Yuezhong Di

Surface area control of nanocomposites Mg(OH) 2 /graphene using a cathodic electrodeposition process: high adsorption capability of methyl orange

The nanocomposites Mg(OH)2/graphene (nano-MG) were controllably prepared by a facile cathodic electrodeposition. The samples were characterized by field emission scanning electron microscopy with energy dispersive spectroscopy (FSEM-EDS), X-ray diffraction (XRD), Raman spectroscopy, thermogravimetric analysis (TGA), N2 adsorption–desorption analysis and UV-vis spectrophotometry. Characterization results suggested that Mg(OH)2 and graphene were combined successfully. Furthermore, the effects of the current density on the specific surface area of nano-MG have been investigated systematically. The specific surface area of nano-MG varied from 110 m2 g−1 to 525 m2 g−1, indicating that a suitable current density (0.07 A cm−2) is favorable for the uniform growth of Mg(OH)2 on the surface of graphene. In addition, the nano-MG (0.425 wt% graphene) with a specific surface area of 525 m2 g−1 was used as an adsorbent to remove Methyl Orange (MO) from water. The results showed that the adsorption of MO onto nano-MG exhibited a maximum adsorption capacity of 1.074 g g−1. Desorption experiments were carried out to explore the feasibility of adsorbent regeneration. And the possible mechanism responsible for electrodeposition and adsorption of MO on nano-MG were also elucidated.

Formation of Ti or TiC nanopowder from TiO2 and carbon powders by electrolysis in molten NaCl–KCl

A new route to produce pure Ti powder or TiC nanopowder with diameters of ∼50 nm by electrolysis in molten KCl–NaCl using TiO2 and carbon powder was reported in this paper. This electrochemical experiment was carried out with an innovative equipment unitizing the chlorination and electrolyzation. A fine titanium powder was obtained after electrolysis at 4.0 V for 5 h at 850 °C. TiC nanopowder could be prepared in the anode chamber with the cell voltage up to 4.5 V. Furthermore, the product was analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that pure Ti or TiC nanopowder can be prepared after electrolysis. The TiC nanopowder exhibited a polymorphic structure, and it had good thermal stability and oxidation resistance below 345 °C in air investigated by TGA and DSC. Cyclic voltammograms were carried out and the electrode reaction mechanisms during the electrolysis process were discussed in the paper.

Mg(OH)2/Graphene Nanocomposites Prepared by Cathodic Electrodeposition for the Adsorption of Congo Red

A facile cathodic electrodeposition process was developed to prepare Mg(OH)2/Graphene nanocomposites (MGN), which was used to remove Congo Red (CR), an anionic dye from aqueous solution. The morphology and phase structure were analyzed by transmission electron microscopy (TEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), Raman and X-ray photoelectron spectroscopy (XPS). The effects of experimental parameters, such as graphene content, adsorption time, initial concentrations of CR and pH values, on the adsorption capacity of CR were studied. The obtained MGN shows the good performance in CR, with an adsorption capacity of 1986.43mgg−1. The equilibrium adsorption and kinetics data fit with Langmuir isotherm and the pseudo-second-order model, respectively. Thermodynamic data suggest that CR adsorption onto MGN is spontaneous (ΔG0: –9.62kJmol−1 at 313K, endothermic (ΔH0: 36.261kJmol−1) and the degree of disorder increased (ΔS0: 146.848JmoL−1K−1) at the solid-solution interface. Moreover, the adsorption activation energy (Ea: 38.929kJmol−1) of CR evaluated from the Arrhenius equation illustrates that it is a physical process. This adsorbent exhibits efficient adsorption properties and high recycling efficiency, making it a promising adsorbent for removing anionic dyes.

Preparation of Low-Carbon Ti2O3 by Carbonthermal Reduction of the Mixture of Titanium Dioxide and Activated Carbon Under Vacuum Condition

Low-carbon Ti2O3 was prepared by carbonthermal reduction of the mixture of titanium dioxide and activated carbon at vacuum condition. The kinetics and phase evolution of Ti2O3 formation process were investigated through X-ray diffraction and gravimetric analysis. The only intermediate phase detected is Ti3O5. The reduction time was reduced sharply to 4 h when temperature was raised to 1300 °C. The best molar ratio of activated carbon and TiO2 is 0.6–1. At this condition, the content of Ti2O3 in slag is up to 95.63% and the content of the carbon element is below 0.004%, which meets the requirements for the further preparation of metal Ti by FFC Cambridge process. At the same time, the microstructure of Ti2O3 generated presented porosity, which would promote the electro-deoxidation process extremely.

Metal flow performance in aluminium electrolytic cells with different side-wall types

ABSTRACT Three-dimensional aluminium electrolytic cells with inclined surface cathodes were simulated in ANSYS and CFX to predict the influence of different side-wall types on the horizontal current and metal flow. The simulated results showed that the ledge thickness decreased with the thermal conductivity of the side wall. The graphitised side wall with the highest thermal conductivity displayed the largest ledge toe extensions of 24.6 cm at the centre of the long side and 28.0 cm at its corner. The long ledge toe extension introduced large inverted horizontal current and increased the maximum metal velocity. Above the largest ledge toe extension, the metal deviation from the equilibrium was 1.6 cm at one quarter of the cell length and 1.8 cm at the cell corner, equal to the metal wave crest in the cell (1.8 cm). With decreasing ledge toe extension, the maximum metal velocity and metal deviation above the ledge toe extension from equilibrium decreased accordingly.

Kinetics and mechanism of vacuum isothermal reduction of magnesia by aluminium

The kinetics and mechanism of vacuum isothermal reduction of calcined magnesite by Al were studied in the present paper. The results showed that the aluminothermic reduction process was divided into two stages. The apparent activation energy values of the two stages were determined to be 144.4 and 235.3 kJ mol−1, respectively. The phase MgAl2O4 was formed in the first stage. In the second stage, the intermediate phase Mg0.4Al2.4O4 was formed and the phase Al2O3 was obtained from the further reduction of Mg0.4Al2.4O4. The diffusion of molten aluminium is the rate-determining step of the reduction process. The out diffusion of magnesium vapour has some effect on the reduction ratio at the briquetting pressure between 60 and 120 MPa, but it is not the major rate-limiting step. Dans cet article, on a étudié la cinétique et le mécanisme de réduction isotherme sous vacuum de la magnésite calcinée par l’Al. Les résultats ont montré que le procédé de réduction aluminothermique était divisé en deux étapes. On a déterminé les valeurs d’énergie d’activation apparente des deux étapes à 144.4 et 235.3 kJ/mol, respectivement. La phase de MgAl2O4 était formée dans la première étape. La phase intermédiaire de Mg0.4Al2.4O4 était formée dans la seconde étape et l’on a ensuite obtenu la phase d’Al2O3 par réduction additionnelle du Mg0.4Al2.4O4. La diffusion de l’aluminium fondu est l’étape cinétiquement déterminante du procédé de réduction. La diffusion vers l’extérieur de la vapeur de magnésium a un certain effet sur le taux de réduction à la pression de briquetage entre 60 et 120 MPa, mais il ne s’agit pas de l’étape majeure cinétiquement limitante.

The influence of various LiF concentrations on the cathodic electrochemical behavior at the tungsten electrode in Na3AlF6–Al2O3 molten salt

The electrochemical deposition process of Al metal at the tungsten electrode in the melts of Na3AlF6–Al2O3 with various LiF concentrations was investigated at 1253 K by various electrochemical techniques. With the analysis of the potentiodynamic cathodic polarization curves, it can be demonstrated that LiF has an effect of increasing the conductivity of the molten salt. From the analysis of the potentiostatic electrolysis and chronopotentiometry curves, it can be deduced that the deposition potential of Na metal is more positive with the increase of LiF concentration. Spontaneous dissolution of the cathodic products occurs for the polarized electrode which is shown by the measurements of open-circuit chronopotentiometry. These show that the scanning time taken for the potential to reach zero is prolonged and the thickness of the reduced species to be dissolved increases with the increase of LiF concentration. Furthermore, it can be deduced that the Al activity also increases with the increase of LiF concentration. On the other hand, the deposited Al is more easily dissolved into the electrolyte and the physical dissolution is more intense with the increase of LiF concentration.

Electrochemical Study of Potassium Fluoride in a Cryolite-Aluminum Oxide Molten Salt

Selective and efficient electrochemical methods to characterize aluminum are necessary. Current methods are based on potentiodynamic polarization, recurrent potential double pulses, chronopotentiometry, open-circuit chronopotentiometry, and potentiostatic electrolysis, but have not been used to characterize the deposition of aluminum in Na3AlF6-Al2O3-KF molten salts. The control processes of the formation of aluminum-tungsten intermetallic compounds, and the deposition of aluminum have been investigated by using steady-state potentiodynamic cathodic polarization curves. The dissolution loss rate of aluminum was determined with an increase in KF concentration by the analysis of recurrent potential double pulses. Using chronopotentiometry, it was confirmed that the deposition potential of aluminum shifted more negative as the KF concentration increased, and a higher KF concentrations induced a higher cathodic overpotential. From open-circuit potential measurements and scanning electron micrographs, it was concluded that aluminum(III) ions react with tungsten substrates to form an aluminum-tungsten compound, and the reaction mechanism of aluminum was determined. These electrochemical methods applied with aluminum electrolysis were accurate, efficient, and reliable.