Mechanism investigation of photocatalytic CO2 reduction to C1 products on transition metal and sulfur co-doped polymeric carbon nitride

ABSTRACTMXenes, a family of two‐dimensional transition metal carbides, carbonitrides and nitrides, have emerged as highly interesting antimicrobial nanomaterials. While mostly Ti‐based MXenes have been explored in this field, our work aims at characterizing and investigating the antibacterial and biocompatibility profiles of two vanadium‐based MXenes (V₂CTₓ and V₄C₃Tₓ) against Escherichia coli and Staphylococcus aureus, two clinically relevant pathobionts. First, the as‐synthesized nanomaterials were chemically and structurally characterized to confirm their morphology and structural integrity. After setting up two distinct experimental models (static and dynamic), the antibacterial activity was evaluated by colony‐forming units (CFUs) counting and scansion electron microscopy (SEM). Cellular cytotoxicity was assessed by lactate dehydrogenase (LDH) release and crystal violet characterization (CV). To further evaluate the MXenes' properties, the antimicrobial activity was tested in in‐vitro infection models using both epithelial (Caco‐2) and macrophage (J774) cells measuring CFUs. To assess the oxidative stress contributing to MXenes' antibacterial activity, reactive oxygen species (ROS) production was valued in infected cells after treatment. V₂CTₓ and V₄C₃Tₓ showed an antibacterial activity concentration and condition dependent. The dynamic incubation improved the bacterial reduction, supporting a “nano‐knife” mechanism linked to the physical disruption of the membrane. Finally, V₂CTₓ and V₄C₃Tₓ significantly reduced the intracellular bacterial burden in infected Caco‐2 epithelial cells in comparison with macrophages. Importantly, MXenes' treatment did not result in marked ROS stimulation, suggesting that their antibacterial activity mainly arose from physical interactions. Our findings highlight that vanadium‐based MXenes have good biocompatibility and are moderately effective antimicrobial nanomaterials, emphasizing the need to use commonly recognized and standardized experimental models to elucidate their potential antimicrobial applications.

Decoupling morphology to reveal intrinsic activity: Quantum-sized vanadium nitride for bifunctional hydrazine splitting.

Traditional two-dimensional transition-metal nitrides used for surface-enhanced Raman scattering (SERS) suffer from difficulties in tuning their localized surface plasmon resonance (LSPR) effect, which does not match commonly used laser wavelengths, resulting in a low Raman enhancement factor and making trace detection challenging. A solvent-assisted molten salt technique is proposed to fabricate tungsten nitride (WN) microflowers assembled from a highly crystalline nanosheet with a large specific surface area of 82.1 m2/g. Using rhodamine 6G as a probe molecule, the substrate achieves a limit of detection as low as 2 × 10-11 M and an enhancement factor of 5.6 × 107, outperforming most nonprecious semiconductor SERS substrates. The excellent enhancement effect originates from the physical enhancement brought about by its LSPR effect. These WN microflowers exhibit excellent SERS performance and remarkable LSPR characteristics, while showing high sensitivity to typical high-risk environmental pollutants. They also possess excellent signal reproducibility, robust chemical stability, and strong anti-interference capability.

Trace-level simultaneous monitoring of multiple heavy metal ions using AlScN-based flexible electrochemical sensor.

High-valent transition-metal nitrides have recently emerged as versatile platforms for N-atom transfer, and their reactivity remains sensitive to subtle electronic perturbations. Cr salen (where "salen" represents N2O2 bis-phenolate bis-Schiff-base ligands) nitrides offer a rare platform in which both the metal center and the redox-active salen ligand are both susceptible to one-electron oxidation, enabling systematic evaluation of how salen ligand substituent effects can change the electronic structure, and ultimately nitride reactivity. Herein, we evaluate a series of CrNSalR complexes to better understand how changing the ancillary ligand donating ability via the para-phenolate substituent (R = NO2, CF3, H, tBu, OMe, OiPr, NMe2) dictates overall electronic structure. For electron-donating R = OMe and R = OiPr, designed to probe the threshold for switching the oxidation locus from metal to ligand, one-electron oxidation results in a metal-centered Cr(VI) nitride, extending the window for metal-based oxidation beyond the previously established R = tBu derivative. In contrast, the R = NO2-substituted analogue, while not promoting bimolecular nitride coupling as observed in Mn congeners, nonetheless renders the CrN unit more electrophilic than previously reported R = CF3-substituted systems. Together, these results expand the electronic landscape of Cr-salen-nitrides and demonstrate how fine-tuning the donating ability of the ancillary salen ligand can be used to systematically manipulate the electronic structure at the nitride.

Flexible transition metal nitrides (TMNs) are considered key candidate materials for constructing next-generation high-performance flexible sensing devices. However, their strong metal-nitrogen bonds require high-temperature synthesis, which tends to cause spontaneous aggregation into three-dimensional bulk materials, making it difficult to obtain ultrathin two-dimensional materials suitable for flexible devices. This study proposes an innovative rapid and nondestructive microwave crystallization method. By ingeniously leveraging the abundant free electrons in quasi-metallic TMN nanostructures, electromagnetic irradiation induces efficient microwave heating, achieving exceptional crystallization within 20 s. This method effectively circumvents the sintering of ultrathin nanostructures inherent to conventional high-temperature annealing and increases the specific surface area of the product by more than 10-fold. Based on this method, dense and robust flexible TMN films with ultrahigh specific surface area and excellent chemical stability have been successfully obtained, enabling highly sensitive surface-enhanced Raman spectroscopy (SERS) detection of polycyclic aromatic hydrocarbons and nanoplastics.

Two-dimensional (2D) Transition Metal Carbides/Nitrides (MXenes) and Transition Metal Borides (MBenes) as Emerging Functional Materials for Electrochemical Detection of Food Contaminants.

Advances in MXene-based materials for high-sulfur-loading lithium–sulfur batteries

MXenes, a rapidly expanding family of two‐dimensional transition metal carbides and nitrides, have emerged as leading materials for wearable bioelectronics due to their metallic conductivity, termination‐rich surfaces, mechanical compliance, and tunable interlayer structures. However, wearable biosensor performance does not arise from conductivity alone, but from coupled interactions among surface termination chemistry, heterointerface engineering, hierarchical architecture, and device integration under dynamic physiological conditions. This review establishes a predictive structure‐interface‐device framework linking MXene chemistry to system‐level performance across electrochemical, mechanical, gas, optical, and energy‐storage modalities. We analyze how termination‐controlled adsorption governs charge transfer and selectivity, how heterojunction formation modulates carrier density and signal amplification, and how interlayer engineering and restacking suppression regulate ion transport, durability, and stability. Beyond materials design, we evaluate system‐level constraints including impedance stability, wireless communication, AI‐enabled analytics, and self‐powered operation. Key translational challenges, such as oxidation resistance, biocompatibility, scalable manufacturing, and reliable performance in complex biofluids, are assessed using quantitative benchmarks relevant to real‐world wearable deployment. By integrating nanoscale interfacial physics with device and systems engineering, this review defines generalizable design principles for durable, selective, and energy‐autonomous MXene‐enabled biosensors for intelligent, connected, and clinically translatable wearable platforms.

Developing effective CO2 separation technology is essential to ensure environmental remediation. In this endeavor, mixed matrix membranes (MMMs), which synergistically integrate polymer matrices with functional nanofillers (e.g., metal-organic frameworks (MOFs), covalent organic frameworks (COFs), graphene oxide (GO), clay, etc.), have emerged as a frontier in CO2 separation. Among the diverse spectrum of nanofillers, MXenes, a class of 2D transition metal carbides, nitrides, and carbonitrides, stand out for their tunable layered structure and rich surface functional groups. These features enable molecular sieving pathways, improve polymer-filler interfacial compatibility, reduce agglomeration, and optimize membrane morphology. In this review, the progress of MXene-based MMMs for CO2 separation is critically examined, with an emphasis on structural characteristics, synthesis techniques, CO2 transport mechanism, and underpinning interfacial dynamics. The review also covers limitations such as defects, aging, stability, and scalability as drivers of innovation, and highlights prospects for sustainable, high-performance, and industrially applicable CO2 separation membranes.

MXenes, a cutting-edge family of two-dimensional transition metal carbides and nitrides, distinguish themselves through an exceptional synergy of metallic conductivity, tunable surface chemistry, and structural versatility, placing them at the forefront of advanced materials research. While extensively studied for energy storage, catalysis, and sensing, their potential in interfacial polymerization for the in situ generation of polymer/nanomaterial hybrids remains largely untapped. In this study, Ti3C2Tx MXene is employed as a conductive and reactive interface to facilitate the in situ generation of Ce-doped MnO2/PEDOT (CMP) nanohybrid through a liquid/liquid (L/L) interface-assisted oxidative polymerization strategy, yielding a MXene-based Ce-doped MnO2/PEDOT nanohybrid (MCMP3). Beyond serving as a structural scaffold, the MXene surface accelerates polymerization, promoting rapid hybrid formation and enabling one-step integration of the conducting polymer and doped metal oxide within a unified architecture. As a result of this MXene-assisted interfacial process, the polymerization proceeds significantly faster, reducing the reaction time from 24 to 4h under ambient conditions. The PXRD, UV-vis, and Raman analyses confirmed the compositional optimization of Ce-doping with the characteristic features of layered K-birnessite-type MnO2. TEM and XPS analyses of the MCMP3 further confirmed its morphology, elemental composition, and successful nanohybrid formation. Pendant drop tensiometry substantiated the MXene-assisted acceleration of polymerization, demonstrating that MXene facilitates rapid polymer growth and interfacial anchoring of amphiphilic intermediates, thereby governing the controlled assembly of MCMP3 at the L/L interface. DFT calculations further elucidated sulfur-mediated chemisorption of EDOT onto Ti active sites of the MXene. These physicochemical characteristics are reflected in the electrochemical response of the MCMP3 nanohybrid, which exhibited a detection limit of 59.7nM toward metronidazole (MDZ), a widely used nitroimidazole antibiotic. This performance confirms the effective electrochemical activity of the hybrid system and supports its potential applicability for MDZ sensing. Additionally, real-time analysis of both milk and native lake water substantiates its viability for pharmaceutical and environmental applications. These findings establish MXene as an exceptional facilitator for the in situ generation of multifunctional polymer/nanomaterial architectures, opening avenues for the design and development of next-generation electrochemical devices.

ABSTRACT In recent years, MXenes, a new family of two‐dimensional materials composed of transition metal carbides, nitrides, and carbonitrides, have garnered substantial scientific attention due to their exceptional and distinctive physical and chemical properties. These properties are largely influenced by their diverse elemental compositions and surface functional groups. MXenes exhibit excellent compatibility with various materials such as polymers, metal oxides, and carbon nanotubes, enabling the fabrication of composites with tailored functionalities. In addition to their recognized use as electrode materials in energy storage devices, MXenes and their composites have also shown significant potential for various environmental applications. These include electrochemical and photocatalytic water splitting, carbon dioxide reduction, water treatment, and sensing technologies, attributed to their high electrical conductivity, strong reduction potential, and biocompatibility. This article delivers an in‐depth summary of the various synthesis techniques, fundamental characteristics, and the latest progress in the field of MXenes and their composites, with special emphasis on their practical applications.

The surfaces and interfaces of catalysts dictate activity, selectivity, and stability in heterogeneous catalysis, yet achieving atomic-level control over charge density flow and reaction energetics across these regions remains challenging. MXenes, a rapidly expanding family of two-dimensional transition-metal carbides, nitrides, and carbonitrides, offer an exceptional platform to address these challenges owing to their compositional tunability, rich surface terminations, and the strong influence of these groups on their physicochemical properties. Surface engineering provides the foundation for tailoring MXene reactivity, where controlled regulation of terminations, heteroatom doping, defect generation, and morphology enables precise tuning of active sites, adsorption energies, and redox potentials. Nevertheless, optimizing a single material may not provide sufficient control over surface charge dynamics and reaction energetics. For this reason, interface engineering that couples MXenes with metals, semiconductors, or carbon materials has become essential, as such heterostructures create Fermi-level equilibration, built-in electric fields, and orbital hybridization that govern charge transport and reshape catalytic pathways. Together, these hierarchical design strategies transform MXenes from simple conductive supports into dynamic catalytic mediators that bridge electro-, photo-, and thermocatalysis. This review summarizes recent progress in MXene surface and interface engineering, elucidates how atomic configurations regulate charge dynamics and catalytic behavior, and outlines design principles for programmable, self-adaptive, and stable MXene catalysts toward sustainable heterogeneous catalysis.

Phase control in the vapor-phase growth of transition metal nitrides is typically restricted by substantial kinetic barriers during precursor dissociation and an inherent thermodynamic instability towards nitrogen loss. Consequently, extreme growth conditions such as high pressure or plasma environments are often required. Here, we circumvent these limitations to stabilize high-valent, metastable 2D semimetallic tungsten nitride (W2N3) by employing a tailored topotactic conversion of a bilayer WS2 van der Waals template. In particular, we preserve the structural symmetry and stacking order of the W metal sublattice, while leveraging thermodynamic control to suppress vacancy aggregation, enabling homogeneous and synchronous nitrogen substitution across the layers. This uniform transformation facilitates "hyper-stoichiometric" nitrogen incorporation, inducing subtle structural distortions to trigger the electronic phase transition from a semiconductor to a semimetal. Beyond W2N3, our approach provides a universal route to synthesize nitrogen-rich, nonequilibrium 2D semimetallic nitrides from the broader family of transition metal dichalcogenides, advancing the development of functional 2D material engineering.

Transition metal nitride coatings often face a trade-off between thermal stability and oxidation resistance at high temperatures. Here, we address this challenge using a mechanism-guided high-throughput combinatorial strategy, implemented through multi-target co-deposition, to rapidly probe the Al-Cr-Ti-Si-N compositional space. An optimal composition window was identified (Al 13.3-24.1 at.%, Cr 7.6-14.6 at.%, Ti 10.4-23.9 at.%, Si 1.3-3.2 at.%). Coatings within this window exhibit high hardness (> 32 GPa), maintain a face-centered cubic (fcc) matrix up to 1,000 °C, and form oxide scales thinner than 0.5 μm after oxidation at 1,000 °C. Multi-scale characterization reveals that these outstanding properties originate from nanoscale synergistic mechanisms. Specifically, spinodal decomposition generates Ti-rich and Al/Cr-rich domains. These domains, coupled with dense dislocation networks and pronounced lattice distortion, collectively underpin mechanical robustness and structural stability. The inner SiO<sub>2</sub> and intermediate (Cr,Al)<sub>2</sub>O<sub>3</sub> layers act together to block oxygen diffusion and metal ion migration, resulting in exceptional oxidation resistance. High-speed dry cutting tests validate the engineering relevance of these coatings, showing a tool life up to 2.4 times longer than that of commercial AlTiN coatings. This work resolves the stability-oxidation trade-off and establishes a generalizable pathway for the rational design of multicomponent ceramic coatings.

Abstract Transition metal nitrides (TMNs) have attracted extensive research attention owing to their excellent physical and chemical properties. As an important branch of TMNs, molybdenum nitrides exhibit unique mechanical, electrical, and optical properties, and thus have broad application prospects in supercapacitors and hydrogen production via water splitting. In recent years, substantial progress has been made in the synthesis of molybdenum nitride crystals, with various methods developed to prepare different molybdenum nitride phases. Notably, gas-phase clusters with controlled composition, size, and structure play a pivotal role in the nucleation and growth of molybdenum nitride crystals, making cluster research critical to understanding the synthesis mechanisms of molybdenum nitrides. Previous studies have reported the fabrication of highly dispersed molybdenum nitride cluster catalysts and confirmed that atomically dispersed clusters serve as key active sites for catalytic reactions. In this work, we constructed a series of molybdenum nitride cluster structures based on the configurations of various bulk molybdenum nitrides. First-principles calculations were performed to evaluate the stability of these clusters and identify the most stable configurations. In addition, we investigated the structural evolution trends of the clusters under different chemical potentials.

Gallium Nitride (GaN) is transforming power electronics and optoelectronics; not only that, but it is also quickly becoming a primary component of the new generation of supercapacitors. GaN is a unique material that combines excellent electrochemical stability and tunable nanostructures with the best electrical properties. This review analyzes recent developments in GaN-based supercapacitor technology, emphasizing the rationale behind the increased research in this area and presenting the main challenges. The enhancement of the field of pure and porous GaN to more elaborate hybrids, including GaN with carbon materials, or transition metal oxides or nitrides, or doping with some metal. The main parameters that have been summarized here include specific capacitance up to 1915.5 mF cm-2, energy and power density up to 13.3 mWh cm-2 and 1000mW cm-3, and cycle stability remains high at 99 % despite 10000-50000 cycles. Chemical view brings together the connections between the different methods of synthesis, which include Chemical Vapor Deposition (CVD), hydrothermal processes, and electrochemical etching, and how these have been applied to affect electrochemical performance. When comparisons are made between electrodes, electrolytes, and device designs, then a better understanding of how GaN accumulates charge and which factors deplete it is achieved.

MXenes, a versatile class of two-dimensional transition-metal carbides, nitrides, and carbonitrides, exhibit exceptional properties for applications in energy, catalysis, and biomedicine. However, their rapid advancement has outpaced understanding of their biological and environmental safety. Recent findings reveal that MXene cytotoxicity is dose-, composition-, and surface-dependent rather than inherent. Ti-based MXenes show conditional biocompatibility, while V- and Cr-based variants present higher risks due to ion release. Variations in synthesis routes, flake size, and surface terminations contribute to inconsistent toxicological data. Surface engineering, green synthesis, and polymeric functionalization have emerged as effective routes to mitigate toxicity. Yet, the lack of standardized testing frameworks limits reliable structure toxicity correlations. Integration of machine learning and nano-informatics offers a path to predictive toxicology and safe-by-design strategies. Embedding toxicity assessment early in development will be vital for regulatory acceptance. Ultimately, harmonizing performance with safety will ensure MXenes’ sustainable translation into biomedical and technological applications.

N-N bond-reinforced 2D transition metal nitrides (rh-VN2/PtN2) as high-stability anodes for Li-ion batteries