Hollow Rodlike MgF₂ with an Ultralow Refractive Index for the Preparation of Multifunctional Antireflective Coatings

Antireflective coatings with superhydrophobic, self-cleaning, and wide-spectrum high-transmittance properties and good mechanical strength have important practical value. In this research, hollow nanorod-like MgF₂ sols with different void volumes were prepared by a template-free solvothermal method to further obtain hollow nanorod-like MgF₂ crystals with an ultralow refractive index of 1.14. Besides, a MgF₂ coating with an adjustable refractive index of 1.10–1.35 was also prepared by the template-free solvothermal method. Then through the combination of base/acid two-step-catalyzed TEOS and hydroxyl modification on the surface of nanosilica spheres, the SiO₂ coating with good mechanical strength, a flat surface, and a refractive index of 1.30–1.45 was obtained. Double-layer broadband antireflective coatings with an average transmittance of 99.6% at 400–1400 nm were designed using the relevant optical theory. After the coating thickness was optimized by the dip-coating method, the double-layer antireflective coatings, whose parameters were consistent with those designed by the theory, were obtained. The bottom layer was a SiO₂ coating with a refractive index of 1.34 and a thickness of 155 nm, and the top layer was a hollow rodlike MgF₂ coating with a refractive index of 1.10 and a thickness of 165 nm. The average transmittance of the obtained MgF₂–SiO₂ antireflective coatings was 99.1% at 400–1400 nm, which was close to the theoretical value. The hydrophobic angle of the coating surface reached 119° at first, and the angle further reached 152° after conducting surface modification by PFOTES. In addition, because the porosity of the coating surface was only 10.7%, the pencil hardness of the coating surface was 5 H and the critical load Lc was 27.05 N. In summary, the obtained antireflective coatings possessed superhydrophobic, self-cleaning, and wide-spectrum high-transmittance properties and good mechanical strength

Plasma-treated Ce/TiO₂–SiO₂ catalyst for the NH₃-SCR of NO<i>_x</i>

<p>Ce/TiO₂–SiO₂ catalysts with different Ti/Si molar ratios are prepared by the incipient impregnation method and their NH₃-SCR activities are evaluated at 100–500°C on a fixed reactor. The Ce/TiO₂–SiO₂ (3/1) catalyst, modified by non-thermal plasma (NTP) treatment and then activated by thermal treatment at 500°C for 4 h, exhibits best performance. Comprehensive deNO<i>_x</i> performance of the catalyst is evidently improved and its efficiency reaches up to 99.21% at 350°C. NO conversion efficiency of the treated catalyst doped with K remains about 90.23% at 300°C and the catalyst also shows improved activity at lower temperatures. Various characterization methods show that the activity enhancement is correlated only with NTP treatment, as it increases the number of Ce³⁺ species, which generates more chemisorbed oxygen, leads to improved dispersion of Brønsted and Lewis acidic sites and finally has an inherent etching effect.</p