Facile synthesis of SrCO3 nanostructures in methanol/water solution without additives
© Lishuo et al.; licensee Springer. 2012
Received: 25 April 2012
Accepted: 30 May 2012
Published: 15 June 2012
Highly dispersive strontium carbonate (SrCO3) nanostructures with uniform dumbbell, ellipsoid, and rod-like morphologies were synthesized in methanol solution without any additives. These SrCO3 were characterized by X-ray diffraction, field emission scanning electron microscopy, and N2 adsorption-desorption. The results showed that the reaction temperature and the methanol/water ratio had important effects on the morphologies of SrCO3 particles. The dumbbell-like SrCO3 exhibited a Broader-Emmett-Teller surface area of 14.9 m2 g−1 and an average pore size of about 32 nm with narrow pore size distribution. The formation mechanism of the SrCO3 crystal was preliminary presented.
Recently, nanomaterials with different morphologies have attracted great attention for their promising applications such as optical materials, efficient catalysts, drug-delivery carriers [1–3], etc. Strontium carbonate (SrCO3) is one of the important reagents used in firework, pigment, and electron manufacturing . There are two main usages of SrCO3: they are used in the production of cathode ray tubes and ferrite magnets for small direct-current motors . However, SrCO3 with different morphologies may own different potential usages. For example, SrCO3 with a needle-like crystal is used in optical polymers to reduce birefringent phenomena . A sphere-shaped crystal with a diameter less than 1 μm is favorable for high-temperature electric components. So far, SrCO3 with various morphologies such as hierarchical branches, hexagonal prisms, straw-like, pancake, ellipsoid, needle, flower ribbon, bundle, dumbbell, sphere, and rod-like have been reported [5, 7–13].
Various methods have been reported on the preparation of SrCO3 nanostructures including hydrothermal , microwave-assisted , microemusion-mediated solvothermal methods , etc. Although nanoscale SrCO3 with special morphologies was obtained, the preparation processes were complex and strict, such as high-pressure, high-temperature, and tedious synthetic procedures as well as high cost were required. Aside from that, large-scale synthesis of SrCO3 nanostructures still remains a considerable challenge.
In this work, a new facile way was reported to synthesize SrCO3 nanostructures by continuously carbonizing Sr(OH)2 with CO2 in methanol/water solution without additives. The effects of the reaction temperature and the methanol/water (m/w) molar ratio on the morphology evolution were investigated. This method is simple, low-cost, and easy to control in producing large-scale monodisperse SrCO3 nanostructures.
In the typical experiment, several grams of Sr(OH)2·8H2O were dissolved into the methanol/water solution and kept at room temperature for 24 h. The concentration of the solution was kept at 0.05 mol l−1 for all the experiments. The solution was put into the reactor and stirred using a propeller agitator with a speed of about 800 rpm. Mixed CO2 of 100 ml min−1(80 ml min−1 N2 + 20 ml min−1 CO2) was induced into the reactor and lasted for 30 min. Then, the gas was cut off and continuously agitated for another 2 h. Finally, the solution was naturally cooled to room temperature. The products were separated by centrifugation and washed with deionized water and ethanol alternately for three times. The obtained carbonate samples were dried at 60°C for 24 h.
The products were characterized by field emission scanning electron microscopy (FESEM; JSM-6700 F, JEOL, Akishima-shi, Japan) and X-ray diffraction (XRD; X’pert PRO MPD, PANalytical B.V., Almelo, The Netherlands); patterns of carbonate were recorded on a diffractometer (using Cu Kα radiation; λ = 0.154 nm) operating at 40 kV/30 mA. A scanning rate of 0.2° s-1 was applied to record the patterns. The N2 adsorption-desorption isotherms were measured at 77 K using an automated surface area and pore size analyzer (QUADRASORB SI-MP, Quantachrome Instruments, Boynton Beach, FL, USA).
Results and discussion
From the XRD pattern, we can know that the SrCO3 from the pure methanol solution have poor crystallinity than those from the methanol/water solution (Figure 2; some crystal planes such as (021), (102), and (200) are only observed in the SrCO3 from the methanol/water solution. The results indicate that the SrCO3 from the methanol/water solution has better developed crystal plane.
In order to investigate the effect of the m/w ratio on the morphology of SrCO3, the crystals were prepared in m/w ratios of 3:2, 1:1, and 2:3. Figure 4 shows the morphologies of the products from the different m/w ratios. It is interesting that the rod-like SrCO3 with different length-diameter ratios were observed in most cases. The results indicated that the m/w ratio has a great effect on the morphology of products. When the ratio of m/w is 3:2 (Figure 4A), irregular plate-like products with a few short rods have been observed in the picture; the rods had a diameter of 90 nm and a length of 600 nm. As the m/w ratio was changed to 1:1, monodisperse rod-like products with a diameter of 120 nm and a length of 1.2 μm were observed (Figure 4B). When the m/w ratio is 2:3, the morphologies (Figure 4C) of the products were similar with those obtained in the m/w ratio of 1:1; it seems that the crystallinity of the products is better than that of Figure 4B.
Although the exact formation mechanism of these morphologies of the SrCO3 crystal is still not clear at present, our results show that the reaction temperature and the m/w ratio have great effects on the morphology. The m/w ratio or the polarity of the mixed solvent had a great effect on the morphology which had been reported by Lou et al.  and Zhang et al. . Studies showed that alcohols can affect the dielectric constant of the medium and change the crystal growth rate . When pure methanol was presented, the -OH of methanol might adsorb to the nuclei of the crystals and change its surface energy and then the morphology of the products. As the temperature was increased, the vibration of -OH groups in methanol was more rapid and absorption effects were weakened . Thus, the morphology of the product has little change at relatively high temperatures of 60°C and 70°C (Figure 3A,B). However, when the methanol/water solution was presented, the forming hydrogen bond between methanol and water prevented the absorption to the nuclei, and rod-like products growing along the c-axis were obtained.
Highly dispersive SrCO3 nanostructures with unique ellipsoid, dumbbell, and rod-like morphologies were successfully synthesized by a facile way in pure methanol or methanol/water solution without additives. The morphology of SrCO3 nanostructures can be controlled flexibly by adjusting the reaction temperature and the m/w ratio. N2 adsorption-desorption result reveals that this dumbbell-like SrCO3 has a mesoporous structure. It is expected that these SrCO3 nanostructures can be used in photocatalysis and electronic manufacturing in the future.
LL is a Ph.D. on chemical engineering science. He researches on crystal growth and design at Guangxi University. Dr. RL works as an associate researcher at the Institute of Process Engineering, Chinese Academy of Sciences. In the National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, he works on crystal growth and morphology controlling. Professors QF and ZT are experts of chemical engineering at Guangxi University.
This work is supported by the National Nature Foundation of China (20976181).
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