Selective growth of Au nanograins on specific positions (tips, edges. heterostructures.

Transcription

1 Selective growth of Au nanograins on specific positions (tips, edges and facets) of Cu 2 O octahedrons to form Cu 2 O-Au hierarchical heterostructures. Han Zhu b, MingLiang Du* a,b, DongLiang Yu b, Yin Wang c, MeiLing Zou b, CongSheng Xu b, YaQin Fu a,b a Key Laboratory of Advanced Textile Materials and Manufacturing Technology, Zhejiang Sci-Tech University, Ministry of Education, Hangzhou , P. R. China; Tel: ; du@zstu.edu.cn b Department of Materials Engineering, College of Materials and Textile, Zhejiang Sci-Tech University, Hangzhou , P. R. China c MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou , China

2 1. Materials Anhydrous copper () chloride (CuCl 2 ) and hydrazine hydrate (N 2 H 4 2H 2 O) were purchased from Aladdin Chemistry Co., Ltd. Chloroauric acid (HAuCl 4 4H 2 O, 99.9%) and hydrogen peroxide (H 2 O 2 ) were acquired from Shanghai Civi Chemical Technology Co., Ltd. Methylene blue was purchased from Tianjin Yongda Chemical Reagent Co., Ltd. Absolute ethyl alcohol was bought from Hangzhou Gaojing Fine Chemical Co., Ltd. All the chemicals were used as received without further purification. Deionized water was used for all solution preparations. 2.1 Synthesis of Various Morphologies of Cu 2 O Nanocrystal In the present work, g CuCl 2 2H 2 O was dissolved in 28 ml aqueous water. After complete dissolution, the mixture was then placed on magnetic blender with vigorous stirring at room temperature. Next, 1 ml of 1.0 M NaOH solution was added into the mixture and the resulting solution turned light blue immediately, indicating the formation of Cu(OH) 2 precipitate. After the complete formation of Cu(OH) 2 precipitate, 120 μl of N 2 H 4 2H 2 O were quickly injected in 3s into the beakers by pipette. The total solution volume of each beaker is 30 ml. The solutions of each beaker were kept at room temperature for 30 min and then centrifuged at 5000 rpm for 5 min. All the as-prepared Cu 2 O crystals were centrifuged at 5000 rpm for 5 min and washed for 4 times with 5 ml deionized water to remove the unreacted chemicals. The final washing step used 10 ml of ethanol, and the precipitate was dispersed in 4 ml ethanol for storage and the follow characterizations. 2.2 Synthesis of Cu 2 O-Au Hierarchical Heterostructures with Various Structures. The Cu 2 O-Au hierarchical heterostructures with various structures were synthesized by simply preparing a mixture of CuCl 2 2H 2 O, N 2 H 4 2H 2 O, NaOH and HAuCl 4. The octahedron Cu 2 O crystals were firstly dissolved in 30 ml deionized water, and then, 0.25, 0.5, 0.75 and 1mL of 1 mm HAuCl 4 aqueous solution were respectively added to samples labeled a, b, c, and d. The typical yellow color of the HAuCl 4 aqueous solution and the brick-red of Cu 2 O disappeared immediately. Instead, large amount of black product were formed. The product solutions were placed on magnetic blender at room temperature with vigorous stirring, aging for 3 h. All the as-prepared Cu 2 O-Au hierarchical heterostructures with various structures were centrifuged at 5000 rpm for 5 min and washed for 3 times with 5 ml deionized water to remove the unreacted chemicals. The final washing step used 10 ml of ethanol, and the precipitate was dispersed in 4 ml ethanol for storage and the follow analysis. 3. Charaterization 3.1 Transmission Electron Microscopy (TEM). The morphologies and structures of the octahedron Cu 2 O crystals and the as-prepared Cu 2 O-Au hierarchical heterostructures with various structures was observed using a JSM-2100 transmission electron microscopy (TEM, JEOL, Japan) at an accelerating voltage of 200 kv and a JSM-6700F field-emission scanning electron microscope (FE-SEM). Samples for FE-SEM were prepared by

3 casting a 5 μl of Cu 2 O-Au aqueous solution on silicon wafers, and dried at room temperature. TEM samples were prepared on ultra-thin carbon-coated copper grid and dried under infrared lamp for 5 minutes. The X-ray diffraction pattern (XRD) of Cu 2 O and Cu 2 O-Au hierarchical heterostructures were characterized with a SIEMENS Diffraktometer D5000 X-ray diffractometer using Cu Kα radiation source at 35 kv, with a scan rate of 0.02 o 2θ s -1 in the 2θ range of o. The XRD samples were prepared by casting the solution samples on a cm 2 glass substrate, and then dried under vacuum for overnight. 3.2 Photocatalytic mesurements For the photocatalysis measurement, 5 mg Cu 2 O and Cu 2 O-Au hierarchical heterostructures with various structures were completely dispersed into 30 ml of methylene blue (MB) aqueous solution (10-3 M). The samples were firstly magnetically stirred in the dark for 3 h to ensure absorption equilibrium of MB onto the surface of octahedron Cu 2 O and Cu 2 O-Au hierarchical heterostructures with various structures. A 25W fluorescent lamp (λ > 400 nm) was used as the light source, which was about 15 cm away from the samples. After given time intervals, 4 ml solution were taken out and centrifuged to remove the photocatalyst for the UV-Vis absorption measurement. The wavelength of maximum absorption and the absorbance of MB at different time intervals were collected by a Lambda 900 UV-vis spectrophotometer (Perkin Elmer, USA).

4 Scheme S1. Schematic illustration of the procedure used to synthesize octahedron Cu 2 O crystals and Cu 2 O-Au heterostructures with various mophologies. Products a. octahedron b. Au nanograins growth along the crystal edges of octahedron c. Au nanograins growth on the crystal faces of octahedron 0.1 M CuCl 2 1 ml ( M) 1.0 M NaOH 1 ml 1 M N 2 H μl H 2 O 20 ml 5 mm HAuCl 4 (aq) 0.25 ml 0.5 ml d. Cu 2 O-Au core-shell nanostructures 1 ml e. Au nanowhiskers 1.5 ml Table S1. Different products and their amount of all chemicals.

5 Electronic Supplementary Material (ESI) for Dalton Transactions Fig. S1. The average diameter of the Au nanograins (AuNGs) Image-Pro Plus 6.2 software was used to obtain the size distributions diagrams of AuNGs and the number of AuNGs is 200. Fig. S2. TEM image of the Cu2O-Au hierarchical architectures and the etching surfaces of the Cu2O octahedrons.

6 Fig. S3. The average length of the Au nanowhiskers (AuNWs). Image-Pro Plus 6.2 software was used to obtain the size distributions diagrams of AuNWs and the number of AuNWs is 200. Fig. S4. Low magnification FE-SEM and TEM images of Cu 2 O octahedron crystals.

7 Fig. S5. The average diameter of Cu 2 O octahedrons crystals Image-Pro Plus 6.2 software were used to obtain the size distributions diagrams of Cu 2 O octahedrons and the number of octahedrons is 200. Fig. S6. The UV-Vis spectrum of methylene blue solution.

8 Fig. S7. Absorbance of MB expressed as a reduction in the intensity of absorbance of 664 nm at different irradiation time with different photocatalysts: (a) H 2 O 2, (b) Cu 2 O octahedrons, AuNGs grown on Cu 2 O octahedrons with different volumes of HAuCl 4 (c) 0.25 ml, (d) 0.50 ml, (e) 0.75 ml and (f) 1.00 ml. Figure 8S (A) UV-Vis spectra of the (a) Cu 2 O octahedrons and (a) Cu 2 O octahedrons after photocatalysis and the Cu 2 O particles absorption bands maxima are both located at 543 nm. (B) UV-Vis spectra of (a) Cu 2 O-AuNWs heterostructures and (b) Cu 2 O-AuNWs heterostructures after photocatalysis and the Cu 2 O-AuNWs heterostructures absorption bands maxima are located at 545 and 574 nm.