Minmin Liu

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.

Novel blue light emitting graphene oxide nanosheets fabricated by surface functionalization

Graphene and graphene oxide (GO) attract increasing attention due to their unique physical and chemical properties and thus the potential applications in optics and electronics. However, the gapless band structure greatly limits their wide applications in opto-electronic devices. Surface functionalization was found to be an effective method to tune the properties of graphene and GO. In the present report, GO hybrid materials with blue-emission were fabricated through the GO surface functionalization with aryl diazonium salts of 2-aminoanthracene. The obtained hybrids were carefully characterized with atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Fourier-transformed infrared spectroscopy (FTIR), Raman spectroscopy and UV-Vis absorption spectroscopy. Significantly different from the cyan emission (∼491 nm) of monomeric 2-aminoanthracene, the as-synthesized GO hybrid composites exhibited strong blue photoluminescence centered at ca. 400 nm. The large blue shift of the luminescence (∼91 nm) obtained from the functionalized GO could be partly ascribed to the rigid chemical environment with anthryl moieties chemically bonded onto GO surface. Such surface-functionalized GO hybrids with unique optical properties render them exciting materials for opto-electronic devices.

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.

Electronic structure of TiO2 nanotube arrays from X-ray absorption near edge structure studies

We report an X-ray absorption near edge structure (XANES) investigation of several TiO2nanotube arrays, including the as-prepared nanotube arrays from electrochemical anodic oxidation of Ti foil (as-prepared ATNTA), as-prepared nanotube arrays after annealing at 580 °C (annealed ATNTA) and annealed ATNTA after electrochemical intercalation with Li (Li-intercalated ATNTA). XANES at the O K-edge and Ti L3,2 and K edges shows distinctly different spectral features for the as-prepared and the annealed ATNTA, characteristic of amorphous and anatase structures, respectively. Intercalation of Li into annealed ATNTA induces a surprising, yet spectroscopically unmistakable, anatase to rutile transition. XANES at the Li K-edge clearly shows ionic features of Li in ATNTA. The charge relocation from Ti 3d to O 2p at the conduction band in TiO2 was also observed when Li ions were intercalated into annealed ATNTA albeit no noticeable reduction of Ti4+ to Ti 3+ was observed. The O K-edge shows a distinctly enhanced feature in the multiple scattering regime, indicating a close to linear O–Li–O arrangement in Li-intercalated ATNTA. These results show bonding changes between Ti and O resulting from the interaction of Li ions in the TiO2 lattices. Such bonding variation has also been supported by X-ray excited optical luminescence (XEOL), which suggests Li+-defect interactions. The implications of these results are discussed.

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.

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.

Novel Pd13Cu3S7 nanotubes with high electrocatalytic activity towards both oxygen reduction and ethanol oxidation reactions

In the search for more effective and stable fuel cell electrocatalysts, we have developed a facile method to synthesize novel Pd13Cu3S7 nanotubes (Pd13Cu3S7 NTs) for the first time. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) measurements have been used to characterize the structure, components and morphology of the Pd13Cu3S7 NTs. Due to their novel structure and composition, the as-prepared Pd13Cu3S7 NTs showed a high oxygen reduction reaction (ORR) catalytic performance, with similar catalytic activity to that of commercial Pt/C but with better stability than Pt/C. Furthermore, the ORR catalyzed by the Pd13Cu3S7 NTs was calculated to be a directly 4e− process. On the other hand, the Pd13Cu3S7 NTs also exhibited excellent ethanol oxidation reaction (EOR) activity (2.7 mA cm−2), which is about five times that of commercial Pd/C (0.55 mA cm−2). An EIS study indicated that the charge transfer resistance of the Pd13Cu3S7 NTs is much lower than that of commercial Pd/C in the EOR.

Novel Nanomaterials as Electrocatalysts for Fuel Cells

Abstract As an important eco-benign power source with high energy conversion efficiency, fuel cells (FCs) have been accepted as one of the most prospective power sources for portable electronic devices and are expected to be one of the best possible solutions for the 21st century energy crisis. In a FC, the sluggish kinetic rates of both fuel oxidation reactions (anode) and the oxygen reduction reaction (cathode) hinder energy conversion efficiency. The degradation of catalysts, high cost, and self-poisoning of Pt-based catalysts have largely limited the wide commercialization of FCs. In recent years, considerable effort has been focused on designing and developing novel nanomaterials with unique structures and excellent electrochemical properties as ideal low-price electrocatalysts for FCs. In this chapter, we highlight the recent advances made in the development of novel FC nanocatalysts in the areas of nonprecious metals, graphene-based and metal–organic framework–derived electrocatalysts.