| Ionic liquid with energy saving, environment friendly, high solubility and selectivity characteristics played an important role in extracting and separating non-ferrous metals as a new type of green solvent.In this paper, deep eutectic based ionic liquids were synthesized with betaine hydrochloride and urea and its physical properties such as melting point, density, conductivity, viscosity were determined. The relationship among density and composition, electrical conductivity and temperature, conductivity and composition as well as the viscosity and temperature were determined. The result indicated that:the eutectic point was 27℃with the molar proportion of 85% urea, which was much lower than the pure urea(133℃) and betaine hydrochloride(227℃).The range of density was 1.273-1.521 g/cm3 when the mole percentage of urea ranged from 60% to 90% in the Urea/C5H12NO2Cl ionic liquid. Density and the mole fraction of urea relation can be expressed as:ρ=(153-93xUrea)/(81.71-26.17xUrea) whereρis the density of ionic liquid, x is mole fraction.The conductivity of Urea/C5H12NO2Cl deep eutectic based ionic liquids increased fast with the increasing of temperature when the composition was constant. The conductivity of Urea/C5H12NO2Cl deep eutectic based ionic liquids increased fast with the increasing of the percentage content of urea when the temperature was constant. The values for Ek ranged from 45.29 to 85.52 kJ/molwhen the mole percentage of urea ranged from 60% to 90%.Viscosity of Urea/C5H12NO2Cl deep eutectic based ionic liquids decreased rapidly with the increasing of temperature. Both conductivity and viscosity of ionic liquids could be described with Arrhenious equation: lnκ=lnκ0-(Eκ)/(RT);lnη=lnη0-(Eη)/(RT) Where k is electrical conductivity in S/m,k0,η0 is pre-exponential factor, R is gas constant in 8.314 J·K-1·mol-1,Ek is activation energy for conduction and Eηis activation energy for viscous flow in kJ/mol.The solubility of ZnO in Urea/C5H12NO2Cl ionic liquid was studied. The solubility of ZnO was significant larger with the increasing of temperature. The solubility of ZnO increased fast with the adding percentage content of betaine hydrochloride. The solubility of ZnO increase fast with the the increasing of temperature. Compared the solubility of ZnO in [BMIM]HSO4 with Urea/C5H12NO2Cl ionic liquid. The results show that:at 65℃-75℃range, the solubility of ZnO in [BMIM] HSO4 was larger than that of Urea/C5H12NO2Cl ionic liquid. However, after 80℃, the solubility of ZnO in Urea/C5H12NO2Cl ionic liquid was larger than that of acidic [BMIM]HSO4 ionic liquid.The solubility of ZnO was high in both of the ionic liquids, thus providing a new electrolyte for electrodepositing metal zinc.The electrochemical window of Urea/C5H12NO2Cl ionic liquid was determined, the electrochemical window was 2 V compared to Ag/Ag+electrode, which the anodic limit potential was+1.3V and the cathodic one was-1.2V.The electrode process of ZnO-Urea/C5H12NO2Cl system was studied by chrono-amperometry and cyclic voltammetry. There was a nuclear ring in cyclic voltammetry of 85% Urea/C5H12NO2Cl ionic liquids on glassy carbon electrode and the scan rate was 100mV/s. That shows the zinc surface deposition on copper electrode may be nucleation control process. The kinetics of zinc deposition was studied detailed by chronoamperometry.The two theoretical boundary conditions of instantaneous and progressive nucleation of metal deposition were expessed by the followed formula: (i/im)2=1.9524(t/tm)-1{1-exp[-1.2564(t/tm)]}2 (i/im)2=1.2254(t/tm)-1{1-exp[-2.3367(t/tm)2]}2Where(t,i) refers to the potentials of zinc deposition was constant,while time reached to t, the instantaneous current density was i; (tm,im) refers to the potentials of zinc deposition was constant while time reached to tm, the maximum current density was im.Compared the experimental data with the theoretical value, we can see that zinc deposition in the copper electrode on the nucleation mechanism was complex, neither consistented with the three-dimensional instantaneous nucleation nor meeted the continuous nucleation, and the mechanism was needed to further study.The cathode reaction was found to be simultaneously controlled by diffusion and electrochemical reaction by way of the cathodic polarization overpotential and cathodic polarization curves.The impact of the zinc deposition layer was studied by different cathode current density, zinc ion concentration, deposition time and temperature. The results showed that current efficiency of zinc electrodeposition higher than 99%. Cathode current efficiency was affected much by current density and temperature.The morphologies of zinc deposits were analyzed by scanning electron microscope.The typical kernel form was observed on the surface of cathode zinc and the tree crystal on the edge of cathode were observed.lt was shown that the zinc deposits on the edge of cathode were thinner than those in the interior region and the tree crystal phenomena became more obvious with the increasing current density.The thickness of zinc deposits on different substrate was different.The metal zinc was quickly deposited on copper substrate and the plating was more compacted than that of stainless steel. Deposition layer was analyzed by EDS spectroscopy.The electrodeposits obtained on Cu electrodes were dense and continuous with the current density of 0.008 A/cm2and 100 g/L CZn2+ for 80 min.The purity of zinc was high and the content could reach more than 95%. |
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