Two-dimensional MXenes: recent emerging applications

Synergistic barium titanate/MXene composite as a high-performance piezo-photocatalyst for efficient dye degradation

Piezo-photocatalysis combines photocatalysis and piezoelectric effects to enhance catalytic efficiency by creating an internal electric field in the photocatalyst, improving carrier separation and overall performance. This study presents a high-performance piezo-photocatalyst for efficient dye degradation using a synergistic barium titanate (BTO)-MXene composite. The composite was synthesized via a facile method, combining the unique properties of BTO nanoparticles with the high conductivity of MXene. The structural and morphological analysis confirmed the successful formation of the composite, with well-dispersed BTO nanoparticles on the MXene surface. The piezo-photocatalytic activity of the composite was evaluated using a typical dye solution (Rhodamine B: RhB) under ultraviolet irradiation and mechanical agitation. The results revealed a remarkable enhancement in dye degradation (90 % in 15 min for piezo-photocatalysis) compared to individual stimuli (58.2 % for photocatalysis and 95.8 % in 90 min for piezocatalysis), highlighting the synergistic effects between BTO and MXene. The enhanced catalytic performance was attributed to the efficient charge separation and transfer facilitated by the composite's structure, leading to increased reactive species generation and dye molecule degradation. Furthermore, the composite exhibited excellent stability and reusability, showcasing its potential for practical applications in wastewater treatment. Overall, this work represents a promising strategy for designing high-performance synergistic catalysts, addressing the pressing need for sustainable solutions in environmental remediation.

Interfacial engineering of a multijunctional In2O3/WO3@Ti4N3Tx S-scheme photocatalyst with enhanced photoelectrochemical properties

Achieving high photoelectrochemical conversion efficiency requires the logical layout of a composite photocatalyst with optimal charge separation and transfer with ideal light harvesting capabilities to enhance the photocatalytic performance and the degradation rate towards organic pollutants. Herein, a novel In2O3/WO3@Ti4N3Tx S-scheme heterojunction was successfully synthesized and confirmed through valence band VB-XPS and Mott Schottky combined analysis. The formed MXene-doped In2O3/WO3@Ti4N3Tx S-scheme significantly enhances the charge flow and spatial separation with an improved oxidation and reduction ability. An in-built interfacial electric field at the WO3-In2O3 boundary enhanced the light-harvesting capacity, whereas Ti4N3Tx MXene offers a unique electron trapping effect which effectively lowers high charge carrier recombination rate-related photocatalytic deficit. It preserves the exceptional redox potency of the photocatalyst by providing a directed acceleration and effective separation of the photogenerated charges. A high carrier density (ND = 7.83 × 1021 cm-3) with a lower negative flat band (VFB = -0.064 V vs. Ag/AgCl) was obtained by Mott-Schottky analysis for 3 wt% In2O3/WO3@Ti4N3Tx, an indicator that a low overpotential is needed to activate photocatalytic reactions. This study, therefore, provides a novel thought for the design and fabrication of an S-scheme heterojunction for photocatalytic reactions for mineralization of organic pollutants in water and clean energy production.

Sensitivity-Enhanced, Room-Temperature Detection of NH3 with Alkalized Ti3C2Tx MXene

A layered Ti3C2Tx MXene structure was prepared by etching MAX-phase Ti3AlC2 with hydro-fluoric acid (HF), followed by alkalization in sodium hydroxide (NaOH) solutions of varying concentrations and for varying durations. Compared to sensors utilizing unalkalized Ti3C2Tx, those employing alkalized Ti3C2Tx MXene exhibited enhanced sensitivity for NH3 detection at room temperature and a relative humidity of 40%. Both the concentration of NaOH and duration of alkalization significantly influenced sensor performance. Among the tested conditions, Ti3C2Tx MXene alkalized with a 5 M NaOH solution for 12 h exhibited optimal performance, with high response values of 100.3% and a rapid response/recovery time of 73 s and 38 s, respectively. The improved sensitivity of NH3 detection can be attributed to the heightened NH3 adsorption capability of oxygen-rich terminals obtained through the alkalization treatment. This is consistent with the observed increase in the ratio of oxygen to fluorine atoms on the surface terminations of the alkalization-treated Ti3C2Tx. These findings suggest that the gas-sensing characteristics of Ti3C2Tx MXene can be finely tuned and optimized through a carefully tailored alkalization process, offering a viable approach to realizing high-performance Ti3C2Tx MXene gas sensors, particularly for NH3 sensing applications.

Hydrothermally Synthesized Z-Scheme Nanocomposite of ZIF-9 Modified MXene for Photocatalytic Degradation of 4-Chlorophenol

4-Chlorophenol (4CP) is a well-known environmental contaminant often detected in wastewater, generally arising from industrial processes such as chemical manufacture, pharmaceutical production, and pesticide formulation. 4CP is a matter of great concern since it is persistent and has the potential to have harmful impacts on both aquatic ecosystems and human health, owing to its hazardous and mutagenic properties. Hence, degradation of 4CP is of utmost significance. This research investigates the photocatalytic degradation of 4CP using a novel Z-scheme heterojunction nanocomposite composed of MXene and ZIF-9. The nanocomposite is synthesized through a two-step hydrothermal method and thoroughly characterized by using XRD, SEM, UV-visible spectroscopy, zeta potential, and electrochemical impedance spectroscopy studies, confirming successful fabrication with improved surface properties. The comparative photocatalytic degradation studies between pristine materials and the nanocomposite were performed, and significant enhancement in performance was observed. The effect of pH on the degradation efficiency is also explored and correlated with the surface charge. The Z-scheme photocatalysis mechanism is proposed, which is supported by time-resolved photoluminescence studies and scavenger experiments. The reusability of the nanocomposite is also evaluated. The study contributes to the development of efficient and sustainable photocatalysts for wastewater treatment.

Advancements in MXene-based composites for electronic skins

MXenes are a class of two-dimensional (2D) materials that have gained significant attention in the field of electronic skins (E-skins). MXene-based composites offer several advantages for E-skins, including high electrical conductivity, mechanical flexibility, transparency, and chemical stability. Their mechanical flexibility allows for conformal integration onto various surfaces, enabling the creation of E-skins that can closely mimic human skin. In addition, their high surface area facilitates enhanced sensitivity and responsiveness to external stimuli, making them ideal for sensing applications. Notably, MXene-based composites can be integrated into E-skins to create sensors that can detect various stimuli, such as temperature, pressure, strain, and humidity. These sensors can be used for a wide range of applications, including health monitoring, robotics, and human-machine interfaces. However, challenges related to scalability, integration, and biocompatibility need to be addressed. One important challenge is achieving long-term stability under harsh conditions such as high humidity. MXenes are susceptible to oxidation, which can degrade their electrical and mechanical properties over time. Another crucial challenge is the scalability of MXene synthesis, as large-scale production methods need to be developed to meet the demand for commercial applications. Notably, the integration of MXenes with other components, such as energy storage devices or flexible electronics, requires further developments to ensure compatibility and optimize overall performance. By addressing issues related to material stability, mechanical flexibility, scalability, sensing performance, and power supply, MXene-based E-skins can develop the fields of healthcare monitoring/diagnostics, prosthetics, motion monitoring, wearable electronics, and human-robot interactions. The integration of MXenes with emerging technologies, such as artificial intelligence or internet of things, can unlock new functionalities and applications for E-skins, ranging from healthcare monitoring to virtual reality interfaces. This review aims to examine the challenges, advantages, and limitations of MXenes and their composites in E-skins, while also exploring the future prospects and potential advancements in this field.