Minghong Wu

Hydrothermal route for cutting graphene sheets into blue-luminescent graphene quantum dots.

2010 WILEY-VCH Verlag Gm Graphene-based materials are promising building blocks for future nanodevices owing to their superior electronic, thermal, and mechanical properties as well as their chemical stability. However, currently available graphene-based materials produced by typical physical and chemical routes, including micromechanical cleavage, reduction of exfoliated graphene oxide (GO), and solvothermal synthesis, are generally micrometer-sized graphene sheets (GSs), which limits their direct application in nanodevices. In this context, it has become urgent to develop effective routes for cutting large GSs into nanometer-sized pieces with a well-confined shape, such as graphene nanoribbons (GNRs) and graphene quantum dots (GQDs). Theoretical and experimental studies have shown that narrow GNRs (width less than ca. 10 nm) exhibit substantial quantum confinement and edge effects that render GNRs semiconducting. By comparison, GQDs possess strong quantum confinement and edge effects when their sizes are down to 100 nm. If their sizes are reduced to ca. 10 nm, comparable with the widths of semiconducting GNRs, the two effects will become more pronounced and, hence, induce new physical properties. Up to now, nearly all experimental work on GNRs and GQDs has focused on their electron transportation properties. Little work has been done on the optical properties that are directly associated with the quantum confinement and/or edge effects. Most GNRand GQD-based electronic devices have been fabricated by lithography techniques, which can realize widths and diameters down to ca. 20 nm. This physical approach, however, is limited by the need for expensive equipment and especially by difficulties in obtaining smooth edges. Alternative chemical routes can overcome these drawbacks. Moreover, surface functionalization can be realized easily. Li et al. first reported a chemical route to functionalized and ultrasmooth GNRs with widths ranging from 50 nm to sub-10 nm. Very recently, Kosynkin et al. reported a simple solution-based oxidative process for producing GNRs by lengthwise cutting and unraveling of multiwalled carbon nanotube (CNT) side walls. Yet, no chemical routes have been reported so far for preparing functionalized GQDs with sub-10 nm sizes. Here, we report on a novel and simple hydrothermal approach for the cutting of GSs into surface-functionalized GQDs (ca. 9.6-nm average diameter). The functionalized GQDs were found to exhibit bright blue photoluminescence (PL), which has never been observed in GSs and GNRs owing to their large lateral sizes. The blue luminescence and new UV–vis absorption bands are directly induced by the large edge effect shown in the ultrafine GQDs. The starting material was micrometer-sized rippled GSs obtained by thermal reduction of GO sheets. Figure 1a shows a typical transmission electron microscopy (TEM) image of the pristine GSs. Their (002) interlayer spacing is 3.64 A (Fig. 1c), larger than that of bulk graphite (3.34 A). Before the hydrothermal treatment, the GSs were oxidized in concentrated H2SO4 and HNO3. After the oxidization treatment the GSs became slightly smaller (50 nm–2mm) and the (002) spacing slightly increased to 3.85 A (Fig. 1c). During the oxidation, oxygen-containing functional groups, including C1⁄4O/COOH, OH, and C O C, were introduced at the edge and on the basal plane, as shown in the Fourier transform infrared (FTIR) spectrum (Fig. 1d). The presence of these groups makes the GSs soluble in water. A series of more marked changes took place after the hydrothermal treatment of the oxidized GSs at 200 8C. First, the (002) spacing was reduced to 3.43 A (Fig. 1c), very close to that of bulk graphite, indicating that deoxidization occurs during the hydrothermal process. The deoxidization is further confirmed by the changes in the FTIR and C 1s X-ray photoelectron spectroscopy (XPS) spectra. After the hydrothermal treatment, the strongest vibrational absorption band of C1⁄4O/COOH at 1720 cm 1 became very weak and the vibration band of epoxy groups at 1052 cm 1 disappeared (Fig. 1d). In the XPS C 1s spectra of the oxidized and hydrothermally reduced GSs (Fig. 2a), the signal at 289 eV assigned to carboxyl groups became weak after the hydrothermal treatment, whereas the sp carbon peak at 284.4 eV was almost unchanged. Figure 2b shows the Raman spectrum of the reduced GSs. A G band at 1590 cm 1 and a D band at 1325 cm 1 were observed with a large intensity ratio ID/IG of 1.26. Second, the size of the GSs decreased dramatically and ultrafine GQDswere isolated by a dialysis process. Figure 3 shows typical TEM and atomic force microscopy (AFM) images of the GQDs. Their diameters are mainly distributed in the range of 5–13 nm (9.6 nm average diameter). Their topographic heights are mostly between 1 and 2 nm, similar to those observed in functionalized GNRs with 1–3 layers. More than 85% of the GQDs consist of 1–3 layers.

A Facile One‐step Method to Produce Graphene–CdS Quantum Dot Nanocomposites as Promising Optoelectronic Materials

[*] Prof. A. Cao, Z. Liu, Prof. M. Wu, Z. Ye, Z. Cai, Y. Chang, Prof. Y. Liu Institute of Nanochemistry and Nanobiology Shanghai University, Shanghai, 200444 (P. R. China) E-mail: ancao@shu.edu.cn Prof. S. Wang, S. Chu, Prof. Q. Gong State Key Laboratory for Mesoscopic Physics, School of Physics Peking University, Beijing, 100871 (P. R. China) E-mail: wangsf@pku.edu.cn Prof. Y. Liu Beijing National Laboratory of Molecular Science College of Chemistry and Molecular Engineering Peking University, Beijing, 100871 (P. R. China) E-mail: yliu@pku.edu.cn

Gram-scale synthesis of single-crystalline graphene quantum dots with superior optical properties

Graphene quantum dots (GQDs) have various alluring properties and potential applications, but their large-scale applications are limited by current synthetic methods that commonly produce GQDs in small amounts. Moreover, GQDs usually exhibit polycrystalline or highly defective structures and thus poor optical properties. Here we report the gram-scale synthesis of single-crystalline GQDs by a facile molecular fusion route under mild and green hydrothermal conditions. The synthesis involves the nitration of pyrene followed by hydrothermal treatment in alkaline aqueous solutions, where alkaline species play a crucial role in tuning their size, functionalization and optical properties. The single-crystalline GQDs are bestowed with excellent optical properties such as bright excitonic fluorescence, strong excitonic absorption bands extending to the visible region, large molar extinction coefficients and long-term photostability. These high-quality GQDs can find a large array of novel applications in bioimaging, biosensing, light emitting diodes, solar cells, hydrogen production, fuel cells and supercapacitors.

Cutting sp2clusters in graphene sheets into colloidal graphene quantum dots with strong green fluorescence

Water-soluble and well-crystallized graphene quantum dots with lateral size about 3.0 nm were fabricated by a hydrothermal cutting method and their photoluminescence (PL) properties as well as the potential for bioimaging were demonstrated.

Antibiotic resistance gene abundances associated with antibiotics and heavy metals in animal manures and agricultural soils adjacent to feedlots in Shanghai; China

Eight antibiotic resistance genes (ARGs), 7 heavy metals, and 6 antibiotics were quantified in manures and soils collected from multiple feedlots in Shanghai. The samples were analyzed to determine if ARG abundances were associated with heavy metal concentration and independent of antibiotics. The results revealed the presence of chloramphenicol, sulfonamides and tetracyclines at concentration ranges of 3.27-17.85, 5.85-33.37 and 4.54-24.66 mg kg(-1), respectively. Typical heavy metals, such as Cu, Zn, and As, were detected at concentration ranges of 32.3-730.1, 75.9-4333.8, and 2.6-617.2 mg kg(-1). All ARGs tested were detected in the collected samples except tetB(P), which was absent in animal manures. Overall, sulfonamide ARGs were more abundant than tetracycline ARGs. Except for sulII, only a weak positive correlation was found between ARGs and their corresponding antibiotics. On the contrary, significant positive correlations (p<0.05) were found between some ARGs and typical heavy metals. For example, sulA and sulIII were strongly correlated with levels of Cu, Zn and Hg. The data demonstrated that the presence of ARGs was relatively independent of their respective antibiotic inducer. In addition to antibiotics, toxic heavy metals, such as Hg, Cu, and Zn, exerted a strong selection pressure and acted as complementary factors for ARG abundance.

Nanosized zinc oxide particles induce neural stem cell apoptosis

Given the intensive application of nanoscale zinc oxide (ZnO) materials in our life, growing concerns have arisen about its unintentional health and environmental impacts. In this study, the neurotoxicity of different sized ZnO nanoparticles in mouse neural stem cells (NSCs) was investigated. A cell viability assay indicated that ZnO nanoparticles manifested dose-dependent, but no size-dependent toxic effects on NSCs. Apoptotic cells were observed and analyzed by confocal microscopy, transmission electron microscopy examination, and flow cytometry. All the results support the viewpoint that the ZnO nanoparticle toxicity comes from the dissolved Zn(2+) in the culture medium or inside cells. Our results highlight the need for caution during the use and disposal of ZnO manufactured nanomaterials to prevent the unintended environmental and health impacts.

Resonance Energy Transfer-Amplifying Fluorescence Quenching at the Surface of Silica Nanoparticles toward Ultrasensitive Detection of TNT

This paper reports a resonance energy transfer-amplifying fluorescence quenching at the surface of silica nanoparticles for the ultrasensitive detection of 2,4,6-trinitrotoluene (TNT) in solution and vapor environments. Fluorescence dye and organic amine were covalently modified onto the surface of silica nanoparticles to form a hybrid monolayer of dye fluorophores and amine ligands. The fluorescent silica particles can specifically bind TNT species by the charge-transfer complexing interaction between electron-rich amine ligands and electron-deficient aromatic rings. The resultant TNT-amine complexes bound at the silica surface can strongly suppress the fluorescence emission of the chosen dye by the fluorescence resonance energy transfer (FRET) from dye donor to the irradiative TNT-amine acceptor through intermolecular polar-polar interactions at spatial proximity. The quenching efficiency of the hybrid nanoparticles with TNT is greatly amplified by at least 10-fold that of the corresponding pure dye. The nanoparticle-assembled arrays on silicon wafer can sensitively detect down to approximately 1 nM TNT with the use of only 10 microL of solution (approximately 2 pg TNT) and several ppb of TNT vapor in air. The simple FRET-based nanoparticle sensors reported here exhibit a high and stable fluorescence brightness, strong analyte affinity, and good assembly flexibility and can thus find many applications in the detection of ultratrace analytes.

Levels, composition profiles and sources of polycyclic aromatic hydrocarbons in urban soil of Shanghai, China.

Levels, composition profiles and sources of polycyclic aromatic hydrocarbons (PAHs) were analyzed in 55 surface soil samples collected from Shanghai urban districts. The total concentrations of 22 PAHs (SigmaPAHs) ranged from 442 to 19,700 microgkg(-1), with a mean of 3780 microgkg(-1), and the sum of 16 priority PAHs (Sigma16PAHs) varied from 347 to 17,900 microgkg(-1), with a mean of 3290 microgkg(-1), and the seven possible carcinogenic PAHs (Sigma7CarPAHs) accounted for 36-58% of Sigma16PAHs. Among different functional areas, the higher level of PAHs was found in the roadside, followed by greenbelt, commercial district, park, and residential district. The composition of PAHs was characterized by the high molecular weight PAHs, among which fluoranthene, pyrene, benzo[b]fluoranthene and chrysene were most dominant components. A correlation analysis showed that there was relatively good correlation among the individual PAHs, but the contents of PAHs were poorly correlated with soil total organic carbon (TOC). A principal component analysis and PAHs isomeric ratios indicate that PAHs in Shanghai urban soil mainly originated from combustion. The toxic assessment suggested that soil PAHs exposure is medium carcinogenic at present level.

Polycyclic aromatic hydrocarbons (PAHs) in urban soils of the megacity Shanghai: occurrence, source apportionment and potential human health risk.

A comprehensive investigation was conducted to the urban soil in the megacity Shanghai in order to assess the levels of PAHs and potential risks to human health, to identify and quantitatively assess source contributions to the soil PAHs. A total of 57 soil samples collected in main urban areas of Shanghai, China were analyzed for 26 PAHs including highly carcinogenic dibenzopyrene isomers. The total concentrations ranged from 133 to 8,650 ng g for ΣPAHs and 83.3 to 7,220 ng g for ΣPAHs, with mean values of 2420 and 1,970 ng g, respectively. DBalP and DBaeP may serve as markers for diesel vehicle emission, while DBahP is a probable marker of coke tar as distinct from diesel emissions. Six sources in Shanghai urban area were identified by PMF model; their relative contributions to the total soil PAH burden were 6% for petrogenic sources, 21% for coal combustion, 13% for biomass burning, 16% for creosote, 23% for coke tar related sources and 21% for vehicular emissions, respectively. The benzo[a]pyrene equivalent (BaP) concentrations ranged from 48.9-2,580 ng g for ΣPAHs, 7.02-869 ng g for ΣPAHs and 35.7-1,990 ng g for ΣDBPs. The BaP concentrations of ΣDBPs made up 72% of ΣPAHs. Nearly half of the soil samples showed concentrations above the safe BaP value of 600 ng g. Exposure to these soils through direct contact probably poses a significant risk to human health from carcinogenic effects of soil PAHs. The index of additive cancer risk (IACR) values in almost one third of urban soil samples were more than the safe value of 1.0, indicating these urban soil PAHs in the study area may pose a potential threat to potable groundwater water quality from leaching of carcinogenic PAH mixtures from soil.

Recent advances in manganese oxide nanocrystals: Fabrication, characterization, and microstructure

Characterization, and Microstructure Zhiwen Chen,*,†,§ Zheng Jiao,*,†,‡ Dengyu Pan,‡ Zhen Li,† Minghong Wu,*,†,‡ Chan-Hung Shek, C. M. Lawrence Wu, and Joseph K. L. Lai †Shanghai Applied Radiation Institute and ‡Institute of Nanochemistry and Nanobiology, School of Environmental and Chemical Engineering, Shanghai University, Shanghai 200444, People’s Republic of China Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong