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Graphitic carbon nitride (C3N4) was hybridized by Bi2WO6 via a hydrothermal method. The high-resolution transmission electron microscopy (HR-TEM) results reveal that an intimate interface between C3N4 and Bi2WO6 forms in the heterojunctions. The UV-vis diffuse reflection spectra show that the resulting C3N4-Bi2WO6 heterojunctions possess more intensive absorption within the visible light range in comparison with pure Bi2WO6. These excellent structural and spectral properties endowed the C3N4-Bi2WO6 heterojunctions with enhanced photocatalytic activities. Significantly, the optimum photocatalytic activity of the 0.5C3N4-0.5Bi2WO6 heterojunction for the degradation of methyl orange (MO) was almost 3 and 155 times higher than those of either individual C3N4 or Bi2WO6. The possible photocatalytic mechanism with superoxide radical species as the main active species in photocatalysis is proposed on the basis of experimental results. Moreover, the heterojunction depicted high stability and durability during six successive cycles.

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Multiphoton imaging techniques that convert low-energy excitation to higher energy emission are widely used to improve signal over background, reduce scatter, and limit photodamage. Lanthanide-doped upconverting nanoparticles (UCNPs) are among the most efficient multiphoton probes, but even UCNPs with optimized lanthanide dopant levels require laser intensities that may be problematic. Here, we develop protein-sized, alloyed UCNPs (aUCNPs) that can be imaged individually at laser intensities >300-fold lower than needed for comparably sized doped UCNPs. Using single UCNP characterization and kinetic modeling, we find that addition of inert shells changes optimal lanthanide content from Yb3+, Er3+-doped NaYF4 nanocrystals to fully alloyed compositions. At high levels, emitter Er3+ ions can adopt a second role to enhance aUCNP absorption cross-section by desaturating sensitizer Yb3+ or by absorbing photons directly. Core/shell aUCNPs 12 nm in total diameter can be imaged through deep tissue in live mice using a laser intensity of 0.1 W cm−2.

SignificanceBlack phosphorus (BP) nanosheet is a “hot” class of 2D material having wide applications in optoelectronics, catalysis, biomedicine, etc. However, facile synthesis of BP nanosheets is not achieved by far. Currently, BP nanosheets are mainly prepared via solution-based exfoliation of bulk crystals, a process that is complicated, time-consuming, and costly. Moreover, the as-prepared BP nanosheets are not stable. Here, we developed a facile bottom-up protocol for preparing BP nanosheets in solution at low temperature. Our synthetic procedure is conceptually simple and can be performed in common chemical laboratories. The estimated synthesis cost is less than 1 US dollar per gram. Our work, therefore, offers the community an unlimited access to such 2D material.