Highly efficient methylene blue removal by TMAOH delaminated Ti3C2Tx MXene suspension and the mechanistic aspect

Ion-modulated graphene oxide and GO@MXene hydrogels: enhanced adsorption performance and stability for methylene blue removal

Ion cross-linking is often used to prepare graphene hydrogels, but the effects of different ion introductions on the properties of graphene hydrogels need to be further explored. In this study, graphene oxide (GO) and GO@MXene non-spherical hydrogels were prepared by introducing different ions, and their adsorption effects on methylene blue (MB) were discussed to determine their feasibility in water treatment. The adsorption efficiencies were significantly variable because the introduction of different ions had different effects on the internal structure and molding process of the hydrogels. The GO and GO@MXene hydrogels crosslinked with Ca2+ demonstrated superior MB adsorption performance compared to those prepared with K+ and Al3+, achieving 85.2% and 85.8% MB removal efficiencies within 9 hours, respectively. Interestingly, the morphology of the hydrogel can be changed by adjusting the drop height, which in turn affects the MB adsorption. The results showed that hydrogels had faster MB removal by preparing them from a higher height (3.5 cm). The results demonstrated that hydrogels prepared from a higher droplet fall height (3.5 cm) exhibited accelerated MB removal, with a 10-20% enhancement in removal efficiency. In addition, the effects of pH and contact time on the adsorption performance of the hydrogels were investigated. The results showed that the best removal effect was achieved under neutral conditions, and the adsorption process was consistent with the pseudo-quadratic kinetic model (R 2 > 0.97). In addition, we found that the introduction of MXene enhanced the water stability of the hydrogels, which increased with the metal ion valence number. Furthermore, our study demonstrated that Ca2+-crosslinked GO and GO@MXene hydrogels exhibit excellent selective adsorption of cationic dyes, achieving MB removal efficiencies of 96.6% and 98.3% in mixed dye systems, respectively. This study not only confirms that the introduction of ions can affect the properties of hydrogels by modulating their morphology, but also provides potential candidates for MB adsorption.

Enhancing both the long-term stability and methylene blue adsorption performance of TiVCTxvia a facile antioxidation treatment

MXenes are widely recognized as excellent dye adsorption materials. However, their propensity to oxidize will greatly reduce their stability and performance. In the present work, a simple antioxidation treatment was applied to TiVCTx using three acid antioxidants (oxalic acid (OA), sodium citrate (SC), and tartaric acid (TA)) and their effects on the stability and methylene blue adsorption performance were investigated. The stability of TiVCTx stored in an aqueous solution within 14 days was assessed using XRD and XPS. The antioxidant-treated TiVCTx showed a significant improvement in both long-term stability and MB adsorption properties, with TA-TiVCTx demonstrating the best performance. The MB adsorption of the as-prepared TiVCTx was physical and multilayer, but it became a multilayer process where physical and chemical adsorptions coexist after antioxidation treatment. The maximum adsorption capacity of TA-TiVCTx reached 8061.03 mg g-1 and remained at 3887.28 mg g-1 after 14 days of storage, far exceeding the performance of other reported adsorbents. It is found that the enhanced stability is attributed to the dense protective layer formed by the chelation between the antioxidant and TiVCTx, and the improved MB adsorption performance is ascribed to the synergistic effect of electrostatic adsorption between TiVCTx and MB and the Bloch reaction between the antioxidants and the MB molecules. The differences in the enhancement effects of the various antioxidants are related to the number of carboxyl and hydroxyl groups in the antioxidant molecules. This work provides useful reference and guidance for obtaining MXenes with better stability and adsorption performance.

MXene as SERS-Active Substrate: Impact of Intrinsic Properties and Performance Analysis

A new member is incorporated into the SERS active materials family daily as a consequence of advances in materials science. Furthermore, it has been demonstrated that MXenes, which display remarkable physicochemical characteristics, are also encompassed within this family. This Review offers a comprehensive and systematic assessment of the potential of MXene structures in the context of SERS applications. First, the historical development of SERS-active substrates and the evolution of various substrates over time are analyzed. Subsequently, the formation and structural properties of MXene structures were subjected to a comprehensive and detailed examination. The principal objective of this Review is to elucidate the rationale behind the preference for MXene as a SERS-active substrate, given its distinctive physicochemical properties. In this context, while MXene's abundant surface functional groups represent a significant advantage, its high electrical conductivity, suitable flexibility, extensive two-dimensional surface areas, and antibacterial activity also warrant consideration in terms of potential applications. It is emphasized that, for MXene nanolayers to demonstrate optimal performance in SERS applications, a plan should be devised to consider these features. By increasing readers' awareness of using MXene as a SERS active substrate, potential opportunities for future application areas may be created.

Enhancement of Methylene Blue Adsorption by Acid-Base Neutralization-Induced Bulging MXene/RGO Composite Foams

Nanocomposite films made from graphene oxide (GO) and MXene have a dense layered structure due to nanosheet self-stacking, limiting their dye adsorption performance. In this study, acid-base neutralization reactions are used to induce MXene/reduced graphene oxide (RGO) films bulging, which opens the stacked layer structure within the membrane and enhances MB adsorption performance. The effects of the pH, temperature, contact time, and initial concentration of MB on the adsorption performance are further investigated. The results indicate that the adsorption process conforms to the pseudo-second-order kinetic and Freundlich isotherm models and is heat-absorbing and spontaneous, and the MXene/RGO foams have an adsorption capacity of up to 1099.5 mg g-1 for MB. In addition, our study show that the MXene/RGO foams not only have better reusability, but also exhibit better adsorption for other dyes. The efficient MB removal is attributed to the increased specific surface area of the composite foams, increased active sites, strong electrostatic interactions between MB and the composite foams, as well as intercalation adsorption. These findings offer new options for solving dye effluent problems.

Unlocking Ultrahigh Initial Coulombic Efficiency of MXene Anode via Presodiation and Electrolyte Optimization

The low initial Coulombic efficiency (ICE) greatly hinders the practical application of MXenes in sodium-ion batteries. Herein, theoretical calculations confirm that -F and -OH terminations as well as the tetramethylammonium ion (TMA+) intercalator in sediment Ti3C2Tx (s-Ti3C2Tx) MXene possess strong interaction with Na+, which impedes Na+ desorption during the charging process and results in low ICE. Consequently, Na+-intercalated sediment Ti3C2Tx (Na-s-Ti3C2Tx) is constructed through Na2S·9H2O treatment of s-Ti3C2Tx. Specifically, Na+ can first exchange with TMA+ of s-Ti3C2Tx and then combine with -F and -OH terminations, thus leading to the elimination of TMA+ and preshielding of -F and -OH. As expected, the resulting Na-s-Ti3C2Tx anode delivers considerably boosted ICE values of around 71% in carbonate-based electrolytes relative to s-Ti3C2Tx. Furthermore, electrolyte optimization is employed to improve ICE, and the results demonstrate that an ultrahigh ICE value of 94.0% is obtained for Na-s-Ti3C2Tx in the NaPF6-diglyme electrolyte. More importantly, Na-s-Ti3C2Tx exhibits a lower Na+ migration barrier and higher electronic conductivity compared with s-Ti3C2Tx based on theoretical calculations. In addition, the cyclic stability and rate performance of the Na-s-Ti3C2Tx anode in various electrolytes are comprehensively explored. The presented simple strategy in boosting ICE significantly enhances the commercialization prospect of MXenes in advanced batteries.

A Dual-Functional MXene-Based Bioanode for Wearable Self-Charging Biosupercapacitors

As a reliable energy-supply platform for wearable electronics, biosupercapacitors combine the characteristics of biofuel cells and supercapacitors to harvest and store the energy from human's sweat. However, the bulky preparation process and deep embedding of enzyme active sites in bioelectrodes usually limit the energy-harvesting process, retarding the practical power-supply sceneries especially during the complicated in vivo motion. Herein, a MXene/single-walled carbon nanotube/lactate oxidase hierarchical structure as the dual-functional bioanode is designed, which can not only provide a superior 3D catalytic microenvironment for enzyme accommodation to harvest energy from sweat, but also offers sufficient capacitance to store energy via the electrical double-layer capacitor. A wearable biosupercapacitor is fabricated in the "island-bridge" structure with a composite bioanode, active carbon/Pt cathode, polyacrylamide hydrogel substrate, and liquid metal conductor. The device exhibits an open-circuit voltage of 0.48 V and the high power density of 220.9 µW cm-2 at 0.5 mA cm-2 . The compact conformal adhesion with skin is successfully maintained under stretching/bending conditions. After repeatedly stretching the devices, there is no significant power attenuation in pulsed output. The unique bioelectrode structure and attractive energy harvesting/storing properties demonstrate the promising potential of this biosupercapacitor as a micro self-powered platform of wearable electronics.

MXenes and MXene-supported nanocomposites: a novel materials for aqueous environmental remediation

Water contamination has become a significant issue on a global scale. Adsorption is a cost-effective way to treat water and wastewater compared to other techniques such as the Advanced Oxidation Processes (AOPs), photocatalytic degradation, membrane filtration etc. Numerous research experts are continuously developing inexpensive substances for the adsorptive removal of organic contaminants from wastewater. A fresh and intriguing area of inquiry has emerged as a result of the development of MXenes. This article aims to provide a preliminary understanding of MXenes from synthesis, structure, and characterization to the scope of further research. The applications of MXenes as a new generation adsorbent for remediation of various kinds of organic pollutants and heavy metals from wastewater are also summarized. MXenes with altered surfaces may make effective adsorbents for wastewater treatment. Lastly, the mechanism of adsorption of organic contaminants and heavy metals on MXenes is also discussed for a better understanding of the readers.

Preparations and Applications of MXene–Metal Composites: A Review

MXene, an advanced family of 2D ceramic material resembling graphene, has had a considerable impact on the field of research because of its unique physiochemical properties. MXene has been synthesized by the selective etching of MAX via different techniques. However, with the passage of time, due to the need for further progress and improvement in MXene materials, ideas have turned toward composite fabrication, which has aided boosting the MXene composites regarding their properties and applications in various areas. Many review papers are published on MXene and their composites with polymer, carbon nanotube, graphene, other carbon, metal oxides and sulfides, etc., except metal composite, and such papers discuss these composites thoroughly. In this review article, we illustrate and explain the development of MXene-based metal composites. Furthermore, we highlight the synthesis techniques utilized for the preparation of MXene composites with metal. We briefly discuss the enhancement of properties of the composites and a wide range of applications as an electrode substance for energy storage devices, electrochemical cells, supercapacitors, and catalytic and anti-corrosive performance. Major obstacles in MXene and metal composite are mentioned and provide future recommendations. Together, they can overcome problems and enable MXene and composites on commercial-scale production.