Publications by authors named "Siqi Qi"

5 Publications

  • Page 1 of 1

Investigation of aerosol absorption with dual-polarization lidar observations.

Opt Express 2020 Mar;28(5):7028-7035

Polarization lidar has been widely used in recent decades to observe the vertical structures of aerosols and clouds in the atmosphere. We developed a dual-polarization lidar system that can detect polarization measurements simultaneously at 355 nm and 532 nm. Dust events and haze episodes over northern China in 2014 were observed by the developed lidar. The results showed that the dust-dominated aerosol depolarization ratios at 532 nm were larger than those at 355 nm, but those of the air pollutants were smaller, indicating that this tool could provide a more accurate classification of aerosols. Moreover, we found a good relationship between the absorption coefficient of aerosols and the ratio of depolarization ratios at 532 nm and 355 nm for dust aerosols. Our results imply that aerosol absorption from polarization measurements may be determined by lidar at the ultraviolet and visible wavelengths.
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http://dx.doi.org/10.1364/OE.390475DOI Listing
March 2020

Ten-year global particulate mass concentration derived from space-borne CALIPSO lidar observations.

Sci Total Environ 2020 Jun 5;721:137699. Epub 2020 Mar 5.

Key Laboratory for Semi-Arid Climate Change of the Ministry of Education, College of Atmospheric Sciences, Lanzhou University, Lanzhou 730000, China.

Passive remote sensing has been widely used in recent decades to obtain global particulate matter (PM) mass concentration at daytime and under cloud-free condition. In this study, a retrieval method was developed for providing PM (PM and PM) mass concentration both at daytime and nighttime using the latest data version (V4.10) from space-borne Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) lidar measurements. The advantage of the method is that PM & PM mass concentrations were obtained for seven aerosol types respectively base on active remote sensing observation at daytime and nighttime, even under cloudy condition. The results show that satellite-based PM mass concentrations are in good agreement with in-situ observations from 1602 ground monitoring sites throughout the world. Moreover, global distributions of PM and PM mass concentration during 2007-2016 were investigated, showing that for Beijing the annual mean PM mass concentration at nighttime is 11.31% less than those at daytime, however for London is 36.62%. It is suggested that diurnal variations in PM mass concentration are closely related to human activities. This work provides a reliable high-resolution database for long-term particulate mass concentrations on the global scale, which is of importance to evaluate aerosol impacts on climate, environment as well as ecosystem.
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http://dx.doi.org/10.1016/j.scitotenv.2020.137699DOI Listing
June 2020

Covalent bonding of sulfur nanoparticles to unzipped multiwalled carbon nanotubes for high-performance lithium-sulfur batteries.

Nanotechnology 2019 Jan 31;30(2):024001. Epub 2018 Oct 31.

Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, 29 Zhongguancun East Road, Haidian District, Beijing 100190, People's Republic of China.

The use of sulfur as a cathode material for lithium-sulfur (Li-S) batteries has attracted significant attention due to its high theoretical specific capacity (1675 mA h g); however, practicality is hindered by a number of obstacles, including the shuttling effect of polysulfides and the low electrical conductivity of sulfur. Herein, ball milling sulfur with unzipped multiwalled carbon nanotubes (UMWNTs) was found to covalently immobilize sulfur nanoparticles to the UMWNTs and resulted in composites (designated as [email protected]) with high electrical conductivity. The unzipping degree of MWNTs was first controlled to optimize the immobilization of sulfur nanoparticles to UMWNTs and the electrochemical performance of the resulting Li-S batteries. The presence of C-S covalent bonds between the UMWNTs and sulfur nanoparticles was verified using x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy, and the formation of C-S bonds was ascribed to the reactions between the mechanically-induced sulfur radicals and the functional groups of UMWNTs. As a result, when used as a cathode material for Li-S batteries, the [email protected] exhibited excellent electrochemical performance, including a good long-term cycling stability and low capacity decay (e.g., ca. 0.09% per cycle over 500 charge/discharge cycles at 1 C) due to the suppression of the shuttling effect by the C-S covalent bonds.
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http://dx.doi.org/10.1088/1361-6528/aae6e5DOI Listing
January 2019

Graphene Oxide Facilitates Solvent-Free Synthesis of Well-Dispersed, Faceted Zeolite Crystals.

Angew Chem Int Ed Engl 2017 11 4;56(45):14090-14095. Epub 2017 Oct 4.

Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, 29 Zhongguancun East Road, Haidian District, Beijing, 100190, China.

Zeolites with molecular dimension pores are widely used in petrochemical and fine-chemical industries. While traditional solvothermal syntheses suffer from environmental, safety, and efficiency issues, the newly developed solvent-free synthesis is limited by zeolite crystal aggregation. Herein, we report well-dispersed and faceted silicalite ZSM-5 zeolite crystals obtained using a solvent-free synthesis facilitated by graphene oxide (GO). The selective interactions between the GO sheets and different facets, which are confirmed by molecular dynamics simulations, result in oriented growth of the ZSM-5 crystals along the c-axis. More importantly, the incorporation of GO sheets into the ZSM-5 crystals leads to the formation of mesopores. Consequently, the faceted ZSM-5 crystals exhibit hierarchical pore structures. This synthetic method is superior to conventional approaches because of the features of the ZSM-5 zeolite.
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http://dx.doi.org/10.1002/anie.201707823DOI Listing
November 2017

Tuning the morphologies of fluorine-doped tin oxides in the three-dimensional architecture of graphene for high-performance lithium-ion batteries.

Nanotechnology 2017 Sep 20;28(39):395404. Epub 2017 Jul 20.

State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, People's Republic of China. Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, 29 Zhongguancun East Road, Haidian District, Beijing 100190, People's Republic of China.

The morphology of electrode materials plays an important role in determining the performance of lithium-ion batteries (LIBs). However, studies on determining the most favorable morphology for high-performance LIBs have rarely been reported. In this study, a series of F-doped SnO (F-SnO and F-SnO) materials with various morphologies was synthesized using ethylenediamine as a structure-directing agent in a facile hydrothermal process. During the hydrothermal process, the F-SnO was embedded in situ into the three-dimensional (3D) architecture of reduced graphene oxide (RGO) to form F-SnO @RGO composites. The morphologies and nanostructures of F-SnO , i.e., F-SnO nanocrystals, F-SnO nanosheets, and F-SnO aggregated particles, were fully characterized using electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy. Electrochemical characterization indicated that the F-SnO nanocrystals uniformly distributed in the 3D RGO architecture exhibited higher specific capacity, better rate performance, and longer cycling stability than the F-SnO with other morphologies. These excellent electrochemical performances were attributed to the uniform distribution of the F-SnO nanocrystals, which significantly alleviated the volume changes of the electrode material and shortened the Li ion diffusion path during lithiation/delithiation processes. The [email protected] composite composed of uniformly distributed F-SnO nanocrystals also exhibited excellent rate performance, as the specific capacities were measured to be 1158 and 648 mA h g at current densities of 0.1 and 5 A g, respectively.
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http://dx.doi.org/10.1088/1361-6528/aa8106DOI Listing
September 2017
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