J. Wagner, J.M. Köhler. Continuous synthesis of gold nanoparticles in a microreactor

Transcription

1 Supporting Information. J. Wagner, J.M. Köhler Continuous synthesis of gold nanoparticles in a microreactor FG Physikalische Chemie / Mikroreaktionstechnik, Institut für Physik, TU Ilmenau Weimarer Str. 32, Ilmenau, Germany Phone: +49 (0) 3677/ , Fax: +49 (0) 3677/ joerg.wagner@tu-ilmenau.de S 1. Experimental S 1.1. Materials Chloroauric acid trihydrate (Roth, Germany), ascorbic acid (Merck, Germany), polyvinyl pyrrolidone (polyvidone, PVP) (Merck, Germany), potassium hydroxide (Merck, Germany), ethanol (Merck, Germany), methanol (Merck, Germany), 2-propanol (Aldrich, Germany), acetic acid (Merck, Germany), trichloro(1h,1h,2h,2h-perfluoro-octyl)silane (TCPFOS, Aldrich, Germany) were used as received. Deionised ultra-pure water (Aqua purificator G 7795, Miele, Germany) was used for all preparations. The following buffers were used to achieve stable phvalues during the syntheses: carbonate buffer ph ~ 9.7 (50 ml 0.05 M NaHCO ml 0.1 M NaOH), phosphate buffer ph ~7.1 (10-fold stock solution: 0.20 g KCl, 0.20 g KH 2 PO 4, 0.92 g Na 2 HPO 4 in 1000 ml deionised water, ph adjusted with HCl). Without buffer the obtained colloidal solution showed a ph of ca. 2.8 after leaving the reactor, due to the acidic reaction of excess ascorbic acid. 1

2 S 1.2. Instrumentation After collection, the dispersions were immediately investigated via UV-Vis spectroscopy and differential centrifugal sedimentation (DCS), where at least two samples of each experiment where investigated to get an impression of the reproducibility. The DCS system (DCS 20000, CPS Instruments Inc., USA) yields directly the particle size distribution of the liquid sample. The morphology of the particles was investigated with a field-emission scanning electron microscope (JSM 6700F, JEOL, USA). For these studies the samples were prepared on thoroughly cleaned (subsequently: heptane, ethanol and water) silicon slides as follows: First a 2 µl drop of the aqueous dispersion was placed on a slide and dried in air. Subsequently the slides were rinsed with water to remove salt crystals and finally dried in a nitrogen stream. SEM images were stored as jpg-files and inverted for clarity reasons, before particles are measured using Motic Images Plus 2.0 software. Optical absorption spectra, of the undiluted dispersions were recorded using a two beam UV-Vis spectrometer (Specord 200, Analytik Jena AG, Germany). All experiments were performed in a clean room to avoid cross contamination and at room temperature, i.e. at 22 C, as controlled by air condition. S 1.3. Microsystem set-up Syringe pumps (SP210iw, World Precision Instruments Inc., USA or , TSE Technical & Equipment GmbH, Germany) equipped with polypropylene syringes ( Omnifix, Roth, Germany) were used for introducing the educt solutions into the microreactor. The microreactor (IPHT Jena, Germany), is designed as shown in Figure 1, and it is described in detail by Kirner et al. 1 It is a chip-shaped three layer assembly of wet etched pyrex glass and silicon, anodically bonded to each other. The dimensions of the chip are 22 mm x 14 mm, while the channel width varies between 178 and 700 µm, and the channel depth is 160 µm. 2

3 The reactor possesses eight split and recombine units, that are designed for an optimal reshaping of the cross section of stacked fluid column parts. The flow direction is changed from horizontally to vertically and vice versa at branching and reunification points, which facilitates an efficient interdiffusion, i.e. an effective mixing. There are two inlets (E1 and E2) and one outlet (A) while the total interior volume is about 8.5 µl. The reactor was connected to the syringes via flexible PTFE tubing (inner diameter: 0.3 mm) and educt solutions were pumped into the micromixer via inlet E1 and E2 at total flow rates between 500 and 8000 µl/min. The produced colloidal solutions left the reactor via outlet A (cf. Figure S1) and were collected in polypropylene centrifuge tubes. Fig. S1. Schematic drawing of the experimental set-up showing the connectivity of the IPHT microreactor ( STATMIX 6,area 22 x 14 mm) Reference: (1) Kirner, T.; Albert, J.; Gunther, M.; Mayer, G.; Reinhackel, K.; Köhler, J. M. Chemical Engineering Journal 2004, 101(1-3),

4 S 1.4. Microreactor surface treatment The first route to alter the properties of the reactor surfaces was simply to work at an elevated ph (~ 9.5). It leads to a negative net charge on this surface and thus to electrostatic repulsion with the negatively charged gold particles, as described in the paper. The alternative method was silanization of the surfaces using the following protocol: 1) rinse with methanol, 2) incubation with methanolic KOH for 45 h at 60 C, 3) drying at 80 C in vacuum, 4) 21 h incubation with 10 ml ethanol containing 10 µl acetic acid and 300 µl of TCPFOS, 5) incubation with methanol at 60 C for 15 min, 6) incubation with 2-propanol at 60 for 17 h, 7) drying at 100 C in vacuum. S 1.5. Synthetic procedures ( I ) influence of flowrate Chloroauric acid (1 mm, containing 0.05 % PVP), ascorbic acid (20 mm), total flowrates ranging from 500 to 8000 µl/min, no buffer (ph ~ 2.8) and carbonate buffer for syntheses at ph ~ 9.5, silanized and native reactor ( II ) influence of concentration ratio (reducing agent / Au 3+ ) Chloroauric acid (1 mm, containing 0.05 % PVP), ascorbic acid at varying concentrations between 1 and 20 mm, total flowrate 2000 µl/min, no buffer (ph ~ 2.8) ( III ) influence of ph Chloroauric acid (1 mm, containing % PVP), ascorbic acid (20 mm), total flowrate 2000 µl/min, ph was varied between 2.8 and 9.5, using buffer systems 4

5 ( IV ) influence of PVP concentration Chloroauric acid (1 mm, containing various amounts of PVP), ascorbic acid (20 mm), total flowrate 2000 µl/min, ph was adjusted to 9.5 using a carbonate buffer system ( V ) comparison to conventional laboratory equipment synthesis in a 25 ml beaker: 2 ml chloroauric acid (1 mm, containing 0.05 % PVP) and 2 ml ascorbic acid (20 mm) were stirred in a beaker, while ph was adjusted to 9.5 and 2.8, respectively synthesis in a 25 ml flask: 3 ml chloroauric acid (1 mm, containing 0.05 % PVP) and 3ml ascorbic acid (20 mm) were magnetically stirred in the flask, while ph was adjusted to 9.5 and 2.8, respectively 5

6 S 2. DCS analyses of the samples prepared in the beaker and flask, respectively: a) b) Size distribution characteristics of the gold particles obtained in a conventional beaker at (a) ph = 2.8 and (b) ph = 9.5 6

7 c) d) Size distribution characteristics of the gold particles obtained in a conventional flask at (c) ph = 2.8 and (d) ph = 9.5 (each graph corresponding to one experiment) 7