HEOPTAHHHECKHE MATEPHAttbl, 2009, moM 45, № 2, c. 205-209
UDC 546.264
SYNTHESIS OF BaCO3 WITH DIFFERENT MORPHOLOGIES USING AMPHIPHILIC PS-PAA COPOLYMER AS MEDIUM
© 2009 Dalai Jin*, Xiaojing Yu*, Linhai Yue**, Ping Sun**
*Center of Materials Engineering, Zhejiang Sci-Tech University, Xiasha University Town, Hangzhou, People's Republic of China ** Chemistry Department, Zhejiang University, Hangzhou, People's Republic of China
e-mail:zjchem_yue@126.com
Barium carbonate (BaCO3) with multiple morphologies have been synthesized using BaCl2 and Na2CO3 in the presence of copolymer of poly(styrene) and poly (acrylic acid), an amphiphilic copolymer by a simple solvent reaction route. X-ray powder diffraction and field emission scanning electron microscopy were used to characterize the obtained products. The mole ratio of the PS/PAA was found to play an important role in determining the morphologies of the final products.
INTRODUCTION
Properties of inorganic materials are well documented to depend strongly on their morphologies. Thus, the design and controlled synthesis of nano/micro-structures with different morphological configurations and size distribution on a large scale is very important in both basic science and technology [1-5].
Barium carbonate (BaCO3) is an important inorganic material known as a thermodynamically most stable crystal modification among the heavy metal carbonates (ACO3, A - Sr, Ba, Pb) and attracted extensive consideration due to its close relationship with aragonite. Barium carbonate is widely used in industry for producing barium salts, pigment, optical glass, ceramic, electric condensers and barium ferrite. Since the morphology of materials and their properties are closely related, different morphologies of BaCO3, such as the sphere-like, dendritic-like, dumbbell-like and spindle-like have been obtained via various synthesis routes. For example, whisker-like as one of the most important one-dimensional structure materials can be widely used in fiber reinforcement of ceramic composites.
The conventional methods for the preparation of BaCO3 include microemulsion-mediated solvothermal route, reversed micelles method, semi-batch crystallizer process, templateassisted method, self-organized formation, sonochemical synthesis, electrodeposition [6-13] and so on. Until now, a practicable and facile method to synthesize metal carbonate with novel morphologies is still a challenge in pursuit of further practical applications. Currently, organic additives and/or templates with complex functionalization patterns are reported to control the nucleation, growth, and alignment of BaCO3 [14, 15]. These functional polymers can control crystal growth via face selective adsorption. Therefore, to extend the appli-
cation of BaCO3 and to deepen the comprehension of its crystal growth behaviors, it is necessary to have a suitable choice of ''capping reagent'' possessing both stability and simplicity for the preparation of BaCO3 with distinguished shapes and especially good uniformity. Herein, we suggested the copolymer of polystyrene (PS) and poly (acrylic acid) (PAA), a soluble amphiphilic copol-ymer, as crystallization directing agent. PS-PAA is composed of two different types of polymer chains, which are covalently bonded together. When dissolved in water, it can self-assemble into a variety of three-dimensional arrays with the structures depending on the mole ratio of different polymer chains and the concentration of the copolymer. The framework constructed by the am-phiphilic copolymer in solution[16] together with the inductive effect of carboxyl on the precipitation make it possible to synthesize barium carbonate composite with special morphology. It proved that uniform BaCO3 rods with high aspect ratio of more than 10 could be obtained by a facile precipitation method using the PS-PAA as medium. The ratio of PS/PAA influenced the morphology of the barium carbonate greatly.
EXPERIMENTAL
Synthesis. Amphiphilic copolymer of polystyrene and poly (acrylic acid) with the ratio of PS/PaA (fv) = = 3 : 1, 2 : 1, 1 : 1 were synthesized in our laboratory first by the following process: Styrene monomer, acrylic acid monomer and a,a'-azobisisobutyronitrile (AIBN) were purified first. Then the copolymerization of styrene with acrylic acid using monomer feed ratio of 3 : 1, 2 : 1, 1 : 1 were carried out in iso-propanol and acetic ester mixed solution at 75°C for 8h with AIBN radical initiator under nitrogen atmosphere. The obtained solid was purified by being dissolved in 0.2M NaOH solution, deposited from
206
DALAI JIN h hp.
The characteristics of the obtained PS-PAA copolymer
Sample P3 P2 P1
PS/PAA 3 : 1 2 : 1 1 : 1
Mw/Mn 1.426 1.446 1.453
Mw 8425 10823 2563
hydrochloric acid and washed by deionized water until the pH of the filtrate equals to around 7 consecutively. The remainder was dried at 70°C for about 10h. The characteristics of the obtained products are listed in Table.
Certain amount of PS-PAA was slowly added into 0.05 mol/L Na2CO3 (A.R., Shanghai Hongguang Chemical Co. Ltd.). The final PS-PAA concentration is 1.44 g/L. 0.2 mol/L BaCl2 (A.R., Guangzhou Chemical Co. Ltd.) solution then dripped down in to the Na2CO3-PS-PAA mixture for about 20 min while strong stirring was applied at 20°C. The precipitation was aged statically for 10 h and then filtered, washed, and sifted through 100 mesh sieve to get the final product. The reference sample was also synthesized without the presence of PS-PAA.
Measurements. The X-ray diffraction (XRD) of the powder sample was examined by a high-resolution Thermo ARL XTRA X-ray diffractometer at room temperature using Cu^a radiation (X = 0.15405 nm). Scan rate of 1°deg/min and step size of 0.02° were applied to record the pattern in the 20 range 20°-50°. The morphology of the sample was inspected using a field emission scanning
111
002 V-w. . A—
112
A
221 132 113
^UUjl-
1
sJ^^UK^ 2
30
40
50
26, deg
Fig. 1. XRD patterns of BaCO3 with (1) no PS-PAA, (2) P3, (3) P2 and (4) P1 as medium.
electron microscope (FE-SEM, XL30, Philips). The general TG-DTA curves were determined by a WCT-1 analyzer at a heating rate of 10°C/min in air atmosphere with the flow rate of 20-30 mL/min.
RESULTS AND DISCUSSION
The phase identification of the as-obtained samples were examined by XRD as shown in Fig. 1. All the samples with the different shapes have the similar XRD patterns. The peaks with d spacing of 3.72, 2.63, 2.15, 2.02 and 1.94 A, can be readily indexed to 111, 112, 221, 132 and 113 respectively according to JCPDS files No. 05-0378 of a orthorhombic structure. No characteristic peaks of other impurities have been detected, indicating that the products are of high purity. It shows that the presence of the copolymer induced the worse crystallization of the products. With the increase of the PAA relative proportion, the products get worse crystallization.
The morphologies of the samples were investigated with scanning electronic microscope (SEM). Fig. 2d show the SEM images of the as-synthesized products. As one can see from the Fig. 2a, the BaCO3 grains are obtained without the presence of PS-PAA which seriously aggregated each other with low dispersivity. The particle size of this sample is in several hundreds nanometers. When PS-PAA was used as additive agent, obvious anisotropic structures of BaCO3 crystal were easily obtained as shown in Fig 2b, 2c. Though decreasing the ratio of PS portion to PAA portion, the aspect ratio of the BaCO3 rods grow larger significantly. When the ratio is 3 : 1, the BaCO3 crystal exhibits a little inclined to be short rods shape with the aspect ratio of 1-5. The dispersivity of the sample is unsatisfied. The crystal surface is smooth enough. When the ratio reducing to 2 : 1, a frame structure built by BaCO3 rods is obtained. The diameters of the rods are uneven. The aspect ratio of the rods increased evidently. When the ratio is 1 : 1, the morphology exhitits clubbed shape with high aspect ratio of more than 15 in good dispersivity. Thermal gravity analysis-differentia thermal analysis (TG-DTA) was applied to estimate the organism quantities in this sample. The results are shown in Fig. 3.
There are four weight loss stages in the TG curve during the program calefaction process from room temperature to 850°C. The weight loss after 700°C together with a large endothermal peak on DTA curve possibly attributs to the decomposition of barium carbonate compared with the reference pure BaCO3 sample. Besides the weight loss stage mentioned above, three more stages of weight loss can be observed on the TG curves. Accordingly, three strong exothermic peaks are detected on the DTA curve. They can be assigned to the oxidation of the organism in the composite. The total weight loss of these three stages is about 12.8%. Not all the used copol-
I
Fig. 2. SEM images of BaCO3 with (a) P3, (b) P2, and (c) P1 as medium.
ymer entered into the final product in comparison with the feeding materials.
A French researcher, Pileni [17], claimed that the control of surfactant in crystal shape was mainly attributed to selective adsorption of molecules on facets during the crystal growth. PS-PAA is an amphiphilic copolymer, which has two kinds of chains with just opposite solubility in water. The PAA chain is hydrophilic. It decompose into anionic COO- group when dissolved in
t,, °C
Fig. 3. TG-DTA curves of BaCO3 (1) without PS-PAA and (2) with P1 as medium.
water, which could bond with the cation, Ba2+, on the surface of the BaCO3 crystal. This is the similar function with that of some anion surfactants, which induce the orientable crystallization of the crystal and resulte the final anisotropic morphologies. While PS chain in the copolymer is hydrophobic, it tended to combine together in polar solution such as water. The copolymer can self-assemble into a variety of three-dimensional arrays with the structures depending on the mole ratio o
Для дальнейшего прочтения статьи необходимо приобрести полный текст. Статьи высылаются в формате PDF на указанную при оплате почту. Время доставки составляет менее 10 минут. Стоимость одной статьи — 150 рублей.