Entity

Time filter

Source Type


Wang X.-Q.,CAS Institute of Physics | Li H.-D.,Chinese Research Academy of Environmental Sciences | Wang J.-T.,CAS Institute of Physics
Physical Chemistry Chemical Physics | Year: 2012

The intriguing electronic and magnetic properties of one-side semihydrogenated silicene and germanene are investigated by means of first-principles calculations. Both one-side semihydrogenated silicene and germanene are confirmed as dynamically stable in the ground state based on phonon-mode analysis. Moreover, we find that semihydrogenation from only one side causes localized and unpaired 3p (4p) electrons in the unhydrogenated Si (Ge) sites and then introduces ferromagnetism to silicene (germanene) sheet with no need for doping, cutting, or etching. One-side semihydrogenated silicene and germanene are both identified as semiconductors with direct energy gaps: their gap values obtained from the HSE06 functional are estimated to be 1.74 eV and 1.32 eV, much greater than the PBE-GGA results of 0.94 eV and 0.41 eV, respectively. From pristine to one-side semihydrogenated and then to fully hydrogenated systems, silicene and germanene change from metallic to magnetic semiconducting and then to nonmagnetic semiconducting. The hydrogenation process provides a novel method to tune the properties of silicene and germanene with unprecedented potentials for future nanoelectronics. © 2012 The Owner Societies. Source


Yang L.,Nankai University | Zhu L.,Nankai University | Liu Z.,Chinese Research Academy of Environmental Sciences
Chemosphere | Year: 2011

The concentrations of four perfluorinated sulfonate acids (PFSAs) and 10 perfluorinated carboxylate acids (PFCAs) were measured in water and sediment samples from Liao River and Taihu Lake, China. In the water samples from Taihu Lake, PFOA and PFOS were the most detected perfluorinated compounds (PFCs); in Liao River, PFHxS was the predominant PFC followed by PFOA, while PFOS was only detected in two of the samples. This suggests that different PFC products are used in the two regions. PFOS and PFOA in both watersheds are at similar level as in the rivers of Japan, but significantly lower than in Great Lakes. The contributions of PFOS and long chain PFCAs in sediments were much higher than in water samples of both watersheds, indicating preferential partition of these PFCs in sediment. The concentrations of PFOS and PFOA were three orders of magnitude of lower than that of polycyclic aromatic hydrocarbons in the same sediments. The average sediment-water partition coefficients (log. Koc) of PFHxS, PFOS and PFOA were determined to be 2.16, 2.88 and 2.28 respectively. © 2011 Elsevier Ltd. Source


Duan J.,Chinese Research Academy of Environmental Sciences | Tan J.,University of Chinese Academy of Sciences
Atmospheric Environment | Year: 2013

In recent years, heavy metal pollution accidents were reported frequently in China. The atmospheric heavy metal pollution is drawing all aspects of attention. This paper summarizes the recent research results from our studies and previous studies in recent years in China. The level, temporal variation, seasonal variation and size distribution of the heavy metals of atmospheric Lead(Pb), Vanadium(V), Manganese(Mn), Nickel(Ni), Chromium(Cr), Cadmium(Cd), Copper(Cu), Zinc(Zn) and Arsenic(As) were characterized in China. The emission characteristics and sources of atmospheric heavy metals and As in China were reviewed. Coal burning, iron and steel industry and vehicle emission are important sources in China. Control policies and effects in China were reviewed including emission standards, ambient air quality standards, phase out of leaded gasoline and so on, and further works for atmospheric heavy metals control were suggested. The comprehensive heavy metals pollution control measures and suggestions were put forward based on the summarization of the development and experience of the atmospheric heavy metal pollution control abroad. © 2013 Elsevier Ltd. Source


Chen H.,Chinese Research Academy of Environmental Sciences | Kenny J.E.,Tufts University
Analyst | Year: 2012

One of the conventionally accepted requirements for parallel factor analysis (PARAFAC) to handle the fluorescence excitation emission matrices (EEMs) is the independence of each component's absorption and emission spectra in simple mixtures of fluorophores. EEMs of samples in which Förster resonance energy transfer (FRET) occurs between fluorophores seem to fail to meet this requirement. A rigorous theoretical treatment of the steady-state kinetics in the present work indicates that the fluorescence in the presence of FRET, excited by relatively weak excitation light intensity, can be reasonably separated into additive contributions from three parts: donors, acceptors and FRET. This prediction is for the first time verified experimentally in sodium dodecyl sulfate micellar solutions containing biphenyl as the energy donor and 2,5-diphenyloxazole as the energy acceptor. The experimental EEMs were well fitted to three components as predicted. A well accepted diagnostic test called core consistency (CC), specifically designed for modeling simple mixtures of fluorophores with PARAFAC, was found to be negative for the 3-component model in the present study. The simultaneous occurrence of good model fit and significantly negative CC when modeling fluorophore mixtures by conventional PARAFAC would be indicative of the presence of physical/chemical processes (e.g., FRET) that deviate from the conventional working requirements for PARAFAC. The extent of FRET has been independently measured or calculated by three methods: 1) decrease in steady state fluorescence of donor; 2) lifetime measurements with population analysis; and 3) Poisson statistics based on PARAFAC-determined distribution constants. The results of the three methods are consistent. The normalized scores of the three components found by PARAFAC also agree to within a few percent with relative concentrations in aqueous and micelle phases determined from distribution constants for the solutions prepared with nine different combinations of total donor and acceptor concentrations. Our theoretical treatment also for the first time spells out in detail the relationship between the PARAFAC scores and concentrations of components, in terms of photophysical constants of the components and spectral shape factors. Source


Yang H.,Huazhong University of Science and Technology | Liu J.,Chinese Research Academy of Environmental Sciences | Yang J.,Huazhong University of Science and Technology
Journal of Hazardous Materials | Year: 2011

Leaching copper from shredded particles of waste printed circuit boards (PCBs) was carried out in sulfuric acid solution using hydrogen peroxide as an oxidant at room temperature. The influence of system variables on copper recovery by leaching was investigated, such as sulfuric concentration, amount of hydrogen peroxide addition, waste PBCs particle size, presence of cupric ion, temperature and time. The results shown that the optimum addition amount was 100mL 15 (wt%) sulfuric acid solution and 10mL of 30% hydrogen peroxide for leaching 10g waste PCBs powder with a solid/liquid ratio of 1/10 for 3h at room temperature (∼23°C). Moreover leaching temperature and initial copper ion concentration had insignificant effect on the leaching recovery of copper. The effect of different particle size of shredded waste PCBs on leaching of copper was investigated under the optimum leaching condition. The results revealed that shredding pieces of waste PCBs smaller than 1mm was efficient and suitable for copper leaching. Then the leaching solution was concentrated to crystallize CuSO4·5H2O, and crystal liquor was reused for the next cycles. © 2011 Elsevier B.V. Source

Discover hidden collaborations