Collision and Oxidation of Silver Nanoparticles on a Gold Nanoband Electrode

Transcription

1 Supporting Information for: Collision and Oxidation of Silver Nanoparticles on a Gold Nanoband Electrode Fan Zhang, Martin A. Edwards, Rui Hao, Henry S. White, * and Bo Zhang * Department of Chemistry, University of Washington, Seattle, WA United States Department of Chemistry, University of Utah, Salt Lake City, UT United States white@chem.utah.edu; zhangb@uw.edu Contents: S1. Summary of collision results for 66 and 40 nm Ag NPs S2. TEM characterization of Ag NPs S3. Description of lattice random walk simulations S4. SEM images of nanoband electrodes used for Ag NP collision S5. Potential dependent multi-peak analysis for 60, 110 nm nanoband electrodes and 12.7 µm ultramicroelectrode (UME) (using 66 nm Ag NPs) S6. Potential dependent multi-peak analysis for 60, 110 nm nanoband electrodes and 12.7 µm UME (using 40 nm Ag NPs) S7. Typical simulated i-t traces. S8. Histograms of peak number for oxidation of 40 nm Ag NPs on different electrodes. S9. Histograms of oxidation fraction during one collision event (40 nm Ag NPs on different electrodes) S1

2 S1. Summary of collision results of 66 and 40 nm Ag NPs Table S1. A summary of 66 nm Ag NPs collisions at different electrodes (Figure 2b) and potentials Electrode type Potential vs. Ag/AgCl QRE Total events number Detection frequency/min Single peak proportion Average subpeak number 60 nm band 0.6 V % V % V % nm band 0.6 V % V % V % nm band 0.6 V % V % V % µm UME 0.6 V % V % V % 3.1 Table S2. A summary of 40 nm Ag NPs collisions at different electrodes (Figure 2b) and potentials Electrode type Potential vs. Ag/AgCl QRE Total events number Detection frequency/min Single peak proportion Average subpeak number 60 nm band 0.6 V % V % V % nm band 0.6 V % V % V % nm band 0.6 V % V % V % µm UME 0.6 V % V % V % 2.8 S2

3 S2. TEM Characterization of Ag NPs Figure S1. Example TEM image (a) and size distribution (b) of the 66 nm citrate-capped Ag NPs used in NP collision experiments. (a) (b) The 66 nm Ag NPs prepared in-house were characterized by imaging with transmission electron microscopy (TEM). Ag NPs were drop-cast onto a carbon-coated Formvar copper TEM grid (Ted Pella) and imaged with an FEI Tecnai G2 F20 TEM operating at 200 kv (Figure S1a). NP sizes were measured using ImageJ. The histogram of the NP size distribution and corresponding Gaussian fit were created using Origin 8.5 (OriginLab) (Figure S1b). The particles were approximately spherical with an average diameter of 66 ± 15 nm. Using this size and the amount of Ag ions used in the synthesis, an upper limit for the particle concentration in the stock solution was calculated to be NPs/mL. S3

4 S3. Description of lattice random walk simulations Lattice random walk simulations were performed in a similar manner to those previously described in Ref 30. The particle position is updated at discrete times, step length δt, and are moved a discrete distance, δx, in each of the three Cartesian directions. These steps are uniquely defined by the particle size (diffusion coefficient) via the Stokes-Einstein equation, and mass via the kinetic (thermal) energy/velocity of the particle, and the mean squared displacement. The resultant expressions are derived as following. δx= (S1) δt= (S2) where ρ Ag = kg m -3 is the density of silver, r is the radius of the particle, which is updated throughout the simulations (vide infra), k B the Boltzmann constant, T = 293 K the absolute temperature and η = mpa s the dynamic viscosity of water. We calculate the charge passed during each collision with the electrode, Q, as the product of the surface area of the spherical particle (4πr 2 ), the duration of the collision (taken to be the time step, δt) and the only fitting parameter in all the simulations, the current density, J Q =J 4πr δt The charge passed was converted to a volume of silver through Faraday s law and ρ Ag, and the radius of the sphere adjusted. The value of δx and δt were then recalculated for the new particle size through equations S1 and S2. To allow comparison with the experimental data, the current passed was filtered and sampled as in the experiments. In a deviation from our previous works (Ref 30), to increase computational efficiency, when the particle was far from the surface we updated the position by multiples of δt by sampling from the binomial distribution. The number of steps taken was less than the distance to the surface (measured in multiples of δx) ensuring we did not miss any collisions. This is mathematically equivalent to our previous simulations, but affords a speed-up of several orders of magnitude. Lattice random walk simulations, filtering and analysis of the number of peaks were all performed in Matlab (version 2017a) and using the parallel computing toolbox to simulate trajectories of multiple particles in parallel. (S3) S4

5 S4. SEM images of nanoband electrodes used for Ag NP collision. Figure S2. SEM images of a 60 nm (a) and 180 nm gold nanoband electrodes (b). (a) (b) S5

6 S5. Potential dependent multi-peak analysis for all electrodes except for the 180 nm nanoband (66 nm Ag NPs) Figure S3. Analysis of the first four sub-peaks for 25 randomly selected multi-peak events recorded at different electrodes. (1) 60 nm nanoband. (2) 110 nm nanoband. (3) 12.7 µm UME. For each electrode, mean peak area, height, half width, and interpeak spacing are shown sequentially. Solid shapes represent single-peak values at different potentials. Conditions: 40 pm Ag NPs (66 nm diameter), 7 mm trisodium citrate, 18 mm potassium nitrate. Note, an equivalent figure for the 180 nm band electrode is shown in Figure 5 in the main text. 60 nm 110 nm (1) (2) 12.7 µm (3) S6

7 S6. Potential dependent multi-peak analysis for all electrodes except for 180 nm nanoband (40 nm Ag NPs) Figure S4. Analysis of the first four sub-peaks for 25 randomly selected multi-peak events recorded at different detection electrodes. (1) 60 nm nanoband. (2) 110 nm nanoband. (3) 12.7 µm UME. For each electrode, mean peak area, height, half width, and inter-peak spacing are shown sequentially. Solid shapes represent single-peak values at different potentials. Conditions: 30 pm Ag NPs (40 nm diameter), 7 mm trisodium citrate, 18 mm potassium nitrate. Note, an equivalent figure for the 180 nm band electrode is shown in Figure 6 in the main text. 60 nm 110 nm (1) (2) 12.7 µm (3) S7

8 S7. Typical simulated i-t traces Figure S5. Typical simulated i-t traces for the collision of 66 nm NPs with a 60 nm band electrode at 0.6 V. (a) and (b) single peak. (c) and (d) multi-peaks. The current density was set at 500 A/cm 2. S8

9 S8. Histograms of peak number for oxidation of 40 nm Ag NPs on different electrodes Figure S6. Histograms of peak number for oxidation of 40 nm Ag NPs on different electrodes at 0.6 V. (a) 60 nm nanoband. (b) 110 nm nanoband. (c) 180 nm nanoband. (d) 12.7 µm UME. Only values from 1 to 10 are shown. S9

10 S9. Histograms of oxidation fraction during one collision event(40 nm Ag NPs on different electrodes). Figure S7. Histograms of oxidation fraction during one collision event (40 nm Ag NPs on different electrodes at 0.6 V). (a) 60 nm nanoband. (b) 110 nm nanoband. (c) 180 nm nanoband. (d) 12.7 µm UME. S10