With hydrogen fuel becoming a more viable alternative to fossil fuels comes the need for inexpensive, low-energy hydrogen production. Here, a low-temperature direct solution-processing method is presented for the deposition of earth-abundant pyrite-type NiSe2 as an efficient hydrogen evolution reaction (HER) catalyst. Thin films of phase-pure NiSe2 are deposited from a precursor ink prepared by room-temperature dissolution of bulk elemental Ni and Se in a binary thiolamine solvent mixture. The nanostructured NiSe2 thin films demonstrate high HER catalytic activity with 100% Faradaic efficiency.

The gram-scale preparation of Fe2(WO4)3 by a new solution-based route and detailed characterization of the material are presented. The resulting Fe2(WO4)3 undergoes a reversible electrochemical reaction against lithium centered around 3.0 V with capacities near 93% of the theoretical maximum. Evolution of the Fe2(WO4)3 structure upon lithium insertion and deinsertion is probed using a battery of characterization techniques, including in situ X-ray diffraction, neutron total scattering, and X-ray absorption spectroscopy (XAS). A structural transformation from monoclinic to orthorhombic phases is confirmed during lithium intercalation. XAS and neutron total scattering measurements verify that Fe2(WO4)3 consists of trivalent iron and hexavalent tungsten ions. As lithium ions are inserted into the framework, iron ions are reduced to the divalent state, while the tungsten ions are electrochemically inactive and remain in the hexavalent state. Lithium insertion occurs via a concerted rotation of the rigid polyhedra in the host lattice driven by electrostatic interactions with the Li+ ions; the magnitude of these polyhedral rotations was found to be slightly larger for Fe2(WO4)3 than for the Fe2(MoO4)3 analog.Keywords: battery; intercalation; lithium ion; NASICON; tungstate;

The translation of batch chemistries to high-throughput flow methods addresses scaling concerns associated with the implementation of colloidal nanoparticle (NP) catalysts for industrial processes. A literature procedure for the synthesis of Ni-NPs was adapted to a continuous millifluidic (mF) flow method, achieving yields >60%. Conversely, NPs prepared in a batch (B) reaction under conditions analogous to the continuous flow conditions gave only a 45% yield. Both mF- and B-Ni-NP catalysts were supported on SiO2 and compared to a Ni/SiO2 catalyst prepared by traditional incipient wetness (IW) impregnation for the hydrodeoxygenation (HDO) of guaiacol under ex situ catalytic fast pyrolysis conditions (350 °C, 0.5 MPa). Compared to the IW method, both colloidal NPs displayed increased morphological control and narrowed size distributions, and the NPs prepared by both methods showed similar size, shape, and crystallinity. The Ni-NP catalyst synthesized by the continuous flow method exhibited similar H-adsorption site densities, site-time yields, and selectivities toward deoxygenated products compared to the analogous batch-prepared catalyst, and it outperformed the IW catalyst with respect to higher selectivity to lower oxygen content products and a 31-fold decrease in deactivation rate. These results demonstrate the utility of synthesizing colloidal Ni-NP catalysts using flow methods that can produce >27 g/day of Ni-NPs (equivalent to >0.5 kg of 5 wt % Ni/SiO2), while maintaining the catalytic properties displayed by the batch equivalent.Keywords: Ex-situ catalytic fast pyrolysis; Hydrodeoxygenation; Lignin model compound; Microreactor; Millifluidics; Nickel nanoparticles;

Macroelectronics is a major focus in electronics research and is driven by large area applications such as flat panel displays and thin film solar cells. Innovations for these technologies, such as flexible substrates and mass production, will require efficient and affordable semiconductor processing. Low-temperature solution processing offers mild deposition methods, inexpensive processing equipment, and the possibility of high-throughput processing. In recent years, the discovery that binary “alkahest” mixtures of ethylenediamine and short chain thiols possess the ability to dissolve bulk inorganic materials to yield molecular inks has lead to the wide study of such systems and the straightforward recovery of phase pure crystalline chalcogenide thin films upon solution processing and mild annealing of the inks. In this review, we recount the work that has been done toward elucidating the scope of this method for the solution processing of inorganic materials for use in applications such as photovoltaic devices, electrocatalysts, photodetectors, thermoelectrics, and nanocrystal ligand exchange. We also take stock of the wide range of bulk materials that can be used as soluble precursors, and discuss the work that has been done to reveal the nature of the dissolved species. This method has provided a vast toolbox of over 65 bulk precursors, which can be utilized to develop new routes to functional chalcogenide materials. Future studies in this area should work toward a better understanding of the mechanisms involved in the dissolution and recovery of bulk materials, as well as broadening the scope of soluble precursors and recoverable functional materials for innovative applications.

N-Heterocyclic carbenes (NHCs) are becoming increasingly popular ligand frameworks for nanocrystal surfaces; however, as of yet the nature of the NHC–nanocrystal interface remains unexplored across different material types. Here we report a facile synthetic route to NHC-stabilized metal and metal chalcogenide nanocrystals. It was observed that NHC–Ag nanocrystals are colloidally stable, but much less so than the corresponding NHC–Ag2E analogues. Comprehensive NMR studies suggest a dynamic NHC–nanocrystal interface for both NHC–Ag and NHC–Ag2S; however, density functional theory calculations reveal a much stronger binding affinity of the NHC ligands to Ag2S compared with Ag nanocrystals, which explains the superior colloidal stability of the metal chalcogenides. This offers new insight into the surface chemistry of neutral L-type carbenes in colloidal nanocrystal chemistry.

Anti-NASICON Fe2(MoO4)3 (P21/c) shows significant structural and electrochemical differences in the intercalation of Li+ and Na+ ions. To understand the origin of this behavior, we have used a combination of in situ X-ray and high-resolution neutron diffraction, total scattering, electrochemical measurements, density functional theory calculations, and symmetry-mode analysis. We find that for Li+-intercalation, which proceeds via a two-phase monoclinic-to-orthorhombic (Pbcn) phase transition, the host lattice undergoes a concerted rotation of rigid polyhedral subunits driven by strong interactions with the Li+ ions, leading to an ordered lithium arrangement. Na+-intercalation, which proceeds via a two-stage solid solution insertion into the monoclinic structure, similarly produces rotations of the lattice polyhedral subunits. However, using a combination of total neutron scattering data and density functional theory calculations, we find that while these rotational distortions upon Na+-intercalation are fundamentally the same as for Li+-intercalation, they result in a far less coherent final structure, with this difference attributed to the substantial difference between the ionic radii of the two alkali metals.

Current state-of-the-art hybrid polymer:lead chalcogenide nanocrystal solar cells require postdeposition, thin film chemical treatments to remove insulating organic ligands from the nanocrystal surface, which is a kinetically hindered process. This is compounded by the fact that it can be especially difficult to obtain colloidally stable suspensions of PbS nanocrystals ligand exchanged with small ligands, and many atomic ligands require dispersion in solvents that are incompatible with polymer solubility. Herein, we report a novel one-step colloidal ligand exchange process for PbS nanocrystals employing lead iodide (PbI2) or ammonium iodide (NH4I) as surface ligands along with n-butylamine that allow the ligand-exchanged nanocrystals to be suspended in solvents compatible with polymer dissolution. While ligand exchange is shown to be near quantitative for both iodide sources, when compared to NH4I-exchanged PbS nanocrystals, the PbI2-exchanged PbS nanocrystals not only exhibit better colloidal stability but also display superior photovoltaic performance. When the PbI2-passivated PbS nanocrystals are combined with the donor polymer poly[2,6-(4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′3′-d]silole)-alt-4,7-(2,1,3-benzothiadiazole)] (Si-PCPDTBT), the optimized hybrid solar cells give a broad spectral response into the NIR, leading to a power conversion efficiency (PCE) of 4.8% under AM 1.5G illumination. Time-resolved photoluminescence and transient absorption spectroscopies suggest that excitonic processes between the PbS nanocrystals and Si-PCPDTBT are more favorable when PbS nanocrystals are ligand exchanged with PbI2, leading to superior device performance.

Solution processing is a practical low-cost strategy for depositing semiconductor thin films. A binary thiol–amine solvent mixture dissolves bulk Cu2S and Sb2S3 under ambient conditions, allowing for solution deposition and low temperature recovery of CuSbS2. The resulting films of earth abundant CuSbS2 possess optoelectronic properties suitable for photovoltaic applications.

Colloidally synthesized quantum dots of CsPbBr3 are highly promising for light-emitting applications. Previous reports based on benchtop diffraction conflict as to the crystal structure of CsPbBr3 quantum dots. We present X-ray diffraction and PDF analysis of X-ray total scattering data that indicate that the crystal structure is unequivocally orthorhombic (Pnma).

Binary solvent mixtures of alkanethiols and 1,2-ethylenediamine have the ability to readily dissolve metals, metal chalcogenides, and metal oxides under ambient conditions to enable the facile solution processing of semiconductor inks; however, there is little information regarding the chemical identity of the resulting solutes. Herein, we examine the molecular solute formed after dissolution of Sn, SnO, and SnS in a binary solvent mixture comprised of 1,2-ethanedithiol (EDT) and 1,2-ethylenediamine (en). Using a combination of solution 119Sn NMR and Raman spectroscopies, bis(1,2-ethanedithiolate)tin(II) was identified as the likely molecular solute present after the dissolution of Sn, SnO, and SnS in EDT–en, despite the different bulk material compositions and oxidation states (Sn0 and Sn2+). All three semiconductor inks can be converted to phase-pure, orthorhombic SnS after a mild annealing step (∼350 °C). This highlights the ability of the EDT–en solvent mixture to dissolve and convert a variety of low-cost precursors to SnS semiconductor material.

A dual-space approach, combining Rietveld and pair distribution function (PDF) analyses, has been applied to temperature-dependent synchrotron X-ray total scattering data collected on vapor diffusion sol–gel derived CaMoO4 nanocrystals. A sharp transition in Ca–O bond distances in the range of 151–163 K was identified by PDF analysis, which is attributed to the thermal activation of rotational disorder associated with the rigid MoO4 tetrahedra.

We demonstrate the ability of a thiol–amine solvent mixture to deposit phase-pure marcasite-type CoSe2 nanostructured thin films as effective hydrogen evolution reaction (HER) electrocatalysts. Electrodes are readily prepared by spin coating a precursor ink onto highly ordered pyrolytic graphite substrates followed by annealing to 350 °C. The resulting CoSe2 films have an onset potential for HER of −117 mV vs RHE and Tafel slopes of ca. 60 mV dec–1. Normalization based on electrochemically active surface area reveals that simple optimization of film thickness, based on the number of layers deposited, leads to electrodes with better surface utilization. Based on the electrocatalytic performance of the solution-processed CoSe2 presented here (η10mA/cm2 = −272 mV vs RHE), this approach shows promise as a simple method to deposit a wide range of useful dichalcogenide electrocatalysts.

The ability to synthesize colloidal semiconductor nanocrystals in a well-controlled manner (i.e., with fine control over size, shape, size dispersion, and composition) has been mastered over the past 15 years. Much of this success stems from careful studies of precursor conversion and nanocrystal growth with respect to phosphine chalcogenide precursors for the synthesis of metal chalcogenide nanocrystals. Despite the high level of success that has been achieved with phosphine chalcogenides, there has been a longstanding interest in exploring alternate chalcogenide precursors because of issues associated with phosphine chalcogenide cost, purity, toxicity, etc. This has resulted in a large body of literature on the use of sulfur and selenium dissolved in octadecene or amines, thio- and selenoureas, and silyl chalcogenides as alternate chalcogenide precursors for metal chalcogenide nanocrystal synthesis.In this Account, emerging work on the use of diorganyl dichalcogenides (R–E–E–R, where E = S, Se, or Te and R = alkyl, allyl, benzyl, or aryl) as alternate chalcogenide precursors for the synthesis of metal chalcogenide nanocrystals is summarized. Among the benefits of these dichalcogenide synthons are the following: (i) they represent the first and only common precursor type that can function as chalcogen transfer reagents for each of the group VI elements (i.e., to make metal oxide, metal sulfide, metal selenide, and metal telluride nanocrystals); (ii) they possess relatively weak E–E bonds that can be readily cleaved under mild thermolytic or photolytic conditions; and (iii) the organic substituents can be tuned to affect the reactivity. These combined attributes have allowed dichalcogenide precursors to be employed for a wide range of metal chalcogenide nanocrystal syntheses, including those for In2S3, SnxGe1–xSe, SnTe, Cu2–xSySe1–y, ZnSe, CdS, CdSe, MoSe2, WSe2, BiSe, and CuFeS2. Interestingly, a number of metastable phases of compositionally complex semiconductors can be kinetically accessed through syntheses utilizing dichalcogenide precursors, likely as a result of their ability to convert at relatively low temperatures. These include the hexagonal wurtzite phases of CuInS2, CuInSe2, Cu2ZnSn(S1–xSex)4, and Cu2SnSe3 nanocrystals. The discovery of crystal phases on the nanoscale that do not exist in their bulk analogues is a developing area of nanocrystal chemistry, and dichalcogenides are proving to be a useful synthetic tool in this regard.The most recent application of dichalcogenide synthons for semiconductor nanocrystals is their use as precursors for surface ligands. While there is a rich history of using thiol ligands for semiconductor nanocrystals, the analogous selenol and tellurol ligands have not been studied, likely because of their oxidative instability. Dichalcogenides have proven useful in this regard, as they can be reduced in situ with diphenylphosphine to give the corresponding selenol or tellurol ligand that binds to the nanocrystal surface. This chemistry has been applied to the in situ synthesis and ligand binding of selenols to PbSe nanocrystals and both selenols and tellurols to CdSe nanocrystals. These initial studies have allowed the photophysics of these nanocrystal–ligand constructs to be investigated; in both cases, it appears that the selenol and tellurol ligands act as hole traps that quench the photoluminescence of the semiconductor nanocrystals.

Blends of semiconducting polymers and inorganic semiconductor nanocrystals are receiving renewed interest as a type of inexpensive, solution-processed third generation solar cell. In these hybrid bulk heterojunctions (BHJs), the interface between the disparate organic and inorganic phases is a dominating factor in the overall performance of the resulting devices. Paramount to this interface is the ligand landscape on the nanocrystal surface, which as a result of the inherently large surface area to volume ratio of the nanocrystals, has a significant spatial and electronic influence on the boundary between the donor polymer and acceptor nanocrystal. We have investigated the importance of this three-part polymer/ligand/nanocrystal interface by studying the ligand effects in hybrid BHJ solar cells. In this article, we highlight the major research advances and the state-of-the-art in hybrid BHJ solar cells with respect to ligand engineering, as well as outline future research avenues deemed necessary for continued technological advancement.

We developed a simple and robust colloidal route for the installation of CdX2 (X = Cl, Br, I) ligands on the surface of CdSe nanocrystals, which effectively displace the native ligands and form stable suspensions. After colloidal ligand exchange, these nanocrystals can be easily solution cast into nanocrystal films. Photoelectrochemical measurements on solution-cast nanocrystal films reveal a striking influence of surface cadmium halide on photocurrent response, with mildly annealed, CdCl2-treated CdSe nanocrystals showing the greatest enhancement in photocurrent to above band gap illumination. The strong dependence of photoresponse on surface halide is thought to result from ligand-induced changes in the electronic structure of the nanocrystal samples. We arrive at this conclusion using a combination of ultrafast transient absorption, time-resolved photoluminescence, and surface photovoltage spectroscopies, which are being applied together for the first time to investigate nanocrystal trap states. From these measurements, we establish a trend for ligand-related sub-band gap states that accounts for electron and hole trapping at the nanocrystal surface. The nature of the electron and hole traps in the nanocrystal films are dependent on the thermal history of the sample as well as the specific halide surface treatment employed. After subjecting the nanocrystal films to mild thermal annealing, we find evidence that suggests a drastic reduction in electron trap states. Additionally, depending on the surface halide treatment employed, the energy of the hole trap states varies, with CdCl2 treatment resulting in energetically shallow hole trap states, and CdBr2 and CdI2 treatments leading to much deeper hole traps. Thus, judicious choice of cadmium halide surface treatment can be used to manipulate the trap state landscape of these ligand exchanged CdSe nanocrystals.

A series of compositionally complex scheelite-structured nanocrystals of the formula A1−xA′xWO4 (A = Ca, Sr, Ba) have been prepared under benign synthesis conditions using the vapor diffusion sol–gel method. Discrete nanocrystals with sub-20 nm mean diameters were obtained after kinetically controlled hydrolysis and polycondensation at room temperature, followed by composition-dependent thermal aging at or below 60 °C. Rietveld analysis of X-ray diffraction data and Raman spectroscopy verified the synthesis of continuous and phase-pure nanocrystal solid solutions across the entire composition space for A1−xA′xWO4, where 0 ≤ x ≤ 1. Elemental analysis by X-ray photoelectron and inductively coupled plasma-atomic emission spectroscopies demonstrated excellent agreement between the nominal and experimentally determined elemental stoichiometries, while energy dispersive X-ray spectroscopy illustrated good spatial elemental homogeneity within these nanocrystals synthesized under benign conditions.

Despite their extremely low solubility in most solvents, hexagonal grey selenium and tellurium are shown to be remarkably soluble in binary mixtures of thiols and ethylenediamine (en) at room temperature and ambient pressure. A 1:4 vol/vol mixture of ethanethiol (EtSH) and en gave saturated solutions of 38 and 9.3 wt% for grey selenium and tellurium, respectively. Crystalline and phase-pure chalcogen is easily recovered from solution by drying and mild heat treatment at 250 °C (for selenium) or evaporation at room temperature (for tellurium). To demonstrate utility for these dissolved chalcogens, it was shown that elemental antimony readily reacts with the dissolved selenium to give a stable, solution processable Sb–Se precursor solution. In the same way, elemental tin reacts with the dissolved tellurium to generate a Sn–Te precursor solution. Upon solution deposition and heat treatment to 250 °C, these precursor solutions yielded crystalline Sb2Se3 and SnTe.

Molecular stibanates derived from the dissolution of bulk Sb2S3 in a binary ethylenediamine and mercaptoethanol solvent mixture have been studied as capping ligands for colloidal CdSe nanocrystals. A phase transfer ligand exchange strategy was utilized to effectively install the stibanate ligands onto the CdSe nanocrystals to form stable colloidal suspensions in polar solvents, such as formamide. This methodology was very effective in the removal of insulating native ligands on the as-prepared nanocrystals, with the resulting stibanate-capped CdSe nanocrystals giving low organic content thin films upon spin coating with improved interparticle coupling after heating to temperatures <300 °C. Photoelectrochemical measurements on stibinate-capped CdSe nanocrystal films showed that this novel ligand leads to a > 25-fold increase in photocurrent response relative to as-prepared CdSe nanocrystal films.

A structural investigation of sub-15 nm xEu:BaTiO3 nanocrystals (x = 0–5 mol%) was conducted to determine the distribution of the Eu3+ ion in the BaTiO3 lattice. Pair distribution function analysis of X-ray total scattering data (PDF), steady-state photoluminescence, and X-ray absorption spectroscopy (XANES/EXAFS) were employed to interrogate the crystal structure of the nanocrystals and the local atomic environment of the Eu3+ ion. The solubility limit of the Eu3+ ion in the nanocrystalline BaTiO3 host synthesized via the vapor diffusion sol–gel method was estimated to be ∼4 mol%. A contraction of the perovskite unit cell volume was observed upon incorporation of 1 mol% of europium, while an expansion was observed for nominal concentrations between 1 and 3 mol%. The average Eu–O distance and europium coordination number decreased from 2.46 Å and 9.9 to 2.42 Å and 8.6 for europium concentrations of 1 and 5 mol%, respectively. Structural trends were found to be consistent with the substitution of Eu3+ for Ba2+via creation of a Ti4+ vacancy at low europium concentrations (<1 mol%), and with the substitution of Eu3+ for both Ba2+ and Ti4+ at high europium concentrations (1–3 mol%). The significance of accounting for local structural distortions to rationalize the distribution of lanthanide ions in the perovskite host is highlighted.

The vapor diffusion sol–gel (VDSG) method was employed for the room-temperature synthesis of ∼10 nm, aliovalently doped 0.4, 0.8, and 1.6 mol% La:BaTiO3 and 0.4, 0.6, and 1.2 mol% Dy:BaTiO3 nanocrystals. Maximum ensemble relative permittivities of 176 and 208 were observed in the 0.8 mol% La:BaTiO3 and the 1.2 mol% Dy:BaTiO3 nanocrystals, respectively, relative to 89 for undoped BaTiO3 (at 1 MHz, 25 °C) due to local disorder induced by aliovalent substitution.

Tandem and triple-junction polymer:nanocrystal hybrid solar cells with identical subcells based on P3HT:CdSe nanocrystal bulk heterojunctions (BHJs) are reported for the first time showing 2-fold and 3-fold increases of open-circuit voltage (VOC), respectively, relative to the single-junction cell. A combination of nanocrystalline ZnO and pH-neutral PEDOT:PSS is used as the interconnecting layer, and the thicknesses of subcells are optimized with the guidance of optical simulations. As a result, the average power conversion efficiency (PCE) exhibits a significant increase from 2.0% (VOC = 0.57 V) in single-junction devices to 2.7% (champion 3.1%, VOC = 1.28 V) in tandem devices and 2.3% (VOC = 1.98 V) in triple-junction devices.Keywords: CdSe; hybrid solar cell; optical simulation; P3HT; tandem solar cell

The crystal structure of sub-15 nm AMoO4 (A = Ca, Sr, Ba) scheelite nanocrystals has been investigated using a dual-space approach that combines Rietveld and pair distribution function (PDF) analysis of synchrotron X-ray diffraction data. Rietveld analysis yields an average crystal structure in which the Mo–O bond distance exhibits an anomalously large contraction (2.8%) upon chemical substitution of Ba2+ for Ca2+. Such a dependence on chemical composition contradicts the well-known rigid character of MoVI–O bonds and the resulting rigidity of MoO4 tetrahedra in scheelites. Unlike Rietveld, PDF analysis yields a local crystal structure in which the Mo–O bond distance shows a negligible contraction (0.4%) upon going from Ba2+ to Ca2+ and, therefore, appears independent of the chemical composition. Analysis of the anisotropic displacement parameters of the oxygen atom reveals that the disagreement between the average and local structural models arises from the presence of static orientational disorder of the MoO4 tetrahedra. Rietveld analysis averages the random rotations of the MoO4 tetrahedra across the scheelite lattice yielding an apparent Mo–O bond distance that is shorter than the true bond distance. In contrast, PDF analysis demonstrates that the structural integrity of the MoO4 tetrahedra remains unchanged upon chemical substitution of the alkaline-earth cation, and that their orientational disorder is accommodated through geometric distortions of the AO8 dodecahedra.

•We synthesize Rh nanoparticles in ionic liquid media using both conventional and microwave heating.•Ionic liquid coordination to the Rh nanoparticle surface was confirmed by FT-IR spectroscopy and XPS.•The Rh nanoparticles were active for the vapor-phase hydrogenation of cyclohexene.A comparative study of the synthesis of Rh nanoparticles (RhNPs) in ionic liquid media (1-butyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide) by conventional and microwave heating is presented. Controlled injection of hydrated RhCl3 precursor into mixtures of the ionic liquid and poly(N-vinylpyrrolidone) under convective electrical heating yielded near-monodisperse (6.9 ± 1.1 nm) RhNPs with a mixture of morphologies. In contrast, identical reactions performed under microwave-assisted heating showed greater morphological selectivity, resulting in largely homogeneous samples of cubic and truncated cubic RhNPs (5.7 ± 0.9 nm). Interestingly, X-ray photoelectron spectroscopic analysis of the microwave-synthesized RhNPs revealed a greater surface population of BMIM-NTf2 when compared to the conventionally prepared RhNPs. This is indicative of a larger degree of incorporation of ionic liquid monomers coordinated to the RhNP surfaces and may be responsible for the enhanced shape selectivity. The catalytic ability of the as-synthesized nanoparticles was probed through vapor-phase cyclohexene hydrogenation reactions, yielding average TOF values of 9.2 for supported RhNPs.Rhodium nanoparticles have been prepared using an ionic liquid and organic polymer as co-capping agents; the effects of microwave-assisted heating are compared to conventional heating, and the resulting products are compared as heterogeneous hydrogenation catalysts under model conditions.

We have employed a simple modular approach to install small chalcogenol ligands on the surface of CdSe nanocrystals. This versatile modification strategy provides access to thiol, selenol, and tellurol ligand sets via the in situ reduction of R2E2 (R = tBu, Bn, Ph; E = S, Se, Te) by diphenylphosphine (Ph2PH). The ligand exchange chemistry was analyzed by solution NMR spectroscopy, which reveals that reduction of the R2E2 precursors by Ph2PH directly yields active chalcogenol ligands that subsequently bind to the surface of the CdSe nanocrystals. Thermogravimetric analysis, FT-IR spectroscopy, and energy dispersive X-ray spectroscopy provide further evidence for chalcogenol addition to the CdSe surface with a concomitant reduction in overall organic content from the displacement of native ligands. Time-resolved and low temperature photoluminescence measurements showed that all of the phenylchalcogenol ligands rapidly quench the photoluminescence by hole localization onto the ligand. Selenol and tellurol ligands exhibit a larger driving force for hole transfer than thiol ligands and therefore quench the photoluminescence more efficiently. The hole transfer process could lead to engineering long-lived, partially separated excited states.Keywords: CdSe; ligand exchange; nanocrystals; photoluminescence; quantum dot;

The ability to solution deposit semiconductor films has received a great deal of recent attention as a way to potentially lower costs for many optoelectronic applications; however, most bulk semiconductors are insoluble in common solvents. Here we describe a novel and relatively nonhazardous binary solvent mixture comprised of 1,2-ethanedithiol and 1,2-ethylenediamine that possesses the remarkable ability to rapidly dissolve a series of nine bulk V2VI3 chalcogenides (V = As, Sb, Bi; VI = S, Se, Te) at room temperature and atmospheric pressure. After solution deposition and low-temperature annealing, the chalcogenides can be fully recovered as good quality, highly crystalline thin films with negligible organic content, as demonstrated for Sb2Se3 and Bi2S3.

Ultrafast transient absorption spectroscopy is used to study charge transfer dynamics in hybrid films composed of the low band gap polymer PCPDTBT and CdSe quantum dots capped with tert-butylthiol ligands. By selectively exciting the polymer, a spectral signature for electrons on the quantum dots appears on ultrafast time scales (≲ 65 fs), which indicates ultrafast electron transfer. From this time scale, the coupling between the polymer chains and the quantum dots is estimated to be J ≳ 17 meV. The reduced quantum dot acceptors exhibit an unambiguous spectral bleach signature, whose amplitude allows for the first direct calculation of the absolute electron transfer yield in a hybrid solar cell (82 ± 5%). We also show that a limitation of the hybrid system is rapid and measurable geminate recombination due to the small separation of the initial charge pair. The fast recombination is consistent with the internal quantum efficiency of the corresponding solar cell. We therefore have identified and quantified a main loss mechanism in this type of third generation solar cell.

An extension of the vapor diffusion sol–gel method to the synthesis of the AMoO4 (A = Ca, Sr, Ba) scheelite family of materials is reported. Sub-30 nm quasispherical nanocrystals were obtained after vapor diffusion at room temperature, followed by thermal aging at 80 °C. Rietveld analysis of X-ray diffraction data, Raman spectroscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy demonstrated that the vapor diffusion sol–gel method affords crystalline and phase-pure AMoO4 nanocrystals with excellent compositional control. The potential lithium storage capacity of the CaMoO4 nanocrystals versus Li at a rate of C/4 was also investigated. The nanocrystals exhibited an extremely large first discharge capacity of 1300 mA h g–1, which stabilized at 250 mA h g–1 after 25 cycles.Keywords: Li-ion battery; nanocrystal; scheelite; sol−gel; vapor diffusion;

Hybrid solar cells with tert-butylthiol exchanged CdSe multipod acceptors and novel semi-random P3HTT-DPP and alternating PCDTBT copolymer donors were studied, giving high performance devices with power conversion efficiencies >3%.

The effect of isovalent chemical substitution on the magnitude and coherence length of local ferroelectric distortions present in sub-20 nm Ba1–xSrxTiO3 (x = 0.0, 0.30, 0.50, 1.0) and BaTi1–yZryO3 (y = 0.0, 0.15, 0.50, 1.0) nanocrystals synthesized at room temperature is investigated using X-ray absorption near edge structure (XANES) and pair distribution function analysis of X-ray total scattering data (PDF). Although the average crystal structure of the nanocrystals is adequately described by a centrosymmetric, cubic Pm3̅m space group, local ferroelectric distortions due to the displacement of the titanium atom from the center of the perovskite lattice are observed for all compositions, except BaZrO3. The symmetry of the ferroelectric distortions is adequately described by a tetragonal P4mm space group. The magnitude of the local displacements of the titanium atom in BaTiO3 nanocrystals is comparable to that observed in single crystals and bulk ceramics, but the coherence length of their ferroelectric coupling is much shorter (≤20 Å). Substitution of Sr2+ for Ba2+ and of Zr4+ for Ti4+ induces a tetragonal-to-cubic transition of the room temperature local crystal structure, analogous to that observed for single crystals and bulk ceramics at similar compositions. This transition is driven by a reduction of the magnitude of the local displacements of the titanium atom and/or of the coherence length of their ferroelectric coupling. Replacing 50% of Ba2+ with Sr2+ slightly reduces the magnitude of the titanium displacement, but the coherence length is not affected. In contrast, replacing 15% of the ferroelectrically active Ti4+ with Zr4+ leads to a significant reduction of the coherence length. Deviations from the ideal solid solution behavior are observed in BaTi1–yZryO3 nanocrystals and are attributed to an inhomogeneous distribution of the barium atoms in the nanocrystal. Composition–structure relationships derived for Ba1–xSrxTiO3 and BaTi1–yZryO3 nanocrystals demonstrate that the evolution of the room temperature local crystal structure with chemical composition parallels that of single crystals and bulk ceramics, and that chemical control over ferroelectric distortions is possible in the sub-20 nm size range. In addition, the potential of PDF analysis of total scattering data to probe compositional fluctuations in nanocrystals is demonstrated.Keywords: nanoparticles; perovskite; total scattering; vapor diffusion Sol−Gel; XANES

Improved dielectric constant, breakdown strength, and energy density are reported for polyimide/sub-10 nm Ba0.7Sr0.3TiO3 (BST) nanocomposites up to the percolation threshold. Homogeneous nanocomposites were prepared via an in situ polymerization technique, whereby a suspension of BST is blended with 1,3-bis(4-aminophenoxy)benzene (BAPB) and pyromellitic dianhydride (PMDA) monomers prior to spin-casting and thermal imidization. The dielectric properties the PMDA-BAPB/BST nanocomposites were measured as a function of BST loading and displayed a 24% increase in breakdown strength and calculated energy densities more than twice that of the pure polymer at 10 vol % BST. The PMDA-BAPB/BST nanocomposites also display improved permittivities (εr = 6.2 at 18 vol % and 1 MHz) and low dielectric loss (tan δ <0.04 for all loadings up to 1 MHz) and are thermally stable above 450 °C in air and 500 °C in nitrogen. The results highlight the benefit of employing extremely small and highly dispersed nanocrystals in capacitive energy storage applications.

Sub-10 nm BaTiO3 nanocrystals were synthesized at room temperature via the vapor diffusion sol–gel method, and their structural evolution during nucleation and growth stages was followed using a series of techniques that probe the atomic structure on different length and time scales. Special emphasis was placed on assessing the evolution of the local symmetry and structural coherence of the resulting nanocrystals, as these are the structural bases for cooperative properties such as ferroelectricity. Although the room-temperature crystal structure of the fully grown nanocrystals appears cubic to Rietveld analysis of synchrotron X-ray diffraction data, Raman spectroscopy and pair distribution function analysis demonstrate the presence of non-centrosymmetric regions arising from the off-centering of the titanium atoms. This finding demonstrates that accounting for diffuse scattering is critical when attempting the structural characterization of nanocrystals with X-ray diffraction. The local symmetry of acentric regions present in BaTiO3 nanocrystals, particularly structural correlations within an individual unit cell and between two adjacent unit cells, is best described by a tetragonal P4mm space group. The orthorhombic Amm2 space group also provides an adequate description, suggesting both types of local symmetry can coexist at room temperature. The average magnitude of the local off-center displacements of the titanium atoms along the polar axis is comparable to that observed in bulk BaTiO3, and their coherence length is on the order of 16 Å. The presence of local dipoles suggests that a large amount of macroscopic polarization can be achieved in nanocrystalline BaTiO3 if the coherence of their ferroelectric coupling is further increased.

Droplet-based microfluidic platforms have the potential to provide superior control over mixing as compared to traditional batch reactions. Ionic liquids have advantageous properties for metal nanoparticle synthesis as a result of their low interfacial tension and complexing ability; however, droplet formation of ionic liquids within microfluidic channels in a two-phase system has not yet been attained because of their complex interfacial properties and high viscosities. Here, breakup of an imidazolium-based ionic liquid into droplets in a simple two-phase system has for the first time been achieved and characterized by using a microchannel modified with a thin film fluoropolymer. This microfluidic/ionic liquid droplet system was used to produce small, spherical gold (4.28 ± 0.84 nm) and silver (3.73 ± 0.77 nm) nanoparticles.Keywords: gold; ionic liquids; microfluidics; nanoparticles; silver; vapor-phase polymerization;

Single crystalline, sub-15 nm BaZrxTi1−xO3 (0 ≤ x ≤ 1) nanocrystals were synthesized at room temperature via the vapor diffusion sol–gel method. As-prepared nanocrystals exhibit noncentrosymmetric regions whose volume fraction increases significantly upon substitution of small amounts of Zr4+ for Ti4+ and reaches a maximum for substitution levels ranging from 10 to 20 mol%.

The 1,2,3,4-thiatriazole-5-thiolate anion (TTT−) was found to be a strongly binding ligand for CdSe nanocrystals, quantitatively exchanging various long-chain ligands to yield stable colloidal suspensions in common polar solvents. The TTT− ligand thermolyzes at <100 °C to produce thiocyanate in situ, resulting in reduced quantum confinement in nanocrystal films. CdSe(TTT) possesses far higher colloidal stability than CdSe(SCN), and that, together with the facile synthesis of TTT−, implies that this is a useful ligand for nanocrystal applications as a masked thiocyanate.

Imidazolium-based ionic liquids have been widely utilized as versatile solvents for metal nanoparticle synthesis; however, reactions to synthesize silver nanoparticles that are performed identically in different commercially obtained lots of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4) give divergent results. This suggests that impurities in these nominally identical solvents play an important role in the resulting silver nanoparticle quality. To test the effect that impurities have on the quality of silver nanoparticles synthesized in BMIM-BF4, silver nanoparticles were synthesized in carefully prepared and purified BMIM-BF4 and compared against silver nanoparticles that were synthesized in the purified BMIM-BF4 that had been spiked with trace amounts of water, chloride, and 1-methylimidazole. It was clearly demonstrated that trace amounts of these common ionic liquid impurities cause significant deviation in size and shape (creating polydisperse and irregularly shaped ensembles of both large and small particles), and also negatively impact the stabilization of the resulting silver nanoparticles.

Organic ligands have the potential to contribute to the reduction potential, or lowest unoccupied molecular orbital (LUMO) energy, of semiconductor nanocrystals. Rationally introducing small, strongly binding, electron-donating ligands should enable improvement in the open circuit potential of hybrid organic/inorganic solar cells by raising the LUMO energy level of the nanocrystal acceptor phase and thereby increasing the energy offset from the polymer highest occupied molecular orbital (HOMO). Hybrid organic/inorganic solar cells fabricated from blends of tert-butylthiol-treated CdSe nanocrystals and poly(3-hexylthiophene) (P3HT) achieved power conversion efficiencies of 1.9%. Compared to devices made from pyridine-treated and nonligand exchanged CdSe, the thiol-treated CdSe nanocrystals are found to consistently exhibit the highest open circuit potentials with VOC = 0.80 V. Electrochemical determination of LUMO levels using cyclic voltammetry and spectroelectrochemistry suggest that the thiol-treated CdSe nanocrystals possess the highest lying LUMO of the three, which translates to the highest open circuit potential. Steady-state and time-resolved photoluminescence quenching experiments on P3HT:CdSe films provide insight into how the thiol-treated CdSe nanocrystals also achieve greater current densities in devices relative to pyridine-treated nanocrystals, which are thought to contain a higher density of surface traps.Keywords: CdSe; hybrid solar cell; open-circuit potential; P3HT; semiconductor nanocrystal

As-prepared CdSe nanocrystals were ligand exchanged using tert-butylthiol, which yielded stable CdSe nanocrystal inks in the strong donor solvent tetramethylurea. The efficacy of ligand exchange was probed by thermogravimetric analysis (TGA) and FT-IR spectroscopy. By studying sequential exchanges of tetradecylphosphonic acid and then tert-butylthiol, TGA and energy dispersive X-ray spectroscopic evidence clearly demonstrated that the ligand exchange is essentially quantitative. The resulting tert-butylthiol-exchanged CdSe nanocrystals undergo facile thermal ligand expulsion (≤200 °C), which was studied by TGA-mass spectrometry. Mild thermal treatment of tert-butylthiol-exchanged CdSe nanocrystal films was found to induce loss of quantum confinement (as evidenced by UV–vis spectroscopy) and provided for increased electrochemical photocurrent, electron mobility, and film stability. Pyridine-exchanged CdSe nanocrystals were employed as a control system throughout to demonstrate the beneficial attributes of tert-butylthiol exchange; namely, lower organic content, better colloidal stability, improved interparticle coupling, and vastly increased electrochemical photocurrent response upon illumination.

A new wurtzite phase of copper tin selenide (CTSe) was discovered, and the resulting nanocrystals were synthesized via a facile solution-phase method. The wurtzite CTSe nanocrystals were synthesized with dodecylamine and 1-dodecanethiol as coordinating solvents and di-tert-butyl diselenide (tBu2Se2) as the selenium source. Specific reaction control (i.e., a combination of 1-dodecanethiol with tBu2Se2) was proven to be critical in order to obtain this new phase of CTSe, which was verified by powder X-ray diffraction and selected area electron diffraction. The wurtzite CTSe nanocrystals possess an optical and electrochemical band gap of 1.7 eV and display an electrochemical photoresponse indicative of a p-type semiconductor.

A systematic investigation of the effects of hydrolytic conditions on the development of PbTiO3 (PTO) from amorphous metal–organic matrices is reported. Metal–organic matrices were obtained using a novel hydrolytic approach which relies on the kinetically controlled delivery of water vapor at the gas–liquid interface of a Pb–Ti alkoxide precursor. Crystallization was induced via standard thermal treatment and followed using X-ray diffraction, visible Raman spectroscopy, and thermal analysis. It was found that the mechanism of the amorphous-to-crystalline phase transition is controlled by the rate and extent of hydrolysis and polycondensation of the Pb–Ti alkoxide: faster and extended hydrolysis favors an amorphous-to-pyrochlore-to-perovskite transition, whereas slower and less extended hydrolysis favors a direct amorphous-to-perovskite transition. The rate and extent of hydrolysis were found to have a significant impact on the magnitude of the tetragonal distortion of the perovskite unit cell as well. Optimization of hydrolytic conditions allowed for well-crystallized, phase pure, tetragonal PTO to be obtained at temperatures as low as 500 °C via a direct amorphous-to-perovskite phase transition. Differences observed in the mechanism of perovskite phase formation are explained in terms of the differential dependence of the dynamics of lead and titanium atoms on hydrolytic conditions, the former being significantly more affected than the latter. Because long-range redistribution of lead atoms is the rate-determining step of the perovskite phase formation, this finding has implications for the design of metal–organic precursors and hydrolytic approaches targeting the preparation of lead-containing functional perovskite oxides.Keywords: amorphous; crystalline; PbTiO3; sol−gel; vapor diffusion;

The incorporation of colloidal semiconductor nanocrystals into the photoabsorbant material of photovoltaic devices may reduce the production costs of solar cells since nanocrystals can be readily synthesized on a large scale and are solution processable. While the lead chalcogenide IV–VI nanocrystals have been widely studied in a variety of photovoltaic devices, concerns over the toxicity of lead have motivated the exploration of less toxic materials. This has led to the exploration of tin and germanium monochalcogenide IV–VI semiconductors, both of which are made up of earth abundant elements and possess properties similar to the lead chalcogenides. This feature article highlights recent efforts made towards achieving synthetic control over nanocrystal size and morphology of the non-lead containing IV–VI monochalcogenides (i.e., SnS, SnSe, SnTe, GeS and GeSe) and their application toward photovoltaic devices.

The photolytic decomposition of triphenylbismuth and di-tert-butyl diselenide under aqueous micellar conditions yields 5-nm bismuth selenide nanocrystals of the BiSe stoichiometry. This is the first example of the bismuth-rich BiSe phase being prepared in a well-dispersed colloidal nanocrystal form.

Nanocrystals of phase-pure tin(II) selenide (SnSe) were synthesized via a solution-phase route employing stoichiometric amounts of di-tert-butyl diselenide as a novel and facile selenium source. The direct band gap of the resulting nanocrystals (Eg = 1.71 eV) is significantly blue-shifted relative to the bulk value (Eg = 1.30 eV), a likely consequence of quantum confinement resulting from the relatively small average diameter of the nanocrystals (μD < 20 nm). Preliminary solar cell devices incorporating SnSe nanocrystals into a poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] matrix demonstrate a significant enhancement in quantum efficiency and short-circuit current density, suggesting that this earth-abundant material could be a valuable component in future photovoltaic devices.

The very low-temperature synthesis (20–80 °C) of sub-15 nm BaxSr1−xTiO3 (0 ≤ x ≤ 1) nanocrystals and characterization of their dielectric properties as a function of composition are reported. A series of BaxSr1−xTiO3 nanocrystals were synthesized under ultrabenign conditions (i.e., low temperatures, ambient pressure and neutral pH) using a vapor diffusion sol–gel technique, whereby water is slowly diffused into a mixture of bimetallic alkoxides to yield the solid-solution nanocrystals in quantitative yield on the gram scale. The unsintered 12 nm Ba0.69Sr0.31TiO3 nanocrystals synthesized at 20 °C possess a maximized dielectric constant (ε′ = 341 at 1 kHz) for the solid solution series, and is more than an order of magnitude greater than the dielectric constant for SrTiO3 (ε′ = 11.0 at 1 kHz). The observed non-monotonic dependence of the dielectric constant on solid solution composition for these small nanocrystals is consistent with theoretical and empirical studies for bulk BaxSr1−xTiO3 ceramics, proving this dielectric effect holds for small nanocrystals.

We report on the activity of fullerene-supported OsO4 catalysts in the achiral dihydroxylation of olefins using N-methylmorpholine N-oxide as co-oxidant. The fullerene-supported OsO4 catalysts can selectively dihydroxylate olefins with conversions up to 95% after 48 h without leaching, and the catalysts can be recovered and recycled several times.

Well-defined tellurium nanorods have been prepared by the photolysis of tBu2Te2 in an aqueous micellar system incorporating dodecanethiol as an auxiliary morphology-directing agent.

Single crystalline, sub-15 nm BaZrxTi1−xO3 (0 ≤ x ≤ 1) nanocrystals were synthesized at room temperature via the vapor diffusion sol–gel method. As-prepared nanocrystals exhibit noncentrosymmetric regions whose volume fraction increases significantly upon substitution of small amounts of Zr4+ for Ti4+ and reaches a maximum for substitution levels ranging from 10 to 20 mol%.

Despite their extremely low solubility in most solvents, hexagonal grey selenium and tellurium are shown to be remarkably soluble in binary mixtures of thiols and ethylenediamine (en) at room temperature and ambient pressure. A 1:4 vol/vol mixture of ethanethiol (EtSH) and en gave saturated solutions of 38 and 9.3 wt% for grey selenium and tellurium, respectively. Crystalline and phase-pure chalcogen is easily recovered from solution by drying and mild heat treatment at 250 °C (for selenium) or evaporation at room temperature (for tellurium). To demonstrate utility for these dissolved chalcogens, it was shown that elemental antimony readily reacts with the dissolved selenium to give a stable, solution processable Sb–Se precursor solution. In the same way, elemental tin reacts with the dissolved tellurium to generate a Sn–Te precursor solution. Upon solution deposition and heat treatment to 250 °C, these precursor solutions yielded crystalline Sb2Se3 and SnTe.

Hybrid solar cells with tert-butylthiol exchanged CdSe multipod acceptors and novel semi-random P3HTT-DPP and alternating PCDTBT copolymer donors were studied, giving high performance devices with power conversion efficiencies >3%.

Colloidally synthesized quantum dots of CsPbBr3 are highly promising for light-emitting applications. Previous reports based on benchtop diffraction conflict as to the crystal structure of CsPbBr3 quantum dots. We present X-ray diffraction and PDF analysis of X-ray total scattering data that indicate that the crystal structure is unequivocally orthorhombic (Pnma).

Well-defined tellurium nanorods have been prepared by the photolysis of tBu2Te2 in an aqueous micellar system incorporating dodecanethiol as an auxiliary morphology-directing agent.

The vapor diffusion sol–gel (VDSG) method was employed for the room-temperature synthesis of ∼10 nm, aliovalently doped 0.4, 0.8, and 1.6 mol% La:BaTiO3 and 0.4, 0.6, and 1.2 mol% Dy:BaTiO3 nanocrystals. Maximum ensemble relative permittivities of 176 and 208 were observed in the 0.8 mol% La:BaTiO3 and the 1.2 mol% Dy:BaTiO3 nanocrystals, respectively, relative to 89 for undoped BaTiO3 (at 1 MHz, 25 °C) due to local disorder induced by aliovalent substitution.

Macroelectronics is a major focus in electronics research and is driven by large area applications such as flat panel displays and thin film solar cells. Innovations for these technologies, such as flexible substrates and mass production, will require efficient and affordable semiconductor processing. Low-temperature solution processing offers mild deposition methods, inexpensive processing equipment, and the possibility of high-throughput processing. In recent years, the discovery that binary “alkahest” mixtures of ethylenediamine and short chain thiols possess the ability to dissolve bulk inorganic materials to yield molecular inks has lead to the wide study of such systems and the straightforward recovery of phase pure crystalline chalcogenide thin films upon solution processing and mild annealing of the inks. In this review, we recount the work that has been done toward elucidating the scope of this method for the solution processing of inorganic materials for use in applications such as photovoltaic devices, electrocatalysts, photodetectors, thermoelectrics, and nanocrystal ligand exchange. We also take stock of the wide range of bulk materials that can be used as soluble precursors, and discuss the work that has been done to reveal the nature of the dissolved species. This method has provided a vast toolbox of over 65 bulk precursors, which can be utilized to develop new routes to functional chalcogenide materials. Future studies in this area should work toward a better understanding of the mechanisms involved in the dissolution and recovery of bulk materials, as well as broadening the scope of soluble precursors and recoverable functional materials for innovative applications.

A series of Eu3+-, Tb3+-, and Tm3+-doped CaWO4 phosphor nanocrystals have been synthesized under benign conditions using the vapor diffusion sol–gel method. The high degree of synthetic flexibility inherent to this approach has enabled the synthesis of a CaWO4:(Eu,Tb) dual-sensitized white light emitting nanocrystal phosphor upon commercial UV excitation at 366 nm with a long lifetime exceeding 1 ms.

This Perspective reviews our recent efforts towards the low-temperature synthesis of complex perovskite oxide ABO3 (A = Sr, Ba; B = Ti, Zr) nanocrystals using the vapor diffusion sol–gel method and the determination of their room-temperature crystal structure. From a synthetic standpoint, emphasis is placed on demonstrating the ability of the vapor diffusion sol–gel approach to yield compositionally complex nanocrystals at low temperatures and atmospheric pressure without the need for postsynthetic heat treatment to achieve a crystalline and phase-pure oxide product. The ability to successfully achieve this is illustrated using Ba1−xSrxTi1−yZryO3 (0 ≤ x ≤ 1, 0 ≤ y ≤ 1) and Eu3+-doped Ba(Ti,Zr)O3 nanocrystals as examples. From the standpoint of the structural analysis, emphasis is placed on highlighting how multiple and complementary spectroscopic techniques that probe atomic correlations in short (≤1 nm), intermediate (∼1–3 nm), and long (≥3 nm) length scales can be employed to gain insight into the atomic structure of the resulting nanocrystals. Examples that clearly illustrate this strategy of structural characterization are the investigation of the size- and composition-dependence of the structure of polar nanoregions in sub-10 nm BaTiO3 and sub-20 nm Ba1−xSrxTiO3 and BaTi1−yZryO3 nanocrystals, and the investigation of the distribution of rare earth dopants in sub-15 nm Eu3+:BaTiO3 nanocrystals.

BaxSr1−xTiO3 perovskite nanocrystals, prepared by the vapor diffusion sol–gel method and characterized by state of the art surface techniques, display significantly different O–H stretching frequencies and adsorption properties towards CO2 as a function of the alkaline earth composition (Ba vs. Sr). The difference of properties can be associated with the more basic nature of BaO-rich than SrO-rich surfaces.

We report on the activity of fullerene-supported OsO4 catalysts in the achiral dihydroxylation of olefins using N-methylmorpholine N-oxide as co-oxidant. The fullerene-supported OsO4 catalysts can selectively dihydroxylate olefins with conversions up to 95% after 48 h without leaching, and the catalysts can be recovered and recycled several times.

The 1,2,3,4-thiatriazole-5-thiolate anion (TTT−) was found to be a strongly binding ligand for CdSe nanocrystals, quantitatively exchanging various long-chain ligands to yield stable colloidal suspensions in common polar solvents. The TTT− ligand thermolyzes at <100 °C to produce thiocyanate in situ, resulting in reduced quantum confinement in nanocrystal films. CdSe(TTT) possesses far higher colloidal stability than CdSe(SCN), and that, together with the facile synthesis of TTT−, implies that this is a useful ligand for nanocrystal applications as a masked thiocyanate.

The very low-temperature synthesis (20–80 °C) of sub-15 nm BaxSr1−xTiO3 (0 ≤ x ≤ 1) nanocrystals and characterization of their dielectric properties as a function of composition are reported. A series of BaxSr1−xTiO3 nanocrystals were synthesized under ultrabenign conditions (i.e., low temperatures, ambient pressure and neutral pH) using a vapor diffusion sol–gel technique, whereby water is slowly diffused into a mixture of bimetallic alkoxides to yield the solid-solution nanocrystals in quantitative yield on the gram scale. The unsintered 12 nm Ba0.69Sr0.31TiO3 nanocrystals synthesized at 20 °C possess a maximized dielectric constant (ε′ = 341 at 1 kHz) for the solid solution series, and is more than an order of magnitude greater than the dielectric constant for SrTiO3 (ε′ = 11.0 at 1 kHz). The observed non-monotonic dependence of the dielectric constant on solid solution composition for these small nanocrystals is consistent with theoretical and empirical studies for bulk BaxSr1−xTiO3 ceramics, proving this dielectric effect holds for small nanocrystals.

Solution processing is a practical low-cost strategy for depositing semiconductor thin films. A binary thiol–amine solvent mixture dissolves bulk Cu2S and Sb2S3 under ambient conditions, allowing for solution deposition and low temperature recovery of CuSbS2. The resulting films of earth abundant CuSbS2 possess optoelectronic properties suitable for photovoltaic applications.

A series of compositionally complex scheelite-structured nanocrystals of the formula A1−xA′xWO4 (A = Ca, Sr, Ba) have been prepared under benign synthesis conditions using the vapor diffusion sol–gel method. Discrete nanocrystals with sub-20 nm mean diameters were obtained after kinetically controlled hydrolysis and polycondensation at room temperature, followed by composition-dependent thermal aging at or below 60 °C. Rietveld analysis of X-ray diffraction data and Raman spectroscopy verified the synthesis of continuous and phase-pure nanocrystal solid solutions across the entire composition space for A1−xA′xWO4, where 0 ≤ x ≤ 1. Elemental analysis by X-ray photoelectron and inductively coupled plasma-atomic emission spectroscopies demonstrated excellent agreement between the nominal and experimentally determined elemental stoichiometries, while energy dispersive X-ray spectroscopy illustrated good spatial elemental homogeneity within these nanocrystals synthesized under benign conditions.