When two-dimensional transition metal carbides/nitrides (MXenes) meet hydrogels, they offer versatile platforms for designing novel soft materials with exciting properties.
The presence of localized trap states on the surface of CsPbCl 3 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., YCl 3 , 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 YCl 3 -treated CsPbCl 3 NC films exhibit an order of magnitude larger photocurrent compared to their nontreated counterparts. Our experimental and theoretical results provide an insightful understanding of the effective passivating roles of Y 3+ and Cl − ions on the surface of CsPbCl 3 NCs, as well as offering a new path to synthesize high-quality NCs for UV light conversion applications.
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.devices. This is because solution processes such as liquid-phase exfoliation is crucial for the dispersion formation and mass production, as well as for the postsynthesis treatments on the 2D nanosheets such as sorting in terms of flake size and thickness, functionalization, compositing, etc., all of which are crucial for the ink formulation process required by printing. [6] Printed electronics technology has acquired considerable interest from both academia and industry recently. [7][8][9] Unlike traditional methods such as vacuum deposition and photolithography, printing technologies hold great promise for fast, high-volume, and low-cost manufacturing, especially for the fabrication of flexible devices. [10][11][12][13][14][15] The combination of 2D materials with printing started as early as 2012 when liquid-phase-exfoliated graphene dispersion was inkjet-printed to fabricate field-effect transistors. [16] It has since progressed from directly using the unoptimized dispersion obtained from the solution processing as inks to making formulated inks targeted toward specific printing methods and target applications (e.g., conductive tracks, transparent electrodes, transistors, photodetectors, energy storage devices such as supercapacitors, batteries, sensors, etc.). [17][18][19][20][21] As a new member to the 2D nanomaterials family, transition metal carbides, nitrides, and carbonitrides, also known as MXenes, possess outstanding electrochemical, electronic, optical, and mechanical properties, and thus have shown great promise in applications including energy storage, electronics, optoelectronics, biomedicine, sensors, and catalysis. [22][23][24][25] Research on MXenes dates back to 2011 when single-layered titanium carbide Ti 3 C 2 was synthesized and separated for the first time, [26] and has since evol...
2D TiC T MXenes were recently shown to exhibit intense surface plasmon (SP) excitations; however, their spatial variation over individual TiC T 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 TiC T 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 TiC T flakes. The independent polarizability of TiC T 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 TiC T has its own set of SPs with distinctive multipolar characters. Moreover, the tunability of the SP energies is highlighted by conducting in situ heating STEM to monitor the change of the surface functionalization of TiC T through annealing at temperatures up to 900 °C. At temperatures above 500 °C, the observed fluorine (F) desorption multiplies the metal-like free electron density of TiC T flakes, resulting in a monotonic blue-shift in the SP energy of all modes. These results underline the great potential for the development of TiC T -based applications, spanning the visible-MIR spectrum, relying on the excitation and detection of single SPs.
MXenes have recently shown impressive optical and plasmonic properties associated with their ultrathin‐atomic‐layer structure. However, their potential use in photonic and plasmonic devices has been only marginally explored. Photodetectors made of five different MXenes are fabricated, among which molybdenum carbide MXene (Mo2CTx) exhibits the best performance. Mo2CTx MXene thin films deposited on paper substrates exhibit broad photoresponse in the range of 400–800 nm with high responsivity (up to 9 A W−1), detectivity (≈5 × 1011 Jones), and reliable photoswitching characteristics at a wavelength of 660 nm. Spatially resolved electron energy‐loss spectroscopy and ultrafast femtosecond transient absorption spectroscopy of the MXene nanosheets reveal that the photoresponse of Mo2CTx is strongly dependent on its surface plasmon‐assisted hot carriers. Additionally, Mo2CTx thin‐film devices are shown to be relatively stable under ambient conditions, continuous illumination and mechanical stresses, illustrating their durable photodetection operation in the visible spectral range. Micro‐Raman spectroscopy conducted on bare Mo2CTx film and on gold electrodes allowing for surface‐enhanced Raman scattering demonstrates surface chemistry and a specific low‐frequency band that is related to the vibrational modes of the single nanosheets. The specific ability to detect and excite individual surface plasmon modes provides a viable platform for various MXene‐based optoelectronic applications.
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 Ti 3 C 3 T x 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 Ti 3 C 2 T x 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 Ti 3 C 3 T x 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.
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 polycrystalline counterparts. However, the inevitable formation of triiodide-based intrinsic defects during hightemperature crystal growth is one of the major challenges impeding the further development of optoelectronic devices based on PSCs. Here, we not only identified the existence of these triiodide ions as hole-trapping centers and their tremendous negative impact on the performance of PSCs, but more importantly, we used a reduction treatment to prevent their formation during crystal growth. The removal of such defect centers resulted in much higher charge carrier mobility and longer carrier lifetime than the untreated counterparts, leading to enhanced photodetection properties. The I 3 −-f ree MAPbI 3 single crystal (MSC) devices consistently generated a more than 100 times higher photocurrent than that generated by I 3 −-rich devices under the same light intensity.
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 Ti 3 C 2 T x MXene sheets, exhibiting simultaneous enhancement in permeability and ion selectivity beyond their inherent trade-off. The perforated nanopores formed by facile H 2 SO 4 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 Ti 3 C 2 T x 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.
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