Colloidal Crystal "Alloys".

Colloidal crystal engineering with DNA has emerged as a powerful tool for precisely controlling the arrangement of nanoscale building blocks in three-dimensional superlattices, where nanoparticles densely modified with DNA can be viewed as "programmable atom equivalents" (PAEs). Although a wide variety of complementary DNA-modified nanoparticles, differentiated by size, shape, and composition, have been assembled into many "ionic" phases, the predictable formation of "alloy" phases remains elusive. Here, we describe the design of "colloidal crystal alloys" by combining gold PAEs of two different sizes (core diameters ranging from 5 to 40 nm) with complementary DNA-modified 2 nm gold nanoparticles (∼15 DNA strands/particle) that act as electron equivalents (EEs). Electron microscopy and small-angle X-ray scattering (SAXS) experiments reveal the formation of four classes of colloidal alloy equivalents: interstitial, substitutional, phase-separated, and intermetallic alloys. In these colloidal alloy phases, PAEs occupy lattice positions, while EEs stabilize the PAE lattice but do not occupy specific lattice sites. A set of chemical design guidelines emerge from this study, analogous to that of the Hume-Rothery rules, allowing for programmed synthesis of different alloy phases depending on PAE particle size ratio, DNA surface coverage, stoichiometric ratio, and thermal annealing pathways. Furthermore, we study the phase separation process via in situ SAXS experiments as well as ex situ electron microscopy, revealing the critical role of kinetics on the phase behavior in these systems.

Composition-tunable transition metal dichalcogenide nanosheets via a scalable, solution-processable method.

The alloying of two-dimensional (2D) transition metal dichalcogenides (TMDs) is an established route to produce robust semiconductors with continuously tunable optoelectronic properties. However, typically reported methods for fabricating alloyed 2D TMD nanosheets are not suitable for the inexpensive, scalable production of large-area (m2) devices. Herein we describe a general method to afford large quantities of compositionally-tunable 2D TMD nanosheets using commercially available powders and liquid-phase exfoliation. Beginning with Mo(1-x)WxS2 nanosheets, we demonstrate tunable optoelectronic properties as a function of composition. We extend this method to produce Mo0.5W0.5Se2 MoSSe, WSSe, and quaternary Mo0.5W0.5SSe nanosheets. High-resolution scanning transmission electron microscopy (STEM) imaging confirms the atomic arrangement of the nanosheets, while an array of spectroscopic techniques is used to characterize the chemical and optoelectronic properties. This transversal method represents an important step towards upscaling tailored TMD nanosheets with a broad range of tunable optoelectronic properties for large-area devices.

Photogenerated charge transfer in Dion-Jacobson type layered perovskite based on naphthalene diimide.

Incorporating organic semiconducting spacer cations into layered lead halide perovskite structures provides a powerful approach to mitigate the typical strong dielectric and quantum confinement effects by inducing charge-transfer between the organic and inorganic layers. Herein we report the synthesis and characterization of thin films of novel DJ-phase organic-inorganic layered perovskite semiconductors using a naphthalene diimide (NDI) based divalent spacer cation, which is shown to accept photogenerated electrons from the inorganic layer. With alkyl chain lengths of 6 carbons, an NDI-based thin film exhibited electron mobility (based on space charge-limited current for quasi-layered 〈n〉 = 5 material) was found to be as high as 0.03 cm2 V-1 s-1 with no observable trap-filling region suggesting trap passivation by the NDI spacer cation.

pH-Triggered Assembly of Endomembrane Multicompartments in Synthetic Cells.

By using electrostatic interactions as driving force to assemble vesicles, the droplet-stabilized method was recently applied to reconstitute and encapsulate proteins, or compartments, inside giant unilamellar vesicles (GUVs) to act as minimal synthetic cells. However, the droplet-stabilized approach exhibits low production efficiency associated with the troublesome release of the GUVs from the stabilized droplets, corresponding to a major hurdle for the droplet-stabilized approach. Herein, we report the use of pH as a potential trigger to self-assemble droplet-stabilized GUVs (dsGUVs) by either bulk or droplet-based microfluidics. Moreover, pH enables the generation of compartmentalized GUVs with flexibility and robustness. By co-encapsulating pH-sensitive small unilamellar vesicles (SUVs), negatively charged SUVs, and/or proteins, we show that acidification of the droplets efficiently produces dsGUVs while sequestrating the co-encapsulated material. Most importantly, the pH-mediated assembly of dsGUVs significantly improves the production efficiency of free-standing GUVs (i.e., released from the stabilizing-droplets) compared to its previous implementation.

Rapid Cycling and Exceptional Yield in a Metal-Organic Framework Water Harvester.

Sorbent-assisted water harvesting from air represents an attractive way to address water scarcity in arid climates. Hitherto, sorbents developed for this technology have exclusively been designed to perform one water harvesting cycle (WHC) per day, but the productivities attained with this approach cannot reasonably meet the rising demand for drinking water. This work shows that a microporous aluminum-based metal-organic framework, MOF-303, can perform an adsorption-desorption cycle within minutes under a mild temperature swing, which opens the way for high-productivity water harvesting through rapid, continuous WHCs. Additionally, the favorable dynamic water sorption properties of MOF-303 allow it to outperform other commercial sorbents displaying excellent steady-state characteristics under similar experimental conditions. Finally, these findings are implemented in a new water harvester capable of generating 1.3 L kgMOF -1 day-1 in an indoor arid environment (32% relative humidity, 27 °C) and 0.7 L kgMOF -1 day-1 in the Mojave Desert (in conditions as extreme as 10% RH, 27 °C), representing an improvement by 1 order of magnitude over previously reported devices. This study demonstrates that creating sorbents capable of rapid water sorption dynamics, rather than merely focusing on high water capacities, is crucial to reach water production on a scale matching human consumption.

Conceptual Advances from Werner Complexes to Metal-Organic Frameworks.

Alfred Werner's work on the geometric aspects of how ligands bind to metal ions at the end of the 19th century has given rise, in the molecular realm, to organometallic, bioinorganic, and cluster chemistries. By stitching together organic and inorganic units into crystalline porous metal-organic frameworks (MOFs), the connectivity, spatial arrangement, and geometry of those molecular complexes can now be fixed in space and become directly addressable. The fact that MOFs are porous provides additional space within which molecules can further be transformed and their chemistry controlled. An aspect not available in molecular chemistry but a direct consequence of Werner's analysis of coordination complexes is the ability to have multivariable functionality in MOFs to bring about a continuum of chemical environments, within the repeating order of the framework, from which a substrate can sample and be transformed in ways not possible in molecular complex chemistry.