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Vol.40. No.8 (1991) 643
ORIGINAL
Interaction between Humic Acids and Anthraquinone Dyes
Noriko SHINOZUKA and Chang LEE
Institute of Industrial Science, University of Tokyo
(22-1, Roppongi 7-chome, Minato-ku, Tokyo, •§106)
Interactions between humic acids and anthraquinone disperse-dyes were studied. A humic acid extracted from a
marine sediment and a commercial one were used to solubilize dyes sparingly soluble in water. The solubility of dyes
in humic acid solution was measured by the shake-flask method. The dye solubility in humic acid solution increases
with humic acid concentration and enhancement was marked for solution of Aldrich humic acid. The addition of salts
decreased the solubility of the dye but the effects were complicated. Differences in salts appeared to affect the
solubility of dye little in both marine and commercial humic acids. Dye solubility increased with temperature,
especially in the case of a 0.1% solution of marine humic acid at high temperature. The spectrum of the dye
solubilized in humic acid solution changed and a twin peak characteristic of 1, 4-isomers of polyaminoanthraquinone
disappeared and a broad peak appeared. The dye solubilized by humic acid may thus possibly exist as a solid state as
a deposit on quartz. From the effects of temperature and change in the spectrum, it is suggested that interactions of
the dye and humic acids may be attributable to a partition like process but structural and compositional factors of
humic acid should also be considered.
1 Introduction
Humic substances are the most popular organic
substances on the earth. They are thought to play
an important role in the environment1). Humic
acid, which is the alkaline soluble and acid
insoluble part of humic substances, shows surface
activity and interact with hydrophobic com-
pounds resulted in the increase of water solubility of hydrophobic compounds2). The hydrophobic
interaction depends on the kind of humic acids
and the solute.
We have studied the interaction between humic
acids extracted from marine sediments and
hydrocarbons3). When the concentration of humic
acid is high enough to form aggregates, hydrocar-
bons are solubilized in aggregates and the marked
increase of the solubility of hydrocarbon is
observed. At the lower humic acid concentration,
the solubility of hydrocarbons increases with
increase of humic acid concentration.
It is well known that disperse-dyes are solubil-
ized in micelles of surfactant, the interaction
between dyes and surfactants have been investi-
gated by many researchers4),5). In this study we used disperse-dyes as a solute in order to evaluate
the interaction between dye and humic acid in
comparison with that of dye and surfactant.
Anthraquinone dyes are found in the soil as a
product by bacteria and sometimes they may be
incorporated into the structure of humic
substances6). Therefore, a study of the interaction
between the dye and humic acids can be expected
to give environmental information. This is
another reason we used anthraquinone disperse-
dyes.
2 Experimental
2•E1 Humic acid preparation
Humic acid used was extracted from the marine
sediment according to the procedure described
before7). In brief; The sediment sampled at Sagami
Bay (34•‹57'12"N, 139•‹15'36"E, 1333m in
depth) was dried and powdered. The powdered
sample was suspended in dilute hydrochloric acid
solution to remove carbonates. After washing
with water, 0.2M NaOH was added with stirring
at 30•Ž under nitrogen to extract humic acid. This
extraction procedure was repeated three times
with separate alkaline solutions. The alkaline
extract was centrifuged to eliminate suspended
mud, followed by acidification below pH 2 with
HCI. The resulting humic acid precipitate was
separated by centrifugation. Dissolution into
alkaline solution and precipitation by acidifica-
tion was repeated three times. The final alkaline
solution filtered with a 0.22μm Millipore filter
was passed through an Amberlite IR-120 cation
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644 J. Jpn. Oil Chem. Soc. (YUKAGAKU)
exchange resin column to obtain the acid form of
humic acid. The effluent was acidified and the
precipitate was freeze-dried (BS-12). Commer-
cially available humic salt (Aldrich Chemical
Co.) was also purified by repeating dissolution
and precipitation alternatively.
2•E2 Disperse-dyes
1, 4, 5, 8-Tetraaminoanthraquinone (TAA) was
obtained from Mitsubishi Kasei Co. and 1, 4-
diaminoanthraquinone was from Sumitomo Kaga-
ku Co.. They were recrystalized from acetone
solution.
All other chemicals used were of guaranteed
reagent grade.
2•E3 Solubilization procedure
Solubility of disperse-dyes was measured by
the so-called shake flask method. An aliquat of
acetone solution of dye was put into a Teflon
flask. After evaporation of the solvent, humic
acid solution was added and shaken for 18h on a
shaker (Tokyo Rikakikai Co. Ltd., Model SS-
80) at 25•Ž. After standing more than 30min, the
solution was filtered through a glass fiber filter
(Whatman GF/C). To the filtrate transferred to a
separatory funnel, dichloromethane was added.
The funnel was shaken for about 2min and the
organic solvent was transferred to a volumetric
flask. The absorption spectrum was measured in
the visible wave length region to determine the
concentration of dye solubilized in humic acid
solution. The pH of humic acid solution was
adjusted to 9 with NaOH or HCl solution, except
otherwise stated.
The extraction of dyes from humic acid solu-
tions above 0.1% into dichloromethane was diffi-
cult because of emulsification of organic solvent
by humic acid solution, so the results were
described for solutions below 0.1%.
3 Results Discussion
3•E1 Elemental composition of humic acid
The elemental composition of humic acid used
are listed in Table-1. The samples may contain
Tabla-1 Elemental composition of humic acids
examined.
Ash free content
small amount of sulphur and phosphorus but these
were not determined. BS-12 shows a relatively
high H/C ratio and a high nitrogen content
compared to the commercial one which was said
to be terrestrial in origin. The elemental composi-
tion of BS-12 is characteristic of the marine humic
acid8).
3•E2 Solubility of Disperse-dyes
The relation between the solubility of TAA and
DAA in humic acid solution and the concentration
of humic acid is shown in Fig.-1. The solubility
increases with the humic acid concentration
linearly in the lower concentration range. The
solubility of DAA is higher than that of TAA but
the difference is small in the case of BS-12. In
Aldrich humic acid solution, the solubility of
DAA rises sharply at the concentration
above 0.005%; DAA is solubilized twice as high
as TAA at that concentration range. The de-
pendency of solubility increase of TAA on the
humic acid concentration is similar in BS-12 and
in Aldrich solution.
The amount solubilized in unit weight of humic
acid is also shown in Fig.-2. BS-12 solubilizes
almost the same amount of dye, independent of its
concentration, while the solubilized amount by
Aldrich humic acid decreases markedly. This
means that BS-12 and dye may interact with
almost at the same ratio until BS-12 forms aggre-
gates. If the partition of dye between humic acid
and water would occur, the partition coefficient
A: Aldrich humic acid,
B: BS-12 humic acid
Fig.-1 Solubility of DAA and TAA in
humic acid solution.
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Vol.40. No.8 (1991) 645
A: Aldrich humic acid,
B: BS-12 humic acid
Fig.-2 Solubility of DAA and TAA against
concentration of humic acid.
may be constant in this concentration range.
A 0.1% solution of BS-12 is considered to be
more than the aggregate forming concentration,
the marked increase of dye solubility was not
observed at this point at 25•Ž.
3•E3 Effect of Salts as additives
When salt was added to the humic acid solution
the solubility of dyes changed. Table-2 shows the
effect of NaClIand CsCl addition on the solubility
of TAA. From the Table, the solubility de-
creases in both BS-12 and Aldrich by the addition
of salts. CsCl is more effective than NaCl in the
case of BS-12 on reducing TAA solubility. On
the other hand, 0.4M NaCl decreases the solubil-
ity markedly in Aldrich solution. A small amount
of salt may decrease the charge of humic acid and
change its conformation. Whitehouse had studied
the effect of salinity on the aqueous solubility of
polynuclear aromatic hydrocarbons and stated
that the salinity effect was complicated9). He also
reported that the salting-in (solubility increase
upon the addition of salt) would occur when both
Table-2 Effect of salt addition on TAA
solubilization.
pH=9, at 25•Ž
humic acid concentration: 0.02%
the solute and the electrolytes were large10). The
concentration of aggregate formation decreases
by salt addition. The dye solubilization in aggre-
gates may affect the solubility of dye, as hydro-
carbons are solubilized in humic acid aggregates11).
The salt effects on the solubility of dyes are very
important to consider the hydrophobic interaction
of substances with humic acids. But at present it
is impossible to predict the effects, each system
must be examined for various salts and concentra-
tions at various temperature.
3•E4 Effect of pH on the solubility of dyes
The pH of humic acid solution would affect the
solubility of dyes, as the conformation of humic
acid becomes bulky at the higher pH. The amount
of TAA solubilized in 0.01% BS-12 solution was
measured at various pH and the results were as
follows: 3.4×10-6M at pH: 5, 3.6×10-6M at
pH: 7, 3.6×10-6M at pH 9. The tendency of
solubility increase with increase in pH could be
seen but the difference was very small. As for
Aldrich humic acid solution, the tendency was
almost the same. From these it was suggested that
the solution pH would not significantly affect on
the solubility of anthraquinone dye over this pH
range.
3•E5 Temperature effect o the solubility of
dyes
The solubility of dyes into humic acid solution
was affected by temperature. The change of
solubility is listed in Table-3. From the table it is
shown that the higher the temperature the greater
the solubility. This means that the solubilization
of dye into humic acid solution is totally an
endothermic process. The solubility enhance-
ment is high at the higher temperature.
A 0.1% solution of BS-12 is thought to be above
aggregate forming concentration11), solubilization
of TAA in the aggregate of humic acid may be
dominant in this solution. In general, the amount
of solubilizate increases with the increase of
Table-3 Temperature effect on solubility of TAA.
dye conc.: ×10-6M
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646 J. Jpn. Oil Chem. Soc. (YUKAGAKU)
temperature in the surfactant micellar system; this
may be the case in BS-12 and the solubility
in 0.1% solution at 35•Ž enhances markedly. As
for 0.02% solution, the effect of temperature is
small compared to 0.1% solution.
3•E6 Dye solubilization in humic acid solution
Absorption spectra of solubilized dyes
Absorption spectra of DAA and TAA in the
various solvents were measured and compared to
the spectrum in humic acid solution. In the humic
acid solution the spectrum is similar to that of a
film of dyes deposited on quartz as shown in Fig.-
3. Twin peaks which are characteristic to the 1,
4 isomers of polyaminoanthraquinone, DAA and
TAA, in organic solvents were not observed in
the solution of humic acids above 0.005%. In-
stead, a broad peak (maximum absorption at
around 600nm in the case of TAA) appeared.
Also the twin peaks were shifted to the shorter
wave length, which resembles to the interaction
between dyes and polyelectrolytes12).
From this spectrum it is suggested that the dye
interacts with humic acid may decrease the ability
of the amino group to enhance the contribution of
the ionic form13). This would also suggest the
importance of nonionic interaction between the
dye and the humic acid. The fact that the
spectrum is simillar to that of dye film deposited
on quartz would indicate the presence of micro-
crystalline dye14).
Interaction between humic acids and anthra-
A: dichloromethane solution
B: in 0.01% humic acid solution
C: in 0.005% humic acid solution
D: in water
absorption is at an arbitrary unitFig.-3 Absorption spectra of TAA in humic
acid (BS-12) solution.
quinone dyesSolubility of anthraquinone disperse-dyes ex-
hibits rather complex behavior in water and in
surfactant solution. It was said15) that the dye in
lower concentration range dissolved in water as
molecularly dispersed state which showed an
absorption maximum at the longer wave length
compared to that of dissolved as microparticles.
TAA interacts with surfactants such as sodium
dodecyl sulfate or nonionic surfactants and forms
complex with them. When TAA is solubilized
into nonionic surfactant micelles, the dye mole-
cule is located in the hydrophobic part of the micelle16). Because of the polar character of these
aminoanthraquinones, they interact with the po-lar part of humic acid. The high solubility in
Aldrich humic acid solution may be attributed to
the high content of hydroxyl group in the commer-
cial humic acid17).
The effect of salt is consistent with the known
effects of solution parameters on the aqueous
behavior of humic acid18) when the salt concentra-
tion is low. As the salt concentration increases,
the molecular size of the humic acid will
increase19) or humic acid molecule may coil. The
charge in the humic acid will decrease as the salt
concentration is increased and will become less
hydrophilic. The dye will be more likely to
associate with uncharged humic acid. On the
other hand, the increased salt could cause salting
out of dyes. If polar groups in humic acid interact
with amino groups in dyes, the interaction would
be stronger with TAA than with DAA. However,
the solubility of DAA is much higher and this
indicates the polar groups interaction insignifi-
cant.
As the hydrogen ion concentration increases,
the molecular structure of humic acid will
change. According to Ghosh and Schnitzer19), in
the pH range from 6.5 to 9.5 the structure of
humic acid remained unchanged. In this study the
effect of pH on the solubility of dyes was
insignificant and consistent with their results.
File and Chiou has suggested20) that the term of
the equilibrium enthalpy for the solutes was
instructive to substantiate the type of interactions
between dissolved humic substances and organic
solutes. The solubility determined in this study
does not necessarily mean the partition coeffi-
cient, the enthalpy could not be calculated for the
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Vol.40. No.8 (1991) 647
system. From the effect of temperature on the
solubility of dyes, as described above, the
adsorption of solute on the humic acid is hardly
considered. Partition-like mechanism may be
dominant in this case as is said to many hydropho-
bic interactions between organic compounds and
humic acid21), but the other specific interaction
which comes from the structure of humic acid and
solute must be taken into consideration. The
degree of aromaticity, which was considered to
the system of humic acid and pyrene to evaluate
the partition coefficient22) may be responsible to
the high solubility of dyes in Aldrich solution; the
result is quite different from that for long chain
hydrocarbons23). The complicated effects of salt
addition should be examined in detail and are
being studied in our laboratory.
(Received Feb. 13, 1991)
References
1) M. Schnitzer and S.U. Khan, •gHumic subst-
ances in the environment•h, Marcel Dekker Inc.,
New York, (1972) p. 1.
2) C.T. Chiou, R.L. Malcolm, T.L. Brinton,
and D.E. Kile, Environ. Sci. Technol., 20, 502
(1986).
3) N. Shinozuka, C. Lee, and S. Hayano, Sci.
Total Environ., 62, 311 (1987).
4) A. Murray and K. Mortimer, J. Soc. Dyers &
Colourists, 87, 173 (1971); S. Kuroiwa and S.
Ogasawara, Nippon Kagaku Kaishi, 1976, 790.
5) B.R. Craven and A. Datyner, J. Soc. Dyers &
Colour., 77, 304 (1961).
6) K. Kumada, A. Suzuki, and K. Aizawa, Nature,
191, 415 (1961).
7) S. Hayano, N. Shinozuka, and M. Hyakutake,
Yukagaku, 31, 357 (1982).
8) M.A. Rashid, •gGeochemistry of Marine Humic
Compounds•h, Springer- Verlag, New York,
(1985) p. 105.
9) B.G. Whitehouse, Marine Chem., 14, 319
(1984).
10) B.G. Whitehouse, Marine Chem., 17, 277
(1985).
11) N. Shinozuka and C. Lee, Marine Chem., (in
press).
12) V. Vitagliano, •gAggregation Processes in
Solution•h Ed. E. Wye- Jones and J. Gormally,
Elsevier Scientific Publishing, Amsterdam
(1983) p. 271.
13) H. Inoue, T. Hoshi, J. Yoshino, and Y.
Tanizawa, Bull. Chem. Soc. Jpn., 45, 1018
(1972).
14) G.S. Egerton and A.G. Roach, J. Soc. Dyers &
Colour., 74, 401 (1958).
15) S. Kuroiwa and S. Ogasawara, Kogyokagaku
Zasshi, 72, 2031, (1969).
16) S. Kuroiwa and Y. Nakamura, Sen-i Gaku
Kaishi., 21, 386, (1965).
17) R.L. Malcolm and P. MacCarthy, Environ. Sci.
Technol., 20, 904, (1986).
18) C.W. Carter and I.W. Suffet, Environ. Sci.
Technol., 16, 732 (1982).
19) K. Ghosh and M. Schnitzer, Soil Sci., 129, 266
(1980).
20) D.E. Kile and C.T. Chiou, •gAquatic Humic
Substances•h Ed. I.H. Suffet and P. MacCar-
thy, American Chemical Soc., New York,
(1989) p. 131.
21) P.F. Landrum, S.R. Nihart, B.J. Eadie, and
W.S. Gardner, Envron. Sci. Technol., 18, 187
(1984).
N.R. Morehead, B.J. Eadie, B. Lake, P.F.
Landrum, and D. Berner, Chemosphere, 15, 403,
(1985).
22) T.D. Gauthier, W.R. Seitz, and C.L. Grant,
Environ. Sci. Technol., 21, 243 (1987).
23) S. Hayano, N. Shinozuka, and C. Lee, Proc.
World Surfactants Congress, Kurle Druck Verlag
Gelnhausen (1984) vol.1, p. 244.
フ ミ ン 酸 と ア ン トラ キ ノ ン染 料 と の
相 互 作 用
篠塚則子 ・李 章鎬
東京大学生産技術研究所(〒106 東京都港区六本木7-22-1)
フ ミン酸 とアン トラキノン分散染料 の相互作用 につい
て検討 した。海底堆積物か ら抽出 したフ ミン酸 と市販 の
フ ミン酸 を用 いて ほとん ど水 に溶 けない染料 を可溶化 し
た。 フ ミン酸溶液への染料の溶解量 はいわ ゆるフラスコ
振 とう法 によって測定 した。 フ ミン酸溶液への染料溶解
量 はフ ミン酸濃 度 と共 に増加 し,Aldrichフ ミン酸溶液
で増加 は顕著であった。塩 の添加 は溶解量 を減少 させ る
が,そ の影響 は複雑 であった。染料 の溶解量 は温度が上
昇すると増加 するが,特 に海洋 フ ミン酸 の0.1%溶 液で
高温 で増加 が大 きかった。 フ ミン酸溶液 に可溶化 された
染料 のスペク トルは変化 し,ポ リア ミノアン トラキ ノンの1, 4・異性体 に特有の ツイ ンピー クが消え,ブ ロー ド
な1つ の ピークとなった。 この事 はフ ミン酸 と相互作用
す る染料 は石英上 に析出 した固体状の染料 と同 じ状態 で
あることを示唆す る。温度の影 響及 びスペ ク トル変化 か
ら,フ ミン酸 と染料 との相互作用 は分 配類似 のプロセス
で起 こる ことが示 唆されるがフ ミン酸 の構造 や組成 の要
素 も考え られる。
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