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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...

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...

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...

Interfaces between nanoscale solids can facilitate coupling between dissimilar materials, leading to emergent and synergistic properties as well as mix-and-match multifunctionality. Seeded-growth methods, whereby one material is grown directly off of the surface of another, can lead to the formation of hybrid nanoparticles containing such solid-state heterojunctions. Successfully applying seeded-growth methods to the synthesis of hybrid nanoparticles, however, requires a precise balance of competing reaction variables, which limits the scope of materials that can be routinely incorporated into them and, accordingly, the types of achievable interfaces. Here, we describe an alternate pathway that overcomes key limitations of seeded-growth methods by synthetically deconvoluting the formation of particle–particle interfaces and the incorporation of desired materials components. Readily accessible hybrid nanoparticles can be rationally modified using sequential anion and cation exchange reactions which transfo...

Nanoscale heterostructures that interface with multiple distinct materials provide opportunities to engineer functional complexity into single-particle constructs. However, existing synthetic pathways to such hybrid nanoparticles emphasize surface-seeded growth, which limits the scope of accessible systems. Here, we introduce an alternative approach that transforms isotropic nanocrystals into asymmetric, multicomponent Janus particles through sequential deposition, reactive phase segregation, and cation exchange processes that are mediated by an unusual class of reactive synthons. After Ag–Au seed particles had formed and had reacted with sulfur, a series of segregated Au1–xAgx–AgAuS and Au1–xAgx–Ag3AuS2 hybrid nanoparticles form. The AgAuS and Ag3AuS2 domains provide a synthetic entryway into solution-mediated cation exchange reactions, with the compositions of the Ag–Au–S synthons defining the components, morphologies, and interfaces of the hybrid nanoparticle products. Upon cation exchange with Pb2+, A...

Semiconductor materials having direct band gaps that overlap well with the solar spectrum are important for a variety of applications in solar energy conversion and optoelectronics. Here, we identify the ternary chalcogenide In4SnSe4 as a direct band gap semiconductor having a band gap of approximately 1.6 eV. In4SnSe4, which contains isolated tetrahedral [SnIn4]8+ clusters embedded in an In–Se framework, was synthesized by precipitation from solution at 300 °C. The In4SnSe4 product consists of microwires having lengths of approximately 5–20 μm and widths of approximately 100–400 nm. Band structure calculations predict a direct electronic band gap of approximately 2.0 eV. Diffuse reflectance UV–visible spectroscopy qualitatively validates the predicted direct band gap, yielding an observed optical band gap of 1.6 eV.

Earth-abundant materials capable of catalyzing the electrochemical decomposition of water into molecular hydrogen and oxygen are necessary components of many affordable water-splitting technologies. However, water oxidation catalysts that facilitate sustained oxygen evolution at device-relevant current densities in strongly acidic electrolytes have been limited almost exclusively to precious metal oxides. Here, we show that nanostructured films of cobalt oxide (Co3O4) on fluorine-doped tin oxide (FTO) substrates, made by first depositing Co onto FTO and heating in air at 400 °C to produce films having a robust electrical and mechanical Co3O4/FTO interface, function as active electrocatalysts for the oxygen evolution reaction (OER) in 0.5 M H2SO4. The Co3O4/FTO electrodes evolve oxygen with near-quantitative Faradaic yields and maintain a current density of 10 mA/cm2 for over 12 h at a moderate overpotential of 570 mV. At lower current densities that require lower overpotentials, sustained oxygen productio...

Nanosheet heterostructures that directly interface multiple distinct metal chalcogenides are important two-dimensional materials with unique synergistic properties. Solution routes to these materials offer potential advantages over existing vapor deposition and exfoliation/restacking methods, but they remain difficult to implement and control. Here, we show that SnSe can be grown in solution on micrometer-sized GeSe nanosheets and establish guidelines for achieving controllable deposition. Heating GeSe nanosheets in oleylamine with various amounts of SnCl2 and TOP-Se reveals distinct regimes that favor growth of SnSe on the edge sites vs basal planes of GeSe. Using continuous injection to better control concentrations and reagent delivery, SnSe can be grown on GeSe to produce two distinct types of crystallographically aligned SnSe@GeSe nanosheet heterostructures.

Colloidal hybrid nanoparticles integrate two or more nanocrystal domains into a single architecture that can have properties not found in, or enhanced relative to those of, the individual components. These hybrid nanomaterials are typically constructed using multistep seeded-growth reaction sequences, which are conceptually analogous to the total synthesis approaches used in molecular synthesis. Here, we discuss in detail the synthetic protocols that lead to the formation of three-component Ag–Pt–Fe3O4 and Au–Pt–Fe3O4 heterotrimers. These instructive model systems highlight the important synthetic details that underpin successful hybrid nanoparticle reactions. We provide detailed, step-by-step protocols for generating these materials, focusing on describing and rationalizing the key reaction parameters that need to be rigorously controlled to minimize unwanted nanoparticle byproducts. The importance of comprehensive analysis using a suite of materials characterization tools is highlighted, as such efforts...

Hydrogen gas obtained by the electrolysis of water has long been proposed as a clean and sustainable alternative to fossil fuels. Noble metals such as Pt are capable of splitting water at low overpotentials, but the implementation of inexpensive solar-driven water-splitting systems and electrolyzers could benefit from the development of robust, efficient, and abundant alternatives to noble metal catalysts. Transition metal phosphides (MxPy) have recently been identified as a promising family of Earth abundant electrocatalysts for the hydrogen-evolution reaction (HER) and are capable of operating with low overpotentials at operationally relevant current densities while exhibiting stability under strongly acidic conditions. In this review, we highlight the progress that has been made in this field and provide insights into the synthesis, characterization, and electrochemical behavior of transition metal phosphides as HER electrocatalysts. We also discuss strategies for the incorporation of metal phosphides ...

Metal phosphides have emerged as promising Earth-abundant alternatives to platinum for catalyzing the hydrogen evolution reaction (HER) in acidic aqueous solutions. Here, Co2P nanoparticles having a hollow, multifaceted, crystalline morphology have been evaluated as HER electrocatalysts at a mass loading of 1 mg cm–2 on Ti foil substrates. The Co2P/Ti electrodes required low overpotentials of −95 and −109 mV to produce operationally relevant cathodic current densities of −10 and −20 mA cm–2, respectively. These values establish Co2P nanoparticles as highly active Earth-abundant HER catalyst materials. Importantly, the Co2P nanoparticles are morphologically equivalent to previously reported CoP nanoparticle HER catalysts, allowing a direct side-by-side evaluation of their HER activities. Such comparisons of different metal phosphide HER catalysts with the same constituent elements and morphologies are important for identifying the key materials characteristics that lead to high activity.

We report the colloidal synthesis of substrate-free MoSe2 nanostructures with a uniform flower-like morphology and tunable average diameters that range from approximately 50–250 nm. The MoSe2 nanoflowers contain a large population of highly crystalline few-layer nanosheets that protrude from a central core. Aliquot studies and control experiments indicate that the nanoflowers are generated through a two-step process that involves the formation of a core in the early stages of the reaction followed by outward nanosheet growth that can be controlled based on the concentrations of reagents. The effects of laser-induced local heating, bulk-scale heating using a temperature stage, and nanostructuring on the ability to trigger and tune interlayer decoupling were also investigated. Notably, laser-induced local heating results in dynamic and reversible interlayer decoupling. Such capabilities provide a pathway for achieving quasi-two-dimensional behavior in three-dimensionally structured and colloidally synthesiz...

The synthesis of transition metal nitride nanoparticles is challenging, in part because the unreactive nature of the most common nitrogen reagents necessitates high-temperature and/or high-pressure reaction conditions. Here we report the solution-phase synthesis and characterization of antiperovskite-type Cu3PdN nanocrystals that are multifaceted, uniform, and highly dispersible as colloidal solutions. Colloidal Cu3PdN nanocrystals were synthesized by reacting copper(II) nitrate and palladium(II) acetylacetonate in 1-octadecene with oleylamine at 240 °C. The Cu3PdN nanocrystals were evaluated as electrocatalysts for the oxygen reduction reaction (ORR) under alkaline conditions, where both Cu3N and Pd nanocrystals are known to be active. The ORR activity of the Cu3PdN nanocrystals appears to be superior to that of Cu3N and comparable to that of Pd synthesized using similar methods, but with significantly improved mass activity than Pd control samples. The Cu3PdN nanocrystals also show greater stability tha...

Hybrid nanoparticles composed of multiple material systems provide a platform for studying the coupling between nanoparticles with distinct properties. Here, we describe a nontraditional synthetic pathway to Au-In2O3 hybrid nanoparticles that contain two distinct plasmonic domains: Au, with a localized surface plasmon resonance (LSPR) in the visible, and In2O3, with a LSPR in the mid-infrared. The hybrid nanocrystals are produced by slowly introduce In(III) stock solution to Au nanoparticle seeds using a syringe pump. Rather than forming through a traditional heterogeneous seeded-growth process, a series of in situ and ex situ studies reveal an alternate multistep pathway. The Au nanoparticles first combine with In to form an alloy of Au and In, which is colloidally stable up to 300 °C in 1-octadecene. The Au-In alloy nanoparticles then transform into intermetallic AuIn2 nanoparticles that are surrounded by a shell of amorphous indium oxide (AuIn2@InOx), followed by the final Au-In2O3 heterodimers upon co...

Amorphous molybdenum phosphide (MoP) nanoparticles have been synthesized and characterized as electrocatalysts for the hydrogen-evolution reaction (HER) in 0.50 M H_2SO_4 (pH 0.3). Amorphous MoP nanoparticles (having diameters of 4.2 ± 0.5 nm) formed upon heating Mo(CO)6 and trioctylphosphine in squalane at 320 °C, and the nanoparticles remained amorphous after heating at 450 °C in H_2(5%)/Ar(95%) to remove the surface ligands. At mass loadings of 1 mg cm^–2, MoP/Ti electrodes exhibited overpotentials of −90 and −105 mV (−110 and −140 mV without iR correction) at current densities of −10 and −20 mA cm^–2, respectively. These HER overpotentials remained nearly constant over 500 cyclic voltammetric sweeps and 18 h of galvanostatic testing, indicating stability in acidic media under operating conditions. Amorphous MoP nanoparticles are therefore among the most active known molybdenum-based HER systems and are part of a growing family of active, acid-stable, non-noble-metal HER catalysts.

Fatty acid salts of transition metals are known to undergo thermal decomposition in high-boiling organic solvents. Although it is a straightforward, promising approach for generating colloidal metal oxide nanocrystals in high yield, its widespread implementation is hindered by irreproducibility. Subtle structural variations and impurities are often introduced during preparation of the carboxylate precursors, which exhibit strong influence on thermal decomposition, and the resulting nucleation and growth of oxide nanocrystals. Here, we studied the colloidal synthesis of wurtzite-type CoO (wz-CoO) nanostructures via thermal decomposition of Co(II) oleate complex [Co(OL)]2. Using Fourier transform infrared spectroscopy, we discovered that the conventional method for preparing [Co(OL)]2 gives rise to an isolable impurity containing a free hydroxide moiety. Furthermore, [Co(OL)]2 did not thermally decompose within the expected temperature range when the impurity was removed. In contrast, pencil-shaped wz-CoO n...

Iron–germanium (Fe–Ge) is a complex alloy system that includes several structurally and compositionally diverse phases that exhibit a range of interesting magnetic properties that can change significantly when reduced to nanoscale dimensions. Fe–Ge nanostructures have been synthesized using chemical and physical deposition methods but have not previously been accessible as solution-synthesized colloidal materials. Here, we show that colloidal Fe–Ge nanostructures can be synthesized via the hot injection of an oleylamine solution of Fe(CO)5 into a solution containing GeI4, oleylamine, oleic acid, and hexamethyldisilazane. This approach effectively merges recent advances in the synthesis of colloidal Ge nanocrystals with methods routinely used to synthesize metal and alloy nanoparticles. At 260 °C, spherical nanocrystals of Ni2In-type Fe3Ge2 form. Heating the solution at 300 °C transforms the spherical Fe3Ge2 nanocrystals into CoGe-type FeGe nanowires. The Fe3Ge2 nanocrystals are ferromagnetic with T c ≈ 26...

Colloidal hybrid nanoparticles, which contain multiple inorganic domains that are joined together through solid–solid interfaces, exhibit particle multifunctionality as well as new and enhanced properties that can emerge from the particle–particle interactions. These hybrid nanoparticles are typically synthesized using heterogeneous seeded nucleation of one nanoparticle on the surface of another as well as using phase segregation, surface dewetting of core–shell nanoparticles, and the fusion of premade nanoparticles. However, to expand the materials diversity and the potential range of applications of such systems, alternative routes to heterogeneous seeded nucleation are needed. Here, we show that solution–liquid–solid and related supersaturation-precipitation strategies, traditionally used in the synthesis of 1D structures such as nanowires and nanorods, can also be applied to the synthesis of colloidal hybrid nanoparticles. Specifically, we show that colloidal Au and Ag nanoparticles can serve as seeds...

Germanium telluride (GeTe) nanostructures are a demonstrated platform for studying the effects of scaling on reversible, amorphous-to-crystalline phase transitions that are important for data storage and computing applications, and for understanding ferroelectric behavior at the nanometer scale. Despite the interest in GeTe, and the apparent advantages of solution-phase processing, there is a dearth of information related to the synthesis of high-quality, morphology-controlled, colloidal GeTe. This paper describes the preparation of colloidal GeTe nanostructures in the presence of surface-stabilizing polymers, which mediate particle–particle interactions and prevent aggregation of GeTe crystallites more effectively than conventional molecular stabilizers. As a result, several novel GeTe nanostructures are formed, including faceted octahedral nanoparticles, amorphous GexTe1–x alloy nanospheres and single-crystal two-dimensional (2D) GeTe nanosheets. The colloidal stability conferred by the polymer may prov...

Colloidal hybrid nanoparticles contain multiple domains that are directly fused together through a solid–solid interface, which facilitates synergistic interactions between the components that can lead to enhanced properties, as well as multifunctionality in a single particle. By nucleating one nanoparticle on the surface of another, a growing number of these hybrid nanoparticles can be synthesized. However, to rapidly expand the materials diversity of such systems, alternative routes to heterogeneous seeded nucleation are needed. Here, we show that solution-mediated chemical transformation reactions, which are well established for pseudomorphically transforming colloidal metal nanoparticles into derivative metal-containing phases, can also be applied to colloidal hybrid nanoparticles. Specifically, we show that Pt–Fe3O4 heterodimers react with Pb(acac)2 and Sn(acac)2 at 180–200 °C in a mixture of benzyl ether, oleylamine, oleic acid, and tert-butylamine borane to form PtPb–Fe3O4 and Pt3Sn–Fe3O4 heterodim...

GeSe is a narrow band gap IV–VI semiconductor that has been attracting increasing attention as a potential alternative material for photovoltaics, along with other optical and electrical applications. However, unlike several other narrow band gap chalcogenide semiconductors, very few examples of GeSe nanostructures have been reported. One-dimensional nanostructures are particularly attractive, because they can serve as building blocks for nanostructured electronic devices. As a step toward both increasing the morphological diversity of GeSe nanomaterials and expanding the library of electronic materials that are accessible as one-dimensional nanostructures, we report here the colloidal synthesis and electrical properties of GeSe nanobelts. The GeSe nanobelts were synthesized by first heating a one-pot reaction mixture of GeI4, TOP-Se, oleylamine, oleic acid, and hexamethyldisilazane to 320 °C, then adding additional TOP-Se and heating for several additional hours. Aliquot studies revealed that an amorphou...

Single-crystal colloidal SnSe nanosheets react with a trioctylphosphine–tellurium complex to transform into porous single-crystal SnTe nanosheets with oriented nanocube protrusions. This chemical transformation reaction, which provides chemical and crystallographic guidelines for designing secondary nanostructural features into single crystal colloidal nanosheets and also results in two-dimensional nanosheets of a three-dimensionally bonded material, proceeds via a diffusion-mediated anion exchange pathway. Intermediate nanosheets reveal that SnTe nucleates with crystallographic alignment on the surface of the SnSe nanosheet, which ultimately is consumed to produce the porous SnTe nanosheet product. The anion exchange reaction is general, successfully converting a library of metal selenides and sulfides to the corresponding tellurides.

Nanoparticles of elemental nickel underpin a large number of magnetic and catalytic applications, and the possibility of tuning these properties via the formation of different allotropes is intriguing. While bulk elemental nickel adopts a face centered cubic (fcc) structure, a growing number of reports suggest that colloidal nickel nanoparticles can crystallize in the metastable hexagonal close packed (hcp) structure. However, there is some disagreement in the literature concerning the formation of hcp-Ni, particularly with respect to the crystallographically-related Ni3C phase. Most notable is a range of lattice constants and magnetic properties that have been attributed to hcp-Ni. Here, we show that reaction time can be used to tune the carbon content of a Ni3C1-x solid solution. Importantly, colloidal nanoparticles of Ni3C1-x can help to experimentally rationalize the range of lattice constants and magnetic properties reported for hcp-Ni and Ni3C, effectively bridging these two end-member systems. All ...

Nanoparticles of elemental germanium have interesting optical and electronic properties and relatively low toxicity, making them attractive materials for biological and optoelectronic applications. The most common routes to colloidal Ge nanoparticles include metathesis reactions involving Zintl salts, hydride reduction of Ge halides, and thermal decomposition of organogermane precursors. Here we describe an alternative “heat-up” method for the synthesis of size- and shape-tunable Ge nanoparticles that are both crystalline and air stable. The readily available reagents GeI4, oleylamine, oleic acid, and hexamethyldisilazane are combined in one pot and heated to 260 °C, where a rapid nucleation event occurs and multifaceted nanoparticles of crystalline Ge form. By varying the concentration of GeI4, the nanoparticle size can be tuned from 6 to 22 nm with narrow size distributions. Adding trioctylphosphine yields cube-shaped particles, and switching the solvent to octadecene yields one-dimensional nanostructur...

Au and the 3d transition metals are immiscible under equilibrium conditions, but nonequilibrium alloys and intermetallic compounds of these elements are of interest for their potential multifunctional optical, catalytic, and magnetic properties. Here we report an optimized synthesis of intermetallic compounds with nominal compositions of Au3Fe1−x, Au3Co1−x, and Au3Ni1−x as nanoparticles. Identification and optimization of the key synthetic variables (solvent, order of reagent addition, stabilizer, heating rate) led to the generation of nanoparticles with high phase purity and sample sizes of >30 mg, which is an order of magnitude larger than what was previously achievable. These intermetallic nanoparticles, which have diffraction patterns consistent with the L12 structure type, were characterized by powder XRD, TEM, EDS, electron diffraction, UV−visible spectroscopy, and SQUID magnetometry. Aliquot studies showed that Au3Fe1−x formed through the initial nucleation of Au nanoparticles, followed by subseque...

Many Ge-based chalcogenide alloys, including GeTe, exhibit a reversible amorphous-to-crystalline phase change that is the basis for a wide range of current and next-generation technologies. Solutio...

Transition metal chalcogenides are important materials because of their range of useful properties and applications, including as thermoelectrics, magnetic semiconductors, superconductors, quantum dots, sensors, and photovoltaics. In particular, iron chalcogenides have received renewed attention following the discovery of superconductivity in PbO-type β-FeSe and related solid solutions. This paper reports a low-temperature solution chemistry route to the synthesis of β-FeSe, β-FeTe, FeTe2, and several members of the β-Fe(Se,Te) solid solution. The samples were analyzed by powder XRD, TEM, EDS, SAED, SEM with elemental mapping, AFM, and SQUID magnetometry. Consistent with the layered crystal structures, the FeSe, FeTe, and Fe(Se,Te) products are predominantly two-dimensional single-crystal nanosheets with thicknesses of approximately 2−3 nm and edge lengths ranging from 200 nm to several micrometers. FeTe2 forms a mixture of nanosheets and one-dimensional sheet-derived nanostructures. None of the samples a...

A variety of binary intermetallic compounds of late transition metals with low-melting post-transition metals have been synthesized in bulk quantities by reacting molten metal dispersions with fine...

A new low-temperature strategy is described for the synthesis of nanocrystalline multimetal oxides. In this approach, intermetallic nanoparticles synthesized via a modified polyol process are used as reactive precursors that help to define both the composition and morphology of multimetal oxides via a two-step thermal oxidation process. We use Bi2PdO4 and Bi2Pt2O7 as model systems for elaborating this new synthetic strategy. For Bi2PdO4, intermetallic Bi2Pd nanocubes are thermally oxidized to form a Bi2O3/Pd nanocomposite, which transforms to textured Bi2PdO4 upon further heating in O2. Bi2Pt2O7 is formed using a similar strategy involving the thermal oxidation of intermetallic Bi−Pt nanoparticles. The reaction pathway is established using a combination of X-ray diffraction analysis, transmission electron microscopy, thermogravimetric analysis, and energy-dispersive spectrometry element mapping data. Given the growing number of intermetallic compounds that are accessible as nanoparticles, this strategy ha...

Metal phosphides can have important properties such as superconductivity, magnetoresistance, magnetocaloric behavior, catalytic activity, and lithium intercalation capacity, which make them useful for a variety of technological applications. Bulk metal phosphides usually require high temperatures and harsh reaction conditions to form, and metal phosphide nanocrystals can also be challenging to synthesize. Here we elaborate on a recently developed alternative approach for synthesizing metal phosphides, which involves the solution-mediated reaction of pre-formed metals with trioctylphosphine (TOP) at temperatures below 370 °C. This chemical conversion strategy is shown to be general and highly versatile, successfully forming a wide range of transition-metal and post-transition-metal phosphides using a range of both bulk and nanoscale metals as precursors. Metal nanocrystals, bulk powders, foils, wires, thin films, lithographically patterned substrates, and supported nanocrystals can all be converted to meta...

Ternary and quaternary transition metal oxides, which offer a wide variety of important physical properties, are traditionally synthesized using high-temperature reactions that often require several days of heating. A new nanoparticle-directed approach for the rapid low-temperature synthesis of nanocrystalline bulk-scale ternary and quaternary transition metal oxides has been developed. Readily available metal oxide nanoparticles can serve as a robust toolkit of highly reactive reagents, which can be mixed in solution in known ratios to form nanomodulated precursors and rapidly transformed, at relatively low temperatures, into more complex oxides. This approach is initially demonstrated for pyrochlore-type Y2Ti2O7 and Eu2Ti2O7 using XRD, DSC, and TEM to monitor the reaction. A nanocomposite of Y2O3 and TiO2 nanoparticles transforms into nanocrystalline Y2Ti2O7 within 2 h of heating to 700 °C, and Eu2Ti2O7 forms within 2 h of heating a nanocomposite of Eu2O3 and TiO2 nanoparticles to 800 °C. NiTiO3, CoTiO3...

A modified polyol process has been used to synthesize intermetallic nanocrystals and nanowire networks directly in solution using a one-pot reaction. The synthesis of AuCu nanocrystals in tetraethylene glycol shows that atomically ordered intermetallic nanocrystals form above 250 °C, while atomically disordered alloy nanocrystals form at lower temperatures. The particle size increases with increasing solvent temperature, and there is a gradual shift from spherical to ellipsoidal morphology. Fully ordered intermetallic AuCu nanocrystals synthesized at 310 °C have an average particle width and height of 10 ± 3 and 8 ± 2 nm, respectively, and exist with faceted ellipsoidal, hexagonal, and cubic shapes. Replacing tetraethylene glycol with ethylene glycol, diethylene glycol, triethylene glycol, and glycerol yields highly branched nanowire networks. The morphology of the nanowire networks remains the same for all of the solvents, but the structure can be tuned from fully disordered alloy to fully ordered interm...

Reduction of aqueous RhCl3 with NaBH4 in the presence of poly(vinyl pyrrolidone) (PVP) yields dense spherical nanostructures. The spherical aggregates, which generally have diameters between 10 and 100 nm, are built from smaller 1−3 nm Rh particles. The dense nanostructures are thermally stable beyond 100 °C, and they have a tendency to form ordered superstructures upon drying. Combining sodium n-dodecyl sulfate (SDS) with PVP modifies the size and morphology of the primary 1−3 nm particles, but does not change the spherical shape of the aggregates except at high concentrations of SDS. Small-angle X-ray scattering measurements show that the large aggregates are formed directly in solution from small Rh particles, consistent with TEM and AFM results. Magnetic measurements indicate that the Rh nanoparticle aggregates are Pauli paramagnetic.

In recent years, many soft-chemical reactions of layered perovskites have been reported, and they can be classified into sets of similar reactions. Simple ion-exchange and intercalation reactions replace or modify the interlayer cations of layered perovskites, and more complex metathesis reactions replace interlayer cations with cationic structural units. Topochemical condensation reactions that involve dehydration and reduction provide access to a variety of metastable structural features in three-dimensional perovskites, and similar reactions can be used to convert among higher order layered perovskite homologues. Other techniques, such as high pressure and anion intercalation/deintercalation, also yield interesting metastable phases. When combined, the individual reactions complement each other, and a powerful toolbox of solid-state reactions emerges. By using layered perovskites as templates, it is possible to retrosynthetically design new product perovskites that retain the structural features of the...

Na2Ln2Ti3-xMnxO10 (Ln = Sm, Eu, Gd, and Dy; 0 ≤ x ≤ 1), a new series of triple-layer Ruddlesden−Popper phases, were synthesized by direct solid-state reaction. The smaller lanthanides enhance manga...

Dion−Jacobson phases are layer perovskites of the general formula A‘[An-1BnO3n+1], where A‘ is typically an exhangeable alkali or alkali earth ion. Because of their low layer charge density, acid-exchanged Dion−Jacobson phases are easily exfoliated to make single-sheet colloids. When the conditions temperature and pH were controlled, densely tiled monolayers of anionic sheets derived from HCa2Nb3O10, HSr2Nb3O10, HCaLaNb2TiO10, and HLaNb2O7 were grown on cationic substrates. Multilayer films were also assembled by alternately adsorbing these sheets and organic polycations.

Germanium nanoparticles with an average size of 5 ± 1 nm were synthesized by the room-temperature reduction of GeCl4 in ethylene glycol using a solution of NaBH4 in triglyme. By modifying the reaction conditions, other morphologies can also be accessed, including larger spherical particles and nanocubes.

Magnetically separable hydrogenation catalysts serve as an example of a multifunctional M13 bacteriophage nanocomposite made by (a) growing Rh nanoparticles lengthwise along the pVIII region via nonspecific electrostatic interactions and (b) anchoring Fe3O4 nanoparticles on the pIII tip via materials-specific interactions identified through phage display methods

Gram-scale quantities of Eu2Ti2O7 with a [110] layered perovskite structure have been synthesized at ambient pressure by thermally oxidizing (750−900 °C) perovskite-type EuTiO3. Eu2Ti2O7 is type 1 phase matchable and shows a SHG efficiency of 80 × α-SiO2.