Here we report the synthesis of barium sulphate (BaSO4) nanoparticles from Ba(OH)2/BaCl2 solutions by a combined method of precipitation and quenching in absence of polymer stabilizers. Transmission electron microscopy (HRTEM), Fourier transforms infrared spectroscopy (FTIR), and X-ray diffraction (XRD) were employed to characterize the particles. The Scherrer formula was applied to estimate the particle size using the width of the diffraction peaks. The obtained results indicate that the synthesized material is mainly composed of nanocrystalline barite, with nearly spherical morphology, and diameters ranging from 4 to 92 nm. The lattice images of nanoparticles were clearly observed by HRTEM, indicating a high degree of crystallinity and phase purity. In addition, agglomerates with diameters between 20 and 300 nm were observed in both lattice images and dynamic light scattering measurements. The latter allowed obtaining the particle size distribution, the evolution of the aggregate size in time of BaSO4 in aqueous solutions, and the sedimentation rate of these solutions from turbidimetry measurements. A short discussion on the possible medical applications is presented.
The baryte group consists of baryte, celestine, anglesite, and anhydrite. Baryte is a sulfate of barium with chemical formula BaSO4. It is generally white or colorless, chemically inert, insoluble in water, with high density, and the main source of barium. Although baryte contains a “heavy” metal (barium), it is not considered to be a toxic chemical reagent by most governments because of its extreme insolubility [
Among the methods to obtain nanoscaled materials, chemical synthesis has numerous advantages such as simple technique, low costs, less instrumentation, doping, and high yield [
The starting reagents barium hydroxide, barium chloride, and sulfuric acid were used as received. Double distilled water was used in all experiments. The prepared barium sulfate was characterized by transmission electron microscopy using a JEOL JEM-2100 microscope with LaB6 filament (accelerating voltage of 200 kV). The samples were prepared by suspending the powders in an ethanol-based liquid and pipetting the suspension onto a carbon/collodion coating. Fourier transform infrared (FT-IR) spectra were measured with a Perkin Elmer 100 spectrometer (in the range of 2000–500 cm−1) by incorporating the samples in KBr (1 : 99 mg) disks to confirm the characteristic vibrational bands. X-ray diffraction (XRD) patterns of BaSO4 were recorded on a panalytical diffractometer, model X’Pert Pro, and CuK-
Selected peaks employed to calculate the particles size with Scherrer’s equation. These are the nine first peaks that appearance powder pattern of BaSO4 synthesized.
|
|
|
Int./U.A. | Rel. Int./% | FWHM/ |
---|---|---|---|---|---|
200 | 19.9969 | 4.43666 | 211.47 | 13.68 | 0.0895 |
011 | 20.4650 | 4.33622 | 513.75 | 33.24 | 0.0892 |
111 | 22.8076 | 3.89586 | 795.40 | 51.46 | 0.0882 |
210 | 23.5789 | 3.77013 | 155.81 | 10.08 | 0.0879 |
002 | 24.8785 | 3.57606 | 448.89 | 29.04 | 0.0875 |
210 | 25.8694 | 3.44128 | 1521.90 | 98.46 | 0.0872 |
120 | 26.8582 | 3.31679 | 1090.44 | 70.55 | 0.0870 |
211 | 28.7665 | 3.10096 | 1545.73 | 100.00 | 0.0868 |
112 | 31.6281 | 2.83364 | 535.66 | 34.65 | 0.0868 |
Both initial particle size distribution and particles size variation were characterized by dynamic light scattering measurements (DLS) on a Brookhaven BI 9000AT goniometer. Measurements were carried out at a fixed angle of 90° using a 633 nm laser. The sedimentation rate was obtained from Turbiscan LAB software in scanning mode. The light source is an electro luminescent diode in near infrared (880 nm). Two synchronous optical sensors receive the transmitted light through the sample (180°) and the backscattered light by the sample (45°). The sample was dispersed in a deionized water solution at a phase fraction of 0.1% w/v. The suspension was sonicated during 15 min before measurement.
The direct precipitation (DP) procedure followed consists in adding a Ba(OH)2·8H2O solution to BaCl2·2H2O in presence of water. The molar ratio of Ba(OH)2 to BaCl2 was 3 : 1. The resulting solution was stirred at room temperature while a sulfuric acid solution (50% (v/v)) was added (step 1, precipitation). The precipitated solid material was washed and filtered four times with hot distilled water (step 2). The sample was frozen at −26°C for 24 hours. Subsequently, the supernatant liquid was carefully decanted and then a volume of distilled water was added again. This procedure was repeated 5 times. The final step involved a freeze-dry cycle and was oven-dried at 105°C for 12 hours (step 3, purification) [
Figure
XRD pattern of synthesized sample (a) and final Rietveld plot for BaSO4 (b). The continuous green line represents the calculated pattern and the red discontinuous line is the observed pattern.
TEM and HRTEM images (Figures
TEM image of BaSO4 nanoparticles (a); HRTEM image showing lattice fringes of BaSO4 nanoparticles (b).
TEM image of BaSO4 nanoparticles (a); typical aggregates (b).
HRTEM image of BaSO4 nanoparticle (a); FFT power spectrum (b); masked power spectrum FFT (c); image after performing inverse FFT on the masked power spectrum (d).
HRTEM image of BaSO4 nanoparticles (a); FFT image (b) (particle 1), (c) (particle 2); masked power spectrum FFT (c) (particle 1), (d) (particle 2); image after performing inverse FFT on the masked power spectrum (c) and (d).
HRTEM image of BaSO4 nanoparticle (a); HRTEM image of BaSO4 nanoparticle (b); a magnification of the section marked with a white square in (a); FFT image (c); masked power spectrum FFT (d); image after performing inverse FFT on the masked power spectrum (e). A crystallographic representation of BaSO4 crystal (f).
In Figure
In Figure
In the HRTEM image (Figure
Figure
FT-IR spectra of BaSO4 nanoparticles.
Figure
Particle size distribution of a BaSO4/W suspension (0.1% w/v) determined by dynamic light scattering.
Particle size variation of a BaSO4/W suspension (0.1% w/v) determined by dynamic light scattering.
Due to the large size of aggregates, it is expected to observe sedimentation and the results from turbidimetry can be observed in Figure
Sedimentation rate obtained from the initial slope of the photon mean free path (
The combined effect of forming aggregates and sedimentation could limit possible medical applications of BaSO4 nanoparticles. Nevertheless, this study was processed without any additives (including stabilizers, antioxidants, and lubricants). In this sense, in general, barium sulfate suspension oral for gastric and colonic radiological work, containing a physiologically inert stabilizer, consists of a solution of a water-soluble cellulose ether and carboxymethylcellulose and also contains a suitable penetrant of cationic origin as lauryl sulfoacetate [
The synthesis of barium sulfate was carried out using a mix of Ba(OH)2/BaCl2, where the barium chloride solution was added to increase the concentration of Ba2+ ions (in excess). Subsequently, with the addition of
The increase in pH could result in an increase in the negative charge of BaSO4. According to Zhang et al., this could be attributed to the adsorption of OH− ions on the positive charge centers of BaSO4 particles [
In general, a precipitation process is described by processes that include the creation of a supersaturation level followed by the generation of nuclei (nucleation) and the subsequent growth [
The synthesis process involves as second step a quenching. Quenching is simply cooling rapidly to a lower temperature, −26°C. The final step in the precipitation process was an artificial aging at −26°C (aging above room temperature). Temperature has a significant influence on solubility and
The results presented here prove that barium sulfate nanoparticles can be prepared in the absence of polymers stabilizers polymeric employing a simple methodology. Moreover, the nanomaterial synthesized has applications as a potential contrast agent for X-ray examination.
Barium sulphate nanoparticles were synthesized using a precipitation method in absence of polymer stabilizers or solvents. The XRD study shows that the synthesized nanoparticles crystallize in orthorhombic system with space group
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors acknowledge financial support by IVIC through project 1077 and technical assistance of Lic. Liz Cubillán (FTIR).