Lingli Cheng

Porous TiO2 hollow nanospheres: synthesis, characterization and enhanced photocatalytic properties

A facile solvothermal process combined with a precursor thermal transformation method has been developed for preparing porous TiO2 hollow nanospheres with a high surface area and a good thermal stability. The porous TiO2 hollow spheres were obtained by using TiOSO4 as a titanium source and carbon nanospheres as a sacrificial template. Their particle size, diameter and morphology can be readily controlled by varying growth parameters, including reaction temperature, time and reagent concentration. The calcination temperature of TiO2–C core-shell nanospheres was found to have a profound effect on the structure and properties of the final products. The photocatalytic activities of the products were evaluated by the photodegradation of methyl orange (MO). The TiO2 hollow spheres obtained from 450 °C thermal treatment exhibited higher photocatalytic activity than commercial Degussa P25 in the presence of Cr(VI). The possible photodegradation mechanism was also investigated.

Three-Dimensional Interconnected Spherical Graphene Framework/SnS Nanocomposite for Anode Material with Superior Lithium Storage Performance: Complete Reversibility of Li2S

Three-dimensional (3D) interconnected spherical graphene framework-decorated SnS nanoparticles (3D SnS@SG) is synthesized by self-assembly of graphene oxide nanosheets and positively charged polystyrene/SnO2 nanospheres, followed by a controllable in situ sulfidation reaction during calcination. The SnS nanoparticles with diameters of ∼10-30 nm are anchored to the surface of the spherical graphene wall tightly and uniformly. Benefiting from the 3D interconnected spherical graphene framework and subtle SnS nanoparticles, the generated Li2S could keep in close contact with Sn to make possible the in situ conversion reaction SnS + 2Li+ + 2e- ↔ Sn + Li2S. As a result, the 3D SnS@SG as the anode material for lithium ion batteries shows a high initial Coulombic efficiency of 75.3%. Apart from the irreversible capacity loss of 3D spherical graphene, the initial Coulombic efficiency of SnS in the 3D SnS@SG composite is as high as 99.7%, demonstrating the almost complete reversibility of Li2S in this system. Furthermore, it also exhibits an excellent reversible capacity (800 mAh g-1 after 100 cycles at 0.1 C and 527.1 mAh g-1 after 300 cycles at 1 °C) and outstanding rate capability (380 mAh g-1 at 5 °C).

SiO2-assisted synthesis of layered MoS2/reduced graphene oxide intercalation composites as high performance anode materials for Li-ion batteries

Layered MoS2/reduced graphene oxide (MoS2/rGO) intercalation composites are synthesized via a SiO2-assisted hydrothermal method. This strategy discards addition of any amorphous carbon precursor for the synthesis of intercalation composites, and may reduce the defect degree and irreversible lithium storage sites in the final products. The structure and morphology characterization of the layered MoS2/rGO intercalation composites shows that the MoS2 composed of single layer or 2–4 layers display a highly exfoliated structure and disperse on the surface of graphene homogeneously and tightly, some of the interlayer spacing of MoS2 are enlarged, ranging from 0.7 to 1.17 nm with the intercalation of graphene. Electrochemical tests demonstrate that the MoS2/rGO-0.5 delivers a high reversible capacity of 1260.5 mA h g−1 in the initial cycle and retains 94.9% capacity after 50 cycles at 100 mA g−1. Furthermore, the capacity can reach 988.3 mA h g−1 even at a high current density of 1000 mA g−1. The excellent electrochemical performance of the MoS2/rGO intercalation composite could be attributed to the excellent match between the structure and morphology of layered MoS2 and graphene and the partial electron transfer from graphene to MoS2, which would maximize the synergistic interaction of the MoS2/rGO composite for reversible lithium storage.

Two physical strategies to reinforce a nonmetallic photocatalyst, g-C3N4: vacuum heating and electron beam irradiation

Herein, we demonstrated two physical strategies, namely, vacuum heating and electron beam irradiation, to reinforce a nonmetallic photocatalyst, g-C3N4. These two post-treatments also improved the visible light absorption properties of g-C3N4; however, electron beam irradiation was more destructive, and it caused a determined change in the chemical bonds and band structure of the compound. According to the post-processing parameters mentioned in this article, vacuum heating (38 ± 2 mTorr for 4 days at 200 °C) enhanced the photocatalytic efficiency of the original g-C3N4 by 2.5 times, whereas electron beam irradiation (760 kGy at 1.8 MeV and 8 mA s−1) improved it by 4.5 times. Finally, the post-treated photocatalysts were stable during photocatalytic oxidation, which is important for practical applications.