Fengling Yang

Design and growth of dendritic Cu2−xSe and bunchy CuSe hierarchical crystalline aggregations

Dendritic nanocrystals of copper selenide were fabricated in situ for the first time by using alcohol as the solvent. Cu2−xSe films composed of hierarchically ordered dendritic nanostructures were prepared on Cu substrates at a rather moderate temperature of 190–200 °C for just 1–3 h, while bunchy CuSe nanostructures could be further constructed above the Cu2−xSe dendrites by prolonging the reaction time of solvothermal growth with ethanol as the solvent. The resulting Cu2−xSe nanodendrites display highly symmetric corolitic morphology while the bunchy CuSe aggregations show particular nanostructures with a pronounced trunk and actinomorphic multi-branches. It is also found that the dendritic structures of crystalline Cu2−xSe could never be obtained when the reaction temperature is less than 190 °C, while the temperature needed is 160 °C for Ag2Se nanodendrites and higher than 220 °C for CdSe nanodendrites. These copper selenide nanostructures with hierarchically ordered 3-dimensional (3D) framework exhibited good absorbance and photoluminescence (PL) property and could bear potential applications in solar cell devices in the future.

From Nanoplates to Microtubes and Microrods: A Surfactant-Free Rolling Mechanism for Facile Fabrication and Morphology Evolution of Ag2S Films

By a simple and facile wet-chemistry technique without any surfactant, various shapes of Ag(2)S crystals--including leaflike pentagonal nanoplates, crinkly nanoscrolls, hexagonal prismlike microtubes, and microrods--were fabricated in situ on a large-area silver-foil surface separately. Detailed experiments revealed that the Ag(2)S nanoplates were formed just by immersing the silver foil in a sulfur/ethanol solution at room temperature and atmospheric pressure, and they subsequently rolled into nanoscrolls and further grew into microtubes and microrods under solvothermal conditions. Inspired by the natural curling of a piece of foliage, we proposed a surfactant-free rolling mechanism to interpret the observed morphological evolution from lamellar to tubular structures. Based on these simple, practical, and green chemical synthetic routes, we can easily synthesize lamellar, scrolled, tubular, and clubbed Ag(2)S crystals by simply adjusting the reaction temperature, pressure, and time. It is very interesting to note that the current rolling process is quite different from the previous reported rolling mechanism that highly depends on the surfactants; we revealed that the lamellar Ag(2)S could be rolled into tubular structures without using any surfactant or other chemical additives, just like the natural rolling process of a piece of foliage. Therefore, this morphology-controlled synthetic route of Ag(2)S crystals may provide new insight into the synthesis of metal sulfide semiconducting micro-/nanocrystals with desired morphologies for further industrial applications. The optical properties of the pentagonal Ag(2)S nanoplates/film were also investigated by UV/Vis and photoluminescence (PL) techniques, which showed large blue-shift of the corresponding UV/Vis and PL spectra.

Design and synthesis of ternary semiconductor Cu7.2(SexS1−x)4 nanocrystallites for efficient visible light photocatalysis

A new series of ternary semiconductor compounds, Cu7.2(SexS1−x)4 (0.2 ≤ x ≤ 0.8) nanocrystallites, that exhibited good photocatalytic activity under visible-light irradiation, were facilely synthesized under mild conditions. The Cu7.2(SexS1−x)4 nanocrystallites were characterized by powder X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy and UV-Vis absorption spectra. From X-ray data it is found that the cell constant a of different samples varies linearly with the composition x as: a (A) = 5.5959 + 0.1586x. UV-Vis absorption spectra indicate that the apparent band gap energies can be tuned by adjusting the composition x so as to better match to the whole solar spectrum. Unlike the most studied TiO2 that only responds to the UV-light irradiation, the present Cu7.2(SexS1−x)4 nanocrystallites exhibited much better photocatalytic activity under visible light on degradation of RhB. It is believed that the photocatalytic superiority of the Cu7.2(SexS1−x)4 nanocrystallites is mainly due to the compositional gradient arisen from uneven distribution of Se/S compositions in the compounds, which may induce a more efficient charge separation/transport in the Cu7.2(SexS1−x)4 photocatalysts.