Yuanhao Gao

A very facile, low temperature, one-step route to in situ fabricate copper sulfide nanosheet thin films

CuS nanosheet thin films with large areas were synthesized in situ on copper substrates through a facile, one-step treatment of copper foil and sulfur powder in the presence of N,N-dimethylformamide (DMF) at low temperature (60 °C or less). Compared with the previous reported solvothermal approach, the current low temperature route is simpler, low cost and low energy consumption. The effects of the reaction temperature on the synthesis and the optical property of CuS nanosheet films were investigated. The resulting CuS nanosheet films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and UV–vis spectrometer. In this study, we also demonstrated this method to prepare copper sulfide nanosheet films on ground-glass and indium tin oxide glass (ITO) substrates. We found that perfect nanosheet crystals could be obtained in all cases. The growth mechanism of CuS nanosheet-based films was proposed. The current method may open up a new way to prepare thin films of metal sulfide at low temperatures.

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.

In situ fabrication of Cu2ZnSnS4 nanoflake thin films on both rigid and flexible substrates

Cu2ZnSnS4 (CZTS) thin film, a highly promising and low-cost absorber layer material for solar cells, has been in situ fabricated on stainless steel and FTO glass substrates for the first time, using a one-step solvothermal treatment of CuZnSn-alloyed film with sulphur or selenium powder. The resulting products were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV-vis-NIR spectroscopy. Raman spectroscopy was used to characterize and confirm the formation of CZTS. The effects of temperature, reaction time, the ratio of Cu/Zn/Sn, and non-elemental reactants on the formation of CZTS nanocrystal films were assessed, and we found that the reaction temperature was a key factor in determining the properties of the final products. Pure CZTS phase forms at a temperature of 250 °C or higher. Our method produces CZTS thin films at 250 °C, the lowest reaction temperature that can be used in the process and the lowest temperature of any current fabrication system. We also found that flexible substrates promote the growth of CZTS nanocrystals. Using flexible substrates in the in situ fabrication of nanocrystalline thin films may make it possible to use CZTS for industrial applications.

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.

Facile non-injection synthesis of high quality CZTS nanocrystals

We present a facile, non-injection synthesis of high quality CZTS nanocrystals by using simple inorganic salts, sulfur powders and (CH3)3COK (KTB) as precursors. The uniqueness and creativity is the utilization of KTB as sulfur activating agent and stabilizing surfactant agent.

Heavy doping of S2 in Cu7.2S4 lattice into chemically homogeneous superlattice Cu7.2Sx nanowires: strong photoelectric response

This is the first time a series of chemically homogeneous superlattice Cu7.2Sx (x = 4.07, 4.52, 6.01, 6.20, 6.45) nanowires have been successfully synthesized by heavy doping of S2 species in Cu7.2S4 lattice through a simple wet-chemical route. This superlattice structure is a polytypoid structure tuned by adjusting the atom ratio of S2 to S in lattice configuration. The perfect superlattice Cu7.2S6.20 structure interestingly consists of two alternating lattice fringes corresponding to the atom layers of Cu–S and Cu–S2 in an even spacing of 5.70 A. The article describes the formation, morphology, composition and structure of the Cu7.2Sx superlattice nanowires. Photoluminescence (PL) spectra and transient photovoltage (TPV) measurements reveal that the generation and separation efficiency of the photogenerated charges of Cu7.2Sx nanowires could be greatly improved by adjusting the S2/S ratio in the lattice configuration, and thus enhance the luminescence quantum efficiency. This study reveals that the S2 species in Cu7.2Sx nanowires play a very important role in determining the dynamic properties of photogenerated charge carriers.

Highly Stable Hierarchical Flower-like β-In2S3 Assembled from 2D Nanosheets with high Adsorption-Photodecolorization Activities for the Treatment of Wastewater

The hierarchical flower-like β-In2S3 catalyst assembled from 2D nanosheets was prepared using an organic-component depletion method utilizing inorganic-organic hybrids indium diethyldithiocarbamate (In-DDTC) as a single-source precursor. The crystallization, morphology and composition of the as-synthesized β-In2S3 were characterized by XRD, SEM, TEM, EDS and XPS, respectively. The β-In2S3 possessed high specific surface area of 134.1 m2 g-1, adsorption capacity of 195.5 mg g-1 for methylene blue, and extreme photodecolorization speed under visible light irradiation for the complete removal of methyl orange (MO) dye within 15 min and tetracycline within 60 min. Although methyl orange concentration decreased quickly, the total organic carbon (TOC) decreased slowly. UV-vis and mass spectrometry (MS) were applied to analyze the intermediates coming from the photodecolorization of MO. In order to estimate the roles of active species during the decolorization of MO, trapping experiments were conducted to determine the main active species during the decolorization process. The results indicated that .O2− radicals and e-1 were the key intermediates. This enhanced activity was attributed to its unique structures assembled from 2D nanosheets with thickness of ca. 5-7 nm, leading to high specific surface area, wide range of pore size distribution and great efficiency in absorbing light and electron/hole separation. The hierarchical flower-like β-In2S3 demonstrated great advantages in the treatment of various wastewater pollutants including textile dyes and antibiotics.

Nanoelectrical investigation and electrochemical performance of nickel-oxide/carbon sphere hybrids through interface manipulation.

Advanced hetero-nanostructured materials for electrochemical devices, such as Li-ion batteries (LiBs), dramatically depend on each functional component and their interfaces to transport and storage charges, where the bottleneck is the sluggish one in series. In this work, we prepare Ni(OH)2@C hybrids through a continuous feeding in reflux and followed by a hydrothermal treatment. The as-prepared Ni(OH)2@C can be further converted into NiO@C hybrids after thermal annealing. As a control, Ni(OH)2&C and NiO&C nanocomposites have also been prepared. Peakforce Tuna measurement shows the conductivity of the NiO@C hybrids is higher than that of NiO&C composites in nanoscale. To further investigate the quality of the interface, 100 charge/discharge cycles of the hybrids are performed in LiBs. The capacity retention of hybrid materials has significantly improved than the simple carbon composites. The enhancement of the electrochemical performance is attributed to the better electric conductivity and smaller charge transfer impedance and strong covalent interface between nickel species and carbon spheres obtained through the controlled seeded deposition.

Doping Zn2+ in CuS Nanoflowers into Chemically Homogeneous Zn0.49Cu0.50S1.01 Superlattice Crystal Structure as High-Efficiency n-Type Photoelectric Semiconductors

Doping Zn(2+) in CuS nanoflower into chemically homogeneous superlattice crystal structure is proposed to convert p-type CuS semiconductor to an n-type CuS semiconductor for significantly enhanced photoelectric response performance. In this study, the chemically homogeneous Zn-doped CuS nanoflowers (Zn0.06Cu0.94S, Zn0.26Cu0.73S1.01, Zn0.36Cu0.62S1.02, Zn0.49Cu0.50S1.01, Zn0.58Cu0.40S1.02) are synthesized by reacting appropriate amounts of CuCl and Zn(Ac)2·2H2O with sulfur powders in ethanol solvothermal process. By tuning the Zn/Cu atomic ratios to ∼1:1, the chemically homogeneous Zn-doped CuS nanoflowers could be converted to the perfect Zn0.49Cu0.50S1.01 superlattice structure, corresponding to the periodic Cu-S-Zn atom arrangements in the entire crystal lattice, which can induce an effective built-in electric field with n-type semiconductor characteristics to significantly improve the photoelectric response performance, such as the lifetime of photogenerated charge carriers up to 6 × 10(-8)-6 × 10(-4) s with the transient photovoltage (TPV) response intensity to ∼44 mV. This study reveals that the Zn(2+) doping in CuS nanoflowers is a key factor in determining the superlattice structure, semiconductor type, and the dynamic behaviors of charge carriers.

Tunable Morphology and Ethanol-Sensing Performance by Sintering Temperature of WO3-Based Ceramics

In this article, the authors describe how WO3 nanoparticles have been synthesized by sol-gel treatment from the precursor of W powder and H2O2 at room temperature, followed by sintering at 400°C, 600°C, 800°C, and 1000°C for 1 h, respectively. The samples were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Obtained results indicated that the gas-sensing properties to ethanol were decreased with the increasing sintering temperature from 400°C to 1000°C. The effects of sintering temperature on the gas-sensing characteristics of the WO3 ceramics were also investigated. The sensor that sintered at 400°C exhibited the maximum sensitivity to ethanol vapor at the operating temperature of 300°C. A possible mechanism for the influence of sintering temperature on the ethanol-sensing properties of WO3 sensors was proposed.