Pt cocatalyst morphology on semiconductor nanorod photocatalysts enhances charge trapping and water reduction.

In photocatalysis, metal-semiconductor hybrid structures have been proposed for ideal photocatalytic systems. In this study, we investigate the effect of morphology and surface nature of Pt cocatalysts on photocatalytic hydrogen evolution activity in Pt-tipped CdSe nanorods. Three distinct morphologies of Pt cocatalysts were synthesized and employed as visible light photocatalysts. The rough tips exhibit the highest activity, followed by the round and cubic tips. Kinetic investigations using transient absorption spectroscopy reveal that the cubic tips exhibit lower charge-separated states feasible for reacting with water and water reduction rates due to their defectless surface facets. In contrast, the rough tips show a similar charge-separation value but a two-fold higher surface reaction rate than the round tips, resulting in a significant enhancement of hydrogen evolution. These findings highlight the importance of rational design on metal cocatalysts in addition to the main semiconductor bodies for maximizing photocatalytic activities.

Convergent paired electrolysis for zinc-mediated diastereoselective cinnamylation of α-amino esters.

A paired electrochemical method is presented for the one-pot synthesis of γ,δ-unsaturated α-amino esters. The method involves the in situ generation of organozinc reagents through zinc chloride reduction on the nickel cathode and the TEMPO-mediated oxidation of amino esters on the carbon anode. The presence of an ester moiety in the amine substrate was found to be crucial for achieving high diastereoselectivity.

Shaping Copper Oxide Layers on Gold Nanoparticle Ensembles by Controlled Electrodeposition with Single Particle Scatterometry.

Electrodeposition of copper on gold nanoelectrode ensembles result in the formation of uniform copper oxide layers on individual nanoparticles. A linear sweep of voltammetric change induces three distinct morphologies dependent upon particle density. Ex situ imaging and in situ scatterometry at a single-particle level identifies multi-step electrochemical growth sequences that deviated from classical nucleation and growth pathways. In addition, the study demonstrated the possibility of synthesizing sophisticated structures based on the symmetry of nanoelectrodes. This result guides the nanoscale morphology control of electrode ensembles with potential application in electrocatalysis and sensing.

Grain Boundary-Rich Copper Nanocatalysts Generated from Metal-Organic Framework Nanoparticles for CO2 -to-C2+ Electroconversion.

Due to severe contemporary energy issues, generating C2+ products from electrochemical carbon dioxide reduction reactions (eCO2 RRs) gains much interest. It is known that the catalyst morphology and active surface structures are critical for product distributions and current densities. Herein, a synthetic protocol of nanoparticle morphology on copper metal-organic frameworks (n-Cu MOFs) is developed by adjusting growth kinetics with termination ligands. Nanoscale copper oxide aggregates composed of small particulates are yielded via calcining the Cu-MOF nanoparticles at a specific temperature. The resulting nanosized MOF-derived catalyst (n-MDC) exhibits Faradaic efficiencies toward ethylene and C2+ products of 63% and 81% at -1.01 V versus reversible hydrogen electrode (RHE) in neutral electrolytes. The catalyst also shows prolonged stability for up to 10 h. A partial current density toward C2+ products is significantly boosted to -255 mA cm-2 in an alkaline flow cell system. Comprehensive analyses reveal that the nanoparticle morphology of pristine Cu MOFs induces homogeneous decomposition of organic frameworks at a lower calcination temperature. It leads to evolving grain boundaries in a high density and preventing severe agglomeration of copper domains, the primary factors for improving eCO2 RR activity toward C2+ production.

Nanoparticle design and assembly for p-type metal oxide gas sensors.

Metal oxide semiconductors have wide band gaps with tailorable electrical properties and high stability, suitable for chemiresistive gas sensors. p-Type oxide semiconductors generally have less sensitivity than their n-type counterparts but provide unique functionality with low humidity dependence. Among various approaches to enhance the p-type characteristics, nanostructuring of active materials is essential to exhibit high sensing performances comparable to n-type materials. Moreover, p-n heterojunction formation can achieve superior sensitivity at low operating temperatures. The representative examples are hollow and urchin-like particles, mesoporous structures, and nanowire networks. These morphologies can generate abundant active surface sites with a high surface area and induce rapid gas diffusion and facile charge transport. For growing interests in environmental and healthcare monitoring, p-type oxide semiconductors and their heterojunctions with well-designed nanostructures gain much attention as advanced gas sensing materials for practical applications. In addition to precise nanostructure design, the combination with other strategies, e.g. light activation and multiple gas sensing analysis using sensor arrays will be able to fabricate the desired gas sensors with exclusive gas detection at ultra-low concentrations operating even at room temperature.

Bimetallic Gold-Silver Nanostructures Drive Low Overpotentials for Electrochemical Carbon Dioxide Reduction.

Alloy formation is an advanced approach to improve desired properties that the monoelements cannot achieve. Alloys are usually designed to tailor intrinsic natures or induce synergistic effects by combining materials with distinct properties. Indeed, unprecedented properties have emerged in many cases, superior to a simple sum of pure elements. Here, we present Au-Ag alloy nanostructures with prominent catalytic properties in an electrochemical carbon dioxide reduction reaction (eCO2RR). The Au-Ag hollow nanocubes are prepared by galvanic replacement of Au on Ag nanocubes. When the Au-to-Ag ratio is 1:1 (Au1Ag1), the alloy hollow nanocubes exhibit maximum Faradaic efficiencies of CO production in a wide potential range and high mass activity and CO current density superior to those of the bare metals. In particular, overpotentials are estimated to be similar to or lower than that of the Au catalyst under various standard metrics. Density functional theory calculations, machine learning, and a statistical consideration demonstrate that the optimal configuration of the *COOH intermediate is a bidentate coordination structure where C binds to Au and O binds to Ag. This active Au-Ag neighboring configuration has a maximum population and enhanced intrinsic catalytic activity on the Au1Ag1 surface among other Au-to-Ag compositions, in good agreement with the experimental results. Further application of Au1Ag1 to a membrane electrode assembly cell at neutral conditions shows enhanced CO Faradaic efficiency and current densities compared to Au or Ag nanocubes, indicating the possible extension of Au-Ag alloys to larger electrochemical systems. These results give a new insight into the synergistic roles of Au and Ag in the eCO2RR and offer a fresh direction toward a rational design of bimetallic catalysts at a practical scale.

Surface overgrowth on gold nanoparticles modulating high-energy facets for efficient electrochemical CO2 reduction.

Electrochemical CO2 reduction reaction (eCO2RR) has been considered one of the potential technologies to store electricity from renewable energy sources into chemical energy. For this aim, designing catalysts with high surface activities is critical for effective eCO2RR. In this study, we introduced a surface overgrowth method on stable Au icosahedrons to generate Au nanostars with large bumps. As a catalyst for eCO2RR, the Au nanostars exhibited a maximum faradaic efficiency (FE) of 98% and a mass activity of 138.9 A g-1 for CO production, where the latter was one of the highest activities among Au catalysts. Despite the deducted electrochemically active surface area per mass, the high-energy surfaces from overgrowth provided a 3.8-fold larger specific activity than the original Au icosahedral seeds, resulting in superior eCO2RR performances that outweigh the trade-off of size and shape in nanoparticles. The Au nanostars also represented prolonged stability due to the durability of high-energy facets. The characterization of surface morphology and density functional theory calculations revealed that predominant Au(321) facets on the Au nanostars effectively stabilized *COOH adsorbates, thus lowering the overpotential and improving the FE for CO production. This overgrowth method is simple and universal for various materials, which would be able to extend into a wide range of electrochemical catalysts.

Structural complexity induced by {110} blocking of cysteine in electrochemical copper deposition on silver nanocubes.

Morphology evolution into intricate structures at the nanoscale is hard to understand, but we can get critical information from the combination of ex situ and in situ spectroelectrochemical techniques. In this study, we investigated the structural complexity generated during electrochemical Cu deposition on individual Ag nanocubes, which was driven by surface regulating cysteine molecules. During the deposition process, selective nucleation occurred on the Ag nanocubes by underpotential deposition, and then sequential structural evolution to a windmill morphology was observed. By adjusting the cysteine coverage, diverse structures were yielded, including face-overgrown, four-leaf clover, and octapod-like structures. Structural analysis along the crystallographic directions demonstrated that cysteine molecules exclusively blocked the growth along 110 and relatively promoted the growth along 100 and 111, respectively. Interestingly, all morphologies maintained a highly symmetric nature from the pristine cube, despite being diverse and sophisticated. These findings would be essential to design complex morphologies and achieve desirable optical and catalytic properties.

Characterization of heterogeneous aryl-Pd(II)-oxo clusters as active species for C-H arylation.

C-H arylation with heterogeneous palladium was investigated. The surface oxidation of Pd nanoparticles with a hypervalent iodine reagent, [Ph2I]BF4, resulted in the generation of Pd(ii)-aryl-oxo clusters, which were characterized as the crucial intermediate.

ZnO-CuO Core-Hollow Cube Nanostructures for Highly Sensitive Acetone Gas Sensors at the ppb Level.

This paper presents a ZnO-CuO p-n heterojunction chemiresistive sensor that comprises CuO hollow nanocubes attached to ZnO spherical cores as active materials. These ZnO-CuO core-hollow cube nanostructures exhibit a remarkable response of 11.14 at 1 ppm acetone and 200 °C, which is a superior result to those reported by other metal-oxide-based sensors. The response can be measured up to 40 ppb, and the limit of detection is estimated as 9 ppb. ZnO-CuO core-hollow cube nanostructures also present high selectivity toward acetone against other volatile organic compounds and demonstrate excellent stability for up to 40 days. The outstanding gas-sensing performance of the developed nanocubes is attributed to their uniform and unique morphology. Their core-shell-like structures allow the main charge transfer pathways to pass the interparticle p-p junctions, and the p-n junctions in each particle increase the sensitivity of the reactions to gas molecules. The small grain size and high surface area of each domain also enhance the surface gas adsorption.

Strategies for Designing Nanoparticles for Electro- and Photocatalytic CO2 Reduction.

Conversion of carbon dioxide (CO2 ) into value-added chemicals has attracted much attention because it can not only resolve global warming issues by reducing CO2 accumulation in the atmosphere, but also produce renewable hydrocarbon fuels that are important feedstocks for the chemical industry. Among the diverse approaches reported, CO2 reduction via electro- and photocatalytic methods is at the center of topics due to potential engineering of reaction performance through rational design of catalyst features. In this Minireview, we highlight recent strategies for designing nanoparticles to maximize the reaction efficiency and selectivity; from a materials viewpoint, these strategies can provide critical information to guide future research directions.

Artificial Control of Cell Signaling Using a Photocleavable Cobalt(III)-Nitrosyl Complex.

Cells use gaseous molecules such as nitric oxide (NO) to transmit both intracellular and intercellular signals. In principle, the endogenous small molecules regulate physiological changes, but it is unclear how randomly diffusive molecules trigger and discriminate signaling programs. Herein, it is shown that gasotransmitters use time-dependent dynamics to discriminate the endogenous and exogenous inputs. For a real-time stimulation of cell signaling, we synthesized a photo-cleavable metal-nitrosyl complex, [CoIII (MDAP)(NO)(CH3 CN)]2+ (MDAP=N,N'-dimethyl-2,11-diaza[3,3](2,6)pyridinophane), which can stably deliver and selectively release NO with fine temporal resolution in the cytosol, and used this to study the extracellular signal-regulated kinases (ERKs), revealing how cells use both exogenous and endogenous NO to disentangle cellular responses. This technique can be to understand how diverse cellular signaling networks are dynamically interconnected and also to control drug delivery systems.

Branched Copper Oxide Nanoparticles Induce Highly Selective Ethylene Production by Electrochemical Carbon Dioxide Reduction.

For long-term storage of renewable energy, the electrochemical carbon dioxide reduction reaction (CO2RR) offers a promising option for converting electricity to permanent forms of chemical energy. In this work, we present highly selective ethylene production dependent upon the catalyst morphology using copper oxide nanoparticles. The branched CuO nanoparticles were synthesized and then deposited on conductive carbon materials. After activation, the major copper species changed to Cu+, and the resulting electrocatalyst exhibited a high Faradaic efficiency (FE) of ethylene reaching over 70% and a hydrogen FE of 30% without any byproducts in a neutral aqueous solution. The catalyst also showed high durability (up to 12 h) with the ethylene FE over 65%. Compared to cubic morphology, the initial branched copper oxide structure formed highly active domains with interfaces and junctions in-between during activation, which caused large surface area with high local pH leading to high selectivity and activity for ethylene production.

A feasible strategy to prepare quantum dot-incorporated carbon nanofibers as free-standing platforms.

Recently, quantum dots (QDs) have often garnered significant attention and have been employed for various applications. Nevertheless, most conventional devices utilize a glass substrate and/or brittle substrate, which is not compatible with next-generation wearable electronics. A suitable method for devising conductive and flexible free-standing platforms that can be combined with various kinds of QDs is thus in great need for next-generation wearable electronics. In this work, we introduce a universal and simple method to coat QDs on carbon nanofibers (CNFs) by a dip-coating process, where many kinds of QDs can be well decorated on the surface of CNFs. As one potential application among many, QD-coated CNFs were examined for their photocatalytic applications and characterization. As a result, it was found that the best performance of CdSe QD-coated CNFs for hydrogen production was 3.8 times higher than that of only QDs with the same 1 mg of QDs. This is an early report on fabricating various kinds of QD-coated CNFs, which can be extended to a myriad set of applications.

Single-Molecule Rotation for EGFR Conformational Dynamics in Live Cells.

Monitoring the dynamics of proteins in live cells on appropriate spatiotemporal scales may provide key information regarding long-standing questions in molecular and cellular regulatory mechanisms. However, tools capable of imaging the conformational changes over time have been elusive. Here, we present a single-molecule stroboscopic imaging probes by developing gyroscopic plasmonic nanoparticles, allowing for replication of protein-protein interactions and the conformational dynamics based on rotational and lateral velocities. This study fundamentally monitors the rotational motion of a membrane protein, epidermal growth factor receptor (EGFR), to decipher undiscovered structural dynamics in live cells without any molecular perturbations. This method offers a strategy to visualize assemblies and conformational changes, and provides unique insights into the mechanism underlying the molecular dynamics for receptors.

Nano-Protrusive Gold Nanoparticle-Hybridized Polymer Thin Film as a Sensitive, Multipatternable, and Antifouling Biosensor Platform.

Hybrid films consisting of anisotropic octahedral gold nanoparticles (AuNPs) and polymers had their surfaces functionalized and were immobilized on surface plasmon resonance (SPR) sensors for biomolecule detection. Specifically, carboxylated octahedral AuNPs (C-Oh-AuNPs) and poly(allylamine hydrochloride) (PAH) were assembled as ultrathin films by using a layer-by-layer process. The ionic strength generated from the functional groups of C-Oh-AuNP and PAH influenced the composition, its surface morphology, and the reactivity of the film toward further chemical reactions such as the synthesis of spherical AuNPs (S-AuNPs). We were thus able to control the size and the structure of the C-Oh-AuNP and S-AuNPs converted to nano-raspberry-shaped particles. This hierarchical AuNP hybrid film exhibits much more sensitive and stable detection of biomolecules than regular flat chip systems, and this result may be due to the SPR of the AuNP at its surface being able to markedly enhance the local optical field of the chip. The micropatterning of the hybrid coating was also studied by using a soft lithographic patterning method. We, in particular, worked on creating multiplex patterns having different combinations of shapes and fluorescent colors. We expect our hybrid coating system with multicode biomolecular arrays to be used as a powerful platform for biosensor applications.

Colloidal zinc oxide-copper(I) oxide nanocatalysts for selective aqueous photocatalytic carbon dioxide conversion into methane.

Developing catalytic systems with high efficiency and selectivity is a fundamental issue for photochemical carbon dioxide conversion. In particular, rigorous control of the structure and morphology of photocatalysts is decisive for catalytic performance. Here, we report the synthesis of zinc oxide-copper(I) oxide hybrid nanoparticles as colloidal forms bearing copper(I) oxide nanocubes bound to zinc oxide spherical cores. The zinc oxide-copper(I) oxide nanoparticles behave as photocatalysts for the direct conversion of carbon dioxide to methane in an aqueous medium, under ambient pressure and temperature. The catalysts produce methane with an activity of 1080 µmol gcat-1 h-1, a quantum yield of 1.5% and a selectivity for methane of >99%. The catalytic ability of the zinc oxide-copper(I) oxide hybrid catalyst is attributed to excellent band alignment of the zinc-oxide and copper(I) oxide domains, few surface defects which reduce defect-induced charge recombination and enhance electron transfer to the reagents, and a high-surface area colloidal morphology.

Engineering Reaction Kinetics by Tailoring the Metal Tips of Metal-Semiconductor Nanodumbbells.

Semiconductor-metal hybrid nanostructures are one of the best model catalysts for understanding photocatalytic hydrogen generation. To investigate the optimal structure of metal cocatalysts, metal-CdSe-metal nanodumbbells were synthesized with three distinct sets of metal tips, Pt-CdSe-Pt, Au-CdSe-Au, and Au-CdSe-Pt. Photoelectrochemical responses and transient absorption spectra showed that the competition between the charge recombination at the metal-CdSe interface and the water reduction on the metal surface is a detrimental factor for the apparent hydrogen evolution rate. For instance, a large recombination rate (krec) at the Pt-CdSe interface limits the quantum yield of hydrogen generation despite a superior water reduction rate (kWR) on the Pt surface. To suppress the recombination process, Pt was selectively deposited onto the Au tips of Au-CdSe-Au nanodumbbells in which the krec was diminished at the Au-CdSe interface, and the large kWR was maintained on the Pt surface. As a result, the optimal structure of the Pt-coated Au-CdSe-Au nanodumbbells reached a quantum yield of 4.84%. These findings successfully demonstrate that the rational design of a metal cocatalyst and metal-semiconductor interface can additionally enhance the catalytic performance of the photochemical hydrogen generation reactions.

Directed C-H Activation and Tandem Cross-Coupling Reactions Using Palladium Nanocatalysts with Controlled Oxidation.

Controlled oxidation of palladium nanoparticles provided high-valent PdIV oxo-clusters which efficiently promote directed C-H halogenation reactions. In addition, palladium nanoparticles can undergo changes in oxidation states to provide both high-valent PdIV and low-valent Pd0 species within one system, and thus a tandem reaction of C-H halogenation and cross-coupling (C-N, C-C, and C-S bond formation) was successfully established.

Preparation and phase transition of FeOOH nanorods: strain effects on catalytic water oxidation.

The evolution of the phase and morphology of FeOOH nanorods prepared by a hydrothermal method is studied via X-ray diffraction (XRD) and in situ transmission electron microscopy. The FeOOH nanorod with a tetragonal structure (ß-FeOOH) is gradually converted into a rhombohedral Fe2O3 nanorod by a simple thermal treatment. The existence of an intermediate FeOOH structure with high lattice strains during the phase transition is identified by Rietveld analysis using XRD. The electrochemical properties of the nanorods are investigated based on the crystal phases to elucidate their relative catalytic activities. The strained-FeOOH nanorods exhibited enhanced catalytic water oxidation activity and stability. Typically, the strained-FeOOH nanorods showed high electrochemical stability under neutral conditions, while tetragonal FeOOH nanorods under the same conditions showed rapid deactivation for water oxidation reaction.