Showing papers in "Nanoscale in 2018"

Characterization techniques for nanoparticles: comparison and complementarity upon studying nanoparticle properties

Abstract: Nanostructures have attracted huge interest as a rapidly growing class of materials for many applications. Several techniques have been used to characterize the size, crystal structure, elemental composition and a variety of other physical properties of nanoparticles. In several cases, there are physical properties that can be evaluated by more than one technique. Different strengths and limitations of each technique complicate the choice of the most suitable method, while often a combinatorial characterization approach is needed. In addition, given that the significance of nanoparticles in basic research and applications is constantly increasing, it is necessary that researchers from separate fields overcome the challenges in the reproducible and reliable characterization of nanomaterials, after their synthesis and further process (e.g. annealing) stages. The principal objective of this review is to summarize the present knowledge on the use, advances, advantages and weaknesses of a large number of experimental techniques that are available for the characterization of nanoparticles. Different characterization techniques are classified according to the concept/group of the technique used, the information they can provide, or the materials that they are destined for. We describe the main characteristics of the techniques and their operation principles and we give various examples of their use, presenting them in a comparative mode, when possible, in relation to the property studied in each case.

Gold nanoparticle-based colorimetric biosensors.

Abstract: Gold nanoparticles (AuNPs) provide excellent platforms for the development of colorimetric biosensors as they can be easily functionalised, displaying different colours depending on their size, shape and state of aggregation. In the last decade, a variety of biosensors have been developed to exploit the extent of colour changes as nano-particles (NPs) either aggregate or disperse, in the presence of analytes. Of critical importance to the design of these methods is that the behaviour of the systems has to be reproducible and predictable. Much has been accomplished in understanding the interactions between a variety of substrates and AuNPs, and how these interactions can be harnessed as colorimetric reporters in biosensors. However, despite these developments, only a few biosensors have been used in practice for the detection of analytes in biological samples. The transition from proof of concept to market biosensors requires extensive long-term reliability and shelf life testing, and modification of protocols and design features to make them safe and easy to use by the population at large. Developments in the next decade will see the adoption of user friendly biosensors for point-of-care and medical diagnosis as innovations are brought to improve the analytical performances and usability of the current designs. This review discusses the mechanisms, strategies, recent advances and perspectives for the use of AuNPs as colorimetric biosensors.

Plasmonic metal–semiconductor photocatalysts and photoelectrochemical cells: a review

Abstract: The incorporation of plasmonic metals into semiconductors is a promising route to improve the performance of photocatalysts and photoelectrochemical cells. This article summarizes the three major mechanisms of plasmonic energy transfer from a metal to a semiconductor, including light scattering/trapping, plasmon-induced resonance energy transfer (PIRET) and hot electron injection (also called direct electron transfer (DET)). It also discusses the rational design of plasmonic metal-semiconductor heterojunctions based on the underlying plasmonic energy transfer mechanisms. Moreover, this article highlights the applications of plasmonic photocatalysts and photoelectrochemical cells in solar water splitting, carbon dioxide reduction and environmental pollutant decomposition.

Synthesis of garlic skin-derived 3D hierarchical porous carbon for high-performance supercapacitors

Abstract: A three-dimensional hierarchical porous carbon is synthesized via a facile chemical activation route with garlic skin as the precursor and KOH as the activating agent. The as-obtained carbon presents a high specific surface area of 2818 m2 g−1 and a hierarchical porous architecture containing macroporous frameworks, mesopores (2–4 nm), and micropores (0.6–1.0 nm). As the electrode material for a supercapacitor, due to its unique interconnected porous structure, this garlic skin-derived carbon exhibits excellent electrochemical performance and cycling stability. At a current density of 0.5 A g−1, the capacitance is up to 427 F g−1 (162 F cm−3). Even at a high current density of 50 A g−1, the capacitance can be maintained to a high value of 315 F g−1 (120 F cm−3). After charging–discharging at a current density of 4.5 A g−1 for 5000 cycles, the capacitance retention is as high as 94%. The results suggest that this garlic skin-derived 3D hierarchical porous carbon is a promising electrode material for high-performance supercapacitors.

Technical challenges of working with extracellular vesicles

Abstract: Extracellular Vesicles (EVs) are gaining interest as central players in liquid biopsies, with potential applications in diagnosis, prognosis and therapeutic guidance in most pathological conditions. These nanosized particles transmit signals determined by their protein, lipid, nucleic acid and sugar content, and the unique molecular pattern of EVs dictates the type of signal to be transmitted to recipient cells. However, their small sizes and the limited quantities that can usually be obtained from patient-derived samples pose a number of challenges to their isolation, study and characterization. These challenges and some possible options to overcome them are discussed in this review.

In situ grown nickel selenide on graphene nanohybrid electrodes for high energy density asymmetric supercapacitors

Abstract: Nickel selenide (NiSe) nanoparticles uniformly supported on graphene nanosheets (G) to form NiSe-G nanohybrids were prepared by an in situ hydrothermal process. The uniform distribution of NiSe on graphene bestowed the NiSe-G nanohybrid with faster charge transport and diffusion along with abundant accessible electrochemical active sites. The synergistic effect between NiSe nanoparticles and graphene nanosheets for supercapacitor applications was systematically investigated for the first time. The freestanding NiSe-G nanohybrid electrode exhibited better electrochemical performance with a high specific capacitance of 1280 F g-1 at a current density of 1 A g-1 and a capacitance retention of 98% after 2500 cycles relative to that of NiSe nanoparticles. Furthermore, an asymmetric supercapacitor device assembled using the NiSe-G nanohybrid as the positive electrode, activated carbon as the negative electrode and an electrospun PVdF membrane containing 6 M KOH as both the separator and the electrolyte delivered a high energy density of 50.1 W h kg-1 and a power density of 816 W kg-1 at an extended operating voltage of 1.6 V. Thus, the NiSe-G nanohybrid can be used as a potential electrode material for high-performance supercapacitors.

Recent progress in transition metal phosphides with enhanced electrocatalysis for hydrogen evolution

Abstract: Increasing demand for hydrogen energy has boosted the exploration of inexpensive and effective catalysts. Transition metal phosphides (TMPs) have been proven as excellent catalysts for the hydrogen evolution reaction (HER). Very recently, the search for TMP-based catalysts has being mainly directed at enhanced electrocatalytic performance. Hence, a concluded guideline for enhancing HER activity is highly desired. In this mini review, we briefly summarize the most recent and instructive developments in the design of TMP-based catalysts with enhanced electrocatalysis for hydrogen evolution from composition and structure engineering strategies. These strategies and perspectives are also meaningful for designing other inexpensive and high-performance catalysts.

One-step synthesis of hollow C-NiCo2S4 nanostructures for high-performance supercapacitor electrodes.

Abstract: Carbon-containing NiCo2S4 hollow-nanoflake structures were fabricated by a one-step solvothermal method using CS2 as a single source for sulfidation and carbonization. The reaction mechanism for the hollow structure with carbon residues was explored based on the formation of a bis(dithiocarbamate)–metal complex and the Kirkendall effect during solvothermal synthesis. The NiCo2S4 nanoflake electrode exhibited a high specific capacitance of 1722 F g−1 (specific capacity 688.8 C g−1) at a current density of 1 A g−1 and an excellent cycling stability (capacity retention of 98.8% after 10 000 cycles). The as-fabricated asymmetric supercapacitor based on NiCo2S4 nanoflakes and activated carbon electrodes revealed a high energy density of 38.3 W h kg−1 and a high power density of 8.0 kW kg−1 with a capacitance retention of 91.5% and a coulombic efficiency of 95.6% after 5000 cycles, highlighting its great potential for practical supercapacitor applications.

Recent advances in nanomaterials for enhanced photothermal therapy of tumors.

Abstract: Nowadays, photothermal therapy (PTT) utilizing photothermal conversion agents (PTAs) to generate sufficient heat under near-infrared (NIR) light irradiation for tumor ablation has attracted extensive research attention. Despite the great advancement, the therapeutic efficacy of PTT in tumor treatment is still compromised by several obstacles, such as low photothermal conversion efficiency, poor stability of PTAs, inadequate tumor accumulation and cellular uptake, and thermal-resistance of tumors, as well as tumor recurrence and metastasis. In this review, we highlight recent advances in nanomaterials that focus on overcoming the above obstacles and thus enhancing the therapeutic outcome of PTT. PTAs with improved photothermal performance and modification strategies for efficient PTT are summarized, which are further classified into three main types, utilizing activatable PTAs, improving the local concentration of PTAs, and overcoming intrinsic drawbacks of PTT (e.g., heat shock responses). Furthermore, the limitations and challenges of nanomaterials for enhanced PTT are also discussed.

In vivo formation of protein corona on gold nanoparticles. The effect of their size and shape

Abstract: The efficacy of drug delivery and other nanomedicine-related therapies largely relies on the ability of nanoparticles to reach the target organ. However, when nanoparticles are injected into the bloodstream, their surface is instantly modified upon interaction with blood components, principally with proteins. It is well known that a dynamic and multi-layered protein structure is formed spontaneously on the nanoparticle upon contact with physiological media, which has been termed protein corona. Although several determinant factors involved in protein corona formation have been identified from in vitro studies, specific relationships between the nanomaterial synthetic identity and its ensuing biological identity under realistic in vivo conditions remain elusive. We present here a detailed study of in vivo protein corona formation after blood circulation of anisotropic gold nanoparticles (nanorods and nanostars). Plasmonic gold nanoparticles of different shapes and sizes were coated with polyethyleneglycol, intravenously administered in CD-1 mice and subsequently recovered. The results from gel electrophoresis and mass spectrometry analysis revealed the formation of complex protein coronas, as early as 10 minutes post-injection. The total amount of protein adsorbed onto the particle surface and the protein corona composition were found to be affected by both the particle size and shape.

Phosphorization boosts the capacitance of mixed metal nanosheet arrays for high performance supercapacitor electrodes.

Abstract: Binary transition metal phosphides hold immense potential as innovative electrode materials for constructing high-performance energy storage devices. Herein, porous binary nickel-cobalt phosphide (NiCoP) nanosheet arrays anchored on nickel foam (NF) were rationally designed as self-supported binder-free electrodes with high supercapacitance performance. Taking the combined advantages of compositional features and array architectures, the nickel foam supported NiCoP nanosheet array (NiCoP@NF) electrode possesses superior electrochemical performance in comparison with Ni-Co LDH@NF and NiCoO2@NF electrodes. The NiCoP@NF electrode shows an ultrahigh specific capacitance of 2143 F g-1 at 1 A g-1 and retained 1615 F g-1 even at 20 A g-1, showing excellent rate performance. Furthermore, a binder-free all-solid-state asymmetric supercapacitor device is designed, which exhibits a high energy density of 27 W h kg-1 at a power density of 647 W kg-1. The hierarchical binary nickel-cobalt phosphide nanosheet arrays hold great promise as advanced electrode materials for supercapacitors with high electrochemical performance.

Design of a porous cobalt sulfide nanosheet array on Ni foam from zeolitic imidazolate frameworks as an advanced electrode for supercapacitors

Abstract: Porous nanosheet-structured electrode materials are very attractive for the high efficiency storage of electrochemical energy. Herein, a porous cobalt sulfide nanosheet array on Ni foam (Co9S8-NSA/NF) is successfully fabricated by a facile method, which involves the uniform growth of 2D Co-based leaf-like zeolitic imidazole frameworks (Co-ZIF-L) on Ni foam followed by subsequent sulfurization with thioacetamide (TAA). Benefiting from the unique porous nanosheet array architecture and conductive substrate, the Co9S8-NSA/NF exhibits excellent electrochemical performance with a high capacitance (1098.8 F g-1 at 0.5 A g-1), good rate capacity (54.6% retention at 10 A g-1) and long-term stability (87.4% retention over 1000 cycles), when acted as a binder-free electrode for supercapacitors. Furthermore, an assembled asymmetric supercapacitor device using the as-fabricated Co9S8-NSA as the positive electrode and activated carbon (AC) as the negative electrode also exhibits a high energy density of 20.0 W h kg-1 at a high power density of 828.5 W kg-1. The method developed here can be extended to the construction of other structured metal (mono or mixed) sulfide electrode materials for more efficient energy storage.

Phase and composition controlled synthesis of cobalt sulfide hollow nanospheres for electrocatalytic water splitting.

Abstract: Developing cheap, highly efficient and stable electrocatalysts for both oxygen and hydrogen evolution reactions (OER and HER) is extremely meaningful to realize large-scale implementation of water splitting technology Herein, we report the phase and composition controlled synthesis of cobalt sulfide (CoSx) hollow nanospheres (HNSs) and their catalytic efficiencies for hydrogen and oxygen evolution reactions in alkaline media Three CoSx compounds, ie, Co9S8, Co3S4, and CoS2 HNSs, were precisely synthesized by simply adjusting the molar ratio of carbon disulfide to cobalt acetate using a facile solution-based strategy Electrochemical results reveal that the as-prepared CoS2 HNSs exhibit superior OER and HER catalytic performance to Co9S8 and Co3S4 HNSs in 10 M KOH, with overpotentials of 290 mV for the OER and 193 mV for the HER at 10 mA cm-2, and the corresponding Tafel slopes of 57 and 100 mV dec-1, respectively In addition, the CoS2 HNSs exhibit remarkable long-term catalytic durability, which is even superior to precious metal catalysts of RuO2 and Pt/C Moreover, an alkaline electrolyzer assembled using CoS2 HNSs as both anode and cathode materials can achieve 10 mA cm-2 at a low cell voltage of 154 V at 60 °C with a faradaic efficiency of 100% for overall water splitting Further analysis demonstrates that the surface morphology, crystallographic structure and coordination environment of Con+ active sites in combination determine the HER/OER activities in the synthesized binary CoSx series, which would provide insight into the rational design of transition metal chalcogenides for highly efficient hydrogen and oxygen-involved electrocatalysis

Multifunctional nanostructured electrocatalysts for energy conversion and storage: current status and perspectives.

Abstract: Electrocatalytic oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) have attracted widespread attention because of their important role in the application of various energy storage and conversion devices, such as fuel cells, metal-air batteries and water splitting devices. However, the sluggish kinetics of the HER/OER/ORR and their dependency on expensive noble metal catalysts (e.g., Pt) obstruct their large-scale application. Hence, the development of efficient and robust bifunctional or trifunctional electrocatalysts in nanodimension for both oxygen reduction/evolution and hydrogen evolution reactions is highly desired and challenging for their commercialization in renewable energy technologies. This review describes some recent developments in the discovery of bifunctional or trifunctional nanostructured catalysts with improved performances for application in rechargeable metal-air batteries and fuel cells. The role of the electronic structure and surface redox chemistry of nanocatalysts in the improvement of their performance for the ORR/OER/HER under an alkaline medium is highlighted and the associated reaction mechanisms developed in the recent literature are also summarized.

Preparation of MoS2/TiO2 based nanocomposites for photocatalysis and rechargeable batteries: progress, challenges, and perspective

Abstract: The rapidly increasing severity of the energy crisis and environmental degradation are stimulating the rapid development of photocatalysts and rechargeable lithium/sodium ion batteries. In particular, MoS2/TiO2 based nanocomposites show great potential and have been widely studied in the areas of both photocatalysis and rechargeable lithium/sodium ion batteries due to their superior combination properties. In addition to the low-cost, abundance, and high chemical stability of both MoS2 and TiO2, MoS2/TiO2 composites also show complementary advantages. These include the strong optical absorption of TiO2vs. the high catalytic activity of MoS2, which is promising for photocatalysis; and excellent safety and superior structural stability of TiO2vs. the high theoretic specific capacity and unique layered structure of MoS2, thus, these composites are exciting as anode materials. In this review, we first summarize the recent progress in MoS2/TiO2-based nanomaterials for applications in photocatalysis and rechargeable batteries. We highlight the synthesis, structure and mechanism of MoS2/TiO2-based nanomaterials. Then, advancements and strategies for improving the performance of these composites in photocatalytic degradation, hydrogen evolution, CO2 reduction, LIBs and SIBs are critically discussed. Finally, perspectives on existing challenges and probable opportunities for future exploration of MoS2/TiO2-based composites towards photocatalysis and rechargeable batteries are presented. We believe the present review would provide enriched information for a deeper understanding of MoS2/TiO2 composites and open avenues for the rational design of MoS2/TiO2 based composites for energy and environment-related applications.

Oxygen self-doped g-C3N4 with tunable electronic band structure for unprecedentedly enhanced photocatalytic performance.

Abstract: As a fascinating conjugated polymer, graphitic carbon nitride (g-C3N4) has attracted much attention for solving the worldwide energy shortage and environmental pollution. In this work, for the first time we report oxygen self-doping of solvothermally synthesized g-C3N4 nanospheres with tunable electronic band structure via ambient air exposure for unprecedentedly enhanced photocatalytic performance. Various measurements, such as XPS, Mott–Schottky plots, and density functional theory (DFT) calculations reveal that such oxygen doping can tune the intrinsic electronic state and band structure of g-C3N4via the formation of C–O–C bond. Our results show that the oxygen doping content can be controlled by the copolymerization of the precursors. As a consequence, the oxygen doped g-C3N4 shows excellent photocatalytic performance, with an RhB photodegradation rate of 0.249 min−1 and a hydrogen evolution rate of 3174 μmol h−1 g−1, >35 times and ∼4 times higher than that of conventional thermally made pure g-C3N4 (0.007 min−1 and 846 μmol h−1 g−1, respectively) under visible light. Our work introduces a new route for the rational design and fabrication of doping modified g-C3N4 photocatalyst for efficient degradation of organic pollutants and H2 production.

Lightweight, compressible and electrically conductive polyurethane sponges coated with synergistic multiwalled carbon nanotubes and graphene for piezoresistive sensors

Abstract: Lightweight, compressible and highly sensitive pressure/strain sensing materials are highly desirable for the development of health monitoring, wearable devices and artificial intelligence. Herein, a very simple, low-cost and solution-based approach is presented to fabricate versatile piezoresistive sensors based on conductive polyurethane (PU) sponges coated with synergistic multiwalled carbon nanotubes (MWCNTs) and graphene. These sensor materials are fabricated by convenient dip-coating layer-by-layer (LBL) electrostatic assembly followed by in situ reduction without using any complicated microfabrication processes. The resultant conductive MWCNT/RGO@PU sponges exhibit very low densities (0.027–0.064 g cm−3), outstanding compressibility (up to 75%) and high electrical conductivity benefiting from the porous PU sponges and synergistic conductive MWCNT/RGO structures. In addition, the MWCNT/RGO@PU sponges present larger relative resistance changes and superior sensing performances under external applied pressures (0–5.6 kPa) and a wide range of strains (0–75%) compared with the RGO@PU and MWCNT@PU sponges, due to the synergistic effect of multiple mechanisms: “disconnect–connect” transition of nanogaps, microcracks and fractured skeletons at low compression strain and compressive contact of the conductive skeletons at high compression strain. The electrical and piezoresistive properties of MWCNT/RGO@PU sponges are strongly associated with the dip-coating cycle, suspension concentration, and the applied pressure and strain. Fully functional applications of MWCNT/RGO@PU sponge-based piezoresistive sensors in lighting LED lamps and detecting human body movements are demonstrated, indicating their excellent potential for emerging applications such as health monitoring, wearable devices and artificial intelligence.

A flexible pressure sensor based on rGO/polyaniline wrapped sponge with tunable sensitivity for human motion detection.

Abstract: High-performance stretchable and wearable electronic skins (E-skins) with high sensitivity and a large sensing range are urgently required with the rapid development of the Internet of things and artificial intelligence. Herein, a reduced graphene oxide (rGO)/polyaniline wrapped sponge is prepared via rGO coating and the in situ synthesis of polyaniline nanowires (PANI NWs) on the backbones of sponge for the fabrication of pressure sensors. From the as-prepared flexible sensor, tunable sensitivity (0.042 to 0.152 kPa-1), wide working range (0-27 kPa), fast response (∼96 ms), high current output (∼300 μA at 1 V), frequency-dependent performance reliable repeatability (∼9000 cycle) and stable signal waveform output can be readily obtained. In addition to tiny physiological activities (voice recognition, swallowing, mouth opening, blowing and breath), robust human motions (finger bending, elbow movement and knee squatting-arising) can also be detected in real-time by the flexible sensors based on rGO/polyaniline wrapped sponge. All the results demonstrate that the flexible pressure sensor based on the functional-sponge is a promising candidate for healthcare monitoring and wearable circuitry in artificial intelligence.

Au25(SR)18: the captain of the great nanocluster ship

Abstract: Noble metal nanoclusters are in the intermediate state between discrete atoms and plasmonic nanoparticles and are of significance due to their atomically accurate structures, intriguing properties, and great potential for applications in various fields. In addition, the size-dependent properties of nanoclusters construct a platform for thoroughly researching the structure (composition)-property correlations, which is favorable for obtaining novel nanomaterials with enhanced physicochemical properties. Thus far, more than 100 species of nanoclusters (mono-metallic Au or Ag nanoclusters, and bi- or tri-metallic alloy nanoclusters) with crystal structures have been reported. Among these nanoclusters, Au25(SR)18—the brightest molecular star in the nanocluster field—is capable of revealing the past developments and prospecting the future of the nanoclusters. Since being successfully synthesized (in 1998, with a 20-year history) and structurally determined (in 2008, with a 10-year history), Au25(SR)18 has stimulated the interest of chemists as well as material scientists, due to the early discovery, easy preparation, high stability, and easy functionalization and application of this molecular star. In this review, the preparation methods, crystal structures, physicochemical properties, and practical applications of Au25(SR)18 are summarized. The properties of Au25(SR)18 range from optics and chirality to magnetism and electrochemistry, and the property-oriented applications include catalysis, chemical imaging, sensing, biological labeling, biomedicine and beyond. Furthermore, the research progress on the Ag-based M25(SR)18 counterpart (i.e., Ag25(SR)18) is included in this review due to its homologous composition, construction and optical absorption to its gold-counterpart Au25(SR)18. Moreover, the alloying methods, metal-exchange sites and property alternations based on the templated Au25(SR)18 are highlighted. Finally, some perspectives and challenges for the future research of the Au25(SR)18 nanocluster are proposed (also holding true for all members in the nanocluster field). This review is directed toward the broader scientific community interested in the metal nanocluster field, and hopefully opens up new horizons for scientists studying nanomaterials. This review is based on the publications available up to March 2018.

Ratiometric photoluminescence sensing based on Ti3C2 MXene quantum dots as an intracellular pH sensor

Abstract: Intracellular pH sensing is of importance and can be used as an indicator for monitoring the evolution of various diseases and the health of cells. Here, we developed a new class of surface-functionalized MXene quantum dots (QDs), Ti3C2, by the sonication cutting and hydrothermal approach and further explored their intracellular pH sensing. The functionalized Ti3C2 QDs exhibit bright excitation-dependent blue photoluminescence (PL) originating from the size effect and surface defects. Meanwhile, Ti3C2 QDs demonstrate a high PL response induced by the deprotonation of the surface defects. Furthermore, combining the highly pH sensitive Ti3C2 QDs with the pH insensitive [Ru(dpp)3]Cl2, we developed a ratiometric pH sensor to quantitatively monitor the intracellular pH values. These novel MXene quantum dots can serve as a promising platform for developing practical fluorescent nanosensors.

Binder-free 2D titanium carbide (MXene)/carbon nanotube composites for high-performance lithium-ion capacitors

Abstract: Two-dimensional (2D) MXenes have a very good application prospect in the field of electrochemical energy storage due to their metallic conductivity, high volumetric capacity, mechanical and thermal stability. Herein, we report the preparation of titanium carbide (Ti3C2Tx)/carbon nanotube (CNT) flexible self-supporting composite films by vacuum filtration. The CNTs can effectively prevent Ti3C2Tx from stacking and improve the electrochemical performance. The as-fabricated Ti3C2Tx/CNT film shows a high reversible capacity of 489 mA h g-1 at a current density of 50 mA g-1 together with good cycling performance. The full-cell lithium-ion capacitor (LIC) is assembled using the Ti3C2Tx/CNT film as the anode and activated carbon as the cathode. The LIC exhibits a high energy density of 67 Wh kg-1 (based on the total weight of the anode and the cathode), and a good capacity retention of 81.3% after 5000 cycles. These results suggest that Ti3C2Tx-CNT films are promising as anode materials for lithium ion capacitors.

Fabrication of hierarchical CoP nanosheet@microwire arrays via space-confined phosphidation toward high-efficiency water oxidation electrocatalysis under alkaline conditions

Abstract: In spite of recent advances in the synthesis of transition metal phosphide nanostructures, the simple fabrication of hierarchical arrays with more accessible active sites still remains a great challenge. In this Communication, we report a space-confined phosphidation strategy toward developing hierarchical CoP nanosheet@microwire arrays on nickel foam (CoP NS@MW/NF) using a Co(H2PO4)2·2H3PO4 microwire array as the precursor. The thermally stable nature of the anion in the precursor is key to hierarchical nanostructure formation. When used as a 3D electrode for water oxidation electrocatalysis, such CoP NS@MW/NF needs an overpotential as low as 296 mV to drive a geometrical catalytic current density of 100 mA cm−2 in 1.0 M KOH, outperforming all reported Co phosphide catalysts in alkaline media. This catalyst also shows superior long-term electrochemical durability, maintaining its activity for at least 65 h. This study offers us a general method for facile preparation of hierarchical arrays for applications.

3D printed scaffolds with gradient porosity based on a cellulose nanocrystal hydrogel

Abstract: 3-Dimensional (3D) printing provides a unique methodology for the customization of biomedical scaffolds with respect to size, shape, pore structure and pore orientation useful for tissue repair and regeneration. 3D printing was used to fabricate fully bio-based porous scaffolds of a double crosslinked interpenetrating polymer network (IPN) from a hydrogel ink of sodium alginate and gelatin (SA/G) reinforced with cellulose nanocrystals (CNCs). CNCs provided favorable rheological properties required for 3D printing. The 3D printed scaffolds were crosslinked sequentially via covalent and ionic reactions resulting in dimensionally stable hydrogel scaffolds with pore sizes of 80–2125 μm and nanoscaled pore wall roughness (visible from scanning electron microscopy) favorable for cell interaction. The 2D wide angle X-ray scattering studies showed that the nanocrystals orient preferably in the printing direction; the degree of orientation varied between 61–76%. The 3D printing pathways were optimised successfully to achieve 3-dimensional scaffolds (Z axis up to 20 mm) with uniform as well as gradient pore structures. This study demonstrates the potential of 3D printing in developing bio-based scaffolds with controlled pore sizes, gradient pore structures and alignment of nanocrystals for optimal tissue regeneration.

Few-layer bismuthene for ultrashort pulse generation in a dissipative system based on an evanescent field.

Abstract: Bismuthene has attracted a great deal of attention because of its unique electronic and optical properties. However, there are few reported applications of bismuthene in nonlinear optical applications. In this research, a dissipative soliton ytterbium-doped mode-locked fiber laser at 1 μm regime with a bismuthene saturable absorber (SA) by using evanescent field interaction for the first time is demonstrated. The nonlinear optical absorption of microfiber-based bismuthene SA is shown experimentally by using a homemade ultrafast fiber laser, whose saturation intensity and modulation depth are about 13 MW cm-2 and 2.2%, respectively. Relying on the excellent nonlinear optical property of the bismuthene SA, the typical dissipative solitons with a repetition rate of 21.74 MHz are generated at a center wavelength of 1034.4 nm. The time-bandwidth product of the pulse is about 23.07 with a pulse width of 30.25 ps. The results demonstrate that bismuthene is a good candidate for application in a 1 μm wave-breaking-free mode-locked fiber laser and nonlinear photonic components.

Screening and multiple detection of cancer exosomes using an SERS-based method.

Abstract: As a kind of most important cancer biomarker, exosomes are getting more frequently investigated in cancer diagnosis. In this study, we proposed an SERS-based method for the screening and simultaneous multiple detection of exosomes using magnetic substrates and SERS probes. Specifically, the capturing substrates are achieved using gold shell magnetic nanobeads modified by aptamers, which can capture most kinds of exosomes by recognizing the generic surface protein CD63. Moreover, the SERS probes are made of gold nanoparticles decorated with a Raman reporter and a specific aptamer for targeting exosomes. Further, for the simultaneous detection of multiple kinds of exosomes, three kinds of SERS probes were designed using different SERS reporters. While detecting specific kinds of exosomes, the capturing substrates were mixed with these three kinds of SERS probes. When the target exosome is present, an apta-immunocomplex can be formed among the target exosomes, the substrate, and the corresponding kind of SERS probes, and the other non-specific SERS probes remain in the suspension. Hence, an SERS signal with a decreased intensity will be detected in the supernatant, indicating the presence of the target exosomes. Finally, this detection method has also been successfully employed for the detection of exosomes in real blood samples; this proves that the proposed SERS-based method is a promising tool for clinical cancer screening based on exosomes.

An ultrafine platinum–cobalt alloy decorated cobalt nanowire array with superb activity toward alkaline hydrogen evolution

Abstract: It is highly desired to design and develop highly efficient electrocatalysts for alkaline hydrogen evolution reactions. Herein, we report the development of ultrafine PtCo alloy nanoparticle decorated one-dimensional Co nanowires grown on Ti mesh (PtCo–Co/TiM). Owing to its favorable composition and structure, the PtCo–Co/TiM can deliver an ultrahigh current density of 46.5 mA cm−2 at an overpotential of 70 mV in 1.0 M KOH, superior to recently reported Pt-based electrocatalysts. This catalyst also provides excellent long-term electrochemical durability with its catalytic activity being maintained for at least 50 h.

Unexpected insights into antibacterial activity of zinc oxide nanoparticles against methicillin resistant Staphylococcus aureus (MRSA)

Abstract: Zinc oxide nanoparticles (ZnO-NPs) are attractive as broad-spectrum antibiotics, however, their further engineering as antimicrobial agents and clinical translation is impeded by controversial data about their mechanism of activity. It is commonly reported that ZnO-NP's antimicrobial activity is associated with the production of reactive oxygen species (ROS). Here we disprove this concept by comparing the antibacterial potency of ZnO-NPs and their capacity to generate ROS with hydrogen peroxide (H2O2). Then, using gene transcription microarray analysis, we provide evidence for a novel toxicity mechanism. Exposure to ZnO-NPs resulted in over three-log reduction in colonies of methicillin resistant S. aureus with minimal increase in ROS or lipid peroxidation. The amount of ROS required for the same amount of killing by H2O2 was much greater than that generated by ZnO-NPs. In contrast to H2O2, ZnO-NP mediated killing was not mitigated by the antioxidant, N-acetylcysteine. ZnO-NPs caused significant up-regulation of pyrimidine biosynthesis and carbohydrate degradation. Simultaneously, amino acid synthesis in S. aureus was significantly down-regulated indicating a complex mechanism of antimicrobial action involving multiple metabolic pathways. The results of this study point to the importance of specific experimental controls in the interpretation of antimicrobial mechanistic studies and the need for targeted molecular mechanism studies. Continued investigation on the antibacterial mechanisms of biomimetic ZnO-NPs is essential for future clinical translation.

Highly efficient charge transfer through a double Z-scheme mechanism by a Cu-promoted MoO3/g-C3N4 hybrid nanocomposite with superior electrochemical and photocatalytic performance

Abstract: Herein, a novel Cu-MoO3/g-C3N4 hybrid nanocomposite was successfully synthesized by a two-step strategy of one-pot pyrolysis followed by the impregnation method. The structure, phase, morphology and electronic environment of MoO3, g-C3N4 and Cu in the composite were determined by various characterization methods. The oxygen vacancies of MoO3 were ascertained by UV-DRS, Raman, and XPS analysis. The formation of the heterostructure was characterised by electrochemical measurements. The photocatalytic performance of the composite was investigated by the water reduction reaction and the reduction of an important inorganic pollutant, Cr(vi). In the presence of Cu NPs, the H2 evolution of the MoO3/g-C3N4 hybrid was found to be 652 μmol h-1 with an apparent energy conversion efficiency of 13.46%, and up to 95% of Cr(vi) was reduced using citric acid as a hole scavenger. The remarkably enhanced photocatalytic performance was attributed to the combined effect of the double Z-scheme mechanism and defective MoO3. The in situ formation process of the MoO3/g-C3N4 hybrid followed a direct Z-scheme charge transfer by generating a great number of defects at the solid-solid interface, similar to that of a conductor, and offered low electrical resistance, whereas loading of Cu NPs built up an indirect Z-scheme charge transfer to establish the double Z-scheme charge transfer mechanism. This hybrid material produces a photocurrent density of 12.1 mA cm-2, in good agreement with the photocatalytic activity. This study highlights the facilitation effect of MoO3 due to oxygen vacancies and charge transfer through the double Z-scheme mechanism to open up a new window in the field of 2D nanostructured photocatalytic materials.

Electrohydrodynamic printing of silver nanowires for flexible and stretchable electronics.

Abstract: A silver nanowire (AgNW) based conductor is a promising component for flexible and stretchable electronics. A wide range of flexible/stretchable devices using AgNW conductors has been demonstrated recently. High-resolution, high-throughput printing of AgNWs remains a critical challenge. Electrohydrodynamic (EHD) printing has been developed as a promising technique to print different materials on a variety of substrates with high resolution. Here, AgNW ink was developed for EHD printing. The printed features can be controlled by several parameters including AgNW concentration, ink viscosity, printing speed, stand-off distance, etc. With this method, AgNW patterns can be printed on a range of substrates, e.g. paper, polyethylene terephthalate (PET), glass, polydimethylsiloxane (PDMS), etc. First, AgNW samples on PDMS were characterized under bending and stretching. Then AgNW heaters and electrocardiogram (ECG) electrodes were fabricated to demonstrate the potential of this printing technique for AgNW-based flexible and stretchable devices.

Polyethylene oxide film coating enhances lithium cycling efficiency of an anode-free lithium-metal battery

Abstract: The practical implementation of an anode-free lithium-metal battery with promising high capacity is hampered by dendrite formation and low coulombic efficiency. Most notably, these challenges stem from non-uniform lithium plating and unstable SEI layer formation on the bare copper electrode. Herein, we revealed the homogeneous deposition of lithium and effective suppression of dendrite formation using a copper electrode coated with a polyethylene oxide (PEO) film in an electrolyte comprising 1 M LiTFSI, DME/DOL (1/1, v/v) and 2 wt% LiNO3. More importantly, the PEO film coating promoted the formation of a thin and robust SEI layer film by hosting lithium and regulating the inevitable reaction of lithium with the electrolyte. The modified electrode exhibited stable cycling of lithium with an average coulombic efficiency of ∼100% over 200 cycles and low voltage hysteresis (∼30 mV) at a current density of 0.5 mA cm-2. Moreover, we tested the anode-free battery experimentally by integrating it with an LiFePO4 cathode into a full-cell configuration (Cu@PEO/LiFePO4). The new cell demonstrated stable cycling with an average coulombic efficiency of 98.6% and capacity retention of 30% in the 200th cycle at a rate of 0.2C. These impressive enhancements in cycle life and capacity retention result from the synergy of the PEO film coating, high electrode-electrolyte interface compatibility, stable polar oligomer formation from the reduction of 1,3-dioxolane and the generation of SEI-stabilizing nitrite and nitride upon lithium nitrate reduction. Our result opens up a new route to realize anode-free batteries by modifying the copper anode with PEO to achieve ever more demanding yet safe interfacial chemistry and control of dendrite formation.