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Ti₃C₂T_xMXene membranes have attracted considerable interest due to their exceptional water transport properties, yet the role of cation intercalation on governing transport remains poorly understood. In this experimental and theoretical study, it shows how intercalation with K⁺, Na⁺, Li⁺, Ca²⁺, and Mg²⁺modulates both the nanochannel architecture and water flux of Ti₃C₂T_xmembranes. Unlike in graphene oxide analogs, cations with larger hydration diameters in Ti₃C₂T_xexpand the interlayer spacing, widening flow channels, enhancing slip length of these nanochannels, and boosting water flux from 31.45 to 61.86 L m⁻² h⁻¹. To overcome intrinsically poor adhesion of Ti₃C₂T_xto polymeric supports, this study incorporates a thin polyvinyl‐alcohol interlayer, which substantially enhances mechanical robustness and structural integrity. Together, these findings elucidate how cation hydration controls water transport and offer a flexible strategy for tailoring MXene membrane performance. 

Two-dimensional (2D) transition metal carbides, nitrides and carbonitrides, known as MXenes, are of interest as electrocatalysts. Tungsten-based MXenes are predicted to have low overpotentials in the hydrogen evolution reaction but their synthesis has proven difficult due to the calculated instability of their hypothetical MAX precursors. In this study, we present a theory-guided synthesis of a tungsten-based MXene, W2TiC2Tx, derived from a non-MAX nanolaminated ternary carbide (W,Ti)4C4−y precursor by the selective etching of one of the covalently bonded tungsten layers. Our results indicate the importance of tungsten and titanium ordering, the presence of vacancy defects in the metal layers, and the lack of oxygen impurities in the carbon layers for the successful selective etching of the precursor. We confirm the atomistic out-of-plane ordering of tungsten and titanium using computational and experimental characterizations. The tungsten-rich basal plane endows W2TiC2Tx MXene with a high electrocatalytic hydrogen evolution reaction performance (∼144 mV overpotential at 10 mA cm−2). This study reports a tungsten-based MXene synthesized from a covalently bonded non-MAX precursor, adding to the synthetic strategies for 2D materials. 

As the demand for sustainable and efficient water treatment solutions grows, the integration of advanced nanomaterials has become a focal point in enhancing membrane technologies. The purpose of this review is to provide a comprehensive and critical analysis of the current state of research on Ti3C2Tx MXenes, highlighting their unique properties, the challenges they address, and the potential they hold for MXene-enhanced biofiltration-membrane systems. The perspective systematically examines how Ti3C2Tx MXenes, with their exceptional electrical conductivity, hydrophilicity, and tunable surface chemistry, can be integrated into biofiltration-membrane systems to improve key performance metrics such as water flux, contaminant rejection, and fouling resistance. Various processes, including biofiltration, adsorption, and nanofiltration, are discussed, where Ti3C2Tx MXenes have been shown to have a potential application. In addition to synthesizing existing literature, experimental validations are presented that demonstrate how MXene incorporation can alter membrane morphology and structure, leading to improved antibacterial properties and enhanced overall performance. These findings underscore the transformative potential of Ti3C2Tx MXenes in developing next-generation biofiltration-membrane technologies that are not only more efficient but also more sustainable. Through this perspective, the key challenges that remain, such as cost implications and long-term stability, are identified, and future research directions are proposed to address these issues. This in-depth analysis highlights the critical role MXenes can play in advancing water treatment technologies, particularly in the context of water reuse, and encourages further interdisciplinary research in this rapidly evolving field. 

A large-scale theory-driven approach predicts many new 2D materials 

MXenes have demonstrated potential for various applications owing to their tunable surface chemistry and metallic conductivity. However, high temperatures can accelerate MXene film oxidation in air. Understanding the mechanisms of MXene oxidation at elevated temperatures, which is still limited, is critical in improving their thermal stability for high-temperature applications. Here, we demonstrate that Ti ${}_3$C ${}_2$T ${}_x$MXene monoflakes have exceptional thermal stability at temperatures up to 600 ${}^{°}$C in air, while multiflakes readily oxidize in air at 300 ${}^{°}$C. Density functional theory calculations indicate that confined water between Ti ${}_3$C ${}_2$T ${}_x$flakes has higher removal energy than surface water and can thus persist to higher temperatures, leading to oxidation. We demonstrate that the amount of confined water correlates with the degree of oxidation in stacked flakes. Confined water can be fully removed by vacuum annealing Ti ${}_3$C ${}_2$T ${}_x$films at 600 ${}^{°}$C, resulting in substantial stability improvement in multiflake films (can withstand 600 ${}^{°}$C in air). These findings provide fundamental insights into the kinetics of confined water and its role in Ti ${}_3$C ${}_2$T ${}_x$oxidation. This work enables the use of stable monoflake MXenes in high-temperature applications and provides guidelines for proper vacuum annealing of multiflake films to enhance their stability. 

In compositionally complex materials, there is controversy on the effect of enthalpy versus entropy on the structure and short-range ordering in so-called high-entropy materials. To help address this controversy, we synthesized and probed 40 M4AlC3 layered carbide phases containing 2 to 9 metals and found that short-range ordering from enthalpy is present until the entropy increases enough to achieve complete disordering of the transition metals in their atomic planes. We transformed all these layered carbide phases into two-dimensional (2D) sheets and showed the effects of the order vs. disorder on their surface properties and electronic behavior. This study suggests the key effect that the competition between enthalpy and entropy has on short-range order in multi-compositional materials.