One-step synthesis of high photocatalytic graphitic carbon nitride porous nanosheets.

As a metal-free photocatalyst, graphitic carbon nitride (g-C3N4) has attracted tremendous attention. Preparation of porous few-layer g-C3N4 nanosheets has been proven to be an effective strategy to obtain high photocatalytic performance. At present, most methods are expensive, time-consuming or complicated. Here, a low-cost, facile and environment-friendly one-step synthesis method of porous few-layer g-C3N4 nanosheets is designed by introducing water in the precursor. Straightforward calcination of the precursor, which decomposes to form ammonia, can produce g-C3N4 nanosheets with the assistance of water. Under the visible light (>400 nm), the photocatalytic H2 evolution performance of the so-obtained nanosheets is 3214 µmol · g-1 · h-1, which is 17.3 times of the original bulk g-C3N4. The apparent quantum yield is 27% under the 380 nm monochromatic light irradiation.

Growth of few-layer WTe2 by a salt-assisted double-tube chemical vapor deposition method with high infrared photosensitivity.

WTe2, as a member of Weyl semimetals, is a vital candidate for the development of broad-wavelength-range photodetectors. At present, the preparation of WTe2 films mainly depends on the chemical vapor deposition (CVD) method. However, the chemical reactivity between W and Te is low, and the controllable synthesis of large-sized layered WTe2 in a stoichiometric ratio is the main challenge for further research. Here, we propose a salt-assisted double-tube CVD method for the one-step preparation of high-quality and large-size WTe2 crystals with a monolayer and few layers. The thickness and lateral dimension of WTe2 crystals can be effectively tuned by the growth temperature and hydrogen concentration, and the dynamic growth mechanism is understood by the combination of surface reaction and mass transport. Furthermore, a high-performance photodetector based on WTe2 is fabricated, which has high responsivity of 118 mA W-1 (1550 nm) and 408 mA W-1 (2700 nm) at room temperature, indicating its great potential for application in infrared optoelectronic devices. The results provide a reference for the preparation of 2D materials by CVD and lay the foundation for the fabrication of next-generation optoelectronic devices with a wide-wavelength-range response.

Highly Efficient Metal-Free Two-Dimensional Luminescent Melem Nanosheets for Bioimaging.

Two-dimensional (2D) luminescent materials have received tremendous attention for their intrinsic properties and promising practical applications. Achieving 2D luminescent materials with high photoluminescence (PL) efficiency is still a great challenge. Here, ultrathin metal-free 2D luminescent nanosheets of 2,5,8-triamino-tri-s-triazine (melem) are synthesized through a facile liquid exfoliation process assisted by ultrasound. The as-obtained melem nanosheets distribute in the size range from a few nanometers to around 150 nm with a thickness of about 5 to 6 atomic layers. Melem nanosheets exhibit efficient blue emission with a PL efficiency as high as 77.09%, much higher than the heavily explored 2D luminescent g-C3N4 nanosheets. The high efficiency of melem nanosheets comes from the absence of atom vacancies and the low carrier mobility. Benefiting from the easy synthesis, good stability, low cell toxicity, and high efficiency, melem nanosheets are successfully applied as bioimaging materials on human breast cancer cells, requiring no extra treatments such as surface coating or functionalization. These metal-free 2D luminescent melem nanosheets hold great potential for various applications including bioimaging and other biorelated applications.