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Low Temperature Electrochemical Deposition of Aluminum in Organic base/Thiourea Based Deep Eutectic Solvents Jinfang Wang, Peng Wang, Qian Wang, Hongyu Mou, Bobo Cao, Dongkun Yu, Debao Wang, Suojiang Zhang, and Tiancheng Mu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b03942 • Publication Date (Web): 10 Oct 2018 Downloaded from http://pubs.acs.org on October 17, 2018

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ACS Sustainable Chemistry & Engineering

Low Temperature Electrochemical Deposition of Aluminum in Organic base/Thiourea Based Deep Eutectic Solvents Jinfang Wang,† Peng Wang,‡ Qian Wang,§ Hongyu Mou,† Bobo Cao,# Dongkun Yu,† Debao Wang,‡ Suojiang Zhang§ and Tiancheng Mu*,† †Department

of Chemistry, Renmin University of China, 59 Zhongguancun Street, Beijing 100872, China. *Email:

[email protected] ‡Shandong

Key Laboratory of Biochemical Analysis, College of Chemistry and Molecular Engineering, Qingdao University of

Science and Technology, Qingdao 266042, China. §Beijing

Key Laboratory of Ionic Liquids Clean Process, Institute of Process Engineering, Chinese Academy of Sciences, Beijing

100190, China. #MOE

Key Laboratory of Bioorganic Phosphorous Chemistry and Chemical Biology, Department of Chemistry, Tsinghua

University, Beijing 100084, China. Supporting Information

ABSTRACT In this study, a series of novel deep eutectic solvents (DESs) based on organic base, and thiourea (TU) and its derivatives were formed. Among them, DBU/TU or methylthiourea (MTU) could be used for the formation of stable -Al2O3 colloid of quiet high concentration (0.6 mol%), which was verified by small-angle X-ray scattering (SAXS) experiments. The solution is highly fluidic with a viscosity of 46.2 mPa·s at 50 °C. The attenuated total reflection infrared spectra (ATR-IR), 27Al nuclear magnetic resonance (NMR), and density functional theory (DFT) calculation proved that -Al2O3 was coordinated with the sulphur atom of methylthiourea. Electrodepositing of aluminum from the system at low temperature (50 °C) and atmospheric environment was achieved. Cyclic voltammogram indicated a good aluminum deposition peak at -0.26 V at 50 °C. SEM, EDS and XRD pattern showed that homogeneous, pure and adherent aluminum layers were obtained. Moreover, these DESs are versatile and can be used for dissolving other metals, metal sulphides, and metal oxides, including CoO, NiO, Ni2O3, MoO3, CuS, Fe, W, Cu and V2VI3 chalcogenides. Therefore, this work extended the scope of green solvent, and made improvement in both low temperature electrolytic alumina and solution processing other metal based materials. Keywords: DES · -Al2O3 dispersion · low temperature · electrodeposition of aluminum

INTRODUCTION Aluminum is one of the important mass production materials and remarkable for its low density and its ability to resist corrosion.1 Aluminium and its alloys are vital to aerospace, transportation and building industries.2 Industrial production of aluminum adopted Hall-Heroult electrolytic process, that is, cryolite-alumina electrolysis,3 which has been used for over one hundred years and it is the only process for aluminium production in commercial use today.

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However, this process has some obvious deficiencies such as high temperature (≈950 °C) hence high energy consumption (13~15 kW·h/kg), and heavy pollution (CO2, CO and HF emissions).4 It is also impossible to deposition of Al by reducing Al3+ directly in aqueous solutions because hydrogen could be evolved prior to Al deposition. As alumina is difficult to dissolve in common used solvents, researchers developed chloroaluminium5 ionic liquids (ILs) and nonchloroaluminium6-7 ILs to achieve low temperature electrolytic aluminum. However, the preparation of raw material (AlCl3) and anode products chlorine also cause heavy pollution to environment.8 Moreover, electrolytic conditions in ILs usually need anhydrous and oxygen-free environments.5 Technology maturity and economical efficiency are two obstacles that hinder the industrial application of electrodepositing aluminum in ILs. It is desirable to design green non-aqueous solvents that can dissolve alumina and electrolyze aluminum at low temperature and atmospheric environment. As ILs analogues, deep eutectic solvents (DESs) proposed by Abbott9 with features of simple preparation, cheap, biodegradable, and non-cyto-toxic have been extensively used in catalysis, organic synthesis, dissolution and separation processes, electrochemistry, and material chemistry.10 Notwithstanding, Abbott et al. have proved that urea can coordinate with the metal in metal chloride and form [MCl(urea)]+, [MCl(urea)2]+, [MCl(urea)3]+ (M = Zn, Sn, Fe, Al, Ga).11 They tried to dissolve alumina using choline chloride/urea DES, while the solubility is less than 1 ppm.12 To significantly improve the concentration of Al2O3 and hence achieve electrodepositing aluminum at low temperature, mixtures of thiourea (TU) and its derivatives (methylthiourea (MTU), dimethylthiourea (DMTU) and trimethylthiourea (TMTU)) which have stronger coordination than urea13 as hydrogen bonding donor (HBD), and organic base (1, 5-diazabicyclo [5.4.0]-5-undecene (DBU), 1, 5-Diazabicyclo [4.3.0] non-5-ene (DBN) and tetramethylguanidine (TMG)) which could capture and release protons under appropriate conditions14-15 as hydrogen bonding acceptor (HBA), were proposed as novel solvents. Experimental phenomena and subsequent analysis both proved the existence of weak interaction between HBD and HBA which is similar to the principle of the DESs formation.16-17 However, they do not have specific melting points (Tm) but only glass transition temperatures (Tg) (see in Figure 1 (c)), and the Tg of these solvents are higher than the HBD, therefore, we could deem them as quasi-DESs (QDESs). Some of them are proposed for dissolving and electrodepositing aluminum.

RESULTS AND DISCUSSION Alumina has a variety of crystal structure, such as   -Al2O3. Powder XRD (Figure S1) pattern shows that the industrial raw materials used for electrolytic aluminum is -Al2O3 which is consistent with the literature,18 so we mainly investigated -Al2O3 in this paper.


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To achieve good dissolution/dispersion results, the behavior of -Al2O3 in various combinations of special selected HBAs (DBU, DBN, and TMG) and HBDs (TU, MTU, DMTU, and TMTU) were investigated. Experimental results show that DESs formed by DBU and MTU (or TU) were most effective in dispersion of -Al2O3, and DBU/MTU is the best (See Table S1). The reason is conjectured as follows: methyl in MTU is an electron donating group,19 which can increase the electron cloud density of sulfur atoms and make the MTU molecules easier to coordinate with metal atom than the TU molecules. Meanwhile, experimental result shows the amount of -Al2O3 dispersed in the solvent did not increase with the increasing of the amount of methyl in thiourea. Two reasons account for it. (1) too much methyl increases the steric resistance of the molecule, which is detrimental for thiourea derivatives to interact with the-Al2O3; (2) methyl occupies the position of hydrogen atom, hence the thiourea derivatives cannot provide hydrogen atom as the HBD. Combined with the above analysis and results we choose MTU as HBD. The formation of DBU/MTU DES was confirmed by ATR-FTIR spectroscopy (Figure 1 (d)), TGA and derivative TGA (DTG) (Figure S2), differential scanning calorimeter (DSC) (Figure 1 (c)), and 1H nuclear magnetic resonance (NMR) spectroscopy (Figure S4). In ATR-FTIR spectra, the slight shifts of stretching vibration peak  (NH) of MTU in 3400 cm-1 and vibration absorption peak  (CN) of DBU in 1673 cm-1 both prove the existence of interaction between DBU and MTU. TGA-DTG curves show that the weight loss peak before and after the mixing is obviously shifted, but the number of peaks does not change. It means that the weak interaction between them affects their decomposition temperature.20 TGA curve of DBU/MTU indicates that the solvent can be used as reaction media at temperatures between 30 and 120 °C without decomposition. TGA curves of other DESs (DBU/TU, DBN/TU, TMG/TU, DBU/DMTU and DBU/TMTU, Figure S3) shows that they are thermally stable blow the range of 125-170 °C. In addition, as

depicted in Figure S4, the slight chemical shift at 2.2 ppm on the C6-H of DBU and the disappeared peak at 7.45 ppm on CH3N-H of MTU indicate the formation of hydrogen bonds between DBU and MTU (the supposed structure see in Figure 1 (a)).21-22 For DBU/MTU at molar ratio of 2:1, no obvious Tm was presented from -120 °C to 140 °C but only a Tg at -40 °C could be observed by DSC curve. Other DESs, including DBU/TU, DBU/DMTU, DBU/TMTU, DBN/TU, and TMG/TU in molar ratio of 2:1, show similar DSC results with only a Tg (Figure 1 (c) and Table S1). Above data and analysis confirmed the existence of weak interactions between the two components which make them liquid at room temperature.


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Fig. 1 Structure of hydrogen bond (a) and ionic bond (b) formed between DBU and MTU; (c) DSC curves of DBU/MTU solution and TU based other DESs (molar ratio 2:1); (d) ATR-FTIR spectra of DBU (black), MTU (red), and the obtained solvent (blue). The density of DBU/MTU decreases slightly with increasing temperature, while the viscosity decreases greatly with increasing temperature (from 998 mPa·s to 7 mPa·s) (Figure S6), Table S2). Therefore, the mass transfer efficiency could be improved by properly increasing the temperature when electrolyzing -Al2O3. The conductivity of DBU is below the detective limit while the DES is conductive (55.6 μS cm-1 for DBU/MTU at 50 °C, Figure S5, Table S3), which could be explained as the partly formation of [DBUH]+ [MTU]- by proton transfer between DBU and MTU (structure see Figure 1 (b)).14 Besides, increasing the temperature can significantly improve the conductivity of the DES (Figure S5), which will facilitate the charge transport during electrolysis. The conductivity of the DBU/MTU DES after adding -Al2O3 (8.33 mS/cm) increased by two orders of magnitude compared with the conductivity of DBU/MTU (55.6 μs/ cm) at 50 °C. This can be explained as follows. Owing to the dual role of coordination13 and hydrogen bonding discussed above, the MTU has a strong polarization and increasing the ionicity of DES,23 thereby increasing the conductivity. DFT calculation supported the above explanation. Figures S7 and S8 show the optimized structures of the DES and electrostatic potential (ESP) distributions of their electronic structures, which predicate possible active sites to interact with -Al2O3. Contrary to the negative regions of ESP around N atom in DBU (A) (Figure S8), ESP in N-H direction of MTU (B) is positive. It means DBU and MTU are more likely to form hydrogen bonds by electrostatic attraction. Besides, ESP around S atom is more negative in DES than that in MTU, which indicates the interaction between the DES and -Al2O3 is stronger than that between MTU and -Al2O3.


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The experimental results coincide with the DFT calculation results. The alumina colloid solution was obtained by simply adding a certain amount of -Al2O3 into the DESs (molar ratio 2:1) and stirring at 95 °C. Figure 2 (b) gives the photo illustration of the DBU/MTU DES before and after adding alumina. The concentration of -Al2O3 could reach 0.6 mol% in DBU/MTU and 0.4 mol% in DBU/TU, respectively. As shown in ATR-FTIR spectra (Figure 2 (a)), a sharp new peak at 2050 cm-1 emerged in the solution after adding -Al2O3, which could be ascribed to the stretching vibration of thiocyanate  (-SCN).24 It indicates that the sulfur atom of the DES coordinates strongly with the metal (Al) of the alumina and has a significant influence on the local physicochemical environments of MTU, then produces a thiocyanate group (-SCN).24 Characteristic UV-Vis absorption (Figure 2 (c)) maxima of alumina colloid solution is a broad peak between ~400 and ~510 nm due to the metal to ligand (-SCN) charge transfer transitions (MLCT).25 This might be attributed to the formation of yellow chromophores from complex of the alumina and the ligand (-SCN).26 It is corresponding to the conclusion of IR above. The slightly movement of weightless peak in TGA curve (see in Figure S9) confirmed the interaction between DES and -Al2O3. To study the interaction strength between DBU/MTU and -Al2O3, topological parameters at bond critical points (BCPs) are collected in Table S4, which are obtained based on atoms in molecules (AIM) theory. The BCPs we are interested in and the molecular graphs are depicted in Figure S10. Electron density (ρBCP) at e1 is 0.0733 which indicates that the interaction strength between DES and -Al2O3 is high. It is commonly considered that the more negative the HBCP, the stronger the corresponding interaction.27 In addition, a strong hydrogen bond (O…H-N) is also found between NH-H of MTU and -Al2O3. Above results indicate that not only coordinate bonding (Al…S-C) but also hydrogen bonding (O…H-N) existed in the complexes formed by DBU/MTU and -Al2O3 (Figure 2 (d)), which resulted in strong interactions between them.


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Fig. 2 ATR-FTIR spectral (a) and Photo illustration (b) of the DBU/MTU DES before (black) and after (red) adding -Al2O3; UV-Vis absorption spectrum (c) and DFT optimized structures (d) of the DBU/MTU DES after adding -Al2O3. In addition, we examined the dissolution/dispersion effect of this solvent on -Al2O3 (commonly known as corundum), and experimental results showed that -Al2O3 could not be dissolved/dispersed in DBU/MTU. It means the solution prefer to interact with the tetrahedron -Al2O3 than octahedral -Al2O3,28 which is in agreement with the literature report.29-30 The microstructures of the DBU/MTU/-Al2O3 and DBU/TU/-Al2O3 colloid solutions are investigated by small-angle X-ray scattering (SAXS). Figure 3 (b) shows the SAXS curves of the ternary systems with different HBD at 30 °C. -Al2O3 in DBU/MTU or DBU/TU DESs showed very similar SAXS patterns typical of stable colloidal solutions.31-32 The intensity shifts to low scattering wavevector from DBU/MTU/-Al2O3 (blue line) to DBU/TU/-Al2O3 colloid solution (red line), which indicates the two colloid solutions have different size.33 The generalized indirect Fourier transformation (GIFT) gives the pair–distance distribution function, p(r), which has been utilized to characterize the microstructure of the colloids.34 As shown in Figure 3 (c), the p(r) curves are nearly symmetric, suggesting that the colloids are spherical-shaped. The gyration radius Rg of the colloid solution and the true radius Ra values were calculated from p(r) functions34-38 and are shown in Figure 3 (c). For comparison, powder aggregated -Al2O3 has a qualitatively different SAXS pattern with a pronounced peak at q=0.025 Å−1. The DBU/MTU/-Al2O3 and DBU/TU/Al2O3 colloid solution can stabilize without any obvious sedimentation and aggregation at ambient air conditions for more than three months, which are also verified by the Tyndall effect (see in Figure S11).


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27Al

NMR spectra of 1.1 M Al(NO3)3·9H2O in D2O, DBU/MTU/0.4 mol% -Al2O3 and DBU/TU/0.4 mol%

-Al2O3 solutions at 50 °C were recorded and shown in Figure 3 (a). For Al(NO3)3·9H2O in D2O, a major resonance was observed at 0 ppm which corresponds to the non-framework hexacoordinated aluminum (i.e. [Al (D2O)6]3+)39 and a minor resonance was observed around 72.8 ppm which is attributed to aluminium-containing species with tetrahedral coordination.40 For DBU/MTU/-Al2O3 and DBU/TU/-Al2O3 solutions, a major resonance was observed at 68.7 ppm which corresponds to the tetrahedral coordination of -Al2O340 while the peak of hexacoordinated aluminum is not observed. The upfield shift of tetrahedral coordination aluminum (from 72.8 to 68.7) might caused by the coordination of sulfur atom then increased the electronic density of aluminum atom.41 It is consistent with the DFT calculations and indicates that -Al2O3 is not ionized, but exists in the form of coordination. Thus we speculate the cathodic reaction as: [Al2O3…MTU] + 3e-→Al(0) + [MTU…O]2-. In addition, the developed DESs can be used for dissolving a variety of metal, metal sulphides, and metal oxides, including CoO, NiO, Ni2O3, MoO3, CuS, Fe, W, Cu (Figure S12) and V2VI3 chalcogenides. It means that the novel DESs are versatile and can be used for solution processing other metals, metal sulphides, and metal oxides, some of which will be reported in our next work.

Fig. 3 (a) SAXS intensity for -Al2O3 colloid solutions in DBU/MTU DES (blue), DBU/TU DES (red) and powder aggregated -Al2O3 (black); (b) pair–distance distribution curves p(r) of the DBU/MTU/-Al2O3 (blue) and DBU/TU/Al2O3 (red); (c) Solution 27Al NMR spectra of 1.1M Al(NO3)3 in D2O (black line), DBU/MTU/0.4 mol% -Al2O3 (red line) and DBU/TU/0.4 mol% -Al2O3 colloid (blue line). Since the DES has low viscosity and certain conductivity after adding -Al2O3, electrodeposition of Al from the system was achieved at low temperature and atmospheric environment. Figure 4 (a) shows a typical cyclic voltammogram (CV) recorded at the glassy carbon (GC) working electrode with the Al wire (99.99%) as the reference electrode and spiral platinum wire as counter electrode at 50 mV s−1 in the DBU/MTU/0.6 mol% -Al2O3 system. Well-defined Al deposition peak was obtained during the initial CV scan.5, 42 The increasing cathodic current density corresponds to the Al deposition at -260 mV, and the


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peak current density reached 0.31 mA cm−2. The same CV was recorded with the DBU/TU as electrolyte (Figure S13). The concentration and temperature-dependent CV of the DBU/MTU/-Al2O3 solution (Figures 4 (c) and S13) were recorded at the GC working electrode with the Al wire as the reference electrode and spiral platinum wire as counter electrode at a scan rate of 50 mV s−1. Figure 4 (c) shows the slightly reduction potential movement from 0.2 mol% to 0.4 mol% -Al2O3, the unsteady current might caused by the increase concentration of active aluminum.7 Figure S14 shows that the current density increases obviously with the temperature increasing, while the reduction potential decreases slightly. It can be explained by Nernst equation43 and indicating that increasing the temperature contributes to the underpotential deposition.44 A constant voltage of −0.26 V was applied on the working electrode (the copper sheet) with Al wire as reference electrode and spiral platinum wire as counter electrode. Homogeneous, bright, adherent Al layers were obtained after plating for 2 hours. As depicted in Figure 4 (b), Al is apt to dendritic growth which is similar to that described in previous report.44 Meanwhile, the detailed nucleation mechanism needs further research. This electrodeposited film was further characterized by energy dispersive spectroscopy (EDS). As shown in Figure S15, the signals correspond to the substrate copper (1.0 KeV) and the deposited Al (1.5 KeV) almost without impurities. The insert picture also shows the polished copper foil covered with a layer of white material. To confirm the purity of the deposition, the obtained film was further characterized by XRD pattern. Figure 4 (d) illustrates the XRD patterns of the Al film on Cu foil obtained after electrodepositing. The peaks marked with ☆ can be indexed to those of substrate copper according to JCPDS File no. 04–0836. Diffraction theta located at 38.45°and 44.69°correspond to the (111) and (200) oriented growth of aluminum according to JCPDS File no. 65–2869. The weak signals of aluminum are due to its low weight ratio. The only signals correspond to the substrate copper and the deposited aluminum both in EDS and XRD analysis verified the purity of deposited aluminum.


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Fig. 4 Electrodeposition of Al (a) Cyclic voltammogram of -Al2O3 in DBU/MTU DES at 0.6 mol% on a copper sheet working electrode with Al wire as reference electrode and spiral platinum wire as counter electrode at 50 mV s−1; (b) SEM images of Al deposition on copper substrate (scale bar: 25 m, insert image scale bar: 4 m); (c) Concentration-dependent CVs of the DBU/MTU/-Al2O3 colloid on a glassy carbon working electrode with the Al wire as the reference electrode and spiral platinum wire as counter electrode at a scan rate of 50 mV s−1; (d) XRD pattern of Al deposition on copper substrate. Electrodeposition was performed by the potentiostatic method [−0.26 V vs Al3+/Al] in 0.6 mol% -Al2O3 in DBU/MTU electrolyte at 50 °C. CONCLUSIONS In summary, a serial of DESs formed by interactions between organic base (DBU, DBN, and TMG) as HBA and thiourea derivatives (TU, MTU, DMTU, and TMTU) as HBD were designed for the dispersion of high-concentration of -Al2O3. ATR-FTIR,

27Al

NMR spectra and DFT calculations have proved that the

alumina was coordinated with the sulphur atom of MTU. SAXS curves demonstrate typical patterns of stable colloidal solutions. After that, the system was used for the low temperature electrolytic alumina. CV curve indicate a good aluminum deposition peak at -0.26 V at 50 °C. SEM, EDS and XRD proved homogeneous, pure and adherent aluminum layers were obtained at low temperature and potential. Besides, the DESs are versatile and can be used for solution processing other metals, which is of significance for solvent treatment and preparation of metal-based materials.

EXPERIMENTAL SECTION Preparation of DESs and Al2O3 dispersion


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The DESs were formed by the simple mixing of DBU with thiourea or thiourea derivatives (molar ratio = 1:1~7:1) at 30 °C for about 0.5 h. The solvents were bubbled with N2 for 24 h at room temperature to remove trace amount of water before use. Then the colloid could be formed by adding -Al2O3 (70 mg) in the solvent (1 g) with agitation at 95 °C. After the dissolution/dispersion of -Al2O3, the color of the solution becomes brown. The concentration of Al2O3 was determined by preparing saturated dispersion (with above method) and running thermogravimetric analysis (TGA Q500) on the liquid. The residual mass (Figure S9) at 450 °C was taken as representative of the concentration of Al2O3.45 Each reported datum was the average value of three independent measurements with deviation less than 0.1%. Instrumentation and characterization Solution

27Al

NMR measurements were conducted on a Bruker Advance Ⅲ 500WB NMR spectrometer

(500 MHz) at 50 °C with 1.1 M Al(NO3)3 as the external standard. The

27Al

chemical shift values were

reported relative to the aqueous solution of Al(NO3)3·9H2O as the external reference and processed by the MestReNova Program. SAXS measurements were carried out at the GeniX3D microsource (Xeuss 2.0, Xenocs Co., Ltd. France). A 13 keV Cu Kα X-ray beam was focused on samples with a FOX3D single reflection optics and PILATUS3 300K detectors. Colloids were prepared with a concentration of 0.4 mol% in quartz capillaries (0.3–0.8 mm), which were removed traces of air bubbles. The use of the Xenocs Low Noise Flow Cell enables the minimization of container scattering and allows our colloids scattering detection for 300 s exposure time. The data were obtained by a software package for system control, data acquisition & analysis based on SPEC from Certified Scientific Software. Electrochemical experiment. The electrochemical experiments were performed on a CHI 660E (Shanghai Chen Hua Instrument Co., Ltd., China) electrochemical analyzer controlled by CHI660E software with a three-electrode system. The cyclic voltammetry (CV) consists of a three electrode system: glassy carbon (GC, d=3 mm), Al wire (99.999%), and spiral Pt wire performed as the working, the reference, and the counter electrodes at preset temperature. The electrodeposition of Al was performed by utilizing a potentiostatic method at 50 °C. The Cu substrate (area = 1 cm2), Al wire (99.999%), and spiral Pt wire worked as the working, reference, and counter electrodes. The GC electrode was polished with 0.3 mm alumina paste, washed by deionised water and ethanol, and dried prior to all measurements. All voltammograms were performed at atmospheric environment with scan rate of 50 mV s-1. The cathode was Cu substrate, and the anode was an Al wire. The cathodes were abraded by using sand paper followed by rinsing with deionised water, then dipped into 10 V% HCl, deionised water and acetone for 5 min, respectively. The anode was cleaned by dipping into 50 V% HCl, deionised water and acetone.46 After deposition, samples were sonication in ipropanol for 2 min followed by dipping in deionised water and then dried in air before characterization.


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Computational methods All the geometry optimizations have been carried out by employing Gaussian 0947 package. DFT has been adopted for the optimization, where B3LYP method has been used combined with the 6-311++G(d, p)48 basis set and the pseudopotential (LANL2DZ)49 basis set. Vibrational frequency calculations have confirmed that the optimized structures were located and characterized as true minima. Electrostatic potential (ESP) and atoms in molecules (AIM)50 methods have been investigated by Multiwfn 3.3.951 based on wavefunctions generated in the optimization processes. ASSOCIATED CONTENT Supporting Information Chemicals and materials, instrumentation and characterization of original NMR, ATR-FTIR and UV-Vis spectra. Author information Corresponding Author *Email: [email protected], Phone: +86-10-62514925. Fax: +86-10-62516444. Notes The authors thank National Natural Science Foundation of China (21773307, 21473252) and Shandong Key Laboratory of Biochemical Analysis, Qingdao University of Science and Technology (QUSTHX201809) for financial support. Conflicts of interest There are no conflicts to declare.

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Electrolyzation of aluminum from-Al2O3 in DBU/MTU quasi-DES at low temperature was realized, which is energy efficiency by avoiding high temperature.


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Low Temperature Electrochemical Deposition of ... - ACS Publications

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