2D MXene-Based Nanoscale Materials for Electrochemical Sensing Toward the Detection of Hazardous Pollutants: A Perspective

MXenes (Mn+1XnTx), a subgroup of 2-dimensional (2D) materials, specifically comprise transition metal carbides, nitrides, and carbonitrides. They exhibit exceptional electrocatalytic and photocatalytic properties, making them well-suited for the detection and removal of pollutants from aqueous environments. Because of their high surface area and remarkable properties, they are being utilized in various applications, including catalysis, sensing, and adsorption, to combat pollution and mitigate its adverse effects. Different characterization techniques like XRD, SEM, TEM, UV-Visible spectroscopy, and Raman spectroscopy have been used for the structural elucidation of 2D MXene. Current responses against applied potential were measured during the electrochemical sensing of the hazardous pollutants in an aqueous system using a variety of electroanalytical techniques, including differential pulse voltammetry, amperometry, square wave anodic stripping voltammetry, etc. In this review, a comprehensive discussion on structural patterns, synthesis, properties of MXene and their application for electrochemical detection of lethal pollutants like hydroquionone, phenol, catechol, mercury and lead, etc. are presented. This review will be helpful to critically understand the methods of synthesis and application of MXenes for the removal of environmental pollutants.

Chemically Exfoliated Titanium Carbide MXene for Highly Sensitive Electrochemical Sensors for Detection of 4-Nitrophenols in Drinking Water

Soil and water contamination by numerous pollutants has been increasingly posing threats to food, water, agriculture, and human health. Using novel nanoscale materials to develop rapid electrochemical sensors is very promising due to the discovery of a number of new two-dimensional (2D) electronic materials. Of particular importance is 2D transition-metal carbide MXene that has been shown to possess transformative properties pertaining to its physical, chemical, and environmental characteristics, leading to their potential sensor applications. Designing electrochemical sensors using MXene has the potential to pave the way for monitoring environmental pollutants. Here, a stacked layer of chemically exfoliated MXene (Ti₃C₂T _x ) was demonstrated as an electrochemical sensor for detection of 4-nitrophenol (4-NP) with high sensitivity and a low limit of detection. Successful selective exfoliation of the MAX (Ti₃AlC₂) phase of the material by chemical etching without oxidation is shown to be the key to achieving higher sensitivity and a lower detection limit. In the optimal conditions, the proposed MXene sensor electrodes were capable of detecting 4-NP in a broad concentration range from 500 nM to 100 μM with a good linear sensing range (regression fit, R = 0.995). The higher sensitivity and notable limit of detection reached about 16.35 μA μM^-1 cm^-2 and 42 nM/L, respectively, with good reproducibility and repeatability. The real-time application of the proposed MXene sensor electrodes was confirmed by testing in tap water samples with excellent recoveries of 95-99%.

Application of palladium nanoparticles supported organo-kaolinite for 4-chloro-2-nitroaniline catalytic reduction and electrochemical detection

Palladium nanoparticles (PdNPs) supported organo-kaolinite was used as a solid catalyst for the reduction and electrochemical detection of 4-chloro-2-nitroaniline (CNA). During the catalytic reduction in presence of NaBH4, the effects...

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.

Facile solvothermal decomposition synthesis of single phase ZnBi38O60 nanobundles for sensitive detection of 4-nitrophenol

We have developed the facile solvothermal decomposition route to fabricate a single phase zinc bismuthate (ZnBi₃₈O₆₀) binary composite nanostructure.

A ternary Cu2O-Cu-CuO nanocomposite: a catalyst with intriguing activity

In this work, the syntheses of Cu2O as well as Cu(0) nanoparticle catalysts are presented. Copper acetate monohydrate produced two distinctly different catalyst particles with varying concentrations of hydrazine hydrate at room temperature without using any surfactant or support. Then both of them were employed separately for 4-nitrophenol reduction in aqueous solution in the presence of sodium borohydride at room temperature. To our surprise, it was noticed that the catalytic activity of Cu2O was much higher than that of the metal Cu(0) nanoparticles. We have confirmed the reason for the exceptionally high catalytic activity of cuprous oxide nanoparticles over other noble metal nanoparticles for 4-nitrophenol reduction. A plausible mechanism has been reported. The unusual activity of Cu2O nanoparticles in the reduction reaction has been observed because of the in situ generated ternary nanocomposite, Cu2O-Cu-CuO, which rapidly relays electrons and acts as a better catalyst. In this ternary composite, highly active in situ generated Cu(0) is proved to be responsible for the hydride transfer reaction. The mechanism of 4-nitrophenol reduction has been established from supporting TEM studies. To further support our proposition, we have prepared a compositionally similar Cu2O-Cu-CuO nanocomposite using Cu2O and sodium borohydride which however displayed lower rate of reduction than that of the in situ produced ternary nanocomposite. The evolution of isolated Cu(0) nanoparticles for 4-nitrophenol reduction from Cu2O under surfactant-free condition has also been taken into consideration. The synthetic procedures of cuprous oxide as well as its catalytic activity in the reduction of 4-nitrophenol are very convenient, fast, cost-effective, and easily operable in aqueous medium and were followed spectrophotometrically. Additionally, the Cu2O-catalyzed 4-nitrophenol reduction methodology was extended further to the reduction of electronically diverse nitroarenes. This concise catalytic process in aqueous medium at room temperature revealed an unprecedented catalytic performance which would draw attention across the whole research community.

A two-oxide nanodiode system made of double-layered p-type Ag2O@n-type TiO2 for rapid reduction of 4-nitrophenol

The mechanism for the reduction reaction of 4-nitrophenol to 4-aminophenol in the presence of a SiO₂/Ag₂O@TiO₂ composite catalyst.

Nanomolar determination of 4-nitrophenol based on a poly(methylene blue)-modified glassy carbon electrode

A poly(methylene blue)-modified glassy carbon electrode (PMB/GCE) was fabricated by electropolymerisation of methylene blue on a GCE and further utilized to investigate the electrochemical determination of 4-nitrophenol (4-NP) by cyclic voltammetry (CV), differential pulse voltammetry and chronocoulometry. The morphology of the PMB on GCE was examined using a scanning electron microscope (SEM). An oxidation peak of 4-NP at the PMB modified electrode was observed at 0.28 V, and in the case of bare GCE, no oxidation peak was observed, which indicates that PMB/GCE exhibits a remarkable effect on the electrochemical determination of 4-NP. Due to this remarkable effect of PMB/GCE, a sensitive and simple electrochemical method was proposed for the determination of 4-NP. The effect of the scan rate and pH was investigated to determine the optimum conditions at which the PMB/GCE exhibits a higher sensitivity with a lower detection limit. Moreover, kinetic parameters such as the electron transfer number, proton transfer number and standard heterogeneous rate constant were calculated. Under optimum conditions, the oxidation current of 4-NP is proportional to its concentration in the range of 15-250 nM with a correlation coefficient of 0.9963. The detection limit was found to be 90 nM (S/N = 3). The proposed method based on PMB/GCE is simple, easy and cost effective. To further confirm its possible application, the proposed method was successfully used for the determination of 4-NP in real water samples with recoveries ranging from 97% to 101.6%. The interference due to sodium, potassium, calcium, magnesium, copper, zinc, iron, sulphate, carbonate, chloride, nitrate and phosphate was found to be almost negligible.

Microelectrode arrays with overlapped diffusion layers as electroanalytical detectors: theory and basic applications

This contribution contains a survey of basic literature dealing with arrays of microelectrodes with overlapping diffusion layers as prospective tools in contemporary electrochemistry. Photolithographic thin layer technology allows the fabrication of sensors of micrometric dimensions separated with a very small gap. This fact allows the diffusion layers of single microelectrodes to overlap as members of the array. Various basic types of microelectrode arrays with interacting diffusion layers are described and their analytical abilities are accented. Theoretical approaches to diffusion layer overlapping and the consequences of close constitution effects such as collection efficiency and redox cycling are discussed. Examples of basis applications in electroanalytical chemistry such as amperometric detectors in HPLC and substitutional stripping voltammetry are also given.