Yue Li

Optical sensor based on hydrogel films with 2D colloidal arrays attached on both the surfaces: anti-curling performance and enhanced optical diffraction intensity

An interesting strategy to create free standing hydrogel composite films with colloidal monolayers attached on both the surfaces, which could act as visualizing sensors with high diffraction intensity, is developed. Owing to the balanced stress on both the surfaces, the colloidal monolayer–hydrogel composite films overcome the curling problem of traditional hydrogel films loaded with a colloidal monolayer on one side. They also display enhanced diffraction intensity compared to those with the attachment of only a single 2D colloidal monolayer due to a multi-diffraction effect. Such sensing hydrogel composite films with anti-curling performance and enhanced optical diffraction intensity are very helpful to improve their practical applications in visual and quantitative detection. In addition, this strategy is universal and could be suitable for fabricating various functional hydrogel films loaded with different nanosphere arrays for novel optical sensors.

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.

Temperature regulation growth of Au nanocrystals: from concave trisoctahedron to dendritic structures and their ultrasensitive SERS-based detection of lindane

A facile temperature regulation strategy is developed for fabrication of Au concave nanocrystals with specific shapes via seed-assisted growth at 25 °C or lower. It has been found that the reaction temperature, even with minor changes, can significantly influence the shape of the nanocrystals, which evolves from the concave trisoctahedral to calyptriform, coral and dendritic structures with the decrease of temperature from 25 °C to 5 °C. The size and optical absorbance spectra of the nanocrystals can be determined just by the addition amount of Au seeds. The formation of the Au concave nanocrystals is attributed to the preferential growth of the nuclei in 〈110〉 and 〈111〉 directions, along which the growth rates are of different temperature dependences. Importantly, the concave trisoctahedral and calyptriform Au nanocrystal-built films have exhibited strong surface enhanced Raman scattering (SERS) activity towards the lindane molecules, with the enhancement factor higher than 107, due to their high density of sharp corners/edges or the tip effect. The Raman peak intensity versus lindane concentration is subject to a linear double logarithmic relation from 30 ppb to 300 ppm, which is attributed to the Freundlich adsorption of lindane molecules on the Au nanocrystals. This work provides not only a simple route for the fabrication of the Au nanocrystals with various specific structures but also efficient SERS substrates for trace detection of organochlorine pesticide residues.

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.

Ultrathin Oxide Layer-Wrapped Noble Metal Nanoparticles via Colloidal Electrostatic Self-Assembly for Efficient and Reusable Surface Enhanced Raman Scattering Substrates

Controllable and flexible fabrication of ultrathin and uniform oxide layer-wrapped noble metal nanoparticles (NPs) has been expected. Here a new strategy is presented for them based on colloidal electrostatic attraction and self-assembly on the metal NPs via one-step laser ablation of noble metal targets in the hydrolysis-induced hydroxide sol solutions at room temperature. The Au NPs, with several tens of nanometers in size, are taken as core part and TiO2 as shell-layer to demonstrate the validity of the presented strategy. It has been shown that the TiO2 shell-wrapped Au NPs are obtained after laser ablation of Au target in the hydrolysis-induced Ti(OH)4 sol solution. The Au NPs are about 35 nm in mean size, and the TiO2 shell layers are amorphous in structure and about 2.5 nm in thickness. The shell thickness is nearly independent of the Au NPs size. Further experiments have shown that the thickness and crystallinity of the shell-layer can be tuned and controlled via changing the temperature or pH value of the Ti(OH)4 sol solution or prolonging the laser ablation duration. The formation of the TiO2 shell-wrapped Au NPs is attributed to attachment and self-assembly of Ti(OH)4 colloids on the laser-induced Au NPs due to the electrostatic attraction between them. Importantly, the presented strategy is universal and suitable for fabrication of many other ultrathin oxide-wrapped noble metal NPs. A series of oxide shell-wrapped noble metal NPs have been successfully fabricated, such as Au@oxides (Fe2O3, Al2O3, CuO, and ZnO) as well as Pt@TiO2 and Pd@TiO2, etc. Further, compared with the pure gold NPs-built film, the TiO2-wrapped Au NPs-built film has exhibited much stronger surface enhanced Raman scattering (SERS) performance to the anions NO3-, which weakly interact with noble metals, and the good reusability for the SERS-based detection of 4-nitrophenol, which could be photodegraded by xenon lamp irradiation. This work provides a flexible and universal route to the ultrathin and uniform oxide layer-wrapped noble metal NPs.

MnMoO4 nanosheet array: an efficient electrocatalyst for hydrogen evolution reaction with enhanced activity over a wide pH range

We report the preparation of MnMoO4 nanosheet array on nickel foam (MnMoO4 NSA/NF) as an excellent 3D hydrogen evolution reaction (HER) electrocatalyst with good catalytic performance applied under basic, acidic and neutral conditions. In 0.5 M H2SO4, this MnMoO4 NSA/NF electrode needs an overpotential of 89 mV to drive current densities of 10 mA cm-2, to achieve the same current density, it demands overpotentials of 105 mV in 1.0 M KOH, 161 mV in 1.0 M PBS (pHxa0=xa07), respectively. After continuous CV scanning for 1000 cycles under different pH conditions, it also demonstrates an excellent stability with ignorable activity decrease. Such preeminent HER performance may be derived from the synergistic effect between manganese (Mn) and molybdenum (Mo) atoms, exposure of more active sites on the nanosheets and effective electron transport along the nanosheets. This MnMoO4 NSA/NF electrocatalyst provides us a highly efficient material for water splitting devices for industrial hydrogen production.

Kinetically-Controlled Growth of Chestnut-Like Au Nanocrystals with High-Density Tips and Their High SERS Performances on Organochlorine Pesticides

A modified seed growth route was developed to fabricate the Au nanocrystals with high-density tips based on kinetically-controlled growth via adjusting the adding rate of Au seeds into growth solution. The obtained Au nanostructures were chestnut-like in morphology and about 100 nm in size. They were built of the radial [111]-oriented nanoneedles and were 30–50 nm in length. There were about 120–150 tips in each nanocrystal. The formation of chestnut-like Au nanocrystals is ascribed to surfactant-induced preferential growth of seeds along direction [111]. Importantly, the chestnut-like Au configuration displayed powerful surface enhanced Raman scattering (SERS) performance (enhance factor > 107), owing to the high density of tips. Further, such film was used as a SERS substrate for the detection of lindane (γ-666) molecules (the typical organochlorine pesticide). The detection limit was about 10 ppb, and the relationship between SERS intensity I and concentration C of 666 accords with the double logarithm linear. This work presents a simple approach to Au nanocrystal with high-density tips, and provides a highly efficacious SERS-substrate for quantitative and trace recognition of toxic chlorinated pesticides.

Nanosecond-Laser-Based Charge Transfer Plasmon Engineering of Solution-Assembled Nanodimers

The ability to re-engineer self-assembled functional structures with nanometer accuracy through solution-processing techniques represents a big challenge in nanotechnology. Herein we demonstrate that Ag+-soldered nanodimers with a steric confinement coating of silica can be harnessed to realize an in-solution nanosecond laser reshaping to form interparticle conductive pathway with finely controlled conductance. The high structural purity of the nanodimers, the rigid silica coating, and the uniform (but still adjustable) sub-1-nm interparticle gap together determine the success of the laser reshaping process. This method is applicable to DNA-assembled nanodimers, and thus promises DNA-based programming toward higher structural complexity. The resulting structures exhibit highly tunable charge transfer plasmons at visible and near-infrared frequencies dictated by the fluence of the laser pulses. Our work provides an in-solution, rapid, and nonperturbative route to realize charge transfer plasmonic coupling along prescribed paths defined by self-assembly, conferring great opportunities for functional metamaterials in the context of chemical, biological, and nanophotonic applications. The ability to continuously control a subnm interparticle gap and the nanomeric width of a conductive junction also provides a platform to investigate modern plasmonic theories involving quantum and nonlocal effects.

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.