The Effects of Various Parameters of the Microwave-Assisted Solvothermal Synthesis on the Specific Surface Area and Catalytic Performance of MgF2 Nanoparticles

High-specific-surface-area MgF₂ was prepared by microwave-assisted solvothermal synthesis. The influences of the solvent and the magnesium precursors, and the calcination atmospheres, on the nanoparticle sizes and specific surface areas, estimated by X-Ray Powder Diffraction, N₂ sorption and TEM analyses, were investigated. Nanocrystallized (~7 nm) magnesium partially hydroxylated fluorides (MgF_2−x(OH)_x) with significant specific surface areas between 290 and 330 m²∙g⁻¹ were obtained. After activation under gaseous HF, MgF_2−x(OH)_x catalysts underwent a large decrease of both their surface area and their hydroxide, rates as shown by their ¹⁹F and ¹H solid-state NMR spectra. Expect for MgF₂ prepared from the acetate precursor, an activity of 30–32 mmol/h∙g was obtained which was about 40% higher compared with that of MgF₂ prepared using Trifluoroacetate method (21.6 mmol/h∙g).

Improving Photocatalytic Degradation Activity of Organic Pollutant by Sn4+ Doping of Anatase TiO2 Hierarchical Nanospheres with Dominant {001} Facets

Herein, high-energy {001} facets and Sn⁴⁺ doping have been demonstrated to be effective strategies to improve the surface characteristics, photon absorption, and charge transport of TiO₂ hierarchical nanospheres, thereby improving their photocatalytic performance. The TiO₂ hierarchical nanospheres under different reaction times were prepared by solvothermal method. The TiO₂ hierarchical nanospheres (24 h) expose the largest area of {001} facets, which is conducive to increase the density of surface active sites to degrade the adsorbed methylene blue (MB), enhance light scattering ability to absorb more incident photons, and finally, improve photocatalytic activity. Furthermore, the Sn_xTi_1−xO₂ (STO) hierarchical nanospheres are fabricated by Sn⁴⁺ doping, in which the Sn⁴⁺ doping energy level and surface hydroxyl group are beneficial to broaden the light absorption range, promote the generation of charge carriers, and retard the recombination of electron–hole pairs, thereby increasing the probability of charge carriers participating in photocatalytic reactions. Compared with TiO₂ hierarchical nanospheres (24 h), the STO hierarchical nanospheres with 5% n_Sn/n_Ti molar ratio exhibit a 1.84-fold improvement in photodegradation of MB arising from the enhanced light absorption ability, increased number of photogenerated electron–hole pairs, and prolonged charge carrier lifetime. In addition, the detailed mechanisms are also discussed in the present paper.

Tunable solar-heat shielding property of transparent films based on mesoporous Sb-doped SnO₂ microspheres

In this paper, mesoporous antimony doped tin oxide (ATO) microspheres are synthesized via a solvothermal method from a methanol system with the surfactant followed by a thermal treatment process. Morphology studies reveal that the spherical products obtained by polyvinylpyrrolidone (PVP) templating result in a higher uniformity in size. Such obtained ATO microspheres with a secondary particle size ranging between 200 and 800 nm consist of packed tiny nanocrystals and have high specific surface area (∼98 m(2) g(-1)). The effect of Sb doping on the structural and electrical properties of SnO2 microspheres is studied. Because of the substitution of Sn(4+) with Sb(5+) accompanied by forming a shallow donor level close to the conduction band of SnO2, a lower resistivity of powder pellet can be achieved, which corresponds to the spectrally selective property of films. The application of ATO microspheres provides an example of transparent coatings; depending on Sb concentration in SnO2 and solid content of coatings, transparent films with tunable solar-heat shielding property are obtained.