Yanzhuo Lv

Synthesis of magnetic ZnO/ZnFe2O4 by a microwave combustion method, and its high rate of adsorption of methylene blue.

The magnetic ZnO/ZnFe2O4 particles have been synthesized by a microwave combustion method using NaAc as fuel. The as-obtained ZnO/ZnFe2O4 was characterized and applied for the removal of methylene blue (MB) from aqueous solution in the batch system. The ZnO/ZnFe2O4 particles display larger S(BET) and smaller size with increase of NaAc dosage. Because a certain amount of gas is generated during NaAc decomposing and the gas prevent the particles from growing larger. More interestingly, even at neutral pH value, the ZnO/ZnFe2O4 obtained with 24 mL NaAc shows high-rate adsorption properties with the MB removal efficiency up to 90% in 0.5 min and a maximum adsorption capacity of 37.27 mg/g.

Synthesis of high surface area, mesoporous MgO nanosheets with excellent adsorption capability for Ni(II) via a distillation treating.

Hexagonal mesoporous MgO nanosheets with a side length of 250 nm and specific surface area of 181.692 m(2)/g were fabricated by a three-step process. Firstly, MgO powders were obtained by sintered Mg5(OH)2(CO3)4⋅4H2O, which was synthesized by a wet precipitation process using ammonium hydrogen carbonate as precipitants. Secondly, the above-MgO were distilled 2 h in a three-necked bottle with condenser device. Lastly, we annealed the distilled-MgO at 500-800 °C to form mesoporous MgO nanosheets. We found the pore size distribution and the thicknesses of nanosheets were determined by the distillation process in step 2 and annealed temperature in step 3. By optimizing the experimental parameters, the mesoporous dis-MgO annealed at 600 °C displayed uniform hexagonal structure with the largest pore volume (0.875 cm(3)/g) and highest BET surface area (181.692 m(2)/g), as well as the maximum adsorption capability of 1684.25 mg/g for Ni(II).

Electrochemical properties of high-voltage LiNi0.5Mn1.5O4 synthesized by a solid-state method

LiNi0.5Mn1.5O4 cathode material has been synthesized by a solid-state reaction designedly using industrial raw materials (Li2CO3, NiO and electrolytic MnO2) in bulk scale, which are all used without further purification. The aim is to find the optimal preparation process of LiNi0.5Mn1.5O4 material for commercial application. The synthesis temperatures are adjusted to form a disordered Fdm structure at 800–950 °C for 12 h and then at 600 °C for 6 h. Meanwhile, some powders have also been calcined at 850 °C for 8–14 h and next annealed at 600 °C for 6 h. XRD patterns, SEM micrographs and distribution curves of particle size shows that the LiNi0.5Mn1.5O4 cathode material calcined at 850 °C for 12 h and then annealed at 600 °C for 6 h exhibits the best crystallinity, crystal shape as well as the best normal distribution. Electrochemical tests show that the LiNi0.5Mn1.5O4 material synthesized at 850 °C for 12 h and then annealed at 600 °C for 6 h has the highest capacity and excellent rate capability. After 200 cycles, the capacity retentions of the sample at 1, 2 and 5 C are as high as 97.8%, 98.5% and 98.0% of its initial capacities (120.8, 118.1 and 111.2 mA h g−1), respectively. The fundamental findings in this work can be applied to guide the synthesis of spinel LiNi0.5Mn1.5O4 as high performance electrode materials for lithium ion batteries, especially for industry.

Improvement of g-C3N4 photocatalytic properties using the Hummers method

In this study, graphitic C3N4 (g-C3N4) with high photocatalytic properties to methylene blue (MB) was synthesized by treating the bulk g-C3N4 using the Hummers method. The bulk g-C3N4 was obtained by calcining dicyandiamide. The g-C3N4 treated by the Hummers method (E-g-C3N4) was characterized and utilized for the photocatalytic removal of MB. The results showed that the Hummers treatment exfoliated the nanosheets bulk g-C3N4 into nanorods and improved the dispersion of E-g-C3N4 in an aqueous solution. It also distinctly enhanced the photocatalytic activity of g-C3N4 to MB, i.e., the removal efficiency increased from 38.45% for the bulk g-C3N4 to 96.61% for the E-g-C3N4.

Improved electrochemical performance of LiNi0.4Ti0.1Mn1.5O4 as cathode of lithium ion battery by carbon-coating

The effects of Ti substitution for Ni, carbon coating on the structure and electrochemical properties of LiMn1.5Ni0.5O4 are studied. LiMn1.5Ni0.5O4, LiNi0.4Ti0.1Mn1.5O4 and carbon-coated LiNi0.4Ti0.1Mn1.5O4 cathode materials have been synthesized by a solid-state reaction using industrial raw materials in bulk scale. X-ray diffraction clearly shows that LiMn1.5Ni0.5O4 has higher crystallinity after Ti doping. Scanning electron microscopy clearly exhibits that Ti doping does not change the basic spinel structure, as well as coated carbon layer covers the surfaces of the LiNi0.4Ti0.1Mn1.5O4 particles. In addition, charge–discharge tests indicate that LiNi0.4Ti0.1Mn1.5O4 sample has higher discharge capacities at the rates of 0.5, 1 and 3 C at 25 °C. It should be noted that carbon-coated LiNi0.4Ti0.1Mn1.5O4 shows higher discharge capacities at the rates of 5, 7 and 10 C at 25 °C as well as various rates for 55 °C. Cyclic performances developed at 25 and 55 °C demonstrate that the capacity retention is remarkably improved compared to the two uncoated samples. The influence of the Ti-doping and carbon-coating on the coulombic efficiency at high temperature (55 °C) has also been investigated. Among the various samples investigated, surface modification with carbon gives an improved coulombic efficiency. The remarkably enhanced electrochemical properties of the carbon-coated sample may be because of the suppression of the solid electrolyte interfacial (SEI) layer development and faster kinetics of both the Li+ diffusion, as well as the charge transfer reaction.

Fabrication of mesoporous magnesium oxide nanosheets using magnesium powder and their excellent adsorption of Ni (II)

Mesoporous MgO nanosheets with a high adsorption rate and excellent adsorption capacity for removing Ni (II) were successfully synthesized by a hydrothermal and annealing method. The Mg(OH)2 was first synthesized by a hydrothermal process using magnesium powder as the starting material. MgO was then obtained by annealing the as-prepared Mg(OH)2 at 450°C. The advantage of the magnesium powder as the starting material is it slowly generated Mg2+. Thus, the low centration of Mg2+ guaranteed a slow rate of forming Mg(OH)2, which benefited with a mesoporous structure. The effect of the hydrothermal time on the structure and adsorption performance was studied. The results showed that the MgO synthesized for 4h had the highest adsorption performance of 2217mg/g and the highest adsorption rate, which resulted in an efficient adsorption of 96% in 5min for Ni (II) with the concentration of 500mg/L.

The effects of sodium fluoride as the electrolyte additive on the electrochemical performances of magnesium–8lithium–0.5zinc electrode in sodium chloride solution

The electrochemical performance of Mg–8Li–0.5Zn electrode in 0.7 mol L−1 NaCl solution with different concentrations of NaF (0.0, 0.2, 0.5, 0.8, 1.0, 1.2 and 1.5 mmol L−1) was investigated by means of potentiodynamic polarization, potentiostatic current–time curves, electrochemical impedance spectroscopy, scanning electron microscopy and utilization efficiencies. The findings indicate that Mg–8Li–0.5Zn electrode in 0.7 mol L−1 NaCl solution with 1.0 mmol L−1 NaF has a higher discharge current density than that in 0.7 mol L−1 NaCl solution with the other concentrations of NaF that were investigated. The addition of 1.0 mmol L−1 NaF to the NaCl electrolyte solution loosens the product film and the oxidation products on the alloy surfaces of the electrode, which produces deeper and larger channels, as observed by the SEM investigation, compared with those in 0.7 mol L−1 NaCl solution without any NaF. The addition of 1.0 mmol L−1 NaF in 0.7 mol L−1 NaCl solution improves the continuous discharging utilization efficiency of Mg–8Li–0.5Zn electrode by more than 18.80%, and enhances the interval discharge utilization efficiency of Mg–8Li–0.5Zn electrode by more than 27.90%.

Effect of an electrolyte additive hexamethylenetetramine on electrochemical behaviors of the Mg–11Li–3.5Al–2Zn–1.5Re–0.5Zr electrode

The electrochemical performance of the Mg–11Li–3.5Al–2Zn–1.5Re–0.5Zr electrode in a 0.7 mol L−1 NaCl solution, containing different concentrations of hexamethylenetetramine (C6H12N4) as an electrolyte additive was investigated by potentiodynamic polarization, potentiostatic current–time, electrochemical impedance spectra measurements and scanning electron microscopy (SEM). The potentiodynamic polarization curves show that the corrosion potential of the electrode increases with the concentration of C6H12N4 in the following order: 0.10 mmol L−1 < 0.05 mmol L−1 < 2.00 mmol L−1 < 0.50 mmol L−1 < 0.80 mmol L−1 < 1.00 mmol L−1 < 0.00 mmol L−1. The potentiostatic current–time curves indicate that the oxidation current density of the electrode in a 0.7 mol L−1 NaCl solution containing 0.10 mmol L−1 of C6H12N4 is the largest among the studied electrolyte solutions, and the polarization resistance of the Mg–11Li–3.5Al–2Zn–1.5Re–0.5Zr electrode in a 0.7 mol L−1 NaCl solution containing 0.10 mmol L−1 of C6H12N4 is smaller than that in a 0.7 mol L−1 NaCl solution. The scanning electron microscopy studies suggest that the presence of C6H12N4 in a 0.7 mol L−1 NaCl solution can loosen oxidation products and promote its coming off, consequently enhancing the discharging performance of the Mg–11Li–3.5Al–2Zn–1.5Re–0.5Zr electrode.

The effect of sodium stannate as the electrolyte additive on the electrochemical performance of the Mg–8Li–1Y electrode in NaCl solution

The effect of different concentrations of sodium stannate (Na2SnO3) as the electrolyte additive in 0.7 mol L−1 NaCl electrolyte solution on the electrochemical performance of the Mg–8Li–1Y alloy electrode prepared by the vacuum induction melting method have been investigated by means of potentiostatic current–time, potentiodynamic polarization, and electrochemical impedance spectroscopy measurements as well as scanning electron microscopy. The performances of the magnesium–hydrogen peroxide (Mg–H2O2) semi-fuel cells with the Mg–8Li–1Y alloy as the anode were also determined. From the study, it has been found that the corrosion potential of the Mg–8Li–1Y electrode is slightly shifted to the negative direction and the corrosion current density is markedly decreased when different concentrations of Na2SnO3 are added to a 0.7 mol L−1 NaCl electrolyte solution. The electrochemical impedance spectroscopy measurements show that the polarization resistance of the Mg–8Li–1Y electrode reduces in the following order with different concentrations of Na2SnO3: 0.20 mmol L−1 > 0.00 mmol L−1 > 0.05 mmol L−1 > 0.10 mmol L−1 > 0.30 mmol L−1. The electrochemical performance, illustrated by potentiostatic current–time curves, of Mg–8Li–1Y electrode in 0.7 mol L−1 NaCl electrolyte solution containing 0.30 mmol L−1 Na2SnO3 is better than that in 0.7 mol L−1 NaCl electrolyte solution containing Na2SnO3 in other concentrations. The addition of Na2SnO3 to the NaCl electrolyte solution loosens the product film and changes the size and thickness of the micro-clumps of the oxidation products. The Mg–H2O2 semi-fuel cell with the Mg–8Li–1Y anode in 0.7 mol L−1 NaCl solution containing 0.30 mmol L−1 Na2SnO3 presents a maximum power density of 112 mW cm−2 at room temperature.

The effect of NaF on the electrochemical behavior of the Mg–11Li–3.5Al–1Zn–1Sn–1Ce–0.1Mn electrode in NaCl solution

In order to improve the electrochemical behavior of the Mg–11Li–3.5Al–1Zn–1Sn–1Ce–0.1Mn electrode in a 0.7 mol L−1 NaCl solution, different concentrations of sodium fluoride (NaF) as the electrolyte additive are added into the electrolyte solution and their effects on the electrochemical performances of the electrode are investigated by the methods of potentiodynamic polarization, potentiostatic oxidation, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) with EDS analysis. It is found that the corrosion current density of the electrode decreases with the concentration of NaF in the following order: 0.5 mmol L−1 > 0.1 mmol L−1 > 1.0 mmol L−1 > 2.0 mmol L−1 > 0.8 mmol L−1 > 0 mmol L−1. The discharge current density of the electrode in the electrolyte solution containing 0.8 mmol L−1 NaF is higher than that in the other concentrations at the discharging potentials of −0.8 V, −1.0 V and −1.2 V. The electrode in the electrolyte solution containing 0.8 mmol L−1 NaF retains a larger reaction surface area during discharge, which leads to the highest discharge activity. The different concentrations of NaF in the 0.7 mol L−1 NaCl electrolyte solution can change the electrochemical behavior of the Mg–11Li–3.5Al–1Zn–1Sn–1Ce–0.1Mn electrode, and the optimum concentration of the electrolyte additive NaF is 0.8 mmol L−1. The Mg–H2O2 semi-fuel cell with the Mg–11Li–3.5Al–1Zn–1Sn–1Ce–0.1Mn anode presents a maximum peak power density of 77 mW cm−2 when it is measured in a 0.7 mol L−1 NaCl solution containing 0.8 mmol L−1 NaF as the anolyte at room temperature, which is higher than that measured in a 0.7 mol L−1 NaCl solution as the anolyte (62 mW cm−2). NaF is an effective anolyte additive for the Mg–11Li–3.5Al–1Zn–1Sn–1Ce–0.1Mn alloy electrode in Mg–H2O2 semi-fuel cells.