Yongming Sui

Synthesis of Cu2O nanoframes and nanocages by selective oxidative etching at room temperature.

In recent years, hollow-structure particles (HSPs) have been widely studied due to their unique structures and potential applications. One successful synthetic strategy involves direct construction of HSPs from functional building blocks by processes such as the Kirkendall effect, acid etching, coordination-polymer self-template-directed growth, and solid-state thermal decomposition process for the preparation of Cu7S4, [2] Fe2O3, [3] ZnO, and MnO2 [5] HSPs. However, all of the reported HSPs require further heator acid-treatment processes, which have disadvantages such as increased costs and environmental pollution. Therefore, it remains a great challenge to develop a simple, mild (at room temperature), and environmentally friendly method for the one-pot synthesis of HSPs with well-defined shape. Cu2O is a typical p-type direct band gap semiconductor with a band gap of 2.17 eV and has potential applications in solar-energy conversion, electrode materials, sensors, and catalysts. Considerable effort has been devoted to obtaining hollow Cu2O structure by employing techniques such as hydrothermal synthesis, microemulsions, template synthesis, and acid etching. Qi and co-workers prepared octahedral Cu2O nanocages by Pd-catalytic reduction of an alkaline copper tartrate complex with glucose followed by a catalytic oxidation process. More recently, truncated rhombic dodecahedral Cu2O nanoframes and nanocages were synthesized by particle aggregation and acid etching. In both synthetic processes, expensive and acidic or toxic solvents were used. Here we report a cheap and green synthetic route for Cu2O nanoframes and nanocages with single-crystal walls. In our synthetic strategy, polyhedral Cu2O particles were first prepared by adding a weak reducing agent (glucose) to a solution of copper citrate complex with polyvinylpyrrolidone (PVP) as capping agent, and then Cu2O nanoframes and nanocages were obtained in situ by oxidative etching at room temperature. Perfect Cu2O nanoframes were taken from the reaction mixture after the solution was exposed to air for 16 days at room temperature. Field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM) images provided insight into the nanostructure and morphology of the Cu2O nanoframes. As shown in Figure 1A, the Cu2O nanoframes are

Facile fabrication of faceted copper nanocrystals with high catalytic activity for p-nitrophenol reduction

This article reports a reproducible and facile approach to synthesize faceted copper nanocrystals (Cu NCs) using an inexpensive copper oxide as a precursor. By simply prolonging the reaction time, Cu cubes and polyhedrons were successfully produced, and the mean size could be effectively controlled in the range of 9 to 21 nm. The catalytic activities of the Cu cubes and polyhedrons were investigated by photometrically monitoring the reduction of p-nitrophenol by an excess of NaBH4. The kinetics of the reduction reaction at different temperatures were investigated to determine the activation parameters. Our investigations indicate that Cu nanocubes exhibit higher catalytic activity than Cu polyhedrons, which can be ascribed to three features: the higher surface-to-volume ratio, the higher surface energy of the {100} facet, and the lower redox potential. In addition, these catalysts can be easily recycled with a slight decrease of the catalytic activities, and are stable in the air. Therefore, this facile route provides a useful platform for the fabrication of Cu catalysts which have the potential to replace noble metals for certain catalytic applications.

Electrodeposition of Cu2O films and their photoelectrochemical properties

Well-defined cuprous oxide (Cu2O) thin film electrodes were electrodeposited on indium-doped tin oxide (ITO) substrates from a slightly acidic Cu(II) acetate solution. The morphologies of Cu2O film were tunable by altering the deposition potential, reaction time, solution temperature and the NaCl concentration. In particular, the Cu2O morphologies evolved from dendritic branching to cube-like with the increasing of the NaCl concentration. A growth mechanism was proposed according to the experimental results. In addition, a photocurrent of 0.06 mA cm−2, an open-circuit photovoltage (Voc) of 0.38 V, and a significant energy conversation efficiency of 0.01% were obtained under 100 mW cm−2 UV-visible illumination of the dendritic Cu2O thin film.

Structural, electrical and optical properties of yttrium-doped ZnO thin films prepared by sol–gel method

Yttrium-doped ZnO thin films were deposited on silica glass substrates by the sol–gel method. The structural, electrical and optical properties of yttrium-doped ZnO thin films were investigated systematically and in detail. All the thin films have a preferred (0 0 2) orientation. When compared with the electrical resistivity values of films without annealing treatment, the values of films annealed in the reducing atmosphere were decreased by about three orders of magnitude. The lowest electrical resistivity value was 6.75 × 10−3 Ω cm, which was obtained in the 0.5 at% yttrium-doped ZnO thin film annealed in nitrogen with 5% hydrogen at 500 °C. In room-temperature photoluminescence (PL) spectra, two PL emission peaks are found in the pure ZnO thin film; one is the near-band-edge (NBE) emission at 3.22 eV and the other is a green emission at about 2.38 eV. Nevertheless, the green emission is not found in the PL of the yttrium-doped ZnO thin films. The low-temperature PL spectrum of the undoped ZnO thin film at 83 K is split into well-resolved free and bound excition emission peaks in the ultraviolet region, but the NBE emission of the 5 at% yttrium-doped ZnO thin film at 83 K has only one broad emission peak.

A one-step green route to synthesize copper nanocrystals and their applications in catalysis and surface enhanced Raman scattering

A nontoxic, simple, inexpensive, and reproducible strategy, which meets the standard of green chemistry, is introduced for the synthesis of copper nanocrystals (Cu NCs) with olive oil as both reducing agent and capping agent. By changing the reaction parameters, the shape, size and surface structure of the Cu NCs can be well controlled. The obtained Cu nanocubes show excellent catalytic properties for the catalytic reduction of dyes and CO oxidation. Moreover, the prepared Cu nanocubes as substrates exhibit surface enhanced Raman scattering (SERS) activity for 4-mercaptopyridine (4-Mpy). Therefore, this facile route provides a useful platform for the fabrication of Cu NCs which have the potential to replace noble metals for certain applications.

One-step solution synthesis of bismuth sulfide (Bi2S3) with various hierarchical architectures and their photoresponse properties

In this paper, we introduce a facile and phosphine-free one-step solution method to synthesize size- and shape-controlled bismuth sulfide (Bi2S3) with hierarchical architectures. Changing variables, such as the reaction temperature, the ratio of precursors, and the concentration of oleic acid were observed to influence the resultant shape of Bi2S3 microstructures. For the formation of Bi2S3 hierarchical architectures, the crystal splitting growth mechanism played the dominant role. The absorption spectra were recorded at room temperature, which revealed that the obtained Bi2S3 product was a direct band gap semiconductor and the band gap Eg was estimated to be about 1.9 eV. Furthermore, the I–V characteristics of the Bi2S3-based device show a significant increase by ca. 1 order of magnitude compared with the dark state, indicating an enhanced conductivity and high sensitivity. The response and decay times are estimated to be about 0.5 and 0.8 s, respectively, which are short enough for it to be an excellent candidate for high-speed and high-sensitivity photodetectors or optical switches. Thus the Bi2S3 hierarchies as building blocks may offer the potential for monolithic, low-cost and large-scale integration with CMOS electronics.

Low-temperature synthesis of porous hollow structured Cu2O for photocatalytic activity and gas sensor application

In this contribution, a facile and low-temperature solution route has been developed to large-scale synthesis of Cu2O with polyhedral, porous and hollow structures by the assistance of surfactant CTAB. The morphologies (six symmetric branches, porous branches and porous-shell hollow spheres) of the Cu2O particles, which can be controlled by changing the amount of CTAB and a possible formation mechanism, is also proposed. Our results found that CTAB not only serves as a soft template to synthesize hollow and porous Cu2O structures, but also acts as a capping agent to adsorb on the {111} plane to obtain six symmetric branches of Cu2O. Moreover, the photocatalytic and gas-sensing properties of the hollow and porous structure Cu2O samples were studied in detail. Due to the special structure character, the Cu2O porous-shell hollow spheres exhibited both strong adsorption abilities and high degradation activities for methyl orange (MO) under visible light irradiation. A gas sensor was also fabricated which showed high sensitivity for ethanol.

Solution synthesis of copper selenide nanocrystals and their electrical transport properties

In this paper, we developed a one-pot solution strategy to synthesize copper selenide NCs with controllable shape and structure. By changing the precursors in the reaction, copper selenide NCs (Cu2−xSe nanoparticles, nanorods and CuSe nanoplates) with various morphologies could be achieved. We proposed a possible mechanism to explain the influence of precursors on the shape of copper selenide NCs and we found that the chemical activities of precursors played key roles in the morphologies and crystal structures of the final products. Moreover, the electrical transport properties of as-prepared products were investigated. The morphologies of copper selenide NCs have a great influence on the electrical transport properties. The copper selenide NCs with nanorods display the best electrochemical performance compared with the other two types. We believe that copper selenide NCs would be promising candidates for electrical transport materials.

Synthesis of Cu–Ir nanocages with enhanced electrocatalytic activity for the oxygen evolution reaction

Iridium (Ir) is widely used as a catalyst in polymer electrolyte membrane water electrolyzers (PEMWEs). However, high cost and limited catalytic performance of Ir hamper its large-scale industrial application. Here, based on a modified galvanic replacement, we introduce Cu nanoparticles as a template to prepare single-crystalline Cu–Ir polyhedral nanocages (NCs). Alloying Ir with 3d transition metal Cu not only significantly reduces the loading of Ir but also remarkably enhances its catalytic activity by forming a unique NC structure and tuning the d-band structure of Ir. The as-prepared single-crystalline Cu1.11Ir NCs exhibit enhanced catalytic activity toward the oxygen evolution reaction (OER) in 0.05 M H2SO4, with a smaller overpotential (286 mV) required for a current density of 10 mA cm−2 and a Tafel slope of 43.8 mV per decade. The mass activity can reach 73 mA mgIr−1 at an overpotential of 0.28 V for Cu1.11Ir NCs. Hence, the obtained Cu1.11Ir NCs would be a promising electrocatalyst for practical electrocatalytic water splitting systems.

Mechanism of p-type conductivity for phosphorus-doped ZnO thin film

A p-type phosphorus-doped ZnO film (ZnO : P) was grown on a quartz substrate by sputtering a ZnO target mixed with 2 wt% P2O5 using a mixture of Ar and O2 and then annealed rapidly at 750 °C for 5 min in air ambient. The lattice constant of the c-axis was 0.5176 nm, smaller than the value of 0.5211 nm of pure ZnO, implying substitutional P at a Zn antisite (PZn). The binding energy of P2p1/3 is 133.5 eV, which is different from that of the P–O bond in P2O5 and of the P–Zn bond in Zn3P2, but close to that of P–O–P and P–O–Zn bonds in zinc phosphate glass mainly composed of ZnO and P2O5. The 80 K photoluminescence spectrum shows neutral acceptor bound exciton emission at 3.34 eV. Based on the above experimental results, it is suggested that P substitutes for a Zn antisite in the ZnO : P and forms an acceptor complex with two Zn vacancies, and the acceptor complex is responsible for p-type conductivity of ZnO : P.