Mechanisms of Diffusion-Reduction Interaction of Microcrystalline Cellulose and Silver Ions

Article abstract of DOI:10.1023/A:1024966121771

The preparation of microcrystalline cellulose samples containing intercalated silver(0) particles includes two main stages: diffusion of silver ions from aqueous AgNO₃ into the microcrystalline cellulose matrix, followed by reduction of the sil

Full text of DOI:10.1023/A:1024966121771

Russian Journal of General Chemistry, Vol. 73, No. 3, 2003, pp. 427 433. Translated from Zhurnal Obshchei Khimii, Vol. 73, No. 3, 2003,
pp. 456 464.
Original Russian Text Copyright
2003 by Kotel’nikova, Demidov, Wegener, Windeisen.
Mechanisms of Diffusion Reduction Interaction
of Microcrystalline Cellulose and Silver Ions
N. E. Kotel’nikova, V. N. Demidov, G. Wegener, and E. Windeisen
Institute of Macromolecular Compounds, Russian Academy of Sciences, St. Petersburg, Russia
St. Petersburg State Institute of Technology, St. Petersburg, Russia
Institute for Wood Research, University of Munich, Germany
Received December 26, 2000
Abstract The preparation of microcrystalline cellulose samples containing intercalated silver(0) particles
includes two main stages: diffusion of silver ions from aqueous AgNO into the microcrystalline cellulose
3
matrix, followed by reduction of the silver ions bound to cellulose macromolecules to Ag(0) and growth of
Ag(0) particles inside the cellulose matrix and on its surface. Mechanisms of interaction of silver ions with
cellulose as reducer and with other reducers and ligands are considered.
The problem of intercalation of transition and main
group metal ions into a natural polymer, cellulose,
attracts enduring researcher’s interest. However, there
are few papers dealing with cellulose interaction with
silver ions [1 3]. At the same time, research in this
field may be useful for development of methods for
cellulose modification and design of new polymeric
materials exhibiting bactericidal properties and new
conducting materials. Silver metal deposition on a
cellulose substrate has been utilized as one of the test
methods for hydroxycellulose. Thus, Moon et al. have
accomplished silver metal deposition from aqueous
solutions of silver salts on filter paper oxidized
under UV irradiation [4]. The referees indicated that
reduction of silver ions from their salt solutions
involve both end aldehyde groups and hydroxy groups
of polysaccharides. We previously found [5] that
microcrystalline cellulose (MCC) is a suitable matrix
for Ag(0) reduction from silver salt solutions. This is
due to specific properties of MCC, i.e. its powder
morphology, high sorption capacity, and ability to
develop active surface during reactions [6].
Then the silver ions are reduced by cellulose end
aldehyde and alcohol groups. As a result, two
oxidized forms of cellulose arise (Scheme 1):
Scheme 1.
O
H
O
O
Cell C
+ H2O
Cell C
+ 3H+,
2
e
O
Cell CH OH
Cell C
+ 2H+,
2
2
e
H
The present paper is a continuation of our previous
studies [5, 7] and deals with the analysis of complexa-
tion processes, mechanisms of chemical binding and
reduction of silver ions to silver metal, and growth of
silver(0) particles in a cellulose matrix.
+
Ag + e = Ag(0).
The presence of silver(0) in cellulose samples has
been confirmed by X-ray phase analysis and X-ray
photoelectron spectroscopy [7]. The appearance of
COO groups as a result of oxidation of cellulose
aldehyde groups by silver ions, has been confirmed
by Raman spectroscopy [7]. In the case of interaction
Interaction of aqueous solutions of silver salts with
a cellulose matrix (Cell) is a complex multistage
process. In the first stage, coordination of the hydrated
+
silver ions [Ag(H O) ] with alcohol groups of cel-
2
2
+
lulose macromolecules takes place, leading to forma-
of the ammonium silver complex [Ag(NH ) ] with
3
2
tion of outer- and inner-sphere complexes I and II.
cellulose, a similar redox process occurs (Scheme 2).
1
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428
KOTEL’NIKOVA et al.
Table 1. Characteristics of cellulose samples containing silver(0) particles
Silver content, wt%
Sample
no.
Reducer, additional
treatment
Sample color, particle
size [n in Ag(0)n]
Sample
in bulka on the surfaceb
1
2
3
Cellc
Cell Ag(0) Cell
Cell Ag(0) Cell, NH3 H O
White
Yellow, small; n 3 11
Red-brown, small, large;
n 3 11, 1000
0.6
0.6
<1.0
1.5
2
4
5
Cell Ag(0) Cell, 250 C
Yellow, small; n 3 11
Red-brown, small, large;
n 3 11, 1000
1.3
6.1
1.2
12.6
Cell Ag
Glyc, NH3 H O
2
6
7
8
9
Cell Ag
Cell Ag
Cell Ag
Cell Ag
Ag(0)
1,10-Phen, Glyc, NaHCO3
NaBH4
Grayish green, gigantic; n > 5000
Yellow, small; n 3 11
3.0
5.3
6.2
7.6
4.1
2.2
2.6
NaBH (repeated treatment) Graish brown, gigantic; n > 1000
4
KH PO , H PO
Gray, gigantic; n > 10000
16.5
2
2
3
4
1
0
Gray, gigantic
a
b
c
X-ray fluorescent analysis.
Scheme 2.
+ 2NH + H O Cell C
X-ray photoelectron spectroscopy.
Initial cellulose.
When the process was performed in aqueous
ammonia, a sample was obtained with a silver(0)
content in bulk lower that 0.6 wt%. Silver(0)
1.5 wt%) appears on the surface of cellulose fibers
sample no. 3).
O
H
O
+
Cell C
+ 2NH ,
4
3
2
2e
(
OH
(
O
+
Cell CH OH + 2NH
Cell C
+ 2NH ,
4
2
3
2
e
Cellulose subjected to thermal treatment at 250 C
H
+
reduces Ag ions in a neutral medium relatively
rapidly during their diffusion into the matrix. This is
probably due to the fact that the content of end al-
dehyde groups is increased by heating. Moreover, the
formation of C=C bonds in the MCC structure under
thermal treatment can facilitate binding Ag ions via
coordination of type A.
[
Ag(NH ) ] + e
Ag(0) + 2NH3.
3
2
Initial cellulose acts as a two-electron reducer
in both cases, whereas Ag+ ions are one-electron
oxidants. Oxidation of one aldehyde or alcohol cel-
lulose group forms two Ag(0) atoms that combine into
+
an Ag(0) particle [8]. These particles and free silver
2
ions are involved into formation of Ag(0) particles.
n
Diffusion reduction processes involving cel-
lulose matrix as reducer. When heated, a mixture of
MCC with aqueous AgNO changes color from white
3
to rose (Table 1, sample no. 1). This fact can be ex-
plained by appearance of primary reduced Ag(0)n
centers (n = 4 10) in the MCC matrix as a result of
electron transfer from the cellulose macromolecule to
Evidence for the appearance of double bonds and
additional aldehyde groups in the cellulose was ob-
tained by studying the effect of the temperature on
13
+
the MCC structure by solid-state high-resolution
NMR spectroscopy [10]. Figure 1a shows the
C
C
Ag ions, which follows cellulose coordination with
13
the latter (see Schemes 1 and 2). This transfer is
induced by visible light. The silver(0) content in this
sample (sample no. 2) is low (0.6 wt% in bulk).
NMR spectrum of MCC, containing 8 typical signals.
Under chemical and temperature effects in various
media natural cellulose undergoes chemical or struc-
tural modifications. The latter are accompanied by
transformation of the cellulose I crystallographic cell.
This transformation can occur by the following paths
(
Fig. 1b): (1) rotation of the anhydroglucose rings
4
about the C O bond, which can occur at 100 C and
higher temperatures, or abound the O C1 bond (the
latter is sterically hindered); and (2) rotation about the
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 3 2003

MECHANISMS OF DIFFUSION REDUCTION INTERACTION
429
5
6
C C bond (rotational isomerism of the hydroxy-
methyl group). The result is dislocation of all H bonds
in the cellulose system typical of the cellulose modi-
fication I and probable partial formation of an H-bond
system typical to other cellulose structural modifica-
tions, as evidenced by data in Table 2 and in [9].
Table 2. Characteristics of microcrystalline cellulose
subjected to thermal treatment
Heating temperature,
C
Weight loss,
wt%
I1a
I2a
Initial cellulose
150
0.25
0.20
0.30
0.50
0.80
0.20
0.30
0.20
0.50
0.80
Heating of cellulose at 150 380 C leads to noti-
1
3
3.5
4.7
21.4
66.0
70.0
ceable changes in its C NMR spectra (Fig. 2,
Table 2). Analysis of the spectra and data in Table 2
indicates changes in X-ray crystallinity and weight
loss. Thus, the weight loss at 250 C is rather large
200
250
280
300
(
21.4 wt%) [9]. Therewith, scission of cellulose
chains, formation of shorter fragments and, corres-
pondingly, formation of additional aldehyde groups
take place. Consequently, Ag reduction in the cel-
lulose matrix proceeds faster and to a greater extent.
The silver(0) content in the sample (sample no. 4) is
a
13
Data obtained by C NMR spectroscopy. I is the intensity
1
6
+
ratio of the down- and upfield components of the C signal at
2.5 and 66.5 ppm, determined by the rotameric composition
of the hydroxymethyl groups; and I is the intensity ratio of
the amorphous and crystalline components of the C signal at
6
2
4
1
.3 wt% in bulk and 1.2 wt% on the surface. Because
8
4 and 88 ppm, determined rotation of the glucoside units
of the low contents, the aldehyde groups and double
bonds are impossible to detect by spectral methods.
4
1
about the C
O bond.
1
3
Considerable changes are observed in the C NMR
spectra of cellulose samples heated above 250 C. All
carbon signals shift and change shape, implying
changed chain arrangement and steric environment of
carbon atoms in the reaction products compared with
the aqueous to MCC phase, i.e. acts as a specific
phase-transfer catalyst.
+
+
Ag Glyc + 2H O
Ag(H O) + Glyc
2 2
aqueous phase
2
-------------- ---------------------------------------------------
6
cellulose
those in the initial cellulose. The C signal shifts from
6.5 to 62.5 ppm, which suggests transformation of
+
+
Ag Glyc + Cell
Ag (Cell) + Glyc
6
cellulose I to cellulose II and/or amorphization. In
addition, a strong and broad signal appears at 120
1
35 ppm, associated with the C=C bond formation in
(a)
C C C
cellulose chains, induced by heating. These results are
consistent with the scheme of thermal degradation of
cellulose, described in [10].
2
3
5
C3,C5
In the presence of a solvent (glycerol), the diffu-
sion reduction process probably occurs in two stages.
In the first stage, in the process of Ag diffusion into
the MCC matrix, several complex forms of silver ions,
i.e. the aqua complexes [Ag(H O) ] , the solvates
Ag(Glyc) , and polynuclear complexes, exist in the
system Ag Glyc H O Cell. It is known that Ag
+
C6
C1
C4
+
2
2
C6
60
+
+
+
C4
2
ions form with alcohols unstable solvates [11].
However, 1,2-ethanediol solvates Ag ions stronger
+
than water [12]. According to [13], the polyatomic
alcohol mannite [(CH OH (CHOH) CH OH)] forms
100
80
(b)
C, ppm
2
4
2
OH
H
the complex AgBO C H O . One can suppose that
2
6
14
6
+
3
OH
Ag ions can form with glycerol fairly strong chelates
and polynuclear coordination compounds, as well as
solvates.
C
H
O
2
HO
O
H
1
O
O 4
HO
5
5
1
4
2
6
C
O
3
OH
Diffusion of silver ions into the MCC matrix
proceeds at high temperatures. Silver ions are pro-
H
OH
+
13
bably transferred from the aqua complex [Ag(H O) ]
Fig. 1. (a) Solid-state high-resolution C NMR spec-
trum of microcrystalline cellulose and (b) proposed
transformation paths of anhydroglucose cellulose units.
2
2
+
+
to the Ag (Glyc) and then Ag Cell forms. Ob-
n
viously, glycerol promotes transfer of silver ions from
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 3 2003

430
KOTEL’NIKOVA et al.
6
C=O
5
>
C=C<
4
3
2
1
180
160
140
120
100
80
60 C, ppm
1
3
Fig. 2. Solid-state high-resolution C NMR spectra of microcrystalline cellulose heated at (1) 150, (2) 200, (3) 250, (4) 280,
5) 300, and (6) 380 C.
(
High-temperature treatment of MCC in the glycerol
1,10-Phenanthroline (Phen), a -electron-deficient
ligand, is a widely used ligand of the above type [17].
medium contributed into structural changes in the
cellulose matrix. It is known that heating at 50 200 C
in glycerol leads to destruction of MCC [14]. Here,
like on heating in air, additional aldehyde groups are
formed. This enhances the reductive power of the
cellulose and favors increased production of silver(0)
in the matrix.
+
In the first stage, Ag complexes with 1,10-phenan-
throline (B) are formed. The composition of these
+
complexes corresponds to the formula [Ag(Phen)2]
[18 20].
The role of glycerol as reaction medium is en-
hanced by its partial oxidation to give a mixture of
glycerol aldehyde, 1,3-dihydroxyacetone, and some
acids (for instance, glyceric acid) [15, 16]. The first
component is able to reduce silver ions. Hence, the
assistance of glycerol and specific temperature
conditions make for greater amounts of silver(0) in
the cellulose matrix compared with those obtained by
other methods. The silver (0) contents in sample no. 5
are 6.1 wt% in bulk and 12.6 wt% on the surface.
The complex participates in the redox process
Scheme 3).
It is known that one of the general methods of
synthesis of noble metal clusters is reduction of their
salts by various reducers in the presence of ligands
stabilizing low oxidation states of the metals [17].
(
As seen from this scheme, 1,10-phenanthroline
inserts into the cellulose matrix, being coordinated
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 3 2003

MECHANISMS OF DIFFUSION REDUCTION INTERACTION
431
Scheme 3.
with Ag(0) . This is indirectly confirmed by the XPS
data: The samples contain both silver(0) and nitrogen
on the surface of cellulose fibers.
visible light during Ag+ diffusion into the MCC
matrix. Once primary Ag(0) centers have appeared,
growth of silver(0) particles commences. The silver(0)
contents in sample no. 7 are 5.3 wt% in bulk and
2
The reaction proceeds in aqueuos-glycerol medium,
and, therefore, the role of glycerol as a polyatomic
alcohol is analogous to that described above. The
process of formation of metal particles is rather
complicated [22] and can be shown by Scheme 4.
2
.2 wt% on the surface. After repeated treatment by
the reducer, the silver(0) content in sample no. 8 is
6
.2 wt% in bulk and 2.6 wt% on the surface.
Diffusion reduction process involving potassium
hypophosphite as reducer. Potassium hypophosphite
most commonly used for reductions in alkaline media.
The hypophosphite anion is a two-electron reducer.
Scheme 4.
L, e
0
0
0
[
Ag (Phen)]
[Ag (Phen) ]
[Ag (Phen) ]
m y
2
n
x
H
N
gigantic
electron-
excessive
clusters
small
(
+)
(3+)
clusters
clusters
Ag+
O P==O + 3OH
O P==O + 2H O + 2e
2
n = 4 10
m > 100
H
O
Ag(0)
Nevertheless, its reductive properties can also be
manifested in acidic media, where the reaction rate is
lower. To activate cellulose in this reaction, after
+
Since the [Ag(Phen) ] complexes are large-sized,
2
their reduction to gigantic particles like [Ag (Phen) ]
m
y
+
in the MCC matrix may be hindered by steric reasons
or provide smaller silver(0) particles. As found by
transmission electron microscopy [22], the size distri-
bution of silver(0) particles in the cellulose samples
prepared in 1,10-phenanthroline medium is bimodal:
Both small ( 10 nm) and large ( 60 nm) particles
are present. The silver(0) contents in sample no. 6 are
completion of Ag diffusion into the MCC matrix we
added to the reaction mixture first phosphoric acid and
then the reducer. In this case, the reduction takes place
mainly in solution. However, reduction in the MCC
matrix is also possible due to its activation, namely,
loosening of its morphological structure as a result of
acid treatment.
3
.0 wt% in bulk and 4.1 wt% on the surface.
Orthophosphoric acid protonates donor cellulose
oxygen atoms. As a result, they lose the ability to
coordinate with silver ions to form outer- and inner-
sphere complexes. Thus, acid medium precludes
participation of MCC in the redox process as reducer,
and reduction of silver ions starts even when KH PO
Diffusion reduction process involving sodium
boron hydride as reducer. Sodium boron hydride is
a strong reducer. The redox reaction involves several
concurrent processes. One of them is reduction of the
Ag ions intercalated into the MCC matrix; the other
one is reduction of the Ag ions fixed on the micro-
fibril surface. It was also established that reduction of
Ag ions also takes place in bulk solvent. The reduc-
tion process can be represented by Scheme 5.
+
2
4
+
is added. The reduction process and subsequent
growth of silver(0) particles occur both on the cel-
lulose surface and in its pores. As shown by XPS [7]
and raster electron microscopy [22], most silver(0)
particles reside on the cellulose fiber surface. There-
fore, the silver(0) content on the surface of this
sample (sample no. 9) is very high : 16.5 wt% against
+
Scheme 5.
7
.6 wt% in bulk.
The redox process can be represented by Scheme 6.
Hence, the preparation of cellulose samples with
The reaction mainly occurs on the Ag(0) active
centres formed by the redox process induced by
intercalated silver(0) particles consists of two main
+
stages. The first one involves diffucion of Ag ions
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 3 2003

432
KOTEL’NIKOVA et al.
Scheme 6
the silver(0) particles is given in Table 2 according to
17, 23, 24]. From these data it follows that the
silver(0) particles intercalated into the cellulose matrix
contain both small and gigantic numbers of atoms.
[
3
Ag+ + H PO
Ag PO
4
+ 3H+,
+ 3H PO + 3H O
3
4
3
2
Ag PO
3 4
3
2
2
High-temperature treatment of microcrystalline cel-
lulose was performed in a vacuum at 150 and 250 C
for 2 h.
3
Ag(0)2 + 3H PO + 2H PO .
3 3 3 4
from aqueous AgNO solutions into the MCC matrix
3
and complexation with it. The second stage involves
reduction of the Ag ions bound to MCC molecules to
Diffusion reduction process involving cellulose
+
matrix as reducer (Table 1). Diffusion of the
+
silver(0) with subsequent formation of silver(0)
particles. At the beginning of the process, in the
Ag(H O)2 aqua complexes into the cellulose matrix
2
was performed by heating cellulose in 0.1 M or 0.2 M
+
course of Ag diffusion into the MCC matrix, silver
aqueous AgNO solutions at 90 100 C under con-
3
+
ions are partially photochemically reduced and form
tinuous stirring for 1 h. The Cell:Ag molar ratios
small Ag(0) particles (n = 4 10) which act as ca-
were 5 or 10. The liquid modulus , i.e. solution-to-
sample weight ratio was 10. In the course of heating
the color of the reaction mixture was changing from
white to pink. After washing and drying, a light
yellow powder was obtained (sample no. 2).
n
talytic centers in the subsequent reduction process.
The reduction is accomplished by the cellulose itself
via oxidation of its end aldehyde and alcohol and
groups or by specific reducers. The subsequent con-
version of primary reduced Ag(0) centers into small
silver(0) particles and their growth to gigantic par-
ticles also proceed just in the cellulose matrix.
To accelerate the redox process, concentrated
aqueous NH was added to the reaction mixture (
3
changed from 10 to 15), and it was heated at 70 C for
40 min. A brown color developed. After thorough
washing with hot water, the solid material was filtered
off and dried at 90 C to obtain a reddish brown
powder for both molar ratios (sample no. 3).
Hence, mechanisms of diffusion reduction interac-
tion of silver ions with cellulose in the presence of
solvents and ligands, as well as mechanisms of reduc-
tion of the ions in the cellulose matrix and on the
surface of cellulose fibers are suggested. It was shown
that the silver(0) content and silver(0) particle size
depend on the reducer type, solvent, reaction medium,
and ligand type.
To elucidate the effect of high-temperature treat-
ment on the reductive power of cellulose, the latter
was heated at 150 C or 250 C for 2 h. Therewith, the
sample got light yellow. It was then treated with
+
It was established that in the systems MCC
0.2 M aqueous AgNO . The Cell:Ag molar ratio was
3
+
+
[
[
A g ( H O ) ] , M C C [ A g ( N H ) ] , M C C
10, and was 10. The mixture was heated at 90 C for
1 h. A reddish brown color developed. After washing
and drying, the residue changed color from reddish
brown to yellow (sample no. 4).
2
2
3 2
+
+
Ag(NH ) ] glycerol, MCC [Ag(Phen) ] glycerol,
3
2
2
+
+
MCC [Ag(H O) ] [BH ] , and MCC [Ag(H O) ]
2
2
4
2
2
H PO , reduction of silver ions to silver(0) takes place
2
2
with subsequent formation of Ag(0) particles. In the
n
To elucidate the effect of the solvent (glycerol) on
the reductive power of cellulose, the latter was kept
absence of specific reducers, silver ions are reduced
to silver(0) due to reductive properties of cellulose.
With strong chemical reducers, such as sodium boron
hydride and potassium hypophosphite, more silver(0)
is formed in the cellulose matrix and growth of
silver(0) particles is stimulated.
in a 0.2 M aqueous-glycerol AgNO solution with vi-
3
+
gorous stirring at 180 C for 10 min. The Cell:Ag
molar ratio 10, and was 10. The reaction mixture
got dark gray. After cooling to room temperature,
concentrated aqueous NH was added ( changed to
3
1
2), and heating was continued for 40 min. A brown
EXPERIMENTAL
color developed. After washing and drying, a reddish
brown powder was obtained (sample no. 5).
Characteristics of the samples of microcrystalline
cellulose and cellulose silver(0) intercalates are given
in Table 1 and in [5, 7]. The bulk and surface con-
centrations of silver(0) were determined by X-ray
fluorescence analysis and X-ray photoelectron spec-
troscopy, respectively. The presence of silver(0) was
confirmed by X-ray phase analysis and X-ray photo-
electron spectroscopy [7, 22]. Relationship between
the sample color and the number of silver(0) atoms in
To elucidate the effect of the solvent (glycerol) and
additional complexation of silver ions with 1,10-
phenanthroline [Ag(0) and Ag(0) stabilizer] on the
n
reductive power of cellulose, the latter was heated in
0.2 M aqueous AgNO at 90 C with stirring for
3
+
1.0 h. The Cell:Ag molar ratio was 10, and was
10. After cooling, aqueous 1,10-phenanthroline
+
hydrate was added (Ag :1,10-phenanthroline hydrate
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 3 2003

MECHANISMS OF DIFFUSION REDUCTION INTERACTION
433
molar ratio 0.3; changed to 15). The mixture was
heated again at 90 C for 10 min. A light yellow color
developed because of the formation of a poorly
soluble complex [Ag(Phen) ]NO . A concentrated
glycerol solution was added ( changed to 35), and
the reaction mixture was heated at 150 C for 5 min;
therewith, it changed color to light brown. After addi-
5. Kotelnikova, N.E., Paakkari, T., Serimaa, R., We-
gener, G., Kotelnikov, V.P., Demidov, V.N., Schu-
karev, A.V., Windeisen, E., and Knozinger, H.,
Macromol. Symp., 1997, no. 114, p. 165.
6. Kotelnikova, N.E., Petropavlovsky, G.A., Sheve-
lev, V.A., Volkova, L.A., and Vasil’eva, G.G., Cellul.
Chem. Technol., 1976, vol. 3, no. 6, p. 3.
2
3
7
. Kotelnikova, N.E., Demidov, V.N., Wegener, G.,
Paakkari, T., Serimaa, R., Schukarev, A.V., and
Gribanov, A.V., Cellul. Chem. Technol., 2002,
vol. 36, no. 2, p. 38.
tion of 1.2 mmol of NaHCO and the reaction mixture
3
was heated again at 150 C for 5 min, as a result of
which it got greenish-gray. After thorough washing
with hot water, filtration, and drying at 90 C, a
greenish gray powder was obtained (sample no. 6).
8
9
. Fieser, L.F. and Fieser, M., Advanced Organic
Chemistry, London: Chapman and Hall, 1961.
. Kotelnikova, N.E., Elkin, A.U., Koltzov, A.I., Petro-
pavlovsky, G.A., and Sazanov, Yu.N., in Metody is-
sledovaniya cellulosy (Methods of Cellulose Re-
search), Riga: Zinatne, 1988, p. 61.
Diffusion reduction process involving sodium
boron hydride as reducer. Microcrystalline cellulose
was heated at 90 C and stirred in 0.2 M aqueous
+
AgNO for 1 h. The Cell:Ag molar ratio was 10, and
3
was 10. The reaction mixture was cooled, and
1
0. Tang, M. and Bacon, R., Carbon, 1964, vols. 2(3),
0
.13 M aqueous NaBH was added at room tempera-
4
no. 2, p. 211.
ture with vigorous stirring. The g value changed to
5. A grayish-brown color immediately developed.
After washing and drying, a grayish brown powder
was obtained (sample no. 7; after repeated treatment
with the reducer, sample no. 8).
11. Gmelin Handbuch der anorganischen Chemie, Silber,
System-Number 61, Berlin: Springer, 1975, vol. B6,
p. 206.
12. Breant, M. and Georges, J., Bull. Soc. Chim. Fr., 1972,
no. 1, p. 382.
1
1
1
3. Grun, A., Monatsh. Chem., 1916, no. 37, p. 409.
4. Petropavlovsky, G.A., Kotelnikova, N.E., Volko-
va, L.A., Cellul. Chem. Technol., 1982, vol. 16,
no. 3, p. 247.
5. Lawrie, J.W., Glycerol and the Glycols. Production,
Properties, and Analysis, New York: Chem. Catalog,
Diffusion reduction process involving potassium
hypophosphite as reducer. Microcrystalline cellulose
was heated in 0.2 M aqueous AgNO3 at 90 C with
+
vigorous stirring for 40 min. The Cell:Ag molar
1
1
1
ratio was 10, and g was 10. After addition of 5 M
aqueous H PO ( changed to 15), heating was con-
3
4
1
928, p. 283.
+
tinued for 40 min, aqueous KH PO was added (Ag :
2
2
6. Nevolin, F.B., Khimiya i tekhnologiya glitserina
(Chemistry and Technology of Glycerol), Moscow:
Izd. Pischevoi Prom sti, 1954.
7. Gubin, S.P., Khimiya klasterov. Prontsipy klassifika-
tsii i struktura (Chemistry of Clusters. Classification
Principles and Structure), Moscow: Nauka, 1987.
8. Gubin, S.P. and Eremenko, N.K., Zh. Vses. Khim.
O va, 1991, vol. 36, no. 6, p. 718.
9. Demidov, V.N., Kukushkin, Yu.N., Iretzky, A.V.,
Djidkova, O.B., and Vedeneeva, L.I., Zh. Obshch.
Khim., 1991, vol. 59, no. 8, p. 1886.
0. Demidov, V.N., Denisov, I.A., Beliaev, A.N., Yakov-
lev, V.N., and Kukushkin, Yu.N., Koord. Khim., 1991,
vol. 17, no. 12, p. 1717.
KH PO molar ratio 0.4, changed to 50), and the
2
2
mixture was additionally heated at 90 C with stirring
for 15 min. A grayish-brown color immediately
developed. After thorough washing, decantation, and
drying at 90 C, a gray powder was obtained (sample
no. 9).
1
1
ACKNOWLEDGMENTS
The authors are grateful to the Deutscher
Forschungsgemeinschaft for financial support of this
work and to the Corresponding Member of the Rus-
sian Academy of Sciences Prof. E.F. Panarin for
discussion and valuable comments.
2
2
1. Demidov, V.N., Zh. Prikl. Khim., 1992, vol. 65, no. 7,
p. 1654.
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RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 3 2003