Humic Group Hygroscopic Properties And Their Chemical Structure -- Humic Fulvic Fugavic Fulgavic

I 0. Sasaki et al., Annals of Environmental Science /2007, Vol 2, 17-22

HUMIC GROUP HYGROSCOPIC PROPERTIES AND THEIR CHEMICAL STRUCTURE Osamu Sasaki, Isamu Kanai, Yuuki Yazawa and Tatsuaki Yamaguchi

.

Graduate School of Engineering, Chiba I nstitute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan Received June 9, 2006; in final form December 13, 2006; Accepted January 2, 2007

ABSTRACT We investigated the relationship between the hygro scopic properties and chemical struct ures of humic and fulvic acids. Humic and fulvic acids were extracted from andosol, Canadian peat and Chinese weathered coal using the IHSS method. Fulvic -like organics produced by the ozone oxidation of humic acid were also prepared by a method reported p reviously. Their main chemical properties related to hygroscopicity were also studied by elemental analysis and the measurement of functional group contents. Humic and fulvic acids were allowed to stand under various relative humidity (RH) conditions and t he amounts of water vapor adsorbed were measured by gravimetry. Water adsorption isotherms were similar for both humic and fulvic acids below RH 80%. Above 80%, water vapor adsorption of fulvic acids and fulvic -like organics increased considerably as compa red with humic acids. Deliquescence was observed for all fulvic acids and fulvic-like organics at higher RH. The amount of water vapor adsorbed at 97% RH by humic substances from different sources was highly correlated with the ratio of oxygen to carbon co ntents.

Keywords: Humic structure, hygroscopic properties, humidity, water retention 1. INTRODUCTION Natural humic materials have been used recently to

ameliorate degraded soils. Under low -moisture conditions, the hygroscopic properties of soil orga nic materials are important for soil wettability, microbial activity, and the dynamics of soil carbon [1 -3]. Humic and fulvic acids are able to adsorb large amounts of water [4]. The hygroscopic properties of humic materials have been well studied; in particular, there have been comparisons between humic acid (HA) and fulvic acid (FA) and the effects of their functional groups and monovalent metal cations [4,5]. Recent studies of the hygroscopic properties of humic materials have been conducted in the field of atmospheric aerosols [6 -8]. However, these aerosol studies were mainly based on the interaction of humic substances (and/or humic like substances) and in organic salts with respect to the types of inorganic salts. Clarification of the relation between the chemical structure of humic materials and their hygroscopic properties is important because it attempts to further address the influence of soil organic matter structure on water sorption, and thus its potential influence on soil wettability and other important aspects. The purpose of this paper is to present an evaluation and discussion of water vapor adsorption by HAs and F As in order to clarify the relationship between their chemical characteristics and their capacity for water vapor adsorption. 2. MATERIALS AND METHODS

2.1. Humic Materials The humic and fulvic acids used in this study were obtained from Japanese andosol (AS), Canadaian peat (CP), and Chinese weathered coal from Xinjiang, (XWC). Humic acid (HA) and fulvic acid (FA) were extracted with the International Humic Substances Society (IHSS) method [9]. AG'" MP-50 resin (Bio-Rad Laboratories, Inc) was used for cation exchange, and Amberlite'" XAD7HP resin (Rohm & Haas Co.) was used for the isolation of fulvic acid instead of Amberlite '" XAD-8 resin, because the production of XAD-8 resin ceased some years ago and XAD7HP resin has the same chemical structure as XAD -8 resin (polymethylmethacrylate). Fulvic -like organics produced by the ozone oxidation of HAs were also prepared as follows [10]. XWC-HA 1.0 g was dissolved in 250 mL of 0.1 N NaOH solution, and this solution was placed in a 500 mL gas-washing bottle as an oxidation reactor. Ozone gas (0.45 mmoVL) was fed into the gas washing bottle by bubbling at a flow rate of 50 Lib for 0.5, 1 .0, 2.0 and 4.0 h, respectively. CP-HA was also used for fulvic-like organics

,

,

-'

0. Sasaki et al., Annals of Environmental Science /2007, Vol 2, 17-22

production. 0.5 g CP-HA was dissolved in 250 mL of 0.1 N NaOH solution and oxidized for 0.25, 0.5, 0.75 and 1.0 h using the same method as that used for XWC -HA oxidation. All oxidized samples were treated and isolated using the simplified IH$S method (Figure I). Fulvic -like organic acids produced by XWC-HA oxidation were named XWCS-0.5, XWCS1.0, XWCS-2.0, XWCS-4.0, and XWCS-0.5+ (Ozone gas, 1.15 mmoVL, 50 Lib; Reaction time, 0.5 h), and those produced by CP -HA were named CPS-0.25, CPS-0.5, CPS-0.75, and CPSI.O, respectively.

0, DiSSolVed in 250mL 0 iN·NaOH Oxidlllion

vapor adsorbed were determined gravimetrically using an electronic balance (Mettler-Toledo, Inc., AB204-S, Precision: O. I mg). Permethylated XWCS -O.5+ (XWCS-0.5+methyl) was also prepared to examine the effect of oxygen functional groups on the capacity for water vapor adsorption of humic substances. Pennethylation was conducted with the Hakomori method [11,12] shown in Figure 2. The Hakomori method is a rapid permethylation method catalyzed by methylsulfmyl carbanion in dimethyl sulfoxide. This method can be applied to methylate carboxyl and hydroxyl groups. Abbreviations of humic substances are listed in Table I. Table 1 Abbreviation, Source, and Character of Humic Substances

WIth 0, bUbOing lor 0 25-4.0M

pH 10 (HOI C8rtJifUgation end filtration

Insoll.Ole

I Hum~. +Orglnic' I

Desorotd Dy 0 1 N·NaOH

Ad~dby x.AO-

7HP reSin

Low moleculer / Fugavic acid

Fulvic-like Organic acids (XWCS/CPS)

Figure 1 Fulvic-like organics production from humic acids by ozone oxidation.

~I I

DMr~..

N.~... DM5,~ .•

;1In1ng for O.Sh al room limp.' - SlImng under N

I

+ atmosphlre for 1 h II 323K

i

i..

j Methylsulflnyl carbanion (MSCA)

I=:;:hllroo:nll~. ..... . - ....

j..

'~H.!I. Umi

lhy1lllon)

f Slirring

( •.••

for 12h II room limp.

I

I DIalyzing by dlslliled wallr

1

Source (Country) Oxidation, h Character Abbreviation Peat (Canada) CP-HA HA CP-FA FA Weathered coal (China, Xinjiang) XWC·HA HA XWC-FA FA Andosol (Japan) AS-HA HA AS-FA FA Peat HA (Canada) FA CPS-0.25 0.25 F CPS-0.50 0.5 A CPS-0.75 0.75 F CPS-I.OO I A Coal HA (China, Xinjiang) FA XWCS-O.5 O.S FA XWCS·I.O I FA XWCS·2.0 2 FA XWCS-4.0 4 F XWCS-O.S+ O.S a A XWCS-O.S+ (China, Xinjiang) Pennethy XWCS-O.5+methyl lated • Ozone, 1.15mmolfL. '2.2. Analysis of Fundamental Properties

FI'HZI drying

lli'fllitJl1YlQ~~l;ml Figure 2 Pennethylation of fulvic acid by the Hakomori method. All samples were freeze-dried and fmely ground, and were maintained in glass vessels in desiccators over saturated LiCI solution at room temperature for wa ter adsorption measurements. The amounts of water

Elemental analysis was perfonned with a Yanaco CHN Corder type MT-S (Yanaco Analytical Instruments Corp., Japan). Carboxyl group content was measured with the calcium acetate method [II, 13] and phenolic hydroxyl group content was measured with the Folin -Ciocalteu method [11, 14]. The EJE6 ratio was calculated by measuring absorbance of the humic substances dissolved in 0.1 N NaOH at 400 and 600 run using a spectrometer (Shimadzu, Model UV1700).

1 8

0. Sasaki et aI., Annals of Environmental Science /2007, V ol 2, J 7-22

Table 2 Elemental and functional characteristics of humic substances Elemental analysis Abbreviatio n

s,

d

wto/a-d.a.f. Ash,

Elemental ratio Functional

groups, mmollg

C H N 0, diff. wtOlo HlC OIC COOH b CP-HA 57.3 5.4 2.0 35.3 3.5 1.13 0.46 3.01 CP-FA 52.4 4.7 0.7 42.2 0.2 1.08 0.60 6.31 n.d. XWC-HA 64.1 3.6 1.5 30.8 3.6 0.67 0.36 4.53 1.41 XWC-FA 43.0 3.5 1.2 52.4 0.0 0.96 0.91 4.28 0.14 AS-HA 59.2 3.5 2.8 34.5 0.7 0.70 0.44 5.50 0.17 AS-FA 48.7 4.3 3.0 44.0 0.2 1.04 0.68 9.12 0.56 CPS-0.25 49.1 3.4 1.3 45.9 0.3 0.82 0.70 7.36 n.d. CPS-0.50 45.5 3.5 1.3 46.7 3.0 0.91 0.77 7.82 n.d. CPS-0.75 47.9 3.5 1.5 45.4 1.7 0.86 0.71 8.14 n.d. CPS-1.0 46.0 3.6 1.6 46.9 1.8 0.94 0.77 8.69 n.d. XWCS-O.5 38.1 2.7 1.6 57.6 2.2 0.85 1.14 7.81 0.82 XWCS-1.0 36.8 2.7 1.3 59.2 2.0 0.87 1.21 8.31 0.81 XWCS-2.0 43.0 3.2 1.7 52.1 1.1 0.89 0.91 6.52 n.d. XWCS-4.0 46.0 3.5 1.8 48.6 1.1 0.91 0.79 8.99 1.09 XWCS-o.5+ 50.1 3.7 1.4 50.1 2.7 0.87 0.67 9.10 0.93 XWCS-o.5+methyl 54.1 4.2 1.6 40.1 2.9 0.56 0.93 3.11 1.00 • Yanaco CHN Corder; 6 Calcium acetate method; C Folin-Chiocalteu method; a d.a.f: Dry ash free basis; n.d.: Not detected.

Phe-OH C n.d.

Table 3 13C NMR estimates of carbon distribution, molecular weight, EJE6 ratio and BET surface area in humic substances

Carbon distribution, %

EJE6 Sa b

Abbreviation Carbonyl Carboxyl Phenolic Aromatic Substituted Aliphatic MnQ CP-HA 7.5 14.0 CP-FA n.d 15.4 XWC-HA 10.7 9.6 XWC-FA 12.3 20.9 AS-HA 12.0 18.0 AS-FA n.d 31.4 CPS-0.25 7.9 19.6 CPS-0.50 n.a. CPS-0.75 n.a. CPS-l.O n.a. XWCS-0.5 8.7 20.9 XWCS-1.0 n.a. XWCS-2.0 n.a. XWCS-4.0 6.6 20.7 XWCS-0.5+ 10.3 23.6 XWCS-0.5+methyl n.a. n.a. n.a. n.a. • Mn: Number-averaged molecular weight; analyzed; n.d.: Not detected.

5.2 3.2 5.9 14.7 15.0 0.0 4.0

14.3 19.0 39.1 7.6 27.0 30.6 21.3

22.2 36.1 13.0 20.4 16.0 6.1 22.3

36.8 26.3 21.6 24.1 12.0 31.9 24.8

4.2

26.9

20.5

18.9

·3.4 2.4

20.9 20.6

25.9 15.1

22.5 .28.0

6 Sa: Surface

17.300 2,600 8,800 n.a. 14,000 1,200 8,800 5;000 3,200 900 n.a. n.a. n.a. 1,800 500

ratio m2/g 5.2 15.1 3.3 n.a. 6.8 17.3 12.4 13.3 14.8 15.3 8.9 7.6 6.6 6.7 7.2

0.64 n.a. 0.93 n.a. n.d. n.a. 1.11 n.a. n.a. n.d. n.a. n.a. n.a. n.a. 0.95

area by BET method with nitrogen; n.a.: Not

Carbon distributions were determined by CPIMAS 13C_NMR spectrometry (Broker, A VANCE 300; MAS frequency 6 kHz; contact time 2 ms; repetition time 3 s; number of scans 2000 -10000). Molecular masses were investigated by gel permeation chromatography (GPC) using pullulan as the calibrant.

GPC was carried out at 70°C on a Shimadzu LC lOA series apparatus equipped with two Plgel 5 J.UIl Mixed-D GPC columns (Polymer Laboratories Ltd.; linear range of molecular weight, 200-400,000) and a refractive index detector. The mobile phase consisted of DMSO at a flow rate of 0.5 mLlmin. The surface

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0. Sasaki et al., Annals of Environmental Science /2007, Vol 2, 17-22

areas were measured by the BET method with nitrogen using a surface area anal yzer (Micromeritics ASAP 2020). The analytical characteristics of HAs, F As and fulvic-like organics are shown in Tables 2 and 3.

2.3. Analysis of Amount of Water Vapor Adsorbed Water vapor adsorption experiments were performed on 200 mg samples maintain ed in weighting bottles in desiccators at different RH values (33 -97%) at 303 K. RH was controlled using selected aqueous saturated salt solutions (MgClz, NaHS0 4, NaCI, KCI, KN0 3, and K2S04) [15]. Samples were withdrawn from the desiccators and weighed un~ il constant weights were obtained. At the end of this period, increases in moisture were expressed as grams of H 20 per gram of initial HAs and FAs that were heat -dried at 378K for 24 h. The amount of water vapor adsorbed was calculated as follows: (amount of water vapor adsorbed) = ([wet sample mass] - [dry sample mass])/(dry sample mass) (I)

adsorption were similar for humic and fu lvic acids below 75% RH. Above 75% RH, water vapor adsorption of F As and fulvic -like organics increased considerably as compared humic acids. These marked increases in the amount of water vapor adsorbed at high RH are similar to those in previous reports [4, 68]. As deliquescence could be observed for all fulvic acids and fulvic-like organics at higher RH values, deliquescent properties may be important in explaining the hygroscopicity of humic substances. 3.3. Relationship between Chemical Characteristi cs and Amount of Water Vapor Adsorbed by Humic Substances The relationship between the amount of water vapor adsorbed at 97% RH and the amount of carboxyl carbon (carboxyl C) as a percentage of total carbon (total C) is shown in Figure 5, and that between the water vapor adsorption and the elemental O/C ratio is shown in Figure 6. :; 1.0 Cl

~

f',

l:

~ 0.8

3. RESULTS AND DISCUSSION

J:o--- .-(S'

g

lJ

.'

XWcs-o.5i XWe-H~J

-g 0.6 3.1. Characteristics of Humic Materials

8-

~ 0.4 The analytical characteristics of the HAs, F As and ~ S III fulvic-like organics are shown in Table 2. The ~ {}--- ---0- . n'0 0.2 carboxyl and oxygen contents of fulvic -like organics 'E produced by ozone oxidation increased from 4.53 0 "E 0 [ mmol COOWg (30.8 wt%) for XWC -HA and 3.01 « 1 5 10 0 mmol COOWg (35.3 wtOlo) for CP-HA to 6.52-9.10 5 Time (day) mmol COOWg (40.1-59.2 wt%) for XWCS and 7.36 8.69 mmol COOWg ( 45.4-46.9 wt%) for CPS, depending on the oxidation time. The carboxyl and . Figure 3 Time courses of the weight changes on water oxygen contents of permethylated XWCS decreased vapor adsorption by hurnic substances. from 9.10 mmol COOWg (50.1 wt%) for XWCS -0.5 to 3.11 mmol COOWg (40.lwt%) for XWCS 0.5+methyl, on permethylation. b.

s c:

3.2. Water Vapor Adsorption The time courses of weight change on water vapor adsorption by humic substances are shown in Figure 3. Weights of humic substances increased rapidly at an early stage. Reaching a constant weight took about 2 weeks for HAs and 3 weeks for F As. De liquescence was observed for all F As and fulvic -like organics above 80% RH. Water vapor adsorption isotherms, measured at 303K for HAs, FAs and fulvic -like organics are shown in Figure 4. Isotherms of water vapor

i

o ~A 0.8

OJ

i

I

o

0.6

-Ir .. CP-

HA 11 CP-FA

o CPs.o.25

J

0.4

'll

0.2

f

1:

j

() ~.5+

20 0 0

40 100

60

60

Relative humldlly (%RH)

Figure 4 Isotherms for water vapor adsorption by humic substances at 303 K.

2 0

O. Sasaki et aI., Annals of Environmental Science /2007, Vol 2, 17-22

Table 2 Elemental and functional characteristics of humic substances Elemental analysis·, wto/o -d.a.f.dAsh,

Elemental ratio Functional

Abbreviation groups, mmoVg

0, iliff. wt% HlC O/C COOH b CP-HA 57.3 5.4 2.0 35.3 3.5 1.13 0.46 3.01 n.d. CP-FA 52.4 4.7 0.7 42.2 0.2 1.08 0.60 6.31 n.d. XWC-HA 64.1 3.6 1.5 30.8 3.6 0.67 0.36 4.53 1.41 XWC-FA 43.0 3.5 1.2 52.4 0.0 0.96 0.91 4.28 0.14 AS-HA 59.2 3.5 2.8 34.5 0.7 0.70 0.44 5.50 0.17 AS-FA 48.7 4.3 3.0 44.0 0.2 1.04 0.68 9.12 0.56 CPS-0.25 49.1 3.4 1.3 45.9 0.3 0.82 0.70 7.36 n.d. CPS-0.50 45.5 3.5 1.3 46.7 3.0 0.91 0.77 7.82 n.d. CPS-0.75 47.9 3.5 1.5 45.4 1.7 0.86 0.71 8.14 n.d. CPS-1.0 46.0 3.6 1.6 46.9 1.8 0.94 0.77 8.69 n.d. XWCS-O.5 38.1 2.7 1.6 57.6 2.2 0.85 1.14 7.81 0.82 XWCS-1.0 36.8 2.7 1.3 59.2 2.0 0.87 1.21 8.31 0.81 XWCS-2.0 43.0 3.2 1.7 52.1 1.1 0.89 0.91 6.52 n.d. XWCS-4.0 46.0 3.5 1.8 48.6 1.1 0.91 0.79 8.99 1.09 XWCS-o.5+ 50.1 3.7 1.4 50.1 2.7 0.87 0.67 9.10 0.93 XWCS-0.5+methyl 54.1 4.2 1.6 40.1 2.9 0.56 0.93 3.11 1.00 ·Yanaco CHN Corder; 6 Calcium acetate method; cFolin -Chiocalteu method; dd.a.f: Dry ash free basis; n.d.: Not detected. C

H

N

Phe-OH C

Table 3 J3C NMR estimates of carbon distribution, molecular weight, EJE6 ratio and BET surface area in humic substances Carbon distribution, % EJE6 Sa b Mo Q Abbreviation Carbonyl Carboxyl Phenolic Aromatic Substituted Aliphatic ratio m2 CP-HA 7.5 14.0 5.2 14.3 22.2 36.8 17,300 5.2 0.64 CP-FA n.d 15.4 3.2 19.0 36.1 26.3 2,600 15.1 n.a. XWC-HA 10.7 9.6 5.9 39.1 13.0 21.6 8,800 3.3 0.93 XWC-FA 12.3 20.9 14.7 7.6 20.4 24.1 n.a. n.a. n.a. AS-HA 12.0 18.0 15.0 27.0 16.0 12.0 14,000 6.8 n.d. AS-FA n.d 31.4 0.0 30.6 6.1 31.9 1,200 17.3 n.a. CPS-0.25 7.9 19.6 4.0 21.3 22.3 24.8 8,800 12.4 1.11 CPS-0.50 n.a. 5,000 13.3 n.a. CPS-0.75 n.a. 3,200 14.8 n.a. CPS-1.0 n.a. 900 15.3 n.d. XWCS-0.5 8.7 20.9 4.2 26.9 20.5 18.9 n.a. 8.9 n.a. XWCS-I.O n.a. n.a. 7.6 n.a. XWCS-2.0 n.a. n.a. 6.6 n.a. XWCS-4.0 6.6 20.7 ·3.4 20.9 25.9 22.5 1,800 6.7 n.a. XWCS-0.5+ 10.3 23.6 2.4 20.6 15.1 28.0 500 7.2 0.95 XWCS-O.5+methyl n.a. n.a. n.a. n.a. • Mn: Number-averaged molecular weight; 6 Sa: Surface area by BET method with nitrogen; n.a.: Not analyzed; detected. n.d.: Not

/g

Carbon distributions were determined by CP/MAS 13C_NMR spectrometry (Bruker, A VANCE 300; MAS frequency 6 kHz; contact time 2 ms; repetition time 3 s; number of scans 2000-10000). Molecular masses were investigated by gel permeation chromatography (GPC) using pullulan as the calibrant.

GPC was carried out at 70°C on a Shimadzu LC lOA series apparatus equipped with two Plgel 5 IlIIl Mixed-D GPC columns (Polymer Laboratories Ltd.; linear range of molecular weight, 200-400,000) and a refractive index detector. The mobile phase co nsisted of DMSO at a flow rate of 0.5 mL/min. The surface

1 9

--

~---------

0. Sasaki et aI.. Annals of Environmental Science /2007. Vol 2, 17-22

areas were measured by the BET method with nitrogen using a surface area analyzer (Micromeritics ASAP 2020). The analytical characteristics of HAs, F As and fulvic-like organics are shown in Tables 2 and 3. 2.3. Analysis of Amount of Water Vapor Adsorbed Water vapor adsorption experiments were performed on 200 mg samples maintained in weighting bottles in desiccators at different RH values (33-97%) at 303 K. RH was controlled using selected aqueous saturated salt solutions (MgCh, NaHS0 4, NaCl, KCl, KN03, and K2S04) [15]. Samples were withdrawn from the desiccators and weighed un~l constant weights were obtained. At the end of this period, increases in moisture were expressed as grams of H20 per gram of initial HAs and F As that were heat-dried at 378K for 24 h. The amount of water vapor adsorbed was calculated as follows: (amount of water vapor adsorbed) = ([wet sample mass] - [dry sample mass])/(dry sample mass) (1)

adsorption were similar for humic and fulvic acids below 75% RH. Above 75% RH, water vapor adsorption of F As and fulvic-like organics increased considerably as compared humic acids. These marked increases in the amount of water vapor adsorbed at high RH are similar to those in previous reports [4, 68]. As deliquescence could be observed for all fulvic acids and fulvic-like organics at higher RH values, deliquescent properties may be important in explaining the hygroscopicity of humic substances. 3.3. Relationship between Chemical Characteristics and Amount of Water Vapor Adsorbed by Humic Substances The relationship between the amount of water vapor adsorbed at 97% RH and the amount of carboxyl carbon (carboxyl C) as a percentage of total carbon (total C) is shown in Figure 5, and that between the water vapor adsorption and the elemental O/C ratio is shown in Figure 6. f" Cl

1.0

I XWcs-o.51

.9 c:

3. RESULTS AND DISCUSSION 3.1. Characteristics of Humic Materials The analytical characteristics of the HAs, F As and fulvic-like organics are shown in Table 2. The carboxyl and oxygen contents of fulvic-like organics produced by ozone oxidation increased from 4.53 mmol COOHlg (30.8 wt%) for XWC-HA and 3.01 mmol COOHlg (35.3 wt%) for CP-HA to 6.52-9.10 mmol COOHlg (40.1-59.2 wt"1o) for XWCS and 7.368.69 mmol COOHlg (45.4--46.9 wt%) for CPS, depending on the oxidation time. The carboxyl and oxygen contents of permethylated XWCS decreased from 9.10 mmol COOHlg (50.1 wt%) for XWCS-0.5 to 3.11 mmol COOHlg (40.1wt%) for XWCS0.5+methyl, on permethylation. 3.2. Water Vapor Adsorption The time courses of weight change on water vapor adsorption by humic substances are shown in Figure 3. Weights of humic substances increased rapidly at an early stage. Reaching a constant weight took about 2 weeks for HAs and 3 weeks for F As. Deliquescence was observed for all F As and fulvic-like organics above 80% RH. Water vapor adsorption isothenns, measured at 303K for HAs, F As and fulvic-like organics are shown in Figure 4. Isothenns of water vapor

~

/I

[lJ XWC-HA

0.8

0

II) "0 IV

0.6

5

a. IV >

'-

I~ V ~ '0 ;: :l

0

E

«

0.4 0.2

o l( 5

0

Time (day)

1 0

1 5

. Figure 3 Time courses of the weight changes on water vapor adsorption by humic substances.

-b

o

.9

to .

t

o f>S.FA

o

0.8

0

I

o 0.8

,

,

(, CP-FA

o CPS-O.25

l

~

I

0.4

o XWCS-O.5+

'8

20 0.2

40 100

80

80

j Figure 4 Isothenns for water vapor adsorption by Relative ""mldlly (%RH)

0

humic substances at 303 K. 0

20

----------_._-----~---~----~~~~~~~~~----~--

---~~~~~~-

-

O. Sasaki et al., Annals of Environmental Science /2007, Vol 2, J 7-22

The amounts of water vapor adsorbed at 97% RH by humic substances increased with increasing carboxyl content and O/C ratio, and the O/C ratio showed a stronger correlation = 0.83) than the carboxyl content = 0.67) for the differ~nt sources. XWCS-O.5+methyl (the permethylated fulvic-like organic sample) adsorbed less water vapor than the other XWCSs, related to the decreased O/C ratio and carboxyl content. This result shows that the O/C ratio and the carboxyl group directly influence the water vapor adsorption capacity of hurnic substances.

(r

(r

• CP·HA o CP·FA • xwC·HA AAS-HA (:, AS-FA t CPS-C.25 + CPS-C.50 + CPS-C.75 t CP5-1.00 x XWCS-C.5 x XWC5-1.0 )( XWC5-2.0 )( XWCS-4.O )( XWCS-C.5+ o XWCS-c.5+methyt

2.5

Y' 0.073 •. 0.35

R'. 0.67

----- -. "--

10

20

....

30

Carboxyl C I Total C (%) • CP·HA o CP·FA • xwC·HA A AS-HA (:, AS-FA + CPS-c.25 + CPS-c.50 + CPS-c.75 + CPS·l.00

2.5

6. .9

2

y·2.33X-D.n

c

R'·o.83

.2

"eo

51

1.5

~

x XWCS-c.5 x XWCS.l.0

[ ~

)( XWCS·2.0 )( XWCS-4.0 0.5

,

Figure 6 Relationship between the carboxyl content and the amount of water vapor adsorbed by humic substances .

)( XWCS-c.5+ o XWCS-c.5+melhyt

0

2.5

~ 0,

2 y·0.1611·127

.

c 9

1

R'. 0.74 1.5

0.5

1.5

~

I

6

I

O/C ratio

Figure 5 Relationship between the elemental O/C ratio and the amount of water vapor adsorbed by humic substances.

> ••

~ ~

;

+ CPS-O.50

I

1- CPS-O.75

If/'

c.

0

• CP·HA o CP.FA • XWC-HA .AS-HA 6 !'SofA + CPS-O.25

0.5

+ CP5-1.00 x XWCS-O.5

;( XWC5-1.0 ;( XWC5-2.0 )( XWC5-4.0

y • O,05x + 0.05

R'. 0.911

;( XWCS-o.5+

0 0

5

10 15 E41E6 ratio

20

Figure 7 Relationship between the E.JE6 ratio and the The EJE6 ratio is an index of light absorption in the visible range. A high E.JE6 ratio corresponds to a amount of water vapor adsorbed by humic substances. relatively low molecular weight, and a low ratio corresponds to a relatively high molecular weight [16, 17]. Figure 7 shows that, although the E.JE6 ratios were 4. CONCLUSIONS correlated with the amount of water adsorbed within the natural humic substances or in XWCSs or in CPSs, the We aimed to clarify the relationship between the water E.JE6 ratios varied among the different sources of humic vapor adsorption capacities of various humic substances substances. This variation suggests that water vapor and their chemical characteristics. In our studies we used adsorption capacity depends on oxygen functional group, humic materials from several sources and th~ir oxidized and not on the molecular products, which have fulvic-like weight. . . characteristics. Although the amoUnt of water vapor Schnitzer [4] reported that oxygen functtonal groups adsorbed varied among the various sources of humic affect water vapor adsorption capacity by HA and FA substances, the water vapor adsorption of the humic obtained from Podzol. In our experiment, we confirmed substances was well correlated with their O/C ratio. that the O/C ratio is an important factor affecting the Humic substances differ in hygroscopicity, and this water adsorption capacity of several kinds of humic difference might affect the wettability, the microbial substances extracted with the IHSS method from peat activity and carbon sequestration when degraded soils in (Canada), weathered coal (China) and Andosol (Japan) at arid lands are ameliorated with humic substances from higher humidities, and that the water adsorption capacity different sources. of humic substances roughly could be explained only by the O/C ratio.

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0. Sasaki et al., Annals of Environmental Science /2007, Vol 2, J 7-22

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62:355-363. 4) Nardi, 5., 1996, Biological Activity of Humus. Chapter 9 in: A. Piccolo (Ed.) Humic Substances in Terrestrial Ecosystems. E lsevier, Amsterdam. 5) Rauthan, B.S., and M. Shnitzer. 198 I. Effects of fulvic acid on the growth and nutrient content of cucumber (Cucumissativus) plants. Plant Soil. 63:491 -495. 6) Sladky, Z. 1959. The effect of extracted humus substances on growth of tomat o plants. BioI. Plant. 1:142-150 7) Xudan, .X. 1986. The effect of foli~ application of fulvic acid on water use, nutrient uptake and wheat YIeld. Austr. J. Agnc. Res. 37.343-350 .

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