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Transition metal- and N-codoped carbon nanotubes (CNTs) have superior catalytic activity because the curling surface enhances the bonding ability of atoms within CNTs to other species. However, it is a great challenge to prepare CNTs with transition metal- and N-doped at high level during the growth of CNTs. Here, (Fe,N-codoped CNT)/(Fe-based nanoparticle) (Fe,N-CNT/FeNP) hybrid nanostructures are for the first time prepared through the carbonization of Fe-doped g-C3N4. The doping of Fe and N is simultaneously realized during the formation of CNTs. Meanwhile, the abundant and homogeneous Fe and N in Fe-doped g-C3N4 ensure high-level and uniform doping of Fe and N in CNTs. The Fe,N-CNT/FeNP hybrid nanostructures have several types of active components, including homogeneously distributed coordinating Fe moieties (FeCxNy or FeNx) and CFe15.1 nanoparticles embedded in Fe,N-CNTs, towards oxygen reduction reaction (ORR). A superior ORR electrocatalytic performance is therefore obtained on the Fe,N-CNT/FeNP nanohybrids. Our preparation method opens an avenue to preparation of CNTs with transition metal- and N-doping at high-level, and the superior performance of Fe,N-CNT/FeNP nanostructures for ORR will be very helpful to the development of fuel cells and metal-air batteries.

Highly asymmetric Au nanostructures, such as split Au nanorings and Au nanocups, exhibit attractive plasmonic properties because of their asymmetric geometries. To facilitate their plasmonic applications, effective and facile synthetic methods for producing asymmetric Au nanostructures with controllable sizes and uniform shapes are highly desirable. Herein, we report on an approach for the synthesis of largely asymmetric colloidal Au nanobottles with synthetically tunable overall and opening sizes. Au nanobottles with overall sizes in the range of ∼100-230 nm are obtained through sacrificial templating with differently sized PbS nano-octahedra. The opening sizes of the produced Au nanobottles can be tailored from ∼10 to ∼120 nm by either adjusting the Au/PbS molar ratio in the growth process or controlling the oxidation degree. The achieved size tunability allows the plasmon resonance wavelength of Au nanobottles to be varied in the range of ∼600-900 nm. Our uniform Au nanobottles, which possess controllable sizes, large cavity volumes, and tunable plasmon resonance wavelengths in the visible to near-infrared range, have been further applied for anticancer drug delivery and photothermal therapy. The effects of surface coating and the opening size of Au nanobottles on the drug encapsulation efficiency (EE) and initial burst drug release are systemically evaluated. A high doxorubicin EE and low initial burst drug release are realized with the dense silica-coated Au nanobottles having an opening size of 44 nm. In addition, chemo-photothermal combined therapy has been demonstrated with the doxorubicin-loaded Au nanobottles. Our results will be helpful for the design of Au nanobottles with different sizes and plasmonic properties as well as provide ample opportunities for exploring various plasmon-enabled applications of Au nanobottles.

The intercalation and delamination processes of Ti3C2Tx are systematically investigated by using alkylammonium hydroxides (TAAOH) with different chain lengths. TAA+ cations have a key function for the intercalation reaction of Ti3C2Tx nanosheets, and the basal spacing and the crystal phase of TAA+-intercalated Ti3C2Tx at different stages are closely related to the size of the intercalated TAA+ ions, and they are hardly changed with the addition of molar equivalents of TAAOH per mole of Ti3C2Tx and the drying conditions. Moreover, the intercalation process is very rapid and it can be carried out by just 4 h treatment. TAA+-intercalated Ti3C2Tx can be delaminated into Ti3C2Tx nanosheets by hand shaking or repeated washing. By introducing a graphene oxide nanosheet suspension into the Ti3C2Tx nanosheet suspension, Ti3C2Tx/RGO fibers are firstly prepared by a wet-spinning method followed by reducing Ti3C2Tx/GO fibers in HI/CH3COOH solution. Then the Ti3C2Tx/RGO fiber is soaked in KMnO4 solution with different concentrations at room temperature, and a MnO2/Ti3C2Tx/RGO ternary hybrid fiber with good flexibility and capacitance is prepared. The MnO2/Ti3C2Tx/RGO ternary hybrid fiber electrode shows the largest volumetric capacitance of 851 F cm−3 in 1 M Na2SO4 electrolyte and good flexibility. By twisting two of these fiber electrodes together, an all-solid-state symmetric MnO2/Ti3C2Tx/RGO//MnO2/Ti3C2Tx/RGO fiber supercapacitor with PVA–LiCl gel electrolyte is assembled. It not only exhibits a volumetric capacitance of 24 F cm−3 and superior cycle stability of 92% after 10 000 cycles, but also shows outstanding flexibility and mechanical properties in which the volumetric capacitance has no obvious change after bending the supercapacitor at 90° 1000 times. Furthermore, the assembled symmetric supercapacitor shows the maximum volumetric energy density of 2.13 mW h cm−3 at a volumetric power density of 8.16 mW cm−3. This work will open a new application field of Ti3C2Tx-based fibers for new wearable energy storage devices with good energy density and flexibility.

The carbothermal reduction reaction (CRR) is the most commonly used method for synthesizing Magneli-phase reduced titanium oxide nanocrystals. Though the reaction process has been investigated from thermodynamics and kinetics perspectives, research focused on the detailed formation mechanism of the interfaces from reactant to product is still limited. In this work, the structures and formation mechanisms of the interfaces between different TinO2n−1 phases were investigated using comprehensive XRD, Raman spectroscopy, and TEM characterization. Both XRD and Raman spectroscopy results indicated that the formation sequence of the TinO2n-1 phases during the CRR was TiO2 → TinO2n−1 (n = 4–9) → Ti3O5 → Ti2O3 → TiO, regardless of the method used to introduce the carbon source. Furthermore, the surface encapsulation of polydopamine (PDA) on TiO2 precursor effectively reduced the reaction temperature compared with samples prepared by ball-mill mixing of TiO2 and carbon. The interfaces of Ti4O7/Ti5O9 and Ti3O5/Ti4O7 were obtained from the CRR using different carbon source introduction methods. TEM results suggested the different coherency of these interfaces, which might be due to different formation mechanisms. By calculating the Gibbs free energies in the temperature range of 298–1598 K for some involved reactions, it was noted that the reaction between TiO2 and carbon proceeds spontaneously to form TinO2n−1 phases (n = 2–10) over the whole temperature range. In contrast, the reaction between TinO2n−1 phases with different n values was not spontaneous when n ≤ 3 from 298 K to 1598 K, which further validated the oriented attachment growth mechanism of the Ti3O5/Ti4O7 interface rather than direct CRR. Finally, the growth mechanisms of the two types of interfaces were summarized at both atomic level and nanoscales.

As the next generation of electrochemical energy storage devices, lithium sulfur (Li–S) batteries have many advantages such as high theoretical specific capacity (1675 mAh g−1) and energy density (2600 kw h kg−1), non-toxicity and low cost. However, the poor electrical conductivity of sulfur cathodes and the shuttling effect of lithium polysulfides during cycling strongly hinder the commercial application of Li–S batteries. In this study, Magneli phase Ti4O7 nanoparticles were successfully prepared on the surface of hollow carbon spheres (HCS) through a carbothermal reduction reaction. The synthesized HCS@Ti4O7 with a mesoporous structure exhibited a uniform spherical morphology with a large specific surface area (512 m2 g−1) and the pore volume of 0.58 cm3 g−1. The introduction of a polydopamine (PDA) layer during the preparation was confirmed to effectively inhibit the grain coarsening of Ti4O7. Moreover, the high content of sulfur loading (70%) did not affect the morphology of HCS@Ti4O7, which suggested its stable architecture. The assembled coin cells exhibited the superior reversible capacity of 1427 mAh g−1 at 0.1C and favorable cycling stability from 1168 mAh g−1 to 601 mAh g−1 after 800 cycles at 0.5C with the capacity decay rate of only 0.06% per cycle. This excellent performance and stability were attributed to the strong chemical binding effects of Ti4O7 on lithium polysulfides and the stable morphology maintenance during cycling. This study provides a novel conception to design and synthesize nanocomposites between reduced metal oxides and carbon with uniform and stable mesoporous structures for high-performance Li–S batteries.

Graphitic carbon nitride (CN) generally needs to be exfoliated into ultrathin nanosheets to reduce photocarrier recombination. However, the exfoliation of CN into nanosheets also reduces the light absorption. How to simultaneously realize low photocarrier recombination and high light absorption remains a challenge in the practical application of CN in photocatalysis. Herein, the light absorption of CN nanosheets was enhanced by introducing hollow TiO2 (h-TiO2) dielectric resonators. The h-TiO2/CN heterostructures were prepared by thermally polymerizing dicyandiamide in the presence of h-TiO2. The electromagnetic resonances of the h-TiO2 resonator creates strong electric field enhancement within, inside, and near external surface of the introduced h-TiO2 nanoshells. The enhanced electric field greatly improves the light absorption of CN located in these regions. The largest hydrogen evolution rate for h-TiO2/CN can reach 6.3 mmol g−1h−1, which is over 3-fold that of pure CN (2.0 mmol g−1h−1). It is also found that the small amount of CN within and inside h-TiO2 majorly contributes to the photocatalytic performance. These findings open a new avenue by which to enhance the performance of photocatalysts and will be helpful in the design of highly efficient photocatalysts for various reactions.

Development of highly stabilized and reversible cathode materials has become a great challenge for sodium-ion batteries. O'3-type layered Mn-based oxides have deserved much attention as one of largely reversible-capacity cathodes featured by the resource-rich and low-toxic elements. However, the fragile slabs structure of typical layered oxides, low Mn-ion migration barriers, and Jahn-Teller distortion of Mn3+ have easily resulted in the severe degradation of cyclability and rate performances. Herein, a new queue-ordered superstructure is built up in the O'3-NaMn0.6 Al0.4 O2 cathode material. Through the light-metal Al substitution in O'3-NaMnO2 , the MnO6 and AlO6 octahedrons display the queue-ordered arrangements in the transition metal (TM) slabs. Interestingly, the presence of this superstructure can strengthen the layered structure, reduce the influence from Jahn-Teller effect, and suppress the TM-ions migrations during long-terms cycles. These characteristics results in O'3-NaMn0.6 Al0.4 O2 cathode deliver a high capacity of 160 mAh g-1 , an enhanced rate capability and the excellent cycling performance. This research strategy can provide the broaden insight for future electrode materials with high-performance sodium-ions storage.

Single-atom (SA) catalysis bridging homogeneous and heterogeneous catalysis offers new opportunities for organic synthesis, but developing SA catalysts with high activity and stability is still a great challenge. Herein, a heterogeneous catalyst of Pd SAs anchored in 3D ordered macroporous ceria (Pd-SAs/3DOM-CeO2 ) is developed through a facile template-assisted pyrolysis method. The high specific surface area of 3DOM CeO2 facilitates the heavily anchoring of Pd SAs, while the introduction of Pd atoms induces the generation of surface oxygen vacancies and prevents the grain growth of CeO2 support. The Pd-SAs/3DOM-CeO2 catalyst exhibits excellent activity toward Suzuki coupling reactions for a broad scope of substrates under ambient conditions, and the Pd SAs can be stabilized in CeO2 in long-term catalytic cycles without leaching or aggregating. Theoretical calculations indicate that the CeO2 supported Pd SAs can remarkably reduce the energy barriers of both transmetalation and reductive elimination steps for Suzuki coupling reactions. The strong metal-support interaction contributes to modulating the electronic state and maintaining the stability of Pd SA sites. This work demonstrates an effective strategy to design and synthesize stable single-atom catalysts as well as sheds new light on the origin for enhanced catalysis based on the strong metal-support interactions.

MoS2 shows a great promise as a low-cost and highly active alternative to platinum-based catalysts for electrochemical hydrogen production from water. The activity of MoS2 is believed from the edge, defect sites, and the basal plane of metallic phase (M-MoS2). Here we report on a facile hydrothermal method for the preparation of MoS2 nanopetals that are in metallic phase and have abundant edges. The amount of sulfur precursors are found to play a critical role on the formation of MoS2 nanopetals. The MoS2 nanopetals exhibit remarkable electrocatalytic activities for the hydrogen evolution reaction (HER), with a low overpotential of 210 mV at the current density of 10 mA cm–2 and a Tafel slope of 44 mV per decade. The MoS2 nanopetals also display very good durability, with a very small negative shift of 11 mV at the current density of 10 mA cm–2, and negligible shift at the current density of 50 mA cm–2 after 2000 cycles. Our facile preparation method and high electrocatalytic activity of MoS2 nanopetals f...

Mn3O4/reduced graphene oxide/single-walled carbon nanotube flexible hybrid film with outstanding flexibility and electrochemical performance is prepared via a vacuum filtration method. The three-dimensional interconnect structure is constructed by reduced graphene oxide and single-walled carbon nanotube, and Mn3O4 nanoplates with pesudocapacitance are embedded into the interconnect structure. The regular interconnect structure and a synergetic effect between graphene oxide/single-walled carbon nanotube and Mn3O4 make the Mn3O4/reduced graphene oxide/single-walled carbon nanotube flexible film electrode exhibit a large areal capacitance of 796 mF cm−2. All-solid-state Mn3O4/reduced graphene oxide/single-walled carbon nanotube flexible supercapacitor is prepared by using the hybrid film as electrodes and sandwiching the PVA–KOH gel electrolyte, it exhibits a large area specific capacitance of 360 mF cm−2 and the capacitance maintains 95% after 5000 charge/discharge cycles. The assembled supercapacitor exhibits both outstanding mechanical performance and a high areal energy density of 32 μW h cm−2 at an areal power density of 0.392 mW cm−2. The Mn3O4/reduced graphene oxide/single-walled carbon nanotube flexible supercapacitors exhibit significant potentiality in flexible and wearable electronics owing to their excellent flexibility, high energy density and long cycle life.

Graphitic carbon nitride (g-C3N4) has been believed to be a promising photocatalyst for water splitting due to its right band gap and band edges. However, the kinetics of hydrogen evolution on g-C3N4 is very slow. Cocatalysts are usually needed to improve the catalytic kinetics. Herein, palladium-doped graphitic carbon nitride (g-C3N4–Pd) is designed by virtue of the tenacious coordination of Pd atoms with the pyridinic nitrogen atoms of six-fold cavities in g-C3N4. The introduction of Pd does not affect the structure and morphology of g-C3N4. Palladium is found to exist as Pd ions in g-C3N4–Pd catalysts. g-C3N4–Pd catalysts exhibit clearly higher hydrogen evolution activities than g-C3N4. The highest hydrogen evolution activity on g-C3N4–Pd is 15.3 times that of g-C3N4. The improvement of hydrogen evolution activity is found to arise from both the alternation of the electron excitation manner and the acceleration of hydrogen evolution kinetics induced by Pd doping. Our findings provide a promising way to...

The application of aluminum (Al)-based nanostructures for visible-range plasmonics, especially for surface-enhanced Raman scattering (SERS), currently suffers from inconsistent local electromagnetic field distributions and/or inhomogeneous distribution of probe molecules. Herein, we lithographically fabricate structurally uniform Al nanostructures which enable homogeneous adsorption of various probe molecules. Individual Al nanostructures exhibit strong local electromagnetic field enhancements, in turn leading to intense SERS activity. The average SERS enhancement factor (EF) for individual nanostructures exceeds 104 for non-resonant probe molecules in the visible spectrum. These Al nanostructures also retain more than 70% of their original SERS intensities after one-month storage, displaying superb stability under ambient conditions. We further achieve tunable polarization-dependent SERS responses using anisotropic Al nanostructures, facilitating the design of sophisticated SERS-based security labels. Our micron-sized security label comprises two-tier security features, including a machine-readable hybrid quick-response (QR) code overlaid with a set of ciphertexts. Our work demonstrates the versatility of Al-based structures in low-cost modern chemical nano-analytics and forgery protection. ASTAR (Agency for Sci., Tech. and Research, S’pore) MOE (Min. of Education, S’pore) Accepted version

Transition metal phosphides have sparked considerable interest as electrocatalysts owing to their excellent catalytic activities towards water splitting. However, the development of a general strategy for the preparation of metal phosphides has remained challenging. In this work, we demonstrate a two-step, aerosol spray-based strategy for the synthesis of various mesoporous monometallic and multimetallic phosphide microspheres. Four monometallic (FeP, CoP, Ni2P, and Cu3P), one bimetallic (Co6Ni4P5) and one trimetallic (Co4Ni3Cu2P10) phosphide samples are successfully prepared, suggesting the generality of our method. In addition, the CoP sample is found to be an excellent material for the hydrogen evolution reaction over a wide pH range through the introduction of corrosion-resistant Cr2O3. On the other hand, its catalytic activity can be switched to the oxygen evolution reaction in combination with Fe2O3. The overpotential for the oxygen evolution reaction to generate a current density of 10 mA cm−2 is as low as 302 mV. This activity can be maintained for at least 50 h. More importantly, a two-electrode electrolyzer constructed from 10% Cr–CoP and 30% Fe–CoP samples delivers a current density of 100 mA cm−2 at a cell voltage of merely 1.67 V, showing the use of these cost-effective materials for bifunctional water splitting.

To date, lanthanide-doped upconversion nanoparticles (UCNPs) have been widely reported as a promising CT contrast agent because they have high atomic numbers and big X-ray attenuation coefficient values. However, it is still a challenge to fabricate a simple multimodal imaging probe with improved image quality for early cancer diagnosis in clinical medicine. Herein, ultra-small, uniform and monodisperse β-NaGdF4:Yb,Er,X% Lu (X = 0, 1, 2.5, 4, 6, 7.5) UCNPs were prepared through a solvothermal method with high-level modulation of both the phase and morphology. Meanwhile, a remarkably enhanced red upconversion luminescence (UCL) in the β-NaGdF4:Yb,Er,X% Lu NPs was successfully realized via Lu3+ doping. It is found that as the content of Lu3+ increases from 0 to 7.5 mol%, the UCL intensity of the red emission first increases and then decreases, with the optimum doping content of Lu3+ ions of 2.5 mol%. The red UCL enhancement is ascribed to the change of the Yb–Er interionic distance controlling the Yb–Er energy transfer rate and the distortion of the local environment of Er3+ ions influencing the 4f–4f transition rates of Er3+ ions, which has been further confirmed by the experimental check of the crystallographic phase and by photoluminescence spectroscopy employing Eu3+ as the structural probe, respectively. More importantly, after being modified with the HS-PEG2000-NH2 ligand, the NH2-PEGylated-NaGdF4:Yb,Er,X% Lu NPs exhibited low cytotoxicity, high biocompatibility, and remarkably enhanced contrast performance in in vitro UCL and in vivo CT imaging. On the basis of our findings, the as-obtained functionalized UCNPs could be considered as a promising versatile dual-mode imaging probe for bioimaging, tumor diagnosis, and cancer therapy.

The catalytic activity of metal nanocrystals is mainly tuned through the control of their shapes and sizes. However, the shapes and sizes of many metal nanocrystals are difficult to control and therefore their catalytic activity is hard to tune. Here, we demonstrate another approach, using differently charged surfactants, for tuning the catalytic activity of metal nanocrystals. Au and Pd nanocrystals capped with cationic cetyltrimethylammonium bromide (CTAB) and anionic citrate are chosen to study the effect of surfactant charges on the catalytic activity. The oxidation of o-phenylenediamine to 2,3-diaminophenazine by H2O2 is selected as a model reaction. The prepared Au and Pd nanocrystals are initially capped with CTAB, which is changed to citrate through surfactant exchange. Owing to the relatively weak electrostatic interaction of CTAB with the nanocrystals, the surfactant exchange does not induce observable changes in nanocrystal shapes and sizes. In contrast, the catalytic activity is greatly improved by the surfactant exchange. XPS analysis and theoretical calculations indicate that the adsorption of anionic citrate enriches the electrons of the nanocrystal surfaces, while the adsorption of CTAB depletes the electrons of the nanocrystal surfaces. The different catalytic activities of CTAB and citrate-capped nanocrystals arise from the different behaviors of electron transfer between the surfactants and the nanocrystal surface. Since the surfacants that electrostatically bind to the metal nanocrystals are facile to exchange into other surfactants, our findings provide an effective way to tuning the catalytic activity of metal nanocrystals.

Vanadium pentoxide/single-walled carbon nanotube (V 2 O 5 -SWCNT) hybrid fibers with good electrochemical performance and flexibility are firstly prepared by using wet-spinning method. V 2 O 5 nanobelt suspension is obtained by mixing V 2 O 5 bulk, 30% H 2 O 2 , H 2 O and followed by hydrothermally treating at 190 °C for 15 h. SWCNT suspension is suspended into V 2 O 5 nanobelt suspension under vigorous stirring, the V 2 O 5 -SWCNT homogenous suspension is obtained. It is injected into a coagulation bath composed of 5 wt % CaCl 2 ethanol-water solution using syringe pump, V 2 O 5 -SWCNT hybrid fibers are prepared by washing with deionized water and drying at room temperature. Reduced graphene oxide (RGO)-SWCNT hybrid fibers are also prepared by the similar wet-spinning approach and followed by reducing GO-SWCNT hybrid fibers in an aqueous solution of hydriodic acid. All solid-state asymmetric V 2 O 5 /SWCNT//RGO/SWCNT fiber supercapacitors are assembled with V 2 O 5 -SWCNT fiber as positive electrode and RGO-SWCNT fiber as negative electrode by using PVA-H 3 PO 4 as gel electrolyte. The assembled device not only shows maximum volumetric energy density of 1.95 mW h cm −3 at a volumetric power density of 7.5 mW cm −3 , superior rate performance and cycling stability, but also exhibits remarkable flexibility to tolerate long-term and repeated bending. This work will open a new application filed of V 2 O 5 -based fibers in wearable energy storage devices.

As a novel molecular and functional imaging modality, X-ray luminescence computed tomography (XLCT) has shown its potentials in biomedical and preclinic applications. However, there are still some limitations of X-ray-excited luminescent materials, such as low luminescence efficiency, poor biocompatibility, and cytotoxicity, making in vivo XLCT imaging quite challenging. In this study, for the very first time, we present on using sub-10 nm β-NaGdF4:X% Eu3+ nanoparticles with poly(acrylic acid) (PAA) surface modification, which demonstrate outstanding luminescence efficiency, uniform size distribution, water dispersity, and biosafety, as the luminescent probes for in vivo XLCT application. The pure hexagonal phase (β-) NaGdF4 has been successfully synthesized and characterized by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM), and then the results of X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectrometry (EDX), and elemental mapping further confirm Eu3+ ion...

Nanostructures made of dielectric materials with high or moderate refractive indexes can support strong electric and magnetic resonances in the optical region. They can therefore function as nanoresonators. In addition to plasmonic metal nanostructures that have been widely investigated, dielectric nanoresonators provide a new type of building blocks for realizing powerful and versatile nanoscale light manipulation. In contrast to plasmonic metal nanostructures, nanoresonators made of appropriate dielectric materials are low-cost, earth-abundant and have very small or even negligible light energy losses. As a result, they will find potential applications in a number of photonic devices, especially those that require low energy losses. In this review, we describe the recent progress on the experimental and theoretical studies of dielectric nanoresonators. We start from the basic theory of the electromagnetic responses of dielectric nanoresonators and their fabrication methods. The optical properties of individual dielectric nanoresonators are then elaborated, followed by the coupling behaviors between dielectric nanoresonators, between dielectric nanoresonators and substrates, and between dielectric nanoresonators and plasmonic metal nanostructures. The applications of dielectric nanoresonators are further described. Finally, the challenges and opportunities in this field are discussed.

Sustainable hydrogen generation via electrocatalytic/photocatalytic water splitting has been widely regarded as the most promising energy carrier and has attracted extensive attention. However, a considerable hydrogen evolution reaction (HER) always involves the rare noble metals. Herein, we report a new HER candidate, an Fe-doped NiS2 (Fe–NiS2) nanosheet, with the performance of high activity and electrochemical stability. We chose the sulfidation of Ni(OH)2 under mild calcinated temperature for Fe–NiS2 formation. The theoretical and experimental results suggest that the Fe3+ doping into the surface lattice of the NiS2 (002) facet lowers the activation energy of H2 generation. The synthesized Fe–NiS2 sample shows good electrocatalytic HER performance with a low Tafel slope of 37 mV dec−1 and a small overpotential of 121 mV at 10 mA cm−2. Moreover, Fe–NiS2 gives considerable stability with a negligible loss of HER value l after a reaction of 1100 min. The Fe–NiS2 sample is also in situ loaded onto the surface of CdS nanorods to act as a co-catalyst for photocatalytic H2 generation with the result of 3.2 mmol h−1 g−1 hydrogen evolution under visible light, 46 times higher than with bare CdS. This work can help us to design new electrocatalysts for water splitting; it also provides a good understanding of the hydrogen evolution pathway.

Despite showing great promise in bioapplications, lanthanide-doped upconversion nanoparticles (UCNPs) are still restricted by low upconversion efficiency. In this work, ultra-small, monodisperse and uniform β-NaYbF4:0.5% Tm NPs were successfully prepared through a solvothermal route, and remarkably enhanced ultraviolet upconversion luminescence (UV UCL) had been achieved via Fe3+ doping. The UV UCL enhancement in NaYbF4:0.5% Tm NPs was investigated in detail. It was found that the UCL intensities of the UV and blue emissions of NPs doped with 5 mol% Fe3+ ions were enhanced by 10 and 6 times, respectively, compared to that of the Fe3+-free sample. The enhancement of UV UCL is mainly ascribed to the high population density of excited Yb3+ and the energy transfer from |2F7/2, 4T1g > (Yb3+–Fe3+ dimer) to 3F2,3 (Tm3+) states. Moreover, through dynamic analysis, we further demonstrate the proposed mechanisms of UC processes. The results suggest that ultra-small UCNPs with enhanced UV UCL may have potential applications in the biomedical field.

Exfoliation and assembly of 2-D materials have been extensively investigated to exploit their performances in the area of catalysis, magnetics and electronics etc., but novel strategies are highly desired to shorten their preparing period and to improve their environment-friendliness. Here we introduce a simple and green hydrothermal process to fabricate ultrathin layered β-Ni(OH)2/g-C3N4 nanohybrids for photocatalytic water splitting application. Different from conventionally separated exfoliation and assembly, the exfoliation of g-C3N4, formation of β-Ni(OH)2 as well as their self-assembly can be one-pot achieved by simple hydrothermal treatment of nickel dichloride and bulk g-C3N4 free of any organic agents for 12 h. Moreover, the thickness of β-Ni(OH)2 nanolayer can be adjusted by controlling the concentration of nickel precursors. The as-obtained nanohybrids have been in detail characterized to have a strong interaction of the assembly components, among which the g-C3N4 is active for photocatalytic water splitting, and β-Ni(OH)2 nanolayer is efficient for acceleration of activation of water oxidation. Their photocatalytic water splitting performances are evaluated in the presence of sacrificial agents, based on which the assembly of β-Ni(OH)2 nanolayers on the surface of exfoliated g-C3N4 lamella is found to obviously promote the charge separation, water oxidation kinetics as well as final photocatalytic performances compared to the pristine g-C3N4. The direct water splitting is also achieved with the AQY of 1.48% under 405-nm visible light irradition. The one-pot hydrothermal method introduced here may be an alternative strategy for g-C3N4, a promising photocatalytic water splitting material, to construct highly efficient solar energy conversion composite systems based on its exfoliated lamella.

The control of the emission from electric and magnetic dipoles is highly desired for the development of optic chips. Although the emission of electric dipole has been successfully controlled by plasmonic nanoantenna, the control of magnetic dipole emission is relatively difficult. Here, we systematically study the effect of electric and magnetic modes of Au nanocups on the emission of electric and magnetic dipoles. The emission of electric dipole can be enhanced by both the electric and magnetic mode of the Au nanocup, while the emission of the magnetic dipole is only increased by the magnetic mode. The enhancement exhibits wavelength dependence. The wavelength of the largest enhancement is determined by the resonance wavelength of electric and magnetic modes. The enhancement values for electric and magnetic dipoles are determined by the near-field electric and magnetic field enhancements, respectively. More importantly, the emission pattern of magnetic dipole is greatly modified by the magnetic mode of Au nanocup. The directional emission of magnetic dipole is first time realized by use of the magnetic mode of the Au nanocup. Our findings deepen the understanding of the plasmon-controlled emission of electric and magnetic dipoles and will be very helpful to the development of the nanophotonic chips.

Porous Au nanostructures have attracted much attention for their wide uses as catalysts, sensors, actuators and surface-enhanced Raman scattering (SERS) substrates. The synthesis of porous Au nanostructures has mainly relied on dealloying approaches, which generally involve high-temperature treatment to form alloys and subsequent harsh chemical etching. Herein we report on an ambient wet-chemistry method for the synthesis of colloidal porous Au nanoparticles. The synthesis takes advantage of the growth of Au on PbS nanocrystals accompanied by the etching of PbS by the growth solution. The obtained porous Au nanoparticles display a SERS enhancement factor of (1.23 ± 0.10) × 107 on the individual particles under off-resonance excitation and a catalytic activity that is several times those of previously reported porous Au particles and porous Au sheets. Our results will have high impact on many SERS-based analytical and biomedical applications and on the field of Au-based catalysis.

The interface between two material phases typically exhibits unique electronic states distinct from their pure phases, thus, providing a very promising channel to construct catalysts with excellent activity and stability. Here, water-induced formation of Ni2 P-Ni12 P5 through a one-step phosphorization of nickel foam (NF) is demonstrated for the first time. The abundant interfaces endow Ni2 P-Ni12 P5 /NF with excellent electrocatalytic hydrogen evolution reaction (HER) activity in alkaline condition, with an overpotential of 76 mV at a current density of 10 mA cm-2 and of 147 mV at a current density of 100 mA cm-2 , and a Tafel slope of 68.0 mV dec-1 . The Ni2 P-Ni12 P5 /NF also exhibits better durability than Pt/C/NF during HER at relatively large overpotential. Density functional theory calculations show that the electronic states at the Ni2 P-Ni12 P5 interface are greatly altered, which enables optimal hydrogen adsorption, accelerates the charge transfer kinetics, and thus enhances the HER electrocatalytic activity. Superior overall water-splitting performance is also obtained by combining Ni2 P-Ni12 P5 /NF with NiFe-layered double hydroxide (LDH) oxygen evolution reaction (OER) catalyst. Overpotentials of the cell for achieving 10 mA cm-2 are only 324 mV. This work provides a facile method for the preparation of interfaces between different nickel phosphide polymorphs toward HER.

The water–gas shift (WGS) reaction plays a key role in hydrogen economy. Owing to the exothermic nature of the reaction, low-temperature WGS catalysts are highly desired. Zn-modified Pd-based catalysts are promising candidates for low-temperature WGS. Herein, the effect of Zn addition on the WGS catalysis is systematically studied by using the Pd(111) and PdZn(111) surface as models. Owing to the addition of Zn, the electron-accepting ability of the catalyst is weakened, while the electron-donating ability is increased. As a result, the adsorptions of electron-donor adsorbates, including H2O, CO, H, cis-COOH, trans-COOH, and H2, are weakened, while the adsorptions of electron-acceptor adsorbates, including O and OH, are strengthened. The same most favorable reaction path is found on Pd(111) and PdZn(111), which is the associative mechanism with the carboxyl dehydrogenation assisted by adsorbed OH. Although the most favorable path is the same, the weakening of CO adsorption makes the rate-determining step ...

Gold nanorods have attracted intensive interest owing to their localized surface plasmon resonance properties and enormous potential applications. The transverse plasmon of Au nanorods is usually weaker than the longitudinal one, hampering certain plasmonic applications. Herein we report on the intensification of the transverse plasmon resonance by coating TiO2 onto Au nanorods. The transverse plasmon mode of the resultant Au@TiO2 nanorods with a sufficiently thick shell can be comparable to or even stronger than the longitudinal one in intensity. Moreover, both the transverse and longitudinal plasmon resonances of the Au@TiO2 nanorods exhibit an asymmetric line shape on their scattering spectra. Electrodynamic simulations and analyses based on a coupled oscillator model suggest that the asymmetric line shape originates from the coupling between the Au core and TiO2 shell. Apart from the shell thickness, the plasmonic properties of the Au@TiO2 nanorods can also be tuned by the dimension of the Au nanorod core. In addition, the polarization-dependent light scattering from the individual Au@TiO2 nanorods has also been investigated. These results will be of high importance for understanding the interactions between noble metals and semiconductors in plasmonic hybrid nanosystems, and for designing novel plasmonic nanostructures with desired optical properties and functions.

Although various metal nanoparticles have been used in organic photovoltaics (OPVs) for enhancing power conversion efficiencies (PCEs) based on surface plasmonic effects, no metal nanoparticles have been found to induce matchable broadband plasmonic enhancement in OPVs until now. Here, we report the introduction of Au@Ag core–shell nanocuboids (NCs) with broadband plasmonic enhancement in OPVs for the first time. The Au@Ag NCs show multimode localized surface plasmon resonance that can be tuned to match the light absorption spectra of OPVs by changing the Ag shell thickness. We find that both light scattering and near field enhancement induced by the NCs can substantially improve the device performance when the NCs are incorporated in the active layers. Under optimum conditions, the PCEs of the OPVs can be relatively improved by up to 22.8% by the NCs. The maximum average PCE of the OPVs we obtained is 10.42%, which is much higher than those of the previously reported plasmonic OPVs. This work demonstrates a convenient approach for improving the photovoltaic performance with broadband enhancement, which is applicable to not only OPVs but also many other types of solar cells.

Localized photoluminescence manipulation of 1L-MoS2 is achieved by using single shape-controlled Ag nanoantenna. By varying the antenna morphology, the photoluminescence of 1L-MoS2 is continuously tunable from enhanced (>2-fold) to weakened (>2-fold) states. A heterogeneous optical platform is realized by depositing various antennas on the same 1L-MoS2 , with an unprecedented range of photoluminescence output being observed simultaneously.

Electrocatalysts play an important role in oxygen reduction reaction (ORR) in promoting the reaction process. Although commercial Pt/C exhibits excellent performance in ORR, the low duration, high cost, and poor methanol tolerance seriously restrict its sustainable development and application. TinO2n&minus, 1 (3 &le, n &le, 10) is a series of titanium sub-oxide materials with excellent electrical conductivity, electrochemical activity, and stability, which have been widely applied in the field of energy storage and catalysis. Herein, we design and synthesize Ti4O7/Ti3O5 (T4/T3) dual-phase nanofibers with excellent ORR catalytic performance through hydrothermal growth, which is followed by a precisely controlled calcination process. The H2Ti3O7 precursor with uniform size can be first obtained by optimizing the hydrothermal growth parameters. By precisely controlling the amount of reducing agent, calcination temperature, and holding time, the T4/T3 dual-phase nanofibers with uniform morphology and coherent interfaces can be obtained. The orientation relationships between T4 and T3 are confirmed to be [ 001 ] T 3 / / [ 031 ] T 4 , ( 100 ) T 3 / / ( 92 6 &macr, ) T 4 , and ( 010 ) T 3 / / ( 1 2 &macr, 6 ) T 4 , respectively, based on comprehensive transmission electron microscopy (TEM) investigations. Furthermore, such dual-phase nanofibers exhibit the onset potential and half-wave potential of 0.90 V and 0.75 V as the ORR electrocatalysts in alkaline media, respectively, which illustrates the excellent ORR catalytic performance. The rotating ring-disk electrode (RRDE) experiment confirmed the electron transfer number of 3.0 for such catalysts, which indicates a mixture of two electron and four electron transfer reaction pathways. Moreover, the methanol tolerance and cycling stability of the catalysts are also investigated accordingly.

As a green pollution-free reaction, oxygen reduction reaction (ORR) plays a significant role in many energy storage and conversion devices. Although commercial Pt/C possesses the highest ORR activity (especially in acidic medium), the high cost, low stability and poor methanol tolerance making the development of non-platinum electrocatalysts with high performance especially important. Herein, we design and synthesize a carbon nanofiber decorated by Ti4O7/Ti3O5 dual-phase nanoparticles (CNF/T4/T3) as ORR catalysts with excellent activity. With the employment of electrospinning followed by precisely controlled calcination process, the composite catalysts with uniform fibrous morphology can be obtained. Such CNF/T4/T3 composite catalysts exhibited an improved electrochemical performance with onset and half-wave potential of 0.91 V and 0.78 V respectively in alkaline solution. By comparing the catalytic performance with the pure T4 or T3 phase decorated on the same carbon nanofiber, it is found that the mixture of the two titanium sub-oxide phases can optimize the onset potential and limited current density at the same time. Density functional theory calculations suggest that different steps of ORR take place on T3 and T4 successively, which is the main reason of the excellent ORR performance for the dual-phase structure. This work provided a novel designing concept for the functional electrocatalysts using electrospinning technique for the application of energy storage and conversion.

Synthesis of hollow metal nanocrystals (NCs) is greatly attractive for their high active surface areas, which gives rise to excellent catalytic activity. Taking PdPt alloy nanostructure as an example, we designed a synthetic tactic for the preparation of hollow metal nanostructures by delicate control over the difference in the reduction kinetic of metal precursors. At a high reduction rate difference, the Pd layer forms from H2PdCl4 and is subsequently etched, leading to the formation of a hollow space. A solid PdPt structure is achieved when the reduction rate of Pd and Pt precursor is comparable. Obviously, the hollow space and composition are tunable as well by adjusting the reduction rate difference. More importantly, the prepared hollow PdPt nanostructures exhibit a branched outer, porous wall, and rough hollow interior. The branched outer and rough hollow interior provide the higher density of unsaturated atoms, whereas the porous wall serves as channels connecting the inner, outer, and reactive ag...

The fixation of atmospheric N2 to NH3 is an essential process for sustaining life. One grand challenge is to develop efficient catalysts to photofix N2 under ambient conditions. Herein we report an...

The development of compressible supercapacitor highly relies on the innovative design of electrode materials with both superior compression property and high capacitive performance. This work reports a highly compressible supercapacitor electrode which is prepared by growing electroactive NiCo2S4 (NCS) nanosheets on the compressible carbon sponge (CS). The strong adhesion of the metallic conductive NCS nanosheets to the highly porous carbon scaffolds enable the CS–NCS composite electrode to exhibit an enhanced conductivity and ideal structural integrity during repeated compression–release cycles. Accordingly, the CS–NCS composite electrode delivers a specific capacitance of 1093 F g–1 at 0.5 A g–1 and remarkable rate performance with 91% capacitance retention in the range of 0.5–20 A g–1. Capacitance performance under the strain of 60% shows that the incorporation of NCS nanosheets in CS scaffolds leads to over five times enhancement in gravimetric capacitance and 17 times enhancement in volumetric capaci...

The synthesis of metal nanostructures with plasmon wavelengths beyond ∼1000 nm is strongly desired, especially for those with small sizes. Herein we report on a AgPd-tipping process on Au nanobipyramids with the resultant red plasmon shifts reaching up to ∼900 nm. The large red plasmon shifts are ascribed to the deposition of the metal at the tips of Au nanobipyramids, which is verified by electrodynamic simulations. The method has been successfully applied to Au nanobipyramids and nanorods with different longitudinal dipolar plasmon wavelengths, demonstrating that the plasmon wavelengths of these Au nanocrystals can be extended to the entire near-infrared region. Pt can also induce the tipping on Au nanobipyramids and nanorods to realize red plasmon shifts, suggesting the generality of our approach. We have further shown that the metal-tipped Au nanobipyramids possess a high photothermal conversion efficiency and good photothermal therapy performance. This study opens up a route to the construction of Au nanostructures with plasmon resonance in a broad spectral region for plasmon-enabled technological applications.

Low-dimensional semiconductors have attracted considerable attention due to their unique structures and remarkable properties, which makes them promising materials for a wide range of applications related to electronics and optoelectronics. Herein, the preparation of 1D Sb2 Se3 nanowires (NWs) with high crystal quality via chemical vapor deposition growth is reported. The obtained Sb2 Se3 NWs have triangular prism morphology with aspect ratio range from 2 to 200, and three primary lattice orientations can be achieved on the sixfold symmetry mica substrate. Angle-resolved polarized Raman spectroscopy measurement reveals strong anisotropic properties of the Sb2 Se3 NWs, which is also developed to identify its crystal orientation. Furthermore, photodetectors based on Sb2 Se3 NW exhibit a wide spectral photoresponse range from visible to NIR (400-900 nm). Owing to the high crystallinity of Sb2 Se3 NW, the photodetector acquires a photocurrent on/off ratio of about 405, a responsivity of 5100 mA W-1 , and fast rise and fall times of about 32 and 5 ms, respectively. Additionally, owing to the anisotropic structure of Sb2 Se3 NW, the device exhibits polarization-dependent photoresponse. The high crystallinity and superior anisotropy of Sb2 Se3 NW, combined with controllable preparation endows it with great potential for constructing multifunctional optoelectronic devices.

Current plasmonic metasurfaces of nanocubes are limited to planar configurations, restricting the ability to create tailored local electromagnetic fields. Here, we report a new chemical strategy to achieve tunable metasurfaces with nonplanar nanocube orientations, creating novel lattice-dependent field localization patterns. We manipulate the interfacial behaviors of Ag nanocubes by controlling the ratio of hydrophilic/hydrophobic molecules added in a binary thiol mixture during the surface functionalization step. The nanocube orientation at an oil/water interface can consequently be continuously tuned from planar to tilted and standing configurations, leading to the organization of Ag nanocubes into three unique large-area metacrystals, including square close-packed, linear, and hexagonal lattices. In particular, the linear and hexagonal metacrystals are unusual open lattices comprising nonplanar nanocubes, creating unique local electromagnetic field distribution patterns. Large-area "hot hexagons" with significant delocalization of hot spots form in the hexagonal metacrystal. With a lowest packing density of 24%, the hexagonal metacrystal generates nearly 350-fold stronger surface-enhanced Raman scattering as compared to the other denser-packing metacrystals, demonstrating the importance of achieving control over the geometrical and spatial orientation of the nanocubes in the metacrystals.

Integration of semiconductors with noble metals to form heteronanostructures can give rise to many interesting plasmonic and electronic properties. A number of such heteronanostructures have been demonstrated comprising noble metals and n-type semiconductors, such as TiO2 , ZnO, SnO2 , Fe3 O4 , and CuO. In contrast, reports on heteronanostructures made of noble metals and p-type semiconductors are scarce. Cu2 O is an unintentional p-type semiconductor with unique properties. Here, the uniform coating of Cu2 O on two types of Au nanorods and systematic studies of the plasmonic properties of the resultant core-shell heteronanostructures are reported. One type of Au nanorods is prepared by seed-mediated growth, and the other is obtained by oxidation of the as-prepared Au nanorods. The (Au nanorod)@Cu2 O nanostructures produced from the as-prepared nanorods exhibit two transverse plasmon peaks, whereas those derived from the oxidized nanorods display only one transverse plasmon peak. Through electrodynamic simulations the additional transverse plasmon peak is found to originate from a discontinuous gap formed at the side of the as-prepared nanorods. The existence of the gap is verified and its formation mechanism is unraveled with additional experiments. The results will be useful for designing metal-semiconductor heteronanostructures with desired plasmonic properties and therefore also for exploring plasmon-enhanced applications in photocatalysis, solar-energy harvesting, and biotechnologies.

The photochemical production of fuels using sunlight is an innovative way for meeting the quickly increasing energy demands. One of the largest challenges is to develop high-performance photocatalysts that can meet the requirements of practical applications. Owing to their intriguing localized surface plasmon resonances, noble metal nanoparticles and nanostructures show a great potential for enhancing the photocatalytic efficiency and thereby have attracted rapidly growing interest recently. Here, for the first time, the latest achievements in the utilization of plasmons in driving CO2 reduction and N2 fixation into high-value products are comprehensively described. The involved plasmonic enhancement mechanisms in the two types of reactions are fully illustrated. A particular emphasis is given to the outlook on the direction and prospects for future work in this topic.

As the counterpart of electric and magnetic dipoles, the toroidal dipole is of paramount importance in the flourishing fields of metamaterials and Nanophotonics, and has therefore been getting much attention recently. Here, we demonstrate that a toroidal dipole can be formed in (dielectric core)@(plasmonic shell) nanostructures as the core refractive index is increased. For nanostructures with relatively large core refractive indices, polarized charge oscillation can be induced in the core by the oscillation of free electrons in the shell. These two oscillations create a toroidal dipole in the nanostructure. The formation of a toroidal dipole induces a scattering dip and a new absorption peak spectrally close to the created scattering dip. We also show that the toroidal dipole-induced absorption and scattering dip become weaker as the imaginary part of the core refractive index is increased. To the best of our knowledge, this is the first observation that the absorption becomes weaker with the increase of the imaginary part of the refractive index. Moreover, because almost all of the electric and magnetic fields are concentrated within the nanostructure, the toroidal dipole-induced scattering dip and absorption peak show resonance wavelength that is independent of the refractive index of the surrounding medium. Such an invariable property can be used as optical references or marks.

Plasmonic sensors that make use of localized surface plasmon resonance provide an excellent platform for hydrogen sensing. In this work, large plasmonic red shifts are obtained on (Au nanobipyramid core)@(Pd shell) bimetallic nanostructures for hydrogen sensing. Au nanobipyramid@Pd nanostructures with different shell thicknesses are synthesized by varying the Pd precursor amount. The Au nanobipyramid@Pd nanostructures with thicker Pd shells are found to exhibit larger responses to hydrogen. The maximal plasmonic red shift reaches 97 nm at 4 vol% hydrogen concentration. The shell morphology of the Au nanobipyramid@Pd nanostructures is further optimized to improve the hydrogen sensing performance. With the optimized nanostructures, the maximal plasmonic red shift is improved to ≈140 nm at 2 vol% hydrogen concentration. Compared with the Au nanobipyramid@Pd nanostructures, Au nanobipyramid/AgPd nanostructures show smaller plasmonic red shifts under the same conditions. The highly enhanced plasmonic shifts and sensitivity to hydrogen make our Au nanobipyramid@Pd nanostructures highly promising for the development of optical hydrogen sensing devices.

We have carried out a combined experimental and simulation study identifying the key physical and optical parameters affecting the presence and degree of fluorescence intensification measured on zinc oxide nanorod (ZnO NR) ends. Previously, we reported on the highly localized, intensified, and prolonged fluorescence signal measured on the NR ends, termed as fluorescence intensification on NR ends (FINE). As a step towards understanding the mechanism of FINE, the present study aims to provide an insight into the unique optical phenomenon of FINE through experimental and simulation approaches and to elucidate the key factors affecting the occurrence, degree, and temporal stability of FINE. Specifically, we examined the effect of the length, width, and growth orientation of single ZnO NRs on the NR-enhanced biomolecular emission profile after decorating the NR surfaces with different amounts and types of fluorophore-coupled protein molecules. We quantitatively and qualitatively profiled the biomolecular fluorescence signal from individual ZnO NRs as a function of both position along the NR long axis and time. Regardless of the physical dimensions and growth orientations of the NRs, we confirmed the presence of FINE from all ZnO NRs tested by using a range of protein concentrations. We also showed that the manifestation of FINE is not dependent on the spectroscopic signatures of the fluorophores employed. We further observed that the degree of FINE is dependent on the length of the NR with longer NRs showing increased levels of FINE. We also demonstrated that vertically oriented NRs exhibit much stronger fluorescence intensity at the NR ends and a higher level of FINE than the laterally oriented NRs. Additionally, we employed finite-difference time-domain (FDTD) methods to understand the experimental outcomes and to promote our understanding of the mechanism of FINE. Particularly, we utilized the electrodynamic simulations to examine both near-field and far-field emission characteristics when considering various scenarios of fluorophore locations, polarizations, spectroscopic characteristics, and NR dimensions. Our efforts may provide a deeper insight into the unique optical phenomenon of FINE and further be beneficial to highly miniaturized biodetection favoring the use of single ZnO NRs in low-volume and high-throughput protein assays.

On page 6322, J. F. Wang and co-workers report a wet-chemistry method for the preparation of colloidal Au nanocups and their plasmonic properties. The Au nanocups are prepared through single-vertex-initiated Au deposition on PbS nano-octahedrons and subsequent selective dissolution of PbS. Owing to the orientation-dependent coupling strengths, the obtained Au nanocups display orientation-dependent plasmonic properties and Raman enhancements when deposited on substrates.