Hongjuan Sun

Three-dimensional graphene-wrapped PANI nanofiber composite as electrode material for supercapacitors

A novel three-dimensional graphene/polyaniline (3DGP) composite was achieved by a hydrothermal method from in situ polymerization of a polyaniline/graphene oxide composite and GO suspension. This 3DGP composite possesses a 3D porous network structure and large specific capacity of 648 F g−1 at a current density of 0.5 A g−1. In particular, the capability can reach 356 F g−1 even at 20.0 A g−1, 537 F g−1 at 1.0 A g−1 can also be achieved after 1000 cycles. Therefore, the 3DGP composite is a suitable and promising electrode material for supercapacitors.

Preparation of graphene nanosheets from microcrystalline graphite by low-temperature exfoliated method and their supercapacitive behavior

Microcrystalline graphite, a kind of cheap and infrequently used graphite material, used for the rapid synthesis of graphene nanosheets (MGS) by thermal reduction–exfoliation of graphite oxide at low temperature (as low as 100xa0°C) is reported. The results indicate that the microcrystalline graphite could be oxidized completely. X-ray diffraction patterns show that the obtained MGS exhibit an amorphous structure. Scanning electron microscopy images show that the MGS samples possess nanoporous structure. The results of N2 adsorption–desorption analysis indicate that the MGS samples possess high Brunauer Emmett Teller surface areas (the highest is 374xa0m2xa0g−1). The results of electrochemical tests show that the MGS exfoliated at 400xa0°C (MGS-400) has better supercapacitive performance than that of MGS exfoliated at 100xa0°C. The specific capacitance value of MGS-400 is about 212xa0Fxa0g−1 at 5xa0mVxa0s−1. And also the MGS samples have good rate performance and cycle stability.

Molecular vibrational spectroscopy characterization of epoxy graphene oxide from density functional calculations.

To further understand the structure of graphene oxide, several structures of graphene oxide were systematically investigated using density functional theory (DFT). Our models consisted of a hexagonal in-plane structure of graphene with epoxy groups, and different oxidation levels. We found that different arrangements of these units yielded a range of vibrational spectra. Raman positions of the D and G bands depend sensitively on the local atomic configurations. Both structure energy and spectra computations indicate that the oxidation functional groups are energetically favorable to aggregate together and to be close to one another on the opposite side of graphene surface.

Release behavior of uranium in uranium mill tailings under environmental conditions

Uranium contamination is observed in sedimentary geochemical environments, but the geochemical and mineralogical processes that control uranium release from sediment are not fully appreciated. Identification of how sediments and water influence the release and migration of uranium is critical to improve the prevention of uranium contamination in soil and groundwater. To understand the process of uranium release and migration from uranium mill tailings under water chemistry conditions, uranium mill tailing samples from northwest China were investigated with batch leaching experiments. Results showed that water played an important role in uranium release from the tailing minerals. The uranium release was clearly influenced by contact time, liquid-solid ratio, particle size, and pH under water chemistry conditions. Longer contact time, higher liquid content, and extreme pH were all not conducive to the stabilization of uranium and accelerated the uranium release from the tailing mineral to the solution. The values of pH were found to significantly influence the extent and mechanisms of uranium release from minerals to water. Uranium release was monitored by a number of interactive processes, including dissolution of uranium-bearing minerals, uranium desorption from mineral surfaces, and formation of aqueous uranium complexes. Considering the impact of contact time, liquid-solid ratio, particle size, and pH on uranium release from uranium mill tailings, reducing the water content, decreasing the porosity of tailing dumps and controlling the pH of tailings were the key factors for prevention and management of environmental pollution in areas near uranium mines.

Structural Regulation and Electroconductivity Change of Nitrogen-Doping Reduced Graphene Oxide Prepared Using p-Phenylene Diamine as Modifier

Using p-phenylene diamine (PPD) as a modifier and nitrogen resource, nitrogen-doping reduced graphene oxide was prepared by one-step refluxing method. The influence of PPD-GO (graphene oxide) mass ratio X on surface functional groups, layer structure, and electroconductivity of nitrogen-doping reduced grapheme oxide (NRGO-X) was investigated by Fourier Transform Infrared Spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), UV-vis absorption spectrum, and electrical measurement. The results showed that GO can be simultaneously reduced and nitrogen-doped by PPD. When PPD-GO mass ratio X ≤ 6, there existed three types of N configurations in NRGO-X, including pyridinic N, pyrrolic N, and graphitic N. However, when X > 6, the pyridinic N disappeared in a six-membered ring. Further, the reduction process of NRGO as well as the nitrogen doping level and type can be regulated by changing the mass ratio X. With the increase of X, the d-spacing of NRGO-X layers increased first and then decreased, while the electrical conductivity increased gradually.

Leaching behavior of U, Mn, Sr, and Pb from different particle-size fractions of uranium mill tailings

Pollution by the release of heavy metals from tailings constitutes a potential threat to the environment. To characterize the processes governing the release of Mn, Sr, Pb, and U from the uranium mill tailings, a dynamic leaching test was applied for different size of uranium mill tailings samples. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS) were performed to determine the content of Mn, Sr, Pb, and U in the leachates. The release of mobile Mn, Sr, Pb, and U fraction was slow, being faster in the initial stage and then attained a near steady-state condition. The experimental results demonstrate that the release of Mn, Sr, Pb, and U from uranium mill tailings with different size fractions is controlled by a variety of mechanisms. Surface wash-off is the release mechanism for Mn. The main release mechanism of Sr and Pb is the dissolution in the initial leaching stage. For U, a mixed process of wash-off and diffusion is the controlling mechanism.

Effect of Reaction Temperature on Structure, Appearance and Bonding Type of Functionalized Graphene Oxide Modified P-Phenylene Diamine

In this study, graphene oxides with different functionalization degrees were prepared by a facile one-step hydrothermal reflux method at various reaction temperatures using graphene oxide (GO) as starting material and p-phenylenediamine (PPD) as the modifier. The effects of reaction temperature on structure, appearance and bonding type of the obtained materials were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The results showed that when the reaction temperature was 10–70 °C, the GO reacted with PPD through non-covalent ionic bonds (–COO−H3+N–R) and hydrogen bonds (C–OH…H2N–X). When the reaction temperature reached 90 °C, the GO was functionalized with PPD through covalent bonds of C–N. The crystal structure of products became more ordered and regular, and the interlayer spacing (d value) and surface roughness increased as the temperature increased. Furthermore, the results suggested that PPD was grafted on the surface of GO through covalent bonding by first attacking the carboxyl groups and then the epoxy groups of GO.

Nitrogen-doped porous 3D graphene with enhanced supercapacitor properties

Nitrogen-doped graphene has attracted increasing attention in recent years. Synthesis of nitrogen-doped 3D graphene with high capacitance and excellent capacitive behavior is highly desirable for high-performance supercapacitor applications. In this study, nitrogen-doped porous 3D graphene was prepared from graphite oxide using the mild one-pot hydrothermal procedure. The p-phenylenediamine and ammonia were selected as the reduction and doping agents, respectively. 3D graphene specimens with various nitrogen doping amounts of 6.52–7.81% were prepared. Scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction and supercapacitor performance were used to investigate the morphologies, structures and capacitance behaviors of the prepared 3D graphene composites. The results indicated that the as-prepared specimens contained different doping nitrogen amounts. NGP-10.6 showed well-connected 3D porous microstructure with largest doping nitrogen content. In turn, nature and content of nitrogen doping provided the graphene with excellent capacitive behavior. The specific capacitance of NGP-10.6 reached 788 F·g−1 at the current density of 0.5 A·g−1 and 296 F·g−1 at 10 A·g−1. Overall, these findings look promising for future applications as outstanding energy storage materials.

Chemical and Mineralogical Characterizations of High Ti-Bearing Blast Furnace Slag in Panzhihua, China

Chemical and mineralogical characterizations of high Ti-bearing blast furnace slag in Panzhihua region, Sichuan province, China, were investigated, and the technical approach “recycling Fe by magnetic separation-extracting Al and Mg by sulfation roasting and water leaching-extracting Ti by acidolysis” was proposed for recycling the valuable elements from the special mineral resources. The results show that the most valuable metal is Ti (20.46 % TiO2, mass fraction). Other metals, such as Al, Mg, and Fe, can also be seen as valuable components to be recovered. Minerals such as perovskite, diopside, and spinel are disseminated in the slag. The Ti element in the slag is distributed widely in many types of mineral phases and Ti component enriches mainly in perovskite phase. It is highly euhedral and mostly disseminates in the diopside, it usually presents an equiaxed or irregular granular shape, and particles are commonly tiny.