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Heavy Metal Sequestration Using Functional Nanoporous Materials
US EPA Workshop on US EPA Workshop on Nanotechnology for Site Nanotechnology for Site
RemediationRemediation
[email protected]@pnl.gov
October 20October 20--21, 200521, 2005
Glen E. Fryxell, Shas V. Mattigod, Kent Parker, Richard Skaggs
EPA’s Clean Air Mercury Rule (CAMR) (3/15/05)Current estimated power plant emissions range from 43 to 52 tons Hg/year (48) (158 tons anthropogenic Hg/year total)
Two options:1) Install MACT and reduce emissions nationwide by 14 tons (29%) by 20082) Or, by 2010, reduce this to 38 tons Hg/year (co-benefit, “CAIR”), and by 2018, reduce this to 15 tons Hg/year
Current air pollution control devices can capture some Hg, but this varies widely depending on a number of variables
Current baseline estimates: $50,000-$70,000 per pound Hg removed ($4.3B to $6.7B)
Near-term goal: 50-70% Hg capture, at 25-50% reduction in cost
Longer-term goal: 90+% capture by 2010
Mercury Emissions
Advantages of nanomaterialsfor heavy metal sequestration
High surface area (capacity)Well defined structureHigh reactivityEasy dispersabilityReadily tailored for application in different environmentsChemistry/materials developed for remediation processes are readily tailored to sensing/detection
Nanomaterials provide:
Surfactant-Oil-Water Phase Diagram
Inverse
Cubic Inverse
Hexagonal
Inverse Cylindrical MicellesMicroemulsion Domain
Cylindrical Micelles
Spherical Micelles
Hexagonal
Surfactant
Water Oil
Inverse SphericalMicelles
CubicLamellar
Micelles as macromolecular templates
Surfactants
R-N+-(CH3)3X-
Micelles
Nanoporous Ceramic SubstratesNanoporous Ceramic Substrates
Sol-gel
Template removal
Nanoporous Ceramics SubstrateNanoporous Ceramics Substrate
Large surface area: ~600 - 1000 m2/g
Controlled pore channels: 1.5 - 40 nm
~5 – 10 grams
“..God made the bulk but the devilcreated the surface” – Enrico Fermi
So the way that we get the surface chemistry we need is….
Molecular self-assembly
Pore Surface
Self-assembly driven by Van der Waalsinteractions between chains, as well as the interaction between the headgroupand the surface.
“Designing Surface Chemistry in Mesoporous Silica” in “Adsorption on Silica Surfaces”; pp. 665-687, Marcel-
Dekker, 2000.
Monolayer AdvantagesWell-established silanation chemistryStabilized surfaceHighest possible ligand densityEasily tunable chemistry
SAMMS: Self-Assembled Monolayers on Mesoporous Supports
20 nm20 nm
A. Self-assembled monolayers
B. Ordered mesoporous oxide+
First reported in:
Science 1997, 276, 923-926.
SAMMS in a Nutshell
Extremely high surface area = high capacityRigid, open pore structure provides for fast sorption kineticsChemical specificity dictated by monolayer interface, easily modified for new target speciesProximity effects allow multiple ligand/cation interactionsSequestration can be driven either by metal/ligand affinity or by adduct insolubilityGood chemical and thermal stability Easily regenerated/recycled
“Environmental and Sensing Applications of Molecular Self-Assembly”
in “Encyclopedia of Nanoscience and Nanotechnology”;
Dekker, 2004, pp. 1135-1145.
Tailoring SAMMS interfacial chemistry to the periodic table
H HeLi Be B C N O F NeNa Mg Al Si P S Cl ArK Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I XeCs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At RnFr Ra Ac Rf Db Sg Bh Hs Mt Uun Uuu Uub 113 Uuq 115 117
Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb LuTh Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr
Chemistry of Materials 1999, 11, 2148-2154J. Physical. Chem. B. 2001, 105, 6337-6346.J. Synchrotron Radiation, 2001, 8, 922-924
Cu-EDA
OOSi
SH
OOSi
SH
HO OOSi
SH
OOSi
SH
OOSi
SH
OOSi
SH
OOSi
SH
OOSi
SH
OOSi
SH
OHOSi
SH
OOSi
SH
OOSi
SH
OOSi
SH
OOSi
SH
HO OOSi
SH
OOSi
SH
OOSi
SH
OOSi
SH
OOSi
SH
OOSi
SH
OOSi
SH
OOSi
SH
OOSi
SH
OOSi
SH
OOSi
SH
OOSi
SH
OOSi
SH
OHOSi
SH
OOSi
SH
OHOSi
SH
Science, 1997, 276, 923-926.J. Synchrotron Radiation, 1999, 6, 633-635Sep. Sci. & Technol. 1999, 3411, 2329-2345Mat. Tech. Adv. Perf. Mat. 1999, 14, 183-193Surf. Sci. & Catalysis, 2000, 105, 729-738.
Thiol
SiO2
Si
O
O O
NHO
PHO
OHO
SiO2
Si
O
O O
NHO
NHO
O
3,2 HOPO
CH3
HOPO Prop-Phos
Cu-FC-EDA Cs
Env. Sci. & Tech. 2001, 35, 3962-3966.
Env. Sci. & Tech. 2005, 39, 1324-1331 .
Env. Sci. & Tech. 2005, 39, 1332-1337 .
J. Materials Chemistry2004, 14, 3356-3363
Chem. Comm. 2002, 1374-1375.
Radiochimica Act2003, 91, 539-545
….all by varying the monolayer ligand field.
Thiol-SAMMS overviewExtensive literature precedent for using thiols to bind “soft” heavy metals (e.g. Hg, Cd, Au, etc.).Silane loading density can be tailored to 4, 5 or 6 silanes/nm2 depending on the synthetic methodology employed.This loading density allows Thiol-SAMMS to absorb as much as 2/3 of its own weight in Hg.
Mercaptopropyl siloxane monolayer lining the pore surface of mesoporous silica. The mercury (shown in blue) binds to the sulfur atoms (sulfur atoms are shown in yellow).
http://www.cluin.org/products/newsltrs/tnandt/view.cfm?issue=0905.cfm#5
(Sept. 2005 issue)
0.01
0.10
1.00
10.00
0 100 200 300 400 500
Time (min)
Conc. (mg/L)
GT-73
SAMMS
Mercury Adsorption Kinetics:Thiol SAMMS
0.0001
0.001
0.01
0.1
1
580 590 600 610 620
Hg Loading (mg/kg)
Hg conc. (mg/L)
EPA Regulatory Level: 0.2 mg/L
TCLP Data for Hg-loaded thiol-SAMMSTCLP Data for Hg-loaded thiol-SAMMS
Actual Hg waste clean-up
10L of lab waste (146 ppm Hg)
Est. disposal cost $2000
86 g of Thiol SAMMS used (final Hg conc. 0.04 ppm)
Treatment cost $180
10-fold reduction in cost.
200L of EVS scrubber waste (4.64 ppm Hg)Est. disposal cost $3400Thiol SAMMS used (final Hg conc. 0.05 ppm)Est. treatment cost $210 15-fold reduction in cost.
Mixed waste oils (0.8-50 ppm Hg)Thiol SAMMS used (final Hg conc. <0.2 ppm)Only method proven effective in hydrophobic media.
Ref: Klasson et al. 1999, 2000 ORNL
Case #1
Case #2Case #3
Preliminary Material Lifetime Cost Comparison
BasisBasis SAMMSSAMMS Resin Act. CResin Act. C
Material Cost ($/kg)Hg Loading (g/kg)Substrate (kg)
Material cost to remove ~1 kg HgWaste Disposal Cost @ $60/cftTotal Treatment Cost ~5.4Mgal
$19,141 $86,349 $3,380,952
Waste Stream Hg Waste Stream Hg ConcConc: : 10 10 ppmppm
110 40 26 0.5 0.002
167 2000 500,000
$18,370 $80,000 $1,000,000
$771 $6,349 $2,380,952
Variations on the SAMMS theme: Functionalized TiO2 Nanoparticles
TiNano40TM Characteristics
Surface Area (BET) 51.2 m2/gParticle Density 3.88 g/cm3Particle Size 40 – 60 nmTiO2 99.8%
Impurities0.2%
(ZrO2, SiO2,Cl, P2O5, ZnO)Crystalline Phase Anatase
0
250
500
750
1000
Inte
nsity
(CP
S)
21-1272> Anatase, syn - TiO2
h20904e1.dsp> Unidentified (1 Peak, d = 2.85 Å)
10 20 30 40 50 60 702-Theta(°)
[h20904e.dif] TiO2 Sample
Phase Identification X-ray diffraction analysis
Env. Sci. & Technol. 2005 (in press).
Functionalization
Env. Sci. & Technol. 2005, 39, 7306-7310.
Cu (II) EDA Functionality for
bonding tetrahedral anions (e.g. arsenate,
chromate)
Chem. Mater. 1999, 11, 2148-2154.
NH2Cu
NH
H2NNH2
NHNH
SiO
SiOSi
O
OO O
O
OCu
NH
NH2
NHNH
SiO
SiOSi
O
OO O
O
NH2
NH2
TcO
OO
TcO4-
Binding mechanism
J. Physical. Chem. B. 2001, 105, 6337-6346.
Performance
y = 3.0072x2.9643
R2 = 0.95370.0E+00
2.0E+04
4.0E+04
6.0E+04
8.0E+04
1.0E+05
1.2E+05
1.4E+05
1.6E+05
0.0 10.0 20.0 30.0 40.0
Tc-99 Equilibrium Activity (pCi/ml)
Tc-9
9 ad
sorb
ed (p
Ci/g
)
y = 26.084x0.5453
R2 = 0.97320.0E+00
1.0E+03
2.0E+03
3.0E+03
4.0E+03
5.0E+03
10.0 100.0 1000.0 10000.0
Solution:Solid Ratio (ml/g)
Dis
tribu
tion
Coe
ffici
ent (
Kd m
l/g)
02468
10121416
0 1 2 3
# of Pore Volumes Injected
Inle
t Pre
ssur
e (p
si)
0.01.02.03.04.05.06.07.08.0
0 10 20 30 40 50 60 70 80 90 100
Column Length (cm)
TiO
2 (w
t %)
Loading
Distribution coefficient
Back pressure
Distribution in soil column
Tc-99 Adsorption ExperimentsMaximum Tc-99 loading: ~1.3 x 105 pCi/g.Tc-99 Kd: 1.5 x 102 – 4.0 x 103 ml/g.
30 mesh sand test matrix
Variations on the SAMMS theme:Promising new materials….
Mesoporous metal phosphates –actinides, pertechnetate, chromate, etc.
Capture the strengths of SAMMS:
High surface area
High functional density
Rigid open pores structure
High affinity
….and use this an opportunity to:
Make the backbone inherently functional
Tailor materials for harsh environments
Functional mesoporous carbons –heavy metals
Conclusions
SAMMS is a very effective method for separation and stabilization of environmentally problematic speciesHigh surface area and dense monolayer coating creates high sorbent capacityRigid open pore structure allows for facile diffusion into the pores, hence rapid sorption kinetics.Specificity is dictated by the monolayer interface, and is easily tailored for a wide variety of heavy metals and radionuclidesNew classes of functional nanomaterials that also capture these strengths are on the horizon.
