOF-Based Electrochemical Sensor for the Detection of P-Nitrophenol

Cr-MOF nanoparticles were synthesized by a simple hydrothermal method, and their morphology and structure were characterized by SEM, TEM, and XRD techniques. The Cr-MOF modified glassy carbon electrode (Cr-MOF/GCE) was well constructed and served as an efficient electrochemical sensor for the detection of p-nitrophenol (p-NP). It was found that the Cr-MOF nanoparticles had significant electrocatalytic activity toward the reduction of p-NP. The Cr-MOF-based electrochemical sensor exhibited a low detection limit of 0.7 μM for p-NP in a wide range of 2~500 μM and could maintain excellent detection stability in a series of interfering media. The electrochemical sensor was also practically applied to detect p-NP in a local river and confirmed its validity, showing potential application prospects.

Activated Glassy Carbon Electrode as an Electrochemical Sensing Platform for the Determination of 4-Nitrophenol and Dopamine in Real Samples

Glassy carbon electrode (GCE) was electrochemically activated using a repetitive cyclic voltammetric technique to develop an activated glassy carbon electrode (AGCE). The developed AGCE was optimized and utilized for the electrochemical assay of 4-nitrophenol (4-NP) and dopamine (DA). Cyclic voltammetry (CV) was employed to investigate the electrochemical behavior of the AGCE. Compared to the bare GCE, the developed AGCE exhibits a significant increase in redox peak currents of 4-NP and DA, which indicates that the AGCE significantly improves the electrocatalytic reduction of 4-NP and oxidation of DA. The electrochemical signature of the activation process could be directly associated with the formation of oxygen-containing surface functional groups (OxSFGs), which are the main reason for the improved electron transfer ability and the enhancement of the electrocatalytic activity of the AGCE. The effects of various parameters on the voltammetric responses of the AGCE toward 4-NP and DA were studied and optimized, including the pH, scan rate, and accumulation time. Differential pulse voltammetry (DPV) was also utilized to investigate the analytical performance of the AGCE sensing platform. The optimized AGCE exhibited linear responses over the concentration ranges of 0.04-65 μM and 65-370 μM toward 4-NP with a lower limit of detection (LOD) of 0.02 μM (S/N = 3). Additionally, the AGCE exhibited a linear responses over the concentration ranges of 0.02-1.0 and 1.0-100 μM toward DA with a lower limit of detection (LOD) of 0.01 μM (S/N = 3). Moreover, the developed AGCE-based 4-NP and DA sensors are distinguished by their high sensitivity, excellent selectivity, and repeatability. The developed sensors were successfully applied for the determination of 4-NP and DA in real samples with satisfactory recovery results.

Simultaneous electrochemical determination of nitrophenol isomers based on macroporous carbon functionalized with amino-bridged covalent organic polycalix[4]arenes

A glassy carbon electrode (GCE) modified by a hybrid, macroporous carbon (MPC) functionalized with triazine bridged covalent organic polycalix[4]arenes (CalCOP) (CalCOP-MPC), has been fabricated and utilized for simultaneous detection of nitrophenols (NP). The obtained CalCOP-MPC were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), which confirmed that MPC had functionalized with CalCOP successfully. Benefiting from the synergistic supramolecular effect of macrocyclic receptor of CalCOP and the excellent electrical properties of MPC, the anodic peaks of o-nitrophenol (o-NP), m-nitrophenol (m-NP), and p-nitrophenol (p-NP) in their mixture can be well separated by the prepared electrode. Differential pulse voltammetry (DPV) measurements at CalCOP-MPC/GCE revealed that the linear ranges of NP isomers were all 1-400 μM, and the detection limit limits were 0.383 μM, 0.122 μM, and 0.212 μM for o-NP, m-NP, and p-NP, respectively. Moreover, the prepared modified electrodes showed a relatively good selectivity and stability, implying the prospect for detecting NP in real environmental samples.

Functionalized MOF PCN-222-loaded quantum dots as an electrochemiluminescence sensing platform for the sensitive detection of p-nitrophenol

The composite PCN-222@CdSe was used to detect PNP.

In Situ Stabilisation of Silver Nanoparticles at Chitosan-Functionalised Graphene Oxide for Reduction of 2,4-Dinitrophenol in Water

This investigation reports the in situ growth of silver nanoparticles onto covalently bonded graphene oxide-chitosan, which serve as supported nanocatalysts for the NaBH4 reduction of 2,4-dinitrophenol in aqueous systems. Fumaryl chloride reacted with chitosan in an acidic environment to yield a tailored polymeric material. The latter was, in turn, treated with the pre-synthesised graphene oxide sheets under acidic conditions to generate the GO-functionalised membrane (GO-FL-CS). The adsorption of Ag+ from aqueous media by GO-FL-CS yielded a set of membranes that were decorated with silver nanoparticles (Ag NPs@GO-FL-CS) without any reducing agent. Various analytical tools were used to characterise these composites, including Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller surface area analysis, X-ray diffraction, scanning electron microscopy/energy-dispersive X-ray analysis, inductively coupled plasma-mass spectrometry, and transmission electron microscopy. The silver-loaded materials were further used for the remediation of 2,4-dinitrophenol from aqueous solutions under batch operation. The BET analysis revealed that the functionalisation of GO with chitosan and Ag NPs (average size 20-60 nm) resulted in a three-fold increased surface area. The optimised catalyst (Ag mass loading 16.95%) displayed remarkable activity with an apparent pseudo-first-order rate constant of 13.5 × 10-3 min-1. The cyclic voltammetry experiment was conducted to determine the nitro-conversion pathway. The reusability/stability test showed no significant reduction efficiency of this metal-laden composite over six cycles. Findings from the study revealed that Ag NPs@GO-FL-CS could be employed as a low-cost and recyclable catalyst to convert toxic nitroaromatics in wastewater.

Spectrophotometric Determination of p-Nitrophenol under ENP Interference

Engineered nanoparticles (ENPs) have been widely developed in various fields in recent years, resulting in an increasing occurrence of nanoparticles in the natural environment. However, the tiny substances have created unexpected confusion in environmental sample testing due to the negative nanoeffect of ENPs. In this paper, a novel technique of spectrophotometric determination of p-nitrophenol (PNP) was developed under the interfering impact of nano-Fe(OH)₃, widely distributed in the natural environment as a typical example of ENPs. Because of the strong absorption at the two characteristic peaks of PNP, namely, 317 nm and 400 nm, nano-Fe(OH)₃ interfered with the colorimetric determination of PNP. Thus, the developed testing method, with HCl acidification at 60°C and ascorbic acid (AA) masking FeCl₃, was proposed and successfully realized the accurate determination of PNP in water samples by ultraviolet spectrophotometry with 317 nm as the absorption wavelength. The final colorimetric system of 5% HCl, 10% CH₃OH, and 1% ascorbic acid was confirmed by optimized batch experiments, and the optimum condition of acidification pretreatment was heating at 60°C for 20 min. Further results demonstrated that the proposed novel method had good accuracy and reproducibility even in high-salinity natural water bodies such as groundwater and surface water. The testing technique presented in this paper provided an interesting and useful tool for problem solving of PNP surveys under ENPs' interference and practically supported water quality assessment for a better environment.

Novel construction of carbon nanofiber/CuCrO2 composite for selective determination of 4-nitrophenol in environmental samples and for supercapacitor application

A simple hydrothermal process has been used to prepare a carbon nanofiber/copper chromium dioxide (CNF/CuCrO₂) composite for the selective detection of 4-nitrophenol (4-NP) and supercapacitor applications. The electrochemical sensor was developed with a glassy carbon electrode (GCE) modified with the CNF/CuCrO₂ composite by the drop-casting method. The structural formation of the prepared materials was confirmed by infrared spectroscopy, electrochemical impedance spectroscopy, Raman spectroscopy, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. To investigate the electrochemical efficiency of the electrode, various electroanalytical techniques, namely, differential pulse voltammetry (DPV), cyclic voltammetry (CV) and galvanostatic charge–discharge tests, were employed. The GCE/CNF/CuCrO₂ modified electrode exhibited excellent electrocatalytic behavior for the detection of 4-NP under optimized conditions with a low detection limit (0.022 μM), long linear response range of 0.1–150 μM, and high sensitivity (20.02 μA μM⁻¹ cm⁻²). The modified electrode was used for the detection of 4-NP in real samples with satisfactory results. In addition, the GCE/CNF/CuCrO₂ electrode has advantages such as stability, reproducibility, repeatability, reliability, low cost, and practical application. The CNF/CuCrO₂ composite coated Ni-foam electrodes also exhibited excellent supercapacitor efficiency, with a high specific capacitance of up to 159 F g⁻¹ at a current density of 5 A g⁻¹ and outstanding cycling stability. Hence, the CNF/CuCrO₂ composite is a suitable material for 4-NP sensors and energy storage applications.

A simple hydrothermal process has been used to prepare a carbon nanofiber/copper chromium dioxide (CNF/CuCrO₂) composite for the selective detection of 4-nitrophenol (4-NP) and supercapacitor applications.

Electrochemical determination of chloramphenicol and metronidazole by using a glassy carbon electrode modified with iron, nitrogen co-doped nanoporous carbon derived from a metal-organic framework (type Fe/ZIF-8)

In this study, an iron-doped metal-organic framework (MOF) Fe/ZIF-8 was synthesized from ZIF-8 at room temperature. Direct carbonization of Fe/ZIF-8 under a nitrogen atmosphere produced nanoporous nitrogen doped carbon nanoparticles decorated with Fe component (Fe/NC). The Fe/NC exhibited a large surface area (1221.185 m² g^-1) and narrow pore-size distribution (3-5 nm). The nanoporous Fe/NC components along with Nafion were used to modify a glassy carbon electrode for the electrochemical determination of chloramphenicol and metronidazole via linear sweep voltammetry. Under optimal conditions, the reduction peak currents (observed at -0.237 V and -0.071 V vs. Ag/AgCl) of these analytes increased linearly with increasing chloramphenicol and metronidazole concentrations in the range of 0.1-100 μM and 0.5-30 μM, with the detection limits estimated to be 31 nM and 165 nM, respectively. This result was attributed to the large surface area, porous structure, high nitrogen content, and as well as the electrocatalytic effect of Fe atoms embeded in the carbon support. The proposed sensor was used for chloramphenicol and metronidazole analysis in samples, providing satisfactory results.

Highly sensitive and selective determination of p-nitrophenol at an interpenetrating networks structure of self-assembled rod-like lanthanum hydroxide-oxidized multi-walled carbon nanotubes nanocomposite

In this study, a novel electrochemical sensor based on self-assembled rod-like lanthanum hydroxide-oxidized multi-walled carbon nanotubes (La(OH)₃-OxMWCNTs) nanocomposite was developed for sensitive determination of p-nitrophenol (p-NP). The La(OH)₃-OxMWCNTs nanocomposite with an interpenetrating networks structure was characterized by field emission electron microscope (FE-SEM), Fourier transform infrared (FT-IR) spectroscopy, Raman spectra and X-ray photoelectron spectroscopy (XPS). The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were performed to study the electrochemical behaviors of La(OH)₃-OxMWCNTs modified glassy carbon electrode (La(OH)₃-OxMWCNTs/GCE). The La(OH)₃-OxMWCNTs/GCE was used for sensitive determination of p-NP by CV and linear sweep voltammetry (LSV). Under the optimum conditions, the peak currents of LSV versus the concentrations of p-NP in the range 1.0-30.0 μmol L^-1 showed a good linear relationship (R²=0.9971), and the limit of detection (LOD) was calculated to be 0.27 μmol L^-1 (signal-to-noise ratio of 3, S/N=3). The recoveries of p-NP in real samples of industrial wastewater and Xiangjiang water at La(OH)₃-OxMWCNTs/GCE were in the range of 95.62-110.75% with relative standard deviation (RSD) in the range of 1.65-3.85%. The intra-day and inter-day precisions were estimated to be less than 2.76% (n= 5), indicating that La(OH)₃-OxMWCNTs/GCE possessed highly stability. In addition, La(OH)₃-OxMWCNTs/GCE sensor showed good anti-interference ability for determination of p-NP in aqueous mixtures containing high concentrations of inorganic and organic interferents, and a decrease of oxidation peak currents by less than 3.57% relative to the initial levels indicated it possessed excellent selectivity. Therefore, La(OH)₃-OxMWCNTs/GCE could be used as a fast, selective and sensitive electrochemical sensor platform for the selective determination and quantification of aqueous p-NP.

An Astragalus membranaceus based eco-friendly biomimetic synthesis approach of ZnO nanoflowers with an excellent antibacterial, antioxidant and electrochemical sensing effect

Nowadays featuring outstanding eco-friendliness, the phytochemical fabrication method of nanostructures is very popular. Here, we propose to utilize the Astragalus membranaceus extract as the reducing and capping agent to stabilize the metal and to avoid the aggregations of nanoparticles during ZnO nanoflowers synthesis procedure. As a result, the whole fabrication procedure was highly efficient and cost-effective without requiring a special environment of high pressure or elevated temperature and without chemical hazards used or produced. After the fabrication, detailed characterization about material morphology and crystal structure was carried out, including scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscope (FTIR). Moreover, the ZnO nanoflowers demonstrated distinctive antibacterial, antioxidant and electrochemical sensing effect. Specifically, ZnO nanoflowers had an antibacterial inhibition zone of 19(±0.7) and 15(±0.8) mm in diameter against the concentration of 50 μL (1 mg/mL) Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), which is greatly improved compared to the reference drug (Kanamycin). Besides, antioxidant activity was also tested using H₂O₂ free radical scavenging assay and 60% 2,2-diphenyl-1-picrylhydrazyl (DPPH) inhibition of 0.5 mg/mL was reported. Finally, controlled by the diffusion process during the charge transfer procedure, 4-nitorphenol was dramatically reduced and a limit of detection of 0.08 μM by ZnO nanoflowers modified electrode was observed during the cyclic voltammetry (CV) experiment. Because the phenolic compounds originating from Astragalus membranaceus helped to facilitate the electron transfer, the limit of detection was lower compared to other materials, such as copper oxide nanoparticles (Cu₂O-NPs), silicon dioxide/silver nanoparticles (SiO₂/Ag-NPs), zinc oxide nanoparticles (ZnO-NPs), activated carbon (AC) and cobalt oxide nanocubes (Co₃O₄). Therefore, featuring easy operation, low-cost and eco-friendliness, our proposed ZnO nanoflowers fabrication method will have a great potential in biomedical and electro-catalytic fields.

Hematite/M (M = Au, Pd) Catalysts Derived from a Double-Hollow Prussian Blue Microstructure: Simultaneous Catalytic Reduction of o- and p-Nitrophenols

Present study deals with hematite/M (M = Au, Pd) catalysts converted from a double-hollow Prussian blue microstructure (DHPM). The unique Prussian blue (PB) microstructure (MS) is prepared by a template-free solvothermal synthetic route in a single-step reaction. An amine-functionalized silicate sol-gel matrix (SSG) has served as the structure-directing agent cum stabilizer for making DHPM. Synthesized DHPM is having a unique structure: a hollow core and an in situ etched porous surface. Growth mechanism is explored and revealed by analyzing several experimental parameters such as HCl concentration, Fe source, effect of the added EtOH, silane concentration, and role of silanes' amine groups. It is identified that the superstructure consisted of well-aligned PB cubes growing radially from the core of the superstructure. Metal (Au and Pd) nanoparticles (NPs) are deposited on both interior and exterior of the PB MS through galvanic displacement reaction, and thus metal NP-loaded hematite phase iron oxide (α-Fe₂O₃) nanomaterials were derived by annealing them in air. Catalytic activities of the hematite/M(M = Au, Pd) MS are investigated toward simultaneous catalytic reduction of o-nitrophenol and p-nitrophenol. The resultant hematite/Pd MS showed high structural stability and catalytic active sites than the hematite/Au MS, which enhances the catalytic properties for the simultaneous catalytic reduction of both nitrophenols.

Rationally designed RGO@CuO@Mn2O3 as an excellent electrocatalyst for the rapid and real-time detection of 2-nitrophenol

Rationally designed and functional electronic structures of TMOs (precisely Cu and Mn) with purposeful morphologies were prepared using a facile synthetic method.

Reduced Graphene Oxide-Conjugated Urchin-Like NiCo2O4 Nanostructures for Individual Detection of o-Nitro and p-Amino Phenol

This work introduced a facile synthesis method of reduced graphene oxide-conjugated urchin-like NiCo2O4 nanostructures via a simple, cost-effective, and environmental-friendly one-pot hydrothermal method. The as-prepared rGO-NiCo2O4 nanocomposites were used to fabricate 3-aminopropyltriethoxysilane-modified glassy carbon electrode (GCE/APTES/rGO-NiCo2O4) for ultrasensitive electrochemical detection of o-nitro (o-NP) and p-amino (p-AP) phenols. The structure and morphology of the nanocomposite were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. Electrochemical experiments revealed that the nanocomposite exhibited remarkable electrochemical performances. A linear relationship is observed with the differential pulse voltammetry experiment between the peak currents and the concentrations in the ranges of 5.0 × 10-9 to 5.0 × 10-7 M (R 2 = 0.996) and 1.0 × 10-6 to 2.5 × 10-5 M (R 2 = 0.992) for o-NP and of 1.0 × 10-8 to 5.0 × 10-7 M (R 2 = 0.996) and 1.0 × 10-6 to 1.0 × 10-4 M (R 2 = 0.987) for p-AP. The calculated detection limits (S/N = 3) are 5.0 × 10-9 M and 1.0 ×10-8 M for o-NP and p-AP, respectively. Furthermore, a very high recovery percentage is obtained with the proposed sensor after successful application in the determination of target analytes in tap water samples.

In situ Preparation of HNbMoO6/C Nanocomposite for Sensitive Detection of Clenbuterol

In this paper, we synthesized HNbMoO₆/C composite through the calcination of octylamine-intercalated HNbMoO₆ precursor. The resulting HNbMoO₆/C composite showed some new phases of MoO₂, MoO₃, NbO₂, Nb₂O₅, and carbon, which was fully confirmed via powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and X-ray photoelectron spectroscopy (XPS) technologies. Besides, the HNbMoO₆/C hybrid was coated on glass carbon electrode to construct an electrochemical sensor for sensitive determination of clenbuterol. The electrochemical behaviors of clenbuterol on the prepared electrode were tested by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) analysis. The results showed that the intercalated carbon can act as active sites to accelerate electron transfer. In addition, more exposed surface areas of the HNbMoO₆/C composite will facilitate the electrolyte to permeate. The oxidation peak current of clenbuterol was linearly related to its concentration in the range of 1.04 × 10^-5 to 7.51 × 10^-4 mol L^-1, and the determination limit was calculated to be 3.03 × 10^-6 mol L^-1 (S/N = 3). This sensor exhibits excellent stability, reproducibility, specificity, and good recoveries when applied to monitor clenbuterol in real samples.

Simultaneous Determination of 2-Nitrophenol and 4-Nitrophenol in Pharmaceutical Industrial Wastewater by Electromembrane Extraction Coupled with HPLC-UV Analysis

Background: In the present study, an electromembrane extraction (EME) followed by a simple high performance liquid chromatography with ultraviolet detection (HPLC-UV) was developed and validated for simultaneous determination of 2-nitrophenol (2-NP) and 4-nitrophenol (4-NP) in pharmaceutical industrial wastewater sample. Main parameters of electromembrane extraction were evaluated and optimized. Methods: 1-octanol was immobilized in the pores of a polypropylene hollow fiber as supported liquid membrane. As a driving force, a 100 volt electrical voltage was applied to transfer the analytes from the sample solution (pH, 7.5) through the supported liquid membrane into an acceptor solution (pH, 12). Results: The best enrichment factors were obtained 36 and 72 for 2-NP and 4-NP, respectively after 15 minutes of extraction. The effect of carbon nanotube, as a solid nano-sorbent on EME efficiency, was also evaluated. The proposed method provided the linearity in the range of 10-1000 ng/mL for 2-NP (R2> 0.9997) and 4-NP (R2> 0.9999) with repeatability range (% RSD) between 2.6-10.3 % (n = 3). The limit of detection was 3 ng/mL and the limit of quantitation was 10 ng/mL. Conclusion: Finally, the method was applied for the determination of 2-NP and 4-NP in industrial wastewater samples with relative recoveries in the range between 67–76 %. EME improved the sensitivity of HPLC-UV for the determination of trace concentrations of these analytes.

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.

An electrochemical sensor for the detection of p-nitrophenol based on a cyclodextrin-decorated gold nanoparticle–mesoporous carbon hybrid

A novel electrochemical sensor based on a cyclodextrin-decorated gold nanoparticle–mesoporous carbon hybrid was constructed for the detection of p-nitrophenol.

Efficient electrochemical determination of p-aminophenol using a novel tricomponent graphene-based nanocomposite

Design and synthesis of a gold nanoparticle@dithiooxamide functionalized graphene (AuNP@DFG) nanocomposite is reported herein, which is employed for the electrochemical determination of p-aminophenol successfully.