The highly effective ZnO/g-C3N4 photocatalysts with different ZnO amount were prepared by an economic and environmentally friendly method. The photocatalysts were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, UV–vis diffuse reflectance spectroscopy, and Brunauer–Emmett–Teller surface area. The results showed that photocatalytic activity of the photocatalyst was much higher than that of pure g-C3N4 via photodegradation of Rhodamine B under visible light irradiation. The kinetic constant of RhB degradation over ZnO(15 wt.%)/g-C3N4 was 3.1 times that of pure g-C3N4. Effect of ZnO content on the photocatalytic activity of ZnO/g-C3N4 was studied in detail. The active species in RhB degradation were examined by adding a series of scavengers. The study on photocatalytic mechanism revealed that the electrons injected directly from the conduction band of g-C3N4 to that of ZnO, resulting in the production of O2− and OH radicals in the conduction band of ZnO. Simultaneously, the rich holes in the valence band of g-C3N4 oxidized Rhodamine B directly to promote the photocatalytic degradation reaction. This work may provide some insight into solving the unsatisfactory catalytic activity and low efficiency converting solar radiation for practical applications of g-C3N4.Graphical abstractCompared to pure C3N4 and ZnO, the as-prepared ZnO/C3N4 photocatalysts exhibit excellent visible light photocatalytic activity. The photocatalytic activity of ZnO/C3N4 improves remarkably with increasing ZnO content from 5 wt.% to 15 wt.%, although it decreases slightly at the higher ZnO level. The enhanced photocatalytic activity of ZnO/C3N4 photocatayst is attributed to the effective separation efficiency of photogenerated electrons and holes in the system.Figure optionsDownload full-size imageDownload high-quality image (176 K)Download as PowerPoint slideHighlights► The ZnO/C3N4 photocatalysts with various ZnO contents were successfully prepared. ► Rate constant of RhB degradation over ZnO(15 wt.%)/C3N4 is 3.1 times that of C3N4. ► Effect of ZnO content on the photoactivity of ZnO/C3N4 was studied in detail. ► Reactive species in RhB degradation were examined by adding a series of scavengers. ► Visible light degradation mechanism of RhB over ZnO/C3N4 was systematically studied.

We have prepared uniform silica nanoparticles (NPs) doped with a two-photon absorbing zwitterionic hemicyanine dye by reverse microemulsion method. Obvious solvatochromism on the absorption spectra of dye-doped NPs indicates that solvents can partly penetrate into the silica matrix and then affect the ground and excited state of dye molecules. For dye-doped NP suspensions, both one-photon and two-photon excited fluorescence are much stronger and recorded at shorter wavelength compared to those of free dye solutions with comparative overall dye concentration. This behavior is possibly attributed to the restricted twisted intramolecular charge transfer (TICT), which reduces fluorescence quenching when dye molecules are trapped in the silica matrix. Images from two-photon laser scanning fluorescence microscopy demonstrate that the dye-doped silica NPs can be actively uptaken by Hela cells with low cytotoxicity.Water-soluble silica NPs doped with a two-photon absorbing zwitterionic hemicyanine dye were prepared. They were found of enhanced one-photon and two-photon excited fluorescence compared to free dye solutions. Images from two-photon laser scanning fluorescence microscopy demonstrate that the dye-doped silica NPs can be actively uptaken by Hela cells.

Dual-color monodisperse polystyrene microspheres have been prepared by two-stage dispersion polymerization, whose addition of the dye-comonomer was deferred until the nucleation stage was complete. Two dyes were covalently incorporated into microspheres by copolymerization without disturbing the final particle size and size distribution. No dye leakage occurs for the microsphere suspension because of covalent bonding of dye molecules. By varying the dye concentrations in microspheres, we obtained fluorescent microspheres with two distinguishing parts of fluorescence and varied fluorescent intensity ratios under a single-wavelength excitation. The microspheres present intense fluorescence for the large amount of encapsulated dye molecules.

We prepared fluorescent microspheres with notably large Stokes shift and long-wavelength fluorescence by applying fluorescence resonance energy transfer (FRET) between two common julolidine dyes. Short distance between dye molecules caused by high dye concentration results in efficient FRET in microspheres. However, adequate dye concentration and moderate molar ratio of the donor and acceptor should be chosen to avoid aggregation of dye molecules, which leads to the decrease of fluorescent intensity. Microrspheres with average distance between dye molecules of 1.94 nm and molar ratio of 3.08:1 realize highly efficient FRET with no fluorescence of donor and intense long-wavelength emission of acceptor. In addition, the applied solvent evaporation method for preparing microspheres provided better protection of dyes from ambient medium than traditional surface-labeled method. These results demonstrate the feasibility of applying FRET in microspheres to expand useful fluorescent probes, and reveal their potential application in bioassays field.

The absorption and photoluminescence of the newly synthesized 5-(9-anthryl)-3-(4-nitrophenyl)-1-phenyl-2-pyrazoline (AN PP) were investigated. The absorption is the absorption of anthryl moiety at about 325–400 nm, superimposed on the broader absorption of 3-(4-nitrophenyl)-1-phenyl-2-pyrazoline moiety peaked at 420 nm. On excitation at 420 nm, the fluorescence spectrum has only one emission band from the pyrazoline moiety. This emission band exhibits a larger red shift with an increase in the polarity of solvents. But on excitation at 365 nm, the fluorescence spectrum has two emission bands coming from the anthryl and pyrazoline moieties, respectively. The intensity ratio of the two bands is different in solvents of different polarity. It is concluded that photo-induced intramolecular energy transfer from the anthryl to pyrazoline moiety exists simultaneously with the charge transfer from N (1) to C (3) in the pyrazoline moiety in the excited state and both compete with each other.