Yiqiang Sun

Hierarchical micro/nanostructured C doped Co/Co3O4 hollow spheres derived from PS@Co(OH)2 for the oxygen evolution reaction

Hierarchical micro/nanostructured C doped Co/Co3O4 hollow spheres were prepared by two-step treatment (annealing at 600 °C in an Ar atmosphere and then at 250 °C in air) of PS@Co(OH)2 core–shell structures templated from PS microspheres without any modification. In 1 M KOH, such hollow nanospheres showed an overpotential of 352 mV at a benchmark oxygen evolution reaction (OER) current density of 10 mA cm−2, which was lower than that of RuO2 (364 mV), Co3O4 hollow nanospheres (410 mV) and C-Co/Co3O4 nanoparticles (462 mV). Importantly, the C-Co/Co3O4 hollow spheres exhibited a small onset potential (1.49 V) due to their more active sites, higher electrical conductivity, larger specific surface area, and excellent electron and ion diffusion permeability. This work provides a strategy to design and fabricate earth-abundant, low-cost electrocatalysts for water splitting in practical applications.

Periodic nanostructured Au arrays on an Si electrode for high-performance electrochemical detection of hydrogen peroxide without an enzyme

Periodic gold nanosphere arrays were prepared on a planar silicon substrate, which could be directly developed as an electrode to sensitively and selectively detect H2O2 without an enzyme via an electrochemical method. The arrays of Au nanospheres were fabricated on a large scale (∼cm2) on the Si substrate using polystyrene (PS) colloidal monolayers as the template, after Au deposition and subsequent annealing. The developed biosensor based on the Au nanosphere arrays on the Si substrate demonstrated excellent catalytic activity towards H2O2 over a wide linear range of 0.2 μM–5 mM with a very low detection limit of 0.1 μM. Importantly, the electrochemical biosensor possessed good stability and high reproducibility. The catalytic activity can be enhanced by reducing the gold nanoparticle size and periodic length in the array. The biosensors based on periodic Au nanosphere arrays used to determine the concentration of H2O2 have the advantages of non-enzymatic detection and non-Pt electrode strategy when compared to the conventional method, which may open up new horizons in the production of outstanding biosensors and can be used as a platform for the preparation of various electrochemical biosensors.

Self-organized hexagonal ordering of quantum dot arrays

We report a structure of (In, Ga)As/GaAs quantum dots which are vertically correlated and laterally aligned in a hexagonal way thus forming three-dimensionally ordered arrays. The growth pathway is based on a mechanism of self-assembly by strain-mediated multilayer vertical stacking on a planar GaAs(100) substrate, rather than molecular-beam epitaxy on a prepatterned substrate. The strain energy of lateral island-island interaction is minimum for the arrangement of hexagonal ordering. However, realization of hexagonal ordering not only depends on a complicated trade-off between lateral and vertical island-island interaction but is also related to a delicate and narrow growth kinetics window.

Controlled synthesis of sponge-like porous Au–Ag alloy nanocubes for surface-enhanced Raman scattering properties

We develop an interesting route to prepare new sponge-like Au–Ag alloy nanocubes (NCs) with controlled porosity and atomic percentage through an interparticle alloying and dealloying process. Au@Ag NCs were first synthesized using Au nanooctahedra as initial seeds. Then, the Au@Ag NCs were covered with SiO2 and thermally annealed, forming solid Au–Ag alloy NCs with a SiO2 layer. After removing the majority of the SiO2 layer and leaching less-stable Ag from solid Au–Ag alloy NCs, uniform sponge-like porous Au–Ag alloy NCs were obtained. In this process, SiO2 not only prevents fusion between adjacent Au@Ag NPs under thermal annealing, but also directs the final shape of sponge-like Au–Ag alloy NPs with a cubic shape as a template. Thanks to the high-density “hotspots” in nanopores, sharp corners and edges, and a synergistic effect between Au and Ag species, such sponge-like Au–Ag alloy NCs showed excellent SERS performance with an enhancement factor of ∼108, which can effectively detect 4-aminothiophenol (4-ATP) at a concentration as low as 1 × 10−10 M. This strategy is universal and it can be extended to prepare sponge-like Au–Ag alloy NPs with different accurate shapes. Such sponge-like nanoporous alloy NPs have many potential applications such as in plasmonics, SERS, drug delivery, photothermal therapy, and catalysis systems.

Rapid and Efficient Self-Assembly of Au@ZnO Core–Shell Nanoparticle Arrays with an Enhanced and Tunable Plasmonic Absorption for Photoelectrochemical Hydrogen Generation

High-quality Au@ZnO core-shell nanoparticle (NP) array films were easily and efficiently fabricated through an air/water interfacial self-assembly. These materials have remarkable visible light absorption capacity and fascinating performance in photoelectrochemical (PEC) water splitting with a photocurrent density of ∼3.08 mA/cm2 at 0.4 V, which is superior to most ZnO-based photoelectrodes in studies. Additionally, the interesting PEC performance could be effectively adjusted by altering the thickness of the ZnO shell and/or the layer number of the array films. Results indicated that the bilayer film based on Au@ZnO NPs with 25 nm shell thickness displayed optimal behavior. The remarkable PEC capability could be ascribed to the enhanced light-harvesting ability of the Au@ZnO structured NPs by the SPR effect and the optimum film thickness. This work demonstrates a desirable paradigm for preparing photoelectrodes based on the synergistic effect of plasmatic NPs as the core and a visible optical absorbent and semiconductor as the shell. Moreover, this work provides a new approach for fabricating optoelectronic anode thin film devices through a self-assembly method.

Strong Electronic Interaction in Dual-Cation-Incorporated NiSe2 Nanosheets with Lattice Distortion for Highly Efficient Overall Water Splitting

Exploring highly efficient and low-cost electrocatalysts for electrochemical water splitting is of importance for the conversion of intermediate energy. Herein, the synthesis of dual-cation (Fe, Co)-incorporated NiSe2 nanosheets (Fe, Co-NiSe2 ) and systematical investigation of their electrocatalytic performance for water splitting as a function of the composition are reported. The dual-cation incorporation can distort the lattice and induce stronger electronic interaction, leading to increased active site exposure and optimized adsorption energy of reaction intermediates compared to single-cation-doped or pure NiSe2 . As a result, the obtained Fe0.09 Co0.13 -NiSe2 porous nanosheet electrode shows an optimized catalytic activity with a low overpotential of 251 mV for oxygen evolution reaction and 92 mV for hydrogen evolution reaction (both at 10 mA cm-2 in 1 m KOH). When used as bifunctional electrodes for overall water splitting, the current density of 10 mA cm-2 is achieved at a low cell voltage of 1.52 V. This work highlights the importance of dual-cation doping in enhancing the electrocatalyst performance of transition metal dichalcogenides.

Optical sensing properties of Au nanoparticle/hydrogel composite microbeads using droplet microfluidics

Uniform Au nanoparticle (NP)/poly (acrylamide-co-acrylic acid) [P(AAm-co-AA)] hydrogel microbeads were successfully prepared using droplet microfluidics technology. The microbeads exhibited a good stimuli-responsive behavior to pH value. Particularly in the pH value ranging from pH 2-pH 9, the composite microbead sizes gradually increased along with the increase of pH value. The homogeneous Au NPs, which were encapsulated in the P(AAm-co-AA) hydrogel microbeads, could transform the volume changes of hydrogel into optical signals by a tested single microbead with a microspectrometre system. The glucose was translated into gluconic acid by glucose oxidase. Thus, the Au NP/P(AAm-co-AA) hydrogel microbeads were used for detecting glucose based on pH effects on the composite microbeads. For this, the single Au NP/P(AAm-co-AA) hydrogel microbead could act as a good pH- or glucose-visualizing sensor.

Surface enhanced Raman scattering properties of dynamically tunable nanogaps between Au nanoparticles self-assembled on hydrogel microspheres controlled by pH

We developed an interesting route for preparing a poly (acrylamide-co-acrylic acid) (P(AAm-co-AA)) hydrogel microsphere with a coating of Au nanospheres (hydrogel microsphere @ Au nanospheres) through self-assembly based on electrostatic interaction. The fabricated composites could be used as highly sensitive enhanced Raman scattering substrates. The nanogaps between adjacent Au nanospheres were dynamically tuned by volume changes in the hydrogel microspheres in the semiwet state under different pH conditions. At pH 6, the hydrogel microsphere @ Au nanospheres demonstrated highly sensitive SERS with an enhancement factor of 109. The product could detect very low concentrations of analytes up to 10-12M 4-aminothiophenol (4-ATP) molecules. This paper proposes a new method for detecting trace amounts of environmental organic pollutants by dynamically tuning the SERS enhancement in the semiwet testing state.

Laser-irradiation induced synthesis of spongy AuAgPt alloy nanospheres with high-index facets, rich grain boundaries and subtle lattice distortion for enhanced electrocatalytic activity

We develop a facile laser-irradiation induced alloying and subsequent chemical etching method to prepare spongy AuAgPt alloy nanospheres (spongy AuAgPt NSs) with high-index facets, rich grain boundaries and subtle lattice distortion as highly active electrooxidation catalysts. The key to preparing such spongy AuAgPt NSs for their excellent electrocatalytic activity is the alloying process induced by laser irradiation, forming rich grain boundaries and subtle lattice distortion due to the quick fusion and quenching process, which is completely different from traditional thermal annealing alloying. After chemical dealloying, the nanopores were formed and a large amount of high-index facets were successfully introduced into the spongy AuAgPt NSs. The spongy AuAgPt NSs exhibited superior methanol oxidation reaction (MOR) activity (1.62 A mgPt−1), which was 5.1 times higher than that of Pt black (0.32 A mgPt−1), and they also showed outstanding stability for the MOR after long-term cycles. The enhanced catalytic activity could be attributed to the abundant high-index facets, grain boundaries and subtle lattice distortion of spongy AuAgPt NSs formed in this laser-irradiation induced alloying and subsequent chemical etching process. The present work provides a new efficient strategy for the rational design of 3D spongy electrocatalysts with both high activity and improved durability for promising applications in electrocatalysis, biosensing, energy conversion, etc.