Wen Ge

Morphology and optical absorption change of Ag/SiO2 core-shell nanoparticles under thermal annealing

Ag/SiO2 core shell nanoparticles can be potentially useful in solar cells with the expectation to enhance light absorption. Thermal stability of such nanoparticles would be an important issue and has not been investigated much in the past. This research studied both morphological and optical absorption changes when heat-treating Ag/SiO2 core shell nanoparticles at various temperatures. At lower temperatures, Ag diffuses out through the porous shell, and remains inside at higher temperatures when the shell becomes solid. The results are instructive to further apply such nanoparticles into solar cells.

Synthesis of hexagonal phase Gd2O2CO3:Yb3+, Er3+ upconversion nanoparticles via SiO2 coating and Nd3+ doping

By SiO2 shell coating and Nd3+ doping, layer-structured hexagonal phase Gd2O2CO3:Yb3+, Er3+ nanoparticles were synthesized successfully through a homogeneous precipitation method. The detailed mechanism was investigated and the results indicate that the SiO2 shell and Nd3+ doping ions can effectively prevent hexagonal phase Gd2O2CO3 from decomposing into cubic phase Gd2O3 during heat treatment, because the SiO2 shell limits the diffusion of CO2 gas and the Nd3+ doping increases the decomposition temperature of Gd2O2CO3. Compared with non-layer-structured GdVO4:20%Yb3+, 2%Er3+, 4%Nd3+ particles with similar diameters and morphologies and lower phonon energies, layer-structured Gd2O2CO3:20%Yb3+, 2%Er3+, 4%Nd3+/SiO2 hexagonal phase particles show much a stronger upconversion emission, suggesting that layer-structured materials are more appropriate as upconversion hosts. Furthermore, the paramagnetic properties of Gd2O2CO3:Yb3+, Er3+, Nd3+/SiO2 nanoparticles were also demonstrated.

Hydrothermal synthesis and formation mechanism of Aurivillius Bi5Fe0.9Co0.1Ti3O15 nanosheets

As potential single-phase multiferroic materials, Aurivillius compounds have attracted much interest in recent years. In this paper, Bi5Fe0.9Co0.1Ti3O15 (BFCTO) nanosheets were first synthesized by a hydrothermal method; lateral length and thickness of them are ∼600 nm and ∼100 nm, respectively. The BFCTO nanosheets were assumed to form by a co-effect of the aggregate process, the oriented attachment of neighboring nanorods, and Ostwald ripening. Besides, an obvious hysteresis loop with 2Mr = ∼0.55 emu g−1 and 2Hc = ∼2600 Oe at 300 K was observed in the final products. Both dielectric permittivity and dielectric loss decrease with the increase of the frequency at room temperature. Our results could serve as guidance to realize a controllable synthesis of Aurivillius nanoparticles and will shed light on designing new nanodevices.

Optimizing the photocatalysis in ferromagnetic Bi6Fe1.9Co0.1Ti3O18 nanocrystal by morphology control

Size and morphology are critical to monitoring the properties of nanocrystals. In this work, Bi6Fe1.9Co0.1Ti3O18 (BFCTO) nanocrystals, which are a visible-light active photocatalyst with room temperature ferromagnetism, were successfully synthesized through a hydrothermal process. Furthermore, the morphology dependent magnetism and band gap of the BFCTO-1.00/BFCTO-1.50/BFCTO-2.00 nanocrystals are studied by adjusting the NaOH concentration to 1.00 M/1.50 M/2.00 M in the hydrothermal process, respectively. As the {117} facet ratio increases, the absorption edge has an obvious red-shift by 32 nm and the corresponding bandgap is reduced from 2.58 to 2.42 eV. Remarkably, the specific surface area normalized degradation rate of BFCTO-1.50 was considerably higher than those of BFCTO-1.00 and BFCTO-2.00 due to the optimal ratio of {001} and {117} facets.

Extended Near-Infrared Photoactivity of Bi6Fe1.9Co0.1Ti3O18 by Upconversion Nanoparticles

Bi6Fe1.9Co0.1Ti3O18 (BFCTO)/NaGdF4:Yb3+, Er3+ (NGF) nanohybrids were successively synthesized by the hydrothermal process followed by anassembly method, and BFCTO-1.0/NGF nanosheets, BFCTO-1.5/NGF nanoplates and BFCTO-2.0/NGF truncated tetragonal bipyramids were obtained when 1.0, 1.5 and 2.0 M NaOH were adopted, respectively. Under the irradiation of 980 nm light, all the BFCTO samples exhibited no activity in degrading Rhodamine B (RhB). In contrast, with the loading of NGF upconversion nanoparticles, all the BFCTO/NGF samples exhibited extended near-infrared photoactivity, with BFCTO-1.5/NGF showing the best photocatalytic activity, which could be attributed to the effect of {001} and {117} crystal facets with the optimal ratio. In addition, the ferromagnetic properties of the BFCTO/NGF samples indicated their potential as novel, recyclable and efficient near-infrared (NIR) light-driven photocatalysts.

Plasmonic properties of Au/SiO2 nanoparticles: effect of gold size and silica dielectric layer thickness

Abstract Metallic nanoparticles with plasmonic properties have extensive potential applications in biodiagnostics and sensing, bioimaging and solar cells, but a comprehensive theoretical and experimental investigation of the phenomenon is far from being complete. In this manuscript, about 30, 40 and 50 nm Au nanoparticles were synthesised by Frens method, and Au/SiO2 nanoparticles were obtained by a modified Stöber method; the thickness of SiO2 layer were adjusted from 15 to 45 nm. The effect of Au size and SiO2 dielectric layer thickness on the plasmonic properties of Au/SiO2 nanoparticles were numerically simulated by 3D comsol and were experimentally studied by UV-vis absorption spectra. UV-vis absorption spectra showed that the increase in Au particle size or SiO2 thickness resulted in a red shift of the surface plasmon resonance absorption peak of Au/SiO2 nanoparticles, which is consistent with the simulation results by 3D comsol. Thicker SiO2 layer and smaller Au nanoparticles led to the decrease of electric field.