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Aluminum-ion batteries have garnered significant interest as a potentially safer and cheaper replacement for conventional lithium-ion batteries, offering a shorter charging time and denser storage capacity. Nonetheless, the progress in this field is considerably hampered by the limited availability of suitable cathode materials that can sustain the reversible intercalation of Al

MXene-based hydrogels, a flourishing family of soft materials, have recently emerged as promising candidates for stretchable electronics. Despite recent progress, most works use MXenes as conductive nanofillers. Herein, by tuning the molecular interactions between MXene nanosheets and other constituents within the hydrogels, we demonstrate Ti3C3Tx MXene can act as a versatile cross-linker to activate the fast gelation of a wide range of hydrogels, starting from various monomer- and polymer-based precursors. The gelation behavior varies significantly across hydrogels. In general, the fast gelation mechanism is attributed to the easier generation of free radicals with the help of Ti3C2Tx MXene and the presence of multiscale molecular interactions between MXene and polymers. The use of MXene as a dynamic cross-linker leads to superior mechanical properties, adhesion, and self-healing ability. Owing to the inherent photothermal behavior of Ti3C3Tx and the heterogeneous phase-transforming features of polymers, a polymer-MXene hydrogel is demonstrated to exhibit distinctive thermosensation-based actuation upon near-infrared illumination, accompanied by rapid shape transformation.

Compared to conventional solvents, ionic liquids (ILs) are highly recognized for their ability to enhance the dispersion of nanoparticles (NPs). However, the thermal stability of the ILs-based nanocomposites is a vital parameter for their processing applications. Here, we scrutinized the thermal stability of a series of different imidazolium ion-based ILs before and after incorporating amorphous porous silicon (ap-Si) NPs. The results show that regardless of the obtained quality dispersion, the thermal stability of the host ILs was never regressed. The combination of ap-Si NPs and bmim-SCN (1-buthyl-3-methyl imidazolium thiocyanate) induced highly dispersed framework with an enhanced thermal stability (∼15 °C shift to higher temperature). Likewise, the emim-BF4 (1-ethyl-3-methylimidazolium tetrafluoroborate) coated the ap-Si NPs forming a very stable dispersion along with a good thermal stability (∼8 °C shift). On the other hand, the thermal stability of bmim-Ac (1-buthyl-3-methylimidazolium acetate) was not affected owing to the high viscosity of bmim-Ac that limited the dispersion of ap-Si NPs at room temperature. Throughout our study, we explored the intermolecular interactions using SEM, TEM, Raman spectroscopy and XRD. We probed the thermal stability of the fabricated dispersions using TGA, and DSC as part of characterization methodology.

The ability of MXenes to efficiently absorb light is greatly enriched by the surface plasmons oscillating at their two-dimensional (2D) surfaces. Thus far, MXenes have shown impressive plasmonic absorptions spanning the visible and infrared (IR) regimes. However, their potential use in IR optoelectronic applications, including photodiodes, has been marginally investigated. Besides, their relatively low resistivity has limited their use as photosensing materials due to their intrinsic high dark current. Herein, heterostructures made of methylammonium lead triiodide (MAPbI

Hydrogels have recently garnered tremendous interest due to their potential application in soft electronics, human-machine interfaces, sensors, actuators, and flexible energy storage. Benefiting from their impressive combination of hydrophilicity, metallic conductivity, high aspect ratio morphology, and widely tuneable properties, when two-dimensional (2D) transition metal carbides/nitrides (MXenes) are incorporated into hydrogel systems, they offer exciting and versatile platforms for the design of MXene-based soft materials with tunable application-specific properties. The intriguing and, in some cases, unique properties of MXene hydrogels are governed by complex gel structures and gelation mechanisms, which require in-depth investigation and engineering at the nanoscale. On the other hand, the formulation of MXenes into hydrogels can significantly increase the stability of MXenes, which is often the limiting factor for many MXene-based applications. Moreover, through simple treatments, derivatives of MXene hydrogels, such as aerogels, can be obtained, further expanding their versatility. This tutorial review intends to show the enormous potential of MXene hydrogels in expanding the application range of both hydrogels and MXenes, as well as increasing the performance of MXene-based devices. We elucidate the existing structures of various MXene-containing hydrogel systems along with their gelation mechanisms and the interconnecting driving forces. We then discuss their distinctive properties stemming from the integration of MXenes into hydrogels, which have revealed an enhanced performance, compared to either MXenes or hydrogels alone, in many applications (energy storage/harvesting, biomedicine, catalysis, electromagnetic interference shielding, and sensing).

Extracting osmotic energy through nanoporous membranes is an efficient way to harvest renewable and sustainable energy using the salinity gradient between seawater and river water. Despite recent advances of nanopore-based membranes, which have revitalized the prospect of blue energy, their energy conversion is hampered by nanomembrane issues such as high internal resistance or low selectivity. Herein, we report a lamellar-structured membrane made of nanoporous Ti3C2Tx MXene sheets, exhibiting simultaneous enhancement in permeability and ion selectivity beyond their inherent trade-off. The perforated nanopores formed by facile H2SO4 oxidation of the sheets act as a network of cation channels that interconnects interplanar nanocapillaries throughout the lamellar membrane. The constructed internal nanopores lower the energy barrier for cation passage, thereby boosting the preferential ion diffusion across the membrane. A maximum output power density of the nanoporous Ti3C2Tx MXene membranes reaches up to 17.5 W·m–2 under a 100-fold KCl gradient at neutral pH and room temperature, which is as high as by 38% compared to that of the pristine membrane. The membrane design strategy employing the nanoporous two-dimensional sheets provides a promising approach for ion exchange, osmotic energy extraction, and other nanofluidic applications.

Perovskite single crystals (PSCs) are considered the next breakthrough in optoelectronics research due to their free-grain boundary and much lower density of trap states compared to those of their ...

In this work, we fabricate photodetectors made of methylammonium lead trihalide perovskite (MLHP) and phosphorus-doped graphitic carbon nitride nanosheets (PCN-S). Using thermal polymerization, PCN...

Semiconductor heterostructures of multiple quantum wells (MQWs) have major applications in optoelectronics. However, for halide perovskites-the leading class of emerging semiconductors-building a variety of bandgap alignments (i.e., band-types) in MQWs is not yet realized owing to the limitations of the current set of used barrier materials. Here, artificial perovskite-based MQWs using 2,2',2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole), tris-(8-hydroxyquinoline)aluminum, and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline as quantum barrier materials are introduced. The structures of three different five-stacked perovskite-based MQWs each exhibiting a different band offset with CsPbBr

As a thriving member of the 2D nanomaterials family, MXenes, i.e., transition metal carbides, nitrides, and carbonitrides, exhibit outstanding electrochemical, electronic, optical, and mechanical properties. They have been exploited in many applications including energy storage, electronics, optoelectronics, biomedicine, sensors, and catalysis. Compared to other 2D materials, MXenes possess a unique set of properties such as high metallic conductivity, excellent dispersion quality, negative surface charge, and hydrophilicity, making them particularly suitable as inks for printing applications. Printing and pre/post-patterned coating methods represent a whole range of simple, economically efficient, versatile, and eco-friendly manufacturing techniques for devices based on MXenes. Moreover, printing can allow for complex 3D architectures and multifunctionality that are highly required in various applications. By means of printing and patterned coating, the performance and application range of MXenes can be dramatically increased through careful patterning in three dimensions; thus, printing/coating is not only a device fabrication tool but also an enabling tool for new applications as well as for industrialization.

The presence of localized trap states on the surface of CsPbCl3 perovskite nanocrystals (NCs) is one of the greatest challenges precluding the development of optoelectronic applications of these NCs. Passivation of these defect sites provides a promising pathway to remediating their electronic and optical properties, such as the photoluminescence quantum yield (PLQY). Herein, we demonstrate a postsynthetic dual-surface treatment using trivalent metal ion salts, i.e., YCl3, as a new passivation approach that enhances the PLQY up to 60% while preserving the NC size and crystal structure. Such remarkable enhancement of the PLQY along with prolongation of the average PL lifetimes of treated NCs samples indicates effective passivation of the surface defects and subsequent suppression of the formation of surface nonradiative recombination centers. As a segue toward optoelectronic applications, we probed the photoelectric performance of the NCs using ultraflexible devices; we found that YCl3-treated CsPbCl3 NC f...

2D Ti3C2Tx MXenes were recently shown to exhibit intense surface plasmon (SP) excitations; however, their spatial variation over individual Ti3C2Tx flakes remains undiscovered. Here, we use scanning transmission electron microscopy (STEM) combined with ultra-high-resolution electron energy loss spectroscopy (EELS) to investigate the spatial and energy distribution of SPs (both optically active and forbidden modes) in mono- and multilayered Ti3C2Tx flakes. With STEM-EELS mapping, the inherent interband transition in addition to a variety of transversal and longitudinal SP modes (ranging from visible down to 0.1 eV in MIR) are directly visualized and correlated with the shape, size, and thickness of Ti3C2Tx flakes. The independent polarizability of Ti3C2Tx monolayers is unambiguously demonstrated and attributed to their unusual weak interlayer coupling. This characteristic allows for engineering a class of nanoscale systems, where each monolayer in the multilayered structure of Ti3C2Tx has its own set of SP...

Ionic liquids (ILs) and ionic liquid-nanoparticle (IL-NP) hybrid electrolytes have garnered a lot of interest due to their unique properties that stimulate their use in various applications. Herein, we investigate the electrochemical and photo-physical properties of organic-inorganic hybrid electrolytes based on three imidazolium-based ionic liquids, i.e., 1-buthyl-3-methylimidazolium thiocyanate ([bmim] [SCN]), 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim] [BF 4 ]) and 1-buthyl-3-methylimidazolium acetate ([bmim] [Ac]) that are covalently tethered to amorphous porous silicon nanoparticles (ap-Si NPs). We found that the addition of ap-Si NPs confer to the ILs a pronounced boost in the electrocatalytic activity, and in mixtures of ap-Si NPs and [bmim] [SCN], the room-temperature current transport is enhanced by more than 5 times compared to bare [bmim] [SCN]. A detailed structural investigation by transmission electron microscope (TEM) showed that the ap-Si NPs were well dispersed, stabilized and highly aggregated in [bmim] [SCN], [emim] [BF 4 ] and [bmim] [Ac] ILs, respectively. These observations correlate well with the enhanced current transport observed in ap-Si NPs/[bmim] [SCN] evidenced by electrochemical measurements. We interpreted these observations by the use of UV–vis absorbance, photoluminescence (PL), FTIR and solid-state NMR spectroscopy. We found that the ap-Si NPs/[bmim] [SCN] hybrid stands out due to its stability and optical transparency. This behavior is attributed to the iron(III) thiocyanate complexion as per the experimental findings. Furthermore, we found that the addition of NPs to [emim] [BF 4 ] alters the equilibrium of the IL, which consequently improved the stability of the NPs through intermolecular interactions with the two ionic layers (anionic and cationic layers) of the IL. While in the case of [bmim] [Ac], the dispersion of ap-Si NPs was restrained because of the high viscosity of this IL.

Developing stable plasmonic materials featuring earth-abundant compositions with continuous band structures, similar to those of typical metals, has received special research interest. Owing to their metal-like behavior, monoclinic MoO

K.J.L. and N.A.M. contributed equally to this work. The authors gratefully acknowledge the financial support provided by King Abdullah University of Science and Technology (KAUST).

Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrene sulfonate) (PSS) is the most commonly used conducting polymer in organic bioelectronics. However, electrochemical capacitances exceeding the current state-of-the-art are required for enhanced transduction and stimulation of biological signals. The long-term stability of conducting polymer films during device operation and storage in aqueous environments remains a challenge for routine applications. In this work, we electrochemically synthesize a PEDOT composite comprising the water dispersible two-dimensional conducting material Ti3C2 MXene. We find that incorporating MXene as a co-dopant along with PSS leads to PEDOT:PSS:MXene films with remarkably high volumetric capacitance (607.0 ± 85.3 F cm−3) and stability (capacity retention = 78.44% ± 1.75% over 500 cycles), outperforming single dopant-comprising PEDOT films, i.e., PEDOT:PSS and PEDOT:MXene electropolymerized under the same conditions on identical surfaces. The stability of microfabricated PEDOT:PSS:MXene electrodes is evaluated under different conditions, i.e., when the films are exposed to sonication (∼100% retention over 6 min), upon immersion in cell culture media for 14 days (∆|Z| = 2.13%), as well as after continuous electrical stimulation. Furthermore, we demonstrate the use of a PEDOT:PSS:MXene electrode as an electrochemical sensor for sensitive detection of dopamine (DA). The sensor exhibited an enhanced electrocatalytic activity toward DA in a linear range from 1 µM to 100 μM validated in mixtures containing common interferents such as ascorbic acid and uric acid. PEDOT:PSS:MXene composite is easily formed on conductive substrates with various geometries and can serve as a high performance conducting interface for chronic biochemical sensing or stimulation applications.

We report a novel flexible solar tracking system based on a photothermal-thermomechanical (PT-TM) actuator comprised of Ti3C2Tx MXene and polyvinylidene fluoride (PVDF) bilayer. The actuation function of the proposed device originates from photothermal and surface plasmon-assisted effects in MXenes, coupled with thermomechanical deformation of in-plane aligned PVDF polymer. Two types of solar tracking modes are evaluated based on the experimental deformation behavior of the PT-TM actuator. We find that the uniaxial East-West solar tracking option increases the overall energy intensity reaching the solar module by over 30%, in comparison with the optimized tilting-controlled mode. We also demonstrate the thermally driven self-oscillation of the MXene-PVDF device, which may have promising potential for optically and thermally driven soft robotics. The PT-TM actuator devices display robust mechanical strength and durability, with no noticeable degradation in their performance after more than 1000 cycles.

Among the existing two-dimensional materials, MXenes, i.e. transition metal carbides, nitrides and/or carbonitrides, stand out for their excellent electrochemical properties. Due to their high charge storage capacity, metal-like conductivity, biocompatibility as well as hydrophilicity, Ti3C2Tx MXene-based inks hold great potential for scalable production of skin conformable electronics via direct printing methods. Herein, we develop an aqueous MXene ink and inkjet-print MXene films on freestanding, flexible, and conducting polymer-based substrates. These skin-adherent MXene electrodes detect electrocardiography signals with high signal-to-noise ratio while exhibiting preserved electrical performance after 1000 cycles of bending with a 50 d long shelf life in ambient conditions. We show that printed MXene films can be further functionalized to perform as multifunctional biosensing units. When integrated with a sodium (Na+) ion selective membrane, MXene electrodes detect Na+ in artificial sweat with a sensitivity of 40 mV per decade. When the films are functionalized with antibodies, they generate an electrical signal in response to a pro-inflammatory cytokine protein (interferon gamma) with a sensitivity of 3.9 mV per decade. Our findings demonstrate how inkjet-printed MXene films simplify the fabrication of next-generation wearable electronic platforms that comprise multimodal sensors.

Y.-P.Z. and J.K.E.-D. contributed equally to this work. The research reported in this publication was supported by King Abdullah University of Science and Technology (KAUST).

2D Ti

Although silicon nanoparticles dispersed in liquids are used in various applications ranging from biolabeling to hydrogen production, their reactivities with their solvents and their catalytic properties remain still unexplored. Here, we discovered that, because of their surface structures and mechanical strain, silicon nanoparticles react strongly with their solvents and may act as catalysts for the dehydrogenation, at room temperature, of secondary alcohols (e.g., isopropanol) into ketones and hydrogen. This catalytic reaction was monitored by gas chromatography, pH measurements, mass spectroscopy, and solid-state NMR. This discovery provides new understanding of the role played by silicon nanoparticles, and nanosilicon in general, in their reactivity in solvents in general, as well as being candidates in catalysis.

Starting from crystalline silicon we synthesised bright suspensions of amorphous porous silicon nanoparticles through unconventional stain etching. Upon excitation with UV light, this novel nanostructured material gives rise to an intense red photoluminescence (PL) which resembles that of some silicon nanostructures. We studied the properties of the prepared nanoparticles using a number of cutting-edge characterization techniques such as TEM, SEM and EDX. The complete crystalline-to-amorphous phase transition, confirmed by the morphological studies, seems fortuitous.