Junwei Zhao

Synthesis, Characterization, and Photocatalytic Activity of Zn-Doped SnO2/Zn2SnO4 Coupled Nanocomposites

Zn-doped SnO2/Zn2SnO4 nanocomposites were prepared via a two-step hydrothermal synthesis method. The as-prepared samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV-vis diffuse reflection spectroscopy, and adsorption-desorption isotherms. The results of FESEM and TEM showed that the as-prepared Zn-doped SnO2/Zn2SnO4 nanocomposites are composed of numerous nanoparticles with the size ranging from 20u2009nm to 50u2009nm. The specific surface area of the as-prepared Zn-doped SnO2/Zn2SnO4 nanocomposites is estimated to be 71.53u2009m2/g by the Brunauer-Emmett-Teller (BET) method. The photocatalytic activity was evaluated by the degradation of methylene blue (MB), and the resulting showed that Zn-doped SnO2/Zn2SnO4 nanocomposites exhibited excellent photocatalytic activity due to their higher specific surface area and surface charge carrier transfer.

Sonochemical Synthesis, Characterization, and Photocatalytic Activity of N-Doped TiO2 Nanocrystals with Mesoporous Structure

N-Doped TiO2 nanocrystals were synthesized via a simple sonochemical route, using titanium tetrachloride, aqueous ammonia, and urea as starting materials. The as-synthesized samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) equipped with an energy dispersion X-ray spectrometer (EDS), transmission electron microscopy (TEM), UV-vis diffuse reflection spectroscopy, Raman spectroscopy, and nitrogen adsorption-desorption isotherms. The results of TEM and nitrogen adsorption-desorption showed that the average size and specific surface area of the as-synthesized nanocrystals are 10u2009nm and 107.2u2009m2/g, respectively. Raman spectral characterization combined with the results of XRD and EDS revealed that N dopant ions were successfully doped into TiO2. Compared with pure TiO2, the adsorption band edge of N-doped TiO2 samples exhibited an obvious red shift to visible region. The photocatalytic activities were evaluated by the degradation of Rhodamine B (RhB) under visible light, and the results showed that the N-doped TiO2 sample synthesized by an optimal amount of urea exhibited excellent photocatalytic activity due to its special mesoporous structure and the incorporation of nitrogen dopant ions.

Facile synthesis of LiMn 2 O 4 microsheets with porous micro-nanostructure as high-rate cathode materials for Li-ion batteries

Porous LiMn2O4 microsheets with micro-nanostructure have been successfully prepared through a simple carbon gel-combustion process with a microporous membrane as hard template. The crystal structure, morphology, chemical composition, and surface analysis of the as-obtained LiMn2O4 microsheets are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscope (XPS). It can be found that the as-prepared LiMn2O4 sample presents the two-dimensional (2-D) sheet structure with porous structure comprised with nano-scaled particles. As cathode materials for lithium-ion batteries, the obtained LiMn2O4 microsheets show superior rate capacities and cycling performance at various charge/discharge rates. The LiMn2O4 microsheets exhibit a higher charge and discharge capacity of 137.0 and 134.7xa0mAhxa0g−1 in the first cycle at 0.5 C, and it remains 127.6xa0mAhxa0g−1 after 50xa0cycles, which accounts for 94.7% discharge capacity retention. Even at 10 C rate, the electrode also delivers the discharge capacity of 91.0xa0mAhxa0g−1 after 300xa0cycles (93.5% capacity retention). The superior electrochemical properties of the LiMn2O4 microsheets could be attributed to the unique microsheets with porous micro-nanostructure, more active sites of the Li-ions insertion/deinsertion for the higher contact area between the LiMn2O4 nano-scaled particles and the electrolyte, and better kinetic properties, suggesting the applications of the sample in high-power lithium-ion batteries.

High rate performance of LiNi{sub 1/3}Co{sub 1/3}Mn{sub 1/3}O{sub 2} cathode material synthesized by a carbon gel–combustion process for lithium ion batteries

Abstract The LiNi 1/3 Co 1/3 Mn 1/3 O 2 electrode material was prepared via a carbon gel–combustion process using resorcinol–formaldehyde gel as fuel and nitrate as an oxidizer. The carbon gel process ensures the molecular-level homogeneity of the chemical product. The gas derived from carbon gel separates the raw material particles and restrains the growth of the grains to some extent, and well-crystallized nanosized powders are obtained with calcination at 700xa0°C for 6xa0h. As the cathode material for lithium-ion batteries, the discharge capacity of LiNi 1/3 Co 1/3 Mn 1/3 O 2 was as high as 175.6xa0mAxa0hxa0g −1 in the first cycle at 0.5xa0C, and it could remain 163.0xa0mAxa0hxa0g −1 within the voltage range of 2.5–4.4xa0V after 50 cycles. The electrode also showed outstanding rate capacities at high discharge rates such as 30xa0C and 50xa0C, suggesting the applications of the material in high power lithium-ion batteries.