ABSTRACT
Single and a few atomic-layer molybdenum disulfide (MoS2) is a promising material in the fields of hydrogen generation, battery, supercapacitor, and environmental protection, owing to the outstanding electronic, optical, and catalytic properties. Although many approaches have been developed for exfoliation of MoS2 sheets, it is still essential to develop simple, convenient, and environmental friendly exfoliation methods. More importantly, the microscopic exfoliation process and the mechanism are still not clear, limiting a deeper understanding of the exfoliation. Herein, we develop a convenient and clean method for exfoliation of the 2H phase MoS2 (2H-MoS2) deposited on an indium tin oxide (ITO) surface. Importantly, the exfoliation process is observed directly and continuously under an optical microscope to reveal the detailed exfoliation process and mechanism. As illustrated, the light illumination triggers the exfoliation of the 2H-MoS2 sheets, and the presence of water is essential in this exfoliation process. The light intensity and wavelength, humidity, and bias all affect the exfoliation process obviously. The exfoliation is caused by the vaporization of the water molecules intercalated in 2H-MoS2 interlayers. By using this method, 2H-MoS2 nanosheets with different thicknesses are prepared on the ITO substrate, and microscopic catalysis mapping of the exfoliated sheets is demonstrated with single-molecule fluorescence microscopy, revealing that the prepared thin-layer 2H-MoS2 nanosheets show improved electrocatalysis activity (roughly 20 times). Our work will not only help deepen the understanding of exfoliation process of two-dimensional nanosheets but also provide an effective tool for the in situ study of various properties of the exfoliated sheets.
ABSTRACT
Multicolor carbon phosphors as emerging light conversion materials, with full recyclability and stable color convertibility, are poised to accelerate the sustainable development of environment-friendly optoelectronics. Herein, we firstly report a facile strategy, combining single-step hydrothermal and differential washing methods, for the preparation of multicolor carbon emitters with nano-dot/micro-belt structures. The as-prepared hybrids exhibit excellent film-forming ability and demonstrate controllable multicolor solid-state luminescence ranging from white and green to blue light emission, by utilizing the synergistic effect between nano-dot and micro-belt structures. Particularly, the hybrid white emitters possess a robust ability of being fully recyclable without any performance degradation and formation of harmful byproducts. Moreover, light-emitting devices (LEDs) coated with the hybrid emitters show stable voltage-independent luminescence behavior in lighting applications. This work provides a simple route to modulate the optical properties of multicolor carbon-based emitters and shows great potential in the sustainable development of lighting-related products.
ABSTRACT
Bismuth vanadate (BiVO4) microcrystals enclosed with up to 42 low and high index facets were synthesized through truncation of BiVO4 octahedral crystals via a simple and highly reproducible hydrothermal method. The size and shape of the truncated BiVO4 crystals could be tuned by varying the acid concentration, reaction temperature and reaction period. Compared to the BiVO4 octahedral crystals without truncation, the 42-faceted ones showed an enhanced photocatalytic activity in the degradation of rhodamine B molecules due to the enhanced charge separation on the exposed low and high index facets. This was confirmed at sub-particle level by the photo-deposition of gold and manganese oxide nanoparticles selectively on hot electron and hole accumulated facets, respectively. Our results will provide a guideline for the synthesis of more efficient BiVO4 and many other multinary metal oxide-based photocatalysts. Moreover, the synthesized microcrystals are perfect materials for the study of photocatalytic property of BiVO4 at single and sub-particle level.
ABSTRACT
Since the discovery of surface enhanced Raman scattering (SERS), the choice of SERS-active materials has been limited mainly to metals, especially gold and silver in the visible spectrum. Although non-metals can also be SERS-active by forming nanostructures or composite structures with SERS-active materials, the mechanism behind it is still unclear and there is no perfect technique to study it. In this work, by constructing a SERS structure on a flexible polydimethylsiloxane film, we provide a way to study the effect of non-metallic nanostructures on Raman enhancement by attaching the above film onto flat and nanostructured surfaces. It was found that a nanoporous silicon surface contributes to an additional, up to five times, Raman enhancement. The pore depth and pore size also influence the observed Raman enhancement. These findings will help us not only to understand the mechanism of SERS involving non-metallic nanostructures, but also to design more efficient SERS structures for various applications.
ABSTRACT
Social media, an open space for the public's opinion and expression, has become an increasingly essential issue in crisis events, leading to secondary crisis communication. Realizing the potential risk of that, this study took the "Occupy Central" spreading on Weibo as a case, and applied topic clustering and sentiment analysis to examine the sequential characteristics of secondary crisis communication on social media in topics and emotions. Results show that the topics Weibo users discussed shifted from a political event to tourism boycott, with emotions turning increasingly negative. The turning point of such a transfer was aroused group conflicts and negative emotions elicited between people from mainland China and Hong Kong. The results indicate the necessity of emphasizing secondary crisis communication during a crisis due to the dynamic and sequential change of topics and public's emotions, which may result in new crises impacting the tourism destination where the initial crisis occurs.
