Liang Fang

High performance NiFe layered double hydroxide for methyl orange dye and Cr(VI) adsorption

The NiFe layered double hydroxides (LDHs) with different mole ratio of Ni/Fe (4:1, 3:1, 7:3 and 1:1) were prepared by a simple coprecipitation method. The adsorption performance were evaluated by the removal of methyl orange (MO) dye and hexavalent chromium(VI) heavy metal ion. It is found that Ni4Fe1-LDH can remove more than 92% of MO in 10 min at the 10 mg/L MO initial concentration, and 97% of Cr(VI) in 1 h at 4 mg/L Cr2O7(2-) initial concentration. The saturated adsorption capacity of Ni4Fe1-LDH is found to be as large as 205.76 mg/g for MO and 26.78 mg/g for Cr(VI). The adsorption behavior of this new adsorbent is fitted well with Langmuir isotherm and the pseudo-second-order kinetic model, indicative of a monolayer and chemical adsorption that synergistically originates from exchangeable anions mechanism and layer charge density. Due to the excellent removal capacity of MO and Cr(VI), the NiFe-LDHs could be a promising adsorbent for wastewater treatment.

Tunable zinc interstitial related defects in ZnMgO and ZnCdO films

We report tunable band gap of ZnO thin films grown on quartz substrates by radio frequency magnetron sputtering. The zinc interstitial (Zni) defects in ZnO films were investigated by X-ray diffraction, Raman scattering, Auger spectra, first-principle calculations, and Hall measurement. Undoped ZnO film exhibits an anomalous Raman mode at 275u2009cm−1. We first report that 275u2009cm−1 mode also can be observed in ZnO films alloyed with Mg and Cd, whose Raman intensities, interestingly, decrease and increase with increasing Mg and Cd alloying content, respectively. Combined with the previous investigations, it is deduced that 275u2009cm−1 mode is attributed to Zni related defects, which is demonstrated by our further experiment and theoretical calculation. Consequently, the concentration of Zni related defects in ZnO can be tuned by alloying Mg and Cd impurity, which gives rise to different conductivity in ZnO films. These investigations help to further understand the controversial origin of the additional Raman mode ...

Effect of Er doping on microstructure and optical properties of ZnO thin films prepared by sol–gel method

Er doped ZnO (EZO) thin films were successfully prepared by sol–gel spin coating method on quartz glass substrates. The effect of Er doping content on the microstructure and optical properties of EZO thin films were investigated. The X-ray diffraction and X-ray photoelectron spectroscopy results indicate that Er was successfully incorporated into the EZO thin films and substituted the Zn sites. The incorporation of Er could affect the band gap (Eg) and optical constants of ZnO thin films. The photoluminescence spectra show that the 1.54xa0μm emission, which originates from the transition of Er3+: 4I13/2xa0→xa04I15/2, was observed in EZO thin films. Furthermore, it is demonstrated that the formation of singly ionized oxygen vacancies (VO·) could be inhibited by the incorporation of Er dopant, which is supported by further defect formation energies calculations.

3-D conformal graphene for stretchable and bendable transparent conductive film

This paper demonstrates the preparation of conformal 3D graphene films on a flexible substrate by chemical vapor deposition (CVD). The 3D conformal graphene films exhibit a low sheet resistance of 195 Ω sq−1 (with a transmittance of 84.2%, at 550 nm) and a high transmittance of 96.9% at 550 nm (with a sheet resistance of 1140 Ω sq−1). CGrs show perfect reliability and stability under both stretching and bending conditions, with a super high tensile strain of up to 28% for monolayer graphene and 77.8% for few-layer graphene.

Metastable phase control of two-dimensional transition metal dichalcogenides on metal substrate

Phase control of two-dimensional (2D) transition metal dichalcogenides (TMDs) is important from both scientific and engineering aspects. However, up to now it remains a challenge to stabilize the metastable phase of TMDs under ambient conditions. Herein, via systematic first-principles calculations, we demonstrate that by the appropriate choice of metal substrate as a support for the transferred layer, the metastable phase of MoS2 can be effectively stabilized. By screening 15 widely used metal substrates, we found that Mo(001), W(001) and Hf(0001) surfaces not only stabilize the metastable 1T′ phase against the common 2H phase, but also prevent the structural transformation of 1T′ → 2H by increasing the transition barrier. Remarkably, we reveal the crucial role of charge transfer from the metal surface to Mo d-orbitals of MoS2 that influences the electron occupation of atomic orbitals associated with crystal splitting, which provides an excellent descriptor to determine the stability of the metastable phase. We also propose a novel field-effect transistor made from a single MoS2 layer with a semiconducting 2H phase region connected to two metallic 1T′ phase regions in contact with a metal electrode (Mo, W, Hf), which exhibits an ideal Schottky-barrier-free interface. These findings are generally applicable, offering an attractive and practical approach to engineer the phase transition of 2D TMDs and design novel nanodevices with multi-functionalities.

Numerical Simulation on Thermal-Electrical Characteristics and Electrode Patterns of GaN LEDs with Graphene/NiOx Hybrid Electrode*

The thermal-electrical characteristic of a GaN light-emitting diode (LED) with the hybrid transparent conductive layers (TCLs) of graphene (Gr) and NiOx is investigated by a finite element method. It is indicated that the LED with the compound TCL of 3-layer Gr and 1 nm NiOx has the best thermal-electrical performance from the view point of the maximum temperature and the current density deviation of multiple quantum wells, and the maximum temperature occurs near the n-electrode rather than p-electrode. Furthermore, to depress the current crowding on the LED, the electrode pattern parameters including p- and n-electrode length, p-electrode buried depth and the distance of n-electrode to active area are optimized. It is found that either increasing p- or n-electrode length and buried depth or decreasing the distance of n-electrode from the active area will decrease the temperature of the LED, while the increase of the n-electrode length has more prominent effect. Typically, when the n-electrode length increases to 0.8 times of the chip size, the temperature of the GaN LED with the 1 nm NiOx/3-layer-Gr hybrid TCLs could drop about 7 K and the current density uniformity could increase by 23.8%, compared to 0.4 times of the chip size. This new finding will be beneficial for improvement of the thermal-electrical performance of LEDs with various conductive TCLs such as NiOx/Gr or ITO/Gr as current spreading layers.

Fabrication, Characteristics and Application in Dye-Sensitized Solar Cell of Vertically Alligned ZnO Nanorod Arrays Guided with Polyethyleneimine via Hydrothermal Method

.A series of vertically aligned ZnO nanorod-array films are grown on fluorine-doped tin oxide (F: SnO2, FTO) coated glass substrates by the solution-based chemical process. The effect of polyethyleneimine (PEI) adding in seed and growth solution on the structure, morphology, UV-Vis absorption spectra and photovoltaic properties of ZnO nanorod array films, has been analyzed. The XRD and SEM results showed that the ZnO nanorod have the hexagonal wurtzite structure with the (002) direction normal to the substrate. It was observed that with the addition of PEI in growth solution, the ZnO nanorods become smaller in diameter and longer in length i.e. greatly enhance their surface area, leading to improve dye adsorption and photovoltaic performance of DSSCs. The efficiency of ZnO nanorod-based DSSC with PEI in growth solution was on average 1.18 % for film A4, which is 84 % higher than for ZnO nanorod-based DSSC without PEI in growth solution.