Interfacial assembly of two-dimensional MXenes

Two-dimensional(2D) transition metal carbides, carbonitrides and nitrides, known as MXenes, are emerging quickly at the frontiers of 2D materials world. Their exotic properties such as the highest electrical conductivity among all solution-processed 2 D materials, the best electromagnetic interference shielding performance outperforming that of copper or aluminum at a nanoscale thickness, as well as the highest volumetric capacitance for pseudocapacitors, have been attracting extensive fundamental research and applications. Their unique surface chemistries, that is, hydrophilic groups terminated on the surface of MXenes after etching and delamination, enable plenty of opportunities for assembling into MXene building blocks. Particularly, assembling at liquid–liquid, liquid–solid, liquid–air, and solid–solid interfaces allows the efficient fabrication of various structures, including MXene surfactants, MXene heterostructures, MXene transparent films. Interfacial assembly of MXenes is of significance in unveiling more versatilities of MXenes as well as impacts on novel MXene-based architectures, based on which enhanced performance of devices is achieved. As such, this review focuses on the interfacial assembly of MXenes, explaining mechanisms behind various assembling and providing classical examples for corresponding interfacial assembling techniques. Applications of these as-assembled architectures are also discussed in brief. We believe this review may shed light on the interfacial chemistry of MXenes, thus guiding more efficient fabrication of MXene-based functional films/coatings/electrodes/devices.

Interfacial assembly of a series of Cu(Ⅱ)-coordinated Schiff bases complexes:Orderly nanostructures and supramolecular chirality

Four achiral Cu(Ⅱ)-coordinated Schiff bases complexes containing aromatic structures were synthesized and their supramolecular assemblies at the air/water interface were investigated.All the compounds could be spread on water surface although they have no alkyl chains.The Schiff base complex molecules with naphthyl groups tended to form J-aggregate in the Langmuir-Blodgett(LB) films transferred from water surface.By investigation of atomic force microscopy,a multilayer film or three-dimensional structures were observed.It was interesting to note that the LB films of achiral compound Cu-NA with naphthyl segment and without methyl groups transferred from water surface showed chirality.The supramolecular chirality in the present LB films was suggested to be due to a cooperative stereoregular-stacking of the functional groups in a helical sense.This research work provides a helpful clue for regulating the nanostructures and supramolecular chiral assembly in organized films.

Synergistic fluorescent hydrogel actuators with selective spatial shape/color-changing behaviors via interfacial supramolecular assembly

Biomimetic intelligent polymeric hydrogel actuators with cooperative fluorescence-color switchable behaviors are expected to find great potential applications in soft robotics,visual detection/display,and camouflage applications.However,it remains challenging to realize the spatial manipulation of synergistic shape/color-changing behaviors.Herein,we report an interfacial supramolecular assembly(ISA)approach that enables the construction of robust fluorescent polymeric hydrogel actuators with spatially anisotropic structures.On the basis of this ISA approach,diverse 2D/3D soft fluorescent hydrogel actuators,including chameleon-and octopi-shaped ones with spatially anisotropic structures,were facilely assembled from two different fluorescent hydrogel building blocks sharing the same physically cross-linked agar network.Spatially control over synergistic shape/color-changing behaviors was then realized in one single anisotropic hydrogel actuator.The proposed ISA approach is universal and expected to open promising avenues for developing powerful bioinspired intelligent soft actuators/robotics with selective spatial shape/color-changing behaviors.

Interfacial growth of N,S-codoped mesoporous carbon onto biomass-derived carbon for superior potassium-ion storage

Carbonaceous materials have been recognized as one of the most promising anode materials for potassium-ion batteries(PIBs)due to their abundant raw materials,controllable structure,superior conductivity,and good chemical inertness.However,the large radius of K ions and the low potassium content of intercalation compounds result in the sluggish storage kinetics and low reversible capacity of carbon anodes.In this work,we present a unique heteroatom-doped carbon composite(denoted as NS-MC/SC)through a facile interfacial assembly route and simple heat-treatment process,where NS-MC is well grafted onto the biomass-derived spore carbon(SC).This unique structural design endows it with abundant mesoporous channels,expanded layer spacing,and highly doped N and S.With these merits,the NS-MC/SC anode in PIBs exhibits a high reversible capacity of 350.4 mAh·g^(-1) at 100 mA·g^(-1) after 300 cycles,and an outstanding cycling stability.Besides,in-situ Raman spectra further verify the high reversibility of K ions insertion/extraction.Importantly,theoretical simulations also reveal that the N,S dual-doping is an efficient approach for improving the potassium-ion storage performance of NS-MC/SC.

Self-assembly of DNA molecules at bio-interfaces and their emerging applications for biomedicines

Interfacial assembly has been intensively investigated in fabricating biomaterials and nanodevices for various applications.Recently,due to the precise sequence programmability,unique molecular recognition ability,and good biocompatibility,deoxyribonucleic acid(DNA)has been explored as superior building blocks to assemble at bio-interface for manipulating biological entities.To the best of our knowledge,the advances in this area have not been systematically summarized.To provide an overview of the area,in this review,the recently developed DNA assembly strategies on bio-interfaces were well summarized,and their representative works are exampled to illustrate how to rationally and elaborately design DNA molecules to realize functional integration and emerging of novel biological functionalities with high controllability and programmability.Furthermore,the biomedical applications of DNA assembly at bio-interface are categorially elaborated.The fascinating and unique advantages of DNA assembly systems are fully discussed in the exemplified applications to show the distinguished perspective of DNA in the future development.At the end of this review,the current limitations and challenges in applications and potential improvement strategies for DNA assembly at bio-interface are fully discussed.The future development direction is deliberated.We envision that this review will help scientists in the interdisciplinary fields gain a more comprehensive understanding of the DNA assembly at bio-interface,and therefore jointly promote the advances in this field.

Ti_(3)C_(2)T_(x)MXene wrapped,carbon-coated porous Si sheets for improved lithium storage performance

Si-based materials have shown great potential as lithium-ion batteries(LIBs)anodes due to their natural reserves and high theoretical capacity.However,the large volume changes during cycles and poor conductivity of Si lead to rapid capacity decay and poor cycling stability,ultimately limiting their commercial applications.Herein,we have skillfully utilized the microporous MCM-22 zeolite as the unique silicon source to produce porous Si(pSi)sheets by a simple magnesiothermic reduction,followed by a carbon coating and further Ti_(3)C_(2)T_(x)MXene assembly,obtaining the ternary pSi@NC@TNSs composite.In the design,porous Si sheets provide more active sites and shorten Li-ion transport paths for electrochemical reactions.The N-doped carbon(NC)layer serves as a bonding layer to couple pSi and Ti_(3)C_(2)T_(x).The conductive network formed by 2D Ti_(3)C_(2)T_(x)and medium NC layer effectively enhances the overall charge transport of the electrode material,and helps to stabilize the electrode structure.Therefore,the as-made pSi@NC@TNSs anode delivers an improved lithium storage performance,exhibiting a high reversible capacity of 925 mAh/g at 0.5 A/g after 100 cycles.This present strategy provides an effective way towards high-performance Si-based anodes for LIBs.

Enhanced photocatalytic activity by the construction of a TiO2/carbon nitride nanosheets heterostructure with high surface area via direct interracial assembly

A TiO2 heterostructure modified with carbon nitride nanosheets （CN-NSs） has been synthesized via a direct interfacial assembly strategy. The CN-NSs, which have a unique two-dimensional structure, were favorable for supporting TiOa nanoparticles （NPs）. The uniform dispersion of TiO2 NPs on the surface of the CN-NSs creates sufficient interfacial contact at their nanojunctions, as was confirmed by electron microscopy analyses. In comparison with other reported metal oxide/CN composites, the strong interactions of the ultrathin CN-NSs layers with the TiO2 nanoparticles restrain their re-stacking, which results in a large specific surface area of 234.0 m2.g-1. The results indicate that the optimized TiOJCN-NSs hybrid exhibits remarkably enhanced photocatalytic efficiency for dye degradation （with k of 0.167 min-1 under full spectrum） and Ha production （with apparent quantum yield -- 38.4% for A = 400 ＋ 15 nm monochromatic light）. This can be ascribed to the improved surface area and quantum efficiency of the hybrid, with a controlled ratio that reaches the appropriate balance between producing sufficient nanojunctions and absorbing enough photons. Furthermore, based on the identification of the main active species for photodegradation, and the confirmation of active sites for H2 evolution, the charge transfer pathway across the TiO2/CN-NSs interface under simulated solar light is proposed.

ZIF-L membrane with a membrane-interlocked-support composite architecture for H/CO separation

Metal–organic framework(MOF)membranes hold great promise in energy-efficient chemical separations.The outstanding challenges of the microstructural design stem from(1)thinning of membranes to immensely reduce the mass-transfer resistance(for high permeances);(2)tuning of orientation to optimize the selective transport of gas molecules,and(3)reinforcement of intercrystalline structure to subside leakage through defective gaps(for high selectivity).Here,we propose the ZIF-L membrane that is completely confined into the voids of the alumina support through an interfacial assembly process,producing an appealing membrane-interlocked-support(MIS)composite architecture that meets the requirements of the microstructural design of MOF membranes.Consequently,the membranes show average H2 permeances of above 4000 GPU and H_(2)/CO_(2) separation factor(SF)of above 200,representing record-high separation performances of ZIF-L membranes and falling into the industrial target zone(H_(2) permeance>1000 GPU and H_(2)/CO_(2) SF>60).Furthermore,the ZIF-L membrane possessing the MIS composite architecture that is established with alumina particles as scaffolds shows mechanical stability,scraped repeatedly by a piece of silicon rubber causing no selectivity loss.

Inkjet printing of epitaxially connected nanocrystal superlattices

Access to a blossoming library of colloidal nanomaterials provides building blocks for complex assembled materials.The journey to bring these prospects to fruition stands to benefit from the application of advanced processing methods.Epitaxially connected nanocrystal(or quantum dot)superlattices present a captivating model system for mesocrystals with intriguing emergent properties.The conventional processing approach to creating these materials involves assembling and attaching the constituent nanocrystals at the interface between two immiscible fluids.Processing small liquid volumes of the colloidal nanocrystal solution involves several complexities arising from the concurrent spreading,evaporation,assembly,and attachment.The ability of inkjet printers to deliver small(typically picoliter)liquid volumes with precise positioning is attractive to advance fundamental insights into the processing science,and thereby potentially enable new routes to incorporate the epitaxially connected superlattices into technology platforms.In this study,we identified the processing window of opportunity,including nanocrystal ink formulation and printing approach to enable delivery of colloidal nanocrystals from an inkjet nozzle onto the surface of a sessile droplet of the immiscible subphase.We demonstrate how inkjet printing can be scaled-down to enable the fabrication of epitaxially connected superlattices on patterned sub-millimeter droplets.We anticipate that insights from this work will spur on future advances to enable more mechanistic insights into the assembly processes and new avenues to create high-fidelity superlattices.