Chunmei Zhang

Three-Dimensional Mesoporous Graphene Aerogel-Supported SnO2 Nanocrystals for High-Performance NO2 Gas Sensing at Low Temperature

A facile and cost-efficient hydrothermal and lyophilization two-step strategy has been developed to prepare three-dimensional (3D) SnO2/rGO composites as NO2 gas sensor. In the present study, two different metal salt precursors (Sn(2+) and Sn(4+)) were used to prepare the 3D porous composites. It was found that the products prepared from different tin salts exhibited different sensing performance for NO2 detection. The scanning electron microscopy and transmission electron microscopy characterizations clearly show the macroporous 3D hybrids, nanoporous structure of reduce graphene oxide (rGO), and the supported SnO2 nanocrystals with an average size of 2-7 nm. The specific surface area and porosity properties of the 3D mesoporous composites were analyzed by Braunauer-Emmett-Teller method. The results showed that the SnO2/rGO composite synthesized from Sn(4+) precursor (SnO2/rGO-4) has large surface area (441.9 m(2)/g), which is beneficial for its application as a gas sensing material. The gas sensing platform fabricated from the SnO2/rGO-4 composite exhibited a good linearity for NO2 detection, and the limit of detection was calculated to be as low as about 2 ppm at low temperature. The present work demonstrates that the 3D mesoporous SnO2/rGO composites with extremely large surface area and stable nanostructure are excellent candidate materials for gas sensing.

Three-dimensional Fe- and N-incorporated carbon structures as peroxidase mimics for fluorescence detection of hydrogen peroxide and glucose

In this study, a simple and one-pot pyrolysis strategy is developed for the mass production of Fe, N-incorporated carbon nanotubes in situ grown on 3D porous carbon foam (denoted as Fe-Phen-CFs), which provides highly active Fe-N and doped-N species, and a large surface area with exposed active sites. The obtained composite exhibits intrinsic peroxidase-like catalytic activities. With the Fe-Phen-CFs as the catalyst, the peroxidase substrate of terephthalic acid (TA) can be oxidized to the fluorescent product of hydroxyterephthalate (HTA) by H2O2, which provides a unique strategy for fluorescence detection of H2O2. With such a process, as low as 68 nM H2O2 could be detected with a linear range from 0.1 to 100 μM. Meanwhile, by integrating glucose oxidase on the Fe-Phen-CFs composite, sensitive detection of glucose is also achieved with a linear range from 0.5 to 200 μM and a limit of detection of 0.19 μM. Most importantly, such a novel TA/Fe-Phen-CFs system can be successfully applied to glucose determination in real human serum samples. The unique nature and 3D structure of the Fe-Phen-CFs composite makes it promising for the fabrication of low-cost, high-performance biosensors.

FeP embedded in N, P dual-doped porous carbon nanosheets: an efficient and durable bifunctional catalyst for oxygen reduction and evolution reactions

It is highly desirable but challenging to develop bifunctional electrocatalysts for efficiently boosting both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in energy storage and conversion devices. Here, a simple yet cost-efficient thermal annealing strategy is developed to synthesize FeP embedded in N, P dual-doped 2D porous carbon nanosheets (FeP@NPCs). The obtained FeP@NPCs exhibited outstanding catalytic activities and durabilities toward both the ORR and OER with a potential gap of 0.74 V between the half-wave potential for the ORR and the OER potential at a current density of 10 mA cm−2 in alkaline electrolytes.

Single Crystal Sub-Nanometer Sized Cu6(SR)6 Clusters : Structure, Photophysical Properties, and Electrochemical Sensing

Organic ligand‐protected metal nanoclusters have attracted extensively attention owing to their atomically precise composition, determined atom‐packing structure and the fascinating properties and promising applications. To date, most research has been focused on thiol‐stabilized gold and silver nanoclusters and their single crystal structures. Here the single crystal copper nanocluster species (Cu6(SC7H4NO)6) determined by X‐ray crystallography and mass spectrometry is presented. The hexanuclear copper core is a distorted octahedron surrounded by six mercaptobenzoxazole ligands as protecting units through a simple bridging bonding motif. Density functional theory (DFT) calculations provide insight into the electronic structure and show the cluster can be viewed as an open‐shell nanocluster. The UV–vis spectra are analyzed using time‐dependent DFT and illustrates high‐intensity transitions involving primarily ligand states. Furthermore, the as‐synthesized copper clusters can serve as promising nonenzymatic sensing materials for high sensitive and selective detection of H2O2.

4-Nitrophenol Reduction by a Single Platinum Palladium Nanocube Caged within a Nitrogen-Doped Hollow Carbon Nanosphere

The improvement of the utilization efficiency and the enhancement of the catalytic activity and stability of precious‐metal‐based nanocatalysts is a hot topic in the field of catalysis. In the present study, a single‐nanoparticle catalyst with a high stability is realized by confining a single surface‐cleaned PtPd alloy nanocube within a N‐doped hollow carbon nanosphere (PtPd@N‐HCS). The microporous carbon shell makes the encaged PtPd nanocube accessible to the reacting molecules. Compared with PtPd nanocubes protected by polyvinylpyrrolidone (PVP‐PtPd) and N‐doped carbon spheres, PtPd@N‐HCS exhibited a better catalytic performance towards 4‐nitrophenol reduction. Under the catalysis of PtPd@N‐HCS, 4‐nitrophenol can be reduced completely to 4‐aminophenol (100 %) in 2 min; however, only 50 and 20 % of 4‐nitrophenol was degraded in 2 min with PVP‐PtPd and N‐HCS as catalysts. Moreover, as a result of the confinement of PtPd nanocubes in hollow nanospheres, PtPd@N‐HCS showed a high catalytic stability with 100 % conversion maintained over at least four cycles.

PtNi Nanocrystals Supported on Hollow Carbon Spheres: Enhancing the Electrocatalytic Performance through High-Temperature Annealing and Electrochemical CO Stripping Treatments

PtNi nanoparticles have been proved to be a type of highly efficient electrocatalyst for the oxygen reduction reaction (ORR) among the Pt-based nanomaterials. However, how to improve the surface catalytic activity and stability of polymer-stabilized Pt-based nanocrystals is still a critical issue for their application in fuel cells. In this work, a one-step solvothermal process was used to synthesize PVP-stabilized PtNi nanocubes supported on hollow carbon spheres. With optimized metal precursor ratio (Pt/Ni = 1:1) and solvothermal temperature (130 °C), PtNi nanocrystals with uniform size and cubic shape can be synthesized and highly dispersed on hollow carbon spheres. To improve the electrocatalytic activity of the PtNi nanocrystals, the synthesized composite was treated by a heating annealing at 300 °C and a subsequent electrochemical CO stripping process. It was found that the two-step treatment can significantly enhance the catalytic activity of the PtNi nanocrystals for ORR with high durability. In addition, the prepared PtNi composite also showed higher catalytic activity and stability for methanol oxidation. The obtained peak current density on the present catalyst can reach 3.89 A/mgPt, which is 9 times as high as commercial Pt/C (0.43 A/mgPt). The present study not only demonstrates a general method to synthesize hollow carbon sphere-supported nanoparticle catalysts but also provides an efficient strategy to active the surface activity of nanoparticles.

3D Network and 2D Paper of Reduced Graphene Oxide/ Cu2O Composite for Electrochemical Sensing of Hydrogen Peroxide

In this study, two-dimensional (2D) and three-dimensional (3D) freestanding reduced graphene oxide-supported Cu2O composites (Cu2O-rGO) were synthesized via simple and cost-efficient hydrothermal and filtration strategies. The structural characterizations clearly showed that highly porous 3D graphene aerogel-supported Cu2O microcrystals (3D Cu2O-GA) have been successfully synthesized, and the Cu2O microcrystals are uniformly assembled in the 3D GA. Meanwhile, paper-like 2D reduced graphene oxide-supported Cu2O nanocrystals (2D Cu2O-rGO-P) have also been prepared by a filtration process. It was found that the products prepared from different precursors and methods exhibited different sensing performances for H2O2 detection. The electrochemical measurements demonstrated that the 3D Cu2O-GA has high electrocatalytic activity for the H2O2 reduction and excellent sensing performance for the electrochemical detection of H2O2 with a detection limit of 0.37 μM and a linear detection range from 1.0 μM to 1.47 mM. Meanwhile, the 2D Cu2O-rGO-P structure also showed good electrochemical sensing performance toward H2O2 detection with a much wider linear response over the concentration range from 5.0 μM to 10.56 mM. Compared to the previously reported sensing materials, the as-obtained 2D and 3D Cu2O-rGO materials exhibited higher electrochemical sensing properties toward the detection of H2O2 with high sensitivity and selectivity. The 2D and 3D Cu2O-rGO composites also exhibited high sensing performance for the real-time detection of H2O2 in human serum. The present study indicates that 2D and 3D graphene-Cu2O composites have promising applications in the fabrication of nonenzymatic electrochemical sensing devices.

Small Naked Pt Nanoparticles Confined in Mesoporous Shell of Hollow Carbon Spheres for High-Performance Nonenzymatic Sensing of H2O2 and Glucose

Nonenzyme direct electrochemical sensing of hydrogen peroxide and glucose by highly active nanomaterial-modified electrode has attracted considerable attention. Among the reported electrochemical sensing materials, hollow carbon sphere (HCS) is an attractive carbon support because of its large specific surface area, porous structure, and easy accessibility for target molecules. In this study, naked Pt nanoparticles with average size of 3.13 nm are confined in mesoporous shells of hollow carbon spheres (Pt/HCS) by using one-step synthesis, which can not only produce highly dispersed Pt nanoparticles with clean surface, but also avoid the relatively slow impregnation–reduction process. The surface area of the obtained Pt/HCS (566.30 m2 g–1) is larger than that of HCS, attributing to the enlarged surface area after Pt nanoparticles deposition. The average pore width of Pt/HCS (3.33 nm) is smaller than that of HCS (3.84 nm), indicating the filling of Pt nanoparticles in the mesopores of carbon shells. By using the as-synthesized Pt/HCS as nonenzymatic sensing material, H2O2 and glucose can be detected with high sensitivity and selectivity. The linear range toward H2O2 sensing is from 0.3 to 2338 μM, and the limit of detection (LOD) is 0.1 μM. For glucose sensing, Pt/HCS exhibited two linear ranges from 0.3 to 10 mM and from 10 to 50 mM with an LOD of 0.1 mM. In addition, the Pt/HCS exhibited higher electrochemical stability than commercial Pt/C in acid solution. The present study demonstrates that Pt/HCS is a promising sensing material for electrochemical detection of both H2O2 and glucose.

Novel Au Catalysis Strategy for the Synthesis of Au@Pt Core–Shell Nanoelectrocatalyst with Self-Controlled Quasi-Monolayer Pt Skin

Design of catalytically active Pt-based catalysts with minimizing the usage of Pt is a major issue in fuel cells. Herein, for the first time, we have developed a Au catalytic reduction strategy to synthesize a Au@Pt core-shell electrocatalyst with a quasi-monolayer Pt skin spontaneously formed from the gold surface catalysis. In the presence of presynthesized gold nanocrystals (used as the catalyst and Au seeds) and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer (used as reductant), under the Au surface catalysis, platinum ions can be reduced and deposited on the gold nanocrystals to form a Pt skin surface with a quasi-monatomic thickness. In the present strategy, Pt ions can be reduced only under the catalysis of gold surface and thus when the surface of Au NPs is covered by a monatomic Pt layer, the reduction reaction of Pt ions will be spontaneously turned off. Therefore, the significant advantage of this synthesis strategy is that the formation of quasi-monolayer Pt skin surface can be self-controlled and is completely free of controlling the dosage of platinum ions and the size distribution of Au cores. The synthesized Au@Pt core@shell structure exhibited enhanced electrocatalytic activities for oxygen reduction reaction and methanol oxidation reaction, which are 6.87 and 10.17 times greater than those of Pt/C catalyst, respectively. The present study provides a new strategy for obtaining high-performance bimetallic/multimetallic electrocatalysts with high utilization of precious metals.

CO gas sensors based on p-type CuO nanotubes and CuO nanocubes: Morphology and surface structure effects on the sensing performance

Metal oxide nanomaterials have been widely applied in the high-performance gas sensors. For metal oxide semiconductors, high surface-to-volume ratio and the exposed crystal facets are the two key factors for determining their gas sensing performances. In order to study the effect of surface structure on the gas sensing properties, in this work, two types of copper oxide (CuO) nanostructures, CuO nanotubes (CuO NTs) with exposed surface plane of (111) and CuO nanocubes (CuO NCs) with exposed surface plane of (110), were obtained from Cu nanowires (Cu NWs) and Cu2O nanocubes (Cu2O NCs), respectively. The morphologies, crystal and surface structures were characterized by high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The gas-sensing performances of CuO NTs and CuO NCs for CO gas detection were then studied. The results demonstrated that compared to CuO NCs, the CuO NTs exhibited lower optimum working temperature and higher sensitivity for CO gas detection. At the operating temperature of 175 °C, the prepared CuO NTs exhibited high sensitivity, good selectivity, fast response and recovery times to CO gas. The present study indicates that for the same semiconductor sensing material, the surface crystal structure has significant influence on the sensing performance.