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.

6

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。

9