Inspection of Enamel Removal Using Infrared Thermal Imaging and Machine Learning Techniques.

Within aerospace and automotive manufacturing, the majority of quality assurance is through inspection or tests at various steps during manufacturing and assembly. Such tests do not tend to capture or make use of process data for in-process inspection and certification at the point of manufacture. Inspection of the product during manufacturing can potentially detect defects, thus allowing consistent product quality and reducing scrappage. However, a review of the literature has revealed a lack of any significant research in the area of inspection during the manufacturing of terminations. This work utilises infrared thermal imaging and machine learning techniques for inspection of the enamel removal process on Litz wire, typically used for aerospace and automotive applications. Infrared thermal imaging was utilised to inspect bundles of Litz wire containing those with and without enamel. The temperature profiles of the wires with or without enamel were recorded and then machine learning techniques were utilised for automated inspection of enamel removal. The feasibility of various classifier models for identifying the remaining enamel on a set of enamelled copper wires was evaluated. A comparison of the performance of classifier models in terms of classification accuracy is presented. The best model for enamel classification accuracy was the Gaussian Mixture Model with expectation maximisation; it achieved a training accuracy of 85% and enamel classification accuracy of 100% with the fastest evaluation time of 1.05 s. The support vector classification model achieved both the training and enamel classification accuracy of more than 82%; however, it suffered the drawback of a higher evaluation time of 134 s.

Friction of Ti3C2Tx MXenes.

2D materials are well-known for their low-friction behavior by modifying the interfacial forces at atomic surfaces. Of the wide range of 2D materials, MXenes represent an emerging material class but their lubricating behavior has been scarcely investigated. Herein, the friction mechanisms of 2D Ti3C2Tx MXenes are demonstrated which are attributed to their surface terminations. We find that Ti3C2Tx MXenes do not exhibit the well-known frictional layer dependence of other 2D materials. Instead, the nanoscale lubricity of 2D MXenes is governed by the termination species resulting from synthesis. Annealing the MXenes demonstrate a 7% reduction in OH termination which translates to a 16-57% reduction of friction in agreement with DFT calculations. Finally, the stability of MXene flakes is demonstrated upon isolation from their aqueous environment. This work indicates that MXenes can provide sustainable lubricity at any thickness which makes them uniquely positioned among 2D material lubricants.

One-Pot Green Process to Synthesize MXene with Controllable Surface Terminations using Molten Salts.

Surface terminations of two-dimensional MXene (Ti3 C2 Tx ) considerably impact its physicochemical properties. Commonly used etching methods usually introduce -F surface terminations or metallic impurities in MXene. We present a new molten-salt-assisted electrochemical etching method to synthesize fluorine-free Ti3 C2 Cl2 . Using electrons as reaction agents, cathode reduction and anode etching can be spatially isolated; thus, no metallics are present in the Ti3 C2 Cl2 product. The surface terminations can be in situ modified from -Cl to -O and/or -S, which considerably shortens the modification steps and enriches the variety of surface terminations. The obtained -O-terminated Ti3 C2 Tx are excellent electrode materials for supercapacitors, exhibiting capacitances of 225 F g-1 at 1.0 Ag-1 , good rate performance (91.1 % at 10 Ag-1 ), and excellent capacitance retention (100 % after 10000 charge/discharge cycles at 10 Ag-1 ), which is superior to multi-layered Ti3 C2 Tx prepared by other etching methods.

Abrupt climate changes during Termination III in Southern Europe.

The Late Quaternary glacial-interglacial transitions represent the highest amplitude climate changes over the last million years. Unraveling the sequence of events and feedbacks at Termination III (T-III), including potential abrupt climate reversals similar to those of the last Termination, has been particularly challenging due to the scarcity of well-dated records worldwide. Here, we present speleothem data from southern Europe covering the interval from 262.7 to 217.9 kyBP, including the transition from marine isotope stage (MIS) 8 to MIS 7e. High-resolution δ13C, δ18O, and Mg/Ca profiles reveal major millennial-scale changes in aridity manifested in changing water availability and vegetation productivity. uranium-thorium dates provide a solid chronology for two millennial-scale events (S8.1 and S8.2) which, compared with the last two terminations, has some common features with Heinrich 1 and Heinrich 2 in Termination I (T-I).

The safety of quinolones and fluoroquinolones in pregnancy: a meta-analysis.

BACKGROUND: Quinolones were contraindicated during pregnancy because of concerns regarding fetal malformations and carcinogenesis in animals. The literature is conflicting regarding their safety in humans. OBJECTIVES: To conduct a meta-analysis evaluating the risk for fetal malformations and pregnancy complications following exposure to quinolones during pregnancy. SEARCH STRATEGY: We searched Embase, PubMed, Medline, the Cochrane database, clinicaltrials.gov, and Dart Databases. We added articles found through the references of included articles. SELECTION CRITERIA: Relevant English citations using the terms quinolone/s, fluoroquinolone/s, and pregnancy in humans. Exclusion criteria were case reports, reviews, and articles without data regarding the study outcomes. DATA COLLECTION AND ANALYSIS: Two authors performed the database search, assessment of eligibility, and abstraction of data from included studies. Disagreement was settled by consensus among all authors. The pooled odds ratios (with 95% CIs) were estimated. The Cochrane's Q-test of heterogeneity and I² were used for the measurement of heterogeneity. A total of 256 papers were retrieved, 13 of which met the inclusion criteria and were then analysed. MAIN RESULTS: No association was found between quinolones and fetal malformations (pooled odds ratio, OR 1.08; 95% CI 0.96-1.21), preterm delivery (pooled OR 0.97; 95% CI 0.75-1.24), stillbirth (pooled OR 1.11; 95% CI 0.34-3.6), or miscarriage (pooled OR 1.78; 95% CI 0.93-3.38). CONCLUSIONS: Quinolones are not associated with unfavourable pregnancy outcomes; however, larger studies are needed before safety is established. Until then, it is suggested that quinolones should not be used as a first-line therapy during the first trimester. TWEETABLE ABSTRACT: Quinolones were associated with favourable pregnancy outcomes; caution should be taken in the first trimester.

How do late terminations of pregnancy affect comparisons of stillbirth rates in Europe? Analyses of aggregated routine data from the Euro-Peristat Project.

OBJECTIVE: To describe how terminations of pregnancy at gestational ages at or above the limit for stillbirth registration are recorded in routine statistics and to assess their impact on comparability of stillbirth rates in Europe. DESIGN: Analysis of aggregated data from the Euro-Peristat project. SETTING: Twenty-nine European countries. POPULATION: Births and late terminations in 2010. METHODS: Assessment of terminations as a proportion of stillbirths and derivation of stillbirth rates including and excluding terminations. MAIN OUTCOME MEASURES: Stillbirth rates overall and excluding terminations. RESULTS: In 23 countries, it is possible to assess the contribution of terminations to stillbirth rates either because terminations are rare occurrences or because they can be distinguished from spontaneous stillbirths. Where terminations were reported, they accounted for less than 1.5% of stillbirths at 22+ weeks in Denmark, between 13 and 22% in Germany, Italy, Hungary, Finland and Switzerland, and 39% in France. Proportions were much lower at 24+ weeks, with the exception of Switzerland (7.4%) and France (39.2%). CONCLUSIONS: Terminations represent a substantial proportion of stillbirths at 22+ weeks of gestation in some countries. Countries where terminations occur at 22+ weeks should publish rates with and without terminations in order to improve international comparisons and the policy relevance of stillbirth statistics. TWEETABLE ABSTRACT: For valid comparisons of stillbirth rates, data about late terminations of pregnancy are needed.

Stillbirth and neonatal death rates across time: the influence of pregnancy terminations and birth defects in a Western Australian population-based cohort study.

BACKGROUND: The stillbirth rate in most high income countries reduced in the early part of the 20(th) century but has apparently been static over the past 2½ decades. However, there has not been any account taken of pregnancy terminations and birth defects on these trends. The current study sought to quantify these relationships using linked Western Australian administrative data for the years 1986-2010. METHODS: We analysed a retrospective, population-based cohort of Western Australia births from 1986 to 2010, with de-identified linked data from core population health datasets. RESULTS: The study revealed a significant decrease in the neonatal death rate from 1986 to 2010 (6.1 to 2.1 neonatal deaths per 1000 births; p < .01), while the overall stillbirth rate remained static. The stillbirth trend was driven by deaths in the extremely preterm period (20-27 weeks; which account for about half of all recorded stillbirths and neonatal deaths), masking significant decreases in the rate of stillbirth at very preterm (28-31 weeks), moderate to late preterm (32-36 weeks), and term (37+ weeks). For singletons, birth defects made up an increasing proportion of stillbirths and decreasing proportion of neonatal deaths over the study period-a shift that appears to have been largely driven by the increase in late pregnancy terminations (20 weeks or more gestation). After accounting for pregnancy terminations, we observed a significant downward trend in stillbirth and neonatal death rates at every gestational age. CONCLUSIONS: Changes in clinical practice related to pregnancy terminations have played a substantial role in shaping stillbirth and neonatal death rates in Western Australia over the 2½ decades to 2010. The study underscores the need to disaggregate perinatal mortality data in order to support a fuller consideration of the influence of pregnancy terminations and birth defects when assessing change over time in the rates of stillbirth and neonatal death.

The normality of the first-trimester placentae collected from elective terminations.

Placentae collected from elective terminations during the first trimester are commonly used as control samples in research. However, it is widely acknowledged that many complications of pregnancies can occur or originate during the early stage of gestation. This raises the question that the placentae collected from the first trimester may not accurately reflect normal placental conditions. In this study, 95 placentae were collected from elective terminations and histology was performed. Out of these, 53 placentae (56 %) exhibited the typical structure of placental villi, indicating normal development. However, 42 placentae (44 %) showed placental hydrops, with varying degrees of severity (mild, moderate, or severe). Placental hydrops has been linked to several complicated pregnancies in the later stages of gestation. Our findings suggest that the development of pregnancy pathologies could start in the first trimester, as observed by the presence of hydrops. Placental researchers should be aware of when using first-trimester placentae from termination as controls in studies. However, it remains unclear whether pathological morphologies resolve or ameliorate as the pregnancy progression or whether such placentae continue to have such pathology, but clinical symptoms/signs do not manifest.

Fracture Mechanisms and Crack Propagation in Monolayer Ti3C2Tx under Nanoindentation: The Influence of Surface Terminations and Vacancy Defects.

Monolayer MXenes are a novel class of two-dimensional transition metal carbides/nitrides with fascinating physicochemical properties. Despite recent advances in the study of MXenes' mechanical properties, a comprehensive understanding of the fundamental physical mechanisms that affect fracture due to surface terminations and vacancy defects in MXenes under nanoindentation remains largely unexplored. Here, we address this gap using molecular dynamics simulations and nanoindentation theory to investigate the effects of surface terminations and vacancy defects on the fracture behavior of Ti3C2Tx MXenes. By inducing the rupture of monolayer MXenes through nanoindentation, we find that bare Ti3C2 exhibits brittle fracture behavior. The presence of surface terminations and vacancy defects reduces the load-carrying capacity and flexibility of MXenes. Interestingly, surface terminations increase the stiffness of the structure, while vacancy defects have the opposite effect. We also find that high concentrations of surface oxidation impart ductile fracture characteristics to MXenes and increase the maximum crack length at failure. Additionally, defects exceeding the critical concentration can effectively prevent brittle crack propagation by causing frequent crack deflection and blunting crack tips. Combining these findings, we propose a new strategy to synergistically enhance the fracture toughness of MXenes through high concentrations of surface oxidation and vacancy defects exceeding the critical concentration without significantly affecting strength and stiffness, thereby avoiding catastrophic failure in MXene monolayers due to brittle fracture. This work provides fundamental insights into the mechanical properties and fracture mechanisms of monolayer 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.

Suppressing Dielectric Loss in MXene/Polymer Nanocomposites through Interfacial Interactions.

Although numerous polymer-based composites exhibit excellent dielectric permittivity, their dielectric performance in various applications is severely hampered by high dielectric loss induced by interfacial space charging and a leakage current. Herein, we demonstrate that embedding molten salt etched MXene into a poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE))/poly(methyl methacrylate) (PMMA) hybrid matrix induces strong interfacial interactions, forming a close-packed inner polymer layer and leading to significantly suppressed dielectric loss and markedly increased dielectric permittivity over a broad frequency range. The intensive molecular interaction caused by the dense electronegative functional terminations (-O and -Cl) in MXene results in restricted polymer chain movement and dense molecular arrangement, which reduce the transportation of the mobile charge carriers. Consequently, compared to the neat polymer, the dielectric constant of the composite with 2.8 wt % MXene filler increases from ∼52 to ∼180 and the dielectric loss remains at the same value (∼0.06) at 1 kHz. We demonstrate that the dielectric loss suppression is largely due to the formation of close-packed interfaces between the MXene and the polymer matrix.

Few-layered Ti3C2Tx MXene synthesized via water-free etching toward high-performance supercapacitors.

MXene has drawn considerable attention in energy storage due to particular physicochemical properties. At present, among most near-ambient temperature preparation methods, water is usually served as the main solvent. However, MXene is usually subjected to fast structural degradation on account of water molecules attacking in aqueous solution. Herein, we report a novel water-free etching strategy for synthesizing few-layered Ti3C2Tx MXenes in deep eutectic solvents at near-ambient temperature. Benefitting from the absence of water and macromolecular structure of deep eutectic solvents, the as-synthesized few-layered Ti3C2Tx (DES-Ti3C2Tx) MXene presents abundant -O terminations and low oxidation degree. As a consequence, the DES-Ti3C2Tx MXene displays excellent specific capacitance of 320 F/g at 2 mV/s. Impressively, the DES-Ti3C2Tx MXene exhibits splendid long-term stability that 97% specific capacitance retention can be acquired over 50 000 cycles at high current density of 50 A/g. Therefore, this study offers a new thought for preparing high performance MXene-based materials by water-free etching method.

MXene: fundamentals to applications in electrochemical energy storage.

A new, sizable family of 2D transition metal carbonitrides, carbides, and nitrides known as MXenes has attracted a lot of attention in recent years. This is because MXenes exhibit a variety of intriguing physical, chemical, mechanical, and electrochemical characteristics that are closely linked to the wide variety of their surface terminations and elemental compositions. Particularly, MXenes are readily converted into composites with materials including oxides, polymers, and CNTs, which makes it possible to modify their characteristics for a variety of uses. MXenes and MXene-based composites have demonstrated tremendous promise in environmental applications due to their excellent reducibility, conductivity, and biocompatibility, in addition to their well-known rise to prominence as electrode materials in the energy storage sector. The remarkable characteristics of 2D MXene, including high conductivity, high specific surface area, and enhanced hydrophilicity, account for the increasing prominence of its use in storage devices. In this review, we highlight the most recent developments in the use of MXenes and MXene-based composites for electrochemical energy storage while summarizing their synthesis and characteristics. Key attention is paid to applications in supercapacitors, batteries, and their flexible components. Future research challenges and perspectives are also described.

Biocompatible and Oxidation-Resistant Ti3 C2 Tx MXene with Halogen-Free Surface Terminations.

Surface chemistry influences not only physicochemical properties but also safety and applications of MXene nanomaterials. Fluorinated Ti3 C2 Tx MXene, synthesized using conventional HF-based etchants, raises concerns regarding harmful effects on electronics and toxicity to living organisms. In this study, well-delaminated halogen-free Ti3 C2 Tx flakes are synthesized using NaOH-based etching solution. The transversal surface plasmon mode of halogen-free Ti3 C2 Tx MXene (833 nm) confirmed red-shift compared to conventional Ti3 C2 Tx (752 nm), and the halogen-free Ti3 C2 Tx MXene has a different density of state by the high proportion of -O and -OH terminations. The synthesized halogen-free Ti3 C2 Tx exhibits a lower water contact angle (34.5°) and work function (3.6 eV) than those of fluorinated Ti3 C2 Tx (49.8° and 4.14 eV, respectively). The synthesized halogen-free Ti3 C2 Tx exhibits high biocompatibility with the living cells, as evidenced by no noticeable cytotoxicity, even at very high concentrations (2000 µg mL⁻1 ), at which fluorinated Ti3 C2 Tx caused ≈50% reduction in cell viability upon its oxidation. Additionally, the oxidation stability of halogen-free Ti3 C2 Tx is enhanced unexpectedly, which cumulatively provides a good rationale for pursuing the halogen-free routes for synthesizing MXene materials for their uses in biomedical and therapeutic applications.

Freeing Fluoride Termination of Ti3C2Tx via Electrochemical Etching for High-Performance Capacitive Deionization.

Ti3C2Tx MXene is a promising Faradic capacitive deionization (CDI) electrode for high salt removal in future desalination, whereas the surface termination group of fluoride (-F) significantly impedes ion access to Ti3C2 and charge-transfer efficiency. Herein, we propose an electrochemically etched strategy to synthesize -F-free Ti3C2Tx through three-electrode cyclic voltammetry scanning within a narrowed potential window in an alkaline electrolyte. The resulting assembly of an asymmetric electrochemical-etched Ti3C2Tx//activated carbon CDI device can deliver an excellent salt removal capacity of 20.27 mg·g-1 with an adsorption rate of 1.01 mg g-1 min-1 owing to the enhanced hydrophilicity and ion transport. The tiny CDI device is demonstrated, which can generate an electric current during the electrosorption of salt ions, thus facilitating the powering of a red light-emitting diode. This study opens a new avenue for the surface chemistry of Ti3C2Tx and is expected to achieve future applications in desalination and renewable energy.

Facile Tailoring of Surface Terminations of MXenes by Doping Nb Element: Toward Extraordinary Pseudocapacitance Performance.

MXenes show promising potential in supercapacitors due to their unique two-dimensional (2D) structure and abundant surface functional groups. However, most studies about MXenes have focused on tailoring surface structures by alternating synthesis methods or post-etch treatments, and little is known about the inherent relationship between surface groups and M elements. Herein, we propose a simple and novel strategy to adjust the surface structure of few-layered MXene flakes by adding a small amount of Nb element. Because of the strong affinity between Nb and O elements, the as-received V1.8Nb0.2CTx and Ti2.7Nb0.3C2Tx MXenes have much fewer -F functional groups and a higher O content than V2CTx and Ti3C2Tx MXenes, respectively. Thus, both V1.8Nb0.2CTx and Ti2.7Nb0.3C2Tx MXenes show enhanced pseudocapacitance performance. Especially, V1.8Nb0.2CTx delivers an ultrahigh volumetric capacitance of 1698 F/cm3 at a scan rate of 2 mV/s. Moreover, benefiting from the high activity of MAX precursors obtained through a fast self-propagating high-temperature synthesis, the etching time to produce V-based MXenes is much shorter than that in previous reports. Therefore, the results presented here are applicable to the surface engineering and rational design of 2D MXene materials and develop them into promising, cost-effective electrode materials for supercapacitors or other energy-storage equipment.

Influence of charges deposited on membranes of human hyperdirect pathway axons on depolarization during subthalamic deep brain stimulation.

Objective.The motor hyperdirect pathway (HDP) is a key target in the treatment of Parkinson's disease with deep brain stimulation (DBS). Biophysical models of HDP DBS have been used to explore the mechanisms of stimulation. Built upon finite element method volume conductor solutions, such models are limited by a resolution mismatch, where the volume conductor is modeled at the macro scale, while the neural elements are at the micro scale. New techniques are needed to better integrate volume conductor models with neuron models.Approach.We simulated subthalamic DBS of the human HDP using finely meshed axon models to calculate surface charge deposition on insulting membranes of nonmyelinated axons. We converted the corresponding double layer extracellular problem to a single layer problem and applied the well-conditioned charge-based boundary element fast multipole method (BEM-FMM) with unconstrained numerical spatial resolution. Commonly used simplified estimations of membrane depolarization were compared with more realistic solutions.Main result.Neither centerline potential nor estimates of axon recruitment were impacted by the estimation method used except at axon bifurcations and hemispherical terminations. Local estimates of axon polarization were often much higher at bifurcations and terminations than at any other place along the axon and terminal arbor. Local average estimates of terminal electric field are higher by 10%-20%.Significance. Biophysical models of action potential initiation in the HDP suggest that axon terminations are often the lowest threshold elements for activation. The results of this study reinforce that hypothesis and suggest that this phenomenon is even more pronounced than previously realized.

Iodine-Functionalized Titanium Carbide MXene with Ultra-Stable Pseudocapacitor Performance.

MXene has attracted a wide spread attention as promising supercapacitor electrode materials owing to excellent electronic conductivity and reversible surface redox capability. In fact, the supercapacitor performance strongly relies onsurface terminations of MXene. However, regulating the types of surface terminations for enhancing the electrochemical performance of MXene is still one of major challenge. Herein, we successfully prepared a MXene containing iodine terminations (I-Ti3C2 MXene) by facile Lewis-acidic-melt etching method and comprehensively investigated its supercapacitor performance. Benefiting from the presence of iodine terminations, the I-Ti3C2 MXene with pseudocapacitor property exhibits significantly higher specific capacitance than that of hydrofluoric acid etching MXene (HF-Ti3C2Tx MXene). Impressively, the I-Ti3C2 MXene shows extraordinary long-term cyclic performance, even when cycled at high current density of 50 A/g, that the specific capacitance retention of 91% can be obtained over 100,000 cycles, corresponding to an average specific capacitance loss of only 0.00009% per cycle. Furthermore, the mechanisms involved were clarfied by systematical characterizations. This work will provide new insights for enhancing the supercapacitor performance of MXene-based materials by surface chemistry modification.

Covalent functionalization of MXenes for tribological purposes - a critical review.

Transition metal carbides, nitrides and carbonitrides (MXenes) have recently attracted notable attention in tribology and, particularly solid lubrication, due to their low shear strength and ability to form low-friction, wear-resistant tribo-layers. Their use as lubricant additives has only shown limited success due to their inherent hydrophilic character, causing a low phase-compatibility and dispersion-stability with pure base oils. To overcome this shortcoming and to boost MXenes' tribological performance as lubricant additive and reinforcement phase in composites, their tuneable surface chemistry moves into the focus of current research. Originating from chemical etching to synthesize MXenes, their outer surface contains a variety of surface terminations, which can function as anchoring points for molecules via covalent grafting/functionalization. By adopting an adequate functionalization strategy, this, in turn, can help to tailor MXenes' hydrophobicity, dispersion stability, restacking tendency, or oxidation resistance. This directly affects their dispersion stability in base oils and improves their phase compatibility with other matrix materials in composites, thus resulting in an enhanced tribological performance. Therefore, this review concisely summarizes the existing state-of-the-art regarding MXenes' covalent functionalization with a particular emphasis on tribological properties and needs, a topic, which has not been holistically reviewed yet. The first chapter sheds light on the existing synthesis approaches with detailed insights regarding the resulting surface terminations, which are crucial for the subsequent chemical functionalization. After summarizing strategies to increase their interlayer distance to improve the accessibility for chemical functionalization and the existing state-of-the art regarding MXene tribology, we critically discuss the existing functionalization strategies using different coupling agents (organosilanes, organophosphorus agents, aryldiazonium agents, among others). Subsequently, we emphasize on the crucial role of homogeneously distributed -OH surface terminations to guarantee the overall success of the functionalization approach and to boost the resulting tribological performance. Lastly, we address the existing challenges and derive future research directions. We anticipate that our article can serve as an excellent guide for MXenes' chemical functionalization, which can be useful in various applications including tribology thus paving the way towards enhanced physical and chemical properties of MXenes.

Switching the Nonlinear Optical Absorption of Titanium Carbide MXene by Modulation of the Surface Terminations.

Surface terminations of two-dimensional materials should have a strong influence on the nonlinear optical (NLO) properties, but the relationship between surface terminations and NLO properties has not yet been reported. In this work, switching the NLO properties of MXenes (Ti3C2Tx) via "surface terminations modulation" is explored. The surface terminations of Ti3C2Tx are modulated by electrochemical treatment, resulting in different states (viz., Ti3C2Tx(pristine), Ti3C2Tx(═O rich), and Ti3C2Tx(-OH rich)). The sign and magnitude of the effective NLO absorption coefficient (ßeff) change with the surface terminations. Ti3C2Tx(═O rich) shows a relatively large saturable absorption (SA) with laser excitation at 515 nm (ßeff = -1020 ± 136.2 cm GW-1), while reverse saturable absorption (RSA) is found in Ti3C2Tx(pristine) and Ti3C2Tx(-OH rich). The RSA of Ti3C2Tx(pristine) and Ti3C2Tx(-OH rich) is attributed to excited-state absorption, while the SA of Ti3C2Tx(═O rich) is associated with Pauli blocking. With laser excitation at 800 nm, the ßeff of Ti3C2Tx(-OH rich) is 113 ± 3.2 cm GW-1, 1.68 times that of Ti3C2Tx(pristine); the RSA is caused by photon-induced absorption. Our results reveal a correlation between surface terminations and NLO properties, highlighting the potential of MXenes in photoelectronics.