Fabrication of Ag@Co-Al Layered Double Hydroxides Reinforced poly(o-phenylenediamine) Nanohybrid for Efficient Electrochemical Detection of 4-Nitrophenol, 2,4-Dinitrophenol and Uric acid at Nano Molar Level

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.

Carboxymethyl β-Cyclodextrin Assistance for the 4-Nitrophenol Reduction Using Cobalt-Based Layered Double Hydroxides

Cobalt-aluminum-layered double hydroxides containing carboxymethyl β-cyclodextrin (CMβCD) were synthesized by coprecipitation and evaluated as a cobalt source for the 4-nitrophenol reduction in an aqueous medium. Several physicochemical techniques (XRD, FTIR, TGA) indicated the intercalation of the anionic cyclodextrin without damages to the hydrotalcite-type structure. These lamellar cobalt-aluminum hybrid materials (CoAl_CMβCD) were evaluated in the 4-nitrophenol reduction and showed higher activities in comparison with the CMβCD-free standard material (CoAl_CO3). To rationalize these results, a set of experimental controls going from physical mixtures of CoAl_CO3 with different cyclodextrins to other cobalt-based materials were investigated, highlighting the beneficial effects of both the layered double hydroxide and CMβCD-based hybrid structures. CMβCD also showed a beneficial effect as an additive during the 4-nitrophenol reduction. CoAl_CO3, dispersed in a fresh CMβCD solution could be re-used for five successive cycles without the loss of activity.

Efficient Dye Degradation and Antimicrobial Behavior with Molecular Docking Performance of Silver and Polyvinylpyrrolidone-Doped Zn-Fe Layered Double Hydroxide

Zn-Fe layered double hydroxide (LDH) was synthesized through the low-temperature-based coprecipitation method. Various concentrations of Ag (1, 3, and 5 wt %) with a fixed amount (5 wt %) of polyvinylpyrrolidone (PVP) were doped into LDH nanocomposites. This research aims to improve the bactericidal properties and catalytic activities of doping-dependent nanocomposites. Adding Ag and PVP to LDH enhanced oxygen vacancies, which increased the amount of hydroxide adsorption sites and the number of active sites. The doped LDH was employed to degrade rhodamine-B dye in the presence of a reducing agent (NaBH4), and the obtained results showed maximum dye degradation in a basic medium compared to acidic and neutral. The bactericidal efficacy of doped Zn-Fe (5 wt %) showed a considerably greater inhibition zone of 3.65 mm against Gram-negative (G-ve) or Escherichia coli (E. coli). Furthermore, molecular docking was used to decipher the mystery behind the microbicidal action of Ag-doped PVP/Zn-Fe LDH and to propose an inhibition mechanism of β-ketoacyl-acyl carrier protein synthase IIE. coli (FabH) and deoxyribonucleic acid gyrase E. coli behind in vitro results.

Nanocomposites with ZrO2@S-Doped g-C3N4 as an Enhanced Binder-Free Sensor: Synthesis and Characterization

This study describes new electrocatalyst materials that can detect and reduce environmental pollutants. The synthesis and characterization of semiconductor nanocomposites (NCs) made from active ZrO₂@S-doped g-C₃N₄ is presented. Electrochemical impedance spectroscopy (EIS) and Mott-Schottky (M-S) measurements were used to examine electron transfer characteristics of the synthesized samples. Using X-ray diffraction (XRD) and high-resolution scanning electron microscopy (HR-SEM) techniques, inclusion of monoclinic ZrO₂ on flower-shaped S-doped-g-C₃N₄ was visualized. High-resolution X-ray photoelectron spectroscopy (XPS) revealed successful doping of ZrO₂ into the lattice of S-doped g-C₃N₄. The electron transport mechanism between the electrolyte and the fluorine tin-oxide electrode (FTOE) was enhanced by the synergistic interaction between ZrO₂ and S-doped g-C₃N₄ as co-modifiers. Development of a platform with improved conductivity based on an FTOE modified with ZrO₂@S-doped g-C₃N₄ NCs resulted in an ideal platform for the detection of 4-nitrophenol (4-NP) in water. The electrocatalytic activity of the modified electrode was evaluated through determination of 4-NP by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) under optimum conditions (pH 5). ZrO₂@S-doped g-C₃N₄ (20%)/FTOE exhibited good electrocatalytic activity with a linear range from 10 to 100 μM and a low limit of detection (LOD) of 6.65 μM. Typical p-type semiconductor ZrO₂@S-doped g-C₃N₄ NCs significantly impact the superior detection of 4-NP due to its size, shape, optical properties, specific surface area and effective separation of electron-hole pairs. We conclude that the superior electrochemical sensor behavior of the ZrO₂@S-doped g-C₃N₄ (20%)/FTOE surfaces results from the synergistic interaction between S-doped g-C₃N₄ and ZrO₂ surfaces that produce an active NC interface.

Gravity-driven layered double hydroxide nanosheet membrane activated peroxymonosulfate system for micropollutant degradation

For the first time in this study, CoAl-layered double hydroxide nanosheet membrane (LDH_m) with abundant active sites was fabricated for peroxymonosulfate (PMS) activation with the mindset to catalytically degrade micropollutants. Depending on the catalyst loading, the developed LDH_m can be driven under gravity at a permeate flux of approximately 80 L/m² h and 210 L/m² h at LDH loading of 0.80 mg/cm² and 0.08 mg/cm², respectively. Notably, the LDH_m (0.63 mg) exhibited excellent PMS activation efficiency as indicated by 87.8% removal of the probe chemical (ranitidine) at 0.2 mM PMS, which was higher than that (37-44%) achieved by conventional LDH (5-20 mg)/PMS (0.2 mM) system. In addition to efficient degradation of several micropollutants, LDH_m/PMS performance was not inhibited by variation in solution pH (4-8) as well as during long-term (29 h) continuous-flow operation. SO₄^•- and ¹O₂ were identified as the primary reactive species in the LDH_m/PMS system, while both Co and Al participated in PMS activation. This study offers a simple strategy for efficient removal of several micropollutants with significantly reduced catalyst leaching, which could be applied sustainably in water treatment.

Rationally Designed Ag@polymer@2-D LDH Nanoflakes for Bifunctional Efficient Electrochemical Sensing of 4-Nitrophenol and Water Oxidation Reaction

The rational design and demonstration of a facile sequential template-mediated strategy to construct noble-metal-free efficient bifunctional electrocatalysts for efficient oxygen evolution reaction (OER) and electrocatalytic detection of hazardous environmental 4-nitrophenol (4-NP) have continued as a major challenging task. Herein, we construct a novel Ag@polymer/NiAl LDH (designated as APL) nanohybrid as an efficient bifunctional electrocatalyst by a simple hydrolysis method. The well-fabricated APL/GCE exhibited an extensive linear range from 0.1 to 100 μM in optimized conditions. It showed a detection limit (LOD) of 0.0096 μM (9.6 nM) (S/N = 3) for 4-NP in pH 6 by differential pulse voltammetry (DPV). Meanwhile, the newly fabricated APL exhibited outstanding OER activity with a very low overpotential of 259 mV to deliver 10 mA cm^-2 current density (J) at a scan rate of 5 mV/s. The Tafel plot value of APL is low (97 mV/dec) compared to that of the benchmark RuO₂ due to a fast kinetic reaction. Besides, the durability of the electrocatalyst was assessed by a chronoamperometry test (CA) for 36 h at 1.55 mV vs RHE, and the long-term cycling stability was analyzed by using cyclic voltammetry (CV); after 5000 cycles, the electrocatalyst was highly stable. These demonstrated results could lead to an alternative electrocatalyst construction for the bifunctionally efficient electrochemical sensing of 4-nitrophenol and oxygen evolution reaction.

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.

Surface-tuned hierarchical ɤ-Fe2O3-N-rGO nanohydrogel for efficient catalytic removal and electrochemical sensing of toxic nitro compounds

4- Nitrophenol (4-NP) is a top rated hazardous environmental pollutant and secondary explosive chemicals. For the sake of ecology and environment safety, the catalytic reduction and detection of 4-NP is highly important. In this work, ɤ-Fe₂O₃-nitrogen doped rGO (ɤ-Fe₂O₃-N-rGO) nanohydrogel was synthesized by green hydrothermal method. The morphology and phase purity of prepared ɤ-Fe₂O₃-N-rGO nanohydrogel were confirmed by various analytical (SEM, TEM, XRD, and XPS) and electrochemical techniques. The morphological structure of ɤ-Fe₂O₃-N-rGO nanohydrogel confirmed that the nanocrystals are well covered over the 2D N-rGO layer. Further, ɤ-Fe₂O₃-N-rGO nanohydrogel was applied for the catalytic reduction and electrochemical detection of ecotoxic 4-NP. A low cost, ɤ-Fe₂O₃-N-rGO nanohydrogel displayed an excellent catalytic activity, high recyclability (>5 cycles) and high conversion efficiency of 4-NP to 4-Aminophenol (4-AP). In addition, ɤ-Fe₂O₃-N-rGO nanohydrogel modified GCE displayed a wide linear sensing range (0.1-1000 μM), and a low detection limit (LOD) of 0.1 μM with excellent sensitivity, high selectivity (<1.2%) and good stability (>4 weeks). The developed sensor electrode shows the low reduction potential of -0.3 V and -0.60 V for the determination of 4-NP. The proposed ɤ-Fe₂O₃-N-rGO nanohydrogel is promising catalyst for the detection and removal of toxic aromatic nitro compounds in real site applications.

Real time detection and monitoring of 2, 4-dinitrophenylhydrazine in industrial effluents and water bodies by electrochemical approach based on novel conductive polymeric composite

Much attention has been given to detection and monitoring of hydrazine-based compounds in recent time because of its significant negative impacts on human health and ecosystem (aquatic lives). This prompted the current study focusing on detection of 2, 4-dinitrophenylhydrazine (2, 4-dnphz) using electrochemically synthesized poly-para amino benzoic acid-manganese oxide (P-pABA-MnO₂) composite film. The synthesized P-pABA-MnO₂ composite film was characterized in terms of its structural and morphological properties by X-ray diffraction spectroscopy and field emission scanning electron microscopy respectively. In addition, functionalities and binding energy of p-PABA-MnO2 were confirmed using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy respectively. Finally, electrochemical properties were investigated using electrochemical impedance spectroscopy and cyclic voltammetry. The synthesized P-pABA-MnO₂ displayed good electrocatalytic reduction property towards 2, 4-dnphz with ultra-low limit of detection (0.08 μM; S/N = 3) and very high sensitivity (52 μAμ^-1Mcm^-2). The proposed sensor based on P-pABA-MnO₂ also demonstrated good stability in terms of repeatability, reproducibility and interferents effects. Lastly, the proposed sensor was satisfactorily used in detection of 2, 4-dnphz in environmental real samples.

Bi2O3 Nanoparticles Decorated Carbon Nanotube: An Effective Nanoelectrode for Enhanced Electrocatalytic 4-Nitrophenol Reduction

4-Nitrophenol (4-NP) is present in most industrial waste water resources as an organic pollutant, and is a highly toxic and environmentally hazardous pollutant. Herein, we report that bismuth oxide (Bi2O3) decorated multi-walled carbon nanotubes (Bi2O3@MWCNTs) are the most prominent electrocatalyst for 4-NP electroreduction in acidic conditions. The electrocatalyst is synthesized by a simple chemical reduction method using ethylene glycol as a capping agent. The synthesized Bi2O3@MWCNTs electrocatalyst has been well-characterized by Fourier-transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy. Bi2O3@MWCNTs have a cubic structure which is confirmed by XRD. TEM imaging reveals Bi2O3 NPs are ~2 nm in size, are grown on MWCNTs and that these nanoparticles are active toward 4-NP electroreduction. The electrochemical studies by cyclic voltammetry measurements show that the Bi2O3@MWCNTs electrocatalyst can sense 4-NP at a very low potential i.e., -0.17 vs. saturated calomel electrode (SCE). Furthermore, electroanalytical parameters like scan rate and concentration dependence were studied with electrochemcial impedance spectroscopy (EIS) and the effect of pH on cathodic current was examined under experimental conditions. The lower limit of detection (LOD) was found to be 0.1 μM for the Bi2O3@MWCNTs nanomaterial and is excellent toward 4-NP. The present study has applications for reducing water pollution and for sorting out related issues.