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Ultralow‐k materials with promising comprehensive performance to meet the increasing requirements of high‐frequency communication are highly desired. Here, a cross‐linked porous polymer SiCOH, synthesized via simple sol–gel method, was used as the filler to prepare SiCOH/PI composite films by physically blending, which demonstrates ultralow dielectric constant at high frequency. Notably, only 2.5% of SiCOH in the composite can significantly reduce the dielectric constant of PI from 3.0 to an ultralow value of 1.7 in the 9.5–12.4 GHz, together with a low dielectric loss of 0.029. Additionally, the SiCOH/PI composite maintains a high tensile strength of 82.4 MPa and a tensile modulus of 1.82 GPa, which is comparable to pure PI film. While the glass transition temperature (Tg) increases to 370°C and the linear expansion coefficient is reduced to 30.7 ppm/°C, both of which are superior to those of pure PI film. Moreover, by introducing the hydrophobic SiCOH into PI, the contact angle of the composite films increased to 92.0°–99.0°. This simple and low‐cost method not only effectively lowers the dielectric constant of PI but also improves the thermal stability, mechanical properties, and hydrophobic ability, greatly boosts the practical application of PI in high‐frequency communication in the future. [ABSTRACT FROM AUTHOR]

Improving polymerization and crystallization properties has become a key point to maximize the intrinsic photocatalytic performance of graphitic carbon nitride (g‐C3N4), however, the critical roles of intermediates in the polymerization and crystallization process are not clear. Herein, highly crystalline g‐C3N4 is obtained by calcinating different amount of dicyandiamide in a closed environment. Ultrahigh atmospheric pressure up to 6.2 MPa can be spontaneously formed due to the produced gaseous intermediates. The best crystallization properties were achieved when 1.8 g of dicyandiamide was used. The photocatalytic hydrogen production rate reaches 9241.3 μmol ⋅ g−1 ⋅ h−1, which is improved by about 12.5 times by comparison. The crystallization and hydrogen production activities cannot be enhanced only by adding an initial gas pressure meanwhile keeping the quality of dicyandiamide constant, confirming that the intermediate concentration determines the polymerization and hydrogen production performance of g‐C3N4. This study is important to improve the intrinsic photocatalytic performance of g‐C3N4 and the composites. [ABSTRACT FROM AUTHOR]

Graphitic carbon nitride (g-C3N4) is a promising visible light photocatalyst but shows only moderate activity due to its high carrier recombination and low charge mobility. Herein, we synthesize a novel kind of nanoporous g-C3N4 microsphere (Np-CNM) with highly improved crystallinity via a “ship-in-a-bottle” strategy using mesoporous hollow silica spheres as nanoreactors. Confined thermal polymerization of the precursor inside the hollow cavity under pressurized conditions provide Np-CNMs with a highly nanoporous structure and improve crystallinity simultaneously which can not only significantly suppress the carrier recombination but also accelerate the interlayer charge transfer. The as-obtained Np-CNMs demonstrate a considerably enhanced photocatalytic hydrogen evolution rate (5785 μmol−1 h−1 g−1) under visible-light irradiation (λ≥ 420 nm), which is more than 44 and 30 times that of bulk g-C3N4 and Np-CNMs produced at atmospheric pressure, respectively. This work identifies a reliable route to obtain highly crystallized nanostructured g-C3N4 microspheres, which are important for constructing high performance photocatalysts. [ABSTRACT FROM AUTHOR]

Porous microspheres with desired pore size and distribution are in high demand for loading various guest materials, especially various pollutants that are several nanometers in size or stably suspended in liquid. Herein, multilevel porous SiO 2 microspheres with arbitrarily adjustable core-shell ratios are prepared by solely regulating the time interval between the start of the hydrolysis reaction and the addition of organic solvent. The core-shell ratio of the SiO 2 microspheres increases gradually with prolongation of the addition time interval; meanwhile, the specific surface area can be adjusted from 543.2 m 2 g -1 to 992.9 m 2 g -1 , and the average pore diameter varies from 2.3 to 5.7 nm together with a high pore volume reaching 0.91 cm 3 g -1 . Moreover, the hierarchical core-shell SiO 2 microspheres with an adjustable core-shell ratio, a large specific surface area, and a multilevel pore size could be obtained on a large scale. These SiO 2 microspheres demonstrate excellent performance in coloading platinum nanoparticles and various dye molecules, suggesting their great potential in treating various pollutants in printing and dyeing wastewater.