S1
Supporting Information
Novel synthesis pathways for highly oxidative iron species: Generation, stability,
and treatment applications of ferrate(IV/V/VI)
Sean T. McBeath,
#*
Yi Zhang,
#
Michael R. Hoffmann
#
Co-First Authors
Linde Laboratories, California Institute of Technology, Pasadena CA 91125, United States
#
S.T.M. and Y.Z. contributed equally to this paper.
*
Corresponding Author: smcbeath@umass.edu
Tables:
0
Figures:
35
Total Pages:
19
S2
S.1. Electrode Characterization
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0
2
4
6
8
10
12
14
16
Potential
, V
RHE
Current,
mA
Figure S1.
Cyclic voltammograms of BDD with OER potential at ~2.7 V
RHE
. CV condition: scan rate 50
mV s
-1
, 0.0 V vs. E
OC
to +3.0 V vs. ref.
S.2. Ferrate Generation
The ABTS indirect ferrate quantification method was chosen due its sensitivity in determining low
concentrations of Fe(VI). In a 50 mL erlenmyer flask, 5 mL of acetate buffer (pH=4.1), 1 mL of ABTS
reagent (1 g/L) and 9 mL of MilliQ water is added. New ABTS reagent solutions were made prior to each
electrolysis experiment and stored in the refrigerator at
4 ̊C
to avoid degradation due to increased
temperature and light exposure. A 0.5 mL ferrate sample was added to the Erlenmeyer flask, followed by
9.5 mL of phosphate buffer, to reach a final volume of 25 mL. This ABTS solution was then analyzed
using the spectrophotometer at 415 nm, a visible maxima for ABTS
•+
. Ferrate concentrations were
determined from experimental measurements as follows:
[
퐹푒
(
푉퐼
)
]
=
∆
퐴
415
푉
푓
휀푙
푉
푠
(1)
Where
ΔA
415
,
V
f
,
Ɛ
,
l
and
V
s
represent the UV-absorbance at 415 nm, the final sample volume, the
absorption coefficient as determined by the standards, the cell path length, and the volume of the ferrate
sample.
S3
0
2
4
6
8
10
12
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
Ferrate (mM)
Absorbance 415 nm
Figure S2.
Ferrate(VI) ABTS calibration curves using K
2
SO
4
(Element 26) in phosphate buffer (pH =
7.0), yielding a molar absorption coefficient of 0.043 mM
-1
cm
-1
.
0
20
40
60
80
100
0.000
0.020
0.040
0.060
0.080
0.100
0.120
0.140
0.160
0.180
10 mM FeCl3
30 mM NaCl
Electrolysis Time
, min
Absorbance (415nm)
, AU
Figure S3.
ABTS absorbance during BDD ferrate (5 mA cm
2
, 10 mM FeCl
3
) and control (5 mA cm
2
, 30
mM NaCl) experiments.
S4
0
20
40
60
80
100
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0.700
10 mM FeCl3
30 mM NaCl
Electrolysis Time
, min
Absorbance (415nm)
, AU
Figure S4.
ABTS absorbance during BDD ferrate (10 mA cm
2
, 10 mM FeCl
3
) and control (10 mA cm
2
,
30 mM NaCl) experiments.
0
20
40
60
80
100
0.000
0.200
0.400
0.600
0.800
1.000
1.200
1.400
1.600
1.800
2.000
10 mM FeCl3
30 mM NaCl (Control)
Electrolysis Time
, min
Absorbance (415nm)
, AU
Figure S5.
ABTS absorbance during BDD ferrate (20 mA cm
2
, 10 mM FeCl
3
) and control (20 mA cm
2
,
30 mM NaCl) experiments.
S5
0
20
40
60
80
100
0.000
0.010
0.020
0.030
0.040
0.050
0.060
0.070
0.080
0.090
0.100
10 mM FeCl3
30 mM NaCl
Electrolysis Time
, min
Absorbance (415nm)
, AU
Figure S6.
ABTS absorbance during NAT ferrate (5 mA cm
2
, 10 mM FeCl
3
) and control (5 mA cm
2
, 30
mM NaCl) experiments.
0
20
40
60
80
100
0.000
0.050
0.100
0.150
0.200
0.250
0.300
0.350
0.400
10 mM FeCl3
30 mM NaCl
Electrolysis Time
, min
Absorbance (415nm)
, AU
Figure S7.
ABTS absorbance during NAT ferrate (10 mA cm
2
, 10 mM FeCl
3
) and control (10 mA cm
2
,
30 mM NaCl) experiments.
S6
0
20
40
60
80
100
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0.700
10 mM FeCl3
30 mM NaCl (Control)
Electrolysis Time
, min
Absorbance (415nm)
, AU
Figure S8.
ABTS absorbance during NAT ferrate (20 mA cm
2
, 10 mM FeCl
3
) and control (20 mA cm
2
,
30 mM NaCl) experiments.
0
20
40
60
80
100
0.000
0.020
0.040
0.060
0.080
0.100
0.120
0.140
0.160
15 mM FeCl3
Electrolysis Time
, min
Absorbance (415nm)
, AU
Figure S9.
ABTS absorbance during NAT ferrate (5 mA cm
2
, 15 mM FeCl
3
) and control (5 mA cm
2
, 45
mM NaCl) experiments.
S7
0
20
40
60
80
100
0.000
0.050
0.100
0.150
0.200
0.250
0.300
0.350
0.400
0.450
0.500
15 mM FeCl3
45 mM NaCl (Control)
Electrolysis Time
, min
Absorbance (415nm)
, AU
Figure S10.
ABTS absorbance during NAT ferrate (10 mA cm
2
, 15 mM FeCl
3
) and control (10 mA cm
2
,
45 mM NaCl) experiments.
0
20
40
60
80
100
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0.700
0.800
0.900
15 mM FeCl3
45 mM NaCl (Control)
Electrolysis Time
, min
Absorbance (415nm)
, AU
Figure S11.
ABTS absorbance during NAT ferrate (20 mA cm
2
, 15 mM FeCl
3
) and control (20 mA cm
2
,
45 mM NaCl) experiments.
S8
0
20
40
60
80
100
0.000
0.050
0.100
0.150
0.200
0.250
0.300
10 mM FeCl3
30 mM NaCl
Electrolysis Time
, min
Absorbance (415nm)
, AU
Figure S12.
ABTS absorbance during AT ferrate (10 mA cm
2
, 10 mM FeCl
3
) and control (10 mA cm
2
, 30
mM NaCl) experiments.
0
20
40
60
80
100
0.0
2.0
4.0
6.0
8.0
10.0
5 mA/cm2 (15 mM FeCl3)
10 mA/cm2 (15 mM FeCl3)
20 mA/cm2 (15 mM FeCl3)
Electrolysis Time
, min
[FeO
4
2-
],
mM
Figure S13.
Ferrate(VI) generation using an NAT electrodes with a Fe
3+
0
= 15 mM and current densities
of at 5, 10 and 20 mA cm
-2
.
S.3. Ferrate Speciation
The BDD and NAT produced ferrate(IV/V/VI) solutions were analysed using Raman spectroscopy
(Renishaw inVia Qontor) to determine whether the different ferrate species (e.g., Fe(IV), Fe(V) and/or
Fe(VI)) could identified. Raman micro-spectroscopy was performed using a 514 nm laser as the exciting
light. Calibration was done using a silicon wafer with a Raman band centered at 520.5 cm
-1
.
S9
500
700
900
1100
1300
1500
1700
1900
0
5000
10000
15000
20000
BDD Ferate
Raman Shift
, cm
-1
Intensity
500
700
900
1100
1300
1500
1700
1900
0
5000
10000
15000
20000
NAT Ferrate
Raman Shift
, cm
-1
Intensity
Figure S14.
Raman spectra graph of final BDD and NAT ferrate solutions after 90 min of electrolysis at
10 mA cm
-2
and an initial FeCl
3
concentration of 10 mM.
The BDD and NAT produced ferrate(IV/V/VI) solutions were also analysed using FTIR spectroscopy
(Thermo Scientific Nicolet iS50) to determine whether the different ferrate species (e.g., Fe(IV), Fe(V)
and/or Fe(VI)) could be identified.
800
1000
1200
1400
1600
1800
2000
100
104
108
112
116
120
MQW
NAT Ferrate
BDD Ferrate
Wavenumber
, cm
-1
Transmitance
, %
S10
Figure S15.
FTIR spectra graph of final BDD and NAT ferrate solutions after 90 min of electrolysis at 10
mA cm
-2
and an initial FeCl
3
concentration of 10 mM.
0
50
100
150
0.0
0.2
0.4
0.6
0.8
1.0
1.2
NAT - Ferrate
NAT - Control
Time
, min
Nitrobenzene,
C/C
0
Figure S16.
Nitrobenzene degradation using NAT derived ferrate(VI) and NaCl control solutions (NB
0
=
0.1 mM, Fe(VI) = 1.52 mM)
0
50
100
150
0.0
0.2
0.4
0.6
0.8
1.0
1.2
BDD - Ferrate
BDD - Control
Time
, min
Nitrobenzene,
C/C
0
Figure S17.
Nitrobenzene degradation using BDD derived ferrate(IV/V) and NaCl control solutions (NB
0
= 0.1 mM, Fe(VI)
Eq
= 3.83 mM)
S11
0
50
100
150
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
BDD - Ferrate
BDD - Control
Time
, min
ln(NB
0
/NB
t
)
Figure S18.
Nitrobenzene degradation using BDD derived ferrate(IV/V) and NaCl control solutions (NB
0
= 0.1 mM, Fe(VI)
Eq
= 3.83 mM)
0
5
10
15
20
25
0.0
0.2
0.4
0.6
0.8
1.0
1.2
NAT - Ferrate
NAT - Control
Time
, min
CBZ,
C/C
0
Figure S19.
CBZ degradation using NAT derived ferrate(VI) and NaCl control solutions (CBZ
0
= 10
μM).
S12
Figure S20.
Second-order reaction rate determination of CBZ and NAT derived ferrate(VI) (CBZ
0
= 10
μM, Fe(VI)
0
= 1.66 mM ).
0.00
0.50
1.00
1.50
2.00
2.50
0.0
0.2
0.4
0.6
0.8
1.0
1.2
BDD - Ferrate
BDD - Control
Time
, min
CBZ,
C/C
0
Figure S21.
CBZ degradation using BDD derived ferrate(IV/V) and NaCl control solutions (CBZ
0
= 10
μM).
S13
0.00
0.50
1.00
1.50
2.00
2.50
0.0
0.2
0.4
0.6
0.8
1.0
1.2
AT - Ferrate
AT - Control
Time
, min
CBZ,
C/C
0
Figure S22.
CBZ degradation using AT derived ferrate(IV/V) and NaCl control solutions (CBZ
0
= 10
μM).
0.00
0.50
1.00
1.50
2.00
2.50
0.0
0.2
0.4
0.6
0.8
1.0
1.2
NAT - Ferrate
NAT - Control
Time
, min
FCZ,
C/C
0
Figure S23.
FCZ degradation using NAT derived ferrate(VI) and NaCl control solutions (FCZ
0
= 10
μM).
S14
0.00
0.50
1.00
1.50
2.00
2.50
0.0
0.2
0.4
0.6
0.8
1.0
1.2
BDD - Ferrate
BDD - Control
Time
, min
FCZ,
C/C
0
Figure S24.
FCZ degradation using BDD derived ferrate(IV/V) and NaCl control solutions (FCZ
0
= 10
μM).
S.4. Ferrate Stability
0
10
20
30
40
50
60
70
80
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
BDD - Ferrate
BDD - Control
Time,
day
Absorbance (415nm)
, AU
Figure S25.
ABTS absorbance data for ferrate(IV/V) degradation long term study (Fe(VI)
Eq
= 13.6 mM).
S15
0
10
20
30
40
50
60
70
80
0.0
0.1
0.1
0.2
0.2
0.3
0.3
NAT - Ferrate
NAT - Control
Time,
day
Absorbance (415nm)
, AU
Figure S26.
ABTS absorbance data for ferrate(VI) degradation long term study (Fe(VI) = 3.9 mM).
0
10
20
30
40
50
60
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
Time,
day
Feerate(VI)
Eq
, mM
Figure S27.
Fe(VI)
Eq
data for ferrate(IV/V) degradation long term study (Fe(VI)
Eq
= 13.6 mM). Fe(VI)
Eq
= Equivalent oxidative capacity of Fe(VI) with ABTS (1:1 molar ratio).
S16
0
10
20
30
40
50
60
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
Time,
day
Feerate(VI)
, mM
Figure S28.
Fe(VI) data for ferrate(VI) degradation long term study (Fe(VI) = 3.9 mM).
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
-5.0
-4.5
-4.0
-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
Week 0
Week 1
Week 2
Week 4
Week 6
Figure S29.
Cyclic voltammograms of BDD derived ferrate(IV/V) solution over 6 week stability test. CV
condition: scan rate 50 mV s
-1
, 0.0 V vs. E
OC
to -1.3 V vs. ref.
S17
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
-2.2
-2.0
-1.8
-1.6
-1.4
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
Week 0
Week 1
Week 2
Week 4
Week 6
Figure S30.
Cyclic voltammograms of NAT derived ferrate(VI) solution over 6 week stability test. CV
condition: scan rate 50 mV s
-1
, 0.0 V vs. E
OC
to -1.3 V vs. ref.
S.5. Ferrate Generation Mechanism.
0
5
10
15
20
25
30
35
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Time,
min
Absorbance (415nm),
AU
Figure S31.
ABTS absorbance during BDD electrolysis and O
3
purging (10 mA cm
2
, 15 mM FeCl
3
).
S18
Figure S32.
Ferrate(IV/V) oxidation experiments with O
3
during electrolysis to form ferrate(VI) (full set
of photos).
0
5
10
15
20
25
30
35
0.00
0.02
0.04
0.06
0.08
0.10
NaCl (45 mM)
PBS
Time,
min
Absorbance (415nm),
AU
Figure S33.
ABTS absorbance of control ozonation of NaCl
and PBS solution.