Suli Liu

Pd nanoparticle assemblies—As the substitute of HRP, in their biosensing applications for H2O2 and glucose

The spherical porous Pd nanoparticle assemblies (NPAs) have been successfully synthesized by starch-assisted chemical reduction of Pd(II) species at room temperature. Such Pd NPAs are not simply used to enlarge the surface area and to promote the electron transfer. They also catalyze the reduction of H(2)O(2) which are regarded as horseradish peroxidase (HRP) substitutes in electron transfer process. By using them as electrocatalysts, as low as 6.8×10(-7) M H(2)O(2) can be detected with a linear range from 1.0×10(-6) to 8.2×10(-4) M. Moreover, through co-immobilization of such Pd NPAs and glucose oxidase (GOx), a sensitive and selective glucose biosensor is developed. The detection principle lies on measuring the increase of cathodic current by co-reduction of dissolved oxygen and the in situ generated H(2)O(2) during the enzymatic reaction. Under optimal conditions, the detection limit is down to 6.1×10(-6) M with a very wide linear range from 4.0×10(-5) to 2.2×10(-2) M. The proposed biosensor shows a fast response, good stability, high selectivity and reproducibility of serum glucose level. It provides a promising strategy to construct fast, sensitive, stable and anti-interferential amperometric biosensors for early diagnosis and prevention of diabetes.

Five-Fold Twinned Pd2NiAg Nanocrystals with Increased Surface Ni Site Availability to Improve Oxygen Reduction Activity

The synthesis of highly active oxygen reduction reaction (ORR) catalysts with good durability and low cost is highly desirable but still remains a significant challenge. In this work, we present the synthesis of five-fold twinned Pd2NiAg nanocrystals (NCs) with a Ni-terminal surface which exhibit excellent electrocatalytic performance for ORR in alkaline media, even better than the performance of the commercial Pt/C catalyst. Using high-angle annular-dark-field imaging together with density functional theory calculations, it is found that the surfaces of the five-fold twinned Pd2NiAg NCs exhibit an unusual valence electron density. The maximum catalytic activity originates from the increased availability of surface Ni sites in five-fold twinned Pd2NiAg NCs and the features of twinned structural defects. This study provides an explanation of the enhanced ORR from the special structure of this novel material, which opens up new avenues for the design of novel classes of electrocatalysts for fuel cells and metal-air batteries.

Using ruthenium polypyridyl functionalized ZnO mesocrystals and gold nanoparticle dotted graphene composite for biological recognition and electrochemiluminescence biosensing

Using ruthenium polypyridyl functionalized ZnO mesocrystals as bionanolabels, a universal biological recognition and biosensing platform based on gold nanoparticle (AuNP) dotted reduced graphene oxide (rGO) composite was developed. AuNP-rGO accelerated electron transfer between the detection probe and the electrode, and increased the surface area of the working electrode to load greater amounts of the capture antibodies. The large surface area of ZnO mesocrystals was beneficial for loading a high content ruthenium polypyridyl complex, leading to an enhanced electrochemiluminescence signal. Using α-fetoprotein (AFP) as a model, a simple and sensitive sandwich-type electrochemiluminescence biosensor with tripropylamine (TPrA) as a coreactant for detection of AFP was constructed. The designed biosensor provided a good linear range from 0.04 to 500 ng mL(-1) with a low detection limit of 0.031 ng mL(-1) at a S/N of 3 for AFP determination. The proposed biological recognition and biosensing platform extended the application of ruthenium polypyridyl functionalized ZnO mesocrystals, which provided a new promising prospect.

Electrochemiluminescence Tuned by Electron-Hole Recombination from Symmetry-Breaking in Wurtzite ZnSe

The research of highly active electrochemiluminescence (ECL) materials with low toxicity and good solubility remains a substantial challenge. In this work, we present a synthesis method to prepare soluble wurtzite (WZ) ZnSe nanocrystals (NCs), which exhibit good ECL properties. Using high-angle annular-dark-field imaging together with electron hologram methods, we observe that the WZ ZnSe NCs exhibit an unusual symmetry-breaking phenomenon, where the translational symmetry of the polarized Zn-Se bond is broken. The formation of a symmetry-breaking region leads to an accumulation of charge. The good ECL response originates from the increased efficiency of electron-hole recombination by the excess charge redistribution in WZ ZnSe NCs. This study of the relationship between ECL behavior and the architecture of NCs suggests that careful control over the NC structures of semiconductors can tailor their charge distribution via symmetry breaking, which opens new avenues for the design of novel classes of agents for optoelectronic applications.

Biomimetic superoxide dismutase stabilized by photopolymerization for superoxide anions biosensing and cell monitoring.

Photopolymerization strategy, as one of the immobilization methods, has attracted considerable interest because of some advantages, such as easy operation, harmlessness to the biomolecules, and long storage stability. (E)-4-(4-Formylstyryl) pyridine (formylstyrylpyridine) was prepared through Heck reaction and used as a photopolymer material to immobilize biomimetic superoxide dismutase under ultraviolet irradiation (UV) irradiation in a short time. The styrylpyridinium moiety of Formylstyrylpyridine was photoreactive and formed a dimer under UV irradiation. Mn2P2O7 multilayer sheet, a novel superoxide dismutase mimic, was synthesized. The formed photopolymer can immobilize Mn2P2O7 firmly under UV irradiation. On the basis of high catalytic activity of Mn2P2O7 biomimetic enzyme and long-term stability of Mn2P2O7-formylstyrylpyridine film, after introducing multiwalled carbon nanotubes (MWCNTs), a novel electrochemical biosensing platform called MWCNTs/Mn2P2O7-formylstyrylpyridine for superoxide anion (O2(•-)) detection was constructed. The biosensor displayed good performance for O2(•-) detection and provided a reliable platform to adhere living cells directly on the modified electrode surface. Therefore, the biosensor was successfully applied to vitro determination of O2(•-) released from living cells, which had a promising prospect for living cells monitoring and diagnosis of reactive oxygen species-related diseases.

Two-dimensional porous γ-AlOOH and γ-Al2O3 nanosheets: hydrothermal synthesis, formation mechanism and catalytic performance

Novel two-dimensional (2D) γ-AlOOH porous nanosheets have been successfully prepared in a mixed system consisting of oleic acid (OA), dodecylamine (DDA), urea, and 1-octadecene. OA acted as a reaction reagent to form the Al-carboxyl precursor, DDA acted as a soft template and induced the γ-AlOOH sheet structure, and urea acted as a porogen. Porous γ-Al2O3 nanosheets were obtained by thermal decomposition of the γ-AlOOH. Furthermore, the obtained sheet-like γ-Al2O3 was used as a support to prepare a monodisperse Ag/γ-Al2O3 nanocatalyst. This catalyst exhibited superior catalytic activity compared to γ-Al2O3 nanosheets, pure Ag nanocrystals (NCs) and Ag/amorphous Al2O3 for the hydrogenation of nitroaromatic compounds, which can be explained by a higher concentration of Lewis type basic sites on sheet-like γ-Al2O3 leading to a higher concentration of nitrobenzene and more efficient hydrogenation.

Two-dimensional nanostructures of non-layered ternary thiospinels and their bifunctional electrocatalytic properties for oxygen reduction and evolution: the case of CuCo2S4 nanosheets

Two-dimensional (2D) transition metal chalcogenide nanostructures exhibit unique electronic, optoelectronic and mechanical properties, showing great potential for innovation of future electronics, renewable energy, sensing, and catalysis fields. Despite achieving great progress, fabricating 2D nanostructures of non-layered ternary thiospinels remains a great challenge, and their bifunctional electrocatalytic properties toward both oxygen reduction and evolution reactions (ORR and OER) have not been explored. In this paper, 2D nanostructures of an earth-abundant non-layered ternary thiospinel compound – CuCo2S4 nanosheets (NSs) – with their (111), (022) and (004) planes mainly exposed, are synthesized via a “leveling metal activity and structure-directed one-pot sulfurization” strategy. The electrocatalytic tests in alkaline solution show that such CuCo2S4 NSs can efficiently catalyze both the ORR and OER, whose bifunctional catalytic properties are superior to binary metal sulfide nanostructures, Pt/C, CuCo2S4 nanoparticles, and recently reported some bifunctional oxygen-electrode catalysts (e.g. CoxSy@C-1000, N-doped G/CNTs, Co3O4/NBGHSs, CoFe2O4, CoxMn3−xO4, MnOx, NiCo2S4 hollow spheres, NiCo2S4@N/S-rGO, etc.). Combined with spin-polarized density functional theory computations based on a computational hydrogen electrode model, their excellent bifunctional catalytic properties originate from the presence of the two special facets, (022) and (004), which have different preferences in terms of the ORR/OER. This work not only enriches the current 2D material family but also paves the way for rational design of advanced multifunctional 2D electrocatalysts for use in renewable energy fields.

Concave octahedral Pd@PdPt electrocatalysts integrating core–shell, alloy and concave structures for high-efficiency oxygen reduction and hydrogen evolution reactions

The development of bifunctional catalysts for both the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) is crucial for facile hydrogen production via water splitting and reducing oxygen to promote electrochemical energy conversion in fuel cells. Here, we prepare a unique concave octahedral Pd@PdPt electrocatalyst, which integrates three structural types, core–shell, concave and alloy structures, using an ethylene glycol system. Scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDS) line-scan, and X-ray photoelectron spectroscopy (XPS) analyses reveal that the concave octahedral Pd core is surrounded by a PdPt alloy shell. Through some control experiments, a possible mechanism for the formation of the nanostructure is proposed. The as-prepared Pd@PdPt NCs exhibit a superior enhanced bifunctional electrocatalytic performance for both the ORR and the HER, even better than that of 20% Pt/C. When used in the ORR, the concave octahedral Pd@PdPt NCs exhibit a superior half-potential of 0.91 V (vs. RHE), a large mass activity of 0.95 A mgPt−1, and a superior stability over 1000 cycles in 0.1 M KOH. When used in the HER, these NCs present a positive onset potential of −5 mV (vs. RHE), a small Tafel slope of 38 mV dec−1, a lower overpotential of ∼39 mV at a current density of 10 mA cm−2 and a long-term durability over 4000 cycles in 0.5 M H2SO4. This study enables the design of multi-structural bifunctional electrocatalysts for the renewable energy field.

Ru Modulation Effects in the Synthesis of Unique Rod-like Ni@Ni2P–Ru Heterostructures and Their Remarkable Electrocatalytic Hydrogen Evolution Performance

The construction of highly efficient and stable Pt-free catalysts for electrochemical hydrogen generation is highly desirable. Herein, we demonstrate the first metal-phosphides-metal system consisting of Ru, Ni2P, and Ni, which forms unique multiheterogeneous Ni@Ni2P-Ru nanorods. Interestingly, a Ru modulation effects that promotes the desorption of H2 to achieve a moderate hydrogen adsorption energy (ΔGH), and enables the formation of Ni@Ni2P nanorods via Ru-Ni coordination to enhance the conductivity was discovered. Due to its optimal ΔGH, improved conductivity and rod-like morphology, this catalyst shows superior electrocatalytic HER performances in both acidic and alkaline conditions, which are superior to those of some recently reported phosphides and close to that of commercial 20% Pt/C. Such a design strategy is not limited to Ni2P and Ru but also may be extended to other similar phosphides and noble metals, providing a new promising approach and an alternative to Pt catalysts for electrocatalytic applications.

Significantly Enhanced Hydrogen Evolution Activity of Freestanding Pd-Ru Distorted Icosahedral Clusters with less than 600 Atoms

Freestanding metal nanoclusters can tune, precisely and effectively, the Gibbs free energy (ΔGH ) of atomic hydrogen on the surface of materials. This enables the enhancement of hydrogen evolution activity. In this paper, we report a study of freestanding Pd-Ru distorted icosahedral clusters (ico-clusters) with less than 600 atoms by using a simple one-pot synthesis method. This Pd-Ru ico-cluster can be used as an efficient electrocatalyst for the hydrogen evolution reaction (HER) in acidic water, which is a promising alternative to Pt. The experimental and theoretical results suggest that the face-centered cubic (fcc) freestanding Pd-Ru distorted ico-clusters with less than 600 atoms ensure increased active edges and distorted defect sites, which reduce the coordination number for the atoms on the catalyst surface. Furthermore, Ru is a more effective hydrogen dissociation source, whereas Pd has a better hydrogen storage function. Pd-Ru can tune the ΔGH of atomic hydrogen adsorbed on a catalyst and reach an optimal equilibrium state that improves the HER performance. Our studies represent a robust approach towards the development of freestanding Pd-Ru distorted ico-clusters and advanced catalysts with non-Pt content for HER and many other heterogeneous reactions.