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Abstract M₅X₄MXenes, a subclass of 2D transition metal carbides, have attracted attention as the thickest 2D material synthesized. Early studies show their promising electrocatalytic activity but overlooked how metal composition and interlayer spacing affect hydrogen evolution reaction (HER). To address this gap, three M₅X₄MXenes, Mo₄VC₄, (TiTa)₅C₄, and (TiNb)₅C₄, are systematically studied and their interlayer spacing and composition modulated through ion exchange with tetramethyl ammonium (TMA⁺vs. Li⁺), providing new insights into their HER activity. These findings reveal that TMA⁺‐intercalated Mo₄VC₄exhibits superior HER activity, achieving areal and gravimetric overpotentials of 172 and 90 mV, respectively, due to its composition (presence of Mo) and expanded interlayer spacing that enhances proton accessibility. The Li⁺exchange increases the overpotential to 212 and 131 mV at 10 mA areal and gravimetric current density, respectively, as reduced interlayer spacing restricts access to active Mo sites. In contrast, (TiNb)₅C₄and (TiTa)₅C₄display higher overpotentials, making them more suitable for supercapacitor or aqueous battery applications due to the wider electrochemical window. This study provides critical insights into the interplay between metal composition and interlayer engineering in M₅X₄MXenes, establishing TMA‐Mo₄VC₄as a promising candidate for sustainable hydrogen production. 

With the accelerated global interest in MXenes, the fastest-growing family of 2D materials, Drexel University hosted the 3rd International Conference, MXenes: Changing the World. This vibrant conference is the only one in the US solely devoted to MXenes, and the presentations and discussions brought together a significant number of top researchers with students. However, dedicated conferences and an increasing number of symposia are popping up worldwide as more applications and adaptations of MXenes are discovered and developed. We see the impact of this material and embrace its momentum as we look to the future. 

Abstract The study reports novel photonic properties of Ti₃C₂T_xMXene flakes horizontally self‐assembled within cellulose nanofiber (CNF) matrix exhibiting unique bright multispectral colors combined with overall high transparency in the transmission regime. The intense reflection colors are reflected by individual flakes acting as effective micromirrors with shifts based on their subsurface positioning within the dielectric layers. Unique color appearances are controlled by an interplay of multiple bandgaps formed by constructive and destructive interferences at flake‐matrix interfaces. These colors manifest at the microscale under bright field optical microscopy, while the total physical film retains high transparency up to 85% and a typical greenish hue characteristic of the MXene content below 1% volume fraction. The diverse spectral appearance of 4 µm ultra‐thin films is ultimately controlled by the positioning of the horizontal flakes within the nanofiber matrix at diverse distances from the top surface. This work expands the understanding of thin films with assembled 2D materials within polymer matrix and their fundamental interactions creating new structural coloration functionalities with the potential for multispectral photonic applications such as camouflaging, photothermal treatment, and optical communication for flexible thin bio‐derived films. 

Nanoparticles with aerodynamic diameters of less than 100 nm pose serious problems to human health due to their small size and large surface area. Despite continuous progress in materials science to develop air remediation technologies, efficient nanoparticle filtration has appeared to be challenging. This study showcases the great promise of MXene-coated polyester textiles to efficiently filter nanoparticles, achieving a high efficiency of ~90% within the 15–30 nm range. Using alkaline earth metal ions to assist textile coating drastically improves the filter performance by ca. 25%, with the structure–property relationship thoroughly assessed by electron microscopy and X-ray computed tomography. Such techniques confirm metal ions’ crucial role in obtaining fully coated and impregnated textiles, which increases tortuosity and structural features that boost the ultimate filtration efficiency. Our work provides a novel perspective on using MXene textiles for nanoparticle filtration, presenting a viable alternative to produce high-performance air filters for real-world applications. 

Abstract MXene‐based nanozymes (recently called MXenzymes) have emerged as promising candidates for environmental remediation, biomedical, (bio‐)catalytic, and sensing technologies due to their surface tunability, tailored electronic properties, remarkable electrical conductivity, and high surface area. These materials offer significant advantages over traditional enzymes, such as enhanced stability, tunable catalytic activity, and multifunctionality. However, despite the increasing number of studies in this field, critical challenges remain, including the long‐term stability, the lack of studies on structure–activity relationships to better understand the catalytic mechanisms, and the scalability required for real‐world applications. This mini‐review provides a comprehensive overview of the most recent advancements in MXenzymes, focusing on the type of MXenes used, the reported enzyme‐like activity, and the role of the photothermal effects in enhancing their catalytic performance. Moreover, key limitations, such as oxidation susceptibility, biocompatibility concerns, and the scarce in‐depth mechanistic studies, are critically examined. Last, the necessary steps to transition from proof‐of‐concept studies to real‐world applications are discussed. By addressing the listed fundamental challenges, MXenzymes could represent a valuable and effective alternative to natural enzymes used in catalysis, medicine, and environmental science. 

Abstract Transparent microelectrode arrays have proven useful in neural sensing, offering a clear interface for monitoring brain activity without compromising high spatial and temporal resolution. The current landscape of transparent electrode technology faces challenges in developing durable, highly transparent electrodes while maintaining low interface impedance and prioritizing scalable processing and fabrication methods. To address these limitations, we introduce artifact‐resistant transparent MXene microelectrode arrays optimized for high spatiotemporal resolution recording of neural activity. With 60% transmittance at 550 nm, these arrays enable simultaneous imaging and electrophysiology for multimodal neural mapping. Electrochemical characterization shows low impedance of 563 ± 99 kΩ at 1 kHz and a charge storage capacity of 58 mC cm⁻² without chemical doping. In vivo experiments in rodent models demonstrate the transparent arrays' functionality and performance. In a rodent model of chemically‐induced epileptiform activity, we tracked ictal wavefronts via calcium imaging while simultaneously recording seizure onset. In the rat barrel cortex, we recorded multi‐unit activity across cortical depths, showing the feasibility of recording high‐frequency electrophysiological activity. The transparency and optical absorption properties of Ti₃C₂Tx MXene microelectrodes enable high‐quality recordings and simultaneous light‐based stimulation and imaging without contamination from light‐induced artifacts.