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Preparation of uniform β-FeO(OH) colloidal particles by hydrolysis of ferric salts under microwave irradiation
~
Reseerc,h Bulletin,Vol.30, No. 5, pp. 537-541, 1995 CopyrightO 1995ElsevierScimoeLt.d Prin~din theUSA.Allrigh~rcm'vcd 0025-5408/95 $9.50+ .00
Pergamon
0025..5408(95)00032-1
PREPARATION OF UNIFORM ~-FeO(OH) COLLOIDAL PARTICLES BY HYDROLYSIS OF FERRIC SALTS UNDER MICROWAVE IRRADIATION *Dong Daichuan, Hong Pinjie and Dai Shushan Yunnan University, Kunming Department of Chemistry, 650091, P.R.China Also with the Department of chemistry, Xinyang, Teachers' College (Received October 2, 1994; Refereed)
ABSTRACT Superfine and uniform ~-FeO(OH) colloidal particles have been prepared by hydrolysis of ferric salts with urea under microwave irradiation. Products were characterized by XRD and TEM. MATERIALS INDEX: iron, oxide, hydroxide Introduction Uniform colloidal particles are important in the development of many new materials. It is, thus, essential to study in both theory and practice the preparation process of such kinds of particles. ~I-FeO(OH) is an important hydrous oxide, which can be used as the basic material to prepare high-quality magnetic-recording materials. Uniform ~-FeO(OH) colloidal particles had been obtained by Matijevic [1] by forced hydrolysis of ferric salts in a closed vessel. However, it had been limited to a small scale because the restrictive conditions. To simplify the conditions and to minimize as much as possible the influence of heterogeneity of the temperature rise so as to meet the requirements of the industrial production, the cooperative effect of the microwave irradiation with the hydrolysis of urea has been successfully used to obtain uniform and superfine ~-FeO(OH) colloidal particles in this study. Experimental A refitted microwave oven with a multiple-model resonant cavity which the reactor sits in was used. The system operates at a 2.45GHZ frequency and can operate at 0-100% of full power (500 watts). 537
538
D. DONGet aL
Vol. 30, No. 5
Solutions of FeCl 3 and HC/, or FeC/3 and CO(NH2) 2 w e r e stoichiometrically placed into an Erlenmeyer flask equipped with a reflux condenser, then 200ml deionized water was added, and the microwave oven was turned on. After reacting for a certain period of time, the flask was placed in a homothermal w at er bath at 94°C, which was the same temperature as the above mentioned, for aging. The solid and solution phases were separated by centrifugation, and the solid phases were dried in an oven before characterization by powder X-ray diffraction(XRD) and transmission electron microscopy (TEM). The XRD were obtained using a D/max-3B diffractometer with CuK a radiation and the TEM was performed using an H-800 instrument.
Results and Discussion Characteristics of p r o d u c t powder. In the case of [Fe3÷] >_ 0.072M, the particles obtained were u n i f o r m ~-FeO(OH) crystallites identified by XRD analysis (Fig. 1). The TEM photograph (Figs. 2A and 2B) shows the rodlike crystallites with a regular shape and a very narrow size distribution. Both the uniformity and size of the particles were better than those made by the conventional method in the same concentration conditions.
.gK
rn It_) ~
.,,5
2.
10.oo
20.00
,0. O0
40. O0
50. O0
6 0 . O0
7 0 . (>0
FIG. 1 The XRD patterns of ~-FeO(OH) crystallites
85 . O0
Vol.30, No. 5
IRONOXYHYDROXIDE
FIG. 2 TEM photograph (x 50000) of [3-FeO(OH)
prepared
539
by microwave-induced
hydrolysis of 0.114M FeCt 3 in the case of [CO(NH2) 2] / [FeC~3] = l0 for A and 5 for B respectively.
Effect of Heating l~Rnner Keeping other experimental conditions unchanged, two different ways of heating, water bath or microwave irradiation, have been used for comparison. The results showed that the microwave irradiation can accelerate the hydrolysis of Fe 3÷. For example, in the case of FeCI3+HCe, the time for reaching hydrolysis equilibrium by microwawe irradiation was ten minutes less than that by waterbath; in the case of FeC/3 + CO(NH2)2, the time for complete hydrolysis by microwave irradiation was half an hour or so less than by water bath (Table 1). This could be attributed to the higher efficiency and smaller temperature gradient of microwave heating as compared to the waterbath. TABLE I
Manner of heatin G microwave waterbath
pH of the reaction solution at various times. (A) Time (rain.) 30 60 90 120 1.62 1.70 2.16 8.0 1.77 2.50
145 6.04
*[FeC/3] = 0.144M, [CO(NHu)2]:[FeCt 3] = 10:I,T = 94°C.
Manner of heating microwave i waterbath
3 1.18 ] 1.53 I
5 1.15 1.38
(B) Time (min.) 10 15 1.05 1,21 1.09
*[FeCi3] = 0.144M, pH (initial) = 3, T = 94°C.
18
20-120
1.05
1.03
1.03
540
D. DONG¢t al.
Vol.30, No. $
Our experiments also revealed that the uniformity of crystalline particles in the presence of microwave field was superior to that in the absence of external field for the system of FeC~3+CO(NH2)2, (Figs. 3A and 3B). This implies that the microwave irradiation may be influencing the nucleation process of ~-FeO(OH). The hydrolysis of Fe ~÷ is a rather complicated process, which could be written as follows: Fe3++ 2H20 -+ FeO(OH) @ + 3H ÷ and, CO(NH2)2, is ionized in water: CO(NH2) 2 ~ NH ~ + NCOthen, N C O - is hydrolysed further: NCO-+ 2H20 --* NH ~ + CO ~ and, 2H ÷+ CO 32- ~ H20 + CO2~ From the above, it was concluded that both processes of hydrolysis of Fe 3÷ and CO(NH2) 2 could be promoted. Furthermore, the very fast temperature rise caused by microwave irradiation accelerated the reactions and promoted the homogeneous nucleation so much that uniform and superfine ~-FeO(OH) particles were obtained.
FIG. 3 TEM photograph (x 50000) of ~-FeO(OH) prepared by microwave irradiation (A) or waterbath heating (B).
Vol. 30, No. 5
IRON OXYHYDROXIDE
541
Effect o f ~ t
Concentration Experiments indicated that the crystal size varied with the ratio of [CO(NH2)2] to [Fe3+], and when [CO(NH2)2] / [Fe3+] > 3, products could be obtained with a yield of nearly 100% of theoretical. For example, when [Fe3+] = 0.144M, as the ratio increased, the average particle size decreased correspondingly (Fig. 2). This was due to the fact that the increase of urea concentration could cause 'explosive' nucleation, which formed a large quantity of host crystal in an instant, and the crystallites were hindered from growing further.
Conclusions This study demonstrates that microwave-induced hydrolysis of ferric salts with dissociation of urea may lead to instantaneous nucleation. Optimizing the parameters such as concentration of the chemical species, ratio and irradiation time, we can obtaine uniform and superfine particles. In addition, the filtering of stock solutions through minute-pore membrance is unnecessary. This novel processing may prove to be a valuable method in the mass production of uniform dispersing colloidal particles. References .
2. 3.
E. Matijvic and P. Scheiner, J. Coll. Interface Sci., 63, 509 (1978). Chen Longwu, Zhang Kaihua and Jiang Jisen, Chem. Bull., 12, 33 (1990). Wang Guangxin, J. Phys. Chem., 7, 655 (1991).
Reseerc,h Bulletin,Vol.30, No. 5, pp. 537-541, 1995 CopyrightO 1995ElsevierScimoeLt.d Prin~din theUSA.Allrigh~rcm'vcd 0025-5408/95 $9.50+ .00
Pergamon
0025..5408(95)00032-1
PREPARATION OF UNIFORM ~-FeO(OH) COLLOIDAL PARTICLES BY HYDROLYSIS OF FERRIC SALTS UNDER MICROWAVE IRRADIATION *Dong Daichuan, Hong Pinjie and Dai Shushan Yunnan University, Kunming Department of Chemistry, 650091, P.R.China Also with the Department of chemistry, Xinyang, Teachers' College (Received October 2, 1994; Refereed)
ABSTRACT Superfine and uniform ~-FeO(OH) colloidal particles have been prepared by hydrolysis of ferric salts with urea under microwave irradiation. Products were characterized by XRD and TEM. MATERIALS INDEX: iron, oxide, hydroxide Introduction Uniform colloidal particles are important in the development of many new materials. It is, thus, essential to study in both theory and practice the preparation process of such kinds of particles. ~I-FeO(OH) is an important hydrous oxide, which can be used as the basic material to prepare high-quality magnetic-recording materials. Uniform ~-FeO(OH) colloidal particles had been obtained by Matijevic [1] by forced hydrolysis of ferric salts in a closed vessel. However, it had been limited to a small scale because the restrictive conditions. To simplify the conditions and to minimize as much as possible the influence of heterogeneity of the temperature rise so as to meet the requirements of the industrial production, the cooperative effect of the microwave irradiation with the hydrolysis of urea has been successfully used to obtain uniform and superfine ~-FeO(OH) colloidal particles in this study. Experimental A refitted microwave oven with a multiple-model resonant cavity which the reactor sits in was used. The system operates at a 2.45GHZ frequency and can operate at 0-100% of full power (500 watts). 537
538
D. DONGet aL
Vol. 30, No. 5
Solutions of FeCl 3 and HC/, or FeC/3 and CO(NH2) 2 w e r e stoichiometrically placed into an Erlenmeyer flask equipped with a reflux condenser, then 200ml deionized water was added, and the microwave oven was turned on. After reacting for a certain period of time, the flask was placed in a homothermal w at er bath at 94°C, which was the same temperature as the above mentioned, for aging. The solid and solution phases were separated by centrifugation, and the solid phases were dried in an oven before characterization by powder X-ray diffraction(XRD) and transmission electron microscopy (TEM). The XRD were obtained using a D/max-3B diffractometer with CuK a radiation and the TEM was performed using an H-800 instrument.
Results and Discussion Characteristics of p r o d u c t powder. In the case of [Fe3÷] >_ 0.072M, the particles obtained were u n i f o r m ~-FeO(OH) crystallites identified by XRD analysis (Fig. 1). The TEM photograph (Figs. 2A and 2B) shows the rodlike crystallites with a regular shape and a very narrow size distribution. Both the uniformity and size of the particles were better than those made by the conventional method in the same concentration conditions.
.gK
rn It_) ~
.,,5
2.
10.oo
20.00
,0. O0
40. O0
50. O0
6 0 . O0
7 0 . (>0
FIG. 1 The XRD patterns of ~-FeO(OH) crystallites
85 . O0
Vol.30, No. 5
IRONOXYHYDROXIDE
FIG. 2 TEM photograph (x 50000) of [3-FeO(OH)
prepared
539
by microwave-induced
hydrolysis of 0.114M FeCt 3 in the case of [CO(NH2) 2] / [FeC~3] = l0 for A and 5 for B respectively.
Effect of Heating l~Rnner Keeping other experimental conditions unchanged, two different ways of heating, water bath or microwave irradiation, have been used for comparison. The results showed that the microwave irradiation can accelerate the hydrolysis of Fe 3÷. For example, in the case of FeCI3+HCe, the time for reaching hydrolysis equilibrium by microwawe irradiation was ten minutes less than that by waterbath; in the case of FeC/3 + CO(NH2)2, the time for complete hydrolysis by microwave irradiation was half an hour or so less than by water bath (Table 1). This could be attributed to the higher efficiency and smaller temperature gradient of microwave heating as compared to the waterbath. TABLE I
Manner of heatin G microwave waterbath
pH of the reaction solution at various times. (A) Time (rain.) 30 60 90 120 1.62 1.70 2.16 8.0 1.77 2.50
145 6.04
*[FeC/3] = 0.144M, [CO(NHu)2]:[FeCt 3] = 10:I,T = 94°C.
Manner of heating microwave i waterbath
3 1.18 ] 1.53 I
5 1.15 1.38
(B) Time (min.) 10 15 1.05 1,21 1.09
*[FeCi3] = 0.144M, pH (initial) = 3, T = 94°C.
18
20-120
1.05
1.03
1.03
540
D. DONG¢t al.
Vol.30, No. $
Our experiments also revealed that the uniformity of crystalline particles in the presence of microwave field was superior to that in the absence of external field for the system of FeC~3+CO(NH2)2, (Figs. 3A and 3B). This implies that the microwave irradiation may be influencing the nucleation process of ~-FeO(OH). The hydrolysis of Fe ~÷ is a rather complicated process, which could be written as follows: Fe3++ 2H20 -+ FeO(OH) @ + 3H ÷ and, CO(NH2)2, is ionized in water: CO(NH2) 2 ~ NH ~ + NCOthen, N C O - is hydrolysed further: NCO-+ 2H20 --* NH ~ + CO ~ and, 2H ÷+ CO 32- ~ H20 + CO2~ From the above, it was concluded that both processes of hydrolysis of Fe 3÷ and CO(NH2) 2 could be promoted. Furthermore, the very fast temperature rise caused by microwave irradiation accelerated the reactions and promoted the homogeneous nucleation so much that uniform and superfine ~-FeO(OH) particles were obtained.
FIG. 3 TEM photograph (x 50000) of ~-FeO(OH) prepared by microwave irradiation (A) or waterbath heating (B).
Vol. 30, No. 5
IRON OXYHYDROXIDE
541
Effect o f ~ t
Concentration Experiments indicated that the crystal size varied with the ratio of [CO(NH2)2] to [Fe3+], and when [CO(NH2)2] / [Fe3+] > 3, products could be obtained with a yield of nearly 100% of theoretical. For example, when [Fe3+] = 0.144M, as the ratio increased, the average particle size decreased correspondingly (Fig. 2). This was due to the fact that the increase of urea concentration could cause 'explosive' nucleation, which formed a large quantity of host crystal in an instant, and the crystallites were hindered from growing further.
Conclusions This study demonstrates that microwave-induced hydrolysis of ferric salts with dissociation of urea may lead to instantaneous nucleation. Optimizing the parameters such as concentration of the chemical species, ratio and irradiation time, we can obtaine uniform and superfine particles. In addition, the filtering of stock solutions through minute-pore membrance is unnecessary. This novel processing may prove to be a valuable method in the mass production of uniform dispersing colloidal particles. References .
2. 3.
E. Matijvic and P. Scheiner, J. Coll. Interface Sci., 63, 509 (1978). Chen Longwu, Zhang Kaihua and Jiang Jisen, Chem. Bull., 12, 33 (1990). Wang Guangxin, J. Phys. Chem., 7, 655 (1991).