ABSTRACT
As an efficient photocatalyst, graphitic carbon nitride (g-C3N4) has been widely used in the field of photocatalytic hydrogen production. However, how to prepare hydrogen efficiently and stably has become a challenge. Herein, we successfully realize metal-free edge modification with phenyl groups by one-step thermal polymerization of urea with 4-phenyl-3-thiosemicarbazide. Consequently, the optimal photocatalytic hydrogen production rate for the modified graphitic carbon nitride is increased by three times to a value of 2390.6 µmol h-1 g-1, while the apparent quantum efficiency (AQE) reaches 8.3 % at a wavelength of 420 nm. We also provide a theoretical explanation for the experiments using density functional theory (DFT) calculations, which suggest that energy level changes and electron redistribution for the modified carbon nitride materials contribute to the observed changes in catalytic performance. This work provides an effective solution for improving the photocatalytic activity of carbon nitride materials and provides theoretical support for the edge modification of carbon nitride materials to promote their photocatalytic hydrogen production efficiency.
ABSTRACT
Polymer dielectrics with excellent processability and high breakdown strength (Eb ) enable the development of high-energy-density capacitors. Although the improvement of dielectric constant (K) of polymer dielectric has been realized by adding high-K inorganic fillers with high contents (>10 vol%), this approach faces significant challenges in scalable film processing. Here, the incorporation of ultralow ratios (<1 vol%) of low-K Cd1- x Znx Se1- y Sy nanodots into a ferroelectric polymer is reported. The polymer composites exhibit substantial and concurrent increase in both K and Eb , yielding a discharged energy density of 26.0 J cm-3 , outperforming the current dielectric polymers and nanocomposites measured at ≤600 MV m-1 . The observed unconventional dielectric enhancement is attributed to the structural changes induced by the nanodot fillers, including transformation of polymer chain conformation and induced interfacial dipoles, which have been confirmed by density function theory calculations. The dielectric model established in this work addresses the limitations of the current volume-average models on the polymer composites with low filler contents and gives excellent agreement to the experimental results. This work provides a new experimental route to scalable high-energy-density polymer dielectrics and also advances the fundamental understanding of the dielectric behavior of polymer nanocomposites at atomistic scales.
