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Gd2O3 nanoparticles modified g-C3N4 photocatalytic composites were synthesized by a simple one-step hydrothermal method. The structure, morphology, optical properties of the prepared photocatalyst were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), field emission transmission electron microscopy (FETEM) and X-ray photoelectron spectroscopy (XPS). The result demonstrates that gadolinium is mainly dispersed on the surface of g-C3N4 in the form of Gd2O3, and does not destroy the lattice structure of g-C3N4. Besides, the gadolinium can cause the red shift of the absorption edge of light, narrow the band gap, and increase the separation efficiency of the photogenerated electron and hole of g-C3N4. Especially, the specific surface area of g-C3N4 can be significantly increased. Furthermore, g-C3N4/Gd-0.05 displays the highest photodegradation performance when it is used for degradation of methyl orange (MO), methylene blue (MB) and Rhodamine B (RhB). The photodegradation rate of g-C3N4/Gd-0.05 composites is 72.4% for MO, 95.5% for RhB, 100% for MB after 120 min under visible light (λ > 420 nm) irradiation. Narrow band gap promotes the separation of photogenerated electron and hole, which enhances the photocatalytic activity of g-C3N4. It is noted that g-C3N4/Gd-0.05 exhibits excellent photocatalytic stability by the photocurrent and the cyclic photodegradation of MO.

The sectional heater of industrial-scale directional solidification furnace was designed for improving the quality of the high performance multi-crystalline silicon ingots used for solar cell fabrication. A global numerical model was adopted to investigate the effect of the modified furnace on the thermal field distribution, the shape of the crystal-melt interface and the thermal stress distribution in the solidified silicon ingot during the directional solidification process. Simulation results indicate that the crystal-melt interface shape in the modified furnace with the sectional heater changes from convex at the earlier stage to slightly flat at the later stage, and the thermal stress level at the bottom corner of the solidified ingots is clearly lower than that in the conventional furnace. Furthermore, the designed furnace with the sectional heater was built and experiments corresponding to the numerical simulations were carried out. It was found that a more uniform minority carrier lifetime distribution, lower dislocation cluster density, and lower oxygen concentration were obtained for the silicon ingot grown using the modified furnace. Additionally, the average conversion efficiency of the solar cells fabricated using the grown ingots was evaluated, and it was found that a higher efficiency was obtained for the cells fabricated using the ingots obtained with the modified furnace (18.64%) compared to that for the cells fabricated using the ingots obtained with the conventional furnace (18.54%).

This study proposes two kinds of bottom insulation with a moveable insulation block, with either a narrower or large horizontal width, for use in an industrial-size seeded directional solidification (DS) furnace to produce high-performance multi-crystalline silicon ingot. A transient global model was established to study the effects of the modified configurations on the thermal field in the solidified silicon ingot during the DS process. The numerical results indicate that the shapes of the s-m and m-c interfaces remained relatively flat or slightly convex throughout the entire DS process when the narrower bottom insulation block design was used, and the highest thermal stress in the bottom corner areas of the ingots was obviously lower. To further verify the simulation results, ingot casting experiments and testing were carried out with the use of photoluminescence and minority lifetime mappings. The results show that the dislocation clusters exhibited a lower density in the modified designs. This phenomenon could be attributed to the uniform impurity and lower thermal stress distributions induced by the flat or slightly convex interface. Additionally, the corresponding average conversion efficiency is discussed.