Xianjun Lyu

Periodic Porous Alloyed Au-Ag Nanosphere Arrays and Their Highly Sensitive SERS Performance with Good Reproducibility and High Density of Hotspots

Periodic porous alloyed Au-Ag nanosphere (NS) arrays with different periodic lengths and tunable composition ratios were prepared on Si substrates on a large scale (∼cm2) using stepwise metal deposition-annealing and subsequent chemical corrosion from a monolayer of colloidal polystyrene (PS) microspheres as the initial template. The porous alloyed Au-Ag NSs possessed a high porosity and bicontinuous morphology composed of hierarchically interconnected ligaments, which were obtained from an optimized dealloying process in nitric acid. Interestingly, when the dealloying time was prolonged, the average size of the porous alloyed NSs slightly decreased, and the width of the ligaments gradually increased. The periodic length of the array could be facilely changed by controlling the initial particle size of the PS template. Moreover, the porous alloyed Au-Ag NS arrays were explored as a platform for the surface-enhanced Raman scattering (SERS) detection of 4-aminothiophenol (4-ATP) and exhibited excellent reproducibility and high sensitivity because of the periodic structure of the arrays and the abundance of inherent hotspots. After optimization experiments, a low concentration of 10-10 M 4-ATP could be detected on these porous Au-Ag NS array substrates. Such highly reproducible SERS activity is meaningful for improving the practical application of portable Raman detection equipment.

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.

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.

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.

Ni0.33Co0.67MoS4 nanosheets as a bifunctional electrolytic water catalyst for overall water splitting

Currently, for overall water splitting, the highest activity for hydrogen evolution reaction (HER) oxygen evolution reaction (OER) are recorded by platinum (Pt) and ruthenium oxide (RuO2) catalysts, respectively. However, the shortage and sumptuosity of these noble metals limit their commercial applications. Herein, we prepared Ni0.33Co0.67MoS4 nanosheets on carbon fiber cloth (Ni0.33Co0.67MoS4/CFC) as bifunctional electrolytic water catalysts for both HER and OER. In the HER process, Ni0.33Co0.67MoS4/CFC exhibited an overpotential of only 48.0xa0mV at a current density of 10 mA cm−2, and the Tafel slope was 73.5 mV dec−1. Moreover, in the OER process, Ni0.33Co0.67MoS4/CFC displayed a low overpotential of 283 mV at current densities of 10 mA cm−2, and the Tafel slope was 68.8 mV dec−1. More importantly, Ni0.33Co0.67MoS4/CFC could act as a bifunctional electrocatalyst to split water under a cell voltage of 1.55 V at a current density of 10 mA cm−2. In addition, negligible decay occurred after 20 h of continuous electrolysis testing. Such noble-metal-free electrocatalysts may provide a strategy for the design of high efficiency overall water splitting catalysts, which are expected to be applied to the actual electrolysis water industry.