Pt Single Atoms Supported on Defect Ceria as an Active and Stable Dual-Site Catalyst for Alkaline Hydrogen Evolution.

This work evaluates the feasibility of alkaline hydrogen evolution reaction (HER) using Pt single-atoms (1.0 wt %) on defect-rich ceria (Pt1/CeOx) as an active and stable dual-site catalyst. The catalyst displayed a low overpotential and a small Tafel slope in an alkaline medium. Moreover, Pt1/CeOx presented a high mass activity and excellent durability, competing with those of the commercial Pt/C (20 wt %). In this picture, the defective CeOx is active for water adsorption and dissociation to create H* intermediates, providing the first site where the reaction occurs. The H* intermediate species then migrate to adsorb and react on the Pt2+ isolated atoms, the site where H2 is formed and released. DFT calculations were also performed to obtain mechanistic insight on the Pt1/CeOx catalyst for the HER. The results indicate a new possibility to improve the state-of-the-art alkaline HER catalysts via a combined effect of the O vacancies on the ceria support and Pt2+ single atoms.

Mutual Information and Correlations across Topological Phase Transitions in Topologically Ordered Graphene Zigzag Nanoribbons.

Graphene zigzag nanoribbons, initially in a topologically ordered state, undergo a topological phase transition into crossover phases distinguished by quasi-topological order. We computed mutual information for both the topologically ordered phase and its crossover phases, revealing the following results: (i) In the topologically ordered phase, A-chirality carbon lines strongly entangle with B-chirality carbon lines on the opposite side of the zigzag ribbon. This entanglement persists but weakens in crossover phases. (ii) The upper zigzag edge entangles with non-edge lines of different chirality on the opposite side of the ribbon. (iii) Entanglement increases as more carbon lines are grouped together, regardless of the lines' chirality. No long-range entanglement was found in the symmetry-protected phase in the absence of disorder.

Living Cationic Ring-Opening Polymerization of Hetero Diels-Alder Adducts to Give Multifactor-Controlled and Fast-Photodegradable Vinyl Polymers.

Precise control of multiple structural parameters associated with vinyl polymers is important for producing materials with the desired properties and functions. While the development of living polymerization methods has provided a way to control the various structural parameters of vinyl polymers, the concomitant control of their sequence and regioregularity remains a challenging task. To overcome this challenge, herein, we report the living cationic ring-opening polymerization of hetero Diels-Alder adducts. The scalable and modular synthesis of the cyclic monomers was achieved by a one-step protocol using readily available vinyl precursors. Subsequently, living polymerization of the cyclic monomers was examined, allowing the synthesis of vinyl polymers while controlling multiple factors, including molecular weight, dispersity, alternating sequence, head-to-head regioregularity, and end-group functionality. The living characteristics of the developed method were further demonstrated by block copolymerization. The synthesized vinyl polymers exhibited unique thermal properties and underwent fast photodegradation even under sunlight.

Recent Advances in Diversity-Oriented Polymerization Using Cu-Catalyzed Multicomponent Reactions.

Diversification of polymer structures is important for imparting various properties and functions to polymers, so as to realize novel applications of these polymers. In this regard, diversity-oriented polymerization (DOP) is a powerful synthetic strategy for producing diverse and complex polymer structures. Multicomponent polymerization (MCP) is a key method for realizing DOP owing to its combinatorial features and high efficiency. Among the MCP methods, Cu-catalyzed MCP (Cu-MCP) has recently paved the way for DOP by overcoming the synthetic challenges of the previous MCP methods. Here the emergence and progress of Cu-MCP, its current challenges, and future perspectives are discussed.

Self-Catalytic Growth of Elementary Semiconductor Nanowires with Controlled Morphology and Crystallographic Orientation.

While the orientation-dependent properties of semiconductor nanowires have been theoretically predicted, their study has long been overlooked in many fields owing to the limits to controlling the crystallographic growth direction of nanowires (NWs). We present here the orientation-controlled growth of single-crystalline germanium (Ge) NWs using a self-catalytic low-pressure chemical vapor deposition process. By adjusting the growth temperature, the orientation of growth direction in GeNWs was selectively controlled to the ⟨110⟩, ⟨112⟩, or ⟨111⟩ directions on the same substrate. The NWs with different growth directions exhibit distinct morphological features, allowing control of the NW morphology from uniform NWs to nanoribbon structures. Significantly, the VLS-based self-catalytic growth of the ⟨111⟩ oriented GeNW suggests that NW growth is possible for single elementary materials even without an appropriate external catalyst. Furthermore, these findings could provide opportunities to investigate the orientation-dependent properties of semiconductor NWs.

Valorization of Click-Based Microporous Organic Polymer: Generation of Mesoionic Carbene-Rh Species for the Stereoselective Synthesis of Poly(arylacetylene)s.

This work reports the functionalization of azide-alkyne click-based microporous organic polymer (CMOP). The generation of triazolium salts and successive deprotonation induced mesoionic carbene species in hollow CMOP (H-CMOP). Rh(I) species could be coordinated to the mesoionic carbene species to form H-CMOP-Rh, showing excellent heterogeneous catalytic performance in the stereoselective polymerization of arylacetylenes.

A Rational Design of Highly Controlled Suzuki-Miyaura Catalyst-Transfer Polycondensation for Precision Synthesis of Polythiophenes and Their Block Copolymers: Marriage of Palladacycle Precatalysts with MIDA-Boronates.

Herein, we report a highly efficient Suzuki-Miyaura catalyst-transfer polycondensation (SCTP) of 3-alkylthiophenes using bench-stable but highly active Buchwald dialkylbiarylphospine Pd G3 precatalysts and N-methylimidodiacetic (MIDA)-boronate monomers. Initially, the feasibility of the catalyst-transfer process was examined by screening various dialkylbiarylphospine-Pd(0) species. After optimizing a small molecule model reaction, we identified both RuPhos and SPhos Pd G3 precatalysts as excellent catalyst systems for this purpose. On the basis of these model studies, SCTP was tested using either RuPhos or SPhos Pd G3 precatalyst, and 5-bromo-4- n-hexylthien-2-yl-pinacol-boronate. Poly(3-hexylthiophene) (P3HT) was produced with controlled molecular weight and narrow dispersity for a low degree of polymerization (DP) only, while attempts to synthesize P3HT having a higher DP with good control were unsuccessful. To improve the control, slowly hydrolyzed 5-bromo-4- n-hexylthien-2-yl-MIDA-boronate was introduced as a new monomer. As a result, P3HT and P3EHT (up to 17.6 kg/mol) were prepared with excellent control, narrow dispersity, and excellent yield (>90%). Detailed mechanistic investigation using 31P NMR and MALDI-TOF spectroscopy revealed that both fast initiation using Buchwald precatalysts and the suppression of protodeboronation due to the protected MIDA-boronate were crucial to achieve successful living polymerization of P3HT. In addition, a block copolymer of P3HT- b-P3EHT was prepared via SCTP by sequential addition of each MIDA-boronate monomer. Furthermore, the same block copolymer was synthesized by one-shot copolymerization for the first time by using fast propagating pinacol-boronate and slow propagating MIDA-boronate.

Endo and Exo Diels-Alder Adducts: Temperature-Tunable Building Blocks for Selective Chemical Functionalization.

The development and application of a novel endo furan-protected maleimide building block is reported. The endo isomer undergoes deprotection at temperatures ∼50 °C below the exo derivative. This enables a simple and powerful approach to quantitatively and selectively introduce functional maleimide groups via temperature modulation.

Enhanced luminescence of CsPbBr3 perovskite nanocrystals on stretchable templates with Au/SiO2 plasmonic nanoparticles.

We propose stretchable plasmonic templates of Au and Au/SiO2 nanoparticles (NPs) to improve the luminescence of CsPbBr3 perovskite nanocrystals (PNCs). These templates are highly flexible and consist of polymer-metal NP composites that facilitate the luminescence enhancement by localized surface plasmons (LSPs) due to coupling with metal NP. This template also prevents the degradation of carrier transport properties for perovskite light-emitting diodes by embedding metal NPs in polymer. The luminescence of PNC film on the template with Au NPs decreases by 21% compared to PNC films on the reference (polymer film without metal NPs), while it increases by 54% for the templates with Au/SiO2 NPs. The observed effects are explained by the luminescence enhancement due to coupling to LSPs formed by the Au/SiO2 NPs and by the prevalence of electron tunneling and dumping for Au NPs.

A Rhizavidin Monomer with Nearly Multimeric Avidin-Like Binding Stability Against Biotin Conjugates.

Developing a monomeric form of an avidin-like protein with highly stable biotin binding properties has been a major challenge in biotin-avidin linking technology. Here we report a monomeric avidin-like protein-enhanced monoavidin-with off-rates almost comparable to those of multimeric avidin proteins against various biotin conjugates. Enhanced monoavidin (eMA) was developed from naturally dimeric rhizavidin by optimally maintaining protein rigidity during monomerization and additionally shielding the bound biotin by diverse engineering of the surface residues. eMA allowed the monovalent and nonperturbing labeling of head-group-biotinylated lipids in bilayer membranes. In addition, we fabricated an unprecedented 24-meric avidin probe by fusing eMA to a multimeric cage protein. The 24-meric avidin and eMA were utilized to demonstrate how artificial clustering of cell-surface proteins greatly enhances the internalization rates of assembled proteins on live cells.

Device performance of inverted polymer solar cells with AgSiO(2) nanoparticles in active layer.

Localized surface plasmon mediated polymer solar cells (PSCs) were fabricated using the Ag/SiO(2) nanoparticles (NPs). The inverted PSC structure without poly (3,4-ethylenedioxythiophene) polystyrene sulfonate ( PEDOT: PSS) was prepared due to the efficient insertion of Ag/SiO(2) NPs in the vicinity of active layer, which led to an enhancement in photo-conversion efficiency (PCE). This enhancement mainly comes from the light scattering by the SiO(2) shell and the localized surface plasmon effect by the Ag core, but we also considered the structural issues such as the NP distribution, the swelling of the active layer and of the metal electrode.

A facile synthesis of fluorescent silver nanoclusters with human ferritin as a synthetic and interfacing ligand.

Water-soluble fluorescent silver nanoclusters (NCs) formed on biomolecule ligands have been extensively studied due to their great potential as new biocompatible fluorescent materials for biosensors. As synthetic ligands, proteins in particular can provide unique structures and functions to the assembled fluorescent silver clusters. A key challenge, however, is to develop appropriate protein ligands and synthetic approaches for cluster formation, especially using native aqueous solutions, to fully preserve the valuable properties of the protein templates. Here we report a human ferritin-templated synthesis of fluorescent silver NCs under neutral aqueous buffer conditions. The unique metal binding property of ferritin and an optimized silver ion reduction allowed us to produce highly stable fluorescent silver NCs that are steadily assembled in the cage-like ferritin proteins. The fluorescent clusters were also successfully assembled on genetically engineered ferritin with antibody-binding protein G. The resulting protein G-ferritin-silver NC complex fully retained the ferritin structure as well as the antibody binding ability. The present silver nanoclusters on ferritin (Ft-Ag NCs) also showed highly specific Cu(2+)-induced fluorescence quenching. By exploiting the large but stable nature of ferritin, we fabricated a highly robust and porous hydrogel sensor system for rapid Cu(2+) detection, where the Ft-Ag NCs were stably encapsulated in surface-bound hydrogels with large pore sizes. Our Ft-Ag NCs that are formed under native aqueous conditions will have great potential as a new fluorescent material with the high structural and functional diversities of ferritin.

Enhanced optical output performance in InGaN/GaN light-emitting diode embedded with SiO2nanoparticles.

We demonstrated the InGaN/GaN-based light-emitting diodes (LEDs) with SiO2 nanoparticles embedded in nanopillar GaN template. With the SiO2 nanoparticles placed between the GaN nanopillars, subsequent overgrowth of GaN layer started only on the exposed tips of the nanopillars and rapidly switched to the lateral growth mode. This resulted in a high quality GaN layer "sitting" on the nanopillars and the layer of pores formed over the SiO2 nanoparticles. For multi-quantum-well LEDs grown on top of such template, ~3 fold increase in optical output was observed compared to reference samples. The effect is attributed mainly to the improved light extraction efficiency due to additional scattering in the nanopillars-SiO2-pores portion of the structure, also to the increased internal quantum efficiency caused by a decreased dislocation density and relaxed strain due to the GaN nanopillars.

Engineering core-shell hollow-sphere Fe3O4@FeP@nitrogen-doped-carbon as an advanced bi-functional electrocatalyst for highly-efficient water splitting.

Given the rapidly increasing energy demand and environmental pollution, to achieve energy conservation and emission reduction, hydrogen production has emerged as a promising alternative to traditional fossil fuels because of its high gravimetric energy density, and renewable and environmentally friendly characteristics. Herein, a core-shell hollow-sphere Fe3O4@FeP@nitrogen-doped-carbon (labeled as H-Fe3O4@FeP@NC) with a dual-interface, novel morphology, and superior conductivity is prepared as an advanced bi-functional electrocatalyst for electrochemical overall water splitting using a collaborative strategy comprising of facile self-assembly and phosphating. The prepared catalyst exhibits superior electrocatalytic activity compared to H-Fe3O4@NC and H-Fe3O4 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Additionally, the overpotential of H-Fe3O4@FeP@NC for OER/HER (258/165 mV at 10 mA/cm2) is significantly lower than those of H-Fe3O4@NC (274/209 mV) and H-Fe3O4 (287/213 mV) at 10 mA/cm2. Meanwhile, the as-synthesized H-Fe3O4@FeP@NC, as an electrode pair, displays a low cell voltage of 1.69 V at 10 mA/cm2 and excellent stability after 100 h, indicating its practical application for overall water splitting. This work presents a practical and economical strategy toward the fabrication of catalyst for efficient water splitting and fuel cell.

Phase diagram and crossover phases of topologically ordered graphene zigzag nanoribbons: role of localization effects.

We computed the phase diagram of zigzag graphene nanoribbons as a function of on-site repulsion, doping, and disorder strength. The topologically ordered phase undergoes topological phase transitions into crossover phases, which are new disordered phases with non-universal topological entanglement entropy that exhibits significant variance. We explored the nature of non-local correlations in both the topologically ordered and crossover phases. In the presence of localization effects, strong on-site repulsion and/or doping weaken non-local correlations between the opposite zigzag edges of the topologically ordered phase. In one of the crossover phases, bothe-/2solitonic fractional charges and spin-charge separation were absent; however, charge-transfer correlations between the zigzag edges were possible. Another crossover phase contains solitonice-/2fractional charges but lacks charge transfer correlations. We also observed properties of non-topological, strongly disordered, and strongly repulsive phases. Each phase on the phase diagram exhibits a different zigzag-edge structure. Additionally, we investigated the tunneling of solitonic fractional charges under an applied voltage between the zigzag edges of undoped topologically ordered zigzag ribbons, and found that it may lead to a zero-bias tunneling anomaly.

Cu-catalyzed multicomponent polymerization to synthesize a library of poly(N-sulfonylamidines).

We report a versatile Cu-catalyzed multicomponent polymerization (MCP) technique that enables the synthesis of high-molecular-weight, defect-free poly(N-sulfonylamidines) from monomers of diynes, sulfonyl azides, and diamines. Through a series of optimizations, we discovered that the addition of excess triethylamine and the use of N,N'-dimethylformamide as a solvent are key factors to ensure efficient MCP. Formation of cyclic polyamidines was a side reaction during polymerization, but it was readily controlled by using diynes or diamines with long or rigid moieties. In addition, this polymerization is highly selective for three-component reactions over click reactions. The combination of the above factors enables the synthesis of high-molecular-weight polymers, which was challenging in previous MCPs. All three kinds of monomers (diynes, sulfonyl azides, and diamines) are readily accessible and stable under the reaction conditions, with various monomers undergoing successful polymerization regardless of their steric and electronic properties. Thus, we synthesized various high-molecular-weight, defect-free polyamidines from a broad range of monomers while overcoming the limitations of previous MCPs, such as low conversion and defects in the polymer structures.

Nanostar and nanonetwork crystals fabricated by in situ nanoparticlization of fully conjugated polythiophene diblock copolymers.

Nanostar and nanonetwork crystals were prepared from fully conjugated poly(3-(2-ethylhexyl)thiophene)-block-polythiophene (P3EHT-b-PT) via a simple INCP process. The structural conformation of the nanocrystals was investigated in detail, revealing that with an increase in the block length of PT, the morphology of the nanocrystals changed from nanospheres to nanorods, nanostars, and to nanonetworks.

Dislocation density dependent electroabsorption in epitaxial lateral overgrown InGaN/GaN quantum structures.

We study electroabsorption (EA) behavior of InGaN/GaN quantum structures grown using epitaxial lateral overgrowth (ELOG) in correlation with their dislocation density levels and in comparison to steady state and time-resolved photoluminescence measurements. The results reveal that ELOG structures with decreasing mask stripe widths exhibit stronger EA performance, with a maximum EA enhancement factor of 4.8 compared to the reference without ELOG. The analyses show that the EA performance follows similar trends with decreasing dislocation density as the essential parameters of the photoluminescence spectra (peak position, width and intensity) together with the photoluminescence lifetimes. While keeping the growth window widths constant, compared to photoluminescence behavior, however, EA surprisingly exhibits the largest performance variation, making EA the most sensitive to the mask stripe widths.

Improved photoluminescence efficiency in UV nanopillar light emitting diode structures by recovery of dry etching damage.

In this study, we have fabricated 375-nm-wavelength InGaN/AlInGaN nanopillar light emitting diodes (LED) structures on c-plane sapphire. A uniform and highly vertical nanopillar structure was fabricated using self-organized Ni/SiO2 nano-size mask by dry etching method. To minimize the dry etching damage, the samples were subjected to high temperature annealing with subsequent chemical passivation in KOH solution. Prior to annealing and passivation the UV nanopillar LEDs showed the photoluminescence (PL) efficiency about 2.5 times higher than conventional UV LED structures which is attributed to better light extraction efficiency and possibly some improvement of internal quantum efficiency due to partially relieved strain. Annealing alone further increased the PL efficiency by about 4.5 times compared to the conventional UV LEDs, while KOH passivation led to the overall PL efficiency improvement by more than 7 times. Combined results of Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) suggest that annealing decreases the number of lattice defects and relieves the strain in the surface region of the nanopillars whereas KOH treatment removes the surface oxide from nanopillar surface.

Quercetin mediated antimicrobial photodynamic treatment using blue light on Escherichia coli O157:H7 and Listeria monocytogenes.

Interest in using an antimicrobial photodynamic treatment (aPDT) for the microbial decontamination of food has been growing. In this study, quercetin, a substance found ubiquitously in plants, was used as a novel exogenous photosensitizer with 405 nm blue light (BL) for the aPDT on foodborne pathogens, and the inactivation mechanism was elucidated. The inactivation of Escherichia coli O157:H7 and Listeria monocytogenes in PBS solution by the quercetin and BL combination treatment reached a log reduction of 6.2 and more than 7.55 at 80 J/cm2 (68 min 21 s), respectively. When EDTA was added to investigate the reason for different resistance between two bacteria, the effect of aPDT was enhanced against E. coli O157:H7 but not L. monocytogenes. This result indicated that the lipopolysaccharide of Gram-negative bacteria operated as a protective barrier. It was experimentally demonstrated that quercetin generated the superoxide anion and hydrogen peroxide as the reactive oxygen species that oxidize and inactivate cell components. The damage to the bacterial cell membrane by aPDT was evaluated by propidium iodide, where the membrane integrity significantly (P < 0.05) decreased from 40 J/cm2 compared to control. In addition, DNA integrity of bacteria was significantly (P < 0.05) more decreased after aPDT than BL treatment. The inactivation results could be applied in liquid food industries for decontamination of foodborne pathogens, and the mechanisms data was potentially utilized for further studies about aPDT using quercetin.