Pristine Ti3C2Tx Research Articles

The phosphorus doping modification of Ti3C2Tx MXene films assisted by tripolyphosphate-crosslinking for flexible supercapacitors

MXenes is a new two-dimensional material with good electrical conductivity and high theoretical pseudocapacitance, which is widely used in various energy storage devices. Heterogeneous atom doping is one of the effective strategies to adjust the properties of MXenes and improve its electrochemical performance. In this work, a facile and cost-effective KTPP (potassium tripolyphosphate, phosphorus source) assistance strategy is demonstrated to dope Ti3C2Tx MXene with phosphorus atoms by heat treatment. The results show that the phosphorus doping level reached 1.25 at.%. As expected, the specific capacitance of the phosphate-doped Ti3C2Tx electrode is 365.1 F g−1 at the scanning rate of 10 mV s−1, which is twice that of the pristine Ti3C2Tx (183.1 F g−1). Besides, the flexible supercapacitor device assembled with Ti3C2Tx-P-300°C-3h sample has a high energy density of 10.76 Wh kg−1 at 483.03 W kg−1 power density and the capacitance retention rate is 84.51 % after 5000 cycles at the current density of 1 A g−1. With bent at different angles (0°, 60°, 90°, 120°), the specific capacitance values of flexible supercapacitor devices have not changed significantly, and the capacitance retention rate reached 90.09 %. The reason for the enhanced electrochemical performance is that the phosphorus doping can increase the active sites of Ti3C2Tx, bring PO bonds that enhance activity, optimize the redox reaction process, and accelerate the ion transport rate. Therefore, a simple and effective method to improve the electrochemical performance of Ti3C2Tx MXene is proposed in this work.

Nitrogen-doping engineering in two-dimensional transition-metal carbides for electrochemical hydrogen evolution

Developing electrocatalysts with the trade-off between overall electrocatalytic performance and economic cost towards hydrogen evolution reaction (HER) is crucial for producing green hydrogen fuels. Although theoretical studies have reported the potential of two-dimensional (2D) MXenes for the HER, their electrocatalytic performance is still unsatisfactory for the particular application due to their low intrinsic active and MXene stacking. To address this problem, we herein modify the electronic structure and increase the interlayer spacing between 2D Ti3C2Tx MXenes through ammonia (NH3)-assisted hydrothermal approach. The effect of synthesis temperature on the nitrogen doping mechanism and electrochemical behaviors for the HER is systemically explored. As a result, the nitrogen (N)-doped Ti3C2Tx MXene fabricated at 160 °C exhibits the highest HER activity among all 2D N-doped Ti3C2Tx nanosheets with the overpotential/Tafel slope of 186.91 mVRHE/115.94 mVRHE dec−1 in an acidic solution. Due to the synergistic contribution of nitrogen, the N-doped Ti3C2Tx-160 °C has mass activity of 337.95 mA mg−1 at 0.3 VRHE, being 27.50-fold higher than that of pristine Ti3C2Tx. This work indicated that heteroatom doping is a facile but efficient approach for modulating the electronic structure and intrinsic activity of MXene-based materials for electrochemical reactions.

Harnessing the Power of Nano‐Ferroelectrics: BaTiO3/MXene (Ti3C2Tx) Composites for Enhanced Lithium Storage

Abstract2D Ti3C2Tx MXene is a desirable electrode material for advanced lithium‐ion batteries (LIBs) in the pursuit of high energy and power densities, owing to its extensive reactive area and surface‐induced pseudo‐capacitance. Here, a novel synergistic strategy for fortifying lithium storage capability is first proposed, by in‐situ anchoring BaTiO3 ferroelectric nanoparticles on few‐layered Ti3C2Tx nanosheets (BT/f‐Ti3C2Tx) using a hydrothermal method. The uniform BaTiO3 nanoparticles effectively prevent the restacking of Ti3C2Tx nanosheets, successfully deplete metastable Ti atoms, and intriguingly form a thin and well‐adhered solid electrolyte interface layer, enhancing the aggregation‐resistant, oxidation‐resistant, and electrochemical properties of Ti3C2Tx. Simultaneously, the internal electric fields, originating from the spontaneous polarization of BaTiO3 ferroelectric nanoparticles, can augment the adsorption of Li+, boosting the lithium storage capacity and reaction kinetics. The resulting composite electrode displays a remarkable charge capacity of 84 mAh g−1 at 10 A g−1, almost five times that of pristine Ti3C2Tx electrode. The excellent rate performance and cyclability make BT/f‐Ti3C2Tx composites highly attractive for LIBs. Furthermore, this synthetic approach presented here is scalable and can be extended to other Ti‐based materials. This strategy is expected to underscore the considerable potential of ferroelectric composites for integration into high‐performance LIBs.

Boron-Doped Ti3C2Tx MXene for Effective and Durable High-Current-Density Ammonia Synthesis.

Ammonia (NH3) synthesis via the nitrate reduction reaction (NO3RR) offers a competitive strategy for nitrogen cycling and carbon neutrality; however, this is hindered by the poor NO3RR performance under high current density. Herein, it is shown that boron-doped Ti3C2Tx MXene nanosheets can highly efficiently catalyze the conversion of NO3RR-to-NH3 at ambient conditions, showing a maximal NH3 Faradic efficiency of 91% with a peak yield rate of 26.2mgh-1mgcat. -1, and robust durability over ten consecutive cycles, all of them are comparable to the best-reported results and exceed those of pristine Ti3C2Tx MXene. More importantly, when tested in a flow cell, the designed catalyst delivers a current density of ‒1000mAcm-2 at a low potential of ‒1.18V versus the reversible hydrogen electrode and maintains a high NH3 selectivity over a wide current density range. Besides, a Zn-nitrate battery with the catalyst as the cathode is assembled, which achieves a power density of 5.24mWcm-2 and a yield rate of 1.15mgh-1mgcat. -1. Theoretical simulations further demonstrate that the boron dopants can optimize the adsorption and activation of NO3RR intermediates, and reduce the potential-determining step barrier, thus leading to an enhanced NH3 selectivity.

In situ growth of TiO2 on Ti3C2Tx MXene for improved gas-sensing performances

In this study, in situ prepared multiple semiconducting TiO2 in a metallic Ti3C2Tx channel were investigated, which were derived from the Ti3AlC2 MAX phase by oxidation treatments. Several tiny TiO2 particles were in situ formed on the Ti3C2Tx MXene surface when it was heated to 150 °C at ambient conditions. The phase transformation of pristine Ti3C2Tx MXene to oxidized TiO2 was accelerated when the gas-sensing channel was heated to higher temperatures up to 200 °C, yielding a TiO2/Ti3C2Tx composite. The experimental results revealed that the heat-treatment temperature played an important role in the gradual development of the morphology and gas-sensing activity of the TiO2/Ti3C2Tx sensing channel. In particular, the optimal heating temperature of the composite resulted in a good response and recovery time for NO2 molecules. Furthermore, first-principles calculations indicated the good sensing ability of the TiO2/Ti3C2Tx composite for NO2 than for other gases. These results suggest a new strategy for developing gas-sensing ability by forming a Schottky barrier through a simple process.

Efficient antibiotic remediation from wastewater using a lamellar free-standing 2D graphene oxide/Ti3C2Tx hybrid membrane

The existence of elevated levels of antibiotics in wastewater has facilitated the emergence and spread of pathogens with antimicrobial resistance (AMR). When combined with the worldwide water scarcity issue, this situation results in detrimental impacts on both the ecosystem and human well-being. Traditional methods employed by wastewater treatment facilities exhibit limited effectiveness in eliminating antibiotics. This paper describes the synthesis and performance of two-dimensional (2D) lamellar free-standing graphene oxide (GO)/Ti3C2Tx membrane for the removal of antibiotics from wastewater. The 50 %GO/Ti3C2Tx composite membrane demonstrated a remarkable increase in water flux, achieving 61.9 L m−2 h−1, surpassing the performance of the pristine GO membrane, which achieved 22.8 L m−2 h−1. Additionally, the GO/Ti3C2Tx composite membranes exhibited outstanding tetracycline rejection, consistently exceeding 99 %, a significant improvement compared to the pristine Ti3C2Tx membrane. The composite membranes of with a ratio of GO to MXene of 50 %, 40 %, 30 % and 20 % had contact angles of 54.5°, 57.4°, 60.6°, and 61.6°, respectively. Combining GO and Ti3C2Tx at specific mass ratios enhanced properties, evidenced by altered interlayer spacing and hydrophilicity. Furthermore, the superior composite membrane demonstrated superior antifouling properties compared to both pristine GO and Ti3C2Tx membranes.

Molten salt-modified Ti3C2Tx MXene with tunable oxygen-functionalized surfaces for effective detection of NO2 at room temperature

The abundant tunable functional groups and room-temperature sensing properties of MXenes have garnered increasing interest in the field of gas sensing. However, the majority of research has exclusively focused on the combined impact of external substances with MXenes functional groups, with limited exploration into the modulation of MXenes’ intrinsic functional groups. In this work, we successfully produced molten salt-modified Ti3C2Tx MXene (M-Ti3C2Tx) with tunable oxygen-functionalized surfaces using the molten salt immersion method and employed it as a chemical resistive gas sensor to detect NO2 at room temperature (RT). Using diverse analytical techniques, we propose the O−addition effect on the surface titanium atoms and the O−substitution effect on the edge carbon atoms, refining the existence form of –O functional groups as well as realizing the effective regulation of the intrinsic functional groups. With a high response (∼25.87%−100 ppm NO2, whose response value is five times higher than that of pristine Ti3C2Tx), relatively rapid response speed (∼99 s−25 ppm NO2), high sensitivity (∼0.29 ppm−1), low detection limits (theoretical LoD is 3.3 ppm), good selectivity and long-term stability (maintain stable within 28 days) at RT, the sensor based on M-Ti3C2Tx demonstrates excellent NO2 sensing performance. To understand the sensing mechanism, density functional theory (DFT) calculations were conducted to explore adsorption behaviors. Theoretical analysis validates that M-Ti3C2Tx has a stronger adsorption capacity for NO2 (Ead = −1.149 eV) owing to the formation of covalent bond between the –O functional group and the nitrogen atom of NO2. The application of the molten salt can effectively modulate the intrinsic functional groups of MXenes, expanding the scope of MXenes surface modification engineering and creating new opportunities for enhancing the gas sensing capabilities of MXenes.

Molecular-Level Interfacial Chemistry Regulation of MXene Enables Energy Storage beyond Theoretical Limit.

Ti3C2Tx MXene often suffers from poor lithium storage behaviors due to its electrochemically unfavorable OH terminations. Herein, we propose molecular-level interfacial chemistry regulation of Ti3C2Tx MXene with phytic acid (PA) to directly activate its OH terminations. Through constructing hydrogen bonds (H-bonds) between oxygen atoms of PA and OH terminations on Ti3C2Tx surface, interfacial charge distribution of Ti3C2Tx has been effectively regulated, thereby enabling sufficient ion-storage sites and expediting ion transport kinetics for high-performance energy storage. The results show that Li ions preferably bind to H-bond acceptors (oxygen atoms from PA), and the flexibility of H-bonds therefore renders their interactions with adsorbed Li ions chemically "tunable", thus alleviating undesirable localized geometric changes of the OH terminations. Meanwhile the H-bond-induced microscopic dipoles can act as directional Li-ion pumps to expedite ion diffusion kinetics with lower energy barrier. As a result, the as-designed Ti3C2Tx/PA achieves a 2.4-fold capacity enhancement compared with pristine Ti3C2Tx (even beyond theoretical capacity), superior long-term cyclability (220.0 mAh g-1 after 2000 cycles at 2.0 A g-1), and broad temperature adaptability (-20 to 50 °C). This work offers a promising interface engineering strategy to regulate microenvironments of inherent terminations for breaking through the energy storage performance of MXenes.

Synergistic Charge Storage Enhancement in Supercapacitors via Ti3C2Tx MXene and CoMoO4 Nanoparticles.

MXene has emerged as a highly promising two-dimensional (2D) layered material with inherent advantages as an electrode material, such as a high electrical conductivity and spacious layer distances conducive to efficient ion transport. Despite these merits, the practical implementation faces challenges due to MXene's low theoretical capacitance and issues related to restacking. In order to overcome these limitations, we undertook a strategic approach by integrating Ti3C2Tx MXene with cobalt molybdate (CoMoO4) nanoparticles. The CoMoO4 nanoparticles bring to the table rich redox activity, high theoretical capacitance, and exceptional catalytic properties. Employing a facile hydrothermal method, we synthesized CoMoO4/Ti3C2Tx heterostructures, leveraging urea as a size-controlling agent for the CoMoO4 precursors. This innovative heterostructure design utilizes Ti3C2Tx MXene as a spacer, effectively mitigating excessive agglomeration, while CoMoO4 contributes its enhanced redox reaction capabilities. The resulting CoMoO4/Ti3C2Tx MXene hybrid material exhibited 698 F g-1 at a scan rate of 5 mV s-1, surpassing that of the individual pristine Ti3C2Tx MXene (1.7 F g-1) and CoMoO4 materials (501 F g-1). This integration presents a promising avenue for optimizing MXene-based electrode materials, addressing challenges and unlocking their full potential in various applications.

Pristine Ti3C2Tx MXene Enables Flexible and Transparent Electrochemical Sensors.

In the era of the internet of things, there exists a pressing need for technologies that meet the stringent demands of wearable, self-powered, and seamlessly integrated devices. Current approaches to developing MXene-based electrochemical sensors involve either rigid or opaque components, limiting their use in niche applications. This study investigates the potential of pristine Ti3C2Tx electrodes for flexible and transparent electrochemical sensing, achieved through an exploration of how material characteristics (flake size, flake orientation, film geometry, and uniformity) impact the electrochemical activity of the outer sphere redox probe ruthenium hexamine using cyclic voltammetry. The optimized electrode made of stacked large Ti3C2Tx flakes demonstrated excellent reproducibility and resistance to bending conditions, suggesting their use for reliable, robust, and flexible sensors. Reducing electrode thickness resulted in an amplified faradaic-to-capacitance signal, which is advantageous for this application. This led to the deposition of transparent thin Ti3C2Tx films, which maintained their best performance up to 73% transparency. These findings underscore its promise for high-performance, tailored sensors, marking a significant stride in advancing MXene utilization in next-generation electrochemical sensing technologies. The results encourage the analytical electrochemistry field to take advantage of the unique properties that pristine Ti3C2Tx electrodes can provide in sensing through more parametric studies.

Iodine-redox-chemistry-modulated ion transport channels in MXene enables high energy storage capacity

Ti3C2Tx MXene anode often faces the great challenge of a low capacity due to its sluggish ion transport kinetics. Herein we report iodine-redox-chemistry-modulated intelligent ion transport channels in Ti3C2Tx MXene, enabling its Li-ion storage beyond theoretical capacity. The −I terminations modified on the Ti3C2Tx surface (I−Ti3C2Tx) are oxidized into linear −I3 in the late stage of the charging process, which dramatically expand the interlayer spacing of Ti3C2Tx to accelerate the Li-ion extraction. Meanwhile such self-expanded ion transport channels are more conducive to the Li-ion insertion in the following discharging process, during which the −I terminations are regenerated. This voltage-responsive and reversible conversion between the −I and −I3 terminations in Ti3C2Tx MXene achieves an intelligent bidirectional adjustment of ion transport channels. As a consequence, the I−Ti3C2Tx delivers high capacity (1.8-fold capacity of the pristine Ti3C2Tx at 0.1 A g−1), outstanding rate capability (4.5 times the capacity of the pristine Ti3C2Tx at 2.0 A g−1), and long-term cycling stability (268.5 mAh g−1 at 1.0 A g−1 over 800 cycles), even in a full cell (300.7 mAh g−1 at 0.1 A g−1) and with a wide temperature environment. This work provides an effective approach for maximizing the actual capacity of Ti3C2Tx MXene.

2D/2D {001}TiO2-x/Ti3C2Tx composite with ultra-high sensing performance for NO2 at room temperature

The remarkable electrical conductivity, abundance of surface functional groups, and large specific surface area make 2D MXenes-based heterostructures highly promising for room temperature gas sensing applications. However, these MXenes-based heterojunctions composed of different materials may suffer from issues, such as crystal incompatibility and bandgap mismatch. Herein, the {001}TiO2-x/Ti3C2Tx composite was prepared in situ by hydrothermal process and subsequent annealing. The {001} facets of TiO2 and oxygen vacancies that provide a heightened exposure of active sites in the composite and more gas diffusion channels, as well as the formation of Schottky barriers between {001}TiO2 nanosheets and Ti3C2Tx, can synergistically enhance the gas performance. The experimental results show that the {001}TiO2-x/Ti3C2Tx composite exhibits 1.9 and 27.5 times higher than the {001}TiO2/Ti3C2Tx composite and pristine Ti3C2Tx to 10 ppm NO2 at room temperature, respectively. Moreover, the {001}TiO2-x/Ti3C2Tx composite presents the great linear response (R2 = 0.99509), selectivity, repeatability and long-term stability to NO2. Density functional theory (DFT) calculations reveal the strong interactions between the {001}TiO2-x/Ti3C2Tx and NO2, indicating excellent sensitivity and selectivity of the composite material towards NO2. This work provides an effective way to construct a series of oxygen-defective Ti3C2Tx-based composites with exposed high-energy facets for enhanced gas sensing performances.

Nicop Anchored Porous Ti3C2tx Support with 3D Interconnected Structure for Advanced Hydrogen Evolution Reaction Electrocatalysts

MXene have gained much attention as promising electrocatalysts for noble metal-free hydrogen evolutrion reaction (HER) electrocatalysts owing to their high electrical conductivity, hydrophilic surfaces, abundant functional groups, and rational design for hybridization with other materials. In this study, a novel porous monolayered-Ti3C2TX@NiCoP (P-Ti3C2Tx@NiCoP) nanostructure was developed with 3D interconnected structure to significantly improve charge transfer capability and electrocatalytic activity. A strategic approach of modifying pristine Ti3C2Tx monolayers and combining them with other active cocatalysts. Specifically, the H2O2-utilized oxidation and HF etching process formed a highly microporous structure with a maximized surface area of monolayered MXenes as the support. A subsequent solvothermal process followed by phosphidation enabled successful anchoring of highly HER-active NiCoP nanoclusters onto abundantly exposed terminal edges of the P-Ti3C2Tx support. The structural porosity of the P-Ti3C2Tx nanoflakes played an important role in creating additional room for embedding catalytically active species while stably imparting high electrical conductivity to accelerate charge transfer to NiCoP nanoclusters. Moreover, inspired by the pH dependent change of structural arrangement of the Ti3C2Tx, we successfully induced 3D-interconnetecd structure by modulating surface electrostatic forces among Ti3C2Tx monolayers. Of note, the 3D-interconnected structure would shift charge transfer behavior from intermolecular to intramolecular aspects and this would contribute to enhanced charge transfer kinetics. With structural modification of support material and effective hybridization of active species, P-Ti3C2Tx@NiCoP showed highly enhanced HER activity with significantly lower overpoential of 115 and 101 mV at a current density of -10 mA cm-2 in 0.5 M H2SO4 and 1.0 M KOH, respectively, along with showing long-term stability over 60 h. As such, our approach of designing structurally modified-Ti3C2Tx and hybridization with other electrocatalytically active species would function as a solid platform for implementing Ti3C2Tx-based hetero-nanostructures to achieve state-of-the-art performance in next-generation energy conversion applications.

Band engineering in Ti2N/Ti3C2Tx-MXene interface to enhance the performance of aqueous NH4+-ion hybrid supercapacitors

The aqueous hybrid supercapacitor (AHSC) based on ammonium ion (NH4+) is an interesting energy storage device with excellent properties. However, the scarcity of appropriate and effective cathode materials limited its practicality. Two-dimensional (2D) transition metal nitrides, carbides, or carbonitrides (MXenes) show potential as cathode materials, but their low capacitance limits their applicability. Here, we synthesized N-functionalized 2D MXene (Ti3C2Tx) with Ti2N interface engineering (Ti2N/Ti3C2Tx), which displayed not only superior capacitance and rate capability but also a cycling stability than pristine Ti3C2Tx. Ex-situ XRD and XPS were used to study the charge storage mechanism at the interface of Ti2N/Ti3C2Tx. Furthermore, density functional theory (DFT) calculations were employed to validate the superior conductivity at the interface of the Ti2N/Ti3C2Tx (Tx = OH) electrode. Moreover, AHSC was assembled with the Ti2N/Ti3C2Tx as cathode, and activated carbon as anode possesses outstanding energy storage performance. This study not only elucidates the charge storage process of Ti2N/Ti3C2Tx but also provides new insights for designing novel cathode materials for energy storage devices.

Layer Engineered MXene Empowered Wearable Pressure Sensors for Non‐Invasive Vital Human–Machine Interfacing Healthcare Monitoring

AbstractPressure sensors with high flexibility and sensitivity face significant challenges in meeting the delicate balance and synergy among suitable active sensing electrode materials, substrates, and their device geometry design. In this contribution, layer‐engineered delaminated Ti‐MXene (DL‐Ti3C2Tx) is introduced, which has relatively wider interlayer spacing through intercalated large organic molecules and accordion‐like open internal microstructure than the narrower pristine Ti3C2Tx MXene (Ti‐MXene), graphene/carbon nanotube's interlayer spacing suitably fulfill the high sensitivity and flexibility requirement through accessible electronic pathways under the external pressure. Notably, a milder in‐situ ambient condition etching is performed to eliminate the associated safety risks for a flexible personal healthcare monitoring pressure sensor. DL‐Ti3C2Tx MXene‐empowered, flexible pressure sensor demonstrates a broad range of sensitivities up to a very high‐pressure of 20.8 kPa at a sensitivity of 242.3 kPa−1 with a fast response and recovery time (<300 ms). A twofold increase in pressure sensitivity performance of DL‐Ti3C2Tx MXene than that of Ti‐MXene, graphene can be attributed to the engineered wider interlayer distance among the delaminated DL‐Ti3C2Tx MXene layers causing a facile interlayer atomic movements, contacts, and reversible compressibility. The current economical, scalable DL‐Ti3C2Tx MXene flexible pressure sensor can provide future safe personal healthcare artificial intelligence with real‐time tracking ability.

Powering the Future: Unleashing the Potential of MXene-Based Dual-Functional Photoactive Cathodes in Photo-Rechargeable Zinc-Ion Capacitor.

Dual-functional photo-rechargeable (photo-R) energy storage devices, which acquire stored energy from solar energy harvesting, are being developed to battle the current energy crisis. In this study, these findings on the photo-driven characteristics of MXene-based photocathodes in photo-R zinc-ion capacitors (ZICs) are presented. Along with the pristine Ti3 C2 Tx MXene, tellurium/Ti3 C2 Tx (Te/Ti3 C2 Tx ) hybrid nanostructure is synthesized via facile chemical vapor transport technique to examine them for photocathodes in ZICs. Interestingly, the evaluated self-powered photodetector devices using MXene-based samples revealed a pyro-phototronic behavior introduced into the samples, with higher desirability observed in Te/Ti3 C2 Tx . The photo-R ZICs results exhibited a capacitance enhancement of 50.86% for Te/Ti3 C2 Tx at two scan rates of 5 and 10mVs-1 under illumination, compared to dark conditions. In contrast, a capacitance enhancement of 30.20% is obtained for the pristine Ti3 C2 Tx at only a 5mVs-1 scan rate. Furthermore, both samples achieved photo-charging voltage responses of ≈960mV, and photoconversion efficiencies of 0.01% (for Te/ Ti3 C2 Tx ) and 0.07% (for Ti3 C2 Tx ). These characteristics in MXene-based single photo-R ZICs are significant and considerable with the distinguished integrated photo-R supercapacitors with solar cells, or coupled energy-harvesting and energy-storing devices reported recently in the literature.

Stable N-doped Ti3C2Tx gas sensors for recoverable detection of ammonia at room temperature

Herein, highly recoverable, and stable, nitrogen-doped Ti3C2Tx-based sensors are developed for ammonia detection at room-temperature. Ti3C2Tx MXene as a room-temperature gas sensor has two main drawbacks: weak recovery and resistance drift. In this work; Ti3C2Tx nano-sheets were derived from the pre-synthesized Ti3AlC2 by selective aluminum etching using HF acid. The sensors fabricated using pristine Ti3C2Tx had high response toward polar gases, particularly ammonia. The sensors’ response to 100 ppm ammonia was 10%. However, they experienced incomplete recovery and baseline resistance drift. To overcome these problems, we introduced a novel method, in which, before fabricating the gas sensors, the surface of synthesized Ti3C2Tx MXene was modified by a nitrogen treatment strategy. In this method, the MXene layers were doped with nitrogen using NH3 gas at 500 °C for 2 h. In nitrogen-doped Ti3C2Tx-based sensors, both recovery and drift problems disappeared. The response of the nitrogen-doped Ti3C2Tx is 3.7% toward 100 ppm ammonia, which is a notable response for a stable, recoverable, room-temperature gas sensor.

Polyaniline/Ti3C2Tx functionalized mask sensors for monitoring of CO2 and human respiration rate

Flexible and wearable gas-sensing devices have become increasingly crucial for monitoring air quality and human health. Disposable masks, mainly composed of polypropylene (PP) fibers, can serve as a potential flexible substrate for sensing devices yet have been largely overlooked during the COVID-19 pandemic. In the present work, flexible Ti3C2Tx/PANI-PP composite gas sensors were fabricated by spray-coating delaminated Ti3C2Tx MXene and in-situ polymerization of aniline on a disposable mask substrate. The resulting hybrid gas sensor displayed a wide detection range (25–1500 ppm), reliable reproducibility, long-term stability, and excellent flexibility and selectivity, a remarkable response (15.2%) towards 500 ppm CO2 gas, which is 6.5 times higher than pristine Ti3C2Tx and 2.4 times higher than pristine PANI. The enhanced sensing performance of the composite sensor is mainly attributed to the synergistic effects of the heterojunctions between Ti3C2Tx and PANI, the improved conductivity, and the enlarged specific surface area. We further investigated the influence of various parameters, including humidity, temperature, bending angles, and folding times on the sensing performance of the composite gas sensor. Finally, a wearable wireless Bluetooth sensing device was fabricated for human exhaled breath monitoring at room temperature, demonstrating the potential application of this Ti3C2Tx/PANI-PP composite sensor for respiratory disease diagnosis.

Ag‐doped Ti3C2Tx sensor: A promising candidate for low‐concentration H2S gas sensing

AbstractTrace hydrogen sulphide (H2S) could reflect the severity of insulation faults in gas‐insulated switchgear (GIS), therefore, accurate and fast detection of low‐concentration H2S is important for on‐line monitoring, fault diagnosis, and state evaluation in GIS. Ag‐Ti3C2Tx chemiresistive‐type sensors were fabricated via drop‐coating with self‐reduction synthesised Ag‐doped Ti3C2Tx. The as‐prepared sensors exhibited an excellent sensitivity and selectivity to H2S with an extremely low detection of limit of 18.57 parts per billion (ppb) at 25°C (room temperature). The response of Ag‐Ti3C2Tx sensor to 10 parts per million (ppm) H2S was enhanced ∼12 times than that of the pristine Ti3C2Tx sensor. The compositing of Ti3C2Tx with Ag nanoparticles (NPs) enabled the fast response/recovery time for H2S detection. Further analysis found that the enhanced H2S sensing performances could be attributed to chemical sensitisation, adsorbed oxygen species regulation and high Brunauer–Emmett–Teller (BET) surface area. This study paves the way for Ag‐Ti3C2Tx as room‐temperature sensing materials to detect low‐concentration H2S in GIS.

Synergistic Effect of TiS3 and Ti3C2Tx MXene for Temperature-Tunable p-/n-Type Gas Sensing

We propose a strategy for highly tunable gas sensors, in which a MXene is combined with a sacrificial material that could be controllably oxidized upon mild annealing to form oxide nanoparticles that alter the sensing response. A controlled annealing of such composite generally retains the integrity of MXene sheets while gradually converting the sacrificial material to a metal oxide that could form semiconductor heterojunctions with MXene, fine-tuning its sensor properties. This strategy is demonstrated using gas sensors based on Ti3C2Tx MXene mixed with TiS3, a semiconducting transition metal trichalcogenide. Compared to pristine MXene, the Ti3C2Tx-TiS3 composite exhibited a significantly improved sensor response to ethanol, which served as a model analyte, both at room temperature and upon annealing. Furthermore, as a less thermally stable material than the MXene, TiS3 oxidizes faster than Ti3C2Tx at elevated temperatures, producing TiO2 nanoparticles that strongly affect the sensing response. A pristine Ti3C2Tx exhibits a p-type sensor response to ethanol at room temperature. Upon annealing, Ti3C2Tx gradually degrades to TiO2, changing the sensor response to n-type above ∼300 °C. The addition of TiS3 allows for the general preservation of MXene as the sensor material, as the temperature of the p–n transition decreases to about 200 °C, at which Ti3C2Tx is generally stable. This approach can likely be applied to a great variety of combinations of various MXenes and sacrificial compounds with sensor properties that could be tuned via annealing for specific analytes or applications.