Electronic Supporting Informtion Colescence of Ag 2 S nd Au Nnocrystls t Room Temperture Jingln Qu, Hui Liu, Yifeng Wei, Xiofeng Wu, Renling Yue, Yunf Chen* nd Jun Yng*, Institute of Process Engineering, Chinese Acdemy of Sciences, Beijing, Chin 100190 Institute of Bioengineering nd Nnotechnology, 31 Biopolis Wy, The Nnos, Singpore 138669 Emil: yfchen@mil.ipe.c.cn (YC); jyng@mil.ipe.c.cn (JY) We re grteful to Prof. Jim Yng Lee (Ntionl University of Singpore) for the use of the XPS fcilities. This work ws supported y IBN (Biomedicl Reserch Council, Agency for Science, Technology nd Reserch, Singpore). Prt of the chrcteriztions, which were supported y 100 Tlents Progrm of The Chinese Acdemy of Sciences, nd the mnuscript were completed t Institute of Process Engineering, Chinese Acdemy of Sciences. S1
Experimentl Procedures 1. Generl mterils The chemicl regents, including silver nitrte (AgNO 3, 99%), hydrogen tetrchlorourte(iii) trihydrte (HAuCl 4 3H 2 O, 99.9%), hexchloropltinic cid hexhydrte (H 2 PtCl 6 6H 2 O, ACS regent, 37.50% Pt sis ), element sulfur ( 99.5%), sodium orohydride (NBH 4, 98%), sodium citrte dehydrte ( 99%), dodecylmine (DDA, 98%), cdmium oxide (CdO, 99%), octdecylphosphonic cid (ODPA, 97%), oleylmine (OLA, technicl grde, 70%), Se powder ( 99%), cetone (98%), nd Nifion 117 solution (5% in mixture of lower liphtic lcohols nd wter) from Sigm-Aldrich, ethnol (ACS regent, 99.5%), methnol (RegentPlus, 99%), nd toluene (ACS regent, 99.5%) from Merck, is(p-sulfontophenyl) phenylphosphne dihydrte dipotssium slt (BSPP, 97%) from Strem Chemicls, queous HClO 4 solution (ACS regent, 70%), nd Vulcn XC-72 cron powders (BET surfce re of 250 m 2 g -1 nd verge prticle size of 40 ~ 50 nm) from Cot, were used s received. All glsswre nd Teflon-coted mgnetic stirring rs were clened with qu regi, followed y copious rinsing with de-ionized wter efore drying in n oven. 2. Phse trnsfer of nole metl ions from wter to toluene In typicl experiment, 50 ml of 1 mm of queous metl slt solution (AgNO 3 or HAuCl 4 ) ws mixed with 50 ml of ethnol contining 1 ml of dodecylmine. After 3 min of stirring, 50 ml of toluene ws dded, nd stirred for nother minute. Phse trnsfer of metl ions from wter to toluene occurred rpidly nd completely, s illustrted y the complete leching of the color in the queous phse. Assuming complete trnsfer of the ions from wter, the metl ion concentrtion in toluene ws 1 mm. The metl ions in toluene were seprted from the queous phse, nd kept for further experiments. 3. Synthesis of Ag 2 S nnocrystls 7.5 mg of elementl sulfur ws dded to 50 ml of toluene solution of Ag I ions in 100 ml flt-ottomed flsk. The mixture ws stirred for 3 h t room temperture. The solution turned from colorless to drk rown, indicting the formtion of Ag 2 S S2
nnocrystls. TEM ndhrtem imges ofs-prepred Ag 2 S nnocrystls were shown in Fig. S1 nd. 4. Synthesis of Au nnocrystls of different sizes Approximtely 13 nm Au nnocrystls were prepred y the citrte reduction of HAuCl 4. An queous solution of HAuCl 4 (1 mm, 20 ml) ws refluxed t 110 C with stirring in n oil th. 0.8 ml of 100 mm queous sodium citrte solution ws dded quickly, which resulted in series of color chnges efore finlly rriving t wine red solution. The mixture ws refluxed for nother 15 min nd llowed to cool to room temperture. The smller 5 nm citrte-protected Au nnocrystls were prepred y different procedure. Briefly, 20 ml of 1 mm queous solution of HAuCl 4 ws mixed with 0.8 ml of 100 mm queous sodium citrte solution used s stilizer. 0.6 ml of 100 mm queous solution of NBH 4 ws then dded dropwise under vigorous stirring, giving rise to red Au hydrosol. The Au hydrosol ws only used fter ging for 24 h to decompose residul NBH 4. 5. Phse trnsfer of Au nnoprticles of different sizes Au nnocrystls of 5 nm in dimeter were trnsferred from wter to toluene following the pproch used for the phse trnsfer of Ag I ions. Typiclly, the citrteprotected Au hydrosol ws mixed with 20 ml of ethnol contining 0.4 ml of dodecylmine. After 3 min of stirring, 20 ml of toluene were dded nd stirred for nother minute to extrct the Au nnocrystls. The TEM nd HRTEM imges of 5 nm Au nnoprticles fter phse trnsfer were shown in Fig. S1c nd d. For the phse trnsfer of Au nnocrystls lrger thn 10 nm, 50 mg of solid BSPP were dded to the Au hydrosol, nd the mixture ws ged for 30 min. Next, Au nnocrystls were trnsferred from wter to toluene following the pproch used for the phse trnsfer of Ag I nd Au III ions. Typiclly, the BSPP-stilized Au hydrosol ws mixed with 20 ml of ethnol contining 0.4 ml of dodecylmine. After 3 min of stirring, 20 ml of toluene were dded nd stirred for nother minute. The TEM nd HRTEM imges of 13 nm Au nnocrystls fter phse trnsfer were shown in Fig. S1e nd f. 6. Synthesis of core-shell CdSe@CdS QDs In totl, 26 mg of CdO (0.2 mmol), 130 mg of ODPA (0.4 mmol), nd 5 ml of S3
OLA were heted to 300 C under Ar flow until the rectnts were completely dissolved, nd then the solution ws cooled to 240 C. The Se solution ws prepred y dissolving 4 mg of Se powder (0.05 mmol) nd 2 mg of NBH 4 (0.05 mmol) in 2 ml of OLA. It ws injected into the rection mixture with rpid stirring. Next, the temperture for the rection system ws reduced to 220 C right wy, where the mixture ws kept for 1 min. The S solution ws prepred y dissolving 1.5 mg of elementl sulfur (0.05 mmol) in 2 ml of OLA. It ws injected into the rection mixture dropwise with rpid stirring. The mixture ws heted t 220 C for nother 5 min nd then cooled to room temperture. The resulting CdSe@CdS nnocrystls were precipitted, wshed twice using cetone, nd re-dispersed in 50 ml of chloroform (to otin nominl CdSe concentrtion of 1 mm). 7. Synthesis of QD-Au hyrids For the preprtion of QD-Au hyrids, 20 ml of core-shell CdSe@CdS QDs in toluene ws mixed with 20 ml of Au III ions in toluene. The mixture ws ged for 1 h to complete the rection. Additionl reducing gent ws not required; dodecylmine could reduce Au III ions in toluene effectively in the presence of CdSe@CdS QDs. 8. Synthesis nd phse trnsfer of lloy Au-Pt nnoprticles For the synthesis of lloy Au-Pt nnoprticles with verge size of 3 nm in dimeter, 10 ml of 1 mm queous HAuCl 4 solution nd 10 ml of 1 mm queous H 2 PtCl 6 solution were mixed together. Then 0.8 ml of 100 mm queous solution of sodium citrte ws dded. Susequently, under vigorous stirring, 0.6 ml of 100 mm queous NBH 4 solution ws dded dropwise. The lloy Au-Pt hydrosol ws only used fter ging for 24 h to decompose residul NBH 4. The phse trnsfer of lloy Au-Pt nnoprticles followed the pproch used for the trnsfer of 5 nm Au nnocrystls. The citrte-protected Au-Pt hydrosol ws mixed with 20 ml of ethnol contining 0.4 ml of dodecylmine. After 3 min of stirring, 20 ml of toluene ws dded nd stirred for nother minute to extrct the lloy Au-Pt nnoprticles, leving ehind colorless queous solution. 9. Colescence etween Au nd Ag 2 S nnocrystls Ag 2 S nnocrystls in 10 ml of toluene were physiclly mixed with Au nnocrystls of different sizes in 10 ml of toluene t room temperture. TEM ws S4
pplied to detect the colescence process etween Au nd Ag 2 S nnocrystls t different times. 10. Removl of Au from QD-Au hyrids using the colescence etween Au nd Ag 2 S nnocrystls For the removl of Au from QD-Au hyrids using Ag 2 S nnocrystls, 10 ml of CdSe@CdS-Au hyrid orgnosol in toluene ws mixed with 10 ml of Ag 2 S orgnosol in toluene. The mixture ws ged for 48 h for completing the trnsfer of Au from QD-Au hyrids to the surfce of Ag 2 S nnocrystls. TEM nd HAADF-STEM were dopted to determine the trnsfer of Au. EDX nlysis under STEM mode ws used to confirm the chemicl components of different prticles in the orgnosol. 11. Extrction of Au from lloy Au-Pt nnoprticles using the colescence etween Au nd Ag 2 S nnocrystls 10 ml of lloy Au-Pt orgnosol in toluene ws mixed with 10 ml of Ag 2 S orgnosol in toluene nd the mixture ws ged for 24 h for completing the extrction of Au from lloy Au-Pt nnoprticles y Ag 2 S. EDX nlysis under STEM mode ws used to confirm the chemicl components in lloy Au-Pt nnoprticles efore nd fter Ag 2 S tretment nd heterodimers formed during the process. 12. Chrcteriztions of the nnocrystls Trnsmission electron microscopy (TEM) ws performed on FEI Tecni G 2 F20 electron microscope operted t 200 kv with the softwre pckge for utomted electron tomogrphy. For TEM mesurements, drop of the nnocrystl solution ws dispensed onto 3-mm cron-coted copper grid. Excess solution ws removed y n sorent pper, nd the smple ws dried under vcuum t room temperture. The verge prticle size nd prticle size distriution were otined from few rndomly chosen res in the TEM imge contining ~200 nnocrystls ech. An energy-dispersive X-ry spectroscopy (EDX) nlyzer ttched to the FEI Tecni G 2 F20 TEM operting in the scnning trnsmission electron microscopy (STEM) mode ws used to nlyze the components of different prticles. The electron em ws only 0.7 nm in dimeter, cple of providing high-resolution nlysis. S5
Powder X-ry diffrction (XRD) ptterns were recorded on Rigku D/Mx-3B diffrctometer, using Cu K α rdition (λ=1.54056 Å). X -ry photoelectron spectr (XPS) nlyses were conducted on n ESCALAB MKII spectrometer (VG Scientific) using Al-K α rdition (1486.71 ev). Smples for XRD nd XPS were concentrted from the toluene solution of different nnocrystls to 0.5 ml using flowing Ar. 10 ml of methnol were then dded to precipitte the nnocrystls, which were recovered y centrifugtion, nd wshed with methnol severl times. They were then dried t room temperture in vcuum. The emission spectr of ll smples were otined with Join Yvon Hori Fluorolog fluorescence spectrometer t n excittion wvelength of 362 nm. 13. Electrochemicl mesurements Electrochemicl mesurements were crried out in stndrd three-electrode cell, which ws connected to PGSTAT 30 potentiostt. A lek-free Ag/AgCl (sturted with KCl) electrode ws used s the reference. The counter electrode ws pltinum mesh (1 1 cm 2 ) ttched to pltinum wire. 13.1 Loding of lloy Au-Pt nnoprticles efore nd fter Ag 2 S tretment on cron support For the loding of the ctlysts on Vulcn XC-72 cron support, 9 mg of cron powders ws introduced into 10 ml of originl lloy Au-Pt orgnosol in toluene nd 10 ml of lloy Au-Pt orgnosol treted y Ag 2 S, respectively. After 24 hours stirring of the mixtures, the lloy Au-Pt/C (~10 wt% Pt on cron support) prticles efore nd fter treted y Ag 2 S were collected using centrifugtion nd wshed 3 times with methnol. They were then dried t room temperture in vcuum. 13.2 Preprtion of working electrode A thin lyer of Nfion-impregnted ctlyst cst on vitreous cron disk ws used s the working electrode. The preprtion of the ctlyst ink followed typicl procedure in the literture with modifiction. 1 The lloy Au-Pt/C efore nd fter Ag 2 S tretment ws ultrsoniclly dispersed in 10 ml of queous solution contining 4 ml of ethnol nd 0.1 ml of the Nfion solution. A clculted volume of the ink S6
ws dispensed onto the 5 mm glssy cron disk electrode to produce nominl ctlyst loding of 20 µg cm -2 (Pt se). The cron electrode ws then dried in strem of wrm ir t 70ºC for 1 hour. 13.3 Methnol oxidtion rection (MOR) The ctlyst performnce in room temperture methnol oxidtion rection (MOR) ws evluted y cyclic voltmmetry. The potentil window from 0 V to 1 V ws scnned t 20 mv s -1 until stle response ws otined efore the voltmmogrms were recorded. The electrolyte ws 1 M methnol in 0.1 M perchloric cid. For ech ctlyst (originl lloy Au-Pt nd lloy Au-Pt treted y Ag 2 S), the current densities were normlized in reference to the geometric re of the glssy cron electrode. 13.4 Oxygen reduction rection (ORR) The ctlyst performnce in room temperture oxygen reduction rection (ORR) ws evluted in 0.1 M HClO 4 electrolyte solution using glss cron rotting disk electrode (RDE) t rottion rte of 1600 rpm. Negtive-going liner sweep voltmmogrms were recorded from 1 to 0 V t 20 mv s -1 t room temperture in the presence of uling ultr-pure oxygen to mintin sturted oxygen tmosphere ner the working electrode. For ech ctlyst (originl lloy Au-Pt nd lloy Au-Pt treted y Ag 2 S), the current densities were lso normlized in reference to the geometric re of the glssy cron electrode. References 1. H. A. Gsteiger, S. S. Koch, B. Somplli nd F. T. Wgner, Appl. Ctl. B, 2005, 56, 9. S7
Tle S1 Electrochemicl mesurements of methnol oxidtion on lloy Au-Pt nnoprticles efore nd fter Ag 2 S tretment. The dt were otined from Fig. S9. Mterils Forwrd scn Forwrd scn pek Bckwrd scn Bckwrd scn pek pek potentil current density pek potentil current density (V) (ma cm -2 ) (V) (ma cm -2 ) Au-Pt 0.74 45.8 0.53 39.4 Au-Pt treted y Ag 2 S 0.70 62.1 0.46 47.9 (mv) Tle S2 Comprison of the ctlytic ctivity of lloy Au-Pt nnoprticles efore nd fter Ag 2 S tretment for the reduction of O 2 t room temperture. The dt were otined from Fig. S9. Mterils Hlf-wve potentil t 1600 rpm Kinetic current density t hlfwve potentil (ma cm -2 ) Au-Pt 462-1.88 Au-Pt treted y Ag 2 S 409-0.89 S8
10 nm 2 nm c d 10 nm 2 nm e f 10 nm 2 nm Fig. S1 ) TEM nd ) HRTEM imges Ag 2 S nnocrystls with verge size of ~15 nm in dimeter, respectively; c) TEM nd d) HRTEM imges of Au nnocrystls with verge size of ~5 nm in dimeter, respectively; e) TEM nd f) HRTEM imge of Au nnocrystls with verge size of ~13 nm in dimeter, respectively. 10 nm 5 nm Fig. S2 Lrge re TEM imge () nd HRTEM imge () of the physicl mixture of Au nd Ag 2 S nnocrystls tke t initil stge. S9
c d 10 nm 10 nm 10 nm 2 nm Fig. S3 c) TEM imges of the physicl mixture of Ag 2 S nd 5 nm Au nnocrystls tken t 0 h, 5 h, nd 10 h, respectively; d) HRTEM imge of single Ag 2 S-Au heterodimer. 10 nm 2 nm c d 10 nm 2 nm Fig. S4 ) TEM nd ) HRTEM imges of core-shell CdSe@CdS QDs, respectively; c) TEM nd d) HRTEM imges of CdSe@CdS-Au hyrids, respectively. S10
10 nm 20 nm c d Fig. S5 ) Lrge-re TEM imge of the mixture of Ag 2 S nnocrystls nd QD-Au hyrids t initil time; ) STEM imge of the mixture of Ag 2 S nnocrystls nd QD-Au hyrids t initil time; c) EDX spectrum of the prticle leled s 1 in STEM imge; d) EDX spectrum of the prticle leled s 2 in STEM imge. S11
10 nm 20 nm c d Energy (KeV) Fig. S6 ) Lrge-re TEM imge of the mixture of Ag 2 S nnocrystls nd QD-Au hyrids t 24 h; ) STEM imge of the mixture of Ag 2 S nnocrystls nd QD-Au hyrids t 24 h; c) EDX spectrum of the prticle leled s 1 in STEM imge; d) EDX spectrum of the prticle leled s 2 in STEM imge. S12
10 nm 20 nm c d Fig. S7 ) Lrge-re TEM imge of the mixture of Ag 2 S nnocrystls nd QD-Au hyrids t 48 h; ) STEM imge of the mixture of Ag 2 S nnocrystls nd QD-Au hyrids t 48 h; c) EDX spectrum of the prticle leled s 1 in STEM imge; d) EDX spectrum of the prticle leled s 2 in STEM imge. S13
10 nm 2 nm Intensity (.u.) Au reference Alloy Au-Pt Pt reference (111) (111) (200) (200) (220) (311) (222) 20 30 40 50 60 70 80 90 2θ / degree (220) (311) (222) Fig. S8 ) TEM imge, ) HRTEM imge, nd c) XRD pttern of lloy Au-Pt nnoprticles prepred y co-reduction of HAuCl 4 nd H 2 PtCl 6 using NBH 4 s reducing gent. c S14
10 nm 1 2 10 nm c d Energy (KeV) Fig. S9 ) Lrge-re TEM imge of Ag 2 S nnocrystls nd lloy Au-Pt nnoprticles t 24 h; ) STEM imge of the mixture of Ag 2 S nnocrystls nd lloy Au-Pt nnoprticles t 24 h; c) EDX spectrum of the prticle leled s 1 in STEM imge; d) EDX spectrum of the prticle leled s 2 in STEM imge. S15
70 56 Au-Pt treted y Ag 2 S Au-Pt 0 Au-Pt treted y Ag 2 S j / ma cm -2 42 28 14 j / ma cm -2-1 -2-3 Au-Pt 0-4 0.0 0.3 0.6 0.9 E / V vs Ag/AgCl 0.0 0.3 0.6 0.9 Fig. S10 Electrochemicl mesurements: ) Cyclic voltmmogrms of lloy Au-Pt nnoprticles efore nd fter Ag 2 S tretment in rgon-purged HClO 4 (0.1M) with methnol (1 M). Sweep rte: 20 mv s -1, room temperture; ) Polriztion curve for ORR over lloy Au-Pt nno-prticles efore nd fter Ag 2 S tretment in n O 2 -sturted HClO 4 solution (1 M). Sweep rte: 20 mv s -1, rotting speed: 1600 rpm, room temperture. S16