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Reacting MoAlB with ZnCl2 forms the metastable boride phase Mo2AlB2, which contrasts the reactivity of ZnCl2 with related carbide/nitride phases.

A quantitative approach was developed to systematically evaluate the antimicrobial activity of CuWO4/CuS hybrid composites. This approach offers a new way to search for effective combinations of two or more semiconductors for pathogen disinfection.

The high temperatures typically required to synthesize refractory compounds preclude the formation of high-energy morphological features, including nanoscopic pores that are beneficial for applications, such as catalysis, that require higher surface areas. Here, we demonstrate a low-temperature multistep pathway to engineer mesoporosity into a catalytic refractory material. Mesoporous molybdenum boride, α-MoB, forms through the controlled thermal decomposition of nanolaminate-containing sheets of the metastable MAB (metal-aluminum-boron) phase Mo

Throughout nature, simple rules explain complex phenomena, such as the selective interaction of chiral objects with circularly polarized light. Here, we demonstrate chiroptical signals from gold na...

ConspectusLayered transition-metal dichalcogenides (TMDs) are intriguing two-dimensional (2D) compounds where metal and chalcogen atoms are covalently bonded in each monolayer, and the monolayers are held together by weak van der Waals forces. Distinct from graphene, which is chemically inert, layered TMDs exhibit a wide range of electronic, optical, catalytic, and magnetic properties dependent upon their compositions, crystal structures, and thicknesses, which make them fundamentally and technologically important. TMD nanostructures are traditionally synthesized using gas-phase chemical deposition methods, which are typically limited to small-scale samples of substrate-bound planar materials. Colloidal synthesis has emerged as an alternative synthesis approach to enable the scalable synthesis of free-standing TMDs. The judicious selection of precursors, solvents, and capping ligands together with the optimization of synthesis parameters such as concentrations and temperatures leads to the fabrication of colloidal TMD nanostructures exhibiting tunable properties. In addition, understanding the formation and transformation of TMD nanostructures in solution contributes to the discovery of important structure-function relationships, which may be extendable to other anisotropic systems.In this Account, we summarize recent progress in the colloidal synthesis, characterization, and applications of TMD nanostructures with tunable compositions, structures, and thicknesses. On the basis of the preparation of Mo- and W-based disulfide, diselenide, and ditelluride nanostructures, we discuss examples of phase engineering where various metastable TMD compounds can be directly accessed at low temperatures in solution. We also analyze the chemistry involved in broadly tuning the composition across the MoSe2-WSe2, WS2-WSe2, and MoTe2-WTe2 solid solutions as well as atomic-level microscopic characterization and the resulting composition-tunable properties. We then highlight how the high densities of defects in the colloidally synthesized TMD nanostructures enable unique catalytic properties, including their ability to facilitate the selective hydrogenation of substituted nitroarenes using molecular hydrogen. Finally, using this library of colloidal TMD nanostructures as substrates, we discuss the pathways by which noble metals deposit onto them in solution. We highlight the importance of the relative strengths of the interfacial metal-chalcogen bonds in determining the sizes and morphologies of the deposited noble metal components. These synthesis capabilities for colloidal TMD nanostructures, which have been generalized to a library of composition-tunable phases, enable new systematic studies of structure-property relationships and chemical reactivity in this important class of 2D materials.

High entropy materials, which contain a large number of randomly distributed elements, have unique catalytic, electrochemical, and mechanical properties. The high configurational entropy of the randomized elements drives the formation of high entropy materials; therefore, high temperatures and quenching are typically required to stabilize them. Because of this, colloidal nanoparticles of high entropy materials are difficult to synthesize and remain rare, despite their desirable high surface areas and solution dispersibilities. Here, we introduce simultaneous multication exchange as an alternative low-temperature pathway to colloidal nanoparticles of high entropy materials. Roxbyite Cu1.8S nanoparticles react with a substoichiometric mixture of Zn2+, Co2+, In3+, and Ga3+ to produce nanoparticles of the high entropy metal sulfide Zn0.25Co0.22Cu0.28In0.16Ga0.11S. The Zn0.25Co0.22Cu0.28In0.16Ga0.11S nanoparticles are thermally stable, and exchange reactions using fewer cations do not produce the high entropy phase. The use of colloidal nanoparticle cation exchange as a synthetic platform provides both entropic and enthalpic driving forces that, in addition to configurational entropy, enable the formation of high entropy phases at solution-accessible temperatures.

Copper selenide nanoparticles are important materials with desirable properties for a broad scope of applications. Copper selenides are additionally known to adopt several different crystal structu...

Nanoparticles that contain multiple materials connected through interfaces, often called heterostructured nanoparticles, are important constructs for many current and emerging applications. Such particles combine semiconductors, metals, insulators, catalysts, magnets, and other functional components that interact synergistically to enable applications in areas that include energy, nanomedicine, nanophotonics, photocatalysis, and active matter. To synthesize heterostructured nanoparticles, it is important to control all of the property-defining features of individual nanoparticles-size, shape, uniformity, crystal structure, composition, surface chemistry, and dispersibility-in addition to interfaces, asymmetry, and spatial organization, which facilitate communication among the constituent materials and enable their synergistic functions. While it is challenging to control all of these nanoscale features simultaneously, nanoparticle cation exchange reactions offer powerful capabilities that overcome many of the synthetic bottlenecks. In these reactions, which are often carried out on metal chalcogenide materials such as roxbyite copper sulfide (Cu

Designer nanoparticles with complex morphologies are of growing interest for a wide range of applications, but making them rationally and scalably remains challenging. Here, we demonstrate a retros...

Cation exchange reactions of colloidal copper sulfide nanoparticles are widely used to produce derivative nanoparticles having unique compositions, metastable crystal structures, and complex heterostructures. The copper sulfide crystal structure plays a key role in the mechanism by which cation exchange occurs and the product that forms. Here, we show that digenite copper sulfide nanoparticles undergo a spontaneous phase transition to tetragonal chalcocite in situ, prior to the onset of cation exchange. Room-temperature sonication of digenite (Cu1.8S) in trioctylphosphine, a Lewis base that drives cation exchange, extracts sulfur to produce tetragonal chalcocite (Cu2S). The subtle structural differences between digenite and tetragonal chalcocite are believed to influence the accessibility of cation diffusion channels and concomitantly the mechanism of cation exchange. Structural relationships in nanocrystal cation exchange are therefore dynamic, and intermediates generated in situ must be considered.

Nanocrystal cation exchange is a post-synthetic process that modifies the composition of a nanoparticle while maintaining other important characteristics, including morphology and crystal structure...

Functionalizing the surfaces of transition metal dichalcogenide (TMD) nanosheets with noble metals is important for electrically contacting them to devices, as well as improving their catalytic and sensing capabilities. Solution-phase deposition provides a scalable approach to the creation of metal-TMD hybrid systems, but controlling such processes remains challenging. Here we elucidate the different pathways by which gold and silver deposit at room temperature onto colloidal 1T-WS2, 2H-WS2, 2H-MoSe2, 2H-WSe2, 1T'-MoTe2 and Td-WTe2 few-layer nanostructures to produce several distinct classes of 0D-2D and 2D-2D metal-TMD hybrids. Uniform gold nanoparticles form on all of the TMDs. By contrast, silver deposits as nanoparticles with a bimodal size distribution on the disulfides and diselenides, and as atomically thin layers on the ditellurides. The various sizes and morphologies of these surface-bound metal species arise from the relative strengths of the interfacial metal-chalcogen bonds during the reduction of Au3+ or Ag+ by the TMDs.

Heterostructured nanorod libraries The synthesis of nanostructures with well-defined interfaces between different materials can enable applications in areas such as catalysis and solar energy harvesting. Nanomaterials containing several different materials are usually synthesized through top-down approaches, such as surface growth or templating techniques, which usually produce small quantities of particles. Steimle et al. performed up to seven cation-exchange reactions (with ions such as Zn 2+ and Co 2+ ) on solution-synthesized copper sulfide nanorods. In principle, more than 65,000 different variations of materials and their interfaces can be made, depending on the order and extent of cation exchange. Science , this issue p. 418

We report predictive guidelines for the substoichiometric cation exchange of model two-component metal sulfide nanorods containing divalent cations of similar hardness. Unit cell volume changes, cation radii, solubility constants, and solid state interfaces influence selectivity during substoichiometric exchange of Cu

Colloidal heterostructured nanoparticles that integrate multiple materials through direct solid–solid interfaces are desirable across a wide range of applications. However, chemical, structural, in...

Vanadium dioxide (VO2) exhibits a metal-insulator transition (MIT) that is accompanied by steep changes in electrical and optical properties, making it an important component of device architectures that require facile switching between metal and insulating states. VO2 nanostructures are particularly useful components of such devices, given their unique size-dependent properties and processing capabilities. Here, we show that VO2 nanostructures can be synthesized by chemical transformation of ZnO nanoparticles, which are readily available and serve as morphological templates. Commercially available and colloidally synthesized ZnO nanoparticles react with VOSO4 in water at room temperature to form amorphous VO2, which can be crystallized to the switchable M1 phase of VO2 upon thermal annealing. Experiments probing various particle dimensions, shapes, surface ligands, and reaction parameters suggest that the reaction occurs by depositing VO2 on the ZnO particles, which serve as a sacrificial template. The Z...

Transition metal dichalcogenides (TMDs) are well known catalysts as both bulk and nanoscale materials. Two-dimensional (2-D) TMDs, which contain single- and few-layer nanosheets, are increasingly studied as catalytic materials because of their unique thickness-dependent properties and high surface areas. Here, colloidal 2H-WS2 nanostructures are used as a model 2-D TMD system to understand how high catalytic activity and selectivity can be achieved for useful organic transformations. Free-standing, colloidal 2H-WS2 nanostructures containing few-layer nanosheets are shown to catalyze the selective hydrogenation of a broad scope of substituted nitroarenes to their corresponding aniline derivatives in the presence of other reducible functional groups. Microscopic and computational studies reveal the important roles of sulfur vacancy-rich basal planes and tungsten-terminated edges, which are more abundant in nanostructured 2-D materials than in their bulk counterparts, in enabling the functional group selectivity. At tungsten-terminated edges and on regions of the basal planes having high concentrations of sulfur vacancies, vertical adsorption of the nitroarene is favored, thus facilitating hydrogen transfer exclusively to the nitro group due to geometric effects. At lower sulfur vacancy concentrations on the basal planes, parallel adsorption of the nitroarene is favored, and the nitro group is selectively hydrogenated due to a lower kinetic barrier. These mechanistic insights reveal how the various defect structures and configurations on 2-D TMD nanostructures facilitate functional group selectivity through distinct mechanisms that depend upon the adsorption geometry, which may have important implications for the design of new and enhanced 2-D catalytic materials across a potentially broad scope of reactions.

Achieving phase selectivity during nanoparticle synthesis is important because crystal structure and composition influence reactivity, growth, and properties. Cation exchange provides a pathway for targeting desired phases by modifying composition while maintaining crystal structure. However, our understanding of how to selectively target different phases in the same system is limited. Here, we demonstrate morphology-dependent phase selectivity for wurtzite (wz) CoS, which is hcp, vs pentlandite Co9S8, which is ccp, during Co2+ exchange of roxbyite Cu1.8S plates, spheres, and rods. The plates form wz-CoS, the spheres form both wz-CoS and Co9S8, and the rods form Co9S8. The plates, spheres, and rods have nearly identical widths but increase in length in the direction that the close-packed planes stack, which influences the ability of the anions to shift from hcp to ccp during cation exchange. This morphology-dependent behavior, which correlates with the number of stacked close-packed planes, relies on an anion sublattice rearrangement that is concomitant with cation exchange, thereby providing a unique pathway by which crystal structure can be controlled and phase selectivity can be achieved during nanocrystal cation exchange.

Colloidal hybrid nanoparticles have generated considerable attention in the inorganic nanomaterials community. The combination of different materials within a single nanoparticle can lead to synergistic properties that can enable new properties, new applications, and the discovery of new phenomena. As such, methodologies for the synthesis of hybrid nanoparticles that integrate metal-metal, metal chalcogenide, metal oxide, and oxide-chalcogenide domains have been extensively reported in the literature. However, colloidal hybrid nanoparticles containing metal phosphide domains are rare, despite being attractive systems for their potentially unique catalytic, photocatalytic, and optoelectronic properties. In this Forum Article, we report a study of the synthesis of colloidal hybrid nanoparticles that couple the metal phosphides Ni