Emission-Tunable Near-infrared Ag 2 S Quantum Dots

Transcription

1 Supporting Information for: Emission-Tunable Near-infrared Ag 2 S Quantum Dots Peng Jiang, Zhi-Quan Tian, Chun-Nan Zhu, Zhi-Ling Zhang and Dai-Wen Pang* Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of Education), College of Chemistry and Molecular Sciences, Research Center for Nanobiology and Nanomedicine (MOE 985 Innovative Platform), State Key Laboratory of Virology, and Wuhan Institute of Biotechnology, Wuhan University, Wuhan, , P. R. China * dwpang@whu.edu.cn Experimental section Materials Hexamethyldisilathiane ((TMS) 2 S, synthesis grade, Sigma Aldrich), oleic acid (OAc, 90%, Sigma Aldrich), myristic acid (MA, 98%, Alfa), 11-mercaptoundecanoic acid (MUA, 95%, Sigma Aldrich), 1-octylamine (OA, 99%, Alfa), trioctylphosphine (TOP, tech. 90%, Alfa), 1-octadecene (ODE, tech. 90%, ACROS), silver acetate, silver nitrate, toluene, anhydrous hexane, and anhydrous methanol, anhydrous ethanol, NaOH were purchased from China National Pharmaceutical Group Corporation. Synthesis of Ag 2 S nanocrystals Preparation of (TMS) 2 S precursor solution: In a glove box, 0.05 mmol of (TMS) 2 S was mixed with 1.5 ml of TOP in a 10 ml glass vial and then the mixture was transferred to a syringe. In a typical synthetic process, 1.6 mmol of MA, 2.4 mmol of OA and 5mL of ODE were added to a 25 ml 3-neck round-bottomed reaction flask. 0.1 mmol of silver acetate powder was also added to the flask under stirring. After purged with argon at 60 C for 30 min, the mixture was heated to 110 C under argon flow. When the silver acetate was completely dissolved, the (TMS) 2 S precursor in the syringe was injected swiftly into the page S1

2 reaction flask under vigorous stirring. After the injection, the temperature of the reaction solution was set at 90 C for the growth of Ag 2 S nanocrystals. Aliquots were taken at different time intervals, and UV-vis and PL spectra were recorded for each aliquot. After cooling down to RT, the as-prepared Ag 2 S nanocrystals were purified by washing with methanol and subsequent centrifuging. The precipitate of Ag 2 S nanocrystals were redispersed in n-hexane or toluene. Synthesis of larger sized Ag 2 S nanocrystals by a seed-mediated growth method Preparation of silver precursor solution: 0.67 mmol of silver nitrate and 10 mmol of OA were dissolved in toluene (0.1 M). Preparation of Sulfur precursor solution: 0.33 mmol of sulfur was dissolved in 10 ml of toluene (0.05 M). In this procedure, 2 mmol of OAc and 5 ml of toluene were added to a 50 ml 3-neck round-bottomed reaction flask. The 1.5 nm Ag 2 S nanocrystals dispersed in toluene synthesized above were all added to the flask under magnetically stirred. Under argon flow, 10 ml of silver precursor solution (0.1 M) and 10 ml of sulfur precursor solution (0.05 M) were synchronously added dropwise into the reaction flask via syringe pump at a rate of 0.5 ml/h. The purification process of the as-prepared Ag 2 S nanocrystals was similar with the process mentioned above. Ligand exchange of the Ag 2 S nanocrystals The Ag 2 S nanocrystals dispersed in 3 ml of hexane was transferred to a 25 ml flask, and then 0.2 mmol of MUA dissolved in 3 ml of ethanol was added to the flask under vigorous stirring. After stirring overnight, the mixture was dried via rotary evaporation process. Finally, the Ag 2 S nanocrystals were dispersed in NaOH solution. Characterizations JEM2010FEF (UHR) microscope with an acceleration voltage of 200 kv was used for transmission electron microscopy (TEM) imaging. The TEM samples were prepared by drying a hexane dispersion of the particles on copper grids coating with amorphous carbon film. The X-ray powder diffraction (XRD) patterns were obtained with Bruka D8 Advanced X-Ray diffractometer (Bruker axs) using Cu K-alpha radiation of wavelength page S2

3 Ǻ, and the scan rate was 0.5 degree/min. Energy-dispersive X-ray (EDX) data was obtained by using JEM 2010 FEF (UHR) microscope equipped with EDX spectrometry (EDAX Inc.). Quantitative elemental analyses were carried out with Genesis software. Fourier transform infrared (FTIR) spectrum was recorded on Thermo Scientific Nicolet is10 spectrometer. The PL decay data was obtained with FL-TCSPC fluorescence spectrophotometer (Horiba Jobin Yvon Inc., France) equipped with 370 nm and 460 nm light-emitting diode (LED) sources. Absorption spectra in the UV-visible region and the NIR region were recorded on UV-2550 and UV-3600 spectrophotometer (SHIMADZU) respectively. Photoluminescence (PL) and PL excitation (PLE) spectra were collected with the Fluorolog-3 fluorescence spectrophotometer (HORIBA JOVIN YVON INC.) equipped with photomultiplier tube (PMT) (less than 850 nm) and liquid nitrogen cooled InGaAs detector (between 800 nm to 1600 nm). page S3

4 Figure S1. Size distribution histograms of Ag 2 S nanocrystals synthesized in step one. page S4

5 Figure S2. Selected area electron diffraction (SAED) image of Ag 2 S nanocrystals synthesized in step one. page S5

6 Figure S3. Fourier transform infrared (FT-IR) spectrum of Ag 2 S nanocrystals synthesized in step one. The peaks located at 2924 cm -1 and 2853 cm -1 were assignable to symmetric and asymmetric stretching vibrations of C-H of myristic acid (MA) and 1-octylamine (OA). 1 The IR peak related to COO groups was located at 1460 cm -1, 2 this indicated that the MA existed on the surface of Ag 2 S nanocrystals. The broad peak between 1110 cm -1 to 1035 cm -1 was due to overlapping C-N stretching modes, 3 implying the existence of OA ligand. The peaks of 2026 cm -1 and 1262 cm -1 were assignable to Si-H and Si-CH 3 4, 5. page S6

7 Figure S4. Integrated fluorescence intensity vs. optical density (absorbance) of Ag 2 S nanocrystals (NCs) in hexane (A) and in H 2 O (B) and ICG in DMSO (C). page S7

8 Figure S5. PL decay for Ag 2 S nanocrystals dispersed in hexane (PL emission: 813 nm). page S8

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10 Figure S7. Size distribution histograms of Ag 2 S nanocrystals synthesized in step two. page S10

11 Figure S8. XRD patterns of the Ag 2 S nanocrystals synthesized in step two. page S11

12 Figure S9. EDX spectra of Ag 2 S nanocrystals synthesized in step two. page S12

13 Figure S10. (A) PL spectra and Photographs of Ag 2 S nanocrystals before and after transferred from hexane to water through ligand exchange; (B) PL intensities of Ag 2 S nanocrystal dispersed in water-phase after continuous illumination with mercury lamp. Reference 1. Zhao, X.; Cai, Y.; Wang, T.; Shi, Y.; Jiang, G., Preparation of Alkanethiolate-Functionalized Core/Shell Fe 3 O Nanoparticles and Its Interaction with Several Typical Target Molecules. Anal. Chem. 2008, 80, (23), Yu, W. W.; Wang, Y. A.; Peng, X. G., Formation and stability of size-, shape-, and structure-controlled CdTe nanocrystals: Ligand effects on monomers and nanocrystals. Chem. Mater. 2003, 15, (22), Cooper, J. K.; Franco, A. M.; Gul, S.; Corrado, C.; Zhang, J. Z., Characterization of Primary Amine Capped CdSe, ZnSe, and ZnS Quantum Dots by FT-IR: Determination of Surface Bonding Interaction and Identification of Selective Desorption. Langmuir 2011, 27, (13), Oh, T., Study on the correlation between dielectric constant and chemical shift in FTIR spectra of SiOC film by chemical vapor deposition after annealing. Phys. Status Solidi C 2010, 7, (2), Xiang-Ti, M., Two Si-H IR bands caused by vacancy-oxygen-hydrogen complexes in neutron transmutation doped. Semicond. Sci. Technol. 1989, 4, (10), 892. page S13