Bull. Soc. Photogr. Imag. Japan. (2020) Vol. 30 No. 2: 10–18

Original Paper

Preparation of Gold Nanoparticles Using Silver Halide Photographic Materials(10): Effect of Ascorbic Acid Concentration
Ken’ichi KUGE1, Hidetaka TOMIMATSU2, Yousuke IMAI3

Abstract:

The formation of gold nanoparticles with the gold deposition development was investigated by altering the concentration of the gold(I) complex (AC) and ascorbic acid (AcA) solutions or their concentration ratio AC/AcA in the developer with three methods: absorption spectrum
measurement, atomic absorption spectroscopy and transmission electron microscopy. Several phenomena, such as the variation in the development rates, existence of an induction period in the development rates, shift in the wavelength of maximum absorption, expansion of theband width, simultaneous formation of silver atoms, and change in the smoothness of the particle surface, were observed. These phenomena
depended not only on the concentration of both solutions but significantly on their ratio. All these phenomena changed at a concentration
ratio equal to unity, and it was suggested that the formation process varied at approximately this ratio. A novel process, whereby silver halide
was reduced by excess AcA to form silver atoms and these atoms subsequently reduced gold ions to form gold atoms, was proposed to explain
the acceleration of the development rates, the disappearance of the induction period, red-shift and expansion of the band, as well as the appearance of a rough surface on the particles.

Key words:

Silver salt photographic materials, Gold deposition development, Gold nanoparticles, Formation mechanism, Ascorbic acid

1. Introduction
Up to now, we have reported the formation of gold nanoparticles
via the gold deposition development method, which is a new approach in silver halide photography1-9). In this process, the latentimage speck (LIS), which is a tiny speck of silver atoms formed on asilver halide grain by exposure, acts as a catalyst for the reduction of
the monovalent gold-ion Au(I) complex (AC) in the developer togold atom. These gold atoms are deposited on the LIS to form a gold
nanoparticle10,11), wherefrom we can obtain an image composed of
the gold nanoparticles.
It was considered that the formation of gold atoms proceeded
through the disproportionation reaction of AC 2, 12). We reported
that the reaction rate increased with the concentration of AC in thedeveloper 3), and the addition of ascorbic acid (AcA) significantly
accelerated the formation of gold atoms 7). Moreover, using energy-dispersive X-ray spectroscopy, we reported that a small amountof silver atoms was formed through the reduction of silver halide by
AcA 8). Therefore, it was suggested that several reactions, such as thedisproportionation reaction of AC, reduction of AC by AcA, or reduction of silver halide by AcA, were proceeding. The details, however, remained ambiguous.
The gold deposition development was mainly analyzed based on
the condition that the concentration ratio of AC and AcA (AC/
AcA) was constant. Upon altering this ratio, it is expected that different formation processes of gold nanoparticles will proceed; thus,

we can obtain information on the reaction mechanisms. Here, we
altered not only the concentrations of AC and AcA but also theirconcentration ratios, and analyzed the formation process of gold
nanoparticles by three methods: absorption spectrum measurement,
atomic absorption spectroscopy, and transmission electron microscopy. Thereafter, we aimed to clarify the formation mechanism ofgold nanoparticles.

2. Experimental method
The photographic emulsion used was composed of near-sphericalsilver iodobromide ultrafine grains with a size of 40–50 nm. Thisemulsion grain was the same as that used in the photographic glass
plate of P5600 (Konica Minolta) for holography, although the emulsion used here was untreated with any sensitization, as in previous
reports 8, 9). An aqueous gelatin solution was added to this emulsion
to adjust the silver to gelatin ratio, and the mixture was coated on a
glass substrate to prepare dry plates. No hardening process was performed. This plate was referred to as plate A. In addition, we purchased the above-mentioned P5600 plate. This plate was produced
after treating the spectral and chemical sensitizations to the emulsion, and underwent a hardening process. This plate was referred toas plate B,
Plate A was exposed with a xenon flash lamp for an exposure timeof 10–3 s. This lamp had been used in some previous reports 1, 5, 8, 13-15)*, although its exposure value was unknown. Plate B was subjected toa high-intensity exposure using a sensitometer (EG&G Mark7)

Received 18th October, 2020; Accepted 5th December, 2020, Published 7th December, 2020
1 Radioisotope Research Center, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
2 Graduate School of Advanced Integration Science, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
3 Faculty of Engineering, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan

Ken’ichi Kuge, Hidetaka Tomimatsu, Yousuke Imai

Preparation of gold nanoparticles using silver halide photographic materials (10): Effect of ascorbic acid concentration

with an exposure time of 10-3 s. The exposure value was 3.77, which
represented the logarithm of the value with a unit of cd·s/m2. Thisvalue was less than the one obtained with the former xenon flash
lamp upon comparing the sensitometry results. In both cases, thewhole area of the plate was uniformly exposed.
Formulas of the developer for gold deposition development are
shown in Table 1 for plate A and Table 2 for plate B. The formula ofthe developer was basically the same as before 7-9). The AcA solution
in the formula was added to the developer just before development
to adjust each concentration listed in Tables 1 and 2. The concentrations of AcA and sodium chloroaurate in the developer, and the ratioof both solutions were altered, while the concentration ratio of potassium thiocyanate and sodium chloroaurate was kept constant at
an optimum value of 4:1 6). As plate A was not hardened, and theemulsion layer on the plate often swelled and peeled off easily during
development, we added sodium sulfate to the developer as a swelling
inhibitor.
Development was conducted at 20 °C for plate A to prevent peel-

Table 1

Formula of gold deposition development for plate A (mol/L)
2×10-4 ‒ 8×10-3

KSCN

NaAuCl4・2H2O

5×10-5 ‒ 2×10-3

KBr

8×10-3

Na2SO42×10-2

1×10-6 ‒ 2×10-3

Ascorbic acid

Table 2

Formula of gold deposition development for plate B (mol/L)

KSCN

4×10-3KBr

8×10-3

NaAuCl4・2H2O

1×10-3
1×10-6 - 1×10-2

Ascorbic acid

Procedure of gold deposition development for plate A
Treatment temperature = 20°C

Development

Developer in Table 1

Stop

Pure water

Wash

Running water

Stop
Fix

Wash

Pure water

5 min ‒ 72 h
5 min
5 min

F-5 fixer

10 minPure water

10 min30 minTable 4
Procedure of gold-deposition development for plate B
Treatment temperature = 25°C

Development

Developer in Table 2

Stop

Pure water

Stop
Fix

Wash
Wash

Pure water

5 min ‒ 24 h
5 min

5 min

F-5 fixer

10 minPure water

10 minRunning water

ing, and at 25 °C for the hardened plate B. The development time
was altered from 5 min to 72 h to obtain the development rates.
Procedures in a development process, such as fixation, are shown in
Table 3 for plate A and Table 4 for plate B.
The absorption spectrum of gold nanoparticles on the plate after
the development treatment was measured with a visible spectrophotometer (Shimadzu, UV 2550). We searched the wavelength of theabsorption maximum (λmax) in the range of 350–750 nm from each
spectrum and obtained the maximum absorbance (Max Abs) in thisrange. Increasing in the maximum absorbance with the development
time was evaluated as the increasing rate of the maximum absorbance.
An atomic absorption spectrometer (Varian, SpectrAcA-50/55)
was used to measure the amount of gold or silver atoms formed on
the plate. We cut out a certain area (25×20 mm2) of the plate after
development, dissolved the gold nanoparticles on the plate withaqua regia, and diluted the solution appropriately. A calibration
curve for gold was prepared from the solution by dissolving a gold
wire with aqua regia, while that for silver was prepared from anaqueous solution of silver nitrate. Increasing in the gold or silver
amount with the development time was evaluated as the formation
rate of the gold or silver amount.
We observed the gold nanoparticles with an electron microscope.
The samples for the observation were prepared using a previous
method8). The emulsion layer was scraped off from the plate after thedevelopment and the gelatin in the layer was decomposed by enzymes to make a suspension of gold nanoparticles. We placed a dropof this solution on a grid coated with a collodion membrane anddried to prepare samples for microscopy evaluation. These samples
were observed with a transmission electron microscope (Hitachi,
H-7650) to measure the particle diameters. Increasing in the particle diameter with the development time was evaluated as the growthrate of the particle size.

3. Experimental results

Table 330 min11

3.1 Dependence on ascorbic acid concentration
Here, the AC concentration was fixed at 1×10-3 mol/L, and the
AcA concentration in the developer was altered from 1×10−2 to
1×10−6 mol/L.
Gold nanoparticles generally absorb green light strongly by localized surface plasmon resonance. Figure 1 shows the AcA concentration dependence of the absorption spectrum of the layer with gold
nanoparticles on plate A. When the AcA concentration was low, thespectrum showed a slightly sharp absorption in the green spectral
region around 540–570 nm. This peak shifted to longer wavelengthand the band became broader with increasing AcA concentration.
The increasing rate of the maximum absorbance is shown in Figure 2. At a low AcA concentration, the rate was low and there wasan induction period, revealing a very small increase at the beginningof development. Therefore, the increase exhibited an S-shaped curve.
The rate accelerated significantly with increasing AcA concentration. A significant increase in the rate and the disappearance of theinduction period were observed between AcA concentrations of
1×10-4 mol/L and 1×10-3 mol/L. A significant acceleration of the12Bull. Soc. Photogr. Imag. Japan. Vol. 30 No. 2 (2020)

rate appeared at the initial stage with the disappearance of this induction period.
The formation rate of the gold amount (MAu) measured withatomic absorption spectrometry for plate B is shown in Figure 3.
The upper figure shows the changes on a long time-scale, while thelower one presents the changes on a short time scale around theinitial increase. At a low AcA concentration, the formation rate was

Abs

3

AcA/mol L-1 & t/min AC = 1x10-3 mol/L: 2x10-3
60: 1x10-3
60-4: 1x10-5 180: 5x10-5 300: 1x10-6 300: 1x10 300: 0360

3.2 Dependence on gold(I) ion complex concentration
The AcA concentration was fixed at 1×10-4 mol/L or 1×10-3
mol/L for this evaluation. The AC concentration in the developer
was altered from 2×10-3 to 5×10-5 mol/L. Plate A was used for theexperiments in this evaluation.

2

3.2.1 Ascorbic acid concentration of 1×10-4 mol/L
The dependence of absorption spectrum on the AC concentrationis shown in Figure 5. When the AC concentration was equal to or
lower than the AcA concentration, the band was broad. The band

10low, indicating an S-shaped curve with the induction period. The
rate accelerated rapidly and the induction period became shorter
with increasing AcA concentration. When the concentration exceeded 1×10-3 mol/L, the induction period almost disappeared.
The formation rate of the silver amount (MAg) measured withatomic absorption spectrometry for plate B is shown in Fig. 4. There
was almost no increase, or possibly a very small increase in theamount of silver up to an AcA concentration of 1×10-3 mol/L,
while there was a sharp increase in the amount at an AcA concentration of 1×10-2 mol/L. Silver atoms were produced quickly at ahigh AcA concentration as described in the previous report8), although the silver amount was approximately 1/10 of the gold one
produced at the same time.

400

500

600

700

Wavelength / nm
10Fig. 1 Absorption spectra of gold nanoparticles formed on plate A at different concentrations of ascorbic acid (AcA) from 0 to 2×10-3 mol/L in
the developer. The concentration of Au(I) complex (AC) was fixed to
1×10-3 mol/L. The development time is presented with each legend.

MAu / 10 -7mol cm-2

4

3
Max Abs-1
AcA / mol L-2: 1x10-3: 1x10-4: 5x10-4: 1x10-5: 1x10-6: 1x10AC = 1x10-3 mol/L
:0

5

2

0

0

500

1000

1500

10

1
5

0
0

100

200

300

400
0

Development time / min-1

AcA / mol L-3-3: 2x10: 1x10: 5x10-5: 1x10-5
AC = 1x10-3 mol/L

50

100

150

Development time / min-4: 1x10: 1x10-6

0:0Fig. 2 Increasing rate of maximum absorbance in each spectrum of gold
nanoparticles formed on plate A. The concentration of ascorbic acid
(AcA) in the developer was altered from 0 to 2×10-3 mol/L, whilethat of Au(I) complex (AC) was fixed to 1×10-3 mol/L.

Fig. 3 Formation rate of gold amount formed on plate B measured withatomic absorption spectroscopy. The concentration of ascorbic acid
(AcA) in the developer was altered from 0 to 1×10-2 mol/L, whilethat of Au(I) complex (AC) was fixed to 1×10-3 mol/L. Top figure:long timescale, bottom figure: short timescale highlighting the initial
increase.

Ken’ichi Kuge, Hidetaka Tomimatsu, Yousuke Imai

Preparation of gold nanoparticles using silver halide photographic materials (10): Effect of ascorbic acid concentration

became sharp with an increase in AC concentration, while the wavelength of the absorption maximum did not vary as much.
The dependence of increasing rate of maximum absorbance on
the AC concentration is shown in Figure 6. At a low AC concentration, there was no induction period and the initial rate was high,while the absorbance was saturated at a small value. With an increase in AC concentration, the initial rate decreased and the induction period appeared at an AC concentration of approximately
1×10-3 mol/L. The absorbance was not saturated on the experimental time scale. However, when the AcA concentration was zero, theinduction period was long and the rate was extremely low. The dif-ference in the rates with and without AcA was remarkable.
The formation rate of the gold amount measured with atomic absorption spectrometry is shown in Figure 7. At a low AC concentration, the initial rate was high and no induction period was observed.
The induction period appeared and became longer along with increasing AC concentration. When the AcA concentration was zero,the induction period was long and the rate became much lower.
The growth rate of the diameter of gold nanoparticles observed

4

MAg / 10 -7mol cm-2

Max Abs

Ag
1-1
AcA / mol L-2: 1x10-3: 1x10-4: 5x10-4: 1x10-5: 1x10-6: 1x10
:0

0.5

0
100

200

300

Fig. 4 Formation rate of silver amount formed on plate B measured withatomic absorption spectroscopy. The concentration of ascorbic acid
(AcA) in the developer was altered from 0 to 1×10-2 mol/L, whilethat of Au(I) complex (AC) was fixed to 1×10-3 mol/L.

2

AC / mol L-3-1 & t/min: 2x10-3 300: 1x10-4 300: 5x10-4 300: 2x10-4 300: 1x10-5 300: 5x10 180
AcA= 1x10-4 mol/L

0
0

1

400

500

600

700

Wavelength / nm
Fig. 5 Absorption spectra of gold nanoparticles formed on plate A at different concentrations of Au(I) complex (AC) from 5×10-5 to 2×10-3
mol/L in the developer. The concentration of ascorbic acid (AcA) was
fixed to 1×10-4 mol/L. One sample with 1×10-3 mol/L AC andwithout AcA was included. The development time is presented witheach legend.

200

300

400

500

Fig. 6 Increasing rate of maximum absorbance in each spectrum of gold
nanoparticles formed on plate A. The concentration of Au(I) complex(AC) in the developer was altered from 5×10-5 to 2×10-3 mol/L,
while that of ascorbic acid (AcA) was fixed to 1×10-4 mol/L. One
sample with 1×10-3 mol/L AC and without AcA was included.

MAu / 10 -7mol cm-2

Abs

2

100

Development time / min

6

AC / mol L-1: 2x10-3: 1x10-3: 5x10-4: 2x10-4
AcA = 1x10-4 mol/L

4: 1x10-3
AcA=0: 1x10-3 360
AcA=0

0

-3

: 1x10AcA=0400

Development time / min

33

AC / mol L-1-3: 2x10-3: 1x10-4: 5x10-4: 2x10-4: 1x10-5: 5x10-4
AcA = 1x10 mol/L

1
0

4

13

2

0
0

100

200

300

400

500

Development time / minFig. 7 Formation rate of gold amount formed on plate A measured withatomic absorption spectroscopy. The concentration of Au(I) complex(AC) in the developer was altered from 5×10-5 to 2×10-3 mol/L,
while that of ascorbic acid (AcA) was fixed to 1×10-4 mol/L. One
sample with 1×10-3 mol/L AC and without AcA was included.

14

Bull. Soc. Photogr. Imag. Japan. Vol. 30 No. 2 (2020)

from the electron micrographs is shown in Figure 8. There was noremarkable induction period and the growth rates were approximately the same each other. At a low AC concentration, the growth
stopped at the stage whereat the diameter was small, although thesize at saturation gradually increased with the AC concentration.

80

40

AC / mol L-1-3: 2x10 -3: 1x10 -4: 5x10 -4: 2x10
AcA = 1x10 -4 mol/L

4: 1x10 -3
AcA=0

20

0
0

100

200

300

400

500

Development time / minFig. 8 Growth rate of diameter of gold nanoparticles formed on plate A
measured from transmission electron micrographs. The concentrationof Au(I) complex (AC) in the developer was altered from 5×10-5 to
2×10-3 mol/L, while that of ascorbic acid (AcA) was fixed to 1×10-4
mol/L. One sample with 1×10-3 mol/L AC and without AcA was
included. The bar on each plotting point represents the standard deviation of the diameter.

3

3.2.2 Ascorbic acid concentration of 1×10-3 mol/L
This section presents the results when the AcA concentration was

Max Abs

Diameter / nm

60

When the AcA concentration was zero, the particle size did notexhibit saturation, and it increased continuously. From the perspective of the increase in particle size, the difference in the growth rates
with and without AcA was not remarkable.

AC / mol L-1& t/min: 2x10-3
60-3: 1x10-4 60: 5x10 60
AcA= 1x10-3 mol/L

AC / mol L-1: 2x10-3: 1x10-3: 5x10-4
AcA = 1x10-3 mol/L

32: 1x10-3
AcA=0

1

0
0

100

200

Development time / minFig. 10 Increasing rate of maximum absorbance in each spectrum of gold
nanoparticles formed on plate A. The concentration of Au(I) complex (AC) in the developer was altered from 5×10-5 to 2×10-3
mol/L, while that of ascorbic acid (AcA) was fixed to 1×10-3 mol/L.
One sample with 1×10-3 mol/L AC and without AcA was included.

Abs: 1x10-3 360
AcA=0

2

1

0

400

500

600

700

Wavelength / nm
Fig. 9 Absorption spectra of gold nanoparticles formed on plate A at different concentrations of Au(I) complex (AC) from 5×10-5 to 2×10-3
mol/L in the developer. The concentration of ascorbic acid (AcA) was
fixed to 1×10-3 mol/L, which was different from the condition in Figures 5–8. One sample with 1×10-3 mol/L AC and without AcA was
included. The development time is presented with each legend.

Fig. 11 Transmission electron micrographs of gold nanoparticles formed onplate A. The concentration of ascorbic acid (AcA) in the developer
was set 0 for (a) and was fixed to 1×10-3 mol/L for (b) to (d), whilethat of Au(I) complex (AC) was altered as, (b) 2×10-3, (a) and (c)1×10-3, and (d) 5×10-4 mol/L. The development time for (a) was
540 min and those for (b) to (d) were 120 min.

Ken’ichi Kuge, Hidetaka Tomimatsu, Yousuke Imai

Preparation of gold nanoparticles using silver halide photographic materials (10): Effect of ascorbic acid concentration

increased ten-fold to 1×10-3 mol/L. In this case, AC/AcA was set
to small values less than two.
The dependence of absorption spectrum on the AC concentrationis shown in Figure 9. When the AC concentration decreased, thewavelength of the absorption maximum shifted significantly to thelong wavelength side and the band became broad. Figure 10 shows
the dependence of increasing rate of maximum absorbance on the
AC concentration. There was no remarkable induction period, andthe rate difference was not evident for the case with AcA. Saturationof absorbance was observed at an AC concentration lower than the
AcA Concentration.
The electron micrographs of gold nanoparticles are shown in Figure 11. At the highest AC concentration of 2×10-3 mol/L or without AcA, the surface of gold nanoparticle was smooth. Conversely,
the surface became rough with decreasing AC concentration, andrevealed many minute protrusions on the surface at an AC concentration of 5×10-4 mol/L. This behavior is the same as that reported
previously 8, 9).
The growth rate of the diameter of gold nanoparticles observed
from the electron micrographs is shown in Figure 12. There was noevident induction period, and no significant difference in the rate forthe case with AcA. Saturation of particle size was observed at thelowest AC concentration of 5×10-4 mol/L, and this result corresponded with the one in Figure 10. For the case without AcA, thegrowth rate was low, while the particle size increased continuously
without saturation.
Discussion
The following phenomena were observed in the formation processof gold nanoparticles when the AC and AcA concentrations were15

altered:(I) The development rates of gold nanoparticles changed. The increasing rate of the absorbance and the formation rate of thegold amount changed significantly, while the growth rate of theparticle size was not as pronounced.
(II) The induction period appeared at the initial stage of these rates.
While the induction periods for the absorbance and gold
amount exhibited similar behaviors, that for the particle size differed.
(III) The wavelength of the absorption maximum in the absorption
spectrum shifted.
(IV) The absorption band width changed.
In addition, the following phenomena, which were previously reported 8, 9), were confirmed:(V) Silver atoms were produced simultaneously with gold atoms under some conditions.
(VI) The surface of the gold nanoparticles was usually smooth, but
under some conditions, a rough surface with minute protrusions
appeared.
These changes seem to depend on the concentrations of AC andAcA. However, it may be more probable that they depend on theconcentration ratio of the two rather than on each concentration. To
analyze this, we altered the concentration ratio of AC to AcA (AC/
AcA) and examined the dependence of the above mentioned changes on this ratio.
The induction periods for the increasing rate of the maximum
absorbance and the formation rate of the gold amount were analyzed. The period for increasing the absorbance from 0 to 0.05 andthat for increasing the gold amount to 2×10−8 mol/cm2 were estimated from the corresponding figures for the maximum absorbanceand gold amount, respectively. These values were set as induction

80AC / mol L-1: 2x10-3: 1x10-3: 5x10-4
AcA=1x10-3 mol/L

200 AC change, AcA=1x10-4mol/L: 1x10-3
AcA=0: Abs,

τ Abs &τ M /min

Diameter / nm

60||
AcA change, AC=1x10-3mol/L: Abs,
: MAu

40

20

0
0

100

200

300

Development time / minFig. 12 Growth rate of diameter of gold nanoparticles formed on plate A
measured from transmission electron micrographs. The concentration of Au(I) complex (AC) in the developer was altered from
5×10-5 to 2×10-3 mol/L, while that of ascorbic acid (AcA) was fixed
to 1×10-3 mol/L. One sample with 1×10-3 mol/L AC and without
AcA was included. The bar on each plotting point represents thestandard deviation of the diameter.

: MAu

AC change, AcA=1x10-3mol/L
: Abs

100

0

0.1

1

10

100

1000

||

AcA
10000
=0

AC/AcA
Fig. 13 
Relationships between the concentration ratio of Au(I) complex(AC) to ascorbic acid (AcA) and the induction periods of the increasing rate of maximum absorption (τAbs) or the formation rate ofgold amount (τM) for the series with altered AcA concentrations anda fixed AC concentration of 1×10-3 mol/L, and for the ones with altered AC concentrations and fixed AcA concentrations of 1×10-4
mol/L and 1×10-3 mol/L.

16

Bull. Soc. Photogr. Imag. Japan. Vol. 30 No. 2 (2020)

periods, τabs and τM. The relationships of τabs and τM with AC/AcA
are shown in Figure 13, and indicated similar behaviors. The induction period was almost zero below the AC/AcA of unity, and significantly increased above the AC/AcA of two. These suggest that there
is a boundary around the AC/AcA of unity.
Similarly, the relationships of the wavelength of absorption maximum λmax with AC/AcA are shown in Figure 14. The wavelength
also showed almost the same behavior at the AC/AcA of approximately unity. When the ratio was unity or less, λmax increased significantly indicating that the peaks shifted to a long wavelength region.
The values of λmax for the AC concentration of 1×10-4 mol/L presented by the black circles were uncertain, because they were obtained from spectra with a small absorbance.
Both figures show that substantial changes occurred at the AC/
AcA of approximately unity. Meanwhile, the formation of silver atoms was observed, as shown in Fig. 4, for AC/AcA=0.1. The surfaceof the gold nanoparticles shown in Figure 11 changed from smoothto rough at the AC/AcA of approximately unity. These changes suggested that the formation mechanism of gold nanoparticles changedin the region where the AcA concentration was higher than the ACconcentration.
However, upon comparing with the case without AcA, the formation rate of gold amount with AcA was high even at an AcA concentration of 1×10-6 mol/L, which was 1/1000 of the AC concentration, as shown in Figure 3. The mechanism may differ in the caseswith and without AcA.
From these results, we can consider that there are three processes
for gold nanoparticle formation from a viewpoint of AcA/AC.
(1) In the case that there is no AcA and only AC: The rates of increase in the absorbance and formation of gold amount were
low, and there was an induction period in the rates measured
with the maximum absorbance and the gold amount, while theinduction period for the particle size was small or insignificant.
The absorption spectrum had a slightly sharp band and absorp-

700: AcA change AC=1x10-3
mol/L: AC change AcA=1x10-4
mol/L-3: AC change AcA=1x10 mol/L

λ max/nm

600

500
0.1

1

10

100

1000

AC/AcA
Fig. 14 
Relationships between the concentration ratio of Au(I) complex(AC) to ascorbic acid (AcA) and the wavelength at the absorption
maximum for the series with altered AcA concentrations and a fixed
AC concentration of 1×10-3 mol/L, and for the ones with altered
AC concentrations and fixed AcA concentrations of 1×10-4 mol/Land 1×10-3 mol/L.

tion occured in the green spectral region.
(2) In the case that the AcA concentration is smaller than the ACconcentration: Particles with only gold atoms were formed. The
increasing and formation rates were higher than that in the absence of AcA, but it had the induction period. The absorption
spectrum had a sharp band and absorption occured in the green
spectral region.
(3) In the case that the AcA concentration is larger than the ACconcentration: Gold particles contained a small amount of silver
atoms. The increasing and formation rates were high and there
was no induction period. The band in absorption spectrum wasbroad and shifted to the longer-wavelength side of the red spectral region.
Therefore, we can relate these three cases to the following threeformation processes of gold nanoparticles:(A) no AcA: Disproportionation reaction of AC.
(B) The AcA concentration is smaller than the AC concentration:
Direct reduction of AC by AcA. This process may be predominant in the reduction of silver halide by AcA, but the rates
must be low.
(C)The AcA concentration is larger than the AC concentration:
Simultaneous reductions of AC and silver halide by AcA. The
reduction of AC may be still predominant; however, excess
AcA can rapidly reduce silver halide.
Processes (A) and (B) proceed with the catalytic action of LISs.
As already reported 7-9), the required minimum number of silver atoms in LIS for catalytic activity differs between the disproportionation reaction of AC and the reduction of AC by AcA. The former
reaction is catalyzed only by LIS of large size. Therefore, the numberof gold nanoparticles generated with process (A) becomes less thanthat with process (B), thereby causing a decrease in the maximum
absorbance and gold amount in process (A).
The reaction rate of process (B) was low despite process (B) being
the predominant reaction.
A possible explanation is as follows: AC and AcA both form acertain complex of monovalent gold ion Au(I) quickly, and approximately all AcA is consumed owing to excess AC. This complex decomposes into a gold atom through the catalytic action of LIS, although the decomposition may be slow. After LIS is embedded inthese gold atoms, following decomposition of the complex proceeds
through similar catalytic action of gold atoms in the particles. This
activity may be similar to that of silver atoms in LIS and the development rate of gold deposition will be low.
The amount of silver atoms produced with process (C) was lessthan that of gold, even though the amount of AcA was significantly
in excess. An explanation is the larger ionization tendency of silver,
but there is another possibility that most of the silver atoms would
react with the AC complex and form silver halide again according to
the following formula:Ag(0) + Au(I) → Ag(I) + Au(0) (1)

The formation of silver atoms by the reduction of silver halide
with AcA catalyzed by LIS is similar to a normal development process. Therefore, the reaction rate to form silver atoms by AcA may be

Ken’ichi Kuge, Hidetaka Tomimatsu, Yousuke Imai

Preparation of gold nanoparticles using silver halide photographic materials (10): Effect of ascorbic acid concentrationhigh and significant amount of silver atoms is formed. The formation of gold atoms through the reaction in Eq. (1) proceeds quickly,
because the silver atoms react directly with the gold ion complex
without any catalyst. This accelerates the reaction of gold deposition
with process (C) and the induction period disappears.
When the process of Eq. (1) proceeds, a mixture of gold atoms
and silver halide is formed. However, as this silver halide is removed
through fixation following the development, gaps will be generated
on the particle surface by this removal, and the surface will becomerough, as shown in Fig. 11(c). The silver atoms detected with atomic
absorption spectroscopy are the residues embedded inside the particle, and the amount of silver becomes small.
Because LIS is composed of silver atoms, it is also possible thatsilver atoms in LIS form gold atoms by Eq. (1) instead of the embedding by gold atoms. However, as the amount of silver atoms in
LIS is very few, the gold particles formed are also very small.
One possible reason why the wavelength of the maximum absorption in the absorption spectra shifts to a longer-wavelength region and the bands becomes broad with process (C) may be thatsilver atoms are included in the particles, thereby changing the
wavelength of the localized surface plasmon resonance. Anotherreason may be that the shape of the particles changes differently
through the reaction of Eq.(1), which affects the wavelength of plasmon resonance.
The behavior of the induction period evaluated with the particle
size was different from that evaluated with the absorption spectrum
or the gold amount. This is explained as follows: We measured theabsorbance or the gold amount for all gold particles together, while
we evaluated the diameter for each particle individually. The size
distribution of the gold particles was fairly wide, as shown in theelectron micrographs in Figure 11 or in the standard deviation of thediameter in Figures 8 and 12. This suggests that the rate of particle
growth differs widely. Meanwhile, the diameter observed with theelectron microscope was not zero, but approximately 7 nm at thedevelopment time of zero, as shown in Figures 8 and 12. It was explained in a previous report 8) that these were LISs of large size owing to the large exposure value, and were larger than the resolutionof an electron microscope. Because a large LIS had a higher development rate, we only observed the growth behavior of large andevident particles at the initial stage of development and measured
the diameters of these particles only. This will apparently diminish
the induction period measured with the particle size. Because thesmaller LISs had a low development rate, the gold particles formedon the small LISs were not observed with the electron microscope at
the initial stage, while they contributed to the absorption spectrum
and gold amount.
The particle size was unsaturated without AcA, while it saturated
at a low AcA concentration for the same AC concentration. The
number of LISs to catalyze the disproportionation reaction is lessthan that to catalyze the reduction of AC by AcA7–9) owing to thedifference in LIS sizes. Because the number of gold particles formed
without AcA becomes few, the amount of usable AC for the growthof each particle increases and these gold particles can continue togrow without saturation.

17

Conclusion

1. The reaction whereby gold nanoparticles were formed with thegold deposition development depended not only on the concentrations of AC and AcA but also on the concentration ratio of
both solutions.
2. Gold atoms were formed by the disproportionation reaction ofmonovalent gold ions in AC without AcA. The reaction rate was
low and had a significant induction period.
3. When the AC concentration was larger than the AcA concentration, the reduction of AC by AcA proceeded. This reaction rate
was higher than that in the disproportionation reaction, but theinduction period was still considerable.
4. When the AcA concentration increased and AC/AcA becameless than unity, the reaction rate increased remarkably and the induction period disappeared. In this case, AcA produced silver atoms simultaneously by reducing silver halide.
5. It is suggested that the reaction between these silver atoms andgold ions will form gold atoms and silver halide. This reaction
proceeds quickly and increases the development rates. Because theformed silver halide is removed through subsequent fixation, theparticle surface becomes rough. This also causes the shift of theabsorption peak, as well as band broadening.

Acknowledgment

The authors thank Konica-Minolta Company for providing theultra-fine-grain emulsion used as plate A in this study. The authors
received immense support with using the atomic absorption spectrometer from the Center for Analytical Instrumentation in Chiba
University, and would like to express their gratitude to Dr. Mass inthis Center, as well as Dr. Okawa at the Graduate School of Engineering in Chiba University for their extensive support. The authors
also thank Dr. Shiba at the Graduate School of Engineering and
Ms. Tachiki of the Faculty of Engineering in Chiba University for
their valuable assistance and guidance with using the electron microscope.

Footnote* Previously we reported that the exposure time of this flash lamp
was 10-6 s. This was because the performance of the lamp had been
informed as such. However, recent measurement has indicated it to
be 10-3 s. It is speculated that μ (micro) seconds and m (milli) seconds had been confused.

References
1.
2.
3.
4.

K. Kuge, M. Arisawa, N. Aoki, A. Hasegawa, Jpn. J. Appl. Phys., 39,6550 (2000).
K. Kuge, K. Kimijima, M. Arisawa, N. Aoki, A. Hasegawa, J. Soc. Photogr. Sci. Technol. Jpn., 64, 242 (2001) (in Japanese).
K. Kuge, K. Suzuki, N. Aoki, A. Hasegawa, J. Soc. Photogr. Sci. Technol.
Jpn., 65, 536 (2002) (in Japanese).
K. Kuge, M. Arisawa, N. Aoki, A. Hasegawa, Imaging Sci. J., 52, 176(2004).

18
5.
6.
7.
8.
9.

Bull. Soc. Photogr. Imag. Japan. Vol. 30 No. 2 (2020)

K. Kuge, T. Nakao, S. Saito, O. Hikosaka, A. Hasegawa, J. Imaging Sci.
Technol., 51, 96 (2007).
K. Kuge, X. Chen, T. Sakai, A. Hasegawa, J. Imaging Sci. Technol., 54,010507 (2010).
K. Kuge, Y. Yu, K. Fuma, R. Ito, T. Sakai, Bull. Chem. Soc. Jpn., 84, 947(2011).
K. Kuge, H. Tomimatsu, F. Shiba, Bull. Soc. Photogr. Imaging Jpn., 26,
23 (2016).
K. Kuge, T. Adachi, H. Tomimatsu, J. Soc. Photogr. Imaging Jpn., 81, 41(2018) (in Japanese).

10. D.C.Birch, G.C.Farnell, R.B.Flint, J.Photogr.Sci., 23, 249 (1975).
11. S. Jablonka, C. Mora, P. M. Nowak, A. Zaleski, J. Information Recording, 23, 249 (1996).
12. A.C.Reeder, H.E.Spencer, J.Imaging Sci., 31, 126 (1987).
13. K. Kuge, T. Tsutsumi, K. Morimoto, S. M. H. Kimura, T. Suzuki, T. Mitsuhashi, A. Hasegawa, J. Imaging Sci. Technol., 53, 010507 (2009).
14. K. Kuge, T. Inaba, S. Suzuki, S. Kodaira, J. Soc. Photogr. Imaging Jpn.,
79, 376 (2016) (in Japanese).
15. K. Kuge, K. Morimoto, Bull. Soc. Photogr. Imaging Jpn., 27, 1 (2017).