Shuijian He

One-pot synthesis of carbon nanodots for fluorescence turn-on detection of Ag+ based on the Ag+-induced enhancement of fluorescence

Carbon quantum dots (C-dots) are promising fluorescence probes for applications in metal ion detection, biosensing and bioimaging and so on. In this study, water soluble carbon nanodots were synthesized through a simple one-step heat treatment of ethylene glycol solution. In the present preparation, the C-dots may be formed through the hydration, crosslinking and carbonization processes. The synthesized C-dots show a green luminescent emission under ultraviolet excitation, which can be used for the detection of Ag+ ions. Interestingly, in a different way to the usual quenching effects of metal ions on the fluorescence of C-dots, Ag+ exhibited an enhancement effect on the photoluminescence of C-dots, which can be attributed to the reduction of Ag+ to silver nanoclusters (Ag0) on the surface of the C-dots. Based on the linear relationship between fluorescence intensity and concentration of Ag+ ions, the prepared C-dots can be used for sensitive and selective detection of silver ions in environmental water with a limit of detection of 320 nM and a linear range of 0–90 μM.

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.

Freestanding 3D Mesoporous Co3O4@Carbon Foam Nanostructures for Ethanol Gas Sensing

Metal oxide materials have been widely used as gas-sensing platforms, and their sensing performances are largely dependent on the morphology and surface structure. Here, freestanding flower-like Co3O4 nanostructures supported on three-dimensional (3D) carbon foam (Co3O4@CF) were successfully synthesized by a facile and low-cost hydrothermal route and annealing procedure. The morphology and structure of the nanocomposites were studied by X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive spectroscopy, and scanning electron microscopy (SEM). The SEM characterizations showed that the skeleton of the porous carbon foam was fully covered by flower-like Co3O4 nanostructures. Moreover, each Co3O4 nanoflower is composed of densely packed nanoneedles with a length of ~10 μm, which can largely enhance the surface area (about 286.117 m(2)/g) for ethanol sensing. Gas sensor based on the as-synthesized 3D Co3O4@CF nanostructures was fabricated to study the sensing performance for ethanol at a temperature range from 180 to 360 °C. Due to the 3D porous structure and the improvement in sensing surface/interface, the Co3O4@CF nanostructure exhibited enhanced sensing performance for ethanol detection with low resistance, fast response and recovery time, high sensitivity, and limit of detection as low as 15 ppm at 320 °C. The present study shows that such novel 3D metal oxide/carbon hybrid nanostructures are promising platforms for gas sensing.

Fe, Co, N-functionalized carbon nanotubes in situ grown on 3D porous N-doped carbon foams as a noble metal-free catalyst for oxygen reduction

Designing and manipulating advanced oxygen reduction reaction (ORR) electrocatalysts are of critical importance for the widespread application of fuel cells. In this work, we report a highly versatile and one-pot pyrolysis route for the mass production of a novel three-dimensional N, Fe, Co-functionalized carbon nanotubes rigidly grown on N-doped carbon foams (3D FeCoN–CNTs/NCFs) serving as a noble-metal free catalyst for the oxygen reduction reaction (ORR). Different from the previously reported carbon materials, in the present 3D porous structure, the N, Fe, Co-doped carbon nanotubes are rigidly grown on the skeleton of 3D nitrogen-doped carbon foams (NCFs), showing a high electrochemical stability. Moreover, due to the synergistic effect of the Fe/Co and the N species with the formation of Fe/Co–Nx complexes in the 3D hybrid carbon material and the multiple active sites on the porous structure, the 3D hybrid displayed superior catalytic performance for ORR, high operation stability and strong methanol/CO crossover resistance in alkaline medium. The stable porous structure and the excellent catalytic performance make the 3D FeCoN–CNTs/NCFs a promising non-precious-metal cathodic electrocatalyst for fuel cells.

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.

Sub-nanometer sized Cu6(GSH)3 clusters: one-step synthesis and electrochemical detection of glucose

We report here a one-pot synthesis of sub-nanometer sized copper clusters capped with a water-soluble ligand, L-glutathione (SGH), through a chemical reduction process. The composition of the as-prepared Cu6(SG)3 nanoclusters was confirmed by electrospray ionization mass spectrometry (ESI-MS) and matrix-assisted laser desorption ionization time-of-flight mass spectroscopy (MALDI-TOF MS). The FTIR, 1H NMR and XPS characterization methods showed that with the production of Cu6(SG)3 clusters and the formation of Cu–S bonds, the surface chemical environment of the clusters exhibited a significant change. The produced water-soluble clusters show aggregation-induced fluorescence upon the addition of ethanol into the cluster aqueous solution. By loading on the TiO2 support, the as-prepared copper nanoclusters were successfully applied to the electrochemical detection of glucose. Compared to large Cu nanoparticles, the Cu6(SG)3 nanoclusters exhibited higher sensitivity and a wider linear range for glucose detection.

Colorimetric detection of iron ions (III) based on the highly sensitive plasmonic response of the N-acetyl-l-cysteine-stabilized silver nanoparticles

We report here a facile colorimetric sensor based on the N-acetyl-L-cysteine (NALC)-stabilized Ag nanoparticles (NALC-Ag NPs) for detection of Fe(3+) ions in aqueous solution. The Ag NPs with an average diameter of 6.55±1.0 nm are successfully synthesized through a simple method using sodium borohydride as reducing agent and N-acetyl-L-cysteine as protecting ligand. The synthesized silver nanoparticles show a strong surface plasmon resonance (SPR) around 400 nm and the SPR intensity decreases with the increasing of Fe(3+) concentration in aqueous solution. Based on the linear relationship between SPR intensity and concentration of Fe(3+) ions, the as-synthesized water-soluble silver nanoparticles can be used for the sensitive and selective detection of Fe(3+) ions in water with a linear range from 80 nM to 80 μM and a detection limit of 80 nM. On the basis of the experimental results, a new detection mechanism of oxidation-reduction reaction between Ag NPs and Fe(3+) ions is proposed, which is different from previously reported mechanisms. Moreover, the NALC-Ag NPs could be applied to the detection of Fe(3+) ions in real environmental water samples.

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.

Hierarchical Cu@MnO2 Core–shell Nanowires: A Nonprecious-Metal Catalyst with an Excellent Catalytic Activity Toward the Reduction of 4-Nitrophenol

A nonprecious catalyst of hierarchical Cu@MnO2 core–shell nanowires was fabricated by a facile hydrothermal route and the nanostructured material showed a high catalytic activity toward the reduction of 4‐nitrophenol in the presence of NaBH4. With an intact core–shell structure and porous MnO2 shell, the Cu@MnO2 nanowires exhibited an excellent catalytic activity with an activity factor of 571 s−1 g−1 and high recyclability with a conversion of 96 % after seven catalytic cycles.

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.