Supporting Information
for
Kinetics and Mechanisms of Nanosilver Oxysulfidation
Jingyu Liu, Kelly G. Pennell, Robert H. Hurt*
1
Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA
Civil and Environmental Engineering Department, University of Massachusetts-Dartmouth, Dartmouth,
Massachusetts 02747, USA
3
School of Engineering, 4Institute for Molecular and Nanoscale Innovation, Brown University, Providence,
Rhode Island 02912, USA
2
*
Corresponding author phone: 401-863-2685; Fax: 401-863-9120; e-mail: [email protected]
Supporting information: 7 Pages, 9 Figures
Additional Details on Methods
Preparation of Citrate Stabilized Colloidal AgNPs (AgNPs-5 nm). Typically, a 55.2 mL solution
containing 0.0204 g (0.12 mmol) AgNO3 and 0.106 g (0.36 mmol) trisodium citrate dihydrate was
prepared in deionized (DI) water. Under vigorous stirring at 60 °C, a freshly prepared 4.8 mL of 0.1 M
NaBH4 solution was added drop by drop into silver precursor solution to reduce Ag+, as indicated by
the prompt solution color change. After stirring for 2 hours, the resulting AgNP colloid was filtered
through a 0.2 µm membrane filter and soluble byproducts were removed by centrifugal ultrafiltration
(Amicon Ultra-15, 3K, Millipore, MA) followed with two cycles of DI water wash, resuspension in
water, and storage at 4 °C in the dark for future use. The AgNP-5 nm stock solution had a total silver
concentration of 447 mg/L (4.14 mM on Ag-atom basis) with soluble silver less than 0.010 mg/L.
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FIGURE S1. Size and morphology characterization of silver materials. (A) TEM image of AgNPs-5
nm; (B) dynamic light scattering (DLS) measured size distribution of AgNP-5 nm aqueous colloid; (C)
TEM image of AgNPs-30nm; (D) size distribution of AgNPs-30 nm in DI water; (E) SEM image of
Ag-µm; and (F) size distribition of Ag-µm in DI water. Silver suspensions for DLS measurement were
prepared by diluting aqueous AgNP-5 nm solution to 2 mM with DI water or by sonicating 1 mg of
powdered silver samples (AgNPs-20 nm and Ag-µm) in 1 mL DI water for 10 min.
S2
FIGURE S2. Controls for electrode interference – measurements of soluble sulfide and silver in Na2SAgNO3 mixtures. AgNO3 was added to 1 mM Na2S solution at a concentration of 0-10 mM, and after
rotating at 20 rpm for 5 min, the dissolved species were isolated by centrifugial ultrafiltration, followed
by sulfide and silver determination using sulfide-ISE and AAs respectively. This control verifies that
sulfide and silver do not coexist in solution under these conditions and silver ion does not interfere
with sulfide-ISE measurement.
FIGURE S3. On-line dissolved oxygen (DO) measurement during AgNP sulfidation, showing
significant acceleration of DO depletion at increased silver and sulfide concentrations. The DO
measurements were started in DI water containing AgNP-30 nm powder (Ag: 216 mg/L and 1079
mg/L), followed by addition of Na2S to concentration at 1 mM and 5 mM respectively at t=10 min.
S3
FIGURE S4. Sulfur species measurement after 24-hr sulfidation of AgNPs-30 nm in 1 mM Na2S.
AgNPs-30 nm (0 - 10 mM) was added into 1 mM Na2S solution, and after rotating at 20 rpm for 24
hours, soluble sulfur species were isolated using centrifugal ultrafiltration. Aliquots of soluble sulfide
solution were used to measure the reduced sulfur (S2-/HS-) concentration by sulfide-ISE, shown in red.
Another aliquot was added with Cu(CH3COO)2 at [Cu2+]=1 mM to precipitate sulfide, and the
remaining soluble oxidized sulfur species (Sn>2-) were analyzed by ICP-ES (Jobin Yvon Emission
JY2000), shown in blue. The top and lower dashed lines give reduced and oxidized sulfur
concentrations in fresh prepared 1 mM Na2S solution respectively. The total sulfur concentration
decreases at elevated AgNP dosage due to the formation of silver sulfide phase, and sulfide oxidation
shows a AgNP dose dependent manner that is catalytically enhanced at low AgNP dosages (0-0.6 mM)
while limited by the rapid sulfide consumption at high AgNP dosages.
S4
FIGURE S5. Effect of pH on AgNP sulfidation. Time-resolved sulfide measurement of AgNP
sulfidation in pH7 phosphate buffer (50 mM). AgNP powder (AgNPs-30nm) was used as reference
nanosilver, and the major sulfide species in 1 mM Na2S solution at pH7 are H2S(aq) (50.2%) and HS(49.8%). Note that the initial (0-10 min) sulfide concentration drop in particle free Na2S solution is
likely due to volatilization induced H2S loss.
FIGURE S6. UV-vis absorption spectra during the AgNP sulfidation process. Citrate stabilized AgNP
colloids (5 nm diameter, [AgNP]input = 2 mM at Ag-atom basis) were mixed with Na2S solution (1
mM), and the surface plasmon resonance peak was monitored by UV-vis spectra at 0, 10, 30, 240, and
1440 min. Sulfidation rapidly degrades the AgNP plasmon resonance peak.
S5
FIGURE S7. HRTEM images showing network formation during AgNP sulfidation. Citrate stabilized
AgNP colloid (5 nm diameter) ([AgNP]input = 2 mM at Ag-atom basis) were sulfidated in 1 mM Na2S
solutions for 24hr, followed by centrifugal ultrafiltration to remove chemical residues.
FIGURE S8. Effect of natural organic matter on AgNP sulfidation. Time-resolved sulfide depletion
measurements of AgNP powder-Na2S reaction and silver free Na2S in DI water and NOM solutions.
Suwannee river humic acid used at 20 mg/L ([AgNP]input = 2 mM at Ag-atom basis).
S6
FIGURE S9. Time-resolved measurements of soluble sulfur concentration during incubation of
AgNPs with sulfites and sulfates (Na2SO3 and Na2SO4), showing no significant reaction. AgNP
powder was added at [AgNP]input = 2 mM on a Ag-atom basis. Sulfur concentrations were analyzed by
ICP.
S7