Polyparameter Linear Free Energy Relationship for Wood
Char-Water Sorption Coefficients of Organic Sorbates
Desiree L. Plata†§*, Jordon D. Hemingway‡§, and Philip M. Gschwend§
†
Mason Laboratories, 9 Hillhouse Avenue, PO Box 208286, Yale University, New
Haven, CT 06520
‡
Department of Marine Chemistry and Geochemistry, Fye Laboratory, Mail Stop #4,
Woods Hole Oceanographic Institution, Woods Hole, MA 02543
§
Ralph M. Parsons Laboratory, 48-413, Department of Civil and Environmental
Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
*corresponding author: desiree.plata@yale.edu
Wood char characteristics, previously modeled black carbons and their sorbent
parameters, toluene equilibration timescale for water-wet char, and comparison of
Freundlich exponents between GAC and char.
Available Items:
Table S1. Wood char characteristics.
Table S2. Known sorbent parameters for model black carbons.
Table S3. Forward stepwise multiple linear regression analysis statistical metrics.
Figure S1. Toluene equilibration timescale for water-wet char.
Figure S2. Comparision of Freundlich exponents between GAC and char.
Figure S3. Surface-area normalized Kd for GAC and char.
Table S1. Characteristics of experimental sorbate materials.
a
Sorbent
%C (w/w)
Quartza
0.016 ± 0.006
Surface area
(m2 g-1)
3.34 ± 0.07
Chestnut Wood Char
71.7 ± 0.2
5.9 ± 0.3
Char-Quartz Mixture
acid-washed, pre-combusted
1.05 ± 0.04
3.4 ± 0.4
Source or
reference
EMD Chemical
Hammes et al.,
Schmidt Lab
(Univ. Zurich)
This work
Table S2. Known sorbent parameters for model black carbons.
Contribution
Surface area
COOH content
(m2 g-1)
(% of NMR or XPS signal)
Sorbate
Equilibration time
Chestnut wood char
This study
3-4 %
5.9
>7 d
556
>7 d
(Hammes et al. 2006)
GAC
Shih & Gschwend
Darco® 20-40 mesh
Kamlet et al.
CAL ®
14 h
Various GACs:
Filtrasorb®-300,
Luehrs et al.
2h, 2h, 2h, 14h, 24h, 3 wks
Filtrasorb®-400,
CAL ®, and WV-G
Poole and Poole
a
CAL® GAC
14 h
Reported as proportion of NMR (nuclear magnetic resonance; a bulk technique) or XPS (x-ray photoelectron spectroscopy; a surface
technique) signal.
Table S3. Results of fitting ppLFER with increasing numbers of parameters (i.e., forward stepwise multiple linear regression
analysis). Adjusted R2 and F values always dropped greatly when a constant was added to the ppLFER. Bold-face, red text represents
the best fits (i.e., highest adjusted R2 and highest F value) for given number of parameters..
one
parameter
v1
adjusted
R2
0.870
v2
F
915
two
parameters
v1 and e1
adjusted
R2
0.894
0.860
778
v1 and s1
b1
0.39
83
b2
0.376
s1
F
582
three
parameters
v1, b1, e1
adjusted
R2
0.963
0.869
454
v1, b1, s1
v1 and a1
0.871
460
79
v1 and b1
0.967
0.591
189
v1 and v2
s2
0.601
197
e1
0.530
e2
F
1441
four
parameters
v1,b1,s2,e1
adjusted
R2
0.974
0.964
1472
v1,b1,s2,s1
v1, b1, a1
0.958
1221
1841
v1, b1, v2
0.969
0.893
574
v1, b1, e2
v1 and e2
0.910
711
148
v1 and s2
0.878
0.512
137
v1 and a2
a1
0.154
25
v1 and b2
a2
0.197
33
F
1777
five
parameters
v1,b1,s2,v2,e1
adjusted
R2
0.975
F
1517
0.975
1860
v1,b1,s2,v2,e2
0.975
1521
v1,b1,s2,a1
0.974
1710
v1,b1,s2,v2,s1
0.975
1517
1820
v1,b1,s2,v2
0.976
1912
v1,b1,s2,v2,a1
0.976
1538
0.970
1885
v1,b1,s2,e2
0.974
1705
v1,b1,s2,v2,a2
0.976
1549
v1,b1,s2
0.973
2292
v1,b1,s2,a2
0.975
1749
v1,b1,s2,v2,b2
0.976
1538
495
v1,b1,a2
0.960
1270
v1,b1,s2,b2
0.974
1777
0.870
455
v1,b1,b2
0.964
1493
0.907
680
Figure S1. Time required to establish equilibrium between water and water-wet char was
about 1 week for toluene.
While a 1-wk equilibration time is sufficient for equilibrium of small compounds,
equilibration times exceeding several weeks can result in other experimental
complications. For example, volatile compounds (with large air-water partition
coefficients) can diffuse through ground-glass joints (even when those joints are
submerged under water), such that significant fractions of the analyte are lost from the
sample container after several weeks. To minimize such losses, we recommend
equilibration times of exactly 1-wk for the most volatile probe species.
Figure S2. Comparison of Freundlich exponents for char (as determined in this study)
and granular activated carbon (GAC) (taken from Shih & Gschwend, 2009). The symbols
are the data and the dashed line shows the one-to-one line (i.e, where the data would fall
if nchar and nGAC were equal). The nchar values are systematically high relative to nGAC.
Figure S3. Surface-area normalized solid-water distribution coefficients for benzene and
toluene adsorbing to GAC and char from aqueous solutions. At low chemical activities
(e.g., 1/10,000 of saturation), the sorbents exhibited similar Kd values. As the surface
coverage increased (i.e., at higher activities) and the most favorable sorption sites become
occupied, larger discrepancies in the Kds between char and GAC emerge.