Download High Speed Water Sterilization using One Dimensional

Supplementary Information for
High Speed Water Sterilization using One
Dimensional Nanostructures
David T. Schoen1†, Alia P. Schoen1†, Liangbing Hu1, Han Sun Kim1, Sarah C. Heilshorn1, Yi
Cui1*
1
Department of Materials Science and Engineering, Stanford University, Stanford, California
94305, USA.†These authors contributed equally to this work.
Supplementary Figures
Supplementary Figure 1 a) Performance of the device over time. Two separate flow
experiments in identical conditions, with a 1 L/hr flow rate and initial E. coli density of 107/mL
were carried out, and samples of solution were taken every 15 seconds. 100 µL of 1000 times
diluted solution was plated onto an agar plate and compared to growth of solution not treated.
Points represent average values taken for 50 mL aliquots, error bars show 1 standard deviation
for each set. It can be seen that the performance of the device appears to improve over time, at
least for the time scale represented here, about 5 minutes. b) Performance of the device for
several different initial concentrations of E. coli., from 107 to 104. For each experiment 100 mL
of bacteria solution was prepared by serial dilution from a 107/mL stock solution. For each
experiment 2 plates were prepared, one of treated and the other of untreated solution and the %
inactivation was determined. The device shows similar performance over many orders of
magnitude, indicating that serial treatment of solution should enable low overall bacteria
concentrations to be reached.
Supplementary Figure 2 Performance of the device with different filtration path lengths and 4
different materials, cotton with AgNWs and CNTs in blue, cotton with AgNWs only in red,
cotton with CNTs only in green, and cotton alone in purple. By far the best performance was
observed for the AgNW/CNT blend, which beat the other devices ultimate performance within
one treatment stage and reached >98% killing after three stages, however both CNT only and
AgNW only devices also work to a lesser degree. Each point represents average inactivation
efficiency for 3 1 mL samples taken during the same experiment, and error bars indicate 1
standard deviation in each direction. The cotton only curve dips below 0 because relatively large
variations in plated cell densities for the highly concentrated plates yielded an average cell
density for the first stage higher than that of the untreated samples.
Supplementary Methods
The simulation in Figure 4 was carried out using the COMSOL Multiphysics Finite Element
software package, using the Nernst-Planck, time dependant application mode in the Chemical
Engineering module. This application mode solves the combined transport equations.
Simulation of the anodic production of oxygen and chlorine at the nanowire surface was
simulated for cases with and without flow. For the case without flow, a rectangular zone 2 cm
tall and 20 µm wide and 20 µm thick was modeled, with a 4 µm long and 60 nm wide and 60 nm
thick NW placed on the bottom edge with its long axis aligned with the model’s long axis. The
long edges of the model were set to 0 ion flux for the 3 modeled ions, Na+, Cl- and H+ equivalent
to applying a symmetric boundary condition. The bottom edge, including the NW surface, was
allowed to react with the ions according to two equations. Current equations for O2 evolution,
and Cl2 evolution follow.
  F * (V − E 0 ) 
 F * (V − E O0 ) 
CH +
O2
2
?? jO2 = kO2  exp−
exp
−

C
2RT
2RT
+





H ,bulk
 C −
 F * (V − E Cl0 ) 
 F * (V − ECl0 ) 
2
2
jCl2 = kCl2  Cl exp−
 − exp

C
2RT
2RT
−




 Cl ,bulk
The flux of H+ ions at this surface is, and Cl- ions . At the top surface concentrations for Na+
and Cl- ions was fixed at 1 mM, and H+ at 10-7 M. The voltage of the top surface was linearly
ramped up to the desired voltage, 20 V, over the course of 1 minute, easing the calculation
difficulty at each incremental time step.
For the situation in which flow is simulated, the conditions were similar to that of the static case,
except that the modeled area is now a 0.6 cm long rectangle, with a single NW of 60 nm circular
cross section in the center, with the NW long axis perpendicular to the simulated plane. The NW
surface has the same boundary conditions as in the static simulation, and the top and bottom
surfaces are now set to the zero flux condition. A flow rate of 1 L/hr is imposed in the +x
direction on all 3 simulated ionic species. The left edge of the simulation is now set to have zero
current and allow only convective flux, while the right edge concentrations for Na+ and Cl- ions
was fixed at 1 mM, and H+ at 10-7 M and the voltage was similarly linearly raised over 60
seconds to 20 V.
Supplementary Tables
Name: Symbol
Sodium Ion Diffusivity
Chlorine Ion Diffusivity
Hydrogen Ion Diffusivity
Equilibrium Potential: E O0 2
Value
1.33*10-9 m2/s
9.31*10-9 m2/s
2.03*10-9 m2/s
1.23 V
1.36 V
Equilibrium Potential: ECl0 2
Exchange Current Density: 1*10-6 A/m2
kO2
Exchange Current
10 A/m2
Density: kCl2
Supplementary Table 1 Values of various materials properties and reaction constants used in
the finite element simulation.