When two-dimensional transition metal carbides/nitrides (MXenes) meet hydrogels, they offer versatile platforms for designing novel soft materials with exciting properties.

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...

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.