Mechanistic insights into on-surface reactions from isothermal temperature-programmed X-ray photoelectron spectroscopy

On-surface synthesis often proceeds under kinetic control due to the irreversibility of key reaction steps, rendering kinetic studies pivotal. The accurate quantification of reaction rates also bears potential for unveiling reaction mechanisms. Temperature-Programmed X-ray Photoelectron Spectroscopy (TP-XPS) has emerged as an analytical tool for kinetic studies with splendid chemical and sufficient temporal resolution. Here, we demonstrate that the common linear temperature ramps lead to fitting ambiguities. Moreover, pinpointing the reaction order remains intricate, although this key parameter entails information on atomistic mechanisms. Yet, TP-XPS experiments with a stepped temperature profile comprised of isothermal segments facilitate the direct quantification of rate constants from fitting time courses. Thereby, rate constants are obtained for a series of temperatures, which allows independent extraction of both activation energies and pre-exponentials from Arrhenius plots. By using two analogous doubly versus triply brominated aromatic model compounds, we found that their debromination on Ag(111) is best modeled by second-order kinetics and thus proceeds via the involvement of a second, non-obvious reactant. Accordingly, we propose that debromination is activated by surface supplied Ag adatoms. This hypothesis is supported by Density Functional Theory (DFT) calculations. We foresee auspicious prospects for this TP-XPS variant for further exploring the kinetics and mechanisms of on-surface reactions.

MXene-Stabilized VS2 Nanostructures for High-Performance Aqueous Zinc Ion Storage

Aqueous zinc-ion batteries (AZIBs) based on vanadium oxides or sulfides are promising candidates for large-scale rechargeable energy storage due to their ease of fabrication, low cost, and high safety. However, the commercial application of vanadium-based electrode materials has been hindered by challenging problems such as poor cyclability and low-rate performance. To this regard, sophisticated nanostructure engineering technology is used to adeptly incorporate VS2 nanosheets into the MXene interlayers to create a stable 2D heterogeneous layered structure. The MXene nanosheets exhibit stable interactions with VS2 nanosheets, while intercalation between nanosheets effectively increases the interlayer spacing, further enhancing their stability in AZIBs. Benefiting from the heterogeneous layered structure with high conductivity, excellent electron/ion transport, and abundant reactive sites, the free-standing VS2/Ti3C2Tz composite film can be used as both the cathode and the anode of AZIBs. Specifically, the VS2/Ti3C2Tz cathode presents a high specific capacity of 285 mAh g-1 at 0.2 A g-1. Furthermore, the flexible Zn-metal free in-plane VS2/Ti3C2Tz//MnO2/CNT AZIBs deliver high operation voltage (2.0 V) and impressive long-term cycling stability (with a capacity retention of 97% after 5000 cycles) which outperforms almost all reported Vanadium-based electrodes for AZIBs. The effective modulation of the material structure through nanocomposite engineering effectively enhances the stability of VS2, which shows great potential in Zn2+ storage. This work will hasten and stimulate further development of such composite material in the direction of energy storage.

Universal inter-molecular radical transfer reactions on metal surfaces

On-surface synthesis provides tools to prepare low-dimensional supramolecular structures. Traditionally, reactive radicals are a class of single-electron species, serving as exceptional electron-withdrawing groups. On metal surfaces, however, such species are affected by conduction band screening effects that may even quench their unpaired electron characteristics. As a result, radicals are expected to be less active, and reactions catalyzed by surface-stabilized radicals are rarely reported. Herein, we describe a class of inter-molecular radical transfer reactions on metal surfaces. With the assistance of aryl halide precursors, the coupling of terminal alkynes is steered from non-dehydrogenated to dehydrogenated products, resulting in alkynyl-Ag-alkynyl bonds. Dehalogenated molecules are fully passivated by detached hydrogen atoms. The reaction mechanism is unraveled by various surface-sensitive technologies and density functional theory calculations. Moreover, we reveal the universality of this mechanism on metal surfaces. Our studies enrich the on-surface synthesis toolbox and develop a pathway for producing low-dimensional organic materials.

Atomic Scale Design of MXenes and Their Parent Materials─From Theoretical and Experimental Perspectives

More than a decade after the discovery of MXene, there has been a remarkable increase in research on synthesis, characterization, and applications of this growing family of two-dimensional (2D) carbides and nitrides. Today, these materials include one, two, or more transition metals arranged in chemically ordered or disordered structures of three, five, seven, or nine atomic layers, with a surface chemistry characterized by surface terminations. By combining M, X, and various surface terminations, it appears that a virtually endless number of MXenes is possible. However, for the design and discovery of structures and compositions beyond current MXenes, one needs suitable (stable) precursors, an assessment of viable pathways for 3D to 2D conversion, and utilization or development of corresponding synthesis techniques. Here, we present a critical and forward-looking review of the field of atomic scale design and synthesis of MXenes and their parent materials. We discuss theoretical methods for predicting MXene precursors and for assessing whether they are chemically exfoliable. We also summarize current experimental methods for realizing the predicted materials, listing all verified MXenes to date, and outline research directions that will improve the fundamental understanding of MXene processing, enabling atomic scale design of future 2D materials, for emerging technologies.

Role of chloride on the instability of blue emitting mixed-halide perovskites

Although perovskite light-emitting diodes (PeLEDs) have seen unprecedented development in device efficiency over the past decade, they suffer significantly from poor operational stability. This is especially true for blue PeLEDs, whose operational lifetime remains orders of magnitude behind their green and red counterparts. Here, we systematically investigate this efficiency-stability discrepancy in a series of green- to blue-emitting PeLEDs based on mixed Br/Cl-perovskites. We find that chloride incorporation, while having only a limited impact on efficiency, detrimentally affects device stability even in small amounts. Device lifetime drops exponentially with increasing Cl-content, accompanied by an increased rate of change in electrical properties during operation. We ascribe this phenomenon to an increased mobility of halogen ions in the mixed-halide lattice due to an increased chemically and structurally disordered landscape with reduced migration barriers. Our results indicate that the stability enhancement for PeLEDs might require different strategies from those used for improving efficiency.

Unraveling the optoelectronic properties of CoSbx intrinsic selective solar absorber towards high-temperature surfaces

The combination of the ability to absorb most of the solar radiation and simultaneously suppress infrared re-radiation allows selective solar absorbers (SSAs) to maximize solar energy to heat conversion, which is critical to several advanced applications. The intrinsic spectral selective materials are rare in nature and only a few demonstrated complete solar absorption. Typically, intrinsic materials exhibit high performances when integrated into complex multilayered solar absorber systems due to their limited spectral selectivity and solar absorption. In this study, we propose CoSbx (2 < x < 3) as a new exceptionally efficient SSA. Here we demonstrate that the low bandgap nature of CoSbx endows broadband solar absorption (0.96) over the solar spectral range and simultaneous low emissivity (0.18) in the mid-infrared region, resulting in a remarkable intrinsic spectral solar selectivity of 5.3. Under 1 sun illumination, the heat concentrates on the surface of the CoSbx thin film, and an impressive temperature of 101.7 °C is reached, demonstrating the highest value among reported intrinsic SSAs. Furthermore, the CoSbx was tested for solar water evaporation achieving an evaporation rate of 1.4 kg m-2 h-1. This study could expand the use of narrow bandgap semiconductors as efficient intrinsic SSAs with high surface temperatures in solar applications.

M5X4: A Family of MXenes

MXenes are two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides typically synthesized from layered MAX-phase precursors. With over 50 experimentally reported MXenes and a near-infinite number of possible chemistries, MXenes make up the fastest-growing family of 2D materials. They offer a wide range of properties, which can be altered by their chemistry (M, X) and the number of metal layers in the structure, ranging from two in M2XTx to five in M5X4Tx. Only one M5X4 MXene, Mo4VC4, has been reported. Herein, we report the synthesis and characterization of two M5AX4 mixed transition metal MAX phases, Ti2.5Ta2.5AlC4 and Ti2.675Nb2.325AlC4, and their successful topochemical transformation into Ti2.5Ta2.5C4Tx and Ti2.675Nb2.325C4Tx MXenes. The resulting MXenes were delaminated into single-layer flakes, analyzed structurally, and characterized for their thermal and optical properties. This establishes a family of M5AX4 MAX phases and their corresponding MXenes. These materials were experimentally produced based on guidance from theoretical predictions, leading to more exciting applications for MXenes.

A systematic study of work function and electronic properties of MXenes from first principles

Functional 2D materials are interesting for a wide range of applications. The rapid growth of the MXene family is due to its compositional diversity, which, in turn, allows significant tuning of the properties, and hence their applicability. The properties are to a large extent dictated by surface terminations. In the present work, we demonstrate the influence of termination species (O, NH, N, S, F, Cl, Br, I) on the changes in electronic structure, work function, dynamical stability, and atomic charges and distances of MXenes (Ti₂C, Nb₂C, V₂C, Mo₂C, Ti₃C_2, and Nb₄C₃). Among these systems, the work function values were not previously reported for ∼60% of the systems, and most of the previously reported MXenes with semiconducting nature are here proven to be dynamically unstable. The results show that the work function generally decreases with a reduced electronegativity of the terminating species, which in turn is correlated to a reduced charge of both the metal and terminating species and an increased metal-termination distance. An exception to this trend is NH terminations, which display a significantly reduced work function due to an intrinsic dipole moment within the termination. Furthermore, the results suggest that halogen terminations improve the electrical conductivity of the materials.

Experimental and Theoretical Investigations of Out-of-Plane Ordered Nanolaminate Transition Metal Borides: M4CrSiB2 (M = Mo, W, Nb)

We report the synthesis of three out-of-plane chemically ordered quaternary transition metal borides (o-MAB phases) of the chemical formula M₄CrSiB₂ (M = Mo, W, Nb). The addition of these phases to the recently discovered o-MAB phase Ti₄MoSiB₂ shows that this is indeed a new family of chemically ordered atomic laminates. Furthermore, our results expand the attainable chemistry of the traditional M₅SiB₂ MAB phases to also include Cr. The crystal structure and chemical ordering of the produced materials were investigated using high-resolution scanning transmission electron microscopy and X-ray diffraction by applying Rietveld refinement. Additionally, calculations based on density functional theory were performed to investigate the Cr preference for occupying the minority 4c Wyckoff site, thereby inducing chemical order.

Pyridinic Nitrogen Modification for Selective Acetylenic Homocoupling on Au(111)

On-surface acetylenic homocoupling has been proposed to construct carbon nanostructures featuring sp hybridization. However, the efficiency of linear acetylenic coupling is far from satisfactory, often resulting in undesired enyne products or cyclotrimerization products due to the lack of strategies to enhance chemical selectivity. Herein, we inspect the acetylenic homocoupling reaction of polarized terminal alkynes (TAs) on Au(111) with bond-resolved scanning probe microscopy. The replacement of benzene with pyridine moieties significantly prohibits the cyclotrimerization pathway and facilitates the linear coupling to produce well-aligned N-doped graphdiyne nanowires. Combined with density functional theory calculations, we reveal that the pyridinic nitrogen modification substantially differentiates the coupling motifs at the initial C-C coupling stage (head-to-head vs head-to-tail), which is decisive for the preference of linear coupling over cyclotrimerization.

Unveiling the formation mechanism of the biphenylene network

We have computationally studied the formation mechanism of the biphenylene network via the intermolecular HF zipping, as well as identified key intermediates experimentally, on the Au(111) surface. We elucidate that the zipping process consists of a series of defluorinations, dehydrogenations, and C-C coupling reactions. The Au substrate not only serves as the active site for defluorination and dehydrogenation, but also forms C-Au bonds that stabilize the defluorinated and dehydrogenated phenylene radicals, leading to "standing" benzyne groups. Despite that the C-C coupling between the "standing" benzyne groups is identified as the rate-limiting step, the limiting barrier can be reduced by the adjacent chemisorbed benzyne groups. The theoretically proposed mechanism is further supported by scanning tunneling microscopy experiments, in which the key intermediate state containing chemisorbed benzyne groups can be observed. This study provides a comprehensive understanding towards the on-surface intermolecular HF zipping, anticipated to be instructive for its future applications.

Immobilization of a TiO2-PEDOT:PSS hybrid heterojunction photocatalyst for degradation of organic effluents

Heterojunction photocatalysts have recently emerged for use in degradation of organic pollutants, typically being suspended in effluent solution to degrade it. Post degradation, the catalyst must be removed from the treated solution, which consumes both energy and time. Moreover, the separation of nano catalysts from the treated solution is challenging. In the present work, we explore fabrication of immobilized TiO₂-PEDOT:PSS hybrid heterojunction catalysts with the support of a PVA (polyvinyl alcohol) matrix. These photocatalytic films do not require any steps to separate the powdered catalyst from the treated water. While the PVA-based films are unstable in water, their stability could be significantly enhanced by heat treatment, enabling efficient removal of organic effluents like methylene blue (MB) and bisphenol-A (BPA) from the aqueous solution under simulated sunlight irradiation. Over 20 cycles, the heterojunction photocatalyst maintained high photocatalytic activity and showed excellent stability. Hence, an immobilization of the TiO₂-PEDOT:PSS hybrid heterojunction is suggested to be beneficial from the viewpoint of reproducible and recyclable materials for simple and efficient wastewater treatment.

Reduction in Antibiotic Delivery Time Following Improving Pediatric Sepsis Outcomes Quality Improvement Initiative at a Major Children's Hospital

OBJECTIVE

Sepsis causes morbidity and mortality in pediatric patients, but timely antibiotic administration can improve sepsis outcomes. The pharmacy department can affect the time from order to delivery of antibiotics. By evaluating the pharmacy process, this study aimed to decrease the time from antibiotic order to delivery to within 45 minutes.

METHODS

All antibiotic orders placed following a positive sepsis screen for acute care patients at a freestanding children's hospital from April 1, 2019, to December 31, 2019, were reviewed. Lean Six Sigma methodology including process mapping was used to identify and implement improvements, including educational interventions for providers. Outcome measures included time from antibiotic order placement to delivery and to administration. Additional assessment of process measures included evaluation of order priority, PowerPlan (an internally created order set) use, and delivery method.

RESULTS

Ninety-eight antibiotic orders for 85 patients were evaluated. In an individual chart of antibiotic delivery time, a trend towards faster delivery time was observed after interventions. Stat orders (40.5 minutes [IQR, 19.5-48]) were delivered more quickly than routine orders (51 minutes [IQR, 45-65]; p < 0.001). Orders using the PowerPlan (20.5 minutes [IQR, 18.5-38]) were delivered more quickly than those that did not (47 minutes [IQR, 34-64]; p < 0.01). Shorter time to administration was observed with pneumatic tube delivery (41 minutes [IQR, 20-50]) than with direct delivery to a health care provider (51 minutes [IQR, 31-83]; p < 0.05) or to the automated dispensing cabinet's refrigerator (47 minutes [IQR, 41-62]; p < 0.0001).

CONCLUSIONS

Multifactorial coordinated interventions within the pharmacy department improve medication delivery time for pediatric sepsis antibiotic orders.

On the Use of Ti3C2 T x MXene as a Negative Electrode Material for Lithium-Ion Batteries

The pursuit of new and better battery materials has given rise to numerous studies of the possibilities to use two-dimensional negative electrode materials, such as MXenes, in lithium-ion batteries. Nevertheless, both the origin of the capacity and the reasons for significant variations in the capacity seen for different MXene electrodes still remain unclear, even for the most studied MXene: Ti₃C₂ T _x . Herein, freestanding Ti₃C₂ T _x MXene films, composed only of Ti₃C₂ T _x MXene flakes, are studied as additive-free negative lithium-ion battery electrodes, employing lithium metal half-cells and a combination of chronopotentiometry, cyclic voltammetry, X-ray photoelectron spectroscopy, hard X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy experiments. The aim of this study is to identify the redox reactions responsible for the observed reversible and irreversible capacities of Ti₃C₂ T _x -based lithium-ion batteries as well as the reasons for the significant capacity variation seen in the literature. The results demonstrate that the reversible capacity mainly stems from redox reactions involving the T _x -Ti-C titanium species situated on the surfaces of the MXene flakes, whereas the Ti-C titanium present in the core of the flakes remains electro-inactive. While a relatively low reversible capacity is obtained for electrodes composed of pristine Ti₃C₂ T _x MXene flakes, significantly higher capacities are seen after having exposed the flakes to water and air prior to the manufacturing of the electrodes. This is ascribed to a change in the titanium oxidation state at the surfaces of the MXene flakes, resulting in increased concentrations of Ti(II), Ti(III), and Ti(IV) in the T _x -Ti-C surface species. The significant irreversible capacity seen in the first cycles is mainly attributed to the presence of residual water in the Ti₃C₂ T _x electrodes. As the capacities of Ti₃C₂ T _x MXene negative electrodes depend on the concentration of Ti(II), Ti(III), and Ti(IV) in the T _x -Ti-C surface species and the water content, different capacities can be expected when using different manufacturing, pretreatment, and drying procedures.

The Role of Metal Adatoms in a Surface‐Assisted Cyclodehydrogenation Reaction on a Gold Surface

Dehydrogenation reactions are key steps in many metal-catalyzed chemical processes and in the on-surface synthesis of atomically precise nanomaterials. The principal role of the metal substrate in these reactions is undisputed, but the role of metal adatoms remains, to a large extent, unanswered, particularly on gold substrates. Here, we discuss their importance by studying the surface-assisted cyclodehydrogenation on Au(111) as an ideal model case. We choose a polymer theoretically predicted to give one of two cyclization products depending on the presence or absence of gold adatoms. Scanning probe microscopy experiments observe only the product associated with adatoms. We challenge the prevalent understanding of surface-assisted cyclodehydrogenation, unveiling the catalytic role of adatoms and their effect on regioselectivity. The study adds new perspectives to the understanding of metal catalysis and the design of on-surface synthesis protocols for novel carbon nanomaterials.

The rise of MAX phase alloys - large-scale theoretical screening for the prediction of chemical order and disorder

MAX phases (M = metal, A = A-group element, X = C and/or N) are layered materials, combining metallic and ceramic attributes. They are also parent materials for the two-dimensional (2D) derivative, MXene, realized from selective etching of the A-element. In this work, we present a historical survey of MAX phase alloying to date along with an extensive theoretical investigation of MAX phase alloys (M = Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, and Ni, A = Al, Ga, In, Si, Ge, Sn, Ni, Cu, Zn, Pd, Ag, Pt, and Au, and X = C). We assess both in-plane chemical ordering (in the so-called i-MAX phases) and solid solution. Out of the 2702 compositions, 92 i-MAX and 291 solid solution MAX phases are predicted to be thermodynamically stable. A majority of these have not yet been experimentally reported. In general, i-MAX is favored for a smaller size of A and a large difference in metal size, while solid solution is favored for a larger size of A and with comparable size of the metals. The results thus demonstrate avenues for a prospective and substantial expansion of the MAX phase and MXene chemistries.

Surface-Assisted Synthesis of N-Containing π-Conjugated Polymers

On-surface synthesis has recently emerged as a powerful strategy to design conjugated polymers previously precluded in conventional solution chemistry. Here, an N-containing pentacene-based precursor (tetraazapentacene) is ex-professo synthesized endowed with terminal dibromomethylene (:CBr₂ ) groups to steer homocoupling via dehalogenation on metallic supports. Combined scanning probe microscopy investigations complemented by theoretical calculations reveal how the substrate selection drives different reaction mechanisms. On Ag(111) the dissociation of bromine atoms at room temperature triggers the homocoupling of tetraazapentacene units together with the binding of silver adatoms to the nitrogen atoms of the monomers giving rise to a N-containing conjugated coordination polymer (P1). Subsequently, P1 undergoes ladderization at 200 °C, affording a pyrrolopyrrole-bridged conjugated polymer (P2). On Au(111) the formation of the intermediate polymer P1 is not observed and, instead, after annealing at 100 °C, the conjugated ladder polymer P2 is obtained, revealing the crucial role of metal adatoms on Ag(111) as compared to Au(111). Finally, on Ag(100) the loss of :CBr2 groups affords the formation of tetraazapentacene monomers, which coexist with polymer P1. Our results contribute to introduce protocols for the synthesis of N-containing conjugated polymers, illustrating the selective role of the metallic support in the underlying reaction mechanisms.

Steering Self-Assembly of Three-Dimensional Iptycenes on Au(111) by Tuning Molecule-Surface Interactions

Self-assembly of three-dimensional molecules is scarcely studied on surfaces. Their modes of adsorption can exhibit far greater variability compared to (nearly) planar molecules that adsorb mostly flat on surfaces. This additional degree of freedom can have decisive consequences for the expression of intermolecular binding motifs, hence the formation of supramolecular structures. The determining molecule-surface interactions can be widely tuned, thereby providing a new powerful lever for crystal engineering in two dimensions. Here, we study the self-assembly of triptycene derivatives with anthracene blades on Au(111) by Scanning Tunneling Microscopy, Near Edge X-ray Absorption Fine Structure and Density Functional Theory. The impact of molecule-surface interactions was experimentally tested by comparing pristine with iodine-passivated Au(111) surfaces. Thereby, we observed a fundamental change of the adsorption mode that triggered self-assembly of an entirely different structure.

Theoretical predictions of phase stability for orthorhombic and hexagonal ternary MAB phases

In the quest for finding novel thermodynamically stable, layered, MAB phases promising for synthesis, we herein explore the phase stability of ternary MAB phases by considering both orthorhombic and hexagonal crystal symmetries for various compositions (MAB, M₂AB₂, M₃AB₄, M₄AB₄, and M₄AB₆ where M = Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, and Co, A = Al, Ga, and In, and B is boron). The thermodynamic stability of seven previously synthesized MAB phases is confirmed, three additional phases are predicted to be stable, and 23 phases are found to be close to stable. Furthermore, the crystal symmetry preference for forming orthorhombic or hexagonal crystal structures is investigated where the considered Al-based MAB phases tend to favour orthorhombic structures whereas Ga- and In-based phases in general prefer hexagonal structures. The theoretically predicted stable MAB phases along with the structural preference is intended to both guide experimental efforts and to give an insight into the stability for different crystal symmetries of MAB phases.

Termination-Accelerated Electrochemical Nitrogen Fixation on Single-Atom Catalysts Supported by MXenes

The synthesis of ammonia (NH₃) from nitrogen (N₂) under ambient conditions is of great significance but hindered by the lack of highly efficient catalysts. By performing first-principles calculations, we have investigated the feasibility for employing a transition metal (TM) atom, supported on Ti₃C₂T₂ MXene with O/OH terminations, as a single-atom catalyst (SAC) for electrochemical nitrogen reduction. The potential catalytic performance of TM single atoms is evaluated by their adsorption behavior on the MXene, together with their ability to bind N₂ and to desorb NH₃ molecules. Of importance, the OH terminations on Ti₃C₂T₂ MXene can effectively enhance the N₂ adsorption and decrease the NH₃ adsorption for single atoms. Based on proposed criteria for promising SACs, our calculations further demonstrate that the Ni/Ti₃C₂O_0.19(OH)_1.81 exhibits reasonable thermodynamics and kinetics toward electrochemical nitrogen reduction.

Magnetic phase diagram of (Mo2/3RE1/3)2AlC, RETb and Dy, studied by magnetization, specific heat, and neutron diffraction analysis

We report the results of magnetization, heat capacity, and neutron diffraction measurements on (Mo_2/3RE_1/3)₂AlC with RE = Dy and Tb. Temperature and field-dependent magnetization as well as heat capacity were measured on a powder sample and on a single crystal allowing the construction of the magnetic field-temperature phase diagram. To study the magnetic structure of each magnetic phase, we applied neutron diffraction in a magnetic field up to 6 T. For (Mo_2/3Dy_1/3)₂AlC in zero field, a spin density wave is stabilized at 16 K, with antiferromagnetic ordering at 13 K. Furthermore, we identify the coexistence of ferromagnetic and antiferromagnetic phases induced by magnetic fields for both RE = Tb and Dy. The origin of the field induced phases is resulting from the competing ferromagnetic and antiferromagnetic interactions.

Investigation of out-of-plane ordered Ti4MoSiB2from first principles

The laminated ternary boride Mo₅SiB₂of T2 structure have two symmetrically inequivalent metallic sites, 16l and 4c, being occupied in a 4:1 ratio. The phase was recently shown to be stable for 80% substitution of Mo for Ti, at the majority site, forming an out-of-plane chemically ordered quaternary boride: Ti₄MoSiB₂. Considering that the hypothetical Ti₅SiB₂is theoretically predicted as not stable, a key difference in bonding characteristics is indicated for full substitution of Mo for Ti at the metallic sites. To explore the origin of formation of Ti₄MoSiB₂, we here investigate the electronic properties and bonding characteristics of Mo₅SiB₂, Ti₄MoSiB₂and Ti₅SiB₂through their density of states, projected crystal orbital Hamilton population (pCOHP), Bader charge partitioning and second order force constants. The bond between the two different metallic sites is found to be key to the stability of the compounds, evident from the pCOHP of this bond showing a peak of bonding states close to the Fermi level, which is completely filled in Mo₅SiB₂and Ti₄MoSiB₂, while only partially filled in Ti₅SiB₂. Furthermore, the lower electronegativity of Ti compared to Mo results in charge accumulation at the Si and B sites, which coincides with a reduced bond strength in Ti₅SiB₂compared to Mo₅SiB₂and Ti₄MoSiB₂. Bandstructure calculations show that all three structures are metallic. The calculated mechanical and elastic properties show reduced bulk (B) and elastic (E) moduli when introducing Ti in Mo₅SiB₂, from 279 and 365 GPa to 176 and 258 GPa, respectively. The Pugh criteria indicates also a slight reduction in ductility, with aG/Bratio increasing from 0.51 to 0.59.

Evolution of adsorption heights in the on-surface synthesis and decoupling of covalent organic networks on Ag(111) by normal-incidence X-ray standing wave

Structural characterization in on-surface synthesis is primarily carried out by Scanning Probe Microscopy (SPM) which provides high lateral resolution. Yet, important fresh perspectives on surface interactions and molecular conformations are gained from adsorption heights that remain largely inaccessible to SPM, but can be precisely measured with both elemental and chemical sensitivity by Normal-Incidence X-ray Standing Wave (NIXSW) analysis. Here, we study the evolution of adsorption heights in the on-surface synthesis and post-synthetic decoupling of porous covalent triazine-phenylene networks obtained from 2,4,6-tris(4-bromophenyl)-1,3,5-triazine (TBPT) precursors on Ag(111). Room temperature deposition of TBPT and mild annealing to ∼150 °C result in full debromination and formation of organometallic intermediates, where the monomers are linked into reticulated networks by C-Ag-C bonds. Topologically identical covalent networks comprised of triazine vertices that are interconnected by biphenyl units are obtained by a thermally activated chemical transformation of the organometallic intermediates. Exposure to iodine vapor facilitates decoupling by intercalation of an iodine monolayer between the covalent networks and the Ag(111) surface. Accordingly, Scanning Tunneling Microscopy (STM), X-ray Photoelectron Spectroscopy (XPS) and NIXSW experiments are carried out for three successive sample stages: organometallic intermediates, covalent networks directly on Ag(111) and after decoupling. NIXSW analysis facilitates the determination of adsorption heights of chemically distinct carbon species, i.e. in the phenyl and triazine rings, and also for the organometallic carbon atoms. Thereby, molecular conformations are assessed for each sample stage. The interpretation of experimental results is informed by Density Functional Theory (DFT) calculations, providing a consistent picture of adsorption heights and molecular deformations in the networks that result from the interplay between steric hindrance and surface interactions. Quantitative adsorption heights, i.e. vertical distances between adsorbates and surface, provide detailed insight into surface interactions, but are underexplored in on-surface synthesis. In particular, the direct comparison with an in situ prepared decoupled state unveils the surface influence on the network structure, and shows that iodine intercalation is a powerful decoupling strategy.

Improved charge storage performance of a layered Mo1.33C MXene/MoS2/graphene nanocomposite

The construction of nanocomposite electrodes based on 2D materials is an efficient route for property enrichment and for exploitation of constituent 2D materials. Herein, a flexible Mo_1.33C i-MXene/MoS₂/graphene (MOMG) composite electrode is constructed, utilizing an environment-friendly method for high-quality graphene and MoS₂ synthesis. The presence of graphene and MoS₂ between MXene sheets limits the commonly observed restacking, increases the interlayer spacing, and facilitates the ionic and electronic conduction. The as-prepared MOMG electrode delivers a volumetric capacitance of 1600 F cm^-3 (450 F g^-1) at the scan rate of 2 mV s^-1 and retains 96% of the initial capacitance after 15 000 charge/discharge cycles (10 A g^-1). The current work demonstrates that the construction of nanocomposite electrodes is a promising route towards property enhancement for energy storage applications.

Predictions of attainable compositions of layered quaternary i-MAB phases and solid solution MAB phases

MAB phases are layered materials combining metallic and ceramic attributes. Their ternary compositions, however, have been limited to a few elemental combinations which makes controlled and tailored properties challenging. Inspired by the recent discovery of Mo_4/3Y_2/3AlB₂ and Mo_4/3Sc_2/3AlB₂i-MAB phases, i.e., quaternary layered MAB phases with in-plane chemical order, we perform an extensive first-principles study to explore formation of chemical order and solid-solutions upon metal alloying of M₂AB₂ phases of 1092 compositions (M from group 3 to 9 and A = Al, Ga, In, Si, Ge, Sn). This large dataset provides 39 chemically ordered (i-MAB) and 52 solid solution (MAB) phases that are predicted to be thermodynamically stable at typical synthesis temperatures, of which a majority have not yet been experimentally reported. The possibility for realizing both i-MAB and solid solution MAB phases, combined with the multiple elemental combinations previously not observed in these boride-based materials, allows for an increased potential for property tuning and potential chemical exfoliation into 2D derivatives.

Elucidating the formation and active state of Cu co-catalysts for photocatalytic hydrogen evolution

The design of active and selective co-catalysts constitutes one of the major challenges in developing heterogeneous photocatalysts for energy conversion applications. This work provides a comprehensive insight into thermally induced bottom-up generation and transformation of a series of promising Cu-based co-catalysts. We demonstrate that the volcano-type HER profile as a function of calcination temperature is independent of the type of the Cu precursor but is affected by changes in oxidation state and location of the copper species. Supported by DFT modeling, our data suggest that low temperature (<200 °C) treatments facilitate electronic communication between the Cu species and TiO2, which allows for a more efficient charge utilization and maximum HER rates. In contrast, higher temperatures (>200 °C) do not affect the Cu oxidation state, but induce a gradual, temperature-dependent surface-to-bulk diffusion of Cu, which results in interstitial, tetra-coordinated Cu+ species. The disappearance of Cu from the surface and the introduction of new defect states is associated with a drop in HER performance. This work examines electronic and structural effects that are in control of the photocatalytic activity and can be transferred to other systems for further advancing photocatalysis.

P14.41 Cost-effectiveness of FET PET for early treatment response assessment in glioma patients following adjuvant temozolomide chemotherapy

BACKGROUND

In light of increasing healthcare costs, higher medical expenses should be justified socio-economically. Therefore, we calculated the effectiveness and cost-effectiveness of PET using the radiolabeled amino acid O-(2-[18F]-fluoroethyl)-L-tyrosine (FET) compared to conventional MRI for early identification of responders to adjuvant temozolomide chemotherapy. A recent study in IDH-wildtype glioma patients suggested that after two cycles, FET-PET parameter changes predicted a significantly longer survival while MRI changes were not significant.

MATERIALS AND METHODS

To determine the effectiveness and cost-effectiveness of serial FET-PET imaging, we analyzed published clinical data and calculated the associated costs in the context of the German healthcare system.Based on a decision-tree model, FET-PET and MRI’s effectiveness was calculated, i.e., the probability to correctly identify a responder as defined by an overall survival ≥15 months. To determine the cost-effectiveness, the incremental cost-effectiveness ratio (ICER) was calculated, i.e., the cost for each additionally identified responder by FET-PET who would have remained undetected by MRI. The robustness of the results was tested by deterministic and probabilistic (Monte Carlo simulation) sensitivity analyses.

RESULTS

Compared to MRI, FET-PET increases the rate of correctly identified responders to chemotherapy by 26%; thus, four patients need to be examined by FET-PET to identify one additional responder. Considering the respective cost for serial FET-PET and MRI, the ICER resulted in €4,396.83 for each additional correctly identified responder by FET-PET. The sensitivity analyses confirmed the robustness of the results.

CONCLUSION

In contrast to conventional MRI, the model suggests that FET PET is cost-effective in terms of ICER values. Concerning the high cost of temozolomide, the integration of FET-PET has the potential to avoid premature chemotherapy discontinuation at a reasonable cost.

Out-Of-Plane Ordered Laminate Borides and Their 2D Ti-Based Derivative from Chemical Exfoliation

Exploratory theoretical predictions in uncharted structural and compositional space are integral to materials discoveries. Inspired by M₅ SiB₂ (T2) phases, the finding of a family of laminated quaternary metal borides, M'₄ M″SiB₂ , with out-of-plane chemical order is reported here. 11 chemically ordered phases as well as 40 solid solutions, introducing four elements previously not observed in these borides are predicted. The predictions are experimentally verified for Ti₄ MoSiB₂ , establishing Ti as part of the T2 boride compositional space. Chemical exfoliation of Ti₄ MoSiB₂ and select removal of Si and MoB₂ sub-layers is validated by derivation of a 2D material, TiO_x Cl_y , of high yield and in the form of delaminated sheets. These sheets have an experimentally determined direct band gap of ≈4.1 eV, and display characteristics suitable for supercapacitor applications. The results take the concept of chemical exfoliation beyond currently available 2D materials, and expands the envelope of 3D and 2D candidates, and their applications.

Boridene: Two-dimensional Mo4/3B2-x with ordered metal vacancies obtained by chemical exfoliation

Extensive research has been invested in two-dimensional (2D) materials, typically synthesized by exfoliation of van der Waals solids. One exception is MXenes, derived from the etching of constituent layers in transition metal carbides and nitrides. We report the experimental realization of boridene in the form of single-layer 2D molybdenum boride sheets with ordered metal vacancies, Mo_4/3B_2-xT_z (where T_z is fluorine, oxygen, or hydroxide surface terminations), produced by selective etching of aluminum and yttrium or scandium atoms from 3D in-plane chemically ordered (Mo_2/3Y_1/3)₂AlB₂ and (Mo_2/3Sc_1/3)₂AlB₂ in aqueous hydrofluoric acid. The discovery of a 2D transition metal boride suggests a wealth of future 2D materials that can be obtained through the chemical exfoliation of laminated compounds.

Acoustomicrofluidic Synthesis of Pristine Ultrathin Ti3C2Tz MXene Nanosheets and Quantum Dots

The conversion of layered transition metal carbides and/or nitrides (MXenes) into zero-dimensional structures with thicknesses and lateral dimensions of a few nanometers allows these recently discovered materials with exceptional electronic properties to exploit the additional benefits of quantum confinement, edge effects, and large surface area. Conventional methods for the conversion of MXene nanosheets and quantum dots, however, involve extreme conditions such as high temperatures and/or harsh chemicals that, among other disadvantages, lead to significant degradation of the material as a consequence of their oxidation. Herein, we show that the large surface acceleration-on the order of 10 million g's-produced by high-frequency (10 MHz) nanometer-order electromechanical vibrations on a chip-scale piezoelectric substrate is capable of efficiently nebulizing, and consequently dimensionally reducing, a suspension of multilayer Ti₃C₂T_z (MXene) into predominantly monolayer nanosheets and quantum dots while, importantly, preserving the material from any appreciable oxidation. As an example application, we show that the high-purity MXene quantum dots produced using this room-temperature chemical-free synthesis method exhibit superior performance as electrode materials for electrochemical sensing of hydrogen peroxide compared to the highly oxidized samples obtained through conventional hydrothermal synthesis. The ability to detect concentrations as low as 5 nM is a 10-fold improvement to the best reported performance of Ti₃C₂T_z MXene electrochemical sensors to date.

The world of two-dimensional carbides and nitrides (MXenes)

A decade after the first report, the family of two-dimensional (2D) carbides and nitrides (MXenes) includes structures with three, five, seven, or nine layers of atoms in an ordered or solid solution form. Dozens of MXene compositions have been produced, resulting in MXenes with mixed surface terminations. MXenes have shown useful and tunable electronic, optical, mechanical, and electrochemical properties, leading to applications ranging from optoelectronics, electromagnetic interference shielding, and wireless antennas to energy storage, catalysis, sensing, and medicine. Here we present a forward-looking review of the field of MXenes. We discuss the challenges to be addressed and outline research directions that will deepen the fundamental understanding of the properties of MXenes and enable their hybridization with other 2D materials in various emerging technologies.

In-plane ordered quaternaryM4/3'M2/3″AlB2phases (i-MAB): electronic structure and mechanical properties from first-principles calculations

We have by means of first principles density functional theory calculations studied the mechanical and electronic properties of the so calledi-MAB phases,M_4/3'M″_2/3AlB₂, whereM' = Cr, Mo, W andM″ = Sc, Y. These phases, experimentally verified for Mo_4/3Sc_2/3AlB₂and Mo_4/3Y_2/3AlB₂, display an atomically laminated structure with in-plane chemical order between theM' andM″ elements. Structural properties, along with elastic constants and moduli, are predicted for different structural symmetries, including the reportedR3̄m(#166) space group. We find all consideredi-MAB phases to be metallic with a significant peak in the electronic structure at the Fermi level and no significant anisotropy in the electronic band structure. The simulations also indicate that they are rather hard and stiff, in particular the Cr-based ones, with a Young's modulusEof 325 GPa forM″ = Sc. The Mo-based phases are similar, withE= 299 GPa forM″ = Sc, which is higher than the corresponding laminated carbides (i-MAX phases).

POS0020 EFFICACY AND SAFETY OF SECUKINUMAB IN PATIENTS WITH ROTATOR CUFF TENDINOPATHY: A 24-WEEK, RANDOMISED, DOUBLE-BLIND, PLACEBO-CONTROLLED, PHASE II PROOF-OF-CONCEPT TRIAL

Background:

Rotator cuff tendinopathy (RC TP) is a multifactorial condition and one of the most common causes of musculoskeletal burden. Current standard of care (SoC) is limited to pain relief with NSAIDs and physiotherapy. Recent evidence indicates that IL-17A-expressing tendon-resident immune cells are present in human overuse tendinopathy, and IL-17A levels are increased in early human tendinopathic tissue samples [1, 2]. Secukinumab (SEC) is a fully human, monoclonal antibody that binds to and neutralises IL-17A.

Objectives:

To evaluate the efficacy and safety of SEC in patients with active overuse RC TP refractory to oral NSAIDs/acetaminophen, physiotherapy or corticosteroid injections.

Methods:

96 patients with symptomatic RC TP with no or <50% rupture were randomly assigned to receive seven subcutaneous injections of SEC 300 mg or placebo (PBO) at baseline and Weeks 1, 2 and 3, followed by every 4 weeks starting at Week 4. The primary endpoint was change from baseline in the Western Ontario Rotator Cuff (WORC) index score at Week 14 for SEC vs PBO (two-sided p<0.1). Secondary endpoints included, visual analogue scale (VAS) pain score, Disability of Arm, Shoulder and Hand Questionnaire (QuickDASH) score, American Shoulder and Elbow Surgeons Shoulder Evaluation Form (ASES), EQ-5D-5L score and patient global assessment (PGA) score. All endpoints were assessed through 24 weeks.

Results:

Clinically relevant improvement in both SEC and PBO groups on top of SoC treatment was observed, with no statistically significant difference demonstrated in the full study population on physical symptoms and function (Table 1). Similar results were observed in the secondary endpoints with marked improvement in both groups over time. Exploratory post-hoc analyses in a subpopulation of 39% of the study subjects with non-acute, moderate to severe disease, SEC provided significant and clinically relevant improvements vs PBO through Week 24 in total WORC score (overall treatment difference: 19.2, p <0.01) and pain (VAS, overall treatment difference: 15, p = 0.02) with early effect observed after two weeks (Figure 1). A favourable treatment effect in the more severe subgroup was demonstrated in other patient-reported outcomes. No serious adverse events were reported.

Conclusion:

Although SEC did not demonstrate a significant benefit vs PBO in the overall patient population with active overuse RC TP, SEC did provide benefit in the subpopulation with non-acute, moderate to severe disease. Larger clinical trials of SEC in this area are warranted.

References:

[1]Millar NL, et al. Sci Rep. 2016;6:27149.

[2]Millar NL, et al. Nat Rev Rheumatol.2017;13:110-122.

Table 1.

Change from baseline in the SEC versus PBO groups in WORC index and pain (VAS)

VisitSEC 300 mgPBOp-valueTotal treated population N=96WORC Index percentage score (0 worst -100 best)aDay 2922.3519.490.45Day 9937.0037.770.87Day 16943.4140.970.64Pain (VAS, 0 best - 100 worst)bDay 29−26.04−23.130.57Day 99−46.11−40.560.28Day 169−52.23−50.740.78Post-hoc population* N=37WORC Index percentage score (0 worst - 100 best)cDay 2930.0910.840.002Day 9948.2631.830.048Day 16955.9835.240.028Pain (VAS, 0 best - 100 worst)dDay 29−29.20−14.850.125Day 99−51.48−35.370.045Day 169−57.01−46.640.217

aDay 1: SEC 42.47, PBO 40.47; bSEC 67.04, PBO 64.85; cSEC 35.93, PBO 32.90, dSEC 71.72, PBO 67.58. Day 1 values are given as absolute values to describe baseline WORC/Pain status

*Post-hoc subpopulation: Baseline: (Disease duration 2-6 months) AND (WORC ≤40 OR Tear Thickness (Bauer) ≥1 OR Sein ≥2)

PBO, placebo; SEC, secukinumab; SoC, standard of care; WORC, Western Ontario Rotator Cuff Index; VAS, visual analogue scale

Figure 1.

Post-hoc analysis of function (WORC) in the treatment groups in non-acute, moderate to severe subpopulation

SEC

SE, standard error; SEC, secukinumab; WORC, Western Ontario Rotator Cuff Index

Disclosure of Interests:

Neal L Millar Grant/research support from: Honoraria or research funding from Novartis and Stryker, Iain McInnes Speakers bureau: AbbVie, Amgen, Bristol-Myers Squibb, Celgene, Janssen, Lilly, Novartis, Pfizer, and UCB, Consultant of: AbbVie, Amgen, Bristol-Myers Squibb, Celgene, Janssen, Lilly, Novartis, Pfizer, and UCB, Grant/research support from: AbbVie, Amgen, Bristol-Myers Squibb, Celgene, Janssen, Lilly, Novartis, Pfizer, and UCB, Linda Mindeholm Employee of: Employee of Novartis, Abdelkader Seroutou Employee of: Employee of Novartis, Jens Praestgaard Employee of: Employee of Novartis, Ursula Schramm Employee of: Employee of Novartis, Rafael Levitch Employee of: Employee of Novartis, Eckhard Weber Employee of: Employee of Novartis, Didier Laurent Employee of: Employee of Novartis, Jeffrey Rosen Consultant of: Research advisor for Novartis, Georg Schett Speakers bureau: Received speakers honoraria from Abbvie, Amgen, BMS, Eli Lilly, Gilead, Janssen, Novartis, UCB, Ronenn Roubenoff Employee of: Employee of Novartis, Matthias Schieker Employee of: Employee of Novartis.

Structure-activity correlation of Ti2CT2MXenes for C-H activation

As a bourgeoning class of 2D materials, MXenes have recently attracted significant attention within heterogeneous catalysis for promoting reactions such as hydrogen evolution and C-H activation. However, the catalytic activity of MXenes is highly dependent on the structural configuration including termination groups and their distribution. Therefore, understanding the relation between the structure and the activity is desired for the rational design of MXenes as high-efficient catalysts. Here, we present that the correlation between the structure and activity of Ti₂CT₂(T is a combination of O, OH and/or F) MXenes for C-H activation can be linked by a quantitative descriptor: the hydrogen affinity (E_H). A linear correlation is observed between the mean hydrogen affinity and the overall ratio of O terminations (x_O) in Ti₂CT₂MXenes, in which hydrogen affinity increases as thex_Odecreases, regardless to the species of termination groups. In addition, the hydrogen affinity is more sensitive to the presence of OH termination than F terminations. Moreover, the linear correlation between the hydrogen affinity and the activity of Ti₂CT₂MXenes for C-H activation of both -CH₃and -CH₂- groups can be extended to be valid for all three possible termination groups. Such a correlation provides fast prediction of the activity of general Ti₂CT₂MXenes, avoiding tedious activation energy calculations. We anticipate that the findings have the potential to accelerate the development of MXenes for heterogeneous catalysis applications.

1002 Calcium administration in Major haemorrhage Protocol

Introduction

Calcium gluconate is an essential part of the major haemorrhage protocol (MHP). It minimizes the exacerbation of transfusion coagulopathies due to the citrate preservative. As fifty percent of trauma patients present with hypocalcaemia prior to transfusion, the risk is pertinent. Given the importance of the issue, surprisingly current guidelines remain sparse. We analysed the percentage of patients who received calcium and their hypocalcaemia incidence.

Method

A Retrospective review of red traumas during June to August 2019. The frequency of MHP and the patient’s ionised plasma calcium levels on VBG (1.15-1.26mmol/L) were identified. Our standard stated 100% of MHP should receive calcium. A massive transfusion was defined as 10 red blood cells units in 24 hours or 4 blood products within 30mins.

Results

27 red traumas were accepted to audit, MHP was activated in 85%. Out of these 75% received calcium and on average after 6.4 units of blood products. The incidence of ionised hypocalcaemia in all MHP patients was 67%.

Conclusions

We identified a standard that supplementary calcium should be supplemented in all MHPs. Hypocalcaemia was more frequency than our research stipulated. Improvement needs to be made to meet standards. We recommend incorporation of Calcium gluconate into major haemorrhage pack and transfusion guidelines.

Ultrafast, One-Step, Salt-Solution-Based Acoustic Synthesis of Ti3C2 MXene

The current quest for two-dimensional transition metal carbides and nitrides (MXenes) has been to circumvent the slow, hazardous, and laborious multistep synthesis procedures associated with conventional chemical MAX phase exfoliation. Here, we demonstrate a one-step synthesis method with local Ti3AlC2 MAX to Ti3C2Tz MXene conversion on the order of milliseconds, facilitated by proton production through solution dissociation under megahertz frequency acoustic excitation. These protons combined with fluorine ions from LiF to selectively etch the MAX phase into MXene, whose delamination is aided by the acoustic forcing. These results have important implications for the future applicability of MXenes, which crucially depend on the development of more efficient synthesis procedures. For proof-of-concept, we show that flexible electrodes fabricated by this method exhibit comparable electrochemical performance to that previously reported.

Bioinspired multisensory neural network with crossmodal integration and recognition

The integration and interaction of vision, touch, hearing, smell, and taste in the human multisensory neural network facilitate high-level cognitive functionalities, such as crossmodal integration, recognition, and imagination for accurate evaluation and comprehensive understanding of the multimodal world. Here, we report a bioinspired multisensory neural network that integrates artificial optic, afferent, auditory, and simulated olfactory and gustatory sensory nerves. With distributed multiple sensors and biomimetic hierarchical architectures, our system can not only sense, process, and memorize multimodal information, but also fuse multisensory data at hardware and software level. Using crossmodal learning, the system is capable of crossmodally recognizing and imagining multimodal information, such as visualizing alphabet letters upon handwritten input, recognizing multimodal visual/smell/taste information or imagining a never-seen picture when hearing its description. Our multisensory neural network provides a promising approach towards robotic sensing and perception.

Abstract SP084: Replication stress response defects predict responses to ICT in non-hypermutated tumors

Immune checkpoint blockade (ICT) has provided robust, durable responses to a subset of patients. Many initial ICT trials were focused on highly mutated cancer types, such as melanoma and lung cancer, largely predicated on the idea that mutation-derived neoantigens would allow for generation of tumor-specific T cells. Subsequent analysis of patient responses in these highly mutated cancer types confirmed that increased tumor mutation burden (TMB) corresponded with improved patient outcomes. Further clinical studies identified additional predictive biomarkers, such as PD-L1 protein expression, and various gene expression signatures. Based on the success of ICT in hypermutated cancer types, further clinical trials with ICT were performed in cancers with overall lower mutational burden. These studies have indicated that many non-hypermutated cancer types with relatively low TMB may be effectively treated with ICT. For example, patients with clear cell renal cell carcinoma (ccRCC) display relatively low TMB overall, and a narrow distribution of TMB across patients, yet clinical response rates to ICT are ~30%, with some durable responses seen. Other tumor types with minimal mutation burdens, including glioblastoma (GBM) and triple negative breast cancer (TNBC), have likewise shown encouraging clinical responses to ICT. We recently demonstrated distinct tumor immunobiology between hypermutated and non-hypermutated tumor types, notably that relative neoantigen load/tumor mutation burden was only a relevant factor for immune infiltration in hypermutated tumor types. Consistent with this, clinical trials have demonstrated that TMB does not predict response to ICT in tumor types with minimal mutational load, such as breast cancer, ccRCC, and GBM. Thus, there remains a critical gap in knowledge as to how to identify which patients with non-hypermutated cancer may benefit from ICT. Here, we demonstrate that a replication stress response (RSR) defect gene expression signature accurately predicts ICT response in 11 independent non-hypermutated patient cohorts from 6 tumor types for which other biomarkers failed. Pre-clinical studies indicate that aberrant origin firing in RSR deficient tumor cells causes exhaustion of replication protein A, resulting in accumulation of immunostimulatory cytosolic DNA. Induction or suppression of RSR deficiencies was sufficient to modulate response to ICT. Taken together, the RSR defect gene signature can accurately identify patients who will benefit from ICT across numerous non-hypermutated tumor types, and pharmacological induction of RSR defects may further expand the benefits of ICT to more patients.

Citation Format: D McGrail, P Pilié, XHF Zhang, J Rosen, L Voorwerk, M Kok, A Heimberger, C Peterson, E Jonasch, S Lin. Replication stress response defects predict responses to ICT in non-hypermutated tumors [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr SP084.

Flexible Free-Standing MoO3/Ti3C2T z MXene Composite Films with High Gravimetric and Volumetric Capacities

Enhancing both the energy storage and power capabilities of electrochemical capacitors remains a challenge. Herein, Ti3C2T z MXene is mixed with MoO3 nanobelts in various mass ratios and the mixture is used to vacuum filter binder free, open, flexible, and free-standing films. The conductive Ti3C2T z flakes bridge the nanobelts, facilitating electron transfer; the randomly oriented, and interconnected, MoO3 nanobelts, in turn, prevent the restacking of the Ti3C2T z nanosheets. Benefitting from these advantages, a MoO3/Ti3C2T z film with a 8:2 mass ratio exhibits high gravimetric/volumetric capacities with good cyclability, namely, 837 C g-1 and 1836 C cm-3 at 1 A g-1 for an ≈ 10 µm thick film; and 767 C g-1 and 1664 C cm-3 at 1 A g-1 for ≈ 50 µm thick film. To further increase the energy density, hybrid capacitors are fabricated with MoO3/Ti3C2T z films as the negative electrodes and nitrogen-doped activated carbon as the positive electrodes. This device delivers maximum gravimetric/volumetric energy densities of 31.2 Wh kg-1 and 39.2 Wh L-1, respectively. The cycling stability of 94.2% retention ratio after 10 000 continuous charge/discharge cycles is also noteworthy. The high energy density achieved in this work can pave the way for practical applications of MXene-containing materials in energy storage devices.

Microscopic evidence for Mn-induced long range magnetic ordering in MAX phase compounds

Zero and low field nuclear magnetic resonance measurements have been performed on MAX phase samples (Cr_1-x Mn _x )₂AC with A = Ge and Ga in order to obtain local microscopic information on the nature of magnetism in this system. Our results unambiguously provide evidence for the existence of long-range magnetic order in (Cr_0.96Mn_0.04)₂GeC and for (Cr_0.93Mn_0.07)₂GaC, but not for (Cr_0.97Mn_0.03)₂GaC. We point to a possible dependence of long range magnetic order in these MAX phase compounds on the A atom.

Tailored synthesis approach of (Mo2/3Y1/3)2AlC i-MAX and its two-dimensional derivative Mo1.33CTz MXene: enhancing the yield, quality, and performance in supercapacitor applications

A vacancy-ordered MXene, Mo_1.33CT_z, obtained from the selective etching of Al and Sc from the parent i-MAX phase (Mo_2/3Sc_1/3)₂AlC has previously shown excellent properties for supercapacitor applications. Attempts to synthesize the same MXene from another precursor, (Mo_2/3Y_1/3)₂AlC, have not been able to match its forerunner. Herein, we show that the use of an AlY_2.3 alloy instead of elemental Al and Y for the synthesis of (Mo_2/3Y_1/3)₂AlC i-MAX, results in a close to 70% increase in sample purity due to the suppression of the main secondary phase, Mo₃Al₂C. Furthermore, through a modified etching procedure, we obtain a Mo_1.33CT_z MXene of high structural quality and improve the yield by a factor of 6 compared to our previous efforts. Free-standing films show high volumetric (1308 F cm^-3) and gravimetric (436 F g^-1) capacitances and a high stability (98% retention) at the level of, or even beyond, those reported for the Mo_1.33CT_z MXene produced from the Sc-based i-MAX. These results are of importance for the realization of high quality MXenes through use of more abundant elements (Y vs. Sc), while also reducing waste (impurity) material and facilitating the synthesis of a high-performance material for applications.

Theoretical Prediction and Synthesis of a Family of Atomic Laminate Metal Borides with In-Plane Chemical Ordering

All atomically laminated MAB phases (M = transition metal, A = A-group element, and B = boron) exhibit orthorhombic or tetragonal symmetry, with the only exception being hexagonal Ti₂InB₂. Inspired by the recent discovery of chemically ordered hexagonal carbides, i-MAX phases, we perform an extensive first-principles study to explore chemical ordering upon metal alloying of M₂AlB₂ (M from groups 3 to 9) in orthorhombic and hexagonal symmetry. Fifteen stable novel phases with in-plane chemical ordering are identified, coined i-MAB, along with 16 disordered stable alloys. The predictions are verified through the powder synthesis of Mo_4/3Y_2/3AlB₂ and Mo_4/3Sc_2/3AlB₂ of space group R3̅m (no. 166), displaying the characteristic in-plane chemical order of Mo and Y/Sc and Kagomé ordering of the Al atoms, as evident from X-ray diffraction and electron microscopy. The discovery of i-MAB phases expands the elemental space of these borides with M = Sc, Y, Zr, Hf, and Nb, realizing an increased property tuning potential of these phases as well as their suggested potential two-dimensional derivatives.

C-H activation of light alkanes on MXenes predicted by hydrogen affinity

C-H activation of light alkanes is one of the most important reactions for a plethora of applications but requires catalysts to operate at feasible conditions. MXenes, a new group of two-dimensional materials, have shown great promise as heterogeneous catalysts for several applications. However, the catalytic activity of MXenes depends on the type and distribution of termination groups. Theoretically, it is desired to search for a relation between the catalytic activity and the termination configuration by employing a simple descriptor in order to avoid tedious activation energy calculations. Here, we show that MXenes are promising for splitting C-H bonds of light alkanes. Furthermore, we present how a quantitative descriptor - the hydrogen affinity - can be used to characterize the termination configuration of Ti₂CT_z (T = O, OH) MXenes, as well as the catalytic activity towards dehydrogenation reactions, using propane as model system. First-principles calculations reveal that the hydrogen affinity can be considered as an intrinsic property of O and OH terminated Ti₂C MXenes, in which the mean hydrogen affinity for the terminated Ti₂C MXenes is linearly correlated to the statistical average of their OH fraction. In addition, the C-H activation energies exhibit a strong scaling relationship to the hydrogen affinity. This quantity can therefore yield quick predictions of catalytic activity of terminated Ti₂C MXenes towards C-H activations, and even predict their chemical selectivity toward scissoring different C-H bonds. We believe that the hydrogen affinity will accelerate the discovery of further applications of the broad family of MXenes in heterogeneous catalysis.