Search

Summary Controllable assembly of molecular and nanoscale building blocks into uniform superstructures up to bulk dimensions remains a key challenge in the next phase of nanotechnology development. Here, we report the self-assembly of superstructures at all scales by taking advantage of the partial miscibility of water and 1-butanol to generate transient aqueous emulsion droplets that can encapsulate the target materials and introduce them into template holes. Further diffusion of water into 1-butanol depletes the emulsion droplets, assembling the building blocks into one well-defined superstructure in each hole. Superstructuring of various types and shapes of nanoparticles, biomolecules, and inorganic compounds could be achieved without the need for surfactants and chemical modifications. The versatility, scalability, low-cost, and accurate positioning are crucial advantages for the future development of advanced precision manufacturing.

Summary Great interest has recently emerged in the development of quantum dots (QDs) that are capable of direct white-light emission for solid-state lighting. The conventional synthesis routes often involve surface modification and ligand displacement, which usually lead to undesired QD aggregation and fluorescence quenching. Here, we report a new strategy to synthesize QDs (ZnS, CdS, CdTe, and CsPbBrxI3-x) directly in colloidal SiO2 to produce QDs@SiO2 composites, displaying direct white-light emissions. By taking advantage of the NH4+ trapped inside the silica colloids, we introduce metal cations through ion-exchange reactions into the microporous network of silica and then produce QDs directly within the silica colloids. This “trapped-NH4+” strategy represents a new platform for the synthesis of novel functional nanocomposites by allowing convenient incorporation of various nanoparticles into sol-gel-derived colloidal matrices.

Oxygen evolution reaction (OER) plays a vital role in green technologies including water splitting and carbon dioxide reduction. As promising alternatives of noble metals–based OER electrocatalysts such as IrO2 and RuO2, the OER performance of nanostructured Co-based materials is far from satisfactory. In this report, a coordination-assisted etching strategy is proposed to incorporate iron into cobalt oxide porous nanoplates, producing composite nanostructures with optimized Co:Fe ratio that manifest significantly enhanced OER performance (an overpotential of 304 mV at 10 mA/cm2 as well as a low Tafel slope of 38 mV/dec). The enhancement can be attributed to the modulated electronic structure of cobalt, favorable absorption energy of OER intermediates, and the formation of more oxygen vacancies. This work highlights the importance of rational integration of iron with cobalt for optimal electrocatalytic performance enabled by the coordination-assisted etching strategy, providing more opportunities for the design and synthesis of mixed metal electrocatalysts for energy conversion and storage.

All-inorganic metal halide perovskite (e.g., CsPbX3, X = Cl, Br, I) nanocrystals show excellent shape-dependent photophysical properties which have motivated the active exploration of new synthetic approaches for higher morphological complexity than those produced by current methods (cubes, plates, rods). Here, for the first time, we demonstrate that the transformation of Cs4PbBr6 to CsPbBr3 coupled with an overgrowth scheme can be exploited to produce CsPbBr3 dodecapods, each of which is composed of 12 well-defined branches. The critical step is the formation of cuboctahedral Cs4PbBr6 seeds in a Cs-rich environment induced by the faster dissolution of CsOAc than PbBr2. A phase transformation from Cs4PbBr6 to CsPbBr3 then leads to the growth of twelve branches from the twelve vertices, producing CsPbBr3 dodecapods with a high photoluminescence quantum yield (50%) and a narrow full width at half maximum (18 nm). We further demonstrate the production of dodecapods of CsPbX3 (X = Cl, I) NCs with tunable emission covering the full visible region (415–685 nm) through an anion exchange process. Furthermore, white light emitting diodes (WLEDs) fabricated with CsPbBr3 nanoflowers demonstrated a 135% color gamut of the National Television System Committee (NTSC) standard. This work not only adds a distinct new morphology to the CsPbX3 nanocrystal family but also sheds light on the fundamental understanding of the growth mechanism of these newly emerged functional materials.

The most common complication during pregnancy, gestational diabetes mellitus (GDM), can cause adverse pregnancy outcomes and result in the mother and infant having a higher risk of developing type 2 diabetes after pregnancy. However, existing therapies for GDM remain scant, with the most common being lifestyle intervention and appropriate insulin treatment. MOTS-c, a mitochondrial-derived peptide, can target skeletal muscle and enhance glucose metabolism. Here, we demonstrate that MOTS-c can be an effective treatment for GDM. A GDM mouse model was established by short term high-fat diet combined with low-dose streptozotocin (STZ) treatment while MOTS-c was administrated daily during pregnancy. GDM symptoms such as blood glucose and insulin levels, glucose and insulin tolerance, as well as reproductive outcomes were investigated. MOTS-c significantly alleviated hyperglycemia, improved insulin sensitivity and glucose tolerance, and reduced birth weight and the death of offspring induced by GDM. Similar to a previous study, MOTS-c also could activate insulin sensitivity in the skeletal muscle of GDM mice and elevate glucose uptake in vitro. In addition, we found that MOTS-c protects pancreatic β-cell from STZ-mediated injury. Taken together, our findings demonstrate that MOTS-c could be a promising strategy for the treatment of GDM.

Summary Advanced oxidation processes (AOPs) are widely proposed for treating persistent pollutants by the ⋅ OH radicals generated from H 2 O 2 decomposition. However, their broad applications in practical settings have been hampered by the low efficiency of H 2 O 2 decomposition. Here, we report that metal sulfides (MoS 2 , WS 2 , Cr 2 S 3 , CoS 2 , PbS, or ZnS) can serve as excellent co-catalysts to greatly increase the efficiency of H 2 O 2 decomposition and significantly decrease the required dosage of H 2 O 2 and Fe 2+ in AOPs. Unsaturated S atoms on the surface of metal sulfides can capture protons to form H 2 S and expose metallic active sites with reductive properties to accelerate the rate-limiting step of Fe 3+ /Fe 2+ conversion. The efficiency of AOPs involving co-catalysts can be further enhanced by visible-light illumination thanks to the sensitization of organic pollutants. This discovery is expected to drive great advances in the use of AOPs for large-scale practical applications such as environmental remediation.

Porous cobalt oxide nanoplates enriched with oxygen vacancies are synthesized using a ligand-assisted polyol reduction method. This method enables large-scale synthesis that offers superior uniformity, solution dispersity and controllable concentration of oxygen vacancies on surface. The large surface area of porous cobalt oxide nanoplates together with enriched oxygen vacancies provide more active sites, which promote faster exchange of intermediates and more efficient electron transfer. The as prepared cobalt oxide nanoplates manifest oxygen evolution reaction (OER) overpotential as low as 306 mV at 10 mA/cm2 in 1 M KOH, which is superior to the values of most reported Co-based electrocatalysts.

Anion exchange membrane water electrolysis (AEMWE) is considered the next generation of green hydrogen production method because it uses low-cost non-noble metal oxide electrocatalyst electrodes and can store high-purity hydrogen under high pressure. However, the commercialization of AEMWE with non-precious metal oxide electrocatalysts is challenging due to low electrocatalytic activity and durability. Overcoming the low kinetics caused by four-electron transfer is vital in addressing the low activity of non-noble metal oxide electrocatalysts for oxygen evolution reaction. This article overviews the synthesis methods and related techniques for various anode electrodes applied to AEMWE systems. We highlight effective strategies that have been developed to improve the performance and durability of the non-precious electrocatalysts and ensure the stable operation of AEMWE, followed by a critical perspective to encourage the development of this technology.

Summary Manipulating the growth mode of colloidal nanocrystals is of both fundamental interest and technological importance because it is often connected to the control of their shape, morphology, and physicochemical properties. In conventional wisdom, island growth during thin-film deposition is restricted to lattice-mismatched materials. Here, we show that deposition of Au on Au nanostructures (e.g., nanoplates, nanorods, and nanospheres) can produce separate Au islands on the seed surface with tunable size and density while preserving the original crystal structure. The island growth in the system is ascribed to the synergistic effect of fast redox kinetics and surface capping of large polymeric ligands. Decreasing the reaction rate or changing the capping ligands could readily transform the deposition of Au on Au nanostructures from island growth to layer-by-layer mode. We further take advantage of the dense hotspots of the islands-on-plate nanostructures and demonstrate their excellence in surface-enhanced Raman scattering detection.

Hexavalent chromium Cr(VI), a highly toxic oxyanion, widely occurs in drinking water supplies. This study designed and synthesized a new type of highly reductive TiO2 nanocrystals for photochemical Cr(VI) removal, via the thermal hydrolysis of TiCl4 in the presence of diethylene glycol (DEG). Surface analyses and hydroxyl radical measurements suggested that DEG was chemically bonded on TiO2 surface that resulted in an internal hole-scavenging effect and a high electron-releasing capacity, making it advantageous to conventional TiO2 materials. Upon UV irradiation, the synthesized TiO2 photocatalyst exhibited fast Cr(VI) reduction kinetics in diverse water chemical conditions. Fast elimination of Cr(VI) was achieved on a time scale of seconds in drinking water matrices. The removal of Cr(VI) by reductive TiO2 exhibited a three-stage kinetic behavior: an initial fast-reaction phase, a lag phase resulting from surface precipitation of Cr(OH)3(s), and a final reaction phase due to surface regeneration from oxidation-reduction induced ripening process. The lag phase disappeared in acidic conditions that prevented the formation of Cr(OH)3(s). The catalyst exhibited extremely high electron-releasing capacity that can be reused for multiple cycles of Cr(VI) removal in drinking water treatment.

Author(s): Ji, Jiahui; Aleisa, Rashed M; Duan, Huan; Zhang, Jinlong; Yin, Yadong; Xing, Mingyang

We prepared an ultrathin porous silica shell-coated Au-Ag alloy nanoparticle (AuAg@p-SiO2NP) and developed it as a novel alkyne-based surface-enhanced Raman scattering (SERS) nanoprobe for the ratiometric Raman imaging of exogenous and endogenous H2O2 in live cells. The AuAg@p-SiO2NPs functionalized with 4-mercaptophenylboronic acid (MPBA) and 4-mercaptophenylacetylene (MPAE, 1986 cm−1) as internal standard were first incubated with dopamine (DA) to incorporate the bridging molecules through the formation of borate bond between DA and MPBA on the surface of nanoparticle. Then, the signaling alkyne molecules of 3-(4-(phenylethynyl) benzylthio) propanoic acid (PEB, 2214 cm−1) were conjugated to the surface of nanoparticle through the formation of amide bond between the carboxyl group on the PEB and the amino group on the DA, forming the ratiometric SERS nanoprobe. In the presence of H2O2, the alkynyl on the PEB is released from the surface of the Au-Ag alloy nanoparticle due to the boronate-to-phenol switch, decreasing the Raman signal at 2214 cm−1 significantly. Since the Raman signal of MPAE at 1986 cm−1 remains unchanged, quantitative analysis of H2O2 concentration can be achieved based on the ratiometric value of I1986/I2214. Under the optimized conditions, the plot of the ratiometric value of I1986/I2214 versus the H2O2 concentration in the range from 0.12 to 8 μM revealed a good linear response with a detection limit of 52 nM based on a signal-to-noise ratio of S/N = 3. The porous SiO2-coated Au-Ag alloy nanoparticle provides a novel SERS substrate with excellent biocompatibility, high stability, and effective anti-interference ability. Together with the alkynyl derivatives as internal standard, the SERS nanoprobe reported here allows the ratiometric detection of H2O2 in live cells and can be further applied to quantify many other biomolecules by using different signaling agents.

A chemically etched CuCo-oxide (CE-CCO) electrode prepared by electrodeposition was used for oxygen evolution reaction electrocatalyst. Surface chemical etching of CuCo-oxide (CCO) introduced oxygen vacancies and thus increased electrical conductivity to promote oxygen generation. During practical applicability testing, when CE-CCO was used as the anode of an anion-exchange membrane water electrolyzer, enhanced oxygen evolution performance was observed (current density = 1390 mA/cm2 at 1.8 Vcell), which, among other reactions, was ascribed to the easy removal of O2 from the aerophobic electrode surface. In addition to featuring low mass transfer resistance even at high current density with substantial gas generation, the CE-CCO electrode featured remarkable durability, exhibiting stable performance over 3600 h under the conditions of continuous O2 evolution. Thus, this work shows that the performance of electrodeposited oxide catalysts can be enhanced by introducing oxygen vacancies, while the energy conversion efficiency of the corresponding water electrolysis systems can be increased by lowering mass transfer resistance via efficient gas removal and reactant supply.

A new gold–titania catalyst has been developed for cryogenic oxidations based on a yolk–shell nanoarchitecture. The synthesis of those structures involves the sequential deposition of a sacrificial silica layer and a titania shell around well-defined gold nanoparticles followed by removal of the silica via NaOH etching. The resulting catalyst contains an amorphous titania shell with sodium titanate and silicon impurities that proved critical for the cryogenic activity; removal of those via HCl treatment kills most of the catalytic conversion. Oxidation of carbon monoxide is possible with this Au@Void@TiO 2 catalyst at temperatures as low as 120 K, by a mechanism different than the one operative at room temperature that involves a weakly-adsorbed CO species with a C O stretching frequency of 2162 cm − 1 , possibly at Au–TiO 2 interfacial sites.

Composite nanostructures with well-defined characteristics are often advantageous catalysts for highly efficient photocatalytic processes. Here, we report the tailored synthesis of C@TiO2 yolk–shell nanostructures and their photocatalytic applications in the degradation of organic dyes. The conductive carbon core serves as an electron-sink to promote the separation of electron–hole pairs photo-excited in the TiO2 shell, improve their lifetime, and enhance the photocatalytic performance of the system. The yolk–shell nanostructures were synthesized through a sol–gel coating of TiO2 on resorcinol-formaldehyde (RF) resin spheres followed by silica-protected calcination and ultimately NaOH etching to remove the silica layer and produce C@TiO2 yolk–shell nanostructures. In order to improve the crystallinity of the TiO2 shell, post-processing including acid treatment and re-calcination was also carried out. The resulting yolk–shell structures have many desirable properties for photocatalytic applications including the existence of a conductive core, well-maintained structural integrity, uniform particle dimensions, favorable mesoscale porosity, tunable crystallinity, and controllable crystalline phase of TiO2. As a result, we have been able to optimize the structure and property of the composite photocatalysts and achieve superior photocatalytic performance to commercial P25-TiO2 catalysts.

Magnetically actuated liquid crystals are potential alternatives to conventional liquid crystal systems in many applications thanks to their advantages of electrodeless operation, remote control, and low cost. However, their practical uses face a major challenge, namely the strong optical absorption of the magnetic components, which are mostly iron oxide-based materials. Here, we overcome this challenge by developing a nanocomposite composed of rod-shaped cellulose microcrystals with magnetite nanoparticles attached to their surfaces. This design takes advantage of the optical transparency and birefringence of the cellulose microcrystals, as well as their anisotropic shape which allows their efficient orientational alignment when their surfaces are modified by magnetite nanoparticles. Only a minimum amount of magnetite nanoparticles is required to enable instant and reversible orientational control of the cellulose microcrystals, ensuring a high degree of transparency of the system. These unique nanocomposites can be fixed in a polymer matrix with defined orientations at different regions by combining magnetic alignment and photolithography processes, producing thin films that appear near-transparent under the illumination of normal light and display patterns with high contrast when sandwiched between cross polarizers. This work reveals the enormous potential of the magnetic assembly strategy and making it a promising candidate for anti-counterfeiting applications.

Colorimetric detection is important for various applications where instant and convenient read-out is needed. Because of their fascinating optical properties, plasmonic nanostructures have inspired numerous colorimetric detections for environmental contaminants, biomolecules, and pharmaceuticals. The underlying mechanism of these colorimetric sensors is that the introduction of analytes can alter the distance, spatial arrangement (orientation), size, morphology, or composition of plasmonic nanostructures, inducing distinguishable changes of spectra and color. In this review, we focus our discussion on the colorimetric detection involving anisotropic nanostructures such as nanorods, nanoplates, nanoflowers, nanobipyramids, nanoframes, and nanocubes, which exhibit many unique advantages compared to their isotropic counterparts. In addition to illustrating the design principles, sensing mechanisms, and applications of these anisotropic nanostructures-based colorimetric methods, we also discuss smart plasmonic sensors based on anisotropic nanomaterials that are used to detect external stimuli such as temperature, pH, light, magnetic field, and mechanical force.

Titanium dioxide (TiO2) is a promising negative electrode for sodium ion batteries (SIBs). Although TiO2 materials with amorphous (A-TiO2) and single-phase crystalline structures (C–TiO2) have been separately explored, the study to compare the fundamental electrochemistry of A-TiO2 and C–TiO2 is limited. In this work, we investigated A-TiO2 and C–TiO2 nanoparticles with identical chemical composition and morphology. C–TiO2 exhibits enhanced electrochemical performance than A-TiO2 in terms of rate capability and cycle life. Cyclic voltammetry (CV) analysis suggests reversible Na ion insertion/extraction in C–TiO2. However, such process is irreversible in the case of A-TiO2. The charge storage mechanisms in both samples were studied to show that diffusion-controlled intercalation process becomes significant in C–TiO2 sample. The C–TiO2 sample has a better Na+ diffusivity measured through the galvanostatic intermittent titration technique (GITT) compared to A-TiO2, which corroborates well with the rate capability study. Furthermore, the evolution of local structure of the TiO2 samples was analyzed by ex situ pair distribution function (PDF) to understand the variation in electrochemical properties. It reveals that the corner-shared Ti–Ti distance along Na ion diffusion pathway increases with the increase of crystallinity, leading to the expanded diffusion channels and therefore more active sites and faster diffusion.

Inspired by how chameleons change their skin color, Du and co-workers have developed a general biomimetic strategy for preparing smart photonic crystal actuators with the fast and reversible colorimetric response and programmable shape transformation.

A controlled sol–gel process has been developed to coat gold nanoparticles with a thin layer of titanium dioxide to produce Au@TiO 2 core–shell catalyst particles, which can be rendered crystalline via calcination at high temperatures. The Au weight percent can be controlled by repeating the coating process while decreasing the water content and core concentration, making it possible to systematically tune the shell thickness over a large range without the need for an excessive number of coating steps. The encapsulating TiO 2 shells protect the Au cores from sintering during processing, which makes it possible to investigate the effect of varying the processing conditions for the catalyst without altering the Au particle size. Catalysts with varying Au weight percents and corresponding shell thicknesses, as well as various calcination temperatures, were tested for their efficacy in the UV-driven reforming of ethanol to produce hydrogen. It was found that an Au weight percent of 0.731% was optimal, along with a calcination temperature of 600 °C, as these conditions produced a sufficiently low Au loading percent while still enabling diffusion of the solution to the core.

We present here our recent studies on the magnetic-field-guided assembly of colloidal matter. Starting from a brief introduction of the magnetic interactions exerted on colloidal nanostructures, we discuss how magnetic fields drive their assembly into one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) ordered structures. This principle is further demonstrated in the assembly of colloidal matter on macroscopic and microscopic magnetized patterns with defined field strengths and spatial distributions.

Summary In this article we review the current research activities on the fabrication of inorganic hollow nanostructures by using self-templating methods. We start with a brief introduction to the traditional template-based methods, including those using hard and soft templates. The concepts and applications of four types of newly developed self-templating approaches are then discussed in detail, including those involving the “surface-protected etching” strategy, Ostwald ripening, the Kirkendall effect, and the galvanic replacement. We finally conclude with a summary and our personal perspectives on the directions in which future work on this field might be focused.

We describe a modified polyol process for the synthesis of silver nanocrystals with uniform sizes ranging from several nanometers to ∼20 nm. The use of polyacrylic acid, in place of polyvinylpyrrolidone in the conventional polyol process, significantly limits the growth of silver nanocrystals, prevents the interparticle aggregation and fusion, and leads to a uniform population of samples with high water solubility. The size of nanocrystals can be conveniently tuned by controlling the reaction time, the concentration and chain length of the polymeric surfactants, and the reaction temperature. Uniform silver nanocrystals within sizes below 20 nm are preferred candidates over larger particles for applications where high density of optical absorption is required, for example, for photothermal conversion in cancer therapy.

This Letter describes the first synthesis of fivefold twinned nanorods and right bipyramids of palladium in an aqueous solution, with ascorbic acid as a reducing agent and in the presence of bromide. Like the silver system, these two types of nanostructures are derived from multiple and single twinned seeds, respectively. The ascorbic acid, bromide, and reaction temperature all play important roles in the synthesis.

Cation-exchange reaction between Ag{sup +} and Cd{sup 2+} was employed to transform single-crystal Ag{sub 2}Se nanowires into single-crystal CdSe nanowires as a case study of transformation from one chalcogenide to another one. The CdSe nanowires of {approx}30 nm in diameter had a wurtzite crystal structure and showed preservation of both the morphology and single crystallinity of the Ag{sub 2}Se nanowires. This synthetic route is useful in producing large quantities of CdSe nanowires with uniform diameters and exceptionally long lengths (>50 {micro}m).

Recent advances in microfabrication have allowed one to pattern the surface of a solid substrate with patches of different wettabilities on the micrometer-sized scale. These textured surfaces provide a well-characterized model system for studying the wetting and dewetting behaviors of liquids on heterogeneous surfaces. They also present a well-defined template to direct the self-organization of liquids on the surfaces of solid substrates, and to form patterned microstructures of various materials without using expensive, clean-room facilities. As demonstrated in a number of studies, the three-dimensional morphologies of the liquid microstructures could be easily controlled by changing the two-dimensional features patterned on the surface of a solid substrate. These demonstrations suggest that microfabrication based on surface patterning and selective wetting or dewetting will offer immediate advantages in applications such as fabrication of microreactor arrays and microfluidic devices, where a liquid (or solution) is the primary material to be patterned.

Zinc sulfide colloidal particles of small dimensions were produced in situ in aqueous solution by precipitating Zn2+ ions with homogeneously released S2− ions at room temperature, which were resulted from the decomposition of Na2S2O3 with (γ-irradiation. Several influence factors including absorbed dose, surfactant concentration and Na2S2O3 concentration were studied by recording UV–VIS spectra. ZnS nanoparticles approximately 3.6 nm in diameter were separated from the solution and characterized with X-ray diffraction and transmission electron microscope.

Polyacrylamide–silver nanocomposites are successfully prepared by irradiating the aqueous solution of AgNO 3 and acrylamide monomer with 60 Co γ -ray. The composites are found to contain nanometer silver particles with a narrow size distribution and a homogeneous dispersion. The existing of isopropanol (as a hydroxyl radical scavenger and chain transfer agent) in system affects the properties of both the dispersed phase and matrix of the nanocomposites. The fast-formed polymer chains probably play a key role in preventing the aggregation of silver particles which are reduced later.