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Honorary Editor General ZHOU GuangZhao (Zhou Guang Zhao) Editor General ZHU ZuoYan Institute of Hydrobiology, CAS, Editor-in-Chief LI LeMin Peking University, China Associate Editor-in-Chief CAO Yong South China University of Technology, China TIAN ZhongQun Xiamen University, China CHEN HongYuan University, China XUE Zi-Ling University of Tennessee, USA FENG ShouHua , China YUAN Quan Dalian Institute of Chemical Physics, CAS, China LIN GuoQiang Shanghai Institute of Organic Chemistry, CAS, China Members

BAO XinHe LIAN TianQuan XIONG RenGen Dalian Institute of Chemical Physics, CAS, China Emory University, USA South East University, China BU XianHe LIANG WenPing XU ChunMing Nankai University, China National Natural Science Foundation of China, China University of Petroleum, China CHAI ZhiFang China YAM Vivian Wing-Wah Institute of High Energy Physics, CAS, China LIN JianHua University of Hong Kong, China CHAN Albert S C Peking University, China YAN DeYue Hong Kong Polytechnic University, China LIU GuoJun Shanghai Jiao Tong University, China CHEN Xian Queen’s University, Canada YANG Bai University of North Carolina-Chapel Hill, USA LIU Jun O Jilin University, China CHEN XiaoMing Johns Hopkins Medicine Institute, USA YANG DongSheng Sun Yat-Sen University, China LU FengCai University of Kentucky, USA Institute of Chemistry, CAS, China CHEN Yi YANG PengYuan Institute of Chemistry, CAS, China NIE ShuMing Fudan University, China CUI ZhanFeng Georgia Institute of Technology and Emory University, USA YANG WeiTao Oxford University, UK Duke University, USA PAN CaiYuan DUAN Xue YANG XueMing Beijing University of Chemical Technology, China University of Science and Technology of China, China Dalian Institute of Chemical Physics, CAS, China FEI WeiYang YANG YuLiang Tsinghua University, China PU Lin University of Virginia, USA Fudan University, China FENG XiaoMing QIAO JinLiang YAO ShouZhuo Sichuan University, China SINOPEC Beijing Research Institute of Chemical Hunan University, China GAO ChangYou Industry, China YAO ZhuJun Zhejiang Universtiy, China SHAO YuanHua Shanghai Institute of Organic Chemistry, CAS, GAO Song Peking University, China China Peking University, China SHEN ZhiQuan YOU XiaoZeng GUO ZiJian Zhejiang University, China , China Nanjing University, China SHUAI ZhiGang YU LuPing HAN BuXing Tsinghua University, China University of Chicago, USA Institute of Chemistry, CAS, China SUN LiCheng ZHANG HongJie HE MingYuan Royal Institute of Technology (KTH), Sweden Changchun Institute of Applied Chemistry, CAS, Research Institute of Petroleum Processing, TANG Ben Zhong China SINOPEC, China Hong Kong University of Science & Technology, ZHANG JinSong HONG MaoChun China University of California, Riverside, USA Fujian Institute of Research on the Structure of TIAN He ZHANG JinZhong Matter, CAS, China East China University of Science & Technology, University of California, Santa Cruz, USA China PeiQiang ZHANG John ZengHui Xiamen University, China TONG Liang New York University, USA Columbia University, USA Georgia State University，USA TUNG ChenHo ZHANG LiHe Technical Institute of Physics and Chemistry, CAS, Peking University, China JIANG GuiBin China ZHANG Xi Research Center for Eco-Environmental Sciences, WAN LiJun Tsinghua University, China CAS, China Institute of Chemistry, CAS, China ZHANG YuKui JIANG Long WANG MeiXiang Dalian Institute of Chemical Physics, CAS, China Institute of Chemistry, CAS, China Institute of Chemistry, CAS, China ZHAO XinSheng JIAO Kui WANG ShiQing Peking University, China Qingdao University of Science and Technology, University of Akron, USA China WANG ZhenGang Xiamen University, China JU HuangXian California Institute of Technology, USA ZHENG LanSun Nanjing University, China WANG ZhongLin Xiamen University, China KONG Wei Georgia Institute of Technology, USA ZHOU QiLin Oregon State University, USA WU YunDong Nankai University, China LI QianShu Hong Kong University of Scence & Technology, ZHU Tong South China National University, China China Peking University, China LI YaDong XIE ZuoWei ZHU Julian X Tsinghua University, China Chinese University of Hong Kong, China Université de Montréal, Canada

Editorial Staff ZHU XiaoWen (Director) SONG GuanQun ZHANG XueMei

SCIENCE CHINA Chemistry

Contents Vol.55 No.8 August 2012

COVER Zinc has been widely used as anti-corrosive coatings in the electroplating industry. However, the conventional processes for preparing zinc coatings suffer from a series of inherent dis- advantages, such as hydrogen embrittlement, pollutant release and high energy consumption. There- fore, it’s necessary to develop high-efficiency and green electrolytes for the electrodeposition of zinc. In this work, it’s first found that the solubilities of ZnO in imidazolium chloride-based ionic liquids are remarkably enhanced by the addition of urea. Shining, dense and well adherent zinc coatings with good purity were electrodeposited from 0.6 M solution of ZnO in 1:1 [Amim]Cl/urea at 323.2−343.2 K. Unlike conventional methods, the deposition process is environmentally friendly, low energy consumption and easy to handle at mild conditions. It’s expected that the solutions of ZnO in imidaz- olium chloride/urea have the potential to replace the traditional electrolytes for low-temperature zinc electroplating and synthesis of functional zinc materials (see the article by ZHENG Yong, DONG Kun, WANG Qian, ZHANG SuoJiang, ZHANG QinQin, LU XingMei on page 15871597).

SPECIAL ISSUE: Ionic Liquid and Green Chemistry Preface: An International Look at Ionic Liquids ROGERS Robin D., ZHANG SuoJiang & WANG JianJi Sci China Chem, 2012, 55(8): 1475–1477

REVIEWS

The preparation of supported ionic liquids (SILs) and their application in rare metals separation ZHU LiLi, GUO Lin, ZHANG ZhenJiang, CHEN Ji & ZHANG ShaoMin Sci China Chem, 2012, 55(8): 1479–1487

Cyano-containing ionic liquids for the extraction of aromatic hydrocarbons from an aromatic/aliphatic mixture MEINDERSMA G. Wytze & DE HAAN André B. Sci China Chem, 2012, 55(8): 1488–1499

© Science China Press and Springer-Verlag Berlin Heidelberg 2012 chem.scichina.com www.springerlink.com

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Ionic liquids: Efficient solvent and medium for the transformation of renewable lignocellulose LONG JinXing, LI XueHui, WANG LeFu & ZHANG Ning Sci China Chem, 2012, 55(8): 1500–1508

ARTICLES

The physicochemical properties of some imidazolium-based ionic liquids and their binary mixtures NING Hui, HOU MinQiang, MEI QingQing, LIU YuanHui, YANG DeZhong & HAN BuXing Sci China Chem, 2012, 55(8): 1509–1518

Liquid-liquid interfacial tension of equilibrated mixtures of ionic liquids and hydrocarbons RODRÍGUEZ Héctor, ARCE Alberto & SOTO Ana Sci China Chem, 2012, 55(8): 1519–1524

Structure-property relationships in ILs: A study of the alkyl chain length dependence in vaporisation enthalpies of pyridinium based ionic liquids ZAITSAU Dzmitry H., YERMALAYEU Andrei V., EMEL’YANENKO Vladimir N., VEREVKIN Sergey P., WELZ-BIERMANN Urs & SCHUBERT Thomas Sci China Chem, 2012, 55(8): 1525–1531

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Sweet ionic liquids-cyclamates: Synthesis, properties, and application as feeding deterrents PERNAK Juliusz, WASIŃSKI Krzysztof, PRACZYK Tadeusz, NAWROT Jan, CIENIECKA-ROSŁONKIEWICZ Anna, WALKIEWICZ Filip & MATERNA Katarzyna Sci China Chem, 2012, 55(8): 1532–1541

Chlorogallate(III) ionic liquids: Synthesis, acidity determination and their catalytic performances for isobutane alkylation XING XueQi, ZHAO GuoYing & CUI JianZhong Sci China Chem, 2012, 55(8): 1542–1547

Computational studies of the structure and cation-anion interactions in 1-ethyl-3-methylimidazolium lactate ionic liquid HE HongYan, ZHENG YanZhen, CHEN Hui, ZHANG XiaoChun, YAO XiaoQian & ZHANG SuoJiang Sci China Chem, 2012, 55(8): 1548–1556

Understanding the interactions between tris(pentafluoroethyl)-trifluorophosphate-based ionic liquid and small molecules from molecular dynamics simulation ZHANG XiaoChun, LIU ZhiPing & LIU XiaoMin Sci China Chem, 2012, 55(8): 1557–1565

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CO2 capture through halogen bonding: A theoretical perspective LI HaiYing, LU YunXiang, ZHU Xiang, PENG ChangJun, HU Jun, LIU HongLai & HU Ying Sci China Chem, 2012, 55(8): 1566–1572

All-atom and united-atom simulations of guanidinium-based ionic liquids LIU XiaoMin, ZHANG XiaoChun, ZHOU GuoHui, YAO XiaoQian & ZHANG SuoJiang Sci China Chem, 2012, 55(8): 1573–1579

Ionic liquid assisted synthesis of flowerlike Cu2O micro-nanocrystals ZHAO Yang, GUO LiPing, SUN Xin & WANG JianJi Sci China Chem, 2012, 55(8): 1580–1586

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Electrodeposition of zinc coatings from the solutions of zinc oxide in imidazolium chloride/urea mixtures ZHENG Yong, DONG Kun, WANG Qian, ZHANG SuoJiang, ZHANG QinQin & LU XingMei Sci China Chem, 2012, 55(8): 1587–1597

Conversion coatings of Mg-alloy AZ91D using trihexyl(tetradecyl) phosphonium bis(trifluoromethanesulfonyl)amide ionic liquid HOWLETT P. C., GRAMET S., LIN J., EFTHIMIADIS J., CHEN X. B., BIRBILIS N. & FORSYTH M. Sci China Chem, 2012, 55(8): 1598–1607

Composite electrolytes based on poly(ethylene oxide) and binary ionic liquids for dye-sensitized solar cells YU YingHao, JIANG Peng, WANG FuRong, WANG LeFu & LI XueHui Sci China Chem, 2012, 55(8): 1608–1613

Iron catalyzed Michael addition: Chloroferrate ionic liquids as efficient catalysts under microwave conditions VASILOIU Maria, GAERTNER Peter & BICA Katharina Sci China Chem, 2012, 55(8): 1614–1619

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Zinc-assisted synthesis of imidazolium-tetrazolate bi-heterocyclic zwitterions with variable alkyl bridge length DRAB David M., SHAMSHINA Julia L., SMIGLAK Marcin, COJOCARU O. Andreea, KELLEY Steven P. & ROGERS Robin D. Sci China Chem, 2012, 55(8): 1620–1626

Development of sequential type iron salt-catalyzed Nazarov/Michael reaction in an ionic liquid solvent system IBARA Chie, FUJIWARA Masamune, HAYASE Shuichi, KAWATSURA Motoi & ITOH Toshiyuki Sci China Chem, 2012, 55(8): 1627–1632

High viscosity of ionic liquids causes rate retardation of Diels-Alder reactions KUMAR Anil & PAWAR Sanjay S. Sci China Chem, 2012, 55(8): 1633–1637

Properties of alkylbenzimidazoles for CO2 and SO2 capture and comparisons to ionic liquids SHANNON Matthew S., HINDMAN Michelle S., DANIELSEN Scott. P. O., TEDSTONE Jason M., GILMORE Ricky D. & BARA Jason E. Sci China Chem, 2012, 55(8): 1638–1647

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CO2 Capture technologies: Current status and new directions using supported ionic liquid phase (SILP) absorbers KOLDING Helene, FEHRMANN Rasmus & RIISAGER Anders Sci China Chem, 2012, 55(8): 1648–1656

Enhanced refolding of lysozyme with imidazolium- based room temperature ionic liquids: Effect of hydrophobicity and sulfur residue BAE Sang-Woo, CHANG Woo-Jin, KOO Yoon-Mo & HA Sung Ho Sci China Chem, 2012, 55(8): 1657–1662

The effect of hydrogen bond acceptor properties of ionic liquids on their cellulose solubility STARK Annegret, SELLIN Martin, ONDRUSCHKA Bernd & MASSONNE Klemens Sci China Chem, 2012, 55(8): 1663–1670

viii

Novel acid initiators for the rapid cationic polymerization of styrene in room temperature ionic liquids VIJAYARAGHAVAN R. & MACFARLANE D. R. Sci China Chem, 2012, 55(8): 1671–1676

Density estimated physicochemical properties of alanine- based ionic liquid [C7mim][Ala] and its application in selective transesterification of soybean oil FANG DaWei, LI Meng, GE RiLe, ZANG ShuLiang, YANG JiaZhen & GAO YanAn Sci China Chem, 2012, 55(8): 1677–1682

Reactivity of N-cyanoalkyl-substituted imidazolium halide salts by simple elution through an azide anion exchange resin DRAB David M., KELLEY Steven P., SHAMSHINA Julia L., SMIGLAK Marcin, COJOCARU O. Andreea, GURAU Gabriela & ROGERS Robin D. Sci China Chem, 2012, 55(8): 1683–1687

Infrared spectroscopic study on chemical and phase equilibrium in triethylammonium acetate LV YiQi, GUO Yan, LUO XiaoYan & LI HaoRan Sci China Chem, 2012, 55(8): 1688–1694

NEWS & COMMENTS

Three international conferences on ionic liquids held in Beijing in 2012 WANG Qian & LU XingMei Sci China Chem, 2012, 55(8): 1695–1696

SCIENCE CHINA Chemistry

• ARTICLES • August 2012 Vol.55 No.8: 1580–1586 · SPECIAL ISSUE · Ionic Liquid and Green Chemistry doi: 10.1007/s11426-012-4654-2

Ionic liquid assisted synthesis of flowerlike Cu2O micro-nanocrystals

ZHAO Yang, GUO LiPing, SUN Xin & WANG JianJi*

Key Laboratory of Green Chemical Media and Reactions, Ministry of Education; School of Chemical and Environmental Sciences, Henan Normal University, Xinxiang 453007, China

Received March 1, 2012; accepted April 12, 2012; published online June 29, 2012

Novel flowerlike Cu2O micro-nanocrystals were prepared by a greener reductive reaction of cupric acetate monohydrate with     ethylene glycol in aqueous solutions of [C8mim]X (X = Cl , Br , BF4 , PF6 ) and [Cnmim][BF4] (n = 4, 6, 8). The obtained mi- crostructures of Cu2O were characterized by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and Fourier Transform Infrared (FT-IR). The effects of cations, anions and concentration of the ionic liquids on the morphology of Cu2O were examined in some details. The results suggest that the formation of flowerlike Cu2O was governed by a [C8mim][BF4] controlled reductive reaction mechanism. As one of their applications, the Cu2O nanoparticles were used for the photocatalytic degradation of methylene blue in aqueous solution, and high photocatalytic activity was observed.

Cu2O, flowerlike micro-nanocrystals, ionic liquid, structure-directing agent, photocatalytic activity

1 Introduction tions, and electrochemical applications [15]. Since ILs have unique chemical and physical properties, such as negligible vapor pressure, low interface tension and extended temper- In recent years, the study of metal oxides has attracted the ature range in the liquid state, high chemical and thermal attention of materials scientists due to their useful optical, stability, and strong ability to dissolve a variety of materials electrical, magnetic, mechanical, and catalytic properties [1]. [16], they have been utilized in inorganic synthesis as new Cuprous oxide (Cu O), an important p-type semiconductor 2 reaction media, and many inorganic nanostructures have with a direct band gap of about 2.17 eV, has received exten- been successfully prepared via various IL-involved pro- sive attention for its diverse applications in solar energy cesses, for example, TiO nanocrystals [17], nanoparticles conversion, catalysis, gas sensors, electrodes for lithium-ion 2 of Au, Pd, Rh, Ir, Pt, Ag, Fe, CaCO , and Bi S and Sb S batteries and magnetic storage [2–6]. Much effort has been 3 2 2 nanorods [18–25]. devoted to the synthesis of uniform nano- and microcrystals In this work, we develop a facile and greener method to with different morphologies, such as nanowires, nanoplates, fabricate novel flowerlike nanostructures consisting of nanotubes, nanocubes, nanocages, pyramids, hollow spheres, Cu O nanosheets by a reductive solvothermal reaction of double tower-tip-shaped Cu O microcrystals and among 2 2 cupric acetate monohydrate with ethylene glycol (EG) in others [7–14]. aqueous ILs solutions. The selected ionic liquids include Room temperature ionic liquids (ILs) are attractive     greener solvents for replacement of conventional volatile [C8mim]X (X = Cl , Br , BF4 , PF6 ) and [Cnmim][BF4] (n organic solvents widely used in chemical reactions, separa- = 4, 6, 8). Structures of the as-prepared products were char- acterized by means of Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), and Fourier Transform *Corresponding author (email: [email protected]) Infrared (FT-IR) measurements. It was shown that the evo-

© Science China Press and Springer-Verlag Berlin Heidelberg 2012 chem.scichina.com www.springerlink.com Zhao Y, et al. Sci China Chem August (2012) Vol.55 No.8 1581 lution of morphology of Cu2O could be controlled by alkyl 2.5 Photocatalytic activity of the Cu2O particles chain length of cations, nature of anions and amount of the used ILs, and reaction time. In addition, photocatalytic deg- To investigate the photocatalytic activity of Cu2O architec- radation of methylene blue in aqueous solution was chosen as tures under visible light irradiation, methylene blue was chosen as a model pollutant. About 0.05 g of the Cu2O par- a test reaction to examine the photocatalytic activity of Cu2O nanoparticles, and positive results have been obtained. ticles with flowerlike and cubic morphologies was dispersed in a 50 mL aqueous methylene blue solution (10 mg L1). The photocatalytic reaction was carried out at room temper- 2 Experimental ature. A 500 W Xe lamp was used as a light source with a 420 nm cutoff filter to provide visible light irradiation. After

2.1 Chemicals the aqueous methylene blue solution was stirred for 30 All 1-bromoalkanes (99%) were from Acros Organic, which minutes in the dark, it was irradiated under visible light for were distilled before use. 1-Methylimidazole (99%), sodium different times. 5 mL of the reaction solution was taken at the interval of 20 minutes for the measurements of UV-vis tetrafluoroborate (NaBF , 99%) and sodium hexafluoro- 4 absorption of aqueous methylene blue solution. phosphate (NaPF6, 99%) were purchased from Shanghai Chem. Co., Cu(CH3COO)2·H2O and ethylene glycol (Ana- lytical grade) were obtained from Tianjin Chem. Co. They 3 Results and discussion were used as received. 3.1 Formation of the flowerlike Cu2O 2.2 Preparation of the ILs Figure 1 shows the XRD patterns of the products, from which the phase composition and purity of as-prepared Ionic liquids [Cnmim][BF4] (n = 4, 6, 8) and [C8mim]X (X     samples could be analyzed. It can be seen that when 1 mmol = Cl , Br , BF4 , PF6 ) were prepared and purified by using Cu(CH3COO)2·H2O was dissolved in pure EG without wa- the procedure described in the literature [26, 27]. All the ter and any ILs, only the Cu peak was observed at the tem- ionic liquids were dried under vacuum at 70 °C for 2–3 days perature of 190 °C and reaction time of 6 h (Figure 1(a)). in the presence of P2O5. The composition and purity of the This suggests Cu2O phase was not formed in this situation. ILs were checked by 1H NMR spectroscopy (Bruker, ad- As the reactant was dissolved in a mixed solvent consisting vance-400 MHz), and they were found to be in good of 15 mL EG and 1 mL water without ILs, Cu and Cu2O agreement with those reported in the literature [26, 27]. phases were found in Figure 1(b). However, as [C8mim][BF4] was involved, the peaks of Cu were disap- peared, and all peaks in the XRD patterns (Figure 1(c)) can 2.3 Preparation of the Cu2O nanoparticles be assigned to the cubic phase of Cu2O (space group Pn-3m;

In a typical process, 1 mmol Cu(CH3COO)2·H2O was dis- α0 = 4.260; JCPDS 65-3288). solved in a binary solvent consisting of 15 mL EG and 1 mL The FT-IR spectrum of the as-prepared Cu2O in the water, and 4 mmol ILs was added. The mixture was soni- presence [C8mim][BF4] was shown in Figure 2. The band at 1 cated in a water bath for 30 min, and then was transferred 623.8 cm can be attributed to the Cu–O vibration of Cu2O. into a Teflon-lined stainless steel autoclave, followed by a Compared with the standard absorption band, this absorp- solvothermal treatment at 150–220 °C for 1–6 h. As the tion band shows a blue shift, mainly due to the small parti- reaction was finished, the solution was cooled to room temperature, and the products were separated by centrifuga- tion, rinsed with absolute ethanol six times, and dried in a vacuum oven at 60 °C for 5 h.

2.4 Characterization of the synthesized Cu2O particles

The structure and purity of the Cu2O particles were charac- terized by XRD on a D8 X diffractometer (Germany, Bruker) with a CuKα radiation (λ = 0.154060 nm) at 2θ ranging from 20° to 80°. The morphology of the as- prepared sample was observed on a JEOL JSM6390LV scanning electron microscopy (Japan) with an accelerating Figure 1 XRD patterns of the Cu O prepared with 1 mmol voltage of 20 kV. Fourier transform infrared spectra were 2 Cu(CH3COO)2·H2O under different conditions: (a) in pure EG; (b) in EG + collected on a Thermo Nicolet Nexus spectrometer (USA). H2O; (c) in EG + H2O + [C8mim][BF4]. 1582 Zhao Y, et al. Sci China Chem August (2012) Vol.55 No.8 cle size effect [28]. The peak at 3440 cm1 is the bending The influence of the reaction time on the morphology of vibration absorption of hydroxyl in water molecules. Cu2O was studied in the presence [C8mim][BF4] at 190 °C. The morphologies of the products were identified by As a result, when the reaction was carried out for 10 min, SEM. It can be seen from Figure 3(a) that the sample ob- one can see that a lot of smooth cubic structure and some tained in a mixed solvent consisting of 15 mL EG and 1 mL flowerlike structure existed (Figure 5(a)). The morphology water without [C8mim][BF4] exists in irregular agglomerate of the products were gradually transformed into flowers at microspheres. In the presence of [C8mim][BF4], Figure 3(b) the range of time from 1 to 6 h (Figure 5(b–d)), and no cube shows the SEM images of the sample composed of many and irregular crystals were observed at the end. However, it uniform flowerlike architecture approximately 3 μm in di- was clear from Figure 6(a–c) that significant difference ameter. The entire flowerlike architecture is assembled from could be found in the diffraction peak intensity of the Cu2O many thin nanosheets with smooth surface. The nanosheets samples prepared at different reaction times. The sample were with the thickness of about 100 nm. For the sake of convenience, w was defined as the molar ratio of Cu(CH3COO)2·H2O to the ILs in the investigation on the effect of the amount of the IL added. It was found that as [C8mim][BF4] (w = 10:1) was added in the reaction system, the broken polyhedron was obtained (Figure 4(a)). In the presence of [C8mim][BF4] (w = 4:1), parts of polyhe- drons began to be corrupted and some nanosheets were formed (Figure 4(b)). Furthermore, the polyhedrons disap- peared gradually and flowerlike nanostructures consisting of nanosheeets were formed (see Figures 4(c–f)) as the molar ratio was changed from w = 3:1 to w = 1:4. This suggested that [C8mim][BF4] played a key role in the formation of the flowerlike Cu2O micro-nanostructure.

Figure 4 SEM images of Cu2O samples prepared at 190 °C for 6 h in the presence of [C8mim][BF4]: (a) w = 10:1, (b) w = 4:1, (c) w = 3:1, (d) w = 1:1, (e) w = 1:2 and (f) w = 1:4.

Figure 2 IR spectrum of Cu2O obtained in the presence of [C8mim][BF4].

Figure 3 SEM images of the samples obtained with 1 mmol Cu(CH COO) ·H O in a mixed solvent consisting of 15 mL EG and 1 mL 3 2 2 Figure 5 SEM images of Cu O prepared at 190 °C and different reaction water at 190 °C for 6 h: (a) without [C mim][BF ], and (b) with 2 8 4 time in the presence of [C mim][BF ]: (a)10 min, (b)1 h, (c) 3 h, and (d) 6 [C mim][BF ]. 8 4 8 4 h. Zhao Y, et al. Sci China Chem August (2012) Vol.55 No.8 1583

Figure 6 XRD patterns of the Cu2O prepared at 190 °C and different reaction time in the presence of [C8mim][BF4]: (a) 1 h, (b) 3 h, (c) 6 h.

Figure 7 SEM images of Cu2O prepared at 190 °C in the presence of    [C8mim]X: (a) X = Cl , (b) X = Br , (c) X = PF6  was poorly crystallized at shorter reaction time (Figure 6(a, b)). Consequently, a longer reaction time was required in order to ensure the crystallization of Cu2O in the system. Besides that, the extend reaction time would help re-organ- ize the structures.

3.2 Effect of anionic nature of the ILs on the mor- phology of Cu2O particles

   [C8mim]X (X = Cl , Br , PF6 ) was used to investigate the Figure 8 SEM images of Cu2O prepared at 190 °C in the presence of effect of anionic nature of the ILs on the morphology of [Cnmim][BF4] (n = 4, 6) at w = 1:4: (a) n = 4, (b) n = 6. Cu2O particles, and the results were shown in Figure 7. It was clearly indicated that only the spherical morphology, 3.4 The possible formation mechanism rather than flowerlike Cu2O, was obtained in the presence of  any of the three ILs. This suggests that it is the BF4 anion On the basis of the results discussed above, it is believed which plays an important role in determining the morphol- that [C8mim][BF4] plays a key role in the formation of the ogy of Cu2O. flowerlike Cu2O. One possible reductive mechanism con- trolled by the ionic liquid was illustrated in Scheme 1. It 3.3 Effect of alkyl chain length of the ILs on the mor- supposes that as [C8mim][BF4] was present in the reaction system, Cu2+ was surrounded by anions of the IL through phology of Cu2O particles electrostatic interaction, and cations associated with anions Here, [Cnmim][BF4] (n = 4, 6) at w = 1:4 was chosen to of the ILs by hydrogen bonds was outside the anions. Thus, investigate the influence of the alkyl chain length of the ILs the polymeric superstructure would be formed by hydrogen on the morphology of Cu2O nanomaterials. Figure 8 shows bonds or other non-covalent interactions between cations a typical SEM image for the Cu2O samples prepared in the and anions of the ILs. Under these circumstance, the newly 2+ presence of [C4mim][BF4]and [C6mim][BF4], respectively. formed Cu2O from the reaction between Cu and EG could It can be seen that the particle morphology was irregular in be coated by the polymeric superstructure of the IL, which the presence of [C4mim][BF4] or [C6mim][BF4], and the would prevent Cu2O nanoparticles from aggregation. Recently, it has been reported that the ionic association flowerlike Cu2O particles could not be obtained. This was quite different from the result obtained in the presence of capacity of [C4mim]Br, [C4mim][BF4], and [C4mim][PF6] in water follows the order of [BF ]> [PF ]> Br [30], We [C8mim][BF4]. Thus, it is evident that alkyl chain length of 4 6 the ILs also has an important effect on the morphology of can speculate that the interaction of [C8mim] with different anions in EG increases in the order of [BF ]> [PF ] > Br. Cu2O. Similar effect has been observed in the formation of 4 6 gold nanostructures [29]. It was shown that by varying the Besides that, it is found that the ILs have amphiphilicity in alkyl chain length attached to imidazolium cation of the solution. [C8mim][BF4] can aggregate in EG, while ionic liquids (n = 0, 2, 4, 6, 8, 10), various particle mor- [C4mim][BF4] can’t [31]. The association of the ILs and the phologies were formed, such as quasispherical, raspberry- formation of their aggregates would have some effects on like, flakes and dendritic structures. the flowerlike micro-nanostructure. 1584 Zhao Y, et al. Sci China Chem August (2012) Vol.55 No.8

Cu2O micro-nanoflowers and irregular Cu2O crystals, pre- pared respectively in the presence and absence of [C8mim] [BF4], were used for the photocatalytic degradation of methylene blue in aqueous solution. Figure 9 (a, b) shows the UV-vis spectra of methylene blue in the presence of flowerlike Cu2O and irregular microcrystal Cu2O as a func- tion of reaction time. It can be seen that the adsorption abil- ity of flowerlike Cu2O is much stronger than that of irregu- lar microcrystal Cu2O. For example, in the case of no light irradiation, the flowerlike Cu2O adsorbs about 15% meth- ylene blue, while polyhedral microcrystal Cu2O adsorbs only about 2% methylene blue from the solution during 20 min. In Figure 9(c), A/A0 was used to measure the degrada- tion efficiency of methylene blue at different radiation times, where A0 is the initial absorbance of methylene blue at its absorption maximum of 664 nm, and a stand for the ab- sorbance of methylene blue at a given radiation time. It can Scheme 1 Schematic illustration of the formation mechanism of Cu2O in the presence of [C8mim][BF4]. be seen that under 2 h irradiation, degradation efficiency of c with flowerlike Cu2O is up to 87%, while no observable degradation takes place by using irregular Cu O microcrys- 3.5 Photocatalytic activity of flowerlike Cu O micro- 2 2 tal. In addition, Cu O film has been prepared by Xu and his nanocrystals 2 co-workers [32] using a potentiostatic method, and only less To study the morphology effect on photocatalytic activity, than 5% methylene blue can be degraded after 150 min so-

Figure 9 The UV-vis spectra and photodegradation efficiency of methylene blue in the presence of flowerlike or irregular microcrystal Cu2O as a function of reaction time: (a) UV-vis spectra of methylene blue in the presence of Cu2O irregular microcrystal; (b) UV-vis spectra of methylene blue in the presence of flowerlike Cu2O; (c) photodegradation efficiency of methylene blue in the presence of Cu2O irregular microcrystal; (d) photodegradation efficiency of methylene blue in the presence of flowerlike Cu2O. Zhao Y, et al. Sci China Chem August (2012) Vol.55 No.8 1585 lar irradiation in the presence of this thin film. This indi- 2006, 110(42): 20801–20807 cates that our flowerlike Cu O micro-nanocrystals have 9 Ebbesen TW, Ajayan PM. Large-scale synthesis of carbon nanotubes. 2 Nature, 1992, 358(16): 220–222 much stronger photocatalytic activity than the Cu2O film 10 Wang D, Mo M, Yu D, Xu L, Li F, Qian Y. Large-scale growth and mainly due to their small size effect. After the visible light shape evolution of Cu2O cubes. Cryst Growth Des, 2003, 3(5): irradiation, Cu2O produces electrons and holes, a large 717–720 11 Teo JJ, Chang Y, Zeng HC. Fabrications of hollow nanocubes of number of electrons is distributed on the Cu2O (111) facet, Cu2O and Cu via reductive self-assembly of CuO nanocrystals. whereas the holes are concentrated on Cu2O (100) and (110) Langmuir, 2006, 22(17): 7369–7377 facets. Because the Cu2O has a strong adsorption capacity 12 Chang Y, Teo JJ, Zeng HC. Formation of colloidal CuO nanocrystal- for oxygen molecules, the electrons adsorbed on the facets lites and their spherical aggregation and reductive transformation to  hollow Cu O nanospheres. Langmuir, 2005, 21(3): 1074–1079 may be scavenged by O2 to yield O2 which reacts with H2O 2 13 Zhang HW, Zhang X, Li HY, Qu ZK, Fan S, Ji MY. Hierarchical and electrons leading to H2O2 and ·OH [33]. This may be growth of Cu2O double tower-tip-like nanostructures in water/oil mi- the main reason for bleach of methylene blue solution. croemulsion. Cryst Growth Des, 2007, 7(4): 820–824 14 Huang, MH, Lin PH, Shape-controlled synthesis of polyhedral nano- crystals and their facet-dependent properties. Adv Funct Mater, 2012, 4 Conclusions 22(1): 14–24 15 (a) Petkovic M, Seddon KR, Rebelo LPN, Pereira CS. Ionic liquids: A pathway to environmental acceptability. Chem Soc Rev, 2011, The Cu2O nanoflowers have successfully been prepared by 40(3): 1383–1403; (b) Visser AE, Swatloski RP, Reichert WM, May- a [C8mim][BF4] assisted solvothermal reaction route. The ton R, Sheff S, Wierzbicki A, Davis JH, Rogers RD. Task-specific optimal morphology of Cu O was obtained at the molar ionic liquids for the extraction of metal ions from aqueous solutions. 2 Chem Commun, 2001, 1: 135–136 (c) Giernoth R. Task-specific ionic ratio 1:4 of Cu(CH3COO)2·H2O to the IL, the temperature of liquids. Angew Chem Int Ed, 2010, 49(16): 2834–2839 190 °C and the reaction time of 6 h. It is found that 16 Xu AR, Wang JJ, Wang HY. Effects of anionic structure and lithium [C8mim][BF4] acts as a structure-directing agent for the salts addition on the dissolution of cellulose in 1-butyl-3- methylimidazolium-based ionic liquid solvent systems. Green Chem, formation of flowerlike Cu2O micro-nanocrystals. Photo- 2010, 12: 268–275 catalytic experiments show that flowerlike Cu2O particles 17 Nakashima T, Kimizuka N. Interfacial synthesis of hollow TiO2 exhibit a high photocatalytic activity for the degradation of microspheres in ionic liquids. J Am Chem Soc, 2003, 125(21): methylene blue in aqueous solution under visible light irra- 6386–6387 diation. It is expected that the present method may be ex- 18 Kim KS, Demberelnyamba D, Lee H. Size-selective synthesis of gold tended to prepare similar micro-/nanostructures of other and platinum nanoparticles using novel thiol-functionalized ionic liq- uids. Langmuir, 2004, 20(3): 556–560 oxide materials. 19 Gelesky MA, Umpierre AP, Machado Giovanna, Correia RRB, Magno WC, Morais J, Ebeling G, Dupont J. Laser-induced fragmentation of transition metal nanoparticles in ionic liquids. J Am This work was supported financially by the National Natural Science Chem Soc. 2005, 127(13): 4588–4589 Foundation of China (21003039), the Innovation Scientists and Techni- 20 Dupont J, Fonseca GS, Umpierre AP, Fichtner PFP, Teixeira SR. cians Troop Construction Projects of Henan Province (092101510300), Transition-metal nanoparticles in imidazolium ionic liquids: and the Program for Science & Technology Innovation Talents in Univer- recycable catalysts for biphasic hydrogenation reactions. J Am Chem sities of Henan Province (2009HASTIT005). Soc, 2002, 124(16): 4228–4229 21 Scheeren CW, Machado G, Dupont J, Fichtner PFP. Texeira SR. Nanoscale Pt(0) particles prepared in imidazolium room temperature. 1 Burda C, Chen XB, Narayanan R, El-Sayed MA. Chemistry and Ionic liquids: Synthesis from an organometallic precursor, properties of nanocrystals of different shapes. Chem Rev, 2005, characterization, and catalytic properties in hydrogenation reactions 105(4): 1025–1102 Inorg Chem, 2003, 42(15): 4738–4742 2 Zhang H, Ren X, Cui ZL. Shape-controlled synthesis of Cu2O nanocrystals assisted by PVP and application as catalyst for synthesis 22 WangY, Yang H. Oleic acid as the capping agent in the synthesis of of carbon nanofibers. J Cryst Growth, 2007, 304: 206–210 noble metal nanoparticles in imidazolium-based ionic liquids. Chem 3 White B, Yin M, Hall A, Le D, Stolbov S, Rahman T, Turro N, Commun, 2006, 2545–2547 23 Zhao Y, Cui GR, Wang JJ, Fan MH. Effects of ionic liquids on the O'Brien S. 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Cu2O and CuO nanospheres: Preparation and applications for 24 ZhaoY, Chen ZH, Wang HY, Wang JJ. Crystallization control of sensitive gas sensors. Chem Mater, 2006, 18(4): 867–871 CaCO3 by ionic liquids in aqueous solution. Cryst Growth Des, 2009, 5 Poizot P, Laruelle S, Grugeon S, Dupont L, Taracon JM. 9(11): 4984–4986 Nano-sizedtransition-metaloxidesas negative-electrode materials for 25 Jiang Y, Zhu YJ. Microwave-assisted synthesis of sulfide M2S3 (M= lithium-ion batteries. Nature, 2000, 407(28): 496–499 Bi, Sb) nanorods using an ionic liquid. J Phys Chem B, 2005, 109(10): 6 Kuo CH, Huang MH. Fabrication of truncated rhombic dodecahedral 4361–4364

Cu2O nanocages and nanoframes by particle aggregation and acidic 26 Clare B, Sirwardana A, MacFarlane DR. Synthesis, purification and etching. J Am Chem Soc, 2008, 130(38): 12815–12820 characterization of ionic liquids. Ionic liquids: Topics in current 7 Cao Yb, Fan JM, Bai LY, Yuan FL, Chen YF. Morphology evolution chemistry, 2009, 290: 1–40 of Cu2O from octahedron to hollow structures. Cryst Growth Des, 27 (a) Wang HY, Wang JJ, Zhang SB. Binding gibbs energy of ionic 2010, 10(1): 232–236 liquids to calf thymus DNA: A fluorescence spectroscopy study. Phys 8 Bernard Ng CH, Fan, WY. Shape evolution of Cu2O nanostructures Chem Chem Phys, 2011, 13(9): 3906–3910 (b) Rebecca CV, Daniel via kinetic and thermodynamic controlled growth. J Phys Chem B, EF. Photoinduced electron-transfer reactions in two room-temper- 1586 Zhao Y, et al. Sci China Chem August (2012) Vol.55 No.8

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of the ionic liquids [C4mim][BF4], [C4mim][PF6], and [Cnmim]Br in 11(1): 129–133

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