Large interlayer spacing Nb4C3Tx (MXene) promotes the ultrasensitive electrochemical detection of Pb2+ on glassy carbon electrodes

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.

Ecotoxicity and environmental safety assessment of two-dimensional niobium carbides (MXenes)

Two-dimensional (2D) MXenes have gained great interest in water treatment, biomedical, and environmental applications. The antimicrobial activity and cell toxicity of several MXenes including Nb4C3Tx and Nb2CTx have already been explored. However, potential side effects related to Nb-MXene toxicity, especially on aquatic pneuma, have rarely been studied. Using zebrafish embryos, we investigated and compared the potential acute toxicity between two forms of Nb-MXene: the multilayer (ML-Nb4C3Tx, ML-Nb2CTx) and the delaminated (DL-Nb2CTx, and DL-Nb4C3Tx) Nb-MXene. The LC50 of ML-Nb4C3Tx, ML-Nb2CTx, DL-Nb2CTx, and DL-Nb4C3Tx were estimated to be 220, 215, 225, and 128 mg/L, respectively. Although DL-Nb2CTx, and DL-Nb4C3Tx derivatives have similar sizes, DL-Nb4C3Tx not only shows the higher mortality (LC50 = 128 mg/L Vs 225 mg/L), but also the highest teratogenic effect (NOEC = 100 mg/L Vs 200 mg/L). LDH release assay suggested more cell membrane damage and a higher superoxide anion production in DL-Nb4C3Tx than DL-Nb2CTx,. Interestingly, both DL-Nb-MXene nanosheets showed insignificant cardiac, hepatic, or behavioral toxic effects compared to the negative control. Embryos treated with the NOEC of DL-Nb2CTx presented hyperlocomotion, while embryos treated with the NOEC of DL-Nb4C3Tx presented hyperlocomotion, suggesting developmental neurotoxic effect and muscle impairment induced by both DL-Nb-MXene. According to the Fish and Wildlife Service (FSW) Acute Toxicity Rating Scale, all tested Nb-MXene nanosheets were classified as "Practically not toxic". However, DL-Nb4C3Tx should be treated with caution as it might cause a neurotoxic effect on fauna when it ends up in wastewater in high concentrations.

Defect-Free Few-Layer M4 C3 Tx (M = V, Nb, Ta) MXene Nanosheets: Synthesis, Characterization, and Physicochemical Properties

High-quality few-layer M4 C3 Tx (M = V, Nb, Ta) MXenes are very important for applications and are necessary for clarifying their physicochemical properties. However, the difficulty in etching for themselves and the existence of MC/MC1-δ and M-Al alloy impurities in their M4 AlC3 precursors seriously hinder the achievement of defect-free few-layer M4 C3 Tx (M = V, Nb, Ta) MXenes nanosheets. Herein, three different defect-free few-layer M4 C3 Tx (M = V, Nb, Ta) nanosheets are obtained by using a universal synthesis strategy of calcination, selective etching, intercalation, and exfoliation. Comprehensive characterizations confirm their defect-free few-layer structure feature, large interlayer spacing (1.702-1.955 nm), types of functional groups (-OH, -F, -O), and abundant valance states (M5+ , M4+ , M3+ , M2+ , M0 ). M4 C3 Tx (M = V, Nb, Ta) free-standing films obtained by vacuum filtration of few-layer M4 C3 Tx inks show good hydrophilia, high thermostability, and conductivity. A roadmap on synthesis of defect-free few-layer M4 C3 Tx (M = V, Nb, Ta) nanosheets are proposed and three key points are summarized. This work provides detailed guidelines for the synthesis of other defect-free few-layer MXenes nanosheets, but also will stimulate extensive functional explorations for M4 C3 Tx (M = V, Nb, Ta) MXenes nanosheets in the future.

Bi-MOF-Derived Carbon Wrapped Bi Nanoparticles Assembly on Flexible Graphene Paper Electrode for Electrochemical Sensing of Multiple Heavy Metal Ions

The development of nanohybrid with high electrocatalytic activity is of great significance for electrochemical sensing applications. In this work, we develop a novel and facile method to prepare a high-performance flexible nanohybrid paper electrode, based on nitrogen-doped carbon (NC) wrapped Bi nanoparticles (Bi-NPs) assembly derived from Bi-MOF, which are decorated on a flexible and freestanding graphene paper (GP) electrode. The as-obtained Bi-NPs encapsulated by an NC layer are uniform, and the active sites are increased by introducing a nitrogen source while preparing Bi-MOF. Owing to the synergistic effect between the high conductivity of GP electrode and the highly efficient electrocatalytic activity of Bi-NPs, the NC wrapped Bi-NPs (Bi-NPs@NC) modified GP (Bi-NPs@NC/GP) electrode possesses high electrochemically active area, rapid electron-transfer capability, and good electrochemical stability. To demonstrate its outstanding functionality, the Bi-NPs@NC/GP electrode has been integrated into a handheld electrochemical sensor for detecting heavy metal ions. The result shows that Zn²⁺, Cd²⁺, and Pb²⁺ can be detected with extremely low detection limits, wide linear range, high sensitivity, as well as good selectivity. Furthermore, it demonstrates outstanding electrochemical sensing performance in the simultaneous detection of Zn²⁺, Cd²⁺, and Pb²⁺. Finally, the proposed electrochemical sensor has achieved excellent repeatability, reproducibility, stability, and reliability in measuring real water samples, which will have great potential in advanced applications in environmental systems.

Advanced growth of 2D MXene for electrochemical sensors

Over the last few years, electroanalysis has made significant advancements, particularly in developing electrochemical sensors. Electrochemical sensors generally include emerging Photoelectrochemical and Electrochemiluminescence sensors, which combine optical techniques and traditional electrochemical bio/non-biosensors. Numerous EC-detecting methods have also been designed for commercial applications to detect biological and non-biological markers for various diseases. Analytical applications have recently focused significantly on one of the novel nanomaterials, the MXene. This material is being extensively investigated for applications in electrochemical sensors due to its unique mechanical, electronic, optical, active functional groups and thermal characteristics. This study extensively discusses the salient features of MXene-based electrochemical sensors, photoelectrochemical sensors, enzyme-based biosensors, immunosensors, aptasensors, electrochemiluminescence sensors, and electrochemical non-biosensors. In addition, their performance in detecting various substances and contaminants is thoroughly discussed. Furthermore, the challenges and prospects the MXene-based electrochemical sensors are elaborated.

A novel ReS2–Nb2CTx composite as a sensing platform for ultrasensitive and selective electrochemical detection of dipyramidole from human serum

The electrochemical detection of dipyridamole (DIPY) is highly essential since it is extensively used for the treatment of cardiovascular diseases and to impart inhibitory effects for cancer patients. In this work, we report the development of a novel composite of MXene and ReS₂ (ReS₂–Nb₂CT_x) by hydrothermal method. It was found that Nb₂CT_x was partially oxidized and ReS₂ nanoparticles were distributed on the surface of Nb₂CT_x during the hydrothermal synthesis. The ReS₂–Nb₂CT_x was used to modify carbon cloth electrodes and used for the electrochemical detection of DIPY. The ratio of ReS₂ was optimized in the composite by varying the atomic ratio from 4 to 9 and it was found that 6ReS₂–Nb₂CT_x showed the best sensing characteristics owing to the optimum interaction between ReS₂ and Nb₂CT_x. The developed sensor was able to detect DIPY linearly in the range 100 pM–1 μM and achieved a limit of detection of (LOD) of 28 pM. The modified electrode exhibited excellent selectivity towards DIPY in the presence of other interferents in addition to its good storage stability and repeatability. Furthermore, the developed sensor was also used for the detection of DIPY in human serum samples. Thus, this work paves the way to develop MXene-based platform for fabrication of flexible device capable of monitoring the acute levels of DIPY.

Analytical methods to determine and sense heavy metal pollutants using MXene and MXene-based composites: Mechanistic prophecy into sensing properties

The presence of heavy metal ions in the biosphere is of grave concern, as these are toxic and impact living organisms. Lack of pure drinking water can spread waterborne diseases like cholera, dysentery, typhoid, etc. The presence of heavy metals like arsenic and radioactive materials can cause cancer. The detection and removal of these heavy metals are important for sustaining life. Herein, MXene comes to the rescue as a crucial and potential material, which can sense and adsorb heavy metal ions. Developed in 2011, MXenes are an emerging class of 2D nanomaterials that are appropriate substitutes for existing heavy metal ions sensing materials and have shown excellent efficiency due to their better hydrophilicity, capacity of transportation of electrons, functionalization, and a great variety in compositions as compared to the other nanomaterials properties. This work gives an insight into the chemistry and synthesis of MXenes for further utilization as a sensor in heavy metal ions toxicity and underlines the key future challenges to knowing the full prospective of MXenes in environmental systems.

Advances and emerging challenges in MXenes and their nanocomposites for biosensing applications

Two-dimensional materials have unique properties and their better functionality has created new paradigms in the field of sensing. Over the past decade, a new family of 2D materials known as MXenes has emerged as a promising material for numerous applications, including biosensing. Their metallic conductivity, rich surface chemistry, hydrophilicity, good biocompatibility, and high anchoring capacity for biomaterials make them an attractive candidate to detect a variety of analytes. Despite such notable properties, there are certain limitations associated with them. This review aims to present a detailed survey of MXene's synthesis; in particular, their superiority in the field of biosensing as compared to other 2D materials is addressed. Their low oxidative stability is still an open challenge, and recent investigations on MXene's oxidation are summarized. The hexagonal stacking network of MXenes acts as a distinctive matrix to load nanoparticles, and the embedded nanoparticles can bind an excess number of biomolecules (e.g., antibodies) thereby improving biosensor performance. We will also discuss the synthesis and corresponding performance of MXenes nanocomposites with noble metal nanoparticles and magnetic nanoparticles. Furthermore, Nb and Ti2C-based MXenes, and Ti3C2-MXene sandwich immunoassays are also reviewed in view of their importance. Different aspects and challenges associated with MXenes (from their synthesis to final applications) and the future perspectives described give new directions to fabricate novel biosensors.

MXene-based electrochemical and biosensing platforms to detect toxic elements and pesticides pollutants from environmental matrices

Fabricating new biosensing constructs with high selectivity and sensitivity is the most needed environmental detection tool. In this context, several nanostructured materials have been envisaged to construct biosensors to achieve superior selectivity and sensitivity. Among them, MXene is regarded as the most promising to develop biosensors due to its fascinating attributes, like high surface area, excellent thermal resistance, good hydrophilicity, unique layered topology, high electrical conductivity, and environmentally-friendlier properties. MXenes-based materials have emerged as a prospective for catalysis, energy storage, electronics, and environmental sensing and remediation applications thanks to the above-mentioned exceptional characteristics. This review elaborates on the contemporary and state-of-the-art advancements in MXene-based electrochemical and biosensing tools to detect toxic elements, pharmaceutically active residues, and pesticide contaminants from environmental matrices. At first, the surface functionalization/modification of MXenes is discussed. Afterwards, a particular focus has been devoted to exploiting MXene to construct electrochemical (bio) sensors to detect various environmentally-related pollutants. Lastly, current challenges in this arena accompanied by potential solutions and directions are also outlined.

Exploring the catalytic activity of Nb4C3Tx MXene towards the degradation of nitro compounds and organic dyes by in situ decoration of palladium nanoparticles

We report on the catalytic activity of Nb4C3Tx based composites towards the catalytic reduction of nitro compounds and organic dyes for the first time.